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11degC across Boiler, why?
Most manufacturers seem to recommend setting flow rates in CH systems to
achieve a rise of 11deg across boiler, why is this? is it the most efficient setting for heat transfer? Tom |
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Tom wrote:
Most manufacturers seem to recommend setting flow rates in CH systems to achieve a rise of 11deg across boiler, why is this? is it the most efficient setting for heat transfer? It's a compromise. For condensing boilers, you want the exhaust output temperature to be as low as possible, otherwise the efficiency will drop as it won't condense properly. On the other hand, you've got to get temperature high enough to heat radiators and central heating. So, the smaller the temperature rise, the higher the efficiency. Even for non-condensing boilers, for non-pressurised systems, the boiler can't get past some 90C or so, otherwise you get localised boiling, which does all sorts of nasty things. Both of these mean that you want the temperature drop across the boiler to be relatively small. |
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On Sat, 18 Sep 2004 16:17:55 +0100, "Tom"
wrote: Most manufacturers seem to recommend setting flow rates in CH systems to achieve a rise of 11deg across boiler, why is this? is it the most efficient setting for heat transfer? Tom This is the case for conventional, non-condensing boilers and represents the optimum for the heat exchanger. In fact the general design rule is to have 82 degree flow and 70 degree return. This also avoids the risk of the boiler entering condensing mode, which for a conventional boiler would result in corrosion. For condensing boilers the heat exchanger can work with a temperature drop of 20 or even 25 degrees and is optimal at as low a temperature as possible -i.e. efficiiency is maximised at lower temperatures. ..andy To email, substitute .nospam with .gl |
#4
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"Andy Hall" wrote in message ... On Sat, 18 Sep 2004 16:17:55 +0100, "Tom" wrote: Most manufacturers seem to recommend setting flow rates in CH systems to achieve a rise of 11deg across boiler, why is this? is it the most efficient setting for heat transfer? Tom This is the case for conventional, non-condensing boilers and represents the optimum for the heat exchanger. In fact the general design rule is to have 82 degree flow and 70 degree return. This also avoids the risk of the boiler entering condensing mode, which for a conventional boiler would result in corrosion. snipped Thanks for that, The background to my question is that I'm contemplating redesigning my CH system in a bungalow I moved into some 6 Months ago; since 4 of the 6 rooms are subjected to high solar gain at different times of the day I'm attracted towards using TRVs on the rads in the 4 rooms which make up approx 80% of the total heat load. I'm further minded to install a Grundfos Alpha pump, however, I'm undecided as to the control mechanism i.e. a flow switch as advocated by IMM in a previous thread or to rely on the boiler stat set to 82degC as you stated. I'm anxious to avoid short cycling of the boiler. I'd be gratefull for your counsel. Regards Tom .. |
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"Tom" wrote in message ... Most manufacturers seem to recommend setting flow rates in CH systems to achieve a rise of 11deg across boiler, why is this? is it the most efficient setting for heat transfer? Tom The prime aim in regular boilers is to avoid condensation in the burner box. Regular boilers should always be set as high as possible, and "never" below 65C flow temp. Some regular boilers only had a high limit stat and the flow temp pre-set. |
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"Tom" wrote in message ... Most manufacturers seem to recommend setting flow rates in CH systems to achieve a rise of 11deg across boiler, why is this? is it the most efficient setting for heat transfer? It is the most efficient for the heat exchanger design which will be a low priced one. Having the heat exchanger within a tight temp range is cheaper and quicker to produce. That is why the expensive condensing boilers have 25C across the heat exchanger as the it is made to a higher spec and with superior manufacture and materials. They can stretch the temp range across it. |
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On Sun, 19 Sep 2004 08:32:57 +0100, "Tom"
wrote: "Andy Hall" wrote in message .. . On Sat, 18 Sep 2004 16:17:55 +0100, "Tom" wrote: Most manufacturers seem to recommend setting flow rates in CH systems to achieve a rise of 11deg across boiler, why is this? is it the most efficient setting for heat transfer? Tom This is the case for conventional, non-condensing boilers and represents the optimum for the heat exchanger. In fact the general design rule is to have 82 degree flow and 70 degree return. This also avoids the risk of the boiler entering condensing mode, which for a conventional boiler would result in corrosion. snipped Thanks for that, The background to my question is that I'm contemplating redesigning my CH system in a bungalow I moved into some 6 Months ago; since 4 of the 6 rooms are subjected to high solar gain at different times of the day I'm attracted towards using TRVs on the rads in the 4 rooms which make up approx 80% of the total heat load. I'm further minded to install a Grundfos Alpha pump, however, I'm undecided as to the control mechanism i.e. a flow switch as advocated by IMM in a previous thread or to rely on the boiler stat set to 82degC as you stated. I'm anxious to avoid short cycling of the boiler. I'd be gratefull for your counsel. Regards Tom . With an Alpha pump together with TRVs the water flow aspect will be taken care of. You would need anyway to put a room thermostat in a room or space where the radiator has no TRV (or you could fit one and turn it fully on). If this is to be a living room, then it mustn't have another source of heat like a gas fire. The aim is tha tthe TRVs in the other rooms should begin to close and reduce the heat load. Remember that these are quite analogue in nature - they don't just suddenly cut off. The room thermostat is then set just above this point, the idea being that the other rooms come up to temperature slightly before the heat source is cut off. You can tweak the flow to the radiator in the room where the thermostat is, to adjust all of this as well. As the load requirement falls, the boiler will cycle or cycle more, inevitably. The trick is to make sure that this does not go on for too long. It does take some experimentation, so one good way if you are not sure of which room to use for the thermostat is to use an RF one and move it around. The flow switch idea does have its uses in that it could be used to shut down the boiler and pump when the flow reduces. However, the inexpensive ones with a magnet and reed switch are not very accurate. You can adjust their effect a bit by putting a bypass around the valve, but really they are intended for sensing little flow or no flow. For example I have one for my secondary heating circuit for the workshop. The pump and controls are in the workshop and I didn't want any electrical signalling connections to the house. The workshop circuit is heated via a heat exchanger from the main system and has a zone valve to allow water from the main system to the primary side of the exchanger. There is a flow switch in the secondary side in the house which detects when the pump is running (at all) and opens the valve. I'm not trying to sense low flow with it. So this could be useful, but I would try the thermostat idea first. ..andy To email, substitute .nospam with .gl |
#8
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"Andy Hall" wrote in message ... On Sun, 19 Sep 2004 08:32:57 +0100, "Tom" wrote: snipped The flow switch idea does have its uses in that it could be used to shut down the boiler and pump when the flow reduces. However, the inexpensive ones with a magnet and reed switch are not very accurate. You can adjust their effect a bit by putting a bypass around the valve, but really they are intended for sensing little flow or no flow. For example I have one for my secondary heating circuit for the workshop. The pump and controls are in the workshop and I didn't want any electrical signalling connections to the house. The workshop circuit is heated via a heat exchanger from the main system and has a zone valve to allow water from the main system to the primary side of the exchanger. There is a flow switch in the secondary side in the house which detects when the pump is running (at all) and opens the valve. I'm not trying to sense low flow with it. Much obliged for your detailed reply, I've been mulling over this flow switch idea and had mused on using it to shut down the boiler and not the Alpha in the hope that when a TRV next opened, the Alpha would increase it's flow against the reduced resistance, the flow switch consequently switching the boiler back on. I assume the Alpha uses little power when throttled down so to speak. I realise that this would require careful balancing of the system perhaps incorporating a permanently connected pressure gauge on the pump outlet and manual throttling valve(s) to facilitate balancing. What do you think? Interesting use of your flow switch to separate the electrics from the shed, I like it. Thanks Tom |
#9
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In an earlier contribution to this discussion,
Tom wrote: Most manufacturers seem to recommend setting flow rates in CH systems to achieve a rise of 11deg across boiler, why is this? is it the most efficient setting for heat transfer? Tom As others have stated, many systems are designed to run with a flow temperature of 82 degC and a return temperature of 71 degC. But why these particular values, I hear you cry? Well, it just so happens that these correspond to 180 and 160 degF - with a 20 degree drop - all nice round numbers! So the whole thing dates from the time when temperatures were measured in Fahrenheit, and energy in good old Britsh Thermal Units. [Wait for the reaction to that one!] The values have simply been converted to Celsius. -- Cheers, Set Square ______ Please reply to newsgroup. Reply address is invalid. |
#10
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On Sun, 19 Sep 2004 08:32:57 +0100, "Tom"
wrote: I'm attracted towards using TRVs on the rads in the 4 rooms which make up approx 80% of the total heat load. I'm further minded to install a Grundfos Alpha pump, however, I'm undecided as to the control mechanism i.e. a flow switch as advocated by IMM in a previous thread or to rely on the boiler stat set to 82degC as you stated. I'm anxious to avoid short cycling of the boiler. You should have TRV on at least all the bedroom rads which is the new rules AFAIR. Ideally all rooms should have TRVs except one (the lounge?) and that room should have the thermostat that turns the system on/off. The optimum system is where the water comes back to the boiler at just above the condensing level for non-condensing boilers or below for condensing. If condensing boiler return temperature is above then it doesn't condense and so the extra money you paid for it is wasted as it's no more efficient than a standard boiler. If the temperature is too low on a non-condensing boiler then you get condensing which corrodes the heat exchanger. I have been told that 56C is the condensing threshold. The normal flow and return is 80C out, 70C back (in round numbers, 82C, 71C if you want, in F it was 180F out, 160F back, rads 100F above room temperature). So rads will be at 75C, about 55C above room temperature. If you run which a larger drop, say 80C out, 60C back, then the rads are at 70C. That 5C difference is significant (see rad makers for curves). The rad could be 10% down on output. Hence for a condensing boiler system you need larger radiators. I wouldn't go with an alpha pump with a standard boiler. Think about it. An alpha pump slows down the flow so as the TRVs cut in the flow back to the boiler is reduced. Water spends more time in the rads so comes back colder. The risk is you get condensing. What I would go for is a standard pump + an automatic bypass (which is cheaper anyway). Then as the TRVs cut in the hot water gets fed back with the cold from the rads and the return temperature flow goes up - no risk of condensing. Of course as the return flow temperature rises the efficiency goes down but the trade off is that you can set the normal flow for a larger drop (assuming you have the rad area to cope) and know that the return temperature can only go up. The effect for short cycling is the same. For a bypass the flow is constant so temperature rise across the boiler is constant. It's the return temperature that rises. Exceed the limit before the thermostat cuts in and the boiler short cycles. For an alpha the flow drops so the rise across the boiler increases. Again exceed the limit and the boiler short cycles. It's all down to the boiler outputting X kW and the house only needing X kW. The way to lengthen the cycle time is to have enough heat capacity (water and rad metal) to absorb the X kW until the main thermostat cuts in. That's all about having a balanced system. BTW this assumes that you don't have a modulating boiler (i.e. one that can vary the output power and so doesn't short cycle). I think some as boilers are as it is easier to do on gas. Most oil boilers aren't. -- Malcolm Malcolm Reeves BSc CEng MIEE MIRSE, Full Circuit Ltd, Chippenham, UK , or ). Design Service for Analogue/Digital H/W & S/W Railway Signalling and Power electronics. More details plus freeware, Win95/98 DUN and Pspice tips, see: http://www.fullcircuit.com or http://www.fullcircuit.co.uk NEW - Desktop ToDo/Reminder program (free) |
