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#1
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Why loft vents for boiler and immersion cylinders?
My heating system is a traditional boiler, loft tank, vented cylinder type
affair. The lower outlet to the coil inside the immersion cylinder tees off to a vent into the small tank in the loft which therefore vents the boiler side of things. The heated water in the cylinder fills from the bottom and the outlet at the top to the taps also tees off to a vent into the large loft tank. All fairly normal and so far so good. A few years ago I was up in the loft for the first time in ages and it was dripping wet in there. Everything stored had gone musty and water was running off the roof felt. Turned out the boiler vent was pumping over into the small tank which was consequently full of hot water and producing clouds of condensation. I tried the pump on its lowest setting and it still happened. I examined the pipe runs for the whole system and concluded that there was no point in a vent being there. The boiler fills up under gravity feed from the small tank and any excess pressure can just go straight back up there if it wants. The boiler certainly isn't going to explode and anyway there's a blow-off valve on the back of it. So I dug out an old radiator valve, slapped it on the end of the vent in the loft and turned it off. It's been that way for years and hasn't made a scrap of difference to anything other than the loft is now dry. So what purpose, if any, was the vent really serving? The vent to the main part of the cylinder doesn't overflow of course because it isn't pumped but again I see no point to it other than maybe to let any air in the cylinder get out. However wouldn't the air be immediately displaced out of a hot tap somewhere the first time the system was filled if there was no vent? -- Dave Baker www.pumaracing.co.uk *** Free account sponsored by SecureIX.com *** *** Encrypt your Internet usage with a free VPN account from http://www.SecureIX.com *** |
#2
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Why loft vents for boiler and immersion cylinders?
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#3
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Why loft vents for boiler and immersion cylinders?
"Aidan" wrote in message ups.com... Dave Baker wrote: So I dug out an old radiator valve, slapped it on the end of the vent in the loft and turned it off. It's been that way for years and hasn't made a scrap of difference to anything other than the loft is now dry. With all due respect, you're daft. Take it off. So what purpose, if any, was the vent really serving? In normal operation it releases any air that gets into the system. Typically dissoled oxygen in the boiler return wil be released from solution when the water is haeted in the boiler and is discharged from the open vent. In the event of a control failure, it is a safety device; it releases steam, prevents the system becoming over-pressurized and bursting. In your system, such a failure would probably now cause the contents of the heating system to be discharged into the loft and the boiler would dry-fire to destruction. It was pumping over probably because it was piped incorrectly. Get someone competent to fix that problem. Conversion to a sealed system would be an improvement, if the boiler is suitable; if you'd like that done, get someone competent to do that. The boiler certainly isn't going to explode and anyway there's a blow-off valve on the back of it. I find your faith in a cheap safety valve to be touching. They don't have to do anything in normal operation. If called upon to operate in anger, a disturbing number fail to work. Many have been dripping inconspicuously for years, the water evaporates from the hot safety valve and the accumulation of limescale deposits concretes the valve immovably shut. Have you tested the valve? The vent to the main part of the cylinder doesn't overflow of course because it isn't pumped but again I see no point to it other than maybe to let any air in the cylinder get out. However wouldn't the air be immediately displaced out of a hot tap somewhere the first time the system was filled if there was no vent? Kin 'ell! Is this a wind up? Leave it alone. Immersion heater contacts frequently weld themselves together, so the heater fails on. The open vent would then discharge steam. If you block it, the steam will blow the contents of the cylinder into the storage tank. If that discharge route is blocked, this happens; http://www.waterheaterblast.com That is a small water heater (12 US gallons). Drivel loves posting that link to promote his thermal stores, but someone proposes plugging the vent on a domestic hot water storage system and he makes no comment; he is a dangerous idiot. Unvented water heaters are good, I disagree. Heat banks give better performance as they can take higher pressures becaus eof the plate heat exchangers, open vented and a minute to zero chance of an explosion. Unvented cylinders require an annual service charge. That alone is enough to discount them totally...especially when a safe, service free, better performing unit is available....the heat bank. but they have at least 3 sequential safety devices for each heating system. They are costly. A vented cylinder cannot be converted. |
#4
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Why loft vents for boiler and immersion cylinders?
