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Hot water to forced air
On Jan 7, 3:13*pm, "
wrote: On Jan 7, 6:47*am, harry wrote: On Jan 7, 2:50*am, Mark wrote: There is only a limited amount of heat available in the primary medium, especially in the case we are considering. In order to transfer the most heat from the primary to the secondary medium, the two have to be kept in contact as long as possible, ie the velocities have to be kept as low as possible in both media in any given heat exchanger. I can't make it any simpler than that for you. Harry, It's funny that you can be snotty about this and be completely wrong. The usual case for a heat exchanger is is higher CFM = more BTU exchanged and lower temperature. Take the case of the solar collector this guy has on his roof. If I put water through it slower, it will come out the other end hotter will it not? *The hotter it is the more useful it is. Good grief. *More useful? *Sure if I want to use it for washing my hands. *Does it contain more heat, pickup more heat going through the heat exchanger than a larger volume of water that moves through faster? *No. *You're once again confusing temperature with heat. The hotter it is, the higher temperature I can achieve and ultimately more heat I can put into my water store. So, a pint of water that is 150F has more heat than 1000 gallons of water at 75? The slower I circulate my solar panel medium/water through the heat exchanger in the water store, the cooler it will come out the other end. That's true, assuming all else is held constant. The cooler the water going back to the solar panel, the more energy it will pick up. That's true, assuming all else is held constant. Still waiting for the answer to the simple question I posed: Now I give you a quiz. * *Our friend here builds his proposed system. *He puts an auto radiator in the return side of his furnace duct work and connects it to a solar collector. * The solar collector heats water to 130F and it gets pumped to the radiator. *The incoming air in the return duct is 65F. * He has a variable speed blower so that he can vary the airflow through the radiator. Which airflow results in the water leaving the radiator at the lowest temp and consequently the most heat transferred? A - 1 CFM airflow B - 2 CFM C - 10 CFM D *100 CFM E - 1000 CFM F - 2000 CFM, the max the blower capacity? Simple problem, where is the answer?- Hide quoted text - - Show quoted text - There is no answer because it also depends on the speed and volume of the water throught the radiator. (If my water pump fails the engine will still overheat evenif the airflow is stillgoing through the radiator) But the more air you put through the radiator the colder that air will be ( and lessuseful) when it comes out as the energy is diluted. Just because there is more air doesn't mean it has removed more energy. How much heat would be transferred if the air temperature was the same as the water temperature? Answer (as you are completely stupid) is none. Regardless of how much air was blown through the radiator. But your's is a stupid question. The OP needs to shift X amount of air through his system. To get the most heat out of his heat exchanger, he needs to slow the air down as it passes through it so increasing the time in contact. In practice usually by increasing the CSA of the ductwork where the HX is located. Hotter water means that more energy can be stored in the hot water store and it can hence be smaller and cheaper. There are issues with the heating plant efficiency but as you don't generally see efficient plant in America you don't have to worry about that. |
Hot water to forced air
On Jan 7, 12:04*pm, harry wrote:
On Jan 7, 2:13*pm, " wrote: On Jan 7, 6:17*am, harry wrote: On Jan 7, 2:50*am, Mark wrote: Harry, It's funny that you can be snotty about this and be completely wrong. Yes you want the two media in intimate contact but you then wrongly conclude that means the velocity should be low.... So you think lower CFM through a radiator pulls more heat out of it, obviously wrong. When does your car overheat? The flaw in your thinking is that you don't consider that there is always more air to replace the air that is moving away and the colder the air in the radiator, the more heat it pulls out. You are the one confusing heat and temperature. The usual case for a heat exchanger is is higher CFM = more BTU exchanged and lower temperature. Take care Mark My car overheats usually when the fan fails. Very little air goes through the radiator core and the core/engine overheats. However the very small amount of air going through the core will be very hot indeed. ( In the previous instance, we are trying to get the air to be as hot as possible). And there you go again. *Just like Mark said, you are confusing temperature and heat. *Let's recap. The OP is proposing to take a heat exchanger similar to a car radiator and place it in the return duct of his furnace. *He will pass hot water from solar panels through the radiator. Is the goal here to get the air as hot as possible? Clearly not. *The objective is to get the most heat out of the water and into the air. *By moving more cold air through that radiator the temperature differential across the heat exchanger is higher and MORE heat is transferred. *Yes, the air coming out or the radiator will not be warmed as much as if there were less air flowing, but there is enough additional air so that it more than make up for the lower temperature and MORE heat is transferred. *That you can't grasp this most basic concept just totally discredits you. Also the same belt drives the water pump,(in traditional cars). If it fails, *velocity of water in the engine is reduced to near zero so it gets hotter. In days of yore, when automotive thermostats failed in the closed position, the velocity of water in the engine would be reduced and so get (surprise surprise) hotter. Again, you don't understand the difference between heat and temperature. *Which takes more energy in the form of heat: A - Raising the temp of 5000 cubic feet of air 1F B- Raising the temp of 10 cubic feet of air 10F? Which air is hotter? However, we are not trying to recover heat from the engine, we are trying to *disperse/dump it it by controlling the cooling water jacket temperature by means of the water immersed thermostat. The final temperature of the air/secondary medium is not an issue. Which of course matters not a wit. The radiator just has to be big enough to dump all the heat in the climatic conditions anticipated. Having a bigger radiator reduces the velocity of the water going through it as well as increasing surface area. (more parallel paths). You might like to reflect that when the water velocity in the radiator is reduced, (ie the thermostat is part closed) it gets hot quicker in the engine . (The heat exchanger in the engine being the cylinders/ cylinder head.) It gets cooler in the radiator. * In both cases more energy is being transferred across the heat exchanger *because the water velocity is reduced and the hence the time spent in the heat exchangers is increased. If we were trying to recover the heat from the engine (as opposed to dumping it), as in a co-generation project, than a completely different design of cooling system would be utilised. The object would be to maintain optimum engine temperature and to recover the energy from the cooling jacket at as high a temperature as possible. Remember too, we are talking about the most efficient use of *heat exchangers, not the total energy shifted. *You seem to have got that confused too. I think it's obvious to all who's confused here. Here's another simple experiment you can try. You have a piece of iron that been heated with a torch. *You want to cool it off. *Do you get it cooled off faster by applying a very small stream of water to it, in which case the water running off is very hot, or by applying a large stream of water and flooding it as much as possible, in which case the water is just luke warm? If we can slow the velocity of the medii through a heat exchanger. we can have a smaller and cheaper one. I see. *So for example we can take all the coils in the AC systems out there and make them 75% smaller and at the same time reduce the blower speed. * That should work great. *And you throw rocks at Americans for being stupid? The limitation being of course that the secondary medium can never be hotter than the primary one and the volumes/specific heats of the medium. Also, as temperatures in primary and secondary medii come closer together, less energy is transferred- Hide quoted text - - Show quoted text - The last sentence is pretty much the only thing you got right here. * And it's also why you want the maximum airflow through that radiator. *If you slow the airflow to the limit, ie no air is flowing, the air surrounding the radiator equals the water temp in the radiator. *You now have max temp air, but 0 air moving and 0 heat being transferred. *Now slowly increase the airflow and while the temp of the air moving through starts to decrease, heat transfer starts because you have cold air coming in contact with the radiator. *As you continue to increase the airflow you get more heat out, more air out, but the air goes down in temp. *The process continues with a decaying exponential in terms of the additional heat that;s available.- Hide quoted text - - Show quoted text -- Hide quoted text - - Show quoted text - You are a bloody halfwit. Harry, 1) i'm not going to debate with you, especially since you are rude... 2) you are wrong about this... try and take this as an opportunity to learn something... 3)think about what i and trad are saying... re BTU and temperature, which holds more heat in BTU, a small red hot needle at 4000 F or 50 gallons of water at 100F? which air flow is pulling more BTU out of an exchanger, 100 CFM at 100F or 1,000CFM at 75F? have a nice day Mark |
Hot water to forced air
On Jan 7, 12:04*pm, harry wrote:
On Jan 7, 2:13*pm, " wrote: On Jan 7, 6:17*am, harry wrote: On Jan 7, 2:50*am, Mark wrote: Harry, It's funny that you can be snotty about this and be completely wrong. Yes you want the two media in intimate contact but you then wrongly conclude that means the velocity should be low.... So you think lower CFM through a radiator pulls more heat out of it, obviously wrong. When does your car overheat? The flaw in your thinking is that you don't consider that there is always more air to replace the air that is moving away and the colder the air in the radiator, the more heat it pulls out. You are the one confusing heat and temperature. The usual case for a heat exchanger is is higher CFM = more BTU exchanged and lower temperature. Take care Mark My car overheats usually when the fan fails. Very little air goes through the radiator core and the core/engine overheats. However the very small amount of air going through the core will be very hot indeed. ( In the previous instance, we are trying to get the air to be as hot as possible). And there you go again. *Just like Mark said, you are confusing temperature and heat. *Let's recap. The OP is proposing to take a heat exchanger similar to a car radiator and place it in the return duct of his furnace. *He will pass hot water from solar panels through the radiator. Is the goal here to get the air as hot as possible? Clearly not. *The objective is to get the most heat out of the water and into the air. *By moving more cold air through that radiator the temperature differential across the heat exchanger is higher and MORE heat is transferred. *Yes, the air coming out or the radiator will not be warmed as much as if there were less air flowing, but there is enough additional air so that it more than make up for the lower temperature and MORE heat is transferred. *That you can't grasp this most basic concept just totally discredits you. Also the same belt drives the water pump,(in traditional cars). If it fails, *velocity of water in the engine is reduced to near zero so it gets hotter. In days of yore, when automotive thermostats failed in the closed position, the velocity of water in the engine would be reduced and so get (surprise surprise) hotter. Again, you don't understand the difference between heat and temperature. *Which takes more energy in the form of heat: A - Raising the temp of 5000 cubic feet of air 1F B- Raising the temp of 10 cubic feet of air 10F? Which air is hotter? However, we are not trying to recover heat from the engine, we are trying to *disperse/dump it it by controlling the cooling water jacket temperature by means of the water immersed thermostat. The final temperature of the air/secondary medium is not an issue. Which of course matters not a wit. The radiator just has to be big enough to dump all the heat in the climatic conditions anticipated. Having a bigger radiator reduces the velocity of the water going through it as well as increasing surface area. (more parallel paths). You might like to reflect that when the water velocity in the radiator is reduced, (ie the thermostat is part closed) it gets hot quicker in the engine . (The heat exchanger in the engine being the cylinders/ cylinder head.) It gets cooler in the radiator. * In both cases more energy is being transferred across the heat exchanger *because the water velocity is reduced and the hence the time spent in the heat exchangers is increased. If we were trying to recover the heat from the engine (as opposed to dumping it), as in a co-generation project, than a completely different design of cooling system would be utilised. The object would be to maintain optimum engine temperature and to recover the energy from the cooling jacket at as high a temperature as possible. Remember too, we are talking about the most efficient use of *heat exchangers, not the total energy shifted. *You seem to have got that confused too. I think it's obvious to all who's confused here. Here's another simple experiment you can try. You have a piece of iron that been heated with a torch. *You want to cool it off. *Do you get it cooled off faster by applying a very small stream of water to it, in which case the water running off is very hot, or by applying a large stream of water and flooding it as much as possible, in which case the water is just luke warm? If we can slow the velocity of the medii through a heat exchanger. we can have a smaller and cheaper one. I see. *So for example we can take all the coils in the AC systems out there and make them 75% smaller and at the same time reduce the blower speed. * That should work great. *And you throw rocks at Americans for being stupid? The limitation being of course that the secondary medium can never be hotter than the primary one and the volumes/specific heats of the medium. Also, as temperatures in primary and secondary medii come closer together, less energy is transferred- Hide quoted text - - Show quoted text - The last sentence is pretty much the only thing you got right here. * And it's also why you want the maximum airflow through that radiator. *If you slow the airflow to the limit, ie no air is flowing, the air surrounding the radiator equals the water temp in the radiator. *You now have max temp air, but 0 air moving and 0 heat being transferred. *Now slowly increase the airflow and while the temp of the air moving through starts to decrease, heat transfer starts because you have cold air coming in contact with the radiator. *As you continue to increase the airflow you get more heat out, more air out, but the air goes down in temp. *The process continues with a decaying exponential in terms of the additional heat that;s available.- Hide quoted text - - Show quoted text -- Hide quoted text - - Show quoted text - You are a bloody halfwit. *The amount of air going through an automotive radiator is niether here nor there because we are dumping the heat to waste so it's temperature is unimportant. The only reason you claim it's neither here nor there is because you can't explain it with your rules of physics which don't pertain to this universe. A car radiator is a simple and perfectly valid example of a heat exchanger. The heat from the coolant is transfered to the air moving through the radiator. With the same amount of coolant flow, the more air you move through, the more heat that is removed. That's one reason many cars today are equipped with an auxialliary fan for the radiator. If it's very hot out, you're stuck in barely moving traffic, etc, and the coolant temp rises above the normal range, a switch turns on the fan to move MORE air through the radiator removing MORE heat with it. Doesn't get any simpler than that. If it worked the way you claim, we'd instead be restricting the air so that the air coming out was as hot as possible. You're confusing temperature with heat. A car radiator with a high volume of air moving through it will transfer MORE heat to the air. The temp of the air coming out will be lower, but there is MORE air and the increase in mass of air more than offsets the fact that it's a lower temp. Another example would be a simple hot water radiator in a house. With no fan you could hold your hand by it and you'd feel some hot air rising. Now place a fan there blowing lots of air through it. The air will not be as warm. Does that mean that LESS heat is being transferred? Of course not. You're getting MORE heat, but the air is at a lower temp because more mass is being heated. Capiche? If the purpose of the excercise was to utilise that heat, then we would want the air to be as hot as possible. Says who? It depends on what you're using the air for. If I'm using the heat for a chemical process and want it to be 120F, then I want it to be 120F, not 200F. If the application requires it to be at a certain minimum temperature, eg heating water in a water heater, then yes you would need it to be at a certain minimum temp. In the stated application, the goal is to transfer the heat to air moving through a furnace to heat a home. As long as the water moving through the heat exchanger is above the temp of the water, you get maximum heat transfer with the fastest airflow, all else being held equal. I've explained this several time now. Let' say the water from the solar collector is at 130F.Start at the limit of zero airflow. The air around the heat exchanger is also 130F because no air is moving. The water temp equals the air temp, no heat is being transferred. Start increasing the airflow and now you will have air coming out that is slightly below 130F and water going back to the collector that is slightly below 130F. Some heat is being transferred. Ramp up the airflow and you get more heat transferred. Will the air temp out of the heat exchanger be less? Sure. Does that mean less heat is being transferred? No, because a lot more air mass is being heated. Capiche? I've answered any questions you've put forth. Yet I get no reply to mine. I'll state my simple question a third time: I give you a quiz. Our friend here builds his proposed system. He puts an auto radiator in the return side of his furnace duct work and connects it to a solar collector. The solar collector heats water to 130F and it gets pumped to the radiator. The incoming air in the return duct is 65F. He has a variable speed blower so that he can vary the airflow through the radiator. Which airflow results in the water leaving the radiator at the lowest temp and consequently the most heat transferred? A - 1 CFM airflow B - 2 CFM C - 10 CFM D 100 CFM E - 1000 CFM F - 2000 CFM, the max the blower capacity? Why won't you answer this very simple question? |
Hot water to forced air
On Sat, 7 Jan 2012 03:17:29 -0800 (PST), harry
wrote: On Jan 7, 2:50Â*am, Mark wrote: There is only a limited amount of heat available in the primary medium, especially in the case we are considering. In order to transfer the most heat from the primary to the secondary medium, the two have to be kept in contact as long as possible, ie the velocities have to be kept as low as possible in both media in any given heat exchanger. I can't make it any simpler than that for you. Harry, It's funny that you can be snotty about this and be completely wrong. Yes you want the two media in intimate contact but you then wrongly conclude that means the velocity should be low.... So you think lower CFM through a radiator pulls more heat out of it, obviously wrong. When does your car overheat? The flaw in your thinking is that you don't consider that there is always more air to replace the air that is moving away and the colder the air in the radiator, the more heat it pulls out. You are the one confusing heat and temperature. The usual case for a heat exchanger is is higher CFM = more BTU exchanged and lower temperature. Take care Mark My car overheats usually when the fan fails. Very little air goes through the radiator core and the core/engine overheats. However the very small amount of air going through the core will be very hot indeed. ( In the previous instance, we are trying to get the air to be as hot as possible). No, actually we are trying to extracrt as much heat from the water as possible - which can be more air with low net temperature gain - or less air with high net temperature gain. The more air/lower temp actually gets more HEAT than the low air high temperature. If you are sitting in the airstream it FEALS like you are getting more heat with the low flow/high temp option, but in reality, you will heat the entire room or home FASTER withthe more air/lower temp option. In this case, the difference would likely be marginal - but it would be there- and would be quantifiable. Also the same belt drives the water pump,(in traditional cars). If it fails, velocity of water in the engine is reduced to near zero so it gets hotter. In days of yore, when automotive thermostats failed in the closed position, the velocity of water in the engine would be reduced and so get (surprise surprise) hotter. And in SOME engines, even today, if you remove the restriction of the (open) thermostat the water flow increases velocity to the point it does not remove enough heat from the block/heads and you get localized overheating of the engine. However, we are not trying to recover heat from the engine, we are trying to disperse/dump it it by controlling the cooling water jacket temperature by means of the water immersed thermostat. The final temperature of the air/secondary medium is not an issue. The radiator just has to be big enough to dump all the heat in the climatic conditions anticipated. Having a bigger radiator reduces the velocity of the water going through it as well as increasing surface area. (more parallel paths). You might like to reflect that when the water velocity in the radiator is reduced, (ie the thermostat is part closed) it gets hot quicker in the engine . (The heat exchanger in the engine being the cylinders/ cylinder head.) It gets cooler in the radiator. In both cases more energy is being transferred across the heat exchanger because the water velocity is reduced and the hence the time spent in the heat exchangers is increased. If we were trying to recover the heat from the engine (as opposed to dumping it), as in a co-generation project, than a completely different design of cooling system would be utilised. The object would be to maintain optimum engine temperature and to recover the energy from the cooling jacket at as high a temperature as possible. Remember too, we are talking about the most efficient use of heat exchangers, not the total energy shifted. You seem to have got that confused too. If we can slow the velocity of the medii through a heat exchanger. we can have a smaller and cheaper one. The limitation being of course that the secondary medium can never be hotter than the primary one and the volumes/specific heats of the medium. Also, as temperatures in primary and secondary medii come closer together, less energy is transferred |
Hot water to forced air
On Sat, 7 Jan 2012 06:37:46 -0800 (PST), "