#11
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"Malcolm Reeves" wrote in message ... You should have TRV on at least all the bedroom rads which is the new rules AFAIR. Ideally all rooms should have TRVs except one (the lounge?) and that room should have the thermostat that turns the system on/off. Fine, Ok to that, existing thermostat in hallway, a non-TRV area. Lounge has additional heat source(SWMBO requirement) + high Solar Gain ,hence TRV. The optimum system is where the water comes back to the boiler at just above the condensing level for non-condensing boilers or below for condensing. If condensing boiler return temperature is above then it doesn't condense and so the extra money you paid for it is wasted as it's no more efficient than a standard boiler. If the temperature is too low on a non-condensing boiler then you get condensing which corrodes the heat exchanger. I have been told that 56C is the condensing threshold. Agreed, I remember in the dim and distant past a HVAC consultant quoting that figure at me in work. The normal flow and return is 80C out, 70C back (in round numbers, 82C, 71C if you want, in F it was 180F out, 160F back, rads 100F above room temperature). So rads will be at 75C, about 55C above room temperature. If you run which a larger drop, say 80C out, 60C back, then the rads are at 70C. That 5C difference is significant (see rad makers for curves). The rad could be 10% down on output. Hence for a condensing boiler system you need larger radiators. Agreed, no problem with that, makes sense. I wouldn't go with an alpha pump with a standard boiler. Think about it. An alpha pump slows down the flow so as the TRVs cut in the flow back to the boiler is reduced. Water spends more time in the rads so comes back colder. The risk is you get condensing. Yessss, I hadn't thought about that, getting too old in the tooth I think!!! What I would go for is a standard pump + an automatic bypass (which is cheaper anyway). Then as the TRVs cut in the hot water gets fed back with the cold from the rads and the return temperature flow goes up - no risk of condensing. OK.--The automatic bypass, do these work in an analogue fashion, do they have differing pressure/resistance curves or are they on/off devices. Of course as the return flow temperature rises the efficiency goes down but the trade off is that you can set the normal flow for a larger drop (assuming you have the rad area to cope) and know that the return temperature can only go up. The effect for short cycling is the same. For a bypass the flow is constant Implying analogue characteristicts? so temperature rise across the boiler is constant. It's the return temperature that rises. Exceed the limit before the thermostat cuts in and the boiler short cycles. For an alpha the flow drops so the rise across the boiler increases. Again exceed the limit and the boiler short cycles. It's all down to the boiler outputting X kW and the house only needing X kW. The way to lengthen the cycle time is to have enough heat capacity (water and rad metal) to absorb the X kW until the main thermostat cuts in. That's all about having a balanced system. Agreed again. BTW this assumes that you don't have a modulating boiler (i.e. one that can vary the output power and so doesn't short cycle). I think some as boilers are as it is easier to do on gas. Most oil boilers aren't. Unfortunately I don't have a modulating or condensing boiler. Much obliged to you for your detailed critique, I will be looking at bypass systems I think. I inherited the boiler (Gloworm Hideaway 60B FF) with the bungalow I moved into 6 Months ago, I shall use the existing pump which will save me a bit. Best Regards Tom |
#12
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On Sun, 19 Sep 2004 12:55:42 +0100, Malcolm Reeves
wrote: On Sun, 19 Sep 2004 08:32:57 +0100, "Tom" wrote: I'm attracted towards using TRVs on the rads in the 4 rooms which make up approx 80% of the total heat load. I'm further minded to install a Grundfos Alpha pump, however, I'm undecided as to the control mechanism i.e. a flow switch as advocated by IMM in a previous thread or to rely on the boiler stat set to 82degC as you stated. I'm anxious to avoid short cycling of the boiler. You should have TRV on at least all the bedroom rads which is the new rules AFAIR. Ideally all rooms should have TRVs except one (the lounge?) and that room should have the thermostat that turns the system on/off. The optimum system is where the water comes back to the boiler at just above the condensing level for non-condensing boilers or below for condensing. That isn't true. Non-condensing boilers are designed to operate most efficiently at 82/70 flow return. If condensing boiler return temperature is above then it doesn't condense and so the extra money you paid for it is wasted as it's no more efficient than a standard boiler. That isn't quite true either. A condensing boiler's efficiency doesn't suddenly improve as if a Holy Grail has been found at the dew point. WHat happens is that the efficiency increases with decrease in temperature both above and below the dew point. When condensing commences at the dew point, all that happens is that the *rate* of increase of efficiency increases with falling temperature. At a flow of 82 degrees, a condensing boiler will be more efficient than a conventional one anyway because the heat exchanger is larger. If the temperature is too low on a non-condensing boiler then you get condensing which corrodes the heat exchanger. I have been told that 56C is the condensing threshold. The normal flow and return is 80C out, 70C back (in round numbers, 82C, 71C if you want, in F it was 180F out, 160F back, rads 100F above room temperature). So rads will be at 75C, about 55C above room temperature. If you run which a larger drop, say 80C out, 60C back, then the rads are at 70C. That 5C difference is significant (see rad makers for curves). The rad could be 10% down on output. Hence for a condensing boiler system you need larger radiators. That is also untrue. You can replace a conventional boiler with a condensing one. When required, in the depths of winter the condensing boiler can run up to the 82 degree level of the conventional one and still be more efficient. For most of the heating season, the condensing boiler will modulate down to a lower output and into an even more efficient working range. It is true that system efficency can be improved by using larger radiators, but it isn't essential. In terms of derating, the manufacturers tables are too high for typical UK boilers. The normal derating factors are to multiply by 0.89 for an 82/70 boiler and by 0.6 for a 70/50 design with a condensing boiler. I wouldn't go with an alpha pump with a standard boiler. Think about it. An alpha pump slows down the flow so as the TRVs cut in the flow back to the boiler is reduced. Water spends more time in the rads so comes back colder. The risk is you get condensing. What I would go for is a standard pump + an automatic bypass (which is cheaper anyway). Then as the TRVs cut in the hot water gets fed back with the cold from the rads and the return temperature flow goes up - no risk of condensing. This is precisely where an Alpha pump is intended to be used. An automatic bypass is intended to deal with the case where both CH and DHW demand has ceased altogether and the boiler has been firing at full tilt. It simply prevents the water from boiling and nothing more. The TRVs do not stop the flow completely if adjusted correctly in relation to the radiator in the non-TRV room. The object is to turn off the boiler via the room thermostat as all rooms have arrived at set point, not for the TRVs to have closed completely. Provided that the boiler thermostat is adjusted correctly, operating temperatures will also be correctly in range. Of course as the return flow temperature rises the efficiency goes down but the trade off is that you can set the normal flow for a larger drop (assuming you have the rad area to cope) and know that the return temperature can only go up. The effect for short cycling is the same. For a bypass the flow is constant so temperature rise across the boiler is constant. It's the return temperature that rises. Exceed the limit before the thermostat cuts in and the boiler short cycles. For an alpha the flow drops so the rise across the boiler increases. Again exceed the limit and the boiler short cycles. It's all down to the boiler outputting X kW and the house only needing X kW. The way to lengthen the cycle time is to have enough heat capacity (water and rad metal) to absorb the X kW until the main thermostat cuts in. That's all about having a balanced system. BTW this assumes that you don't have a modulating boiler (i.e. one that can vary the output power and so doesn't short cycle). I think some as boilers are as it is easier to do on gas. Most oil boilers aren't. ..andy To email, substitute .nospam with .gl |
#13
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On Sun, 19 Sep 2004 10:38:33 +0100, "Tom"
wrote: "Andy Hall" wrote in message .. . On Sun, 19 Sep 2004 08:32:57 +0100, "Tom" wrote: snipped The flow switch idea does have its uses in that it could be used to shut down the boiler and pump when the flow reduces. However, the inexpensive ones with a magnet and reed switch are not very accurate. You can adjust their effect a bit by putting a bypass around the valve, but really they are intended for sensing little flow or no flow. For example I have one for my secondary heating circuit for the workshop. The pump and controls are in the workshop and I didn't want any electrical signalling connections to the house. The workshop circuit is heated via a heat exchanger from the main system and has a zone valve to allow water from the main system to the primary side of the exchanger. There is a flow switch in the secondary side in the house which detects when the pump is running (at all) and opens the valve. I'm not trying to sense low flow with it. Much obliged for your detailed reply, I've been mulling over this flow switch idea and had mused on using it to shut down the boiler and not the Alpha in the hope that when a TRV next opened, the Alpha would increase it's flow against the reduced resistance, the flow switch consequently switching the boiler back on. I assume the Alpha uses little power when throttled down so to speak. I realise that this would require careful balancing of the system perhaps incorporating a permanently connected pressure gauge on the pump outlet and manual throttling valve(s) to facilitate balancing. What do you think? I doubt if you need to make it that complicated. As long as the boiler output is not hugely larger than the house requirement, simply using a room thermostat, TRVs and an Alpha should give a good result. If you get the radiator without the TRV adjusted to the correct operating point such that the TRVs are not completely closing as the room thermostat operates, you will get the desired effect. Another approach would be to get one of the optimising room thermostats which controls the boiler and prevents temperature overshoot - e.g. CM67 or TP75. This will give a more controlled result than a simple thermostat. ..andy To email, substitute .nospam with .gl |
#14