On 4 Mar 2006 14:19:50 -0800, "Aidan" wrote:
Kin 'ell! Is this a wind up? Leave it alone. Immersion heater contacts frequently weld themselves together, so the heater fails on. The open vent would then discharge steam. If you block it, the steam will blow the contents of the cylinder into the storage tank. If that discharge route is blocked, this happens; http://www.waterheaterblast.com That is a small water heater (12 US gallons). Drivel loves posting that link to promote his thermal stores, but someone proposes plugging the vent on a domestic hot water storage system and he makes no comment; he is a dangerous idiot. Unvented water heaters are good, but they have at least 3 sequential safety devices for each heating system. They are costly. A vented cylinder cannot be converted. An interesting story is the sinking of the Fleur de Lys, a fishing vessel. This one went down, fortunately not killing anybody, when its 120 litre HW cylinder, a class 4 type (weakest rating normally used for open vented systems) was being used in a pressurised system. A firm of plumbers who didn't know what they were doing had replaced the cylinder and fitted the wrong type. http://www.maib.gov.uk/cms_resources...ety_504222.pdf The cause of the explosion was listed as follows: "The hot water storage cylinder ruptured because the water in it overheated and steam generated, causing overpressure. The rupture of the cylinder probably occurred at about 3.4bar, four times working pressure of the cylinder. The pressure relief valve must have been set at this pressure or above, or it was seized in the closed position. The cylinder probably overheated when the immersion heater thermostat failed to shut off the electrical supply to the heater. There were no safety devices fitted to the system to prevent overheating and overpressure as a result of thermostat failure." Returning to the original point of blocking the vent - it is quite common to have an isolating gate valve etc. on the cold feed to the cylinder. If this is closed when the heat source is still on and the vent is blocked, a potential bomb will have been created. We can see from the fishing boat example that there does not need to be a great deal of pressure at all to achieve an unfortunate situation. -- ..andy |
#5
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Why loft vents for boiler and immersion cylinders?
Aidan wrote in message ups.com... Dave Baker wrote: So I dug out an old radiator valve, slapped it on the end of the vent in the loft and turned it off. It's been that way for years and hasn't made a scrap of difference to anything other than the loft is now dry. With all due respect, you're daft. I'm actually a rather competent engineer who was hoping for reasoned opinion on the merits of this vent. Take it off. No thanks. As I say everything works very well as is. So what purpose, if any, was the vent really serving? In normal operation it releases any air that gets into the system. Typically dissoled oxygen in the boiler return wil be released from solution when the water is haeted in the boiler and is discharged from the open vent. Firstly, the water in the boiler system always has an open vent path via the fill point at the bottom of the tank in the loft. If water can get down that I see no reason why dissolved oxygen can't get back up it. Secondly, The vast bulk of the water in the system is in the radiators and that's where the vast bulk of any dissolved oxygen will end up. There is no way for bottom fed radiators to have this oxygen removed than by bleeding from the valves at the top. A bleed valve at the top of the boiler system would surely do the same rather than having to have a permanently open vent. In the event of a control failure, it is a safety device; it releases steam, prevents the system becoming over-pressurized and bursting. In your system, such a failure would probably now cause the contents of the heating system to be discharged into the loft and the boiler would dry-fire to destruction. Nonsense. The system isn't pressurised other than by the head of water from the loft tank. The contents of the system can't be discharged into the loft other than by the same pipe from the bottom of the loft tank which is continuously filling it up anyway. It was pumping over probably because it was piped incorrectly. Possibly but it was certainly ok for many years and the only change made to the system in 19 years was a new pump which was fitted by a Corgi plumber. Now it's possible this was fitted to pump in the opposite direction from the original pump but I can't instantly see how this would make a deal of difference anyway. I'm open to suggestions as how it might. At present the vent is on the return side of the pump so if anything I would think this would give the least chance of pumping over. Get someone competent to fix that problem. Conversion to a sealed system would be an improvement, if the boiler is suitable; if you'd like that done, get someone competent to do that. The boiler certainly isn't going to explode and anyway there's a blow-off valve on the back of it. I find your faith in a cheap safety valve to be touching. They don't have to do anything in normal operation. If called upon to operate in anger, a disturbing number fail to work. Many have been dripping inconspicuously for years, the water evaporates from the hot safety valve and the accumulation of limescale deposits concretes the valve immovably shut. Have you tested the valve? It's been checked, cleaned and the washer replaced a couple of times and is fine. In any case the system is always vented to the bottom of the loft tank as I have said. The vent to the main part of the cylinder doesn't overflow of course because it isn't pumped but again I see no point to it other than maybe to let any air in the cylinder get out. However wouldn't the air be immediately displaced out of a hot tap somewhere the first time the system was filled if there was no vent? Kin 'ell! Is this a wind up? Leave it alone. I have every intention of leaving it alone because it cause no problems as I have made clear. Please try to confine yourself to the physics and hydraulics of the issue rather than pontificating. Immersion heater contacts frequently weld themselves together, so the heater fails on. The open vent would then discharge steam. If you block it, the steam will blow the contents of the cylinder into the storage tank. If that discharge route is blocked, this happens; There is no electric heater in the tank. http://www.waterheaterblast.com That is a small water heater (12 US gallons). Drivel loves posting that link to promote his thermal stores, but someone proposes plugging the vent on a domestic hot water storage system and he makes no comment; he is a dangerous idiot. Unvented water heaters are good, but they have at least 3 sequential safety devices for each heating system. They are costly. A vented cylinder cannot be converted. -- Dave Baker www.pumaracing.co.uk *** Free account sponsored by SecureIX.com *** *** Encrypt your Internet usage with a free VPN account from http://www.SecureIX.com *** |
#6
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Why loft vents for boiler and immersion cylinders?