wrote: On Jan 6, 4:58Â*pm, wrote: On Fri, 6 Jan 2012 05:55:31 -0800 (PST), " wrote: On Jan 6, 2:30Â*am, harry wrote: Tch. Â*The longer the secondary medium remains in contact with the primary medium, the nearer to the primary medium temperature it becomes. Or, to make it simple for you, the longer you leave a pan on a hot stove, the hotter the pan becomes. Â*If you left the pan permanently on the stove,it would eventually reach the same temperatrure as the hotplate (neglecting losses) We're not talking about getting the air temp passing through the heat exchanger to the same temp, or even close in temp, to the hot water passing through it. Â*We were talking about how you get as much heat out of the water and into the house as possible. To follow your example, let's say that an electric stove heating element is red hot. How do I get the most heat out of it and cool it off the fastest? Â* If I place a cold pan on there and leave it there, heat is transferred to the pan and it's temp rises. Â*At some point it peaks and the temp of the pan and heating element equalize. Â*Then they both start to slowly cool off. Â* They both have been in contact for a long time. Now instead, let's take 6 cold pans one at a time and put each one on there for 30 secs. Which method is going to cool off that hot element faster and transfer more heat in a given period of time? Â* Answer: the six cold pans. The exact same thing works with the simple radiator/heat exchanger that the poster is proposing to use. Â* The MORE air he moves through it, the more heat he will transfer. There are of course diminishing returns and if the radiator were big enough, eventually the temp of the air and the water would be equal and there would be no more heat to transfer. Â* But from a practical standpoint, he isn't going to be using a radiator anywhere near that large. If you put the pan on the hotplate for two seconds and took it off virtually no heat would be transferred. Yeah, but that would be like giving the radiator one brief shot of air and then no more air. So, to achieve maximum heat transfer Â*both medium need to remain in the heat exchanger for as long as possible. Â*(Time=max) According to that, all the AC systems out there must be very inefficient because last time I checked they use blowers to move the air at high speed. Â*I guess they should just slow the whole thing down so the air barely moves. Â*What you fail to realize is that if you did that, you'd have a very small amount of very cold air instead of a very large volume of air that is cold, but not at the coldest possible temp. Â*Moving the air quickly brings more warmer air in contact with the evaporator and transfers MORE heat. Capiche? The ideal is that the secondary medium achieves the same temperature as the primary medium, not achievable in practice or for system design reasons or even desireable in some cases. Uh huh. Â* Now I give you a quiz. Â* Â*Our friend here builds his proposed system. Â*He puts an auto radiator in the return side of his furnace duct work and connects it to a solar collector. Â* The solar collector heats water to 130F and it gets pumped to the radiator. Â*The incoming air in the return duct is 65F. Â* He has a variable speed blower so that he can vary the airflow through the radiator. Which airflow results in the water leaving the radiator at the lowest temp and consequently the most heat transferred? A - 1 CFM airflow B - 2 CFM C - 10 CFM D Â*100 CFM E - 1000 CFM F - 2000 CFM, the max the blower capacity? There are other practical considerations to take into account mostly to do with cost. I am pretty sure engineers in America must know this and you are a minority.- Hide quoted text - - Show quoted text - I'm sure the engineers here will be interested in hearing your answer to the above question. Mabee we need to get a bit more "scientific" about it. You want to put as many BTUs of heat (using north american (canadian)n terminology) into the air from the water. A BTU is the amoiunt of heat energy involved in cahanging i pound of water 1 degree F. Water weighs 10 lbs per imperial gallon. (works better than 8.35 per US gallon for calculations). Lets say we have a 40 gallon reservoir of water at 127 degrees F and we pump it through a heat exchanger at a rate that reduces the temperature of the water returning to the reservoir to 87 degrees F.. Â*That means we got 1600 BTUs of heat out of the water, into the air. Â*To do that in 1 hour would require a water flow of 40 gallons per hour, or .66 gallons per minute. If the return air is at 68 degrees F, and the furnace fan moves 2000 cfm, what will the air temperature coming out of the heat exchanger be? 1 BTU will raise the temperature of 1 cu ft of air 55 degrees F, or 55 cu ft of air 1 degree F. Â*So to absorb 1600 BTUs of heat from the water into the air, we need (1600x55=) 88000 cu ft of air raised one degree F, so at 2000 cfm, or 120000cfh, we would on,y raise the temperature Â*by 0.73 degrees F. Â*If we drop the water temperatre leaving the exchanger at 77 degrees, the air would be raised by 0.91 degrees F. Â*SO the variables that ALL make a difference are the airflow, the waterflow, the temperature drop across the water side of the exchanger, and the desired outlet air temperature. Â*If you balance the water flow against the air flow you can make your delta T between the water and the air whatever you want it to be. - which is where a BYPASS system as I explained, allows you to get the results you want by varying the amount of air passing the exchanger and the water flow through the exchanger once you get the basic size of the exchanger close. Why the need for variable dampers? Do you disagree that you get the most heat out of the heat exchanger by moving all the furnace air through it? No I'm not disagreeing. IF using a "bypass" system the dampers would take the "bypass" out of the system when there is no appreciable heat to be gained from the system, allowing the solar panels to get the water hotter so the delta T would be higher, raising the efficiency - and therefore extracting more heat from the system.. Same thing could be accomplished by a set of water control valves tho keep the heat in the reservoir untill the temperature was high enough to do an efficient job of heating the interior of the house. Water valving is more complex, and the difference in efficiency switching water vs switching air, would be small enough to not make the complexity worth while. Shutting off the air flow through the secondary heat exchanger MIGHT increase the efficiency enough to make it worth while. It would also eliminate the problem of extracting heat FROM the return air, into the water, when the solar input was too low to provide a net heat gain. Can't do that without water controls in a non-bypass system. I'm NOT saying this method would necessarily be BETTER for the OP, but it definitely bears looking into for the reasons given. Recap: No additional restriction in the main ductwork. Smaller heat echanger could possibly be employed Less complicated water controls Possibly higher total efficiency. Add to this, the installation might be simpler - just 2 cut - ins to the return duct (or even just one if the "bypass" augments the cold air return from heated airspace) - and for an "experimental system" it makes implementation a lot easier and more easily reversible. A simple "zone damper" like a Famco POPC or Suncourt 8 inch motorized unit , at about $70 would do the job., but a modulating unit like the Alan AZRDMOD series would provide variable control if desired, for more like $200. The only reason I see for using less than all the airflow is because without severly restricting the airflow, the air coming out is going to be almost the same temp as the return air coming in. So, to avoid draft/comfort issues, you might want it to come out warmer. BUT, and this is a big but, if that is the goal, then you'd have to change the blower because even at the lowest blower speed I doubt any system he's gonna put together is going to raise the air temp more than a deg or so. And I don't think you're proposing that he just damper off a huge portion of the existing airflow, leave the blower as is, are you? Nope. That's why I call it a "bypass" Instead of restricting total airflow, I am advocating he SUPPLEMENT the airflow Add a duct blower , like a Fantech FR225 - about 450-500 cfm for 8 inch "bypass" duct. That's why I dismissed using just solar from the beginning and I assumed he was talking about using it to supplement the furnace heating only when the furnace was running. If he wants to run the system all day long, using solar, that gets into a whole additional list of potential drawbacks, many of which I believe would make it impractical. It would require having the circulating fan on "constant" which I do all year, just as a matter of course, for filtering and comfort purposes. So, at least for me - not a drawback. As my 28/40KBTU furnace only runs 8 hours a day on the COLDEST days here in Ontario, and averages closer to 6 hours on low fire - I only need a total of 168000 btu heat input to keep the house comfortable.. If I have 6 hours of useable sunlight, a solar assist system could conceivably provide well over 10% of my heating needs throughout the winter, and a lot more heat, and a much higher percentage, during the "knee seasons" when more sun is available and less heat required. The payback would still be SLOW - my total annual gas bill for heat and hot water is about $700 per year - - - but the house would be more comfortable in the early fall before I turn on the furnace, and late spring, when I shut it off. The OP isn't the only one who's considered it - but I'd need to provide the solar panels too - which he already has. |
Hot water to forced air
On Sat, 7 Jan 2012 07:13:25 -0800 (PST), "
wrote: On Jan 7, 6:47Â*am, harry wrote: On Jan 7, 2:50Â*am, Mark wrote: There is only a limited amount of heat available in the primary medium, especially in the case we are considering. In order to transfer the most heat from the primary to the secondary medium, the two have to be kept in contact as long as possible, ie the velocities have to be kept as low as possible in both media in any given heat exchanger. I can't make it any simpler than that for you. Harry, It's funny that you can be snotty about this and be completely wrong. The usual case for a heat exchanger is is higher CFM = more BTU exchanged and lower temperature. Take the case of the solar collector this guy has on his roof. If I put water through it slower, it will come out the other end hotter will it not? Â*The hotter it is the more useful it is. Good grief. More useful? Sure if I want to use it for washing my hands. Does it contain more heat, pickup more heat going through the heat exchanger than a larger volume of water that moves through faster? No. You're once again confusing temperature with heat. NOT necessarily - with a higher TEMPERATURE primary fluid, the Delta T at the secondary heat echanger will be higher, so the efficiency of the exchanger will be higher, and more heat will be transferred to the secondary fluid. The hotter it is, the higher temperature I can achieve and ultimately more heat I can put into my water store. So, a pint of water that is 150F has more heat than 1000 gallons of water at 75? No, but if the efficiency of the heat transfer can be increased by 50% by having a higher delta T at the secondary heat exchanger, it is POSSIBLE that slowing the flow rate through the primary to increase the primary fluid temperature MAY provide more actual HEAT to the house. It would depend on the efficiencies of both heat exchangers. It also depends if we are talking a closed series loop, where the waterflow in both exchangers would be equal, or if we are talking separate loops, where the GPM flow through each exchanger was optimized. I'm ASSUMING we are talking a hybrid system, with a frost-resistant primary fluid, and THREE heat exchangers in the equation - solar to primary fluid - primary fluid to heat storage, (water) and heat storage to secondary fluid (air) where the echange fluid flows can all be separately controlled. NOT a simple question with a simple answer that is always right. The slower I circulate my solar panel medium/water through the heat exchanger in the water store, the cooler it will come out the other end. That's true, assuming all else is held constant. The cooler the water going back to the solar panel, the more energy it will pick up. That's true, assuming all else is held constant. Still waiting for the answer to the simple question I posed: Now I give you a quiz. Our friend here builds his proposed system. He puts an auto radiator in the return side of his furnace duct work and connects it to a solar collector. The solar collector heats water to 130F and it gets pumped to the radiator. The incoming air in the return duct is 65F. He has a variable speed blower so that he can vary the airflow through the radiator. Which airflow results in the water leaving the radiator at the lowest temp and consequently the most heat transferred? A - 1 CFM airflow B - 2 CFM C - 10 CFM D 100 CFM E - 1000 CFM F - 2000 CFM, the max the blower capacity? Simple problem, where is the answer? Simple question, with simple answer that is only a SMALL part of a more complex question. Answer F will extract the most heat from the water IF there is more heat available than can be extracted at 100cfm.. If 100cfm will extract enough heat to get the water exit temperature to within a few degrees of the duct inlet temperature, 500,000 cfm will not extract any more heat - and the return temperature of the water will not be below the 65 degree F air inlet temperature. If the heat echanger was 100% efficient you would get 65 BTU per gallon (imperial) out of the heat echanger in one minute at 1GPM or 60 GPH primary flow rate. So to answer your "simple" question, we need to know the flow rate of the "primary fluid", as well as it's temperature, to know how much "heat" is available. There is only 1 btu of heat per degee F of temperature change in 10 lbs of water. 10 times the water flow gives 10 times the POTENTIAL heat. |
Hot water to forced air
On Jan 7, 3:45*pm, wrote:
On Sat, 7 Jan 2012 06:37:46 -0800 (PST), " wrote: On Jan 6, 4:58*pm, wrote: On Fri, 6 Jan 2012 05:55:31 -0800 (PST), " wrote: On Jan 6, 2:30*am, harry wrote: Tch. *The longer the secondary medium remains in contact with the primary medium, the nearer to the primary medium temperature it becomes. Or, to make it simple for you, the longer you leave a pan on a hot stove, the hotter the pan becomes. *If you left the pan permanently on the stove,it would eventually reach the same temperatrure as the hotplate (neglecting losses) We're not talking about getting the air temp passing through the heat exchanger to the same temp, or even close in temp, to the hot water passing through it. *We were talking about how you get as much heat out of the water and into the house as possible. To follow your example, let's say that an electric stove heating element is red hot. How do I get the most heat out of it and cool it off the fastest? * If I place a cold pan on there and leave it there, heat is transferred to the pan and it's temp rises. *At some point it peaks and the temp of the pan and heating element equalize. *Then they both start to slowly cool off. * They both have been in contact for a long time. Now instead, let's take 6 cold pans one at a time and put each one on there for 30 secs. Which method is going to cool off that hot element faster and transfer more heat in a given period of time? * Answer: the six cold pans. The exact same thing works with the simple radiator/heat exchanger that the poster is proposing to use. * The MORE air he moves through it, the more heat he will transfer. There are of course diminishing returns and if the radiator were big enough, eventually the temp of the air and the water would be equal and there would be no more heat to transfer. * But from a practical standpoint, he isn't going to be using a radiator anywhere near that large. If you put the pan on the hotplate for two seconds and took it off virtually no heat would be transferred. Yeah, but that would be like giving the radiator one brief shot of air and then no more air. So, to achieve maximum heat transfer *both medium need to remain in the heat exchanger for as long as possible. *(Time=max) According to that, all the AC systems out there must be very inefficient because last time I checked they use blowers to move the air at high speed. *I guess they should just slow the whole thing down so the air barely moves. *What you fail to realize is that if you did that, you'd have a very small amount of very cold air instead of a very large volume of air that is cold, but not at the coldest possible temp. *Moving the air quickly brings more warmer air in contact with the evaporator and transfers MORE heat. Capiche? The ideal is that the secondary medium achieves the same temperature as the primary medium, not achievable in practice or for system design reasons or even desireable in some cases. Uh huh. * Now I give you a quiz. * *Our friend here builds his proposed system. *He puts an auto radiator in the return side of his furnace duct work and connects it to a solar collector. * The solar collector heats water to 130F and it gets pumped to the radiator. *The incoming air in the return duct is 65F. * He has a variable speed blower so that he can vary the airflow through the radiator. Which airflow results in the water leaving the radiator at the lowest temp and consequently the most heat transferred? A - 1 CFM airflow B - 2 CFM C - 10 CFM D *100 CFM E - 1000 CFM F - 2000 CFM, the max the blower capacity? There are other practical considerations to take into account mostly to do with cost. I am pretty sure engineers in America must know this and you are a minority.- Hide quoted text - - Show quoted text - I'm sure the engineers here will be interested in hearing your answer to the above question. Mabee we need to get a bit more "scientific" about it. You want to put as many BTUs of heat (using north american (canadian)n terminology) into the air from the water. A BTU is the amoiunt of heat energy involved in cahanging i pound of water 1 degree F. Water weighs 10 lbs per imperial gallon. (works better than 8.35 per US gallon for calculations). Lets say we have a 40 gallon reservoir of water at 127 degrees F and we pump it through a heat exchanger at a rate that reduces the temperature of the water returning to the reservoir to 87 degrees F.. *That means we got 1600 BTUs of heat out of the water, into the air. *To do that in 1 hour would require a water flow of 40 gallons per hour, or .66 gallons per minute. If the return air is at 68 degrees F, and the furnace fan moves 2000 cfm, what will the air temperature coming out of the heat exchanger be? 1 BTU will raise the temperature of 1 cu ft of air 55 degrees F, or 55 cu ft of air 1 degree F. *So to absorb 1600 BTUs of heat from the water into the air, we need (1600x55=) 88000 cu ft of air raised one degree F, so at 2000 cfm, or 120000cfh, we would on,y raise the temperature *by 0.73 degrees F. *If we drop the water temperatre leaving the exchanger at 77 degrees, the air would be raised by 0.91 degrees F. *SO the variables that ALL make a difference are the airflow, the waterflow, the temperature drop across the water side of the exchanger, and the desired outlet air temperature. *If you balance the water flow against the air flow you can make your delta T between the water and the air whatever you want it to be. - which is where a BYPASS system as I explained, allows you to get the results you want by varying the amount of air passing the exchanger and the water flow through the exchanger once you get the basic size of the exchanger close. Why the need for variable dampers? *Do you disagree that you get the most heat out of the heat exchanger by moving all the furnace air through it? *No I'm not disagreeing. That's good. I guess that leaves harry all to himself. IF using a "bypass" system the dampers would take the "bypass" out of the system when there is no appreciable heat to be gained from the system, allowing the solar panels to get the water hotter so the delta T would be higher, raising the efficiency - and therefore extracting more heat from the system.. You have the same situation with the solar collectors as you do with the radiator. Slowing the water flow or air flow isn't going to get you more heat or improve the efficiency. Same thing could be accomplished by a set of water control valves tho keep the heat in the reservoir untill the temperature was high enough to do an efficient job of heating the interior of the house. What reservoir? It would have to be one hell of a reservoir to make any difference in heating the house. I think it's simple. Either on a decent sunny day you get enough energy out of the solar panels to make it worthwhile to fire the' blower up or not. Once it starts it's probably gonna run most of the time, even on days where you just need a little heat. On colder days the furnace will have to come on too. *Water valving is more complex, and the difference in efficiency switching water *vs switching air, would be small enough to not make the complexity worth while. Shutting off the air flow through the secondary heat exchanger MIGHT increase the efficiency enough to make it worth while. It would also eliminate the problem of extracting heat FROM the return air, into the water, when *the solar input was too low to provide a net heat gain. Can't do that without water controls in a non-bypass system. *I'm NOT saying this method would necessarily be BETTER for the OP, but it definitely bears looking into for the reasons given. *Recap: No additional restriction in the main ductwork. Smaller heat echanger could possibly be employed Smaller than what? How are you going to heat a house with a smaller heat exchanger? For it to work, I'd say he's going to need as large a one as he can fit practically, or pay for, etc. Less complicated water controls *Possibly higher total efficiency. *Add to this, the installation might be simpler - just 2 cut - ins to the return duct (or even just one if the *"bypass" augments the cold air return from heated airspace) - and for an "experimental system" it makes implementation a lot easier and more easily reversible. A simple "zone damper" like a Famco POPC or Suncourt 8 inch motorized *unit , at about $70 would do the job., but a modulating unit like the Alan AZRDMOD series would provide variable control if desired, *for more like $200. The only reason I see for using less than all the airflow is because without severly restricting the airflow, the air coming out is going to be almost the same temp as the return air coming in. So, to avoid draft/comfort issues, you might want it to come out warmer. * BUT, and this is a big but, if that is the goal, then you'd have to change the blower because even at the lowest blower speed I doubt any system he's gonna put together is going to raise the air temp more than a deg or so. *And I don't think you're proposing that he just damper off a huge portion of the existing airflow, leave the blower as is, are you? Nope. That's why I call it a "bypass" Instead of restricting total airflow, I am advocating he SUPPLEMENT the airflow *Add a duct blower , like a Fantech FR225 - about 450-500 cfm for 8 inch "bypass" duct. That's why I dismissed using just solar from the beginning and I assumed he was talking about using it to supplement the furnace heating only when the furnace was running. *If he wants to run the system all day long, using solar, that gets into a whole additional list of potential drawbacks, many of which I believe would make it impractical. It would require having the circulating fan on "constant" which I do all year, just as a matter of course, for filtering and comfort purposes. So, ... Yeah, we;ve been down that path before. And you know my opinion, which is circulating air all the time in most cases is an energy losing proposition. Look at the typical duct work. In my house for example, I have long runs that go 50ft through an unfinished basement, then up two stories through outside walls. The last thing I want to do is be moving air through them where it can lose energy 24/7. |
Hot water to forced air
On Sat, 7 Jan 2012 13:31:04 -0800 (PST), "
wrote: Â*Recap: No additional restriction in the main ductwork. Smaller heat echanger could possibly be employed Smaller than what? How are you going to heat a house with a smaller heat exchanger? For it to work, I'd say he's going to need as large a one as he can fit practically, or pay for, etc. How big does he need ? A standard tube and shell heat echanger can be good for 50,000 to 60,000 BTU per square foot.. A smaller exchanger with higher air velocity can be every bit as good as a large one with low air velocity - and being "off line" or "parallel" has NO EFFECT on the duct resistance. Less complicated water controls Â*Possibly higher total efficiency. Â*Add to this, the installation might be simpler - just 2 cut - ins to the return duct (or even just one if the Â*"bypass" augments the cold air return from heated airspace) - and for an "experimental system" it makes implementation a lot easier and more easily reversible. A simple "zone damper" like a Famco POPC or Suncourt 8 inch motorized Â*unit , at about $70 would do the job., but a modulating unit like the Alan AZRDMOD series would provide variable control if desired, Â*for more like $200. The only reason I see for using less than all the airflow is because without severly restricting the airflow, the air coming out is going to be almost the same temp as the return air coming in. So, to avoid draft/comfort issues, you might want it to come out warmer. Â* BUT, and this is a big but, if that is the goal, then you'd have to change the blower because even at the lowest blower speed I doubt any system he's gonna put together is going to raise the air temp more than a deg or so. Â*And I don't think you're proposing that he just damper off a huge portion of the existing airflow, leave the blower as is, are you? Nope. That's why I call it a "bypass" Instead of restricting total airflow, I am advocating he SUPPLEMENT the airflow Â*Add a duct blower , like a Fantech FR225 - about 450-500 cfm for 8 inch "bypass" duct. That's why I dismissed using just solar from the beginning and I assumed he was talking about using it to supplement the furnace heating only when the furnace was running. Â*If he wants to run the system all day long, using solar, that gets into a whole additional list of potential drawbacks, many of which I believe would make it impractical. It would require having the circulating fan on "constant" which I do all year, just as a matter of course, for filtering and comfort purposes. So, ... Yeah, we;ve been down that path before. And you know my opinion, which is circulating air all the time in most cases is an energy losing proposition. Look at the typical duct work. In my house for example, I have long runs that go 50ft through an unfinished basement, then up two stories through outside walls. The last thing I want to do is be moving air through them where it can lose energy 24/7. Well, around HERE, nobody in their right mind rund heating ducts in outside walls. And with the cost of housing, unfinished, unheated basements are an almost unheard-of "luxury". Hardly call your house "typical" here. In MY house, themain "trunk" hot air duct runs through the laundry-room /wife's office, exposed on the bottom to the room, and the top to the main floor above - with accoustic tile ceiling. The heat ducts to the upper floor runs through the center load-bearing wall, and the ductwork to the main floor registers run between the floor joists between the main floor decking and the accoustic tile ceiling of the rec room / my office and the laundry room/ wife's office. The one stupid thing they DID do is running the water lines to the upstairs bathroom up the outer wall from the main floor bath. My house is VERY TYPICAL of housing in my area - circa 1970 - and most are built even more efficient today. Most houses built here since the mid to late 40s are built in a similar fashion |