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On Sun, 19 Sep 2004 13:59:34 +0100, "Tom"
wrote: "Malcolm Reeves" wrote in message .. . You should have TRV on at least all the bedroom rads which is the new rules AFAIR. Ideally all rooms should have TRVs except one (the lounge?) and that room should have the thermostat that turns the system on/off. Fine, Ok to that, existing thermostat in hallway, a non-TRV area. Lounge has additional heat source(SWMBO requirement) + high Solar Gain ,hence TRV. You might find that you get smoother results if you put it on the upstairs landing. It will be less suscepitble to the effects of opening the front door. The optimum system is where the water comes back to the boiler at just above the condensing level for non-condensing boilers or below for condensing. If condensing boiler return temperature is above then it doesn't condense and so the extra money you paid for it is wasted as it's no more efficient than a standard boiler. If the temperature is too low on a non-condensing boiler then you get condensing which corrodes the heat exchanger. I have been told that 56C is the condensing threshold. Agreed, I remember in the dim and distant past a HVAC consultant quoting that figure at me in work. It's around 52-54 degrees. The normal flow and return is 80C out, 70C back (in round numbers, 82C, 71C if you want, in F it was 180F out, 160F back, rads 100F above room temperature). So rads will be at 75C, about 55C above room temperature. If you run which a larger drop, say 80C out, 60C back, then the rads are at 70C. That 5C difference is significant (see rad makers for curves). The rad could be 10% down on output. Hence for a condensing boiler system you need larger radiators. Agreed, no problem with that, makes sense. See separate note on derating of radiator specs. I wouldn't go with an alpha pump with a standard boiler. Think about it. An alpha pump slows down the flow so as the TRVs cut in the flow back to the boiler is reduced. Water spends more time in the rads so comes back colder. The risk is you get condensing. Yessss, I hadn't thought about that, getting too old in the tooth I think!!! What I would go for is a standard pump + an automatic bypass (which is cheaper anyway). Then as the TRVs cut in the hot water gets fed back with the cold from the rads and the return temperature flow goes up - no risk of condensing. OK.--The automatic bypass, do these work in an analogue fashion, do they have differing pressure/resistance curves or are they on/off devices. They are pretty much on/off and are intended to deal with the case where DHW and CH both stop demanding and the boiler is in full burn. The setting should be arranged so that the valve is closed in all cases exept where this happens. The idea is *not* to allow any feedback of flow water to the boiler except under these conditions when the only purpose is to keep a flow going and to prevent boiling. Of course as the return flow temperature rises the efficiency goes down but the trade off is that you can set the normal flow for a larger drop (assuming you have the rad area to cope) and know that the return temperature can only go up. The effect for short cycling is the same. For a bypass the flow is constant Implying analogue characteristicts? so temperature rise across the boiler is constant. It's the return temperature that rises. Exceed the limit before the thermostat cuts in and the boiler short cycles. For an alpha the flow drops so the rise across the boiler increases. Again exceed the limit and the boiler short cycles. It's all down to the boiler outputting X kW and the house only needing X kW. The way to lengthen the cycle time is to have enough heat capacity (water and rad metal) to absorb the X kW until the main thermostat cuts in. That's all about having a balanced system. Agreed again. BTW this assumes that you don't have a modulating boiler (i.e. one that can vary the output power and so doesn't short cycle). I think some as boilers are as it is easier to do on gas. Most oil boilers aren't. Unfortunately I don't have a modulating or condensing boiler. Much obliged to you for your detailed critique, I will be looking at bypass systems I think. I inherited the boiler (Gloworm Hideaway 60B FF) with the bungalow I moved into 6 Months ago, I shall use the existing pump which will save me a bit. You can do that provided that the pump is set to compromise with the requirements of full heat demand and at the point when the TRVs are closing. You also need to arrange that the room thermostat is turning off the boiler when there is still some flow left through the TRVs. Best Regards Tom ..andy To email, substitute .nospam with .gl |
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"Andy Hall" wrote in message ... On Sun, 19 Sep 2004 13:59:34 +0100, "Tom" wrote: "Malcolm Reeves" wrote in message .. . You should have TRV on at least all the bedroom rads which is the new rules AFAIR. Ideally all rooms should have TRVs except one (the lounge?) and that room should have the thermostat that turns the system on/off. Fine, Ok to that, existing thermostat in hallway, a non-TRV area. Lounge has additional heat source(SWMBO requirement) + high Solar Gain ,hence TRV. You might find that you get smoother results if you put it on the upstairs landing. It will be less suscepitble to the effects of opening the front door. It's a Bungalow, and because of the layout of the dwelling we hardly ever use the front door in practice. The optimum system is where the water comes back to the boiler at just above the condensing level for non-condensing boilers or below for condensing. If condensing boiler return temperature is above then it doesn't condense and so the extra money you paid for it is wasted as it's no more efficient than a standard boiler. If the temperature is too low on a non-condensing boiler then you get condensing which corrodes the heat exchanger. I have been told that 56C is the condensing threshold. Agreed, I remember in the dim and distant past a HVAC consultant quoting that figure at me in work. It's around 52-54 degrees. The normal flow and return is 80C out, 70C back (in round numbers, 82C, 71C if you want, in F it was 180F out, 160F back, rads 100F above room temperature). So rads will be at 75C, about 55C above room temperature. If you run which a larger drop, say 80C out, 60C back, then the rads are at 70C. That 5C difference is significant (see rad makers for curves). The rad could be 10% down on output. Hence for a condensing boiler system you need larger radiators. Agreed, no problem with that, makes sense. See separate note on derating of radiator specs. I wouldn't go with an alpha pump with a standard boiler. Think about it. An alpha pump slows down the flow so as the TRVs cut in the flow back to the boiler is reduced. Water spends more time in the rads so comes back colder. The risk is you get condensing. Yessss, I hadn't thought about that, getting too old in the tooth I think!!! What I would go for is a standard pump + an automatic bypass (which is cheaper anyway). Then as the TRVs cut in the hot water gets fed back with the cold from the rads and the return temperature flow goes up - no risk of condensing. OK.--The automatic bypass, do these work in an analogue fashion, do they have differing pressure/resistance curves or are they on/off devices. They are pretty much on/off and are intended to deal with the case where DHW and CH both stop demanding and the boiler is in full burn. Since my query I found the specs on the honeywell DU145 and whereas they claim that it is designed to operate as a boiler bypass *or* where radiator thermostats are fitted, the curves they publish are very flat indicating that they open over a very small pressure change, in the absence of detailed info on the actual pressure variations which occur in a typical TRV domestic CH system it's difficult for me to make a reasoned judgment. Are you aware of any other Automatic Bypass Valves which have steeper curves. The setting should be arranged so that the valve is closed in all cases exept where this happens. The idea is *not* to allow any feedback of flow water to the boiler except under these conditions when the only purpose is to keep a flow going and to prevent boiling. Of course as the return flow temperature rises the efficiency goes down but the trade off is that you can set the normal flow for a larger drop (assuming you have the rad area to cope) and know that the return temperature can only go up. The effect for short cycling is the same. For a bypass the flow is constant Implying analogue characteristicts? so temperature rise across the boiler is constant. It's the return temperature that rises. Exceed the limit before the thermostat cuts in and the boiler short cycles. For an alpha the flow drops so the rise across the boiler increases. Again exceed the limit and the boiler short cycles. It's all down to the boiler outputting X kW and the house only needing X kW. The way to lengthen the cycle time is to have enough heat capacity (water and rad metal) to absorb the X kW until the main thermostat cuts in. That's all about having a balanced system. Agreed again. BTW this assumes that you don't have a modulating boiler (i.e. one that can vary the output power and so doesn't short cycle). I think some as boilers are as it is easier to do on gas. Most oil boilers aren't. Unfortunately I don't have a modulating or condensing boiler. Much obliged to you for your detailed critique, I will be looking at bypass systems I think. I inherited the boiler (Gloworm Hideaway 60B FF) with the bungalow I moved into 6 Months ago, I shall use the existing pump which will save me a bit. You can do that provided that the pump is set to compromise with the requirements of full heat demand and at the point when the TRVs are closing. You also need to arrange that the room thermostat is turning off the boiler when there is still some flow left through the TRVs. Thanks Andy, would you agree that the Alpha might induce condensing conditions in my standard boiler, assuming that thermostats and TRV are susceptible to frequent adjustments in my household :-( Cheers Tom |
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On Sun, 19 Sep 2004 14:53:59 +0100, Andy Hall
wrote: The optimum system is where the water comes back to the boiler at just above the condensing level for non-condensing boilers or below for condensing. That isn't true. Non-condensing boilers are designed to operate most efficiently at 82/70 flow return. Not according to HRM technical department. It also stands to reason that all other things being equal the lower the boiler average water temperature the more energy you get from the fuel, i.e. the cooler the flue gas. SEDBUK cap standard boiler efficiencies specifically to stop boiler makers designing standard boilers on the edge of condensing and thus improving their efficiency at the risk of shorter life (due to condensing causing corrosion). Hence the sedbuk figures need to be viewed in the light of being capped when comparing condensing and non-condensing boilers :-/. If condensing boiler return temperature is above then it doesn't condense and so the extra money you paid for it is wasted as it's no more efficient than a standard boiler. That isn't quite true either. A condensing boiler's efficiency doesn't suddenly improve as if a Holy Grail has been found at the dew point. WHat happens is that the efficiency increases with decrease in temperature both above and below the dew point. When condensing commences at the dew point, all that happens is that the *rate* of increase of efficiency increases with falling temperature. So what you are saying is that a larger difference than 82/70 does improve efficiency. Like I said. The specific latent heat extracted at the dew point is a lump of energy, either you have it or you don't. If you are running above the dew point you don't have it and the boiler is working in standard mode not condensing. At a flow of 82 degrees, a condensing boiler will be more efficient than a conventional one anyway because the heat exchanger is larger. True a larger heat exchanger will get more heat out of the fuel and thus be more efficient. However, condensing boilers are $$$ more money and if the only benefit is the larger heat exchanger (i.e. not condensing) would the savings be worth it? I'm just changing my heating to oil fire standard boiler not a condensing since on consideration of the extra boiler cost, problems (smells, plume etc.) vs the potential savings (perhaps GBP20 pa) I have chosen a standard oil boiler. I'm fitting this now in case they change the rules in