"Aidan" wrote in message ups.com... In normal operation it releases any air that gets into the system. Typically dissoled oxygen in the boiler return wil be released from solution when the water is haeted in the boiler and is discharged from the open vent. In the event of a control failure, it is a safety device; it releases steam, prevents the system becoming over-pressurized and bursting. In your system, such a failure would probably now cause the contents of the heating system to be discharged into the loft and the boiler would dry-fire to destruction. If the boiler has a blow-off valve the boiler is most probably suitable for sealed systems ..... and a combined feed and expansion pipe. If so, then he has a one pipe F&E system, except the pipe is probably 15mm not 22mm. Then it will not dry fire itself to destruction as a high limit is on the boiler. |
#7
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Why loft vents for boiler and immersion cylinders?
Sorted
I've just been up into the loft and airing cupboard and mapped out all the pipe runs. If you look at this basic diagram. http://www.diydata.com/planning/cent...ing/boiler.htm Then my pump would be on the blue line immediately adjacent to the boiler, pumping into it and then back out into the line that feeds the vent and then the rads and cylinder. The vent is therefore in the wrong place, before the rads rather than after them and hence seeing all the pump pressure. Turning the pump round wouldn't help because then the feed from the bottom of the loft tank would see this pressure instead thus similarly reducing flow through the rads. So at present I only get normal flow because the vent is blocked and the expansion/feed pipe does any venting required. When I get round to fixing all the niggles in the system I'll reorganise everything to correct this. As I say though, whether vented, for the first 15 years here, or unvented for the last 4 I've always had piping hot rads and hot water and I guess just the pressure head from the loft tank has sufficed to keep the system running ok. Black mark to the guy who fitted all this before I moved in I suppose. -- Dave Baker www.pumaracing.co.uk *** Free account sponsored by SecureIX.com *** *** Encrypt your Internet usage with a free VPN account from http://www.SecureIX.com *** |
#9
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Why loft vents for boiler and immersion cylinders?
On Sun, 5 Mar 2006 01:06:20 -0000, "Dave Baker" Dave
wrote: Sorted I've just been up into the loft and airing cupboard and mapped out all the pipe runs. If you look at this basic diagram. http://www.diydata.com/planning/cent...ing/boiler.htm Then my pump would be on the blue line immediately adjacent to the boiler, pumping into it and then back out into the line that feeds the vent and then the rads and cylinder. The vent is therefore in the wrong place, before the rads rather than after them and hence seeing all the pump pressure. Turning the pump round wouldn't help because then the feed from the bottom of the loft tank would see this pressure instead thus similarly reducing flow through the rads. So at present I only get normal flow because the vent is blocked and the expansion/feed pipe does any venting required. When I get round to fixing all the niggles in the system I'll reorganise everything to correct this. As I say though, whether vented, for the first 15 years here, or unvented for the last 4 I've always had piping hot rads and hot water and I guess just the pressure head from the loft tank has sufficed to keep the system running ok. Black mark to the guy who fitted all this before I moved in I suppose. If your pump is on the blue line adjacent to the boiler, it's the pump that's in the wrong place relative to the other pipes. It's not so much an issue of whether the pump is before the heating circuit or after it, but rather that there is a pressure differential between the feed/expansion pipe and the vent. If your set up is as shown on the web site except that the pump is adjacent to the boiler, you have a classic pumping over situation because the two pipes to the tank are on opposite sides of the pump. Actually, the setup in the diagram is not a lot better because the F/E pipe and the vent have the boiler between them. Since there is a level of flow resistance through the boiler there will be a pressure differential so in the case illustrated there is a possibility of air being sucked down the vent if the boiler flow resistance is high - e.g. with pump on high speed. If you imagine the flow through the boiler stopped (for the sake of illustration) you can see that the effect would be that the water level in the tank would rise and air would enter through the vent. In normal operation it would depend on the pump setting, the height of the tank and the flow resistance of the boiler and heating/HW circuits. A better design would have the flow from the boiler going to an air separator - e.g. www.bes.ltd.uk part 11334 - and the F/E and vent pipes separately joining it. The pump goes after that followed by motorised valve(s) and the heating and HW circuits. The returns of those would be commoned and go directly to the boiler. This achieves two key objectives: - The F/E and vent pipes are close together. This means that there is very little pressure differential and no chance of sucking down or pumping over. Where a separator isn't used, but the pipes join the circuit, it is recommended that there is not more than a 150mm space between the two connection points. - There is a clear path from the boiler flow to the vent. This helps with venting but also the safety purpose of an easy path for the escape of steam in the event of control or other failure. An additional benefit of the air separator is that the system becomes very easy to vent and little or no air should collect in the radiators after the initial filling and expulsion of dissolved air. -- ..andy |
#10
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Why loft vents for boiler and immersion cylinders?