Hot water to forced air
On Jan 4, 12:53*pm, JIMMIE wrote:
My son has a home that he added a solar water heater to a few years ago. Works great , too great. The unit far exceeds his demand for hot water. He wants to add some coils to his forced air HVAC system so he can use the solar heated water to heat his home. He was expecting there to be a coil he could place in his HVAC system but cant find what he is looking for or knows what to ask/google for. Any help would be greatly appreciated. One of the issues he is trying to figure out is how much radiator he will need to efficently couple the heat fron the solar panels to the interior of the house. I think he knows the one he is going to install in the fireplace is going to be way too small. I dont doubt it will heat the den the fireplace is in. I should be able to estimate this once he gets his test system up and going by measuring change in temp of the room and change in temp of the water flowing through the radiator. Jimmie |
Hot water to forced air
On Jan 7, 9:31*pm, "
wrote: On Jan 7, 3:45*pm, wrote: On Sat, 7 Jan 2012 06:37:46 -0800 (PST), " wrote: On Jan 6, 4:58*pm, wrote: On Fri, 6 Jan 2012 05:55:31 -0800 (PST), " wrote: On Jan 6, 2:30*am, harry wrote: Tch. *The longer the secondary medium remains in contact with the primary medium, the nearer to the primary medium temperature it becomes. Or, to make it simple for you, the longer you leave a pan on a hot stove, the hotter the pan becomes. *If you left the pan permanently on the stove,it would eventually reach the same temperatrure as the hotplate (neglecting losses) We're not talking about getting the air temp passing through the heat exchanger to the same temp, or even close in temp, to the hot water passing through it. *We were talking about how you get as much heat out of the water and into the house as possible. To follow your example, let's say that an electric stove heating element is red hot. How do I get the most heat out of it and cool it off the fastest? * If I place a cold pan on there and leave it there, heat is transferred to the pan and it's temp rises. *At some point it peaks and the temp of the pan and heating element equalize. *Then they both start to slowly cool off. * They both have been in contact for a long time. Now instead, let's take 6 cold pans one at a time and put each one on there for 30 secs. Which method is going to cool off that hot element faster and transfer more heat in a given period of time? * Answer: the six cold pans. The exact same thing works with the simple radiator/heat exchanger that the poster is proposing to use. * The MORE air he moves through it, the more heat he will transfer. There are of course diminishing returns and if the radiator were big enough, eventually the temp of the air and the water would be equal and there would be no more heat to transfer. * But from a practical standpoint, he isn't going to be using a radiator anywhere near that large. If you put the pan on the hotplate for two seconds and took it off virtually no heat would be transferred. Yeah, but that would be like giving the radiator one brief shot of air and then no more air. So, to achieve maximum heat transfer *both medium need to remain in the heat exchanger for as long as possible. *(Time=max) According to that, all the AC systems out there must be very inefficient because last time I checked they use blowers to move the air at high speed. *I guess they should just slow the whole thing down so the air barely moves. *What you fail to realize is that if you did that, you'd have a very small amount of very cold air instead of a very large volume of air that is cold, but not at the coldest possible temp. *Moving the air quickly brings more warmer air in contact with the evaporator and transfers MORE heat. Capiche? The ideal is that the secondary medium achieves the same temperature as the primary medium, not achievable in practice or for system design reasons or even desireable in some cases. Uh huh. * Now I give you a quiz. * *Our friend here builds his proposed system. *He puts an auto radiator in the return side of his furnace duct work and connects it to a solar collector. * The solar collector heats water to 130F and it gets pumped to the radiator. *The incoming air in the return duct is 65F. * He has a variable speed blower so that he can vary the airflow through the radiator. Which airflow results in the water leaving the radiator at the lowest temp and consequently the most heat transferred? A - 1 CFM airflow B - 2 CFM C - 10 CFM D *100 CFM E - 1000 CFM F - 2000 CFM, the max the blower capacity? There are other practical considerations to take into account mostly to do with cost. I am pretty sure engineers in America must know this and you are a minority.- Hide quoted text - - Show quoted text - I'm sure the engineers here will be interested in hearing your answer to the above question. Mabee we need to get a bit more "scientific" about it. You want to put as many BTUs of heat (using north american (canadian)n terminology) into the air from the water. A BTU is the amoiunt of heat energy involved in cahanging i pound of water 1 degree F. Water weighs 10 lbs per imperial gallon. (works better than 8.35 per US gallon for calculations). Lets say we have a 40 gallon reservoir of water at 127 degrees F and we pump it through a heat exchanger at a rate that reduces the temperature of the water returning to the reservoir to 87 degrees F... *That means we got 1600 BTUs of heat out of the water, into the air. |
Hot water to forced air
On Jan 7, 10:53*pm, wrote:
On Sat, 7 Jan 2012 13:31:04 -0800 (PST), " wrote: *Recap: No additional restriction in the main ductwork. Smaller heat echanger could possibly be employed Smaller than what? *How are you going to heat a house with a smaller heat exchanger? *For it to work, I'd say he's going to need as large a one as he can fit practically, or pay for, etc. *How big does he need ? A standard tube and shell heat echanger can be good for 50,000 to 60,000 BTU per square foot.. A smaller exchanger with higher air velocity can be every bit as good as a large one with low air velocity - and being "off line" or "parallel" has NO EFFECT on the duct resistance. Less complicated water controls *Possibly higher total efficiency. *Add to this, the installation might be simpler - just 2 cut - ins to the return duct (or even just one if the *"bypass" augments the cold air return from heated airspace) - and for an "experimental system" it makes implementation a lot easier and more easily reversible. A simple "zone damper" like a Famco POPC or Suncourt 8 inch motorized *unit , at about $70 would do the job., but a modulating unit like the Alan AZRDMOD series would provide variable control if desired, *for more like $200. The only reason I see for using less than all the airflow is because without severly restricting the airflow, the air coming out is going to be almost the same temp as the return air coming in. So, to avoid draft/comfort issues, you might want it to come out warmer. * BUT, and this is a big but, if that is the goal, then you'd have to change the blower because even at the lowest blower speed I doubt any system he's gonna put together is going to raise the air temp more than a deg or so. *And I don't think you're proposing that he just damper off a huge portion of the existing airflow, leave the blower as is, are you? Nope. That's why I call it a "bypass" Instead of restricting total airflow, I am advocating he SUPPLEMENT the airflow *Add a duct blower , like a Fantech FR225 - about 450-500 cfm for 8 inch "bypass" duct. That's why I dismissed using just solar from the beginning and I assumed he was talking about using it to supplement the furnace heating only when the furnace was running. *If he wants to run the system all day long, using solar, that gets into a whole additional list of potential drawbacks, many of which I believe would make it impractical. It would require having the circulating fan on "constant" which I do all year, just as a matter of course, for filtering and comfort purposes. So, ... Yeah, we;ve been down that path before. *And you know my opinion, which is circulating air all the time in most cases is an energy losing proposition. Look at the typical duct work. *In my house for example, I have long runs that go 50ft through an unfinished basement, then up two stories through outside walls. The last thing I want to do is be moving air through them where it can lose energy 24/7. Well, around HERE, nobody in their right mind rund heating ducts in outside walls. And with the cost of housing, unfinished, unheated basements are an almost unheard-of "luxury". Hardly call your house "typical" here. *In MY house, themain "trunk" hot air duct runs through the laundry-room /wife's office, exposed on the bottom to the room, and the top to the main floor above - with accoustic tile ceiling. The heat ducts to the upper floor *runs through the center load-bearing wall, and the ductwork to the main floor registers run between the floor joists between the main floor decking and the accoustic tile ceiling of the rec room / my office and the laundry room/ wife's office. *The one stupid thing they DID do is running the water lines to the upstairs bathroom up the outer wall from the main floor bath. *My house is VERY TYPICAL of housing in my area - circa 1970 - and most are built even more efficient today. Most houses built here since the mid to late 40s are built in a similar fashion- Hide quoted text - - Show quoted text - So no change since1940? That is why you Yanks are living in the past with all this obsolete crap..Technology has moved on in seventy years. Amazing. They put a man on the moon but have such crapi n theri homes. |
Hot water to forced air
On Jan 8, 5:02*am, harry wrote:
Yes it is. *Also If the return water to a boiler(or solar collector) is cooler, more heat can be extracted from the combustion gases so making the boiler more efficient. It is a key factor in boiler efficiency, especially condensing boilers.https://en.wikipedia.org/wiki/Conden...er#Efficiency- Hide quoted text - - Show quoted text - harry, let's stick to the issue that started all this. The OP wants to put a heat exchanger in his furnace return duct that will use heated water coming from solar panels to add heat to the house. I stated that to get the most heat out of the heat exchanger, he wants the airflow through it to be as high as possible. You vehemently objected to that, claiming it was untrue. Here is the exact exchange that started this long thread: Trader: " You'd always get maximum heat extraction with the most airflow through the heat exchanger, so why the need for a system of dampers to vary the flow? Harry: That is not correct. The factors are Time, Turbulence and Temperature difference (between the media) All need to be maximised to get maximum heat transfer in any given heat exchanger.. So far, we have three people here who say you are wrong, CL, Mark and I. CL even came up with a great heat exchanger spec sheet for the exact type of heat exchanger that would be perfect for the application and it shows that we are all right. The spec sheet is right he http://www.heatexchangersonline.com/airtowater.htm Look at the first heat exchanger. Operating with 140F incoming water at 6 GPM, the performance is listed as: Airflow CFM BTUS 500 28 600 29 700 34 800 36 900 37 1018 38 It could not be any clearer. As airflow goes up, so does the amount of heat transfered. Just like more heat is transferred from a car radiator to the air when more air is moving through it. Which you claim is irrelevant, but everyone else knows it is an example of a very common heat exchanger. Now, you can either read that spec sheet and man up and admit you were wrong, or you can hurl more insults. |
Hot water to forced air
On Sun, 8 Jan 2012 02:05:52 -0800 (PST), harry
wrote: On Jan 7, 10:53Â*pm, wrote: On Sat, 7 Jan 2012 13:31:04 -0800 (PST), " wrote: Â*Recap: No additional restriction in the main ductwork. Smaller heat echanger could possibly be employed Smaller than what? Â*How are you going to heat a house with a smaller heat exchanger? Â*For it to work, I'd say he's going to need as large a one as he can fit practically, or pay for, etc. Â*How big does he need ? A standard tube and shell heat echanger can be good for 50,000 to 60,000 BTU per square foot.. A smaller exchanger with higher air velocity can be every bit as good as a large one with low air velocity - and being "off line" or "parallel" has NO EFFECT on the duct resistance. Less complicated water controls Â*Possibly higher total efficiency. Â*Add to this, the installation might be simpler - just 2 cut - ins to the return duct (or even just one if the Â*"bypass" augments the cold air return from heated airspace) - and for an "experimental system" it makes implementation a lot easier and more easily reversible. A simple "zone damper" like a Famco POPC or Suncourt 8 inch motorized Â*unit , at about $70 would do the job., but a modulating unit like the Alan AZRDMOD series would provide variable control if desired, Â*for more like $200. The only reason I see for using less than all the airflow is because without severly restricting the airflow, the air coming out is going to be almost the same temp as the return air coming in. So, to avoid draft/comfort issues, you might want it to come out warmer. Â* BUT, and this is a big but, if that is the goal, then you'd have to change the blower because even at the lowest blower speed I doubt any system he's gonna put together is going to raise the air temp more than a deg or so. Â*And I don't think you're proposing that he just damper off a huge portion of the existing airflow, leave the blower as is, are you? Nope. That's why I call it a "bypass" Instead of restricting total airflow, I am advocating he SUPPLEMENT the airflow Â*Add a duct blower , like a Fantech FR225 - about 450-500 cfm for 8 inch "bypass" duct. That's why I dismissed using just solar from the beginning and I assumed he was talking about using it to supplement the furnace heating only when the furnace was running. Â*If he wants to run the system all day long, using solar, that gets into a whole additional list of potential drawbacks, many of which I believe would make it impractical. It would require having the circulating fan on "constant" which I do all year, just as a matter of course, for filtering and comfort purposes. So, ... Yeah, we;ve been down that path before. Â*And you know my opinion, which is circulating air all the time in most cases is an energy losing proposition. Look at the typical duct work. Â*In my house for example, I have long runs that go 50ft through an unfinished basement, then up two stories through outside walls. The last thing I want to do is be moving air through them where it can lose energy 24/7. Well, around HERE, nobody in their right mind rund heating ducts in outside walls. And with the cost of housing, unfinished, unheated basements are an almost unheard-of "luxury". Hardly call your house "typical" here. Â*In MY house, themain "trunk" hot air duct runs through the laundry-room /wife's office, exposed on the bottom to the room, and the top to the main floor above - with accoustic tile ceiling. The heat ducts to the upper floor Â*runs through the center load-bearing wall, and the ductwork to the main floor registers run between the floor joists between the main floor decking and the accoustic tile ceiling of the rec room / my office and the laundry room/ wife's office. Â*The one stupid thing they DID do is running the water lines to the upstairs bathroom up the outer wall from the main floor bath. Â*My house is VERY TYPICAL of housing in my area - circa 1970 - and most are built even more efficient today. Most houses built here since the mid to late 40s are built in a similar fashion- Hide quoted text - - Show quoted text - So no change since1940? That is why you Yanks are living in the past with all this obsolete crap..Technology has moved on in seventy years. Amazing. They put a man on the moon but have such crapi n theri homes. No, it just shows that this house is far more advanced than Traders - which runs the heat pipes up the outside wall and has an unheated basement. How is your Euro-shack any better than mine? |
Hot water to forced air
On Jan 8, 7:08*pm, wrote:
On Sun, 8 Jan 2012 02:05:52 -0800 (PST), harry wrote: On Jan 7, 10:53*pm, wrote: On Sat, 7 Jan 2012 13:31:04 -0800 (PST), " wrote: *Recap: No additional restriction in the main ductwork. Smaller heat echanger could possibly be employed Smaller than what? *How are you going to heat a house with a smaller heat exchanger? *For it to work, I'd say he's going to need as large a one as he can fit practically, or pay for, etc. *How big does he need ? A standard tube and shell heat echanger can be good for 50,000 to 60,000 BTU per square foot.. A smaller exchanger with higher air velocity can be every bit as good as a large one with low air velocity - and being "off line" or "parallel" has NO EFFECT on the duct resistance. Less complicated water controls *Possibly higher total efficiency. *Add to this, the installation might be simpler - just 2 cut - ins to the return duct (or even just one if the *"bypass" augments the cold air return from heated airspace) - and for an "experimental system" it makes implementation a lot easier and more easily reversible. A simple "zone damper" like a Famco POPC or Suncourt 8 inch motorized *unit , at about $70 would do the job., but a modulating unit like the Alan AZRDMOD series would provide variable control if desired, *for more like $200. The only reason I see for using less than all the airflow is because without severly restricting the airflow, the air coming out is going to be almost the same temp as the return air coming in. So, to avoid draft/comfort issues, you might want it to come out warmer. * BUT, and this is a big but, if that is the goal, then you'd have to change the blower because even at the lowest blower speed I doubt any system he's gonna put together is going to raise the air temp more than a deg or so. *And I don't think you're proposing that he just damper off a huge portion of the existing airflow, leave the blower as is, are you? Nope. That's why I call it a "bypass" Instead of restricting total airflow, I am advocating he SUPPLEMENT the airflow *Add a duct blower , like a Fantech FR225 - about 450-500 cfm for 8 inch "bypass" duct. That's why I dismissed using just solar from the beginning and I assumed he was talking about using it to supplement the furnace heating only when the furnace was running. *If he wants to run the system all day long, using solar, that gets into a whole additional list of potential drawbacks, many of which I believe would make it impractical. It would require having the circulating fan on "constant" which I do all year, just as a matter of course, for filtering and comfort purposes. So, ... Yeah, we;ve been down that path before. *And you know my opinion, which is circulating air all the time in most cases is an energy losing proposition. Look at the typical duct work. *In my house for example, I have long runs that go 50ft through an unfinished basement, then up two stories through outside walls. The last thing I want to do is be moving air through them where it can lose energy 24/7. Well, around HERE, nobody in their right mind rund heating ducts in outside walls. And with the cost of housing, unfinished, unheated basements are an almost unheard-of "luxury". Hardly call your house "typical" here. *In MY house, themain "trunk" hot air duct runs through the laundry-room /wife's office, exposed on the bottom to the room, and the top to the main floor above - with accoustic tile ceiling. The heat ducts to the upper floor *runs through the center load-bearing wall, and the ductwork to the main floor registers run between the floor joists between the main floor decking and the accoustic tile ceiling of the rec room / my office and the laundry room/ wife's office. *The one stupid thing they DID do is running the water lines to the upstairs bathroom up the outer wall from the main floor bath. *My house is VERY TYPICAL of housing in my area - circa 1970 - and most are built even more efficient today. Most houses built here since the mid to late 40s are built in a similar fashion- Hide quoted text - - Show quoted text - So no change since1940? *That is why you Yanks are living in the past with all this obsolete crap..Technology has moved on in seventy years. Amazing. They put a man on the moon but have such crapi n theri homes. * No, *it just shows that this house is far more advanced than Traders - which runs the heat pipes up the outside wall and has an unheated basement. *How is your Euro-shack any better than mine?- Hide quoted text - - Show quoted text - I am beyond central heating. I have such insulation that the heat from theTV, refrigerators and the sun etc keeps the place warm except in very dull and windy weather. I have no heating bill and net profit (to me) electricity. http://www.flickr.com/photos/ara-chl...7627608971673/ It recently appeared on national TV. But my house is not typical of UK houses which do have central heating. Fuel usage is probably less than half what you use in America in the typical new UK house due to more efficient boilers and control sytems and more insulation. A couple of years back I looked at some new houses being constructed in America.(Des Moines) Appalling. They were installing the sort of stuff were were junking thirty years ago. There is nothing wrong with unheated basements so long as they are outside the thermal envelope. (Though I thought they were reserved for poor homeless family members these days?) Running heating pipes up the outside of a building is pretty weird though. |
Hot water to forced air
On Jan 8, 2:05*pm, "
wrote: On Jan 8, 5:02*am, harry wrote: Yes it is. *Also If the return water to a boiler(or solar collector) is cooler, more heat can be extracted from the combustion gases so making the boiler more efficient. It is a key factor in boiler efficiency, especially condensing boilers.https://en.wikipedia.org/wiki/Conden...fficiency-Hide quoted text - - Show quoted text - harry, let's stick to the issue that started all this. *The OP wants to put a heat exchanger in his furnace return duct that will use heated water coming from solar panels to add heat to the house. *I stated that to get the most heat out of the heat exchanger, he wants the airflow through it to be as high as possible. *You vehemently objected to that, claiming it was untrue. Here is the exact exchange that started this long thread: Trader: *" You'd always get maximum heat extraction with the most airflow through the heat exchanger, so why the need for a system of dampers to vary the flow? Harry: That is not correct. The factors are Time, Turbulence and Temperature difference (between the media) All need to be maximised to get maximum heat transfer in any given heat exchanger.. So far, we have three people here who say you are wrong, CL, Mark and I. *CL even came up with a great heat exchanger spec sheet for the exact type of heat exchanger that would be perfect for the application and it shows that we are all right. The spec sheet is right he http://www.heatexchangersonline.com/airtowater.htm Look at the first heat exchanger. *Operating with 140F incoming water at 6 GPM, the performance is listed as: Airflow CFM * * BTUS 500 * * * 28 600 * * * 29 700 * * * 34 800 * * * 36 900 * * * 37 1018 * * 38 It could not be any clearer. *As airflow goes up, so does the amount of heat transfered. *Just like more heat is transferred from a car radiator to the air when more air is moving through it. Which you claim is irrelevant, but everyone else knows it is an example of a very common heat exchanger. Dumping heat to waste (Car radiator example) is an entirely different thing to recovering it for use and irrelevant to this case. The issue is the OP has only a small amount of heat available so needs to be efficient. The volume of air he can put through his HX is fixed. To recover the most heat, the exit air temperature needs to be as high as possible which can be achieved by reducing the velocity through the HX. This means that the temperature primary water exit from the HX is as low as possible which increases the efficiency of the solar collector. The option of increasing volume of airflow is not available and is not helpful in any event I can't make it any simpler than that for you. There are three variables not one. Time, turbulence and temperature. To maximise heat transfer, any of them can be increased. It's very basic.They are NOT my idea. Has been known since Adam was a lad. I think you may be confusing in your mind air velocity(meters/min) and air volume moved (cubic meters/min.) Or feet. They are not the same thing. |