April 2005. Hence for a condensing boiler system you need larger radiators. That is also untrue. You can replace a conventional boiler with a condensing one. When required, in the depths of winter the condensing boiler can run up to the 82 degree level of the conventional one and still be more efficient. For most of the heating season, the condensing boiler will modulate down to a lower output and into an even more efficient working range. How does a non modulating boiler modulate? The water comes out of the boiler at 80C goes through the radiators which cools it by 10C (if they are exactly right for the room loss) and returns to the boiler at 70C. If you want it to return cooler the radiators have to be bigger since the heat they give up to the room is dependent on their size and the (fixed) room temperature. You could run with a lower flow temperature but then you'd have less drop across the boiler which as we have already agreed is less efficient. In the case of a condensing boiler the condensing gain would probably exceed the standard heat exchange section drop in efficiency but it still won't be as good as if it was running at the design figures. I wouldn't go with an alpha pump with a standard boiler. Think about it. An alpha pump slows down the flow so as the TRVs cut in the flow back to the boiler is reduced. Water spends more time in the rads so comes back colder. The risk is you get condensing. What I would go for is a standard pump + an automatic bypass (which is cheaper anyway). Then as the TRVs cut in the hot water gets fed back with the cold from the rads and the return temperature flow goes up - no risk of condensing. This is precisely where an Alpha pump is intended to be used. An automatic bypass is intended to deal with the case where both CH and DHW demand has ceased altogether and the boiler has been firing at full tilt. It simply prevents the water from boiling and nothing more. No. An automatic bypass says it is for TRVs. In any case what will a bypass do in the situation you have above. If you are trying to get heat out of boiler after the fuel has cut off you need a pump over run. That is something that runs the pump for a few minutes after the thermostats have cut off and the boiler stopped firing. Usually a thermostat on the boiler I believe rather than a timer but the effect is the same. Some boilers don't need it as the cut off quick enough that the water can absorb the extra heat. A three way valve must be open to at least one way and you must have a path (non TRV rads or tank). What stops the flow is the pump not running. If you have flow but not enough then that's where an automatic bypass comes in. Pump head (pressure) rises and the valve opens. The TRVs do not stop the flow completely if adjusted correctly in relation to the radiator in the non-TRV room. The object is to turn off the boiler via the room thermostat as all rooms have arrived at set point, not for the TRVs to have closed completely. Provided that the boiler thermostat is adjusted correctly, operating temperatures will also be correctly in range. If the TRVs are even partially closed then the flow is reduced. An alpha will keep the head constant-ish resulting in less flow and thus lower return temperature. A standard + bypass will result in constant head (the setting the bypass is set to), and a constant-ish flow -- Malcolm Malcolm Reeves BSc CEng MIEE MIRSE, Full Circuit Ltd, Chippenham, UK , or ). Design Service for Analogue/Digital H/W & S/W Railway Signalling and Power electronics. More details plus freeware, Win95/98 DUN and Pspice tips, see: http://www.fullcircuit.com or http://www.fullcircuit.co.uk NEW - Desktop ToDo/Reminder program (free) |
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On Sun, 19 Sep 2004 16:01:36 +0100, "Tom"
wrote: It's a Bungalow, and because of the layout of the dwelling we hardly ever use the front door in practice. OK, so I would suggest positioning the thermostat away from areas where there can be sudden increases or decreases of heat such as the kitchen or if you have supplementary heating, the living room. Since my query I found the specs on the honeywell DU145 and whereas they claim that it is designed to operate as a boiler bypass *or* where radiator thermostats are fitted, the curves they publish are very flat indicating that they open over a very small pressure change, in the absence of detailed info on the actual pressure variations which occur in a typical TRV domestic CH system it's difficult for me to make a reasoned judgment. Are you aware of any other Automatic Bypass Valves which have steeper curves. I am pretty sure that all are fairly similar. Danfoss is another make. Thanks Andy, would you agree that the Alpha might induce condensing conditions in my standard boiler, assuming that thermostats and TRV are susceptible to frequent adjustments in my household :-( I think that it's unlikely provided that you set the boiler thermostat high enough. I would take it one step at a time. - Give the system a good clean out as you fit the TRVs. This is a good opportunity to take the radiators outside and give them a good hose through. Don't forget to note the lockshield valve positions. Afterwards a flush with a system cleanser is a good plan - run hot for the recommended period of time. Flush, Refill and add inhibitor. - Balance the non TRV radiator so that the TRVs are starting to close as the room thermostat cuts off the boiler. You will know the rough point because if the boiler is cut off too early, the other rooms will be too cool. If much later, the radiators with TRVs will start to cool and the boiler will run for shorter periods. I would leave the pump unless you find that the system becomes noisy as the TRVs are starting to close. You will know if the existing pump is a problem if you find that it gets noisy and you have to turn it down but that on that setting when all TRVs are open, the boiler runs for short periods. The other thinkg is that you won't really be able to do this until the weather turns cooler. Cheers Tom ..andy To email, substitute .nospam with .gl |
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On Sun, 19 Sep 2004 13:59:34 +0100, "Tom"
wrote: What I would go for is a standard pump + an automatic bypass (which is cheaper anyway). Then as the TRVs cut in the hot water gets fed back with the cold from the rads and the return temperature flow goes up - no risk of condensing. OK.--The automatic bypass, do these work in an analogue fashion, do they have differing pressure/resistance curves or are they on/off devices. Does it matter? The combined system has a pump driving the head and the flow. Even if the bypass valve has a very sharp response the pump doesn't. The sharp or soft response of a bypass combines with the pump curve. Or, if you like, a sharp response bypass will keep the maximum head at say 3m (if is it set to 3m), whereas a soft response one will keep the maximum head at say 2.5m to 3.5m depending on how much it has to open. In either case the bypass will open enough to let the flow stay constant-ish. BTW a bypass is just a spring loaded valve. A knob on the top (or similar) allows you to set the maximum head. When that is reached the valve opens, just enough so that the head stays at that level. The increase in flow then allows the pump head to decrease and the system settles to a stable value. -- Malcolm Malcolm Reeves BSc CEng MIEE MIRSE, Full Circuit Ltd, Chippenham, UK , or ). Design Service for Analogue/Digital H/W & S/W Railway Signalling and Power electronics. More details plus freeware, Win95/98 DUN and Pspice tips, see: http://www.fullcircuit.com or http://www.fullcircuit.co.uk NEW - Desktop ToDo/Reminder program (free) |
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On Sun, 19 Sep 2004 19:02:39 +0100, Malcolm Reeves
wrote: On Sun, 19 Sep 2004 14:53:59 +0100, Andy Hall wrote: The optimum system is where the water comes back to the boiler at just above the condensing level for non-condensing boilers or below for condensing. That isn't true. Non-condensing boilers are designed to operate most efficiently at 82/70 flow return. Not according to HRM technical department. It also stands to reason that all other things being equal the lower the boiler average water temperature the more energy you get from the fuel, i.e. the cooler the flue gas. The operating range possible with a conventional boiler is so narrow anyway that this makes very little difference. The heat exchangers used are relatively small. SEDBUK cap standard boiler efficiencies specifically to stop boiler makers designing standard boilers on the edge of condensing and thus improving their efficiency at the risk of shorter life (due to condensing causing corrosion). Hence the sedbuk figures need to be viewed in the light of being capped when comparing condensing and non-condensing boilers :-/. The SEDBUK figures really confuse the issue because of the factors used. For the purposes of looking at boiler behaviour it is much more useful to use the measuring methods used in the rest of Europe. These specify certain temperatures and firing rates. If condensing boiler return temperature is above then it doesn't condense and so the extra money you paid for it is wasted as it's no more efficient than a standard boiler. That isn't quite true either. A condensing boiler's efficiency doesn't suddenly improve as if a Holy Grail has been found at the dew point. WHat happens is that the efficiency increases with decrease in temperature both above and below the dew point. When condensing commences at the dew point, all that happens is that the *rate* of increase of efficiency increases with falling temperature. So what you are saying is that a larger difference than 82/70 does improve efficiency. Like I said. I don't think you did, but the point is that a larger temperature difference together with a larger heat exchanger certainly does help. The specific latent heat extracted at the dew point is a lump of energy, either you have it or you don't. If you are running above the dew point you don't have it and the boiler is working in standard mode not condensing. You are missing the point. While it is true that latent heat is extracted below the dew point and results in a greater efficiency, this is not a step function as people seem to believe -it is an increase in the rate of change of efficiency with falling temperature.. You also have to account for the burn rate of the boiler and the heat delivery to the load. At a flow of 82 degrees, a condensing boiler will be more efficient than a conventional one anyway because the heat exchanger is larger. True a larger heat exchanger will get more heat out of the fuel and thus be more efficient. However, condensing boilers are $$$ more money and if the only benefit is the larger heat exchanger (i.e. not condensing) would the savings be worth it? The answer is that both aspects are useful, as is the control system running the boiler. Generally these are more sophisticated than with conventional boilers and are able to match the heat generated with the load and to minimise the temperature of operation. All of these factors improve efficiency. The difference in cost is becoming less and less, and from next year the whole issue will be academic since changes to the Building Regulations will mandate condensing boilers anyway. In terms of cost saving, I have found it to be in the predicted band of 25-30% I'm just changing my heating to oil fire standard boiler not a condensing since on consideration of the extra boiler cost, problems (smells, plume etc.) vs the potential savings (perhaps GBP20 pa) I have chosen a standard oil boiler. I'm fitting this now in case they change the rules in April 2005. You must be spending very little on energy if £20 represents 25% of your energy cost. There are no real problems with modern condensing models in terms of pluming. Much improvement has been made over early designs. Where you get the idea that there are smells, I have no idea. Hence for a condensing boiler system you need larger radiators. That is also untrue. You can replace a conventional boiler with a condensing one. When required, in the depths of winter the condensing boiler can run up to the 82 degree level of the conventional one and still be more efficient. For most of the heating season, the condensing boiler will modulate down to a lower output and into an even more efficient working range. How does a non modulating boiler modulate? The water comes out of the boiler at 80C goes through the radiators which cools it by 10C (if they are exactly right for the