Better get a heating engineer in fast.
On Sat, 4 Mar 2006 15:30:11 -0000, "Dave Baker" Dave wrote: My heating system is a traditional boiler, loft tank, vented cylinder type affair. The lower outlet to the coil inside the immersion cylinder tees off to a vent into the small tank in the loft which therefore vents the boiler side of things. The heated water in the cylinder fills from the bottom and the outlet at the top to the taps also tees off to a vent into the large loft tank. All fairly normal and so far so good. A few years ago I was up in the loft for the first time in ages and it was dripping wet in there. Everything stored had gone musty and water was running off the roof felt. Turned out the boiler vent was pumping over into the small tank which was consequently full of hot water and producing clouds of condensation. I tried the pump on its lowest setting and it still happened. I examined the pipe runs for the whole system and concluded that there was no point in a vent being there. The boiler fills up under gravity feed from the small tank and any excess pressure can just go straight back up there if it wants. The boiler certainly isn't going to explode and anyway there's a blow-off valve on the back of it. So I dug out an old radiator valve, slapped it on the end of the vent in the loft and turned it off. It's been that way for years and hasn't made a scrap of difference to anything other than the loft is now dry. So what purpose, if any, was the vent really serving? The vent to the main part of the cylinder doesn't overflow of course because it isn't pumped but again I see no point to it other than maybe to let any air in the cylinder get out. However wouldn't the air be immediately displaced out of a hot tap somewhere the first time the system was filled if there was no vent? ----== Posted via Newsfeeds.Com - Unlimited-Unrestricted-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups ----= East and West-Coast Server Farms - Total Privacy via Encryption =---- |
#11
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Why loft vents for boiler and immersion cylinders?
Dave Baker wrote: With all due respect, you're daft. I'm actually a rather competent engineer who was hoping for reasoned opinion on the merits of this vent. Stick to racing engines. I'm an HVAC Engineer. I suggest you take it off. Take it off. No thanks. As I say everything works very well as is. So far. Firstly, the water in the boiler system always has an open vent path via the fill point at the bottom of the tank in the loft. If water can get down that I see no reason why dissolved oxygen can't get back up it. It's often on the return and it's commonly lower. The oxygen won't get to it, it will corrode the radiators, Secondly, The vast bulk of the water in the system is in the radiators and that's where the vast bulk of any dissolved oxygen will end up. There is no way for bottom fed radiators to have this oxygen removed than by bleeding from the valves at the top. A bleed valve at the top of the boiler system would surely do the same rather than having to have a permanently open vent. In the event of a control failure, it is a safety device; it releases steam, prevents the system becoming over-pressurized and bursting. In your system, such a failure would probably now cause the contents of the heating system to be discharged into the loft and the boiler would dry-fire to destruction. Nonsense. The system isn't pressurised other than by the head of water from the loft tank. The contents of the system can't be discharged into the loft other than by the same pipe from the bottom of the loft tank which is continuously filling it up anyway. It would be discharged into the F&E tank through the cold feed pipe. It was pumping over probably because it was piped incorrectly. Possibly but it was certainly ok for many years You may think so. I do not. You didn't notice anything amiss, this doesn't mean it was OK. the system in 19 years was a new pump which was fitted by a Corgi plumber. Ye're doomed, doomed I tell ye. Now it's possible this was fitted to pump in the opposite direction from the original pump but I can't instantly see how this would make a deal of difference anyway. I'm open to suggestions as how it might. At present the vent is on the return side of the pump so if anything I would think this would give the least chance of pumping over. I find your faith in a cheap safety valve to be touching. They don't have to do anything in normal operation. If called upon to operate in anger, a disturbing number fail to work. Many have been dripping inconspicuously for years, the water evaporates from the hot safety valve and the accumulation of limescale deposits concretes the valve immovably shut. Have you tested the valve? Kin 'ell! Is this a wind up? Leave it alone. I have every intention of leaving it alone because it cause no problems as I have made clear. Please try to confine yourself to the physics and hydraulics of the issue rather than pontificating. I have done. You're convinced you know everything worth knowing about it and can't believe that someone else may know more. Take it off. Dave Baker www.pumaracing.co.uk |
#12
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Why loft vents for boiler and immersion cylinders?