Hot water to forced air
On Sun, 8 Jan 2012 11:59:09 -0800 (PST), harry
wrote: Â*How is your Euro-shack any better than mine?- Hide quoted text - - Show quoted text - I am beyond central heating. I have such insulation that the heat from theTV, refrigerators and the sun etc keeps the place warm except in very dull and windy weather. I have no heating bill and net profit (to me) electricity. http://www.flickr.com/photos/ara-chl...7627608971673/ It recently appeared on national TV. We have places like that here too. But they are not "typical" here - or there. Ond on the whole, American, and particularly Canadian homes are more energy efficient than the average British dwelling, by a fair amount. But my house is not typical of UK houses which do have central heating. Fuel usage is probably less than half what you use in America in the typical new UK house due to more efficient boilers and control sytems and more insulation. What is the normal R value in the walls and roof of the average new british house? What is required by "code". How much gas does it take to heat a 1300 sq foot home in the coldest part of Britain (which is still, on the whole, not as cold as most of Canada)??? A couple of years back I looked at some new houses being constructed in America.(Des Moines) Appalling. They were installing the sort of stuff were were junking thirty years ago. They build differently in the USA than we do up here in the "great white north". 6 inch walls with strayed foam insulation are not out of the ordinary here any more. The house my father built 30 years ago was heated by 1/2 cord of wood per winter- and it was a "conventional" urban split level of over 2000 square feet. There is nothing wrong with unheated basements so long as they are outside the thermal envelope. (Though I thought they were reserved for poor homeless family members these days?) Running heating pipes up the outside of a building is pretty weird though. |
Hot water to forced air
On Jan 8, 11:38*pm, wrote:
On Sun, 8 Jan 2012 11:59:09 -0800 (PST), harry wrote: *How is your Euro-shack any better than mine?- Hide quoted text - - Show quoted text - I am beyond central heating. I have such insulation that the heat from theTV, refrigerators and the sun etc keeps the place warm except in very dull and windy weather. I have no *heating bill and net profit (to me) electricity. http://www.flickr.com/photos/ara-chl...7627608971673/ It recently appeared on national TV. *We have places like that here too. *But they are not "typical" here - or there. Ond on the whole, American, and particularly Canadian homes are more energy efficient than the average British dwelling, by a fair amount. But my house is not typical of UK houses which do have central heating. Fuel usage is probably less than half what you use in America in the typical new UK house due to more efficient boilers and control sytems and more insulation. *What is the normal R value in the walls and roof of the average new british house? *What is required by "code". How much gas does it take to heat a *1300 sq foot home in the coldest part of Britain (which is still, on the whole, not as cold as *most of Canada)??? A couple of years back I looked at some new houses *being constructed in America.(Des Moines) Appalling. *They were installing the sort of stuff were were junking thirty years ago. *They build differently in the USA than we do up here in the "great white north". 6 inch walls with strayed foam insulation are not out of the ordinary here any more. *The house my father built 30 years ago was heated by 1/2 cord of wood *per winter- and it was a "conventional" urban *split level of over 2000 square feet. There is nothing wrong with unheated basements so long as they are outside the thermal envelope. (Though I thought they were reserved for poor homeless family members these days?) Running heating pipes up the outside of a building is pretty weird though.- Hide quoted text - - Show quoted text - We do things in"U" values here (reciprocal of R) http://www.knaufinsulation.co.uk/sel..._-_e,w,ni.aspx All is in metric. http://www.simetric.co.uk/sibtu.htm We are much warmer here than in Canada due to the maritime climate. |
Hot water to forced air
On Jan 8, 3:24*pm, harry wrote:
On Jan 8, 2:05*pm, " wrote: On Jan 8, 5:02*am, harry wrote: Yes it is. *Also If the return water to a boiler(or solar collector) is cooler, more heat can be extracted from the combustion gases so making the boiler more efficient. It is a key factor in boiler efficiency, especially condensing boilers.https://en.wikipedia.org/wiki/Conden...ncy-Hidequoted text - - Show quoted text - harry, let's stick to the issue that started all this. *The OP wants to put a heat exchanger in his furnace return duct that will use heated water coming from solar panels to add heat to the house. *I stated that to get the most heat out of the heat exchanger, he wants the airflow through it to be as high as possible. *You vehemently objected to that, claiming it was untrue. Here is the exact exchange that started this long thread: Trader: *" You'd always get maximum heat extraction with the most airflow through the heat exchanger, so why the need for a system of dampers to vary the flow? Harry: That is not correct. The factors are Time, Turbulence and Temperature difference (between the media) All need to be maximised to get maximum heat transfer in any given heat exchanger.. So far, we have three people here who say you are wrong, CL, Mark and I. *CL even came up with a great heat exchanger spec sheet for the exact type of heat exchanger that would be perfect for the application and it shows that we are all right. The spec sheet is right he http://www.heatexchangersonline.com/airtowater.htm Look at the first heat exchanger. *Operating with 140F incoming water at 6 GPM, the performance is listed as: Airflow CFM * * BTUS 500 * * * 28 600 * * * 29 700 * * * 34 800 * * * 36 900 * * * 37 1018 * * 38 It could not be any clearer. *As airflow goes up, so does the amount of heat transfered. *Just like more heat is transferred from a car radiator to the air when more air is moving through it. Which you claim is irrelevant, but everyone else knows it is an example of a very common heat exchanger. Dumping heat to waste (Car radiator example) is an entirely different thing to recovering it for use and irrelevant to this case. A car radiator is a shining example of a heat exchanger that shows that the MORE air you move through it the MORE heat you transfer. The fact that it directly contradicts your false claims is the only reason you think it's an entirely different thing. In the case of the system the OP wants to build the "waste" heat just goes into the home. Capiche? The issue is the OP has only a small amount of heat available so needs to be efficient. The volume of air he can put through his HX is fixed. To recover the most heat, the exit air *temperature needs to be as high as possible which can be achieved by reducing the velocity through the HX. There you go yet again. You are confusing HEAT and TEMPERATURE. I have told you that over and over. Mark has told you that. CL agrees that the more air you put through the heat exchanger the more heat you transfer. Is the air not as hot coming out when you put more air through it? YES. But there is more air MASS that is being heated and more total heat being transferred. This means that the temperature primary water exit from the HX is as low as possible which increases the efficiency of the solar collector. Uh huh. And how do you get as low a temp of water flowing out of the heat exchanger sitting in the duct? By moving the MOST air through it. How do you get the lowest temp of water flowing back to an engine from a radiator? By moving the MOST air through it. Exactly the same principle. At some with enough airflow you get the exiting water and air temps equal and that is when you have transferred all the heat. Capiche? The option of increasing volume of airflow is not available and is not helpful in any event It's directly relevant, because if you paid attention to the discussion, what was being discussed was a bypass system that moves PART of the total air volume through the heat exchanger. Dampers would control the amount. Capiche? I can't make it any simpler than that for you. There are three variables not one. Time, turbulence and temperature. You forgot MASS. Yes, with a FIXED MASS in contact with another MASS, the longer they stay in contact the more heat is transferred. Let's say you have 10 identical masses in the form of metal cubes. One of those cubes is heated to 500F. The others are all at 0F. I do the following two cases: A - I take one of the 0F cubes and place it on top of the 500F cube and leave it there for 5 mins. B - I take one of the 0F cubes and place it on top of the 500F cube for 1 min. Then I replace it with another 0F cube for 1 min. I do that for the same 5 min period. Which results in the 500F cube being cooled off the most? Which results in the most heat transferred? Answer B because you have a larger temperature differential because you're constantly replacing the mass being heated. That is exactly what is happening in the heat exchanger. Now according to your faulty logic, less energy is being transferred because the 5 cubes are not as hot as the one cube left there for the entire time. You are confusing HEAT with TEMPERATURE. To maximise heat transfer, any of them can be increased. It's very basic.They are NOT my idea. *Has been known since Adam was a lad. One way you increase the temperature differential is to constantly replace mass that is being cooled with new mass. That is exactly what happens when you increase the airflow in the heat exchanger or the car radiator. Capiche? I think you may be confusing in your mind air velocity(meters/min) and air volume moved (cubic meters/min.) *Or feet. They are not the same thing.- Hide quoted text - - Show quoted text - You are confusing HEAT and TEMPERATURE. Three of us in this thread say you are wrong. Not a single person agrees with your version of physics. And again, it would be extremely helpful if you could address specific questions. We've addressed and answered anything you put forth. I've given you several examples and asked questions that show your science is just wrong. You never answer them and just go somewhere else. Best example, CL came up with an actual data sheet for the kind of water to air heat exchanger that the guy could use for his application. I gave you the link to the data sheet. You can read and interpret a data sheet, can you not? Yet we have no reply to that, you just ignore it and go on to something else. Here it is one more time: The spec sheet is right he http://www.heatexchangersonline.com/airtowater.htm Look at the first heat exchanger. Operating with 140F incoming water at 6 GPM, the performance is listed as: Airflow CFM BTUS 500 28 600 29 700 34 800 36 900 37 1018 38 It could not be any clearer. As airflow goes up, so does the amount of heat transfered. Just like more heat is transferred from a car radiator to the air when more air is moving through it. Now either look at that datasheet and explain how it doesn't say that the more air that you move through the heat exchanger, the more heat you get out, or else shut up. You really have re-inforced your position as the village idiot on this one. And despite being dead wrong, you continue to claim that those of us in the US or Candada are the uneducated, inferior ones with no grasp on science or technology. I suggest you look in the mirror. |
Hot water to forced air
On Jan 9, 2:52*pm, "
wrote: On Jan 8, 3:24*pm, harry wrote: On Jan 8, 2:05*pm, " wrote: On Jan 8, 5:02*am, harry wrote: Yes it is. *Also If the return water to a boiler(or solar collector) is cooler, more heat can be extracted from the combustion gases so making the boiler more efficient. It is a key factor in boiler efficiency, especially condensing boilers.https://en.wikipedia.org/wiki/Conden...Hidequotedtext - - Show quoted text - harry, let's stick to the issue that started all this. *The OP wants to put a heat exchanger in his furnace return duct that will use heated water coming from solar panels to add heat to the house. *I stated that to get the most heat out of the heat exchanger, he wants the airflow through it to be as high as possible. *You vehemently objected to that, claiming it was untrue. Here is the exact exchange that started this long thread: Trader: *" You'd always get maximum heat extraction with the most airflow through the heat exchanger, so why the need for a system of dampers to vary the flow? Harry: That is not correct. The factors are Time, Turbulence and Temperature difference (between the media) All need to be maximised to get maximum heat transfer in any given heat exchanger.. So far, we have three people here who say you are wrong, CL, Mark and I. *CL even came up with a great heat exchanger spec sheet for the exact type of heat exchanger that would be perfect for the application and it shows that we are all right. The spec sheet is right he http://www.heatexchangersonline.com/airtowater.htm Look at the first heat exchanger. *Operating with 140F incoming water at 6 GPM, the performance is listed as: Airflow CFM * * BTUS 500 * * * 28 600 * * * 29 700 * * * 34 800 * * * 36 900 * * * 37 1018 * * 38 It could not be any clearer. *As airflow goes up, so does the amount of heat transfered. *Just like more heat is transferred from a car radiator to the air when more air is moving through it. Which you claim is irrelevant, but everyone else knows it is an example of a very common heat exchanger. Dumping heat to waste (Car radiator example) is an entirely different thing to recovering it for use and irrelevant to this case. A car radiator is a shining example of a heat exchanger that shows that the MORE air you move through it the MORE heat you transfer. *The fact that it directly contradicts your false claims is the only reason you think it's an entirely different thing. In the case of the system the OP wants to build the "waste" heat just goes into the home. *Capiche? The issue is the OP has only a small amount of heat available so needs to be efficient. The volume of air he can put through his HX is fixed. To recover the most heat, the exit air *temperature needs to be as high as possible which can be achieved by reducing the velocity through the HX. There you go yet again. *You are confusing HEAT and TEMPERATURE. I have told you that over and over. Mark has told you that. CL agrees that the more air you put through the heat exchanger the more heat you transfer. *Is the air not as hot coming out when you put more air through it? * YES. *But there is more air MASS that is being heated and more total heat being transferred. This means that the temperature primary water exit from the HX is as low as possible which increases the efficiency of the solar collector. Uh huh. *And how do you get as low a temp of water flowing out of the heat exchanger sitting in the duct? *By moving the MOST air through it. *How do you get the lowest temp of water flowing back to an engine from a radiator? *By moving the MOST air through it. *Exactly the same principle. *At some with enough airflow you get the exiting water and air temps equal and that is when you have transferred all the heat. *Capiche? The option of increasing volume of airflow is not available and is not helpful in any event It's directly relevant, because if you paid attention to the discussion, what was being discussed was a bypass system that moves PART of the total air volume through the heat exchanger. *Dampers would control the amount. Capiche? I can't make it any simpler than that for you. There are three variables not one. Time, turbulence and temperature. You forgot MASS. *Yes, with a FIXED MASS in contact with another MASS, the longer they stay in contact the more heat is transferred. * Let's say you have 10 *identical masses in the form of metal cubes. *One of those cubes is heated to 500F. * The others are all at 0F. I do the following two cases: A - I take one of the 0F cubes and place it on top of the 500F cube and leave it there for 5 mins. B - I take one of the 0F cubes and place it on top of the 500F cube for 1 min. *Then I replace it with another 0F cube for 1 min. *I do that for the same 5 min period. Which results in the 500F cube being cooled off the most? * Which results in the most heat transferred? Answer B because you have a larger temperature differential because you're constantly replacing the mass being heated. *That is exactly what is happening in the heat exchanger. Now according to your faulty logic, less energy is being transferred because the 5 cubes are not as hot as the one cube left there for the entire time. *You are confusing HEAT with TEMPERATURE. To maximise heat transfer, any of them can be increased. It's very basic.They are NOT my idea. *Has been known since Adam was a lad. One way you increase the temperature differential is to constantly replace mass that is being cooled with new mass. *That is exactly what happens when you increase the airflow in the heat exchanger or the car radiator. *Capiche? I think you may be confusing in your mind air velocity(meters/min) and air volume moved (cubic meters/min.) *Or feet. They are not the same thing.- Hide quoted text - - Show quoted text - You are confusing HEAT and TEMPERATURE. *Three of us in this thread say you are wrong. *Not a single person agrees with your version of physics. * *And again, it would be extremely helpful if you could address specific questions. We've addressed and answered anything you put forth. I've given you several examples and asked questions that show your science is just wrong. *You never answer them and just go somewhere else. Best example, CL came up with an actual data sheet for the kind of water to air heat exchanger that the guy could use for his application. *I gave you the link to the data sheet. *You can read and interpret a data sheet, can you not? *Yet we have no reply to that, you just ignore it and go on to something else. Here it is one more time: The spec sheet is right he http://www.heatexchangersonline.com/airtowater.htm Look at the first heat exchanger. *Operating with 140F incoming water at 6 GPM, the performance is listed as: Airflow CFM * * BTUS 500 * * * 28 600 * * * 29 700 * * * 34 800 * * * 36 900 * * * 37 1018 * * 38 It could not be any clearer. *As airflow goes up, so does the amount of heat transfered. *Just like more heat is transferred from a car radiator to the air when more air is moving through it. Now either look at that datasheet and explain how it doesn't say that the more air that you move through the heat exchanger, the more heat you get out, or else shut up. You really have re-inforced your position as the village idiot on this one. * And despite being dead wrong, you continue to claim that those of us in the US or Candada are the uneducated, inferior ones with no grasp on science or technology. *I suggest you look in the mirror.- Hide quoted text - - Show quoted text - In the case dicussed, we do not have an infinite number of "cubes" .We have to wring the maximum amount of energy out of the one we have. That is the whole point of the excercise. We are NOT talking temperature differentials. The car radiator (on a car) is irrelevent to the case under discussion because there IS an infinite number of "cubes". (Ie air to cool it with). Removed from the car and used for this purpose is an entire different ball game. But you can't get your head round any of this. Go back and read my last post. |
Hot water to forced air
On Mon, 9 Jan 2012 00:18:28 -0800 (PST), harry
wrote: On Jan 8, 11:38Â*pm, wrote: On Sun, 8 Jan 2012 11:59:09 -0800 (PST), harry wrote: Â*How is your Euro-shack any better than mine?- Hide quoted text - - Show quoted text - I am beyond central heating. I have such insulation that the heat from theTV, refrigerators and the sun etc keeps the place warm except in very dull and windy weather. I have no Â*heating bill and net profit (to me) electricity. http://www.flickr.com/photos/ara-chl...7627608971673/ It recently appeared on national TV. Â*We have places like that here too. Â*But they are not "typical" here - or there. Ond on the whole, American, and particularly Canadian homes are more energy efficient than the average British dwelling, by a fair amount. But my house is not typical of UK houses which do have central heating. Fuel usage is probably less than half what you use in America in the typical new UK house due to more efficient boilers and control sytems and more insulation. Â*What is the normal R value in the walls and roof of the average new british house? Â*What is required by "code". How much gas does it take to heat a Â*1300 sq foot home in the coldest part of Britain (which is still, on the whole, not as cold as Â*most of Canada)??? A couple of years back I looked at some new houses Â*being constructed in America.(Des Moines) Appalling. Â*They were installing the sort of stuff were were junking thirty years ago. Â*They build differently in the USA than we do up here in the "great white north". 6 inch walls with strayed foam insulation are not out of the ordinary here any more. Â*The house my father built 30 years ago was heated by 1/2 cord of wood Â*per winter- and it was a "conventional" urban Â*split level of over 2000 square feet. There is nothing wrong with unheated basements so long as they are outside the thermal envelope. (Though I thought they were reserved for poor homeless family members these days?) Running heating pipes up the outside of a building is pretty weird though.- Hide quoted text - - Show quoted text - We do things in"U" values here (reciprocal of R) http://www.knaufinsulation.co.uk/sel..._-_e,w,ni.aspx All is in metric. http://www.simetric.co.uk/sibtu.htm We are much warmer here than in Canada due to the maritime climate. I heat my "snow belt" Ontario home for $700 worth of natural gas a year - which also provides all my domestic hot water. |
Hot water to forced air
On Jan 9, 10:23*pm, wrote:
On Mon, 9 Jan 2012 00:18:28 -0800 (PST), harry wrote: On Jan 8, 11:38*pm, wrote: On Sun, 8 Jan 2012 11:59:09 -0800 (PST), harry wrote: *How is your Euro-shack any better than mine?- Hide quoted text - - Show quoted text - I am beyond central heating. I have such insulation that the heat from theTV, refrigerators and the sun etc keeps the place warm except in very dull and windy weather. I have no *heating bill and net profit (to me) electricity. http://www.flickr.com/photos/ara-chl...7627608971673/ It recently appeared on national TV. *We have places like that here too. *But they are not "typical" here - or there. Ond on the whole, American, and particularly Canadian homes are more energy efficient than the average British dwelling, by a fair amount. But my house is not typical of UK houses which do have central heating. Fuel usage is probably less than half what you use in America in the typical new UK house due to more efficient boilers and control sytems and more insulation. *What is the normal R value in the walls and roof of the average new british house? *What is required by "code". How much gas does it take to heat a *1300 sq foot home in the coldest part of Britain (which is still, on the whole, not as cold as *most of Canada)??? A couple of years back I looked at some new houses *being constructed in America.(Des Moines) Appalling. *They were installing the sort of stuff were were junking thirty years ago. *They build differently in the USA than we do up here in the "great white north". 6 inch walls with strayed foam insulation are not out of the ordinary here any more. *The house my father built 30 years ago was heated by 1/2 cord of wood *per winter- and it was a "conventional" urban *split level of over 2000 square feet. There is nothing wrong with unheated basements so long as they are outside the thermal envelope. (Though I thought they were reserved for poor homeless family members these days?) Running heating pipes up the outside of a building is pretty weird though.- Hide quoted text - - Show quoted text - We do things in"U" values here (reciprocal of R) http://www.knaufinsulation.co.uk/sel.../building_regu... All is in metric. http://www.simetric.co.uk/sibtu.htm We are much warmer here than in Canada due to the maritime climate. *I heat my "snow belt" Ontario home for $700 worth of natural gas a year - which also provides all my domestic hot water Well that's pretty cheap. Probably gas is more expensive here in the UK too. |
Hot water to forced air
On Jan 9, 1:50*pm, harry wrote:
You forgot MASS. *Yes, with a FIXED MASS in contact with another MASS, the longer they stay in contact the more heat is transferred. * Let's say you have 10 *identical masses in the form of metal cubes. *One of those cubes is heated to 500F. * The others are all at 0F. I do the following two cases: A - I take one of the 0F cubes and place it on top of the 500F cube and leave it there for 5 mins. B - I take one of the 0F cubes and place it on top of the 500F cube for 1 min. *Then I replace it with another 0F cube for 1 min. *I do that for the same 5 min period. Which results in the 500F cube being cooled off the most? * Which results in the most heat transferred? Answer B because you have a larger temperature differential because you're constantly replacing the mass being heated. *That is exactly what is happening in the heat exchanger. Now according to your faulty logic, less energy is being transferred because the 5 cubes are not as hot as the one cube left there for the entire time. *You are confusing HEAT with TEMPERATURE. To maximise heat transfer, any of them can be increased. It's very basic.They are NOT my idea. *Has been known since Adam was a lad. One way you increase the temperature differential is to constantly replace mass that is being cooled with new mass. *That is exactly what happens when you increase the airflow in the heat exchanger or the car radiator. *Capiche? I think you may be confusing in your mind air velocity(meters/min) and air volume moved (cubic meters/min.) *Or feet. They are not the same thing.- Hide quoted text - - Show quoted text - You are confusing HEAT and TEMPERATURE. *Three of us in this thread say you are wrong. *Not a single person agrees with your version of physics. * *And again, it would be extremely helpful if you could address specific questions. We've addressed and answered anything you put forth. I've given you several examples and asked questions that show your science is just wrong. *You never answer them and just go somewhere else. In the case dicussed, we do not have an infinite number of "cubes" . Well, you're wrong again, this time on two points. First, in the example I gave you, the metal cubes were replaced 5 times. That is a long way from infinite. Second, in the heat exchanger in the furnace duct, we sure do have infinite cubes. It's called airflow and as long as the system is running, new colder air is constantly moving across the heat exchanger as long as the system is running. Just like one cold metal cube replaces the one that has warmed 1 minute in the simple example. Imagine little blocks of air being changed every minute. Then every 10 secs, then every sec, etc. There you have the furnace heat exchanger. Now the problem here is that again, you never answer my questions. Do you or do you not agree that by replacing those metal cubes that have warmed slightly with new cold 0F cubes the 500F cube is cooled faster than just leaving one cube there for the full 5 mins? Here's the experiment again: Let's say you have 10 identical masses in the form of metal cubes. One of those cubes is heated to 500F. The others are all at 0F. I do the following two cases: A - I take one of the 0F cubes and place it on top of the 500F cube and leave it there for 5 mins. B - I take one of the 0F cubes and place it on top of the 500F cube for 1 min. Then I replace it with another 0F cube for 1 min. I do that for the same 5 min period. Which results in the 500F cube being cooled off the most? Which results in the most heat transferred? Do you agree or disagree that the answer is B? A simple yes or no at this point please. This is a question an elementary school kid could answer based on experience. And one that a high school science student could answer based on science. And if you agree the answer is B, which we all know it is, then what is happening is exactly the same as in the heat exchanger in the furnace duct. The only difference is that we're using air instead of metal cubes to cool the heat exchanger. We don't have infinite air, nor is that required. The MORE air we put throught the heat exchanger, the MORE heat that is transferred. If we put enough air through it we've extracted all the heat. We have to wring the maximum amount of energy out of the one we have. That is the whole point of the excercise. We are NOT talking temperature differentials. The car radiator (on a car) is irrelevent to the case under discussion because there IS an infinite number of "cubes". (Ie air to cool it with). OMG, you are so totally confused here it's unbelievable. A car radiator has air flowing through it just as the heat exchanger in the furnace ducts does. Both are infinite in the sense that the airflow is continous as long as the systems are operating. Exactly like it would be in the metal cube example if I kept replacing those metal cubes every 1 min for the duration of the experiment. I actually can't believe you just made this even more bizarre claim. This from the guy that is always slamming the US over being behind in technology? You really are lost in the wilderness here. Removed from the car and used for this purpose is an entire different ball game. But you can't get your head round any of this. Go back and read my last post.- Hide quoted text - I can't understand any of this? First, a radiator from a car would work under exactly the same principles whether in a car or a furnace duct. The physics don't change. Second, there is no need to use an unspecified car radiator. CL provided a data sheet to a heat exchanger manufactured exactly for the purpose of being a water to air exchanger for this kind of application. We've given you the link 3 or 4 times now. The datasheet clearly shows that as you increase airflow the BTUs of heat transferred increase. You can see that the increase slows as a decaying exponential, which is EXACTLY what I told you 10 posts ago. But you won't even address that datasheet because there is no way around it. You just trim it from every post. Here it is one more time: The spec sheet is right he http://www.heatexchangersonline.com/airtowater.htm Look at the first heat exchanger. Operating with 140F incoming water at 6 GPM, the performance is listed as: Airflow CFM BTUS 500 28 600 29 700 34 800 36 900 37 1018 38 Your problems with science here are many. One big one is that you don't understand the difference between heat and temperature. Another is that you think the physics of heat transfer change whether the heat tranfer is used to warm a house or to cool a car because in the car it's "waste" heat. And you can't grasp the concept of infinity very well either. |
Hot water to forced air
On Jan 10, 3:15*pm, "
wrote: On Jan 9, 1:50*pm, harry wrote: You forgot MASS. *Yes, with a FIXED MASS in contact with another MASS, the longer they stay in contact the more heat is transferred. * Let's say you have 10 *identical masses in the form of metal cubes. *One of those cubes is heated to 500F. * The others are all at 0F. I do the following two cases: A - I take one of the 0F cubes and place it on top of the 500F cube and leave it there for 5 mins. B - I take one of the 0F cubes and place it on top of the 500F cube for 1 min. *Then I replace it with another 0F cube for 1 min. *I do that for the same 5 min period. Which results in the 500F cube being cooled off the most? * Which results in the most heat transferred? Answer B because you have a larger temperature differential because you're constantly replacing the mass being heated. *That is exactly what is happening in the heat exchanger. Now according to your faulty logic, less energy is being transferred because the 5 cubes are not as hot as the one cube left there for the entire time. *You are confusing HEAT with TEMPERATURE. To maximise heat transfer, any of them can be increased. It's very basic.They are NOT my idea. *Has been known since Adam was a lad. One way you increase the temperature differential is to constantly replace mass that is being cooled with new mass. *That is exactly what happens when you increase the airflow in the heat exchanger or the car radiator. *Capiche? I think you may be confusing in your mind air velocity(meters/min) and air volume moved (cubic meters/min.) *Or feet. They are not the same thing.- Hide quoted text - - Show quoted text - You are confusing HEAT and TEMPERATURE. *Three of us in this thread say you are wrong. *Not a single person agrees with your version of physics. * *And again, it would be extremely helpful if you could address specific questions. We've addressed and answered anything you put forth. I've given you several examples and asked questions that show your science is just wrong. *You never answer them and just go somewhere else. In the case dicussed, we do not have an infinite number of "cubes" . Well, you're wrong again, this time on two points. First, in the example I gave you, the metal cubes were replaced 5 times. *That is a long way from infinite. Second, in the heat exchanger in the furnace duct, we sure do have infinite cubes. *It's called airflow and as long as the system is running, new colder air is constantly moving across the heat exchanger as long as the system is running. Just like one cold metal cube replaces the one that has warmed 1 minute *in the simple example. Imagine little blocks of air being changed every minute. *Then every 10 secs, then every sec, etc. *There you have the furnace heat exchanger. Now the problem here is that again, you never answer my questions. *Do you or do you not agree that by replacing those metal cubes that have warmed slightly with new cold 0F cubes the 500F cube is cooled faster than just leaving one cube there for the full 5 mins? Here's the experiment again: Let's say you have 10 *identical masses in the form of metal cubes. *One of those cubes is heated to 500F. * The others are all at 0F. I do the following two cases: A - I take one of the 0F cubes and place it on top of the 500F cube and leave it there for 5 mins. B - I take one of the 0F cubes and place it on top of the 500F cube for 1 min. *Then I replace it with another 0F cube for 1 min. *I do that for the same 5 min period. Which results in the 500F cube being cooled off the most? * Which results in the most heat transferred? Do you agree or disagree that the answer is B? A simple yes or no at this point please. *This is a question an elementary school kid could answer based on experience. *And one that a high school science student could answer based on science. And if you agree the answer is B, which we all know it is, then what is happening is exactly the same as in the heat exchanger in the furnace duct. * The only difference is that we're using air instead of metal cubes to cool the heat exchanger. * We don't have infinite air, nor is that required. *The MORE air we put throught the heat exchanger, the MORE heat that is transferred. *If we put enough air through it we've extracted all the heat. We have to wring the maximum amount of energy out of the one we have. That is the whole point of the excercise. We are NOT talking temperature differentials. The car radiator (on a car) is irrelevent to the case under discussion because there IS an infinite number of "cubes". (Ie air to cool it with). OMG, you are so totally confused here it's unbelievable. A car radiator has air flowing through it just as the heat exchanger in the furnace ducts does. *Both are infinite in the sense that the airflow is continous as long as the systems are operating. * Exactly like it would be in the metal cube example if I kept replacing those metal cubes every 1 min for the duration of the experiment. *I actually can't believe you just made this even more bizarre claim. *This from the guy that is always slamming the US over being behind in technology? *You really are lost in the wilderness here. Removed from the car and used for this purpose is an entire different ball game. But you can't get your head round any of this. Go back and read my last post.- Hide quoted text - I can't understand any of this? First, a radiator from a car would work under exactly the same principles whether in a car or a furnace duct. *The physics don't change. *Second, there is no need to use an unspecified car radiator. CL provided a data sheet to a heat exchanger manufactured exactly for the purpose of being a water to air exchanger for this kind of application. *We've given you the link 3 or 4 times now. *The datasheet clearly shows that as you increase airflow the BTUs of heat transferred increase. *You can see that the increase slows as a decaying exponential, which is EXACTLY what I told you 10 posts ago. *But you won't even address that datasheet because there is no way around it. *You just trim it from every post. Here it is one more time: The spec sheet is right hehttp://www.heatexchangersonline.com/airtowater.htm Look at the first heat exchanger. *Operating with 140F incoming water at 6 GPM, the performance is listed as: Airflow CFM * * BTUS 500 * * * 28 600 * * * 29 700 * * * 34 800 * * * 36 900 * * * 37 1018 * * 38 Your problems with science here are many. *One big one is that you don't understand the difference between heat and temperature. *Another is that you think the physics of heat transfer change whether the heat tranfer is used to warm a house or to cool a car because in the car it's "waste" heat. And you can't grasp the concept of infinity very well either.- Hide quoted text - - Show quoted text - I think you have the problem. I have looked at the table. The specification given are for one particular pressure difference / velocity of water in the primary side..(in the first vertical column.) If you put less water through it, the outcoming water would be cooler. And nowhere does it mention the entry/exit air temperature. Again you have to work these out. It gives the water entering temperature. The temperature it leaves at varies depending on air temperature on entry and velocity for that particular CFM. (As do the BTUs transferred.) These figures are for guidance only and demonstrate a range of options/ operating conditions. It's not possible to specify all possible conditions. I don't understand why you can't understand the simple concept that the longer you keep your hand on a hot stove, the hotter it (your hand) will get. In the OP, the object of the excercise was to get the air as hot as possible. |
Hot water to forced air
On Tue, 10 Jan 2012 01:02:35 -0800 (PST), harry
wrote: On Jan 9, 10:23Â*pm, wrote: On Mon, 9 Jan 2012 00:18:28 -0800 (PST), harry wrote: On Jan 8, 11:38Â*pm, wrote: On Sun, 8 Jan 2012 11:59:09 -0800 (PST), harry wrote: Â*How is your Euro-shack any better than mine?- Hide quoted text - - Show quoted text - I am beyond central heating. I have such insulation that the heat from theTV, refrigerators and the sun etc keeps the place warm except in very dull and windy weather. I have no Â*heating bill and net profit (to me) electricity. http://www.flickr.com/photos/ara-chl...7627608971673/ It recently appeared on national TV. Â*We have places like that here too. Â*But they are not "typical" here - or there. Ond on the whole, American, and particularly Canadian homes are more energy efficient than the average British dwelling, by a fair amount. But my house is not typical of UK houses which do have central heating. Fuel usage is probably less than half what you use in America in the typical new UK house due to more efficient boilers and control sytems and more insulation. Â*What is the normal R value in the walls and roof of the average new british house? Â*What is required by "code". How much gas does it take to heat a Â*1300 sq foot home in the coldest part of Britain (which is still, on the whole, not as cold as Â*most of Canada)??? A couple of years back I looked at some new houses Â*being constructed in America.(Des Moines) Appalling. Â*They were installing the sort of stuff were were junking thirty years ago. Â*They build differently in the USA than we do up here in the "great white north". 6 inch walls with strayed foam insulation are not out of the ordinary here any more. Â*The house my father built 30 years ago was heated by 1/2 cord of wood Â*per winter- and it was a "conventional" urban Â*split level of over 2000 square feet. There is nothing wrong with unheated basements so long as they are outside the thermal envelope. (Though I thought they were reserved for poor homeless family members these days?) Running heating pipes up the outside of a building is pretty weird though.- Hide quoted text - - Show quoted text - We do things in"U" values here (reciprocal of R) http://www.knaufinsulation.co.uk/sel.../building_regu... All is in metric. http://www.simetric.co.uk/sibtu.htm We are much warmer here than in Canada due to the maritime climate. Â*I heat my "snow belt" Ontario home for $700 worth of natural gas a year - which also provides all my domestic hot water Well that's pretty cheap. Probably gas is more expensive here in the UK too. Gas is 13.773 cents per cubic meter, plus 4.8698 cents transportatio, plus .977 cents storage, plus 3.7504 cents delivery plus a $20 monthly "meter charge" - so about $0.235 per cubic meter, plus $20 per month.. SO - at $700/year, that is $240 per year for the meter charge, and 460 for gas - which is 1957.5 cu meters per year, including the water heater. Actually LESS than that, because the $700 includes the 13% HST. My total gas bill for the month of Nov 18 to Dec 18 was 5 $53.47 - about the same as 3 20lb barbq tanks of propane. |
Hot water to forced air
On Tue, 10 Jan 2012 09:38:50 -0800 (PST), harry
wrote: On Jan 10, 3:15Â*pm, " wrote: On Jan 9, 1:50Â*pm, harry wrote: You forgot MASS. Â*Yes, with a FIXED MASS in contact with another MASS, the longer they stay in contact the more heat is transferred. Â* Let's say you have 10 Â*identical masses in the form of metal cubes. Â*One of those cubes is heated to 500F. Â* The others are all at 0F. I do the following two cases: A - I take one of the 0F cubes and place it on top of the 500F cube and leave it there for 5 mins. B - I take one of the 0F cubes and place it on top of the 500F cube for 1 min. Â*Then I replace it with another 0F cube for 1 min. Â*I do that for the same 5 min period. Which results in the 500F cube being cooled off the most? Â* Which results in the most heat transferred? Answer B because you have a larger temperature differential because you're constantly replacing the mass being heated. Â*That is exactly what is happening in the heat exchanger. Now according to your faulty logic, less energy is being transferred because the 5 cubes are not as hot as the one cube left there for the entire time. Â*You are confusing HEAT with TEMPERATURE. To maximise heat transfer, any of them can be increased. It's very basic.They are NOT my idea. Â*Has been known since Adam was a lad. One way you increase the temperature differential is to constantly replace mass that is being cooled with new mass. Â*That is exactly what happens when you increase the airflow in the heat exchanger or the car radiator. Â*Capiche? I think you may be confusing in your mind air velocity(meters/min) and air volume moved (cubic meters/min.) Â*Or feet. They are not the same thing.- Hide quoted text - - Show quoted text - You are confusing HEAT and TEMPERATURE. Â*Three of us in this thread say you are wrong. Â*Not a single person agrees with your version of physics. Â* Â*And again, it would be extremely helpful if you could address specific questions. We've addressed and answered anything you put forth. I've given you several examples and asked questions that show your science is just wrong. Â*You never answer them and just go somewhere else. In the case dicussed, we do not have an infinite number of "cubes" . Well, you're wrong again, this time on two points. First, in the example I gave you, the metal cubes were replaced 5 times. Â*That is a long way from infinite. Second, in the heat exchanger in the furnace duct, we sure do have infinite cubes. Â*It's called airflow and as long as the system is running, new colder air is constantly moving across the heat exchanger as long as the system is running. Just like one cold metal cube replaces the one that has warmed 1 minute Â*in the simple example. Imagine little blocks of air being changed every minute. Â*Then every 10 secs, then every sec, etc. Â*There you have the furnace heat exchanger. Now the problem here is that again, you never answer my questions. Â*Do you or do you not agree that by replacing those metal cubes that have warmed slightly with new cold 0F cubes the 500F cube is cooled faster than just leaving one cube there for the full 5 mins? Here's the experiment again: Let's say you have 10 Â*identical masses in the form of metal cubes. Â*One of those cubes is heated to 500F. Â* The others are all at 0F. I do the following two cases: A - I take one of the 0F cubes and place it on top of the 500F cube and leave it there for 5 mins. B - I take one of the 0F cubes and place it on top of the 500F cube for 1 min. Â*Then I replace it with another 0F cube for 1 min. Â*I do that for the same 5 min period. Which results in the 500F cube being cooled off the most? Â* Which results in the most heat transferred? Do you agree or disagree that the answer is B? A simple yes or no at this point please. Â*This is a question an elementary school kid could answer based on experience. Â*And one that a high school science student could answer based on science. And if you agree the answer is B, which we all know it is, then what is happening is exactly the same as in the heat exchanger in the furnace duct. Â* The only difference is that we're using air instead of metal cubes to cool the heat exchanger. Â* We don't have infinite air, nor is that required. Â*The MORE air we put throught the heat exchanger, the MORE heat that is transferred. Â*If we put enough air through it we've extracted all the heat. We have to wring the maximum amount of energy out of the one we have. That is the whole point of the excercise. We are NOT talking temperature differentials. The car radiator (on a car) is irrelevent to the case under discussion because there IS an infinite number of "cubes". (Ie air to cool it with). OMG, you are so totally confused here it's unbelievable. A car radiator has air flowing through it just as the heat exchanger in the furnace ducts does. Â*Both are infinite in the sense that the airflow is continous as long as the systems are operating. Â* Exactly like it would be in the metal cube example if I kept replacing those metal cubes every 1 min for the duration of the experiment. Â*I actually can't believe you just made this even more bizarre claim. Â*This from the guy that is always slamming the US over being behind in technology? Â*You really are lost in the wilderness here. Removed from the car and used for this purpose is an entire different ball game. But you can't get your head round any of this. Go back and read my last post.- Hide quoted text - I can't understand any of this? First, a radiator from a car would work under exactly the same principles whether in a car or a furnace duct. Â*The physics don't change. Â*Second, there is no need to use an unspecified car radiator. CL provided a data sheet to a heat exchanger manufactured exactly for the purpose of being a water to air exchanger for this kind of application. Â*We've given you the link 3 or 4 times now. Â*The datasheet clearly shows that as you increase airflow the BTUs of heat transferred increase. Â*You can see that the increase slows as a decaying exponential, which is EXACTLY what I told you 10 posts ago. Â*But you won't even address that datasheet because there is no way around it. Â*You just trim it from every post. Here it is one more time: The spec sheet is right hehttp://www.heatexchangersonline.com/airtowater.htm Look at the first heat exchanger. Â*Operating with 140F incoming water at 6 GPM, the performance is listed as: Airflow CFM Â* Â* BTUS 500 Â* Â* Â* 28 600 Â* Â* Â* 29 700 Â* Â* Â* 34 800 Â* Â* Â* 36 900 Â* Â* Â* 37 1018 Â* Â* 38 Your problems with science here are many. Â*One big one is that you don't understand the difference between heat and temperature. Â*Another is that you think the physics of heat transfer change whether the heat tranfer is used to warm a house or to cool a car because in the car it's "waste" heat. And you can't grasp the concept of infinity very well either.- Hide quoted text - - Show quoted text - I think you have the problem. I have looked at the table. The specification given are for one particular pressure difference / velocity of water in the primary side..(in the first vertical column.) If you put less water through it, the outcoming water would be cooler. And nowhere does it mention the entry/exit air temperature. Again you have to work these out. It gives the water entering temperature. The temperature it leaves at varies depending on air temperature on entry and velocity for that particular CFM. (As do the BTUs transferred.) These figures are for guidance only and demonstrate a range of options/ operating conditions. It's not possible to specify all possible conditions. I don't understand why you can't understand the simple concept that the longer you keep your hand on a hot stove, the hotter it (your hand) will get. In the OP, the object of the excercise was to get the air as hot as possible. I thought it was to get the room (or house) as warm as possible - which - as you have noted before - is 2 different things. |
Hot water to forced air
On Jan 10, 6:25*pm, wrote:
On Tue, 10 Jan 2012 01:02:35 -0800 (PST), harry wrote: On Jan 9, 10:23*pm, wrote: On Mon, 9 Jan 2012 00:18:28 -0800 (PST), harry wrote: On Jan 8, 11:38*pm, wrote: On Sun, 8 Jan 2012 11:59:09 -0800 (PST), harry wrote: *How is your Euro-shack any better than mine?- Hide quoted text - - Show quoted text - I am beyond central heating. I have such insulation that the heat from theTV, refrigerators and the sun etc keeps the place warm except in very dull and windy weather.. I have no *heating bill and net profit (to me) electricity. http://www.flickr.com/photos/ara-chl...7627608971673/ It recently appeared on national TV. *We have places like that here too. *But they are not "typical" here - or there. Ond on the whole, American, and particularly Canadian homes are more energy efficient than the average British dwelling, by a fair amount. But my house is not typical of UK houses which do have central heating. Fuel usage is probably less than half what you use in America in the typical new UK house due to more efficient boilers and control sytems and more insulation. *What is the normal R value in the walls and roof of the average new british house? *What is required by "code". How much gas does it take to heat a *1300 sq foot home in the coldest part of Britain (which is still, on the whole, not as cold as *most of Canada)??? A couple of years back I looked at some new houses *being constructed in America.(Des Moines) Appalling. *They were installing the sort of stuff were were junking thirty years ago. *They build differently in the USA than we do up here in the "great white north". 6 inch walls with strayed foam insulation are not out of the ordinary here any more. *The house my father built 30 years ago was heated by 1/2 cord of wood *per winter- and it was a "conventional" urban *split level of over 2000 square feet. There is nothing wrong with unheated basements so long as they are outside the thermal envelope. (Though I thought they were reserved for poor homeless family members these days?) Running heating pipes up the outside of a building is pretty weird though.- Hide quoted text - - Show quoted text - We do things in"U" values here (reciprocal of R) http://www.knaufinsulation.co.uk/sel.../building_regu.... All is in metric. http://www.simetric.co.uk/sibtu.htm We are much warmer here than in Canada due to the maritime climate. *I heat my "snow belt" Ontario home for $700 worth of natural gas a year - which also provides all my domestic hot water Well that's pretty cheap. *Probably gas is more expensive here in the UK too. Gas is *13.773 cents per cubic meter, plus 4.8698 cents transportatio, plus .977 cents storage, plus 3.7504 cents delivery plus a $20 monthly "meter charge" - so about $0.235 per cubic meter, plus $20 per month.. SO - at $700/year, that is $240 per year for the meter charge, and 460 for gas - which is 1957.5 cu meters per year, including the water heater. Actually LESS than that, because the $700 includes the 13% HST. My total gas bill for the month of Nov 18 to Dec 18 was 5 $53.47 - about the same as 3 20lb barbq tanks of propane.- Hide quoted text - - Show quoted text - So, what is the calorific value of your gas? Not sure about it as here, I don't use any. I think it's 40 MJ/m³.@ 40mbar. |
Hot water to forced air
On Jan 10, 12:38*pm, harry wrote:
I think you have the problem. I have looked at the table. The specification given are for one particular pressure difference / velocity *of water in the primary side..(in the first vertical column.) *If you put less water through it, the outcoming water would be cooler. Yes, it's for 6 GPM of water flowing through the heat exchanger. And it shows water at temps of 140F, 160F, and 180F. And HOW MUCH HEAT IS TRANSFERRED VERSUS AIRFLOWS OF 500, 600, 700, 800, 1000 CFM As the airflow goes up, so does the BTUs of heat transferred. Do you agree that is what it shows or not? And yes, if you made another chart that showed say 3GPM per minute of water flow instead of 6GPM, the water would be coming out cooler. You would then have LESS heat transferred. And you'd have a similar table showing that as airflow increases from 500 to 1000CFM, the amount of heat transferred increases with it. That table for 6GPM isn't some unique point where special rules of physics apply. It shows how the heat exchanger works and is an operating point within the scope of this discusssion, where if the OP built his system he could get 30K BTUS of heat out of it. Look at the other heat exchangers that are larger and show greater flow rates. Find me one that does not show that as you increase airflow, the BTUs of heat transferred go up. And nowhere does it mention the entry/exit air temperature. *Again you have to work these out. Now I agree that is one missing piece of information that should be spec'd on the data sheet. Without it we don't know the specific air entry temp that resulted in those BTU numbers. However, it doesn't matter. Whatever the air entry numbers, clearly: The spec sheet does state: " These air to water units are ideal for heating water in residential and public buildings. Compact and lightweight, these units are designed to maximize heat transfer by utilizing a series of 3/8" copper tubes with a high density of aluminum fins. These fins are spaced in such a way that the fin density is an impressive 12 fins per inch. This unique design allows for heating loads of 50,000 to 60,000 Btu per square foot (please see performance chart below)." And with water entering at 140F to 180F it's obviously being used in that chart to heat air. At that point, it does not matter what the incoming air temp is. Let's assume for the moment that the particular chart used 65F air. The chart shows the BTUs of heat tranferred versus increasing airflow. As you increase airflow, the BTUs go up. Now, if the incoming air were cooler, say 40F, you'd transfer more BTUs of heat because the temp differential between the hot and cold sides of the heat exchanger is greater. If the incoming air is 100F, you'd transfer less BTUs because the temp differential is smaller. You would then have a very similar chart that starts out with a given BTU of heat transfer at 500CFM and INCREASES as you increase the airflow to 600, 700, 1000 CFM. Capiche? It gives the water entering temperature. *The temperature it leaves at varies depending on air temperature on entry *and velocity for that particular CFM. (As do the BTUs transferred.) Sure does. Do you agree that this chart also clearly shows the BTUs of heat transferred INCREASED steadily with the airflow? That MORE heat is transferred in that table as the airflow increases? That it is that way for the table on every size of heat exchanger? Yes or no? These figures are for guidance only and demonstrate a range of options/ operating conditions. It's not possible to specify all possible conditions. No **** Sherlock. But remarkably, the application the heat exchanger is targeted for is exactly what the OP was looking for. And the water flow rate and the airflow rate are within the range that a system to heat a home via solar would be. In other words, that chart shows exactly what the OP could use. It's not some curve from some bizarre or unique heat exchanger. I don't understand why you can't understand the simple concept that the longer you keep your hand on a hot *stove, the hotter it (your hand) will get. I can't understand why you can't understand the simple concept that a heat exchanger, be it this one, or a car radiator has a CONTINUOUS MASS moving through it. We don't have a single hand, we have say 100 people with hands at 98F, that each place their hand on the warm stove for 30 secs. That transfers MORE heat than one person leaving their hand there because new hands at 98F are constantly replacing hands that have warmed slightly. The greater the temp delta, the greater the heat transfer. You stated that yourself. You wind up with 100 people with slightly warmer hands instead of one person with a hot hand. Does that mean less heat is transferred? Of course not because the mass of those 100 hands more than makes up for the fact that they are only slightly warm. Capiche? Same thing applies to a home radiator on a hot water or steam system. The more air you move past it, the lower the air temp will be, but the more heat you will extract from the radiator and the cooler the exit water temp will be. Same thing applies to a car radiator. And it matter not a wit that it's waste heat being transferred to the atmosphere, so please don't start that again. In the OP, the object of the excercise was to get the air as hot as possible.- Hide quoted text - There you go again. It's been stated to you many times now by Mark, CL, and I that the object of the excercise was to heat the house. Which means getting the most heat out of the heat exchanger, not the hottest air. You are confusing TEMPERATURE with HEAT. Try looking up the definition. As one more example, I could go down and turn the blower down on my furnace to 100CFM instead of 1300CFM. Assuming it would not kick off due to the high limit safety switch, I would then be getting very hot air out of it. Does that mean I'm getting MORE heat and it's going to heat my house faster, etc? No. I'd be getting LESS heat even though the small amount of air coming out is a lot hotter. Capiche? |
Hot water to forced air
On Jan 11, 3:04*pm, "
wrote: On Jan 10, 12:38*pm, harry wrote: I think you have the problem. I have looked at the table. The specification given are for one particular pressure difference / velocity *of water in the primary side..(in the first vertical column.) *If you put less water through it, the outcoming water would be cooler. Yes, it's for 6 GPM of water flowing through the heat exchanger. *And it shows water at temps of *140F, 160F, and 180F. *And HOW MUCH HEAT IS TRANSFERRED VERSUS AIRFLOWS OF 500, 600, 700, 800, 1000 CFM As the airflow goes up, so does the BTUs of heat transferred. Do you agree that is what it shows or not? And yes, if you made another chart that showed say 3GPM per minute of water flow instead of 6GPM, the water would be coming out cooler. *You would then have LESS heat transferred. *And you'd have a similar table showing that as airflow increases from 500 to 1000CFM, the amount of heat transferred increases with it. That table for 6GPM isn't some unique point where special rules of physics apply. *It shows how the heat exchanger works and is an operating point within the scope of this discusssion, where if the OP built his system he could get 30K BTUS of heat out of it. Look at the other heat exchangers that are larger and show greater flow rates. *Find me one that does not show that as you increase airflow, the BTUs of heat transferred go up. And nowhere does it mention the entry/exit air temperature. *Again you have to work these out. Now I agree that is one missing piece of information that should be spec'd on the data sheet. *Without it we don't know the specific air entry temp that resulted in those BTU numbers. * However, it doesn't matter. *Whatever the air entry numbers, clearly: The spec sheet does state: " These air to water units are ideal for heating water in residential and public buildings. Compact and lightweight, these units are designed to maximize heat transfer by utilizing a series of 3/8" copper tubes with a high density of aluminum fins. These fins are spaced in such a way that the fin density is an impressive 12 fins per inch. This unique design allows for heating loads of 50,000 to 60,000 Btu per square foot (please see performance chart below)." And with water entering at 140F to 180F it's obviously being used in that chart to heat air. *At that point, it does not matter what the incoming air temp is. *Let's assume for the moment that the particular chart used 65F air. *The chart shows the BTUs of heat tranferred versus increasing airflow. *As you increase airflow, the BTUs go up. Now, if the incoming air were cooler, say 40F, you'd transfer more BTUs of heat because the temp differential between the hot and cold sides of the heat exchanger is greater. If the incoming air is 100F, you'd transfer less BTUs because the temp differential is smaller. *You would then have a very similar chart that starts out with a given BTU of heat transfer at 500CFM and INCREASES as you increase the airflow to 600, 700, 1000 CFM. *Capiche? It gives the water entering temperature. *The temperature it leaves at varies depending on air temperature on entry *and velocity for that particular CFM. (As do the BTUs transferred.) Sure does. *Do you agree that this chart also clearly shows the BTUs of heat transferred INCREASED steadily with the airflow? *That MORE heat is transferred in that table as the airflow increases? * That it is that way for the table on every size of heat exchanger? *Yes or no? These figures are for guidance only and demonstrate a range of options/ operating conditions. It's not possible to specify all possible conditions. No **** Sherlock. *But remarkably, the application the heat exchanger is targeted for is exactly what the OP was looking for. *And the water flow rate and the airflow rate are within the range that a system to heat a home via solar would be. *In other words, that chart shows exactly what the OP could use. *It's not some curve from some bizarre or unique heat exchanger. I don't understand why you can't understand the simple concept that the longer you keep your hand on a hot *stove, the hotter it (your hand) will get. I can't understand why you can't understand the simple concept that a heat exchanger, be it this one, or a car radiator has a CONTINUOUS MASS moving through it. We don't have a single hand, *we have say 100 people with hands at 98F, that each place their hand on the warm stove for 30 secs. *That transfers MORE heat than one person leaving their hand there because new hands at 98F are constantly replacing hands that have warmed slightly. *The greater the temp delta, the greater the heat transfer. * You stated that yourself. You wind up with 100 people with slightly warmer hands instead of one person with a hot hand. *Does that mean less heat is transferred? *Of course not because the mass of those 100 hands more than makes up for the fact that they are only slightly warm. *Capiche? Same thing applies to a home radiator on a hot water or steam system. *The more air you move past it, the lower the air temp will be, but the more heat you will extract from the radiator and the cooler the exit water temp will be. Same thing applies to a car radiator. *And it matter not a wit that it's waste heat being transferred to the atmosphere, so please don't start that again. In the OP, the object of the excercise was to get the air as hot as possible.- Hide quoted text - There you go again. *It's been stated to you many times now by Mark, CL, and I that the object of the excercise was to heat the house. * Which means getting the most heat out of the heat exchanger, not the hottest air. * You are confusing TEMPERATURE with HEAT. * Try looking up the definition. You are confusing both with extracting the most efficiency out of a limited supply of heat. As one more example, I could go down and turn the blower down on my furnace to 100CFM instead of 1300CFM. * Assuming it would not kick off due to the high limit safety switch, I would then be getting very hot air out of it. *Does that mean I'm getting MORE heat and it's going to heat my house faster, etc? No. *I'd be getting LESS heat even though the small amount of air coming out is a lot hotter. * Capiche? if you turned down the burner the heat exchanger would work more efficiently. The combustion products would be going through the heat exchanger slower. A greater PERCENTAGE of the heat would be transferred. More bang for buck. I don't know what's wrong with you but I'm getting bored. |
Hot water to forced air
On Jan 11, 3:04*pm, "
wrote: On Jan 10, 12:38*pm, harry wrote: I think you have the problem. I have looked at the table. The specification given are for one particular pressure difference / velocity *of water in the primary side..(in the first vertical column.) *If you put less water through it, the outcoming water would be cooler. Yes, it's for 6 GPM of water flowing through the heat exchanger. *And it shows water at temps of *140F, 160F, and 180F. *And HOW MUCH HEAT IS TRANSFERRED VERSUS AIRFLOWS OF 500, 600, 700, 800, 1000 CFM As the airflow goes up, so does the BTUs of heat transferred. Do you agree that is what it shows or not? And yes, if you made another chart that showed say 3GPM per minute of water flow instead of 6GPM, the water would be coming out cooler. *You would then have LESS heat transferred. *And you'd have a similar table showing that as airflow increases from 500 to 1000CFM, the amount of heat transferred increases with it. The water would be coming out cooler because it was moving slower. More heat would be removed from the water than in the previous case. So, to remove the maximum amount of heat from the water it has to go slower. Are you a troll or just thick? |
Hot water to forced air
On Wed, 11 Jan 2012 00:13:13 -0800 (PST), harry
wrote: On Jan 10, 6:25Â*pm, wrote: On Tue, 10 Jan 2012 01:02:35 -0800 (PST), harry wrote: On Jan 9, 10:23Â*pm, wrote: On Mon, 9 Jan 2012 00:18:28 -0800 (PST), harry wrote: On Jan 8, 11:38Â*pm, wrote: On Sun, 8 Jan 2012 11:59:09 -0800 (PST), harry wrote: Â*How is your Euro-shack any better than mine?- Hide quoted text - - Show quoted text - I am beyond central heating. I have such insulation that the heat from theTV, refrigerators and the sun etc keeps the place warm except in very dull and windy weather. I have no Â*heating bill and net profit (to me) electricity. http://www.flickr.com/photos/ara-chl...7627608971673/ It recently appeared on national TV. Â*We have places like that here too. Â*But they are not "typical" here - or there. Ond on the whole, American, and particularly Canadian homes are more energy efficient than the average British dwelling, by a fair amount. But my house is not typical of UK houses which do have central heating. Fuel usage is probably less than half what you use in America in the typical new UK house due to more efficient boilers and control sytems and more insulation. Â*What is the normal R value in the walls and roof of the average new british house? Â*What is required by "code". How much gas does it take to heat a Â*1300 sq foot home in the coldest part of Britain (which is still, on the whole, not as cold as Â*most of Canada)??? A couple of years back I looked at some new houses Â*being constructed in America.(Des Moines) Appalling. Â*They were installing the sort of stuff were were junking thirty years ago. Â*They build differently in the USA than we do up here in the "great white north". 6 inch walls with strayed foam insulation are not out of the ordinary here any more. Â*The house my father built 30 years ago was heated by 1/2 cord of wood Â*per winter- and it was a "conventional" urban Â*split level of over 2000 square feet. There is nothing wrong with unheated basements so long as they are outside the thermal envelope. (Though I thought they were reserved for poor homeless family members these days?) Running heating pipes up the outside of a building is pretty weird though.- Hide quoted text - - Show quoted text - We do things in"U" values here (reciprocal of R) http://www.knaufinsulation.co.uk/sel.../building_regu... All is in metric. http://www.simetric.co.uk/sibtu.htm We are much warmer here than in Canada due to the maritime climate. Â*I heat my "snow belt" Ontario home for $700 worth of natural gas a year - which also provides all my domestic hot water Well that's pretty cheap. Â*Probably gas is more expensive here in the UK too. Gas is Â*13.773 cents per cubic meter, plus 4.8698 cents transportatio, plus .977 cents storage, plus 3.7504 cents delivery plus a $20 monthly "meter charge" - so about $0.235 per cubic meter, plus $20 per month.. SO - at $700/year, that is $240 per year for the meter charge, and 460 for gas - which is 1957.5 cu meters per year, including the water heater. Actually LESS than that, because the $700 includes the 13% HST. My total gas bill for the month of Nov 18 to Dec 18 was 5 $53.47 - about the same as 3 20lb barbq tanks of propane.- Hide quoted text - - Show quoted text - So, what is the calorific value of your gas? Not sure about it as here, I don't use any. I think it's 40 MJ/m³.@ 40mbar. 900 btu/cu ft which is 31,783 BTU/cu meter - more or less. |
Hot water to forced air
On Wed, 11 Jan 2012 10:56:18 -0800 (PST), harry
wrote: On Jan 11, 3:04Â*pm, " wrote: On Jan 10, 12:38Â*pm, harry wrote: I think you have the problem. I have looked at the table. The specification given are for one particular pressure difference / velocity Â*of water in the primary side..(in the first vertical column.) Â*If you put less water through it, the outcoming water would be cooler. Yes, it's for 6 GPM of water flowing through the heat exchanger. Â*And it shows water at temps of Â*140F, 160F, and 180F. Â*And HOW MUCH HEAT IS TRANSFERRED VERSUS AIRFLOWS OF 500, 600, 700, 800, 1000 CFM As the airflow goes up, so does the BTUs of heat transferred. Do you agree that is what it shows or not? And yes, if you made another chart that showed say 3GPM per minute of water flow instead of 6GPM, the water would be coming out cooler. Â*You would then have LESS heat transferred. Â*And you'd have a similar table showing that as airflow increases from 500 to 1000CFM, the amount of heat transferred increases with it. That table for 6GPM isn't some unique point where special rules of physics apply. Â*It shows how the heat exchanger works and is an operating point within the scope of this discusssion, where if the OP built his system he could get 30K BTUS of heat out of it. Look at the other heat exchangers that are larger and show greater flow rates. Â*Find me one that does not show that as you increase airflow, the BTUs of heat transferred go up. And nowhere does it mention the entry/exit air temperature. Â*Again you have to work these out. Now I agree that is one missing piece of information that should be spec'd on the data sheet. Â*Without it we don't know the specific air entry temp that resulted in those BTU numbers. Â* However, it doesn't matter. Â*Whatever the air entry numbers, clearly: The spec sheet does state: " These air to water units are ideal for heating water in residential and public buildings. Compact and lightweight, these units are designed to maximize heat transfer by utilizing a series of 3/8" copper tubes with a high density of aluminum fins. These fins are spaced in such a way that the fin density is an impressive 12 fins per inch. This unique design allows for heating loads of 50,000 to 60,000 Btu per square foot (please see performance chart below)." And with water entering at 140F to 180F it's obviously being used in that chart to heat air. Â*At that point, it does not matter what the incoming air temp is. Â*Let's assume for the moment that the particular chart used 65F air. Â*The chart shows the BTUs of heat tranferred versus increasing airflow. Â*As you increase airflow, the BTUs go up. Now, if the incoming air were cooler, say 40F, you'd transfer more BTUs of heat because the temp differential between the hot and cold sides of the heat exchanger is greater. If the incoming air is 100F, you'd transfer less BTUs because the temp differential is smaller. Â*You would then have a very similar chart that starts out with a given BTU of heat transfer at 500CFM and INCREASES as you increase the airflow to 600, 700, 1000 CFM. Â*Capiche? It gives the water entering temperature. Â*The temperature it leaves at varies depending on air temperature on entry Â*and velocity for that particular CFM. (As do the BTUs transferred.) Sure does. Â*Do you agree that this chart also clearly shows the BTUs of heat transferred INCREASED steadily with the airflow? Â*That MORE heat is transferred in that table as the airflow increases? Â* That it is that way for the table on every size of heat exchanger? Â*Yes or no? These figures are for guidance only and demonstrate a range of options/ operating conditions. It's not possible to specify all possible conditions. No **** Sherlock. Â*But remarkably, the application the heat exchanger is targeted for is exactly what the OP was looking for. Â*And the water flow rate and the airflow rate are within the range that a system to heat a home via solar would be. Â*In other words, that chart shows exactly what the OP could use. Â*It's not some curve from some bizarre or unique heat exchanger. I don't understand why you can't understand the simple concept that the longer you keep your hand on a hot Â*stove, the hotter it (your hand) will get. I can't understand why you can't understand the simple concept that a heat exchanger, be it this one, or a car radiator has a CONTINUOUS MASS moving through it. We don't have a single hand, Â*we have say 100 people with hands at 98F, that each place their hand on the warm stove for 30 secs. Â*That transfers MORE heat than one person leaving their hand there because new hands at 98F are constantly replacing hands that have warmed slightly. Â*The greater the temp delta, the greater the heat transfer. Â* You stated that yourself. You wind up with 100 people with slightly warmer hands instead of one person with a hot hand. Â*Does that mean less heat is transferred? Â*Of course not because the mass of those 100 hands more than makes up for the fact that they are only slightly warm. Â*Capiche? Same thing applies to a home radiator on a hot water or steam system. Â*The more air you move past it, the lower the air temp will be, but the more heat you will extract from the radiator and the cooler the exit water temp will be. Same thing applies to a car radiator. Â*And it matter not a wit that it's waste heat being transferred to the atmosphere, so please don't start that again. In the OP, the object of the excercise was to get the air as hot as possible.- Hide quoted text - There you go again. Â*It's been stated to you many times now by Mark, CL, and I that the object of the excercise was to heat the house. Â* Which means getting the most heat out of the heat exchanger, not the hottest air. Â* You are confusing TEMPERATURE with HEAT. Â* Try looking up the definition. You are confusing both with extracting the most efficiency out of a limited supply of heat. As one more example, I could go down and turn the blower down on my furnace to 100CFM instead of 1300CFM. Â* Assuming it would not kick off due to the high limit safety switch, I would then be getting very hot air out of it. Â*Does that mean I'm getting MORE heat and it's going to heat my house faster, etc? No. Â*I'd be getting LESS heat even though the small amount of air coming out is a lot hotter. Â* Capiche? if you turned down the burner the heat exchanger would work more efficiently. The combustion products would be going through the heat exchanger slower. A greater PERCENTAGE of the heat would be transferred. More bang for buck. I don't know what's wrong with you but I'm getting bored. There is the whole aspect of diminishing returns that both Trader and Harry are forgetting about - PERHAPS Harry more than Trader. The difference in efficiency is real, but how great? = particularly since we are working with a closed loop system, and the heat not recovered stays in the system, raising the input temp the next time 'round, which will increase the efficiency. It's not like we are wasting any heat (or at least not huge amounts) by not recovering it on the first pass. And passing more air through the exchanger does increase the BTUs extraced - but by how much, particularly when lowering the "dwell time" does reduce the efficiency somewhat. At what point does the loss of efficiency from the one side over-balance the loss of theoretical heat transfer from the other. My gut feeling is the gains/losses from either side of the arguement are close enough that there will be a fairly broad band of overlap where the difference in heat transferred will be RELATIVELY insignificant in the grand scheme of things. You get to the point where "close enough IS close enough.". |