room loss) and returns to the boiler at 70C. If you want it to return cooler the radiators have to be bigger since the heat they give up to the room is dependent on their size and the (fixed) room temperature. You could run with a lower flow temperature but then you'd have less drop across the boiler which as we have already agreed is less efficient. You are missing the point. The temperature difference across a heat exchanger is limited by the heat exchanger itself. So on a conventional boiler, arranging a greater heating load by having more emission will simply result in the flow being cooler. It doesn't buy you anything. In the case of a condensing boiler the condensing gain would probably exceed the standard heat exchange section drop in efficiency but it still won't be as good as if it was running at the design figures. For a modulating condensing boiler, there is no specific "design temperature". They will work at 82/70 if put into a standard system and the level of heat demand is high. It is typical to run at 70/50 with new radiator systems but you don't have to do so. You can run UFH systems at 50/30 if the boiler will do it, and some will. The lower the temperature, the greater the efficiency and below the dew point the rate of change increases. I wouldn't go with an alpha pump with a standard boiler. Think about it. An alpha pump slows down the flow so as the TRVs cut in the flow back to the boiler is reduced. Water spends more time in the rads so comes back colder. The risk is you get condensing. What I would go for is a standard pump + an automatic bypass (which is cheaper anyway). Then as the TRVs cut in the hot water gets fed back with the cold from the rads and the return temperature flow goes up - no risk of condensing. This is precisely where an Alpha pump is intended to be used. An automatic bypass is intended to deal with the case where both CH and DHW demand has ceased altogether and the boiler has been firing at full tilt. It simply prevents the water from boiling and nothing more. No. An automatic bypass says it is for TRVs. In any case what will a bypass do in the situation you have above. You are assuming that TRVs are digital devices that suddenly cut off the flow when the temperature is reached. They are not, and are simple wax expansion devices that gradually reduce the flow. The value in a bypass is if you get to a situation where all radiators have been turned off. If you are trying to get heat out of boiler after the fuel has cut off you need a pump over run. That is something that runs the pump for a few minutes after the thermostats have cut off and the boiler stopped firing. Yes, I'm fully aware of that. Usually a thermostat on the boiler I believe rather than a timer but the effect is the same. Some boilers don't need it as the cut off quick enough that the water can absorb the extra heat. A three way valve must be open to at least one way and you must have a path (non TRV rads or tank). What stops the flow is the pump not running. If you have flow but not enough then that's where an automatic bypass comes in. Pump head (pressure) rises and the valve opens. Obviously. The TRVs do not stop the flow completely if adjusted correctly in relation to the radiator in the non-TRV room. The object is to turn off the boiler via the room thermostat as all rooms have arrived at set point, not for the TRVs to have closed completely. Provided that the boiler thermostat is adjusted correctly, operating temperatures will also be correctly in range. If the TRVs are even partially closed then the flow is reduced. An alpha will keep the head constant-ish resulting in less flow and thus lower return temperature. No because when this happens the heat emission will have dropped. The purpose is to reduce the power to the pump as the flow resistance increases. A standard + bypass will result in constant head (the setting the bypass is set to), and a constant-ish flow No it won't because the bypass opens in effect digitally at a certain head. After that, it has a pressure/flow characteristic. ..andy To email, substitute .nospam with .gl |
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"Malcolm Reeves" wrote in message ... On Sun, 19 Sep 2004 08:32:57 +0100, "Tom" wrote: I'm attracted towards using TRVs on the rads in the 4 rooms which make up approx 80% of the total heat load. I'm further minded to install a Grundfos Alpha pump, however, I'm undecided as to the control mechanism i.e. a flow switch as advocated by IMM in a previous thread or to rely on the boiler stat set to 82degC as you stated. I'm anxious to avoid short cycling of the boiler. You should have TRV on at least all the bedroom rads which is the new rules AFAIR. Nothing says it is madatory in the regs. Ideally all rooms should have TRVs except one (the lounge?) and that room should have the thermostat that turns the system on/off. The stat should be in the coolest room which is usualy the hall. The optimum system is where the water comes back to the boiler at just above the condensing level for non-condensing boilers or below for condensing. If condensing boiler return temperature is above then it doesn't condense and so the extra money you paid for it is wasted as it's no more efficient than a standard boiler. Condensing boilers are far more efficient as they have a larger heat exchanger, condensing or not. If the temperature is too low on a non-condensing boiler then you get condensing which corrodes the heat exchanger. I have been told that 56C is the condensing threshold. Not so. The normal flow and return is 80C out, 70C back (in round numbers, 82C, 71C if you want, in F it was 180F out, 160F back, rads 100F above room temperature). So rads will be at 75C, about 55C above room temperature. If you run which a larger drop, say 80C out, 60C back, then the rads are at 70C. That 5C difference is significant (see rad makers for curves). The rad could be 10% down on output. Hence for a condensing boiler system you need larger radiators. Modern condensing boilers have load compensation control which is a great be benefit on part load. Most systems are on part load for most of the time. I wouldn't go with an alpha pump with a standard boiler. I would use a condesning boiler. Think about it. An alpha pump slows down the flow so as the TRVs cut in the flow back to the boiler is reduced. Water spends more time in the rads so comes back colder. The risk is you get condensing. You only get condensing when the return temp is far to low. What I would go for is a standard pump + an automatic bypass (which is cheaper anyway). And difficult to get right. Do not use one of these with a condensing boiler. Then as the TRVs cut in the hot water gets fed back with the cold from the rads and the return temperature flow goes up - no risk of condensing. Of course as the return flow temperature rises the efficiency goes down but the trade off is that you can set the normal flow for a larger drop (assuming you have the rad area to cope) and know that the return temperature can only go up. The effect for short cycling is the same. For a bypass the flow is constant so temperature rise across the boiler is constant. It's the return temperature that rises. Exceed the limit before the thermostat cuts in and the boiler short cycles. For an alpha the flow drops so the rise across the boiler increases. Again exceed the limit and the boiler short cycles. It's all down to the boiler outputting X kW and the house only needing X kW. The way to lengthen the cycle time is to have enough heat capacity (water and rad metal) to absorb the X kW until the main thermostat cuts in. That's all about having a balanced system. BTW this assumes that you don't have a modulating boiler (i.e. one that can vary the output power and so doesn't short cycle). I think some as boilers are as it is easier to do on gas. Most oil boilers aren't. You need to know more about regular v condensing boilers and much, much more. |
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"Andy Hall" wrote in message ... On Sun, 19 Sep 2004 13:59:34 +0100, "Tom" wrote: "Malcolm Reeves" wrote in message .. . You should have TRV on at least all the bedroom rads which is the new rules AFAIR. Ideally all rooms should have TRVs except one (the lounge?) and that room should have the thermostat that turns the system on/off. Fine, Ok to that, existing thermostat in hallway, a non-TRV area. Lounge has additional heat source(SWMBO requirement) + high Solar Gain ,hence TRV. You might find that you get smoother results if you put it on the upstairs landing. It will be less suscepitble to the effects of opening the front door. The optimum system is where the water comes back to the boiler at just above the condensing level for non-condensing boilers or below for condensing. If condensing boiler return temperature is above then it doesn't condense and so the extra money you paid for it is wasted as it's no more efficient than a standard boiler. If the temperature is too low on a non-condensing boiler then you get condensing which corrodes the heat exchanger. I have been told that 56C is the condensing threshold. Agreed, I remember in the dim and distant past a HVAC consultant quoting that figure at me in work. It's around 52-54 degrees. The normal flow and return is 80C out, 70C back (in round numbers, 82C, 71C if you want, in F it was 180F out, 160F back, rads 100F above room temperature). So rads will be at 75C, about 55C above room temperature. If you run which a larger drop, say 80C out, 60C back, then the rads are at 70C. That 5C difference is significant (see rad makers for curves). The rad could be 10% down on output. Hence for a condensing boiler system you need larger radiators. Agreed, no problem with that, makes sense. See separate note on derating of radiator specs. I wouldn't go with an alpha pump with a standard boiler. Think about it. An alpha pump slows down the flow so as the TRVs cut in the flow back to the boiler is reduced. Water spends more time in the rads so comes back colder. The risk is you get condensing. Yessss, I hadn't thought about that, getting too old in the tooth I think!!! What I would go for is a standard pump + an automatic bypass (which is cheaper anyway). Then as the TRVs cut in the hot water gets fed back with the cold from the rads and the return temperature flow goes up - no risk of condensing. OK.--The automatic bypass, do these work in an analogue fashion, do they have differing pressure/resistance curves or are they on/off devices. They are pretty much on/off They are not. The valve opens according to pressure.the higher the more it opens. and are intended to deal with the case where DHW and CH both stop demanding and the boiler is in full burn. The setting should be arranged so that the valve is closed in all cases exept where this happens. The idea is *not* to allow any feedback of flow water to the boiler except under these conditions when the only purpose is to keep a flow going and to prevent boiling. Of course as the return flow temperature rises the efficiency goes down but the trade off is that you can set the normal flow for a larger drop (assuming you have the rad area to cope) and know that the return temperature can only go up. The effect for short cycling is the same. For a bypass the flow is constant Implying analogue characteristicts? so temperature rise across the boiler is constant. It's the return temperature that rises. Exceed the limit before the thermostat cuts in and the boiler short cycles. For an alpha the flow drops so the rise across the boiler increases. Again exceed the limit and the boiler short cycles. It's all down to the boiler outputting X kW and the house only needing X kW. The way to lengthen the cycle time is to have enough heat capacity (water and rad metal) to absorb the X kW until the main thermostat cuts in. That's all about having a balanced system. Agreed again. BTW this assumes that you don't have a modulating boiler (i.e. one that can vary the output power and so doesn't short cycle). I think some as boilers are as it is easier to do on gas. Most oil boilers aren't. Unfortunately I don't have a modulating or condensing boiler. Much obliged to you for your detailed critique, I will be looking at bypass systems I think. I inherited the boiler (Gloworm Hideaway 60B FF) with the bungalow I moved into 6 Months ago, I shall use the existing pump which will save me a bit. To save money that is fine. For anew system go Alpha and flow stitch and condensing boiler. You can do that provided that the pump is set to compromise with the requirements of full heat demand and at the point when the TRVs are closing. You also need to arrange that the room thermostat is turning off the boiler when there is still some flow left through the TRVs. Best Regards Tom .andy To email, substitute .nospam with .gl |