In article ,
Dave Baker Dave wrote: http://www.diydata.com/planning/cent...ing/boiler.htm Then my pump would be on the blue line immediately adjacent to the boiler, pumping into it.............. That's where our pump is.... in the return line, and immediately next to the boiler. It is the original 1970 plumbing and works ok. .............and then back out into the line that feeds the vent and then the rads and cylinder. The vent is therefore in the wrong place, before the rads rather than after them and hence seeing all the pump pressure. ISTM that if the radiator loops are free-flowing, then the pump will pull a low pressure on the pipe feeding the loops, lower than the head required by the vent pipe. Radiator circulation is tickety-boo. But if the radiator loops get blocked, (by sludge, or later fitted valves?) then the pump will preferentially do a local circulation, in just the loop between the header tank and the vent pipe. Any chance that that is what you are seeing? BTW: My old plumbing book has a gruesome tale about a plumber who blocked a vent pipe with a cork, to try and reduce the amount of water lost during a drain down. The resultant vaccuum caused parts of the plumbing to collapse inwards. Blocking a vent pipe may not be good news. -- Tony Williams. |
#13
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Why loft vents for boiler and immersion cylinders?
On Sun, 5 Mar 2006 00:17:08 -0000 someone who may be "Dave Baker"
Dave wrote this:- I'm actually a rather competent engineer So you claim. However, in my view a competent engineer would have found out what was going on and then sorted it out at source, rather then dealing with the symptoms without knowing what they were doing. Finding out what was going on is fairly simple, as it is an elementary part of building services engineering. For example in a library one can find, "Faber and Kell's Heating and Air-conditioning of Buildings", the book on the subject. In there one should find some examples of piping layouts. http://www.foyles.co.uk/foyles/display.asp?K=181613010522833&M=310&WHERE=(keyword +INCLUDES+'heating')&SS=( Finding out would also involve tracing out the pipes, something you say you have only just done. who was hoping for reasoned opinion on the merits of this vent. From my 1984 edition of the above book, page 190, "In no circumstances should the feed and expansion pipe be combined with the system vent pipe as case D. This practice was shown to be dangerous more than 50 years ago." The reason why it is dangerous should be obvious. It is to do with what happens if this one pipe is restricted or blocked, especially if it is only 15mm. You are living on borrowed time and should sort it out immediately. BTW, your one safety valve may have been cleaned and the washer replaced a few times. What pressure is it set at? How often is the operation of the valve tested? Can it pass the necessary volume of hot water/steam? -- David Hansen, Edinburgh I will *always* explain revoked encryption keys, unless RIP prevents me http://www.opsi.gov.uk/acts/acts2000/00023--e.htm#54 |
#14
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Why loft vents for boiler and immersion cylinders?
In article ,
Dave Baker Dave wrote: Possibly but it was certainly ok for many years and the only change made to the system in 19 years was a new pump which was fitted by a Corgi plumber. Now it's possible this was fitted to pump in the opposite direction from the original pump but I can't instantly see how this would make a deal of difference anyway. I'm open to suggestions as how it might. At present the vent is on the return side of the pump so if anything I would think this would give the least chance of pumping over. Is there a bypass fitted? Commonly just a link pipe between feed and expansion with perhaps a gate valve in it? -- *The fact that no one understands you doesn't mean you're an artist Dave Plowman London SW To e-mail, change noise into sound. |
#15
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Why loft vents for boiler and immersion cylinders?