Hot water to forced air
On Wed, 11 Jan 2012 11:03:05 -0800 (PST), harry
wrote: On Jan 11, 3:04Â*pm, " wrote: On Jan 10, 12:38Â*pm, harry wrote: I think you have the problem. I have looked at the table. The specification given are for one particular pressure difference / velocity Â*of water in the primary side..(in the first vertical column.) Â*If you put less water through it, the outcoming water would be cooler. Yes, it's for 6 GPM of water flowing through the heat exchanger. Â*And it shows water at temps of Â*140F, 160F, and 180F. Â*And HOW MUCH HEAT IS TRANSFERRED VERSUS AIRFLOWS OF 500, 600, 700, 800, 1000 CFM As the airflow goes up, so does the BTUs of heat transferred. Do you agree that is what it shows or not? And yes, if you made another chart that showed say 3GPM per minute of water flow instead of 6GPM, the water would be coming out cooler. Â*You would then have LESS heat transferred. Â*And you'd have a similar table showing that as airflow increases from 500 to 1000CFM, the amount of heat transferred increases with it. The water would be coming out cooler because it was moving slower. More heat would be removed from the water than in the previous case. So, to remove the maximum amount of heat from the water it has to go slower. Are you a troll or just thick? Both theories are valid - but when the rubber hits the road - or in this case Fluid 1 hits fluid 2 - how much difference will each make??? The only way to know is by setting up a system and testing. Not DIFFICULT to do as a test before final install with a variable speed blower and heat exchanger, and a flow control valve to contol both water and air flow. Don't need to measure air temperature change/heat absorption because if the heat leaves the water, it went to the air. You need to be able to measure inlet and outlet water temps and water flow, as well as air flow. That's all. I'd definitely be doing this before making any mods to the heating/air handling system in the house. And PERHAPS a thermosyphon circulation system would be self optimizing???? Just a thought. |
Hot water to forced air
On Jan 12, 3:18*am, wrote:
On Wed, 11 Jan 2012 11:03:05 -0800 (PST), harry wrote: On Jan 11, 3:04*pm, " wrote: On Jan 10, 12:38*pm, harry wrote: I think you have the problem. I have looked at the table. The specification given are for one particular pressure difference / velocity *of water in the primary side..(in the first vertical column.) *If you put less water through it, the outcoming water would be cooler. Yes, it's for 6 GPM of water flowing through the heat exchanger. *And it shows water at temps of *140F, 160F, and 180F. *And HOW MUCH HEAT IS TRANSFERRED VERSUS AIRFLOWS OF 500, 600, 700, 800, 1000 CFM As the airflow goes up, so does the BTUs of heat transferred. Do you agree that is what it shows or not? And yes, if you made another chart that showed say 3GPM per minute of water flow instead of 6GPM, the water would be coming out cooler. *You would then have LESS heat transferred. *And you'd have a similar table showing that as airflow increases from 500 to 1000CFM, the amount of heat transferred increases with it. The water would be coming out cooler because it was moving slower. More heat would be removed from the water than in the previous case. So, to remove the maximum amount of heat from the water it has to go slower. Are you a troll or just thick? *Both theories are valid - but when the rubber hits the road - or in this case Fluid 1 hits fluid 2 - how much difference will each make??? The only way to know is by setting up a system and testing. Not DIFFICULT to do as a test before final install with a variable speed blower and heat exchanger, and a flow control valve to contol both water and air flow. Don't need to measure air temperature change/heat absorption because if the heat leaves the water, it went to the air. You need to be able to measure inlet and outlet water temps and water flow, as well as air flow. That's all. I'd definitely be doing this before making any mods to the heating/air handling system in the house. *And PERHAPS a thermosyphon circulation system would be self optimizing???? Just a thought.- Hide quoted text - - Show quoted text - Theoretically you are right Thermosyphoning works if the distance viertically is greater by a factor of three at least than the horizontal difference in heatings sytems. Pipework needs to be bigger and tight bends avoided. I have never seen it used in the application you propose but plenty in wet heating sytems and domestic hot water, especially old ones. I only ever installed one myself, it was in a remote place where the electricity supply was unreliable. The resistance of the system has to be kept really low. |
Hot water to forced air
On Jan 12, 3:11*am, wrote:
On Wed, 11 Jan 2012 10:56:18 -0800 (PST), harry wrote: On Jan 11, 3:04*pm, " wrote: On Jan 10, 12:38*pm, harry wrote: I think you have the problem. I have looked at the table. The specification given are for one particular pressure difference / velocity *of water in the primary side..(in the first vertical column.) *If you put less water through it, the outcoming water would be cooler. Yes, it's for 6 GPM of water flowing through the heat exchanger. *And it shows water at temps of *140F, 160F, and 180F. *And HOW MUCH HEAT IS TRANSFERRED VERSUS AIRFLOWS OF 500, 600, 700, 800, 1000 CFM As the airflow goes up, so does the BTUs of heat transferred. Do you agree that is what it shows or not? And yes, if you made another chart that showed say 3GPM per minute of water flow instead of 6GPM, the water would be coming out cooler. *You would then have LESS heat transferred. *And you'd have a similar table showing that as airflow increases from 500 to 1000CFM, the amount of heat transferred increases with it. That table for 6GPM isn't some unique point where special rules of physics apply. *It shows how the heat exchanger works and is an operating point within the scope of this discusssion, where if the OP built his system he could get 30K BTUS of heat out of it. Look at the other heat exchangers that are larger and show greater flow rates. *Find me one that does not show that as you increase airflow, the BTUs of heat transferred go up. And nowhere does it mention the entry/exit air temperature. *Again you have to work these out. Now I agree that is one missing piece of information that should be spec'd on the data sheet. *Without it we don't know the specific air entry temp that resulted in those BTU numbers. * However, it doesn't matter. *Whatever the air entry numbers, clearly: The spec sheet does state: " These air to water units are ideal for heating water in residential and public buildings. Compact and lightweight, these units are designed to maximize heat transfer by utilizing a series of 3/8" copper tubes with a high density of aluminum fins. These fins are spaced in such a way that the fin density is an impressive 12 fins per inch. This unique design allows for heating loads of 50,000 to 60,000 Btu per square foot (please see performance chart below)." And with water entering at 140F to 180F it's obviously being used in that chart to heat air. *At that point, it does not matter what the incoming air temp is. *Let's assume for the moment that the particular chart used 65F air. *The chart shows the BTUs of heat tranferred versus increasing airflow. *As you increase airflow, the BTUs go up. Now, if the incoming air were cooler, say 40F, you'd transfer more BTUs of heat because the temp differential between the hot and cold sides of the heat exchanger is greater. If the incoming air is 100F, you'd transfer less BTUs because the temp differential is smaller. *You would then have a very similar chart that starts out with a given BTU of heat transfer at 500CFM and INCREASES as you increase the airflow to 600, 700, 1000 CFM. *Capiche? It gives the water entering temperature. *The temperature it leaves at varies depending on air temperature on entry *and velocity for that particular CFM. (As do the BTUs transferred.) Sure does. *Do you agree that this chart also clearly shows the BTUs of heat transferred INCREASED steadily with the airflow? *That MORE heat is transferred in that table as the airflow increases? * That it is that way for the table on every size of heat exchanger? *Yes or no? These figures are for guidance only and demonstrate a range of options/ operating conditions. It's not possible to specify all possible conditions. No **** Sherlock. *But remarkably, the application the heat exchanger is targeted for is exactly what the OP was looking for. *And the water flow rate and the airflow rate are within the range that a system to heat a home via solar would be. *In other words, that chart shows exactly what the OP could use. *It's not some curve from some bizarre or unique heat exchanger. I don't understand why you can't understand the simple concept that the longer you keep your hand on a hot *stove, the hotter it (your hand) will get. I can't understand why you can't understand the simple concept that a heat exchanger, be it this one, or a car radiator has a CONTINUOUS MASS moving through it. We don't have a single hand, *we have say 100 people with hands at 98F, that each place their hand on the warm stove for 30 secs. *That transfers MORE heat than one person leaving their hand there because new hands at 98F are constantly replacing hands that have warmed slightly. *The greater the temp delta, the greater the heat transfer. * You stated that yourself. You wind up with 100 people with slightly warmer hands instead of one person with a hot hand. *Does that mean less heat is transferred? *Of course not because the mass of those 100 hands more than makes up for the fact that they are only slightly warm. *Capiche? Same thing applies to a home radiator on a hot water or steam system. *The more air you move past it, the lower the air temp will be, but the more heat you will extract from the radiator and the cooler the exit water temp will be. Same thing applies to a car radiator. *And it matter not a wit that it's waste heat being transferred to the atmosphere, so please don't start that again. In the OP, the object of the excercise was to get the air as hot as possible.- Hide quoted text - There you go again. *It's been stated to you many times now by Mark, CL, and I that the object of the excercise was to heat the house. * Which means getting the most heat out of the heat exchanger, not the hottest air. * You are confusing TEMPERATURE with HEAT. * Try looking up the definition. You are confusing both with extracting the most efficiency out of a limited supply of heat. As one more example, I could go down and turn the blower down on my furnace to 100CFM instead of 1300CFM. * Assuming it would not kick off due to the high limit safety switch, I would then be getting very hot air out of it. *Does that mean I'm getting MORE heat and it's going to heat my house faster, etc? No. *I'd be getting LESS heat even though the small amount of air coming out is a lot hotter. * Capiche? if you turned down the burner the heat exchanger would work more efficiently. *The combustion products would be going through the heat exchanger slower. A greater *PERCENTAGE of the heat would be transferred. More bang for buck. I don't know what's wrong with you but I'm getting bored. *There is the whole aspect of diminishing returns that both Trader and Harry are forgetting about - PERHAPS Harry more than Trader. The difference in efficiency is real, but how great? = particularly since we are working with a closed loop system, and the heat not recovered stays in the system, raising the input temp the next time 'round, which will increase the efficiency. It's not like we are wasting any heat (or at least not huge amounts) by not recovering it on the first pass. And passing more air through the exchanger does increase the BTUs extraced *- but by how much, particularly when lowering the "dwell time" does reduce the efficiency somewhat. At what point does the loss of efficiency from the one side over-balance the loss of theoretical heat transfer from the other. *My gut feeling is the gains/losses from either side of the arguement are close enough that there will be a fairly broad band of overlap where the difference in heat transferred will be RELATIVELY insignificant in the grand scheme of things. You get to the point where "close enough IS close enough.".- Hide quoted text - - Show quoted text - I think that is what I was telling him. |
Hot water to forced air
On Jan 11, 1:56*pm, harry wrote:
On Jan 11, 3:04*pm, " wrote: On Jan 10, 12:38*pm, harry wrote: I think you have the problem. I have looked at the table. The specification given are for one particular pressure difference / velocity *of water in the primary side..(in the first vertical column.) *If you put less water through it, the outcoming water would be cooler. Yes, it's for 6 GPM of water flowing through the heat exchanger. *And it shows water at temps of *140F, 160F, and 180F. *And HOW MUCH HEAT IS TRANSFERRED VERSUS AIRFLOWS OF 500, 600, 700, 800, 1000 CFM As the airflow goes up, so does the BTUs of heat transferred. Do you agree that is what it shows or not? And yes, if you made another chart that showed say 3GPM per minute of water flow instead of 6GPM, the water would be coming out cooler. *You would then have LESS heat transferred. *And you'd have a similar table showing that as airflow increases from 500 to 1000CFM, the amount of heat transferred increases with it. That table for 6GPM isn't some unique point where special rules of physics apply. *It shows how the heat exchanger works and is an operating point within the scope of this discusssion, where if the OP built his system he could get 30K BTUS of heat out of it. Look at the other heat exchangers that are larger and show greater flow rates. *Find me one that does not show that as you increase airflow, the BTUs of heat transferred go up. And nowhere does it mention the entry/exit air temperature. *Again you have to work these out. Now I agree that is one missing piece of information that should be spec'd on the data sheet. *Without it we don't know the specific air entry temp that resulted in those BTU numbers. * However, it doesn't matter. *Whatever the air entry numbers, clearly: The spec sheet does state: " These air to water units are ideal for heating water in residential and public buildings. Compact and lightweight, these units are designed to maximize heat transfer by utilizing a series of 3/8" copper tubes with a high density of aluminum fins. These fins are spaced in such a way that the fin density is an impressive 12 fins per inch. This unique design allows for heating loads of 50,000 to 60,000 Btu per square foot (please see performance chart below)." And with water entering at 140F to 180F it's obviously being used in that chart to heat air. *At that point, it does not matter what the incoming air temp is. *Let's assume for the moment that the particular chart used 65F air. *The chart shows the BTUs of heat tranferred versus increasing airflow. *As you increase airflow, the BTUs go up. Now, if the incoming air were cooler, say 40F, you'd transfer more BTUs of heat because the temp differential between the hot and cold sides of the heat exchanger is greater. If the incoming air is 100F, you'd transfer less BTUs because the temp differential is smaller. *You would then have a very similar chart that starts out with a given BTU of heat transfer at 500CFM and INCREASES as you increase the airflow to 600, 700, 1000 CFM. *Capiche? It gives the water entering temperature. *The temperature it leaves at varies depending on air temperature on entry *and velocity for that particular CFM. (As do the BTUs transferred.) Sure does. *Do you agree that this chart also clearly shows the BTUs of heat transferred INCREASED steadily with the airflow? *That MORE heat is transferred in that table as the airflow increases? * That it is that way for the table on every size of heat exchanger? *Yes or no? These figures are for guidance only and demonstrate a range of options/ operating conditions. It's not possible to specify all possible conditions. No **** Sherlock. *But remarkably, the application the heat exchanger is targeted for is exactly what the OP was looking for. *And the water flow rate and the airflow rate are within the range that a system to heat a home via solar would be. *In other words, that chart shows exactly what the OP could use. *It's not some curve from some bizarre or unique heat exchanger. I don't understand why you can't understand the simple concept that the longer you keep your hand on a hot *stove, the hotter it (your hand) will get. I can't understand why you can't understand the simple concept that a heat exchanger, be it this one, or a car radiator has a CONTINUOUS MASS moving through it. We don't have a single hand, *we have say 100 people with hands at 98F, that each place their hand on the warm stove for 30 secs. *That transfers MORE heat than one person leaving their hand there because new hands at 98F are constantly replacing hands that have warmed slightly. *The greater the temp delta, the greater the heat transfer. * You stated that yourself. You wind up with 100 people with slightly warmer hands instead of one person with a hot hand. *Does that mean less heat is transferred? *Of course not because the mass of those 100 hands more than makes up for the fact that they are only slightly warm. *Capiche? Same thing applies to a home radiator on a hot water or steam system. *The more air you move past it, the lower the air temp will be, but the more heat you will extract from the radiator and the cooler the exit water temp will be. Same thing applies to a car radiator. *And it matter not a wit that it's waste heat being transferred to the atmosphere, so please don't start that again. In the OP, the object of the excercise was to get the air as hot as possible.- Hide quoted text - There you go again. *It's been stated to you many times now by Mark, CL, and I that the object of the excercise was to heat the house. * Which means getting the most heat out of the heat exchanger, not the hottest air. * You are confusing TEMPERATURE with HEAT. * Try looking up the definition. You are confusing both with extracting the most efficiency out of a limited supply of heat. As one more example, I could go down and turn the blower down on my furnace to 100CFM instead of 1300CFM. * Assuming it would not kick off due to the high limit safety switch, I would then be getting very hot air out of it. *Does that mean I'm getting MORE heat and it's going to heat my house faster, etc? No. *I'd be getting LESS heat even though the small amount of air coming out is a lot hotter. * Capiche? *if you turned down the burner the heat exchanger would work more efficiently. *The combustion products would be going through the heat exchanger slower. A greater *PERCENTAGE of the heat would be transferred. More bang for buck. I don't know what's wrong with you but I'm getting bored.- Hide quoted text - - Show quoted text - Try sticking to the example, instead of changing it. We're not talking about changing the burner rate. We're talking about changing the AIRFLOW rate of the furnace with a given burner rate. Whatever the burner rate, you get more heat out of that example of a heat exchanger the MORE air that flows through it. Yes, that air will be at a lower temperature, but given the increase in air mass, it still picks up MORE heat going through the furnace. Capiche? And where do you address the whole rest of my post? As usual, you don't. You just try to steer the discussion somewhere else. |
Hot water to forced air
On Jan 11, 10:11*pm, wrote:
On Wed, 11 Jan 2012 10:56:18 -0800 (PST), harry wrote: On Jan 11, 3:04*pm, " wrote: On Jan 10, 12:38*pm, harry wrote: I think you have the problem. I have looked at the table. The specification given are for one particular pressure difference / velocity *of water in the primary side..(in the first vertical column.) *If you put less water through it, the outcoming water would be cooler. Yes, it's for 6 GPM of water flowing through the heat exchanger. *And it shows water at temps of *140F, 160F, and 180F. *And HOW MUCH HEAT IS TRANSFERRED VERSUS AIRFLOWS OF 500, 600, 700, 800, 1000 CFM As the airflow goes up, so does the BTUs of heat transferred. Do you agree that is what it shows or not? And yes, if you made another chart that showed say 3GPM per minute of water flow instead of 6GPM, the water would be coming out cooler. *You would then have LESS heat transferred. *And you'd have a similar table showing that as airflow increases from 500 to 1000CFM, the amount of heat transferred increases with it. That table for 6GPM isn't some unique point where special rules of physics apply. *It shows how the heat exchanger works and is an operating point within the scope of this discusssion, where if the OP built his system he could get 30K BTUS of heat out of it. Look at the other heat exchangers that are larger and show greater flow rates. *Find me one that does not show that as you increase airflow, the BTUs of heat transferred go up. And nowhere does it mention the entry/exit air temperature. *Again you have to work these out. Now I agree that is one missing piece of information that should be spec'd on the data sheet. *Without it we don't know the specific air entry temp that resulted in those BTU numbers. * However, it doesn't matter. *Whatever the air entry numbers, clearly: The spec sheet does state: " These air to water units are ideal for heating water in residential and public buildings. Compact and lightweight, these units are designed to maximize heat transfer by utilizing a series of 3/8" copper tubes with a high density of aluminum fins. These fins are spaced in such a way that the fin density is an impressive 12 fins per inch. This unique design allows for heating loads of 50,000 to 60,000 Btu per square foot (please see performance chart below)." And with water entering at 140F to 180F it's obviously being used in that chart to heat air. *At that point, it does not matter what the incoming air temp is. *Let's assume for the moment that the particular chart used 65F air. *The chart shows the BTUs of heat tranferred versus increasing airflow. *As you increase airflow, the BTUs go up. Now, if the incoming air were cooler, say 40F, you'd transfer more BTUs of heat because the temp differential between the hot and cold sides of the heat exchanger is greater. If the incoming air is 100F, you'd transfer less BTUs because the temp differential is smaller. *You would then have a very similar chart that starts out with a given BTU of heat transfer at 500CFM and INCREASES as you increase the airflow to 600, 700, 1000 CFM. *Capiche? It gives the water entering temperature. *The temperature it leaves at varies depending on air temperature on entry *and velocity for that particular CFM. (As do the BTUs transferred.) Sure does. *Do you agree that this chart also clearly shows the BTUs of heat transferred INCREASED steadily with the airflow? *That MORE heat is transferred in that table as the airflow increases? * That it is that way for the table on every size of heat exchanger? *Yes or no? These figures are for guidance only and demonstrate a range of options/ operating conditions. It's not possible to specify all possible conditions. No **** Sherlock. *But remarkably, the application the heat exchanger is targeted for is exactly what the OP was looking for. *And the water flow rate and the airflow rate are within the range that a system to heat a home via solar would be. *In other words, that chart shows exactly what the OP could use. *It's not some curve from some bizarre or unique heat exchanger. I don't understand why you can't understand the simple concept that the longer you keep your hand on a hot *stove, the hotter it (your hand) will get. I can't understand why you can't understand the simple concept that a heat exchanger, be it this one, or a car radiator has a CONTINUOUS MASS moving through it. We don't have a single hand, *we have say 100 people with hands at 98F, that each place their hand on the warm stove for 30 secs. *That transfers MORE heat than one person leaving their hand there because new hands at 98F are constantly replacing hands that have warmed slightly. *The greater the temp delta, the greater the heat transfer. * You stated that yourself. You wind up with 100 people with slightly warmer hands instead of one person with a hot hand. *Does that mean less heat is transferred? *Of course not because the mass of those 100 hands more than makes up for the fact that they are only slightly warm. *Capiche? Same thing applies to a home radiator on a hot water or steam system. *The more air you move past it, the lower the air temp will be, but the more heat you will extract from the radiator and the cooler the exit water temp will be. Same thing applies to a car radiator. *And it matter not a wit that it's waste heat being transferred to the atmosphere, so please don't start that again. In the OP, the object of the excercise was to get the air as hot as possible.- Hide quoted text - There you go again. *It's been stated to you many times now by Mark, CL, and I that the object of the excercise was to heat the house. * Which means getting the most heat out of the heat exchanger, not the hottest air. * You are confusing TEMPERATURE with HEAT. * Try looking up the definition. You are confusing both with extracting the most efficiency out of a limited supply of heat. As one more example, I could go down and turn the blower down on my furnace to 100CFM instead of 1300CFM. * Assuming it would not kick off due to the high limit safety switch, I would then be getting very hot air out of it. *Does that mean I'm getting MORE heat and it's going to heat my house faster, etc? No. *I'd be getting LESS heat even though the small amount of air coming out is a lot hotter. * Capiche? if you turned down the burner the heat exchanger would work more efficiently. *The combustion products would be going through the heat exchanger slower. A greater *PERCENTAGE of the heat would be transferred. More bang for buck. I don't know what's wrong with you but I'm getting bored. *There is the whole aspect of diminishing returns that both Trader and Harry are forgetting about - PERHAPS Harry more than Trader. Give me a break here. I haven't forgot about diminishing returns: A - I can refer you back many posts ago where I said that the more airflow you pass through the heat exchanger the more heat you get out and that the additional heat gained decays exponentially with the increased airflow. And yes, if you put enough air through it, all the heat is extracted and the outgoing water temp and the air temp are equal and no more heat can be extracted. I clearly stated that many times here too. B - I posted the data from the heat exchanger data sheet you provided which fits the application nicely. It shows that additional heat is still being extracted at over 1000CFM. Yes, the additional gains are diminishing. C - This started over the issue of placing dampers in the airflow stream. I said you might as well just use max airflow, because there is no downside to doing that from the heat exchange standpoint and you will have heat exchange at a maximum. I think you agree with that, no? The difference in efficiency is real, but how great? = particularly since we are working with a closed loop system, and the heat not recovered stays in the system, raising the input temp the next time 'round, which will increase the efficiency. It doesn't increase the efficiency. That water leaving the heat exchanger from the furnace is now HOTTER and will consequently pick up LESS heat going through the solar array, which is just another heat exchanger. Put 65F water into the solar array and you get max heat out of it. Put in 150F water, or whatever the max temp it is capable of achieving, and you get zero heat out of it. It's not like we are wasting any heat (or at least not huge amounts) by not recovering it on the first pass. You sure are wasting it, per the above. And passing more air through the exchanger does increase the BTUs extraced *- but by how much, particularly when lowering the "dwell time" does reduce the efficiency somewhat. Totally wrong, per the above. At what point does the loss of efficiency from the one side over-balance the loss of theoretical heat transfer from the other. It doesn't *My gut feeling is the gains/losses from either side of the arguement are close enough that there will be a fairly broad band of overlap where the difference in heat transferred will be RELATIVELY insignificant in the grand scheme of things. You get to the point where "close enough IS close enough.".- Hide quoted text - - Show quoted text - Your gut is wrong. Sending that water back to the solar array with all the heat extracted from it in the furnace is how you get the maximum heat out of it, which is what the OP wants. If that isn't possible, the next best thing is to get as much heat as possible extracted from it. And you do that by using maximum airflow. |
Hot water to forced air
On Jan 11, 2:03*pm, harry wrote:
On Jan 11, 3:04*pm, " wrote: On Jan 10, 12:38*pm, harry wrote: I think you have the problem. I have looked at the table. The specification given are for one particular pressure difference / velocity *of water in the primary side..(in the first vertical column.) *If you put less water through it, the outcoming water would be cooler. Yes, it's for 6 GPM of water flowing through the heat exchanger. *And it shows water at temps of *140F, 160F, and 180F. *And HOW MUCH HEAT IS TRANSFERRED VERSUS AIRFLOWS OF 500, 600, 700, 800, 1000 CFM As the airflow goes up, so does the BTUs of heat transferred. Do you agree that is what it shows or not? And yes, if you made another chart that showed say 3GPM per minute of water flow instead of 6GPM, the water would be coming out cooler. *You would then have LESS heat transferred. *And you'd have a similar table showing that as airflow increases from 500 to 1000CFM, the amount of heat transferred increases with it. The water would be coming out cooler because it was moving slower. More heat would be removed from the water than in the previous case. So, to remove the maximum amount of heat from the water it has to go slower. Are you a troll or just thick?- Hide quoted text - - Show quoted text - As Mark pointed out to you days ago, you sure are an arrogant smart ass for someone who is completely wrong here. Again, you are confusing TEMPERATURE with HEAT. Yes, with a slower water flow you'd have cooler water coming out and more heat extracted from that water. But you have half the MASS of water flowing. You completely fail to take that very basic fact into account. With half the water flowing, although the water coming out is cooler, meaning more heat has been extracted, less HEAT has been transferred because you've only cooled half the MASS of water. Capiche? One good way of seeing the folly of your ways is to look at limits. Let's take a home radiator with a fan in front of it. Let's say 6 GPM of 180F water is flowing through it and we are getting X BTUs of heat out of it. Let's say the water exiting it is 130F. Now, I turn down the flow rate of water to 3 GPM. What happens: A - The water coming out is cooler, let's say 110F. B - The air is coming out cooler. C - Less heat is transferred because while MORE heat has been extacted from the water that is flowing, you now only have 1/2 the water mass flowing. Capiche? You can continue that process down to the limit where if you limit the flow enough, the water temp exiting will be equal to the house air temp, say 70F. Let's say that occurs at .5 (point 5) GPM At that point, you have the maximum heat extracted from a very small volume of water, it's 10% of the initial flow rate. The water is now cooled completely, but the heat exchange is the lowest and the amount of the heat going into the home is a small fraction of what it was at 5 GPM Capiche? And you say what? That this is how you transfer maximum heat into the house? That as I close off the valve on a radiator, because the outgoing water is cooler, I'm getting more heat into the house? From your post, that is indeed what you are saying. The interesting thing here is that when you have a grasp of the basic science, it all fits together. In your world, you're stumped and have to make up new rules for car radiators, saying they don't work the same because it's waste heat, ignore manufacturer's data sheets for heat exchangers clearly show heat transfer increasing with airflow, etc. |
Hot water to forced air
On Jan 11, 10:18*pm, wrote:
On Wed, 11 Jan 2012 11:03:05 -0800 (PST), harry wrote: On Jan 11, 3:04*pm, " wrote: On Jan 10, 12:38*pm, harry wrote: I think you have the problem. I have looked at the table. The specification given are for one particular pressure difference / velocity *of water in the primary side..(in the first vertical column.) *If you put less water through it, the outcoming water would be cooler. Yes, it's for 6 GPM of water flowing through the heat exchanger. *And it shows water at temps of *140F, 160F, and 180F. *And HOW MUCH HEAT IS TRANSFERRED VERSUS AIRFLOWS OF 500, 600, 700, 800, 1000 CFM As the airflow goes up, so does the BTUs of heat transferred. Do you agree that is what it shows or not? And yes, if you made another chart that showed say 3GPM per minute of water flow instead of 6GPM, the water would be coming out cooler. *You would then have LESS heat transferred. *And you'd have a similar table showing that as airflow increases from 500 to 1000CFM, the amount of heat transferred increases with it. The water would be coming out cooler because it was moving slower. More heat would be removed from the water than in the previous case. So, to remove the maximum amount of heat from the water it has to go slower. Are you a troll or just thick? *Both theories are valid - but when the rubber hits the road - or in this case Fluid 1 hits fluid 2 - how much difference will each make??? Go read my example posted back to harry about the home radiator. You're now also confusing temperature with heat. The only way to know is by setting up a system and testing. You think that's how engineers build heat exchanger systems? By trial and error? |
Hot water to forced air
On Jan 13, 10:54*am, "
wrote: On Jan 11, 2:03*pm, harry wrote: On Jan 11, 3:04*pm, " wrote: On Jan 10, 12:38*pm, harry wrote: I think you have the problem. I have looked at the table. The specification given are for one particular pressure difference / velocity *of water in the primary side..(in the first vertical column.) *If you put less water through it, the outcoming water would be cooler. Yes, it's for 6 GPM of water flowing through the heat exchanger. *And it shows water at temps of *140F, 160F, and 180F. *And HOW MUCH HEAT IS TRANSFERRED VERSUS AIRFLOWS OF 500, 600, 700, 800, 1000 CFM As the airflow goes up, so does the BTUs of heat transferred. Do you agree that is what it shows or not? And yes, if you made another chart that showed say 3GPM per minute of water flow instead of 6GPM, the water would be coming out cooler. *You would then have LESS heat transferred. *And you'd have a similar table showing that as airflow increases from 500 to 1000CFM, the amount of heat transferred increases with it. The water would be coming out cooler because it was moving slower. More heat would be removed from the water than in the previous case. So, to remove the maximum amount of heat from the water it has to go slower. Are you a troll or just thick?- Hide quoted text - - Show quoted text - As Mark pointed out to you days ago, you sure are an arrogant smart ass for someone who is completely wrong here. Again, you are confusing TEMPERATURE with HEAT. Yes, with a slower water flow you'd have cooler water coming out and more heat extracted from that water. But you have half the MASS of water flowing. *You completely fail to take that very basic fact into account. With half the water flowing, although the water coming out is cooler, meaning more heat has been extracted, less HEAT has been transferred because you've only cooled half the MASS of water. * Capiche? One good way of seeing the folly of your ways is to look at limits. * Let's take a home radiator with a fan in front of it. *Let's say 6 GPM of 180F water is flowing through it and we are getting X BTUs of heat out of it. * Let's say the water exiting it is 130F. * Now, I turn down the flow rate of water to 3 GPM. *What happens: A - The water coming out is cooler, let's say 110F. B - The air is coming out cooler. C - Less heat is transferred because while MORE heat has been extacted from the water that is flowing, you now only have 1/2 the water mass flowing. Capiche? You can continue that process down to the limit where if you limit the flow enough, the water temp exiting will be equal to the house air temp, say 70F. Let's say that occurs at .5 (point 5) GPM At that point, you have the maximum heat extracted from a very small volume of water, it's 10% of the initial flow rate. *The water is now cooled completely, but the heat exchange is the lowest and the amount of the heat going into the home is a small fraction of what it was at 5 GPM Capiche? And you say what? *That this is how you transfer maximum heat into the house? *That as I close off the valve on a radiator, because the outgoing water is cooler, I'm getting more heat into the house? From your post, that is indeed what you are saying. The interesting thing here is that when you have a grasp of the basic science, it all fits together. In your world, you're stumped and have to make up new rules for car radiators, saying they don't work the same because it's waste heat, ignore manufacturer's data sheets for heat exchangers clearly show heat transfer increasing with airflow, etc.- Hide quoted text - - Show quoted text - exhaust air thats too cool will make occupants feel cooler espically at higer speed airflows. a modern high efficency forced air furnace is a excellent example, during cool down the blower remais on and can feel cold if your standing in front of the air vent |
Hot water to forced air
On Fri, 13 Jan 2012 07:36:14 -0800 (PST), "
wrote: On Jan 11, 10:11Â*pm, wrote: On Wed, 11 Jan 2012 10:56:18 -0800 (PST), harry wrote: On Jan 11, 3:04Â*pm, " wrote: On Jan 10, 12:38Â*pm, harry wrote: I think you have the problem. I have looked at the table. The specification given are for one particular pressure difference / velocity Â*of water in the primary side..(in the first vertical column.) Â*If you put less water through it, the outcoming water would be cooler. Yes, it's for 6 GPM of water flowing through the heat exchanger. Â*And it shows water at temps of Â*140F, 160F, and 180F. Â*And HOW MUCH HEAT IS TRANSFERRED VERSUS AIRFLOWS OF 500, 600, 700, 800, 1000 CFM As the airflow goes up, so does the BTUs of heat transferred. Do you agree that is what it shows or not? And yes, if you made another chart that showed say 3GPM per minute of water flow instead of 6GPM, the water would be coming out cooler. Â*You would then have LESS heat transferred. Â*And you'd have a similar table showing that as airflow increases from 500 to 1000CFM, the amount of heat transferred increases with it. That table for 6GPM isn't some unique point where special rules of physics apply. Â*It shows how the heat exchanger works and is an operating point within the scope of this discusssion, where if the OP built his system he could get 30K BTUS of heat out of it. Look at the other heat exchangers that are larger and show greater flow rates. Â*Find me one that does not show that as you increase airflow, the BTUs of heat transferred go up. And nowhere does it mention the entry/exit air temperature. Â*Again you have to work these out. Now I agree that is one missing piece of information that should be spec'd on the data sheet. Â*Without it we don't know the specific air entry temp that resulted in those BTU numbers. Â* However, it doesn't matter. Â*Whatever the air entry numbers, clearly: The spec sheet does state: " These air to water units are ideal for heating water in residential and public buildings. Compact and lightweight, these units are designed to maximize heat transfer by utilizing a series of 3/8" copper tubes with a high density of aluminum fins. These fins are spaced in such a way that the fin density is an impressive 12 fins per inch. This unique design allows for heating loads of 50,000 to 60,000 Btu per square foot (please see performance chart below)." And with water entering at 140F to 180F it's obviously being used in that chart to heat air. Â*At that point, it does not matter what the incoming air temp is. Â*Let's assume for the moment that the particular chart used 65F air. Â*The chart shows the BTUs of heat tranferred versus increasing airflow. Â*As you increase airflow, the BTUs go up. Now, if the incoming air were cooler, say 40F, you'd transfer more BTUs of heat because the temp differential between the hot and cold sides of the heat exchanger is greater. If the incoming air is 100F, you'd transfer less BTUs because the temp differential is smaller. Â*You would then have a very similar chart that starts out with a given BTU of heat transfer at 500CFM and INCREASES as you increase the airflow to 600, 700, 1000 CFM. Â*Capiche? It gives the water entering temperature. Â*The temperature it leaves at varies depending on air temperature on entry Â*and velocity for that particular CFM. (As do the BTUs transferred.) Sure does. Â*Do you agree that this chart also clearly shows the BTUs of heat transferred INCREASED steadily with the airflow? Â*That MORE heat is transferred in that table as the airflow increases? Â* That it is that way for the table on every size of heat exchanger? Â*Yes or no? These figures are for guidance only and demonstrate a range of options/ operating conditions. It's not possible to specify all possible conditions. No **** Sherlock. Â*But remarkably, the application the heat exchanger is targeted for is exactly what the OP was looking for. Â*And the water flow rate and the airflow rate are within the range that a system to heat a home via solar would be. Â*In other words, that chart shows exactly what the OP could use. Â*It's not some curve from some bizarre or unique heat exchanger. I don't understand why you can't understand the simple concept that the longer you keep your hand on a hot Â*stove, the hotter it (your hand) will get. I can't understand why you can't understand the simple concept that a heat exchanger, be it this one, or a car radiator has a CONTINUOUS MASS moving through it. We don't have a single hand, Â*we have say 100 people with hands at 98F, that each place their hand on the warm stove for 30 secs. Â*That transfers MORE heat than one person leaving their hand there because new hands at 98F are constantly replacing hands that have warmed slightly. Â*The greater the temp delta, the greater the heat transfer. Â* You stated that yourself. You wind up with 100 people with slightly warmer hands instead of one person with a hot hand. Â*Does that mean less heat is transferred? Â*Of course not because the mass of those 100 hands more than makes up for the fact that they are only slightly warm. Â*Capiche? Same thing applies to a home radiator on a hot water or steam system. Â*The more air you move past it, the lower the air temp will be, but the more heat you will extract from the radiator and the cooler the exit water temp will be. Same thing applies to a car radiator. Â*And it matter not a wit that it's waste heat being transferred to the atmosphere, so please don't start that again. In the OP, the object of the excercise was to get the air as hot as possible.- Hide quoted text - There you go again. Â*It's been stated to you many times now by Mark, CL, and I that the object of the excercise was to heat the house. Â* Which means getting the most heat out of the heat exchanger, not the hottest air. Â* You are confusing TEMPERATURE with HEAT. Â* Try looking up the definition. You are confusing both with extracting the most efficiency out of a limited supply of heat. As one more example, I could go down and turn the blower down on my furnace to 100CFM instead of 1300CFM. Â* Assuming it would not kick off due to the high limit safety switch, I would then be getting very hot air out of it. Â*Does that mean I'm getting MORE heat and it's going to heat my house faster, etc? No. Â*I'd be getting LESS heat even though the small amount of air coming out is a lot hotter. Â* Capiche? if you turned down the burner the heat exchanger would work more efficiently. Â*The combustion products would be going through the heat exchanger slower. A greater Â*PERCENTAGE of the heat would be transferred. More bang for buck. I don't know what's wrong with you but I'm getting bored. Â*There is the whole aspect of diminishing returns that both Trader and Harry are forgetting about - PERHAPS Harry more than Trader. Give me a break here. I haven't forgot about diminishing returns: A - I can refer you back many posts ago where I said that the more airflow you pass through the heat exchanger the more heat you get out and that the additional heat gained decays exponentially with the increased airflow. And yes, if you put enough air through it, all the heat is extracted and the outgoing water temp and the air temp are equal and no more heat can be extracted. I clearly stated that many times here too. B - I posted the data from the heat exchanger data sheet you provided which fits the application nicely. It shows that additional heat is still being extracted at over 1000CFM. Yes, the additional gains are diminishing. C - This started over the issue of placing dampers in the airflow stream. I said you might as well just use max airflow, because there is no downside to doing that from the heat exchange standpoint and you will have heat exchange at a maximum. I think you agree with that, no? The difference in efficiency is real, but how great? = particularly since we are working with a closed loop system, and the heat not recovered stays in the system, raising the input temp the next time 'round, which will increase the efficiency. It doesn't increase the efficiency. That water leaving the heat exchanger from the furnace is now HOTTER and will consequently pick up LESS heat going through the solar array, which is just another heat exchanger. Put 65F water into the solar array and you get max heat out of it. Put in 150F water, or whatever the max temp it is capable of achieving, and you get zero heat out of it. It's not like we are wasting any heat (or at least not huge amounts) by not recovering it on the first pass. You sure are wasting it, per the above. And passing more air through the exchanger does increase the BTUs extraced Â*- but by how much, particularly when lowering the "dwell time" does reduce the efficiency somewhat. Totally wrong, per the above. Not totally wrong, if when you decrease the air flow you also increase the surface area - so you get the same CFM flow but at a lower velocity.. All goes to the TOTAL design of the system. Can't just change one parameter and expect to totally optimize the system. At what point does the loss of efficiency from the one side over-balance the loss of theoretical heat transfer from the other. It doesn't Â*My gut feeling is the gains/losses from either side of the arguement are close enough that there will be a fairly broad band of overlap where the difference in heat transferred will be RELATIVELY insignificant in the grand scheme of things. You get to the point where "close enough IS close enough.".- Hide quoted text - - Show quoted text - Your gut is wrong. Sending that water back to the solar array with all the heat extracted from it in the furnace is how you get the maximum heat out of it, which is what the OP wants. If that isn't possible, the next best thing is to get as much heat as possible extracted from it. And you do that by using maximum airflow. I more or less agree with you - but with a solar "loop: if the heat is not all extracted the first time round it just means the fluid will be hotter coming by the next time - which may increase the efficiency so more heat is extracted next time through.. Depends a lot on how much solar input he is getting. And as far as the dampers - I NEVER advocated putting dampers in the MAIN airflow. My damper suggestion was to get away from the "restricted airflow" straw man somebody put up, putting the heat exchanger "off-line" to avoid the restricted air flow. And even then - yes, they are likely pretty close to superfluous. |
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