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"Tom" wrote in message ... Thanks Andy, would you agree that the Alpha might induce condensing conditions in my standard boiler, assuming that thermostats and TRV are susceptible to frequent adjustments in my household :-( As long at the boiler is set to 80C this is highly unlikely when the system is warmed up. You may require a minimum flow through the boiler. Then I would forget the Alpha a go for am open rad and room stat. |
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On Sun, 19 Sep 2004 23:45:34 +0100, "IMM" wrote:
They are not. The valve opens according to pressure.the higher the more it opens. In fact if you look at the data sheet you will see that for a given setting, they are roughly a constant pressure drop device over a range of flows. ..andy To email, substitute .nospam with .gl |
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On Sun, 19 Sep 2004 23:50:08 +0100, "IMM" wrote:
"Tom" wrote in message ... Thanks Andy, would you agree that the Alpha might induce condensing conditions in my standard boiler, assuming that thermostats and TRV are susceptible to frequent adjustments in my household :-( As long at the boiler is set to 80C this is highly unlikely when the system is warmed up. You may require a minimum flow through the boiler. Then I would forget the Alpha a go for am open rad and room stat. You can set the nominal power level on the Alpha above or below nominal setting. Even so, I agree that if the existing pump is OK, it makes more sense to try that first and only switch to an Alpha if there is a problem with noise in the radiators closed down case (i.e. reduce pump setting), but that that is not enough wit everything open. ..andy To email, substitute .nospam with .gl |
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"Malcolm Reeves" wrote in message ... On Sun, 19 Sep 2004 14:53:59 +0100, Andy Hall wrote: The optimum system is where the water comes back to the boiler at just above the condensing level for non-condensing boilers or below for condensing. That isn't true. Non-condensing boilers are designed to operate most efficiently at 82/70 flow return. Not according to HRM technical department. It also stands to reason that all other things being equal the lower the boiler average water temperature the more energy you get from the fuel, i.e. the cooler the flue gas. It is true that "generally" the lower the operating temperature the higher the efficiency. But regular boilers are designed to operate at maximum efficiency at higher temperatures. Any gains at running at lower temp is very marginal. You could fit a blending valve on the flow return to ensure that only water higher than 55C is returned back to the boiler. Then you would need to set the boiler temp 11C higher to ensure the delta T. Exceeding the Delta T for long periods can harm the heat exchanger. SEDBUK cap standard boiler efficiencies specifically to stop boiler makers designing standard boilers on the edge of condensing and thus improving their efficiency at the risk of shorter life (due to condensing causing corrosion). Hence the sedbuk figures need to be viewed in the light of being capped when comparing condensing and non-condensing boilers :-/. Sedbuk is being phased out. If condensing boiler return temperature is above then it doesn't condense and so the extra money you paid for it is wasted as it's no more efficient than a standard boiler. That isn't quite true either. A condensing boiler's efficiency doesn't suddenly improve as if a Holy Grail has been found at the dew point. WHat happens is that the efficiency increases with decrease in temperature both above and below the dew point. When condensing commences at the dew point, all that happens is that the *rate* of increase of efficiency increases with falling temperature. So what you are saying is that a larger difference than 82/70 does improve efficiency. Like I said. The specific latent heat extracted at the dew point is a lump of energy, either you have it or you don't. If you are running above the dew point you don't have it and the boiler is working in standard mode not condensing. At a flow of 82 degrees, a condensing boiler will be more efficient than a conventional one anyway because the heat exchanger is larger. True a larger heat exchanger will get more heat out of the fuel and thus be more efficient. However, condensing boilers are $$$ more money These days not that much and in April they will be standard, except for the odd boiler here and there where pluming is a problem. Condensing boilers can be made not to plume. and if the only benefit is the larger heat exchanger (i.e. not condensing) would the savings be worth it? Using a large quick recovery coil in a cylinder enhances condensing and in most newish homes DHW now used more gas than CH. When the new insulation regs bite in a few years CH will use far more than CH. I'm just changing my heating to oil fire standard boiler not a condensing since on consideration of the extra boiler cost, problems (smells, plume etc.) vs the potential savings (perhaps GBP20 pa) I have chosen a standard oil boiler. I'm fitting this now in case they change the rules in April 2005. Standard oil boilers make more sense economically. They are much cheaper and less latent heat is produced by oil. As most people use n gas condensing makes much more sense as more heat is extracted and they are much cheaper. When all boilers are condensers, prices will drop. You may have jumped the gun. Hence for a condensing boiler system you need larger radiators. That is also untrue. You can replace a conventional boiler with a condensing one. When required, in the depths of winter the condensing boiler can run up to the 82 degree level of the conventional one and still be more efficient. For most of the heating season, the condensing boiler will modulate down to a lower output and into an even more efficient working range. How does a non modulating boiler modulate? The water comes out of the boiler at 80C goes through the radiators which cools it by 10C (if they are exactly right for the room loss) and returns to the boiler at 70C. If you want it to return cooler the radiators have to be bigger since the heat they give up to the room is dependent on their size and the (fixed) room temperature. You could run with a lower flow temperature but then you'd have less drop across the boiler which as we have already agreed is less efficient. In the case of a condensing boiler the condensing gain would probably exceed the standard heat exchange section drop in efficiency but it still won't be as good as if it was running at the design figures. I wouldn't go with an alpha pump with a standard boiler. Think about it. An alpha pump slows down the flow so as the TRVs cut in the flow back to the boiler is reduced. Water spends more time in the rads so comes back colder. The risk is you get condensing. What I would go for is a standard pump + an automatic bypass (which is cheaper anyway). Then as the TRVs cut in the hot water gets fed back with the cold from the rads and the return temperature flow goes up - no risk of condensing. This is precisely where an Alpha pump is intended to be used. An automatic bypass is intended to deal with the case where both CH and DHW demand has ceased altogether and the boiler has been firing at full tilt. It simply prevents the water from boiling and nothing more. No. An automatic bypass says it is for TRVs. In any case what will a bypass do in the situation you have above. If you are trying to get heat out of boiler after the fuel has cut off you need a pump over run. That is something that runs the pump for a few minutes after the thermostats have cut off and the boiler stopped firing. Usually a thermostat on the boiler I believe rather than a timer but the effect is the same. Some boilers don't need it as the cut off quick enough that the water can absorb the extra heat. A three way valve must be open to at least one way and you must have a path (non TRV rads or tank). What stops the flow is the pump not running. If you have flow but not enough then that's where an automatic bypass comes in. Pump head (pressure) rises and the valve opens. The TRVs do not stop the flow completely if adjusted correctly in relation to the radiator in the non-TRV room. The object is to turn off the boiler via the room thermostat as all rooms have arrived at set point, not for the TRVs to have closed completely. Provided that the boiler thermostat is adjusted correctly, operating temperatures will also be correctly in range. If the TRVs are even partially closed then the flow is reduced. An alpha will keep the head constant-ish resulting in less flow and thus lower return temperature. A standard + bypass will result in constant head (the setting the bypass is set to), and a constant-ish flow -- Malcolm Malcolm Reeves BSc CEng MIEE MIRSE, Full Circuit Ltd, Chippenham, UK , or ). Design Service for Analogue/Digital H/W & S/W Railway Signalling and Power electronics. More details plus freeware, Win95/98 DUN and Pspice tips, see: http://www.fullcircuit.com or http://www.fullcircuit.co.uk NEW - Desktop ToDo/Reminder program (free) |
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"Andy Hall" wrote in message ... On Sun, 19 Sep 2004 23:50:08 +0100, "IMM" wrote: "Tom" wrote in message ... Thanks Andy, would you agree that the Alpha might induce condensing conditions in my standard boiler, assuming that thermostats and TRV are susceptible to frequent adjustments in my household :-( As long at the boiler is set to 80C this is highly unlikely when the system is warmed up. You may require a minimum flow through the boiler. Then I would forget the Alpha a go for am open rad and room stat. You can set the nominal power level on the Alpha above or below nominal setting. If all TRVs are close, no flow. It is best to get a flow switch rated at the minum boiler flow. below this flow the boiler burner is cut out. The pump can still pump through the boiler. http://www.crydom.co.uk/ http://www.axdistribution.com/FluidM...ow_switchs.htm Even so, I agree that if the existing pump is OK, it makes more sense to try that first and only switch to an Alpha if there is a problem with noise in the radiators closed down case (i.e. reduce pump setting), but that that is not enough wit everything open. .andy To email, substitute .nospam with .gl |
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On Mon, 20 Sep 2004 00:19:40 +0100, "IMM" wrote:
"Andy Hall" wrote in message .. . On Sun, 19 Sep 2004 23:50:08 +0100, "IMM" wrote: "Tom" wrote in message ... Thanks Andy, would you agree that the Alpha might induce condensing conditions in my standard boiler, assuming that thermostats and TRV are susceptible to frequent adjustments in my household :-( As long at the boiler is set to 80C this is highly unlikely when the system is warmed up. You may require a minimum flow through the boiler. Then I would forget the Alpha a go for am open rad and room stat. You can set the nominal power level on the Alpha above or below nominal setting. If all TRVs are close, no flow. It is best to get a flow switch rated at the minum boiler flow. below this flow the boiler burner is cut out. The pump can still pump through the boiler. http://www.crydom.co.uk/ http://www.axdistribution.com/FluidM...ow_switchs.htm I see your point, but these are far from being precision devices. For example, the Crydom ones have a 2:1 or 3:1 switch on/off flow rate, and these are max and min figures. One would have to put some valves around and in series with the switch to tune it to the correct behaviour. I suppose a more accurate flow sensor that measures the flow coupled to some electronics sould be used, but this is going to cost a bit. Even so, I agree that if the existing pump is OK, it makes more sense to try that first and only switch to an Alpha if there is a problem with noise in the radiators closed down case (i.e. reduce pump setting), but that that is not enough wit everything open. .andy To email, substitute .nospam with .gl ..andy To email, substitute .nospam with .gl |