On Sun, 05 Mar 2006 09:22:08 +0000 (GMT), Tony Williams
wrote: In article , Dave Baker Dave wrote: http://www.diydata.com/planning/cent...ing/boiler.htm Then my pump would be on the blue line immediately adjacent to the boiler, pumping into it.............. That's where our pump is.... in the return line, and immediately next to the boiler. It is the original 1970 plumbing and works ok. .............and then back out into the line that feeds the vent and then the rads and cylinder. The vent is therefore in the wrong place, before the rads rather than after them and hence seeing all the pump pressure. ISTM that if the radiator loops are free-flowing, then the pump will pull a low pressure on the pipe feeding the loops, lower than the head required by the vent pipe. Radiator circulation is tickety-boo. But if the radiator loops get blocked, (by sludge, or later fitted valves?) then the pump will preferentially do a local circulation, in just the loop between the header tank and the vent pipe. Any chance that that is what you are seeing? All of this can be very easily avoided and the risk of pumping over eliminated by positioning the FE and vent pipes on the same side of the boiler. There should be a clear path from the boiler flow side to the vent with nothing in the way in terms of pumps or valves. The FE pipe can be connected to a point on the circuit within 150mm of where the vent pipe connects. The pump is located after that, followed by the motorised valve(s). An even better solution is to use an Aerjec air separator which will do the correct plumbing connections in one place as well as helping to purge the system of air as it is circulated following refilling and in general. The flow through the radiators then becomes irrelevant and if inhibitor is used, no significant corrosion or sludgng either. Another issue to consider is that if TRVs are used then the flow resistance through the CH circuit will increase anyway as they start to close, so it having an arrangement where avoiding pumping over/sucking down is on the basis of clear path through the CH circuit is never going to be clear of potential problems. -- ..andy |
#16
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Why loft vents for boiler and immersion cylinders?
"David Hansen" wrote in message ... On Sun, 5 Mar 2006 00:17:08 -0000 someone who may be "Dave Baker" Dave wrote this:- I'm actually a rather competent engineer So you claim. However, in my view a competent engineer would have found out what was going on and then sorted it out at source, rather then dealing with the symptoms without knowing what they were doing. Finding out what was going on is fairly simple, as it is an elementary part of building services engineering. For example in a library one can find, "Faber and Kell's Heating and Air-conditioning of Buildings", the book on the subject. In there one should find some examples of piping layouts. http://www.foyles.co.uk/foyles/display.asp?K=181613010522833&M=310&WHERE=(keyword +INCLUDES+'heating')&SS=( Finding out would also involve tracing out the pipes, something you say you have only just done. who was hoping for reasoned opinion on the merits of this vent. From my 1984 edition of the above book, page 190, "In no circumstances should the feed and expansion pipe be combined with the system vent pipe as case D. This practice was shown to be dangerous more than 50 years ago." I don't know what context this passage was written. Combined feed and expansion pipes are common and inceasingly copmmon as 99% of boioer has a high limit stat If a boiler has a high limit stat (suitabkle for sealed system) it can have a combined feed & expansion pipe that must be 22mm minimum. The reason why it is dangerous should be obvious. It is to do with what happens if this one pipe is restricted or blocked, A a normal sealed system in millions of homes:- If the blow-off valve is seized and the main boiler stat fails as well, the only protection is the high limit device. It is exactly the same protection level with a combined feed and expansion pipe, except that to block a 22mm pipe will a hell of a lot more difficult on the flow at high level, where they are supposed to be, and are specifically for this reason (no crud at high level), than a blow-off valve failing. Which means a combined feed and expansion pipe setup is safer. The reason why 22mm pipe is used as a minum (some require that size because of system size), is so that the probability of being blocked is minimum. A blow-off pipe on a sealed system in most domestic homes is only 15mm. especially if it is only 15mm. You are living on borrowed time and should sort it out immediately. He says he has a blow-off valve. If so, the explosion danger is minimum. If the boiler is suitable for a sealed systemn, which it appears to be with a blow off valve on it (I am assuming the valve is integral with the boiler, not an add on), then it will have a high limit stat which improve boiler protection. If not suitable for sealed systems then he has no boiler protection. BTW, your one safety valve may have been cleaned and the washer replaced a few times. What pressure is it set at? How often is the operation of the valve tested? Can it pass the necessary volume of hot water/steam? |
#17
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Why loft vents for boiler and immersion cylinders?
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#18
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Why loft vents for boiler and immersion cylinders?