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"Andy Hall" wrote in message ... On Mon, 20 Sep 2004 00:19:40 +0100, "IMM" wrote: "Andy Hall" wrote in message .. . On Sun, 19 Sep 2004 23:50:08 +0100, "IMM" wrote: "Tom" wrote in message ... Thanks Andy, would you agree that the Alpha might induce condensing conditions in my standard boiler, assuming that thermostats and TRV are susceptible to frequent adjustments in my household :-( As long at the boiler is set to 80C this is highly unlikely when the system is warmed up. You may require a minimum flow through the boiler. Then I would forget the Alpha a go for am open rad and room stat. You can set the nominal power level on the Alpha above or below nominal setting. If all TRVs are close, no flow. It is best to get a flow switch rated at the minum boiler flow. below this flow the boiler burner is cut out. The pump can still pump through the boiler. http://www.crydom.co.uk/ http://www.axdistribution.com/FluidM...ow_switchs.htm I see your point, but these are far from being precision devices. For example, the Crydom ones have a 2:1 or 3:1 switch on/off flow rate, and these are max and min figures. One would have to put some valves around and in series with the switch to tune it to the correct behaviour. That is the cheap way. Precise flow switchs, even adjustable, are available, but not cheap as they tend to be for commercial applications. I suppose a more accurate flow sensor that measures the flow coupled to some electronics sould be used, but this is going to cost a bit. Even so, I agree that if the existing pump is OK, it makes more sense to try that first and only switch to an Alpha if there is a problem with noise in the radiators closed down case (i.e. reduce pump setting), but that that is not enough wit everything open. .andy To email, substitute .nospam with .gl .andy To email, substitute .nospam with .gl |
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On Sun, 19 Sep 2004 23:40:39 +0100, "IMM" wrote:
You should have TRV on at least all the bedroom rads which is the new rules AFAIR. Nothing says it is madatory in the regs. Building regs part L 2002 guidelines say: "If a whole heating system is replaced, the controls must permit independent temperature control in two separate zones: the living and sleeping areas. This can be achieved with a single room thermostat and thermostatic radiator valves." Ideally all rooms should have TRVs except one (the lounge?) and that room should have the thermostat that turns the system on/off. The stat should be in the coolest room which is usualy the hall. Opinions on this differ. Mine is that I want the room control where I am, the lounge (being couch potato :-)). I don't care if the hall is at 17 or 18 or 19. The lounge is where I care about the temperature so that's what I want to control. In any case, as you can see from above, the building regs now suggest the lounge for the stat. Condensing boilers are far more efficient as they have a larger heat exchanger, condensing or not. We are probably talking about oil (me), gas (you). Yes condensing boilers have a bigger heat exchanger but "far" more efficient? For oil, a standard boiler on sedbuk rates at about 85% (capped). Condensing range is 90-95%. Saving is thus 5-10%. In my case I want a wall mount oil fired and from sedbuk there is only one oil fired wall mounted (and it's not available anymore). That one is only 90% and a lot more than GBP200 more expensive! Sedbuk reckons running costs are 400 pa for my sort of house which I'd agree with. So 5% saving is 20 pa. Pay back is 10yrs I wouldn't go with an alpha pump with a standard boiler. I would use a condesning boiler. For a condensing boiler an alpha would be good, which is what I said. With an alpha the return temperature goes down. Bad news for a standard boiler but just what you want for a condensing. What I would go for is a standard pump + an automatic bypass (which is cheaper anyway). And difficult to get right. What is difficult? As the TRVs cut in the flow resistance increases and the pump head rises. You just need to have the bypass set higher than the fully open condition. After that everything is automatic. You need to know more about regular v condensing boilers and much, much more. From someone who doesn't seem to know about part L or the performance figures it seems very patronising. -- Malcolm Malcolm Reeves BSc CEng MIEE MIRSE, Full Circuit Ltd, Chippenham, UK , or ). Design Service for Analogue/Digital H/W & S/W Railway Signalling and Power electronics. More details plus freeware, Win95/98 DUN and Pspice tips, see: http://www.fullcircuit.com or http://www.fullcircuit.co.uk NEW - Desktop ToDo/Reminder program (free) |
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On Sun, 19 Sep 2004 20:19:21 +0100, Andy Hall
wrote: The operating range possible with a conventional boiler is so narrow anyway that this makes very little difference. The heat exchangers used are relatively small. Perhaps we are talking about gas (you) and oil (me). Condensing boilers do have a larger heat exchanger. However, if you look at the sedbuk figures you'll see best standard is 85% (capped), condensing range 90-95%. So the efficiency difference is only 5-10% and with a lower return temp on a standard boiler, or a high return on a condensing, the difference is less again. The SEDBUK figures really confuse the issue because of the factors used. For the purposes of looking at boiler behaviour it is much more useful to use the measuring methods used in the rest of Europe. These specify certain temperatures and firing rates. If the figures are available. The only database I know of with all the uk boiler. If you have a URL for another database please post it. Also, for oil, isn't it a problem that UK use kerosene and europe uses gas oil so europe figures will be different anyway. So what you are saying is that a larger difference than 82/70 does improve efficiency. Like I said. I don't think you did, but the point is that a larger temperature difference together with a larger heat exchanger certainly does help. A = Large Heat Exchanger + Large difference B = Large Heat Exchanger + Small difference C = Small Heat Exchanger + Large difference D = Small Heat Exchanger + Small difference A is better than B. C is better than D. A is better than C (but boiler cost is more). B is better than D (but boiler cost is more). The difference in cost is becoming less and less, and from next year the whole issue will be academic since changes to the Building Regulations will mandate condensing boilers anyway. Not clear if that will cover oil, but just in case I'm putting mine in now. In terms of cost saving, I have found it to be in the predicted band of 25-30% For oil that flies in the face of the sedbuk figures which suggest 5%-10% for floor mounted. 5% for wall mounted (which I need). You must be spending very little on energy if £20 represents 25% of your energy cost. GBP20 is 5% of GBP400 my estimated fuel cost. There are no real problems with modern condensing models in terms of pluming. Much improvement has been made over early designs. Where you get the idea that there are smells, I have no idea. Oil smells. I suspect you are talking more about gas. A condensing boiler with its lower flue gas temperature is much more likely to accumulate fumes at low level (that's why they plume after all). The advice on siting says to take account of the plume possibility. My flue will face my neighbour. Do I want to risk the possibility I might be dropping smelly fumes into his garden (and over his washing line). For, perhaps GBP20 pa when I won't break even on the boiler costs for 10yrs. NO. If the TRVs are even partially closed then the flow is reduced. An alpha will keep the head constant-ish resulting in less flow and thus lower return temperature. No because when this happens the heat emission will have dropped. The purpose is to reduce the power to the pump as the flow resistance increases. We are talking about non-modulating boilers aren't we? I am since 99% of oil boilers are not modulating. I don't know how common modulation is on gas. So on a non modulating boiler how does the heat emission drop? Come to that since we were talking about short cycling then how does a modulating boiler short cycle since they would modulate before that and thus very unlikely to short cycle. A standard + bypass will result in constant head (the setting the bypass is set to), and a constant-ish flow No it won't because the bypass opens in effect digitally at a certain head. After that, it has a pressure/flow characteristic. It's a valve with a spring. It will have some slope to its characteristic. See http://www.sunvic.co.uk/bypass.html which repeats what I said. I would say the sunvic curve is soft. For my house I have calculated a head of about 1m (about 0.1 bar) and a flow of 0.8 m3/hr. So I'd set my valve at #3 (this assumes the pump matches this, in practice the head would be higher to get the flow as I can only restrict the flow). The valve would start to open at 0.15 bar (1.5m) and by 2 bar (2m) all my flow would be via the bypass. The head range is thus 1.5-2m. Not exactly digital. -- Malcolm Malcolm Reeves BSc CEng MIEE MIRSE, Full Circuit Ltd, Chippenham, UK , or ). Design Service for Analogue/Digital H/W & S/W Railway Signalling and Power electronics. More details plus freeware, Win95/98 DUN and Pspice tips, see: http://www.fullcircuit.com or http://www.fullcircuit.co.uk NEW - Desktop ToDo/Reminder program (free) |
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On Mon, 20 Sep 2004 10:25:39 +0100, Malcolm Reeves
wrote: On Sun, 19 Sep 2004 20:19:21 +0100, Andy Hall wrote: The operating range possible with a conventional boiler is so narrow anyway that this makes very little difference. The heat exchangers used are relatively small. Perhaps we are talking about gas (you) and oil (me). Predominantly I was. Condensing boilers do have a larger heat exchanger. However, if you look at the sedbuk figures you'll see best standard is 85% (capped), condensing range 90-95%. So the efficiency difference is only 5-10% and with a lower return temp on a standard boiler, or a high return on a condensing, the difference is less again. The trouble is that the SEDBUK figures tend to obfuscate what is happening with the boiler. The SEDBUK figures really confuse the issue because of the factors used. For the purposes of looking at boiler behaviour it is much more useful to use the measuring methods used in the rest of Europe. These specify certain temperatures and firing rates. If the figures are available. The only database I know of with all the uk boiler. If you have a URL for another database please post it. Also, for oil, isn't it a problem that UK use kerosene and europe uses gas oil so europe figures will be different anyway. The manufacturers should have them if they are selling their products outside the UK. I'm not sure whether gas oil and kerosene would result in different efficiency figures - different calorific values possibly. So what you are saying is that a larger difference than 82/70 does improve efficiency. Like I said. I don't think you did, but the point is that a larger temperature difference together with a larger heat exchanger certainly does help. A = Large Heat Exchanger + Large difference B = Large Heat Exchanger + Small difference C = Small Heat Exchanger + Large difference D = Small Heat Exchanger + Small difference A is better than B. C is better than D. A is better than C (but boiler cost is more). B is better than D (but boiler cost is more). OK. The difference in cost is becoming less and less, and from next year the whole issue will be academic since changes to the Building Regulations will mandate condensing boilers anyway. Not clear if that will cover oil, but just in case I'm putting mine in now. In terms of cost saving, I have found it to be in the predicted band of 25-30% For oil that flies in the face of the sedbuk figures which suggest 5%-10% for floor mounted. 5% for wall mounted (which I need). I was talking about gas. You must be spending very little on energy if £20 represents 25% of your energy cost. GBP20 is 5% of GBP400 my estimated fuel cost. There are no real problems with modern condensing models in terms of pluming. Much improvement has been made over early designs. Where you get the idea that there are smells, I have no idea. Oil smells. I suspect you are talking more about gas. It does anyway though, doesn't it? A condensing boiler with its lower flue gas temperature is much more likely to accumulate fumes at low level (that's why they plume after all). The advice on siting says to take account of the plume possibility. My flue will face my neighbour. Do I want to risk the possibility I might be dropping smelly fumes into his garden (and over his washing line). For, perhaps GBP20 pa when I won't break even on the boiler costs for 10yrs. NO. Well again, gas ones don't have this issue or don't have to have this issue. If the TRVs are even partially closed then the flow is reduced. An alpha will keep the head constant-ish resulting in less flow and thus lower return temperature. No because when this happens the heat emission will have dropped. The purpose is to reduce the power to the pump as the flow resistance increases. We are talking about non-modulating boilers aren't we? I am since 99% of oil boilers are not modulating. I don't know how common modulation is on gas. Nowadays very - on gas condensing boilers. o on a non modulating boiler how does the heat emission drop? Come to that since we were talking about short cycling then how does a modulating boiler short cycle since they would modulate before that and thus very unlikely to short cycle. Right. I was referring to conventional gas boilers without modulation. A standard + bypass will result in constant head (the setting the bypass is set to), and a constant-ish flow No it won't because the bypass opens in effect digitally at a certain head. After that, it has a pressure/flow characteristic. It's a valve with a spring. It will have some slope to its characteristic. See http://www.sunvic.co.uk/bypass.html which repeats what I said. I would say the sunvic curve is soft. For my house I have calculated a head of about 1m (about 0.1 bar) and a flow of 0.8 m3/hr. So I'd set my valve at #3 (this assumes the pump matches this, in practice the head would be higher to get the flow as I can only restrict the flow). The valve would start to open at 0.15 bar (1.5m) and by 2 bar (2m) all my flow would be via the bypass. The head range is thus 1.5-2m. Not exactly digital. If you look at data sheets for devices like the Honeywell it shows it as a set of almost straight lines depending on setting. Once the valve opens it presents as a virtually constant pressure drop device. ..andy To email, substitute .nospam with .gl |
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In article , Malcolm
Reeves wrote: The SEDBUK figures really confuse the issue because of the factors used. For the purposes of looking at boiler behaviour it is much more useful to use the measuring methods used in the rest of Europe. These specify certain temperatures and firing rates. If the figures are available. The only database I know of with all the uk boiler. If you have a URL for another database please post it. I would guess that what Andy is referring to the fact that the SEDBUK efficiencies are derived from formulae which can be found in the [free] SAP-2001 book Appendix D. For an on/off boiler this is 0.5(Efull+EPart)-2.5, for a modulating boiler 0.5(Efull+EPart)-2.0, less 4% if the boiler has a pilot light - other formulae apply to combis of various types. Efull and Epart are the efficiencies at full and 30% load. Using 50/50 part and full load figures is reckoned to give a fairly accurate measure of likely efficiency under UK climatic conditions. It would be quite possible that some other EU country uses a different mix and if you were comparing two boilers with significantly different part and full load performance their relative assumed in-use efficiencies would be different to that shown by SEDBUK. -- Tony Bryer SDA UK 'Software to build on' http://www.sda.co.uk Free SEDBUK boiler database browser http://www.sda.co.uk/qsedbuk.htm |
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On Mon, 20 Sep 2004 10:46:27 +0100, Andy Hall
wrote: The manufacturers should have them if they are selling their products outside the UK. I'm not sure that they do. The oil difference is quite significant I think. In uk only kerosene can be low level flue so its all kerosene. Europe is all gas oil I think (and I guess they allow gas oil low level flues). I'm not sure whether gas oil and kerosene would result in different efficiency figures - different calorific values possibly. Lots of differences. The nozzle at least needs to change, perhaps more. Certainly a retest. Oil smells. I suspect you are talking more about gas. It does anyway though, doesn't it? I'd have gas if I could :-). Anyway a good reason IMO to have a higher flue temperature so exhaust dissipates upwards. If you look at data sheets for devices like the Honeywell it shows it as a set of almost straight lines depending on setting. Once the valve opens it presents as a virtually constant pressure drop device. Mine is a sunvic, perhaps they work better? -- Malcolm Malcolm Reeves BSc CEng MIEE MIRSE, Full Circuit Ltd, Chippenham, UK , or ). Design Service for Analogue/Digital H/W & S/W Railway Signalling and Power electronics. More details plus freeware, Win95/98 DUN and Pspice tips, see: http://www.fullcircuit.com or http://www.fullcircuit.co.uk NEW - Desktop ToDo/Reminder program (free) |
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I'm further minded to install a Grundfos Alpha pump, however, I'm
undecided as to the control mechanism i.e. a flow switch as advocated by IMM in a previous thread or to rely on the boiler stat set to 82degC as you stated. Unfortunately, relying on the boiler stat would not meet building regulations. You must have a flow switch, a room thermostat (in a room without a TRV) or other similar mechanism that entirely cuts the boiler when no heat is required. Christian. |
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Malcolm Reeves wrote:
On Sun, 19 Sep 2004 23:40:39 +0100, "IMM" wrote: You should have TRV on at least all the bedroom rads which is the new rules AFAIR. Nothing says it is madatory in the regs. Building regs part L 2002 guidelines say: "If a whole heating system is replaced, the controls must permit independent temperature control in two separate zones: the living and sleeping areas. This can be achieved with a single room thermostat and thermostatic radiator valves." *can* be achieved... It can also be achieved by using zoning with 2 thermostats or (I can't believe I'm writing this) 2 boilers, one running the living areas, and one for the bedrooms. Neil |
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On Mon, 20 Sep 2004 14:04:41 +0100, "Neil Jones"
wrote: Malcolm Reeves wrote: On Sun, 19 Sep 2004 23:40:39 +0100, "IMM" wrote: You should have TRV on at least all the bedroom rads which is the new rules AFAIR. Nothing says it is madatory in the regs. Building regs part L 2002 guidelines say: "If a whole heating system is replaced, the controls must permit independent temperature control in two separate zones: the living and sleeping areas. This can be achieved with a single room thermostat and thermostatic radiator valves." *can* be achieved... It can also be achieved by using zoning with 2 thermostats or (I can't believe I'm writing this) 2 boilers, one running the living areas, and one for the bedrooms. True, but as I read it the post was saying you didn't have to do that, NOT, you didn't have to do that IF, you did something else. It is mandatory to do some zone control - which for most TRVs are the easiest route. The original poster has TRVs AFAIR, I was just adding that he needed to keep them. -- Malcolm Malcolm Reeves BSc CEng MIEE MIRSE, Full Circuit Ltd, Chippenham, UK , or ). Design Service for Analogue/Digital H/W & S/W Railway Signalling and Power electronics. More details plus freeware, Win95/98 DUN and Pspice tips, see: http://www.fullcircuit.com or http://www.fullcircuit.co.uk NEW - Desktop ToDo/Reminder program (free) |
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"Neil Jones" wrote in message ... Malcolm Reeves wrote: On Sun, 19 Sep 2004 23:40:39 +0100, "IMM" wrote: You should have TRV on at least all the bedroom rads which is the new rules AFAIR. Nothing says it is madatory in the regs. Building regs part L 2002 guidelines say: "If a whole heating system is replaced, the controls must permit independent temperature control in two separate zones: the living and sleeping areas. This can be achieved with a single room thermostat and thermostatic radiator valves." *can* be achieved... It can also be achieved by using zoning with 2 thermostats or (I can't believe I'm writing this) 2 boilers, one running the living areas, and one for the bedrooms. It is on about "logical" zones, not physical zones. |
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"Malcolm Reeves" wrote in message ... On Mon, 20 Sep 2004 14:04:41 +0100, "Neil Jones" wrote: Malcolm Reeves wrote: On Sun, 19 Sep 2004 23:40:39 +0100, "IMM" wrote: You should have TRV on at least all the bedroom rads which is the new rules AFAIR. Nothing says it is madatory in the regs. Building regs part L 2002 guidelines say: "If a whole heating system is replaced, the controls must permit independent temperature control in two separate zones: the living and sleeping areas. This can be achieved with a single room thermostat and thermostatic radiator valves." *can* be achieved... It can also be achieved by using zoning with 2 thermostats or (I can't believe I'm writing this) 2 boilers, one running the living areas, and one for the bedrooms. True, but as I read it the post was saying you didn't have to do that, NOT, you didn't have to do that IF, you did something else. It is mandatory to do some zone control Where does it say that. A zone is an independently controlled, in time and temp, section of the heating system. A TVR does not converts a room into a zone. - which for most TRVs are the easiest route. The original poster has TRVs AFAIR, I was just adding that he needed to keep them. -- Malcolm Malcolm Reeves BSc CEng MIEE MIRSE, Full Circuit Ltd, Chippenham, UK , or ). Design Service for Analogue/Digital H/W & S/W Railway Signalling and Power electronics. More details plus freeware, Win95/98 DUN and Pspice tips, see: http://www.fullcircuit.com or http://www.fullcircuit.co.uk NEW - Desktop ToDo/Reminder program (free) |
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On Mon, 20 Sep 2004 17:43:57 +0100, "IMM" wrote:
"Malcolm Reeves" wrote in message .. . On Mon, 20 Sep 2004 14:04:41 +0100, "Neil Jones" wrote: Malcolm Reeves wrote: On Sun, 19 Sep 2004 23:40:39 +0100, "IMM" wrote: You should have TRV on at least all the bedroom rads which is the new rules AFAIR. Nothing says it is madatory in the regs. Building regs part L 2002 guidelines say: "If a whole heating system is replaced, the controls must permit independent temperature control in two separate zones: the living and sleeping areas. This can be achieved with a single room thermostat and thermostatic radiator valves." *can* be achieved... It can also be achieved by using zoning with 2 thermostats or (I can't believe I'm writing this) 2 boilers, one running the living areas, and one for the bedrooms. True, but as I read it the post was saying you didn't have to do that, NOT, you didn't have to do that IF, you did something else. It is mandatory to do some zone control Where does it say that. A zone is an independently controlled, in time and temp, section of the heating system. A TVR does not converts a room into a zone. - which for most TRVs are the easiest route. The original poster has TRVs AFAIR, I was just adding that he needed to keep them. Eh? I just quoted Building regs guide for part L above. That says you have to do it which makes it mandatory. They are only considering zones to be at different control temperatures not different on/off times. But of course you can go that far if you want. -- Malcolm Malcolm Reeves BSc CEng MIEE MIRSE, Full Circuit Ltd, Chippenham, UK , or ). Design Service for Analogue/Digital H/W & S/W Railway Signalling and Power electronics. More details plus freeware, Win95/98 DUN and Pspice tips, see: http://www.fullcircuit.com or http://www.fullcircuit.co.uk NEW - Desktop ToDo/Reminder program (free) |
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On Mon, 20 Sep 2004 20:29:52 +0100, Malcolm Reeves
wrote: Eh? I just quoted Building regs guide for part L above. That says you have to do it which makes it mandatory. They are only considering zones to be at different control temperatures not different on/off times. But of course you can go that far if you want. The Approved Documents to the Building Regulations are not of themselves legally binding. It says as much in the introduction of most. They represent *a* way of complying with the statute but are not the *only* way. If you can propose an alternative to the suggestion, this can be just as valid, although it may be necessary to agree the point with the BCO. ..andy To email, substitute .nospam with .gl |
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