Dave Baker wrote: In the event of a control failure, it is a safety device; it releases steam, prevents the system becoming over-pressurized and bursting. In your system, such a failure would probably now cause the contents of the heating system to be discharged into the loft and the boiler would dry-fire to destruction. Nonsense. The system isn't pressurised other than by the head of water from the loft tank. The contents of the system can't be discharged into the loft other than by the same pipe from the bottom of the loft tank which is continuously filling it up anyway. You and Drivel have misunderstood what I have written. It is not nonsense, it is common sense. If the boiler thermostat fails in the ON position, the temperature of the water will quite likely exceed 100 degC. The water in the boiler will boil, producing steam. This happens. Your heating system will THEN be pressurized by the steam and the steam pressure will become greater than the static pressure provided by the head of water in the F&E tank. The water in the heating system will be pushed up the cold feed pipe into the F&E tank. It will be pushed out rapidly, probably faster than the F&E overflow pipe can remove it. There will be no water in the boiler and it will continue firing. This assumes that the cold feed pipe is clear and that there is not a stopcock (acting as a non return valve) fitted to it. The cold feed on my heating system was totally blocked with limescale when I bought the house. This is a common fault. I had to cut out the tee and replace it. There had been a longstanding leak from the heating system through the coil in the indirect cylinder. With a non-fubarred system, such a failure would cause steam to be blown out of the open vent, but cold make-up water would enter the system through the cold feed. This could continue indefinitely. You can't get 2-way flow (steam up & water down) in one pipe, which is probably what Faber & Kell were referring to. Their book (20 years since I had a copy) deals with commercial installations on which such a combined CF &OV would be inadvisable. |
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Why loft vents for boiler and immersion cylinders?
Tony Williams wrote: BTW: My old plumbing book has a gruesome tale about a plumber who blocked a vent pipe with a cork, to try and reduce the amount of water lost during a drain down. The resultant vaccuum caused parts of the plumbing to collapse inwards. Blocking a vent pipe may not be good news. Good point sir! Probably the copper hot water storage cylinder, which will be crushed by atmospheric pressure if you were to drain it without relieving the vacuum (hose out bathroom window, no hot taps open). On unvented hot water storage cylinders the mandatory T&P relief valve also acts as a vacuum breaker valve (I think, goes off to get book to check). |
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Why loft vents for boiler and immersion cylinders?
On 5 Mar 2006 04:21:34 -0800, "Aidan" wrote:
Tony Williams wrote: BTW: My old plumbing book has a gruesome tale about a plumber who blocked a vent pipe with a cork, to try and reduce the amount of water lost during a drain down. The resultant vaccuum caused parts of the plumbing to collapse inwards. Blocking a vent pipe may not be good news. Good point sir! Probably the copper hot water storage cylinder, which will be crushed by atmospheric pressure if you were to drain it without relieving the vacuum (hose out bathroom window, no hot taps open). True... I was able very easily to collapse a vented system cylinder to a very small size using a domestic vacuum cleaner - it was quite surprising. As a heating engineer who visited to service my parents' system on one occasion remarked ".. as thin as bloody fag paper.." -- ..andy |
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Why loft vents for boiler and immersion cylinders?
"Aidan" wrote in message oups.com... Tony Williams wrote: BTW: My old plumbing book has a gruesome tale about a plumber who blocked a vent pipe with a cork, to try and reduce the amount of water lost during a drain down. The resultant vaccuum caused parts of the plumbing to collapse inwards. Blocking a vent pipe may not be good news. Good point sir! Probably the copper hot water storage cylinder, which will be crushed by atmospheric pressure if you were to drain it without relieving the vacuum (hose out bathroom window, no hot taps open). I have seen that happen a few times, evn being open vented and not blocked On unvented hot water storage cylinders the mandatory T&P relief valve also acts as a vacuum breaker valve (I think, goes off to get book to check). |
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Why loft vents for boiler and immersion cylinders?
On Sun, 5 Mar 2006 13:45:05 -0000, "Doctor Drivel"
wrote: | |"Aidan" wrote in message roups.com... | | Tony Williams wrote: | | BTW: My old plumbing book has a gruesome tale about | a plumber who blocked a vent pipe with a cork, to try | and reduce the amount of water lost during a drain | down. The resultant vaccuum caused parts of the | plumbing to collapse inwards. Blocking a vent pipe | may not be good news. | | Good point sir! Probably the copper hot water storage cylinder, which | will be crushed by atmospheric pressure if you were to drain it without | relieving the vacuum (hose out bathroom window, no hot taps open). | |I have seen that happen a few times, evn being open vented and not blocked | | On unvented hot water storage cylinders | the mandatory T&P relief valve | also acts as a vacuum breaker valve | (I think, goes off to get book to check). Done that myself :-( Should have known better. :-( -- Dave Fawthrop dave hyphenologist co uk Freedom of Speech, Expression, Religion, and Democracy are the keys to Civilization, together with legal acceptance of Fundamental Human rights. |
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Why loft vents for boiler and immersion cylinders?
"Aidan" wrote in message oups.com... Dave Baker wrote: In the event of a control failure, it is a safety device; it releases steam, prevents the system becoming over-pressurized and bursting. In your system, such a failure would probably now cause the contents of the heating system to be discharged into the loft and the boiler would dry-fire to destruction. Nonsense. The system isn't pressurised other than by the head of water from the loft tank. The contents of the system can't be discharged into the loft other than by the same pipe from the bottom of the loft tank which is continuously filling it up anyway. You and Drivel have misunderstood what I have written. It is not nonsense, it is common sense. I never mosunderstodd at all and I agree with you. I was looking into what he had. If the boiler is a sealed compatible boiler (which it "appears" to be) then there is no immediate chance of explosion, and as I said get it sorted ASAP. If the boiler thermostat fails in the ON position, the temperature of the water will quite likely exceed 100 degC. The water in the boiler will boil, producing steam. This happens. Your heating system will THEN be pressurized by the steam and the steam pressure will become greater than the static pressure provided by the head of water in the F&E tank. If a sealed compatible boiler then the high limit cuts in. Another protection level. The water in the heating system will be pushed up the cold feed pipe into the F&E tank. It will be pushed out rapidly, probably faster than the F&E overflow pipe can remove it. There will be no water in the boiler and it will continue firing. This assumes that the cold feed pipe is clear and that there is not a stopcock (acting as a non return valve) fitted to it. The cold feed on my heating system was totally blocked with limescale when I bought the house. This is a common fault. I had to cut out the tee and replace it. There had been a longstanding leak from the heating system through the coil in the indirect cylinder. That is why on combined feed & expansion pipes it has to be 22mm minimum. The one pipe has system water move up and down the pipe, so water with inhibitor will be passing the tee reducing the liklihood of only fresh water being there leaving behind scale. In very hard water areas it is best to fit a 28mm tee and a small length of 28mm pipe. An aerator can be fitted instead of a tee. Have compression joints for disconnection purposes and the unit can have the odd clear out in case. The aerators have a greater volume inside, so les lilely to scaleup, and are recommended by the likes of Baxi and Potterton on combined feed and expansion pipes. With a non-fubarred system, such a failure would cause steam to be blown out of the open vent, but cold make-up water would enter the system through the cold feed. This could continue indefinitely. You can't get 2-way flow (steam up & water down) in one pipe, which is probably what Faber & Kell were referring to. Their book (20 years since I had a copy) deals with commercial installations on which such a combined CF &OV would be inadvisable. Yep. You can also get water circulation in one pipe. I have come across that before. |
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Why loft vents for boiler and immersion cylinders?
"Aidan" wrote in message oups.com... Doctor Drivel wrote: I never misunderstodd at all and I agree with you. I was looking into what he had. If the boiler is a sealed compatible boiler (which it "appears" to be) then there is no immediate chance of explosion, and as I said get it sorted ASAP. You can't have read it then. Re the pressure relief valve, he said; It's been checked, cleaned and the washer replaced a couple of times and is fine. In any case the system is always vented to the bottom of the loft tank as I have said. He has dismantled the safety valve. ...and cleaned it. The ones I've seen in the past 10 or 15 years were factory pre-set, no user adjustable parts. It's probably a spring-loaded antique and the setting has been lost in dismantling. Some of them you could split and clean, he has done that. That does not mean it is now unoperatational. The boiler is probably a similar vintage. Almost certainly not suitable for sealed system operation and no manual-reset secondary thermostat. "every" boiler I have seen with an integral pressure relief valve has been suitable for a sealed system (why is it there?), that is going back to boilers made 30 years ago (a few still around). In ye olden dayes, a presure relief valve was fitted to the flow pipe of open vented boilers. This would blow off in the kitchen. It was made illegal and required a pipe to outside. Then they never required one at all on open vented systems. Now it hasn't got an open vent or a working safety valve either. I told him to check the suitability of the boiler for sealed systems. I would be confident the valve would work. |
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Why loft vents for boiler and immersion cylinders?
On Sun, 5 Mar 2006 11:04:58 -0000 someone who may be "Doctor Drivel"
wrote this:- I don't know what context this passage was written. "A traditional boiler, loft tank, vented cylinder type affair." He says he has a blow-off valve. Correct. However, that does not answer the three questions I asked about it. -- David Hansen, Edinburgh I will *always* explain revoked encryption keys, unless RIP prevents me http://www.opsi.gov.uk/acts/acts2000/00023--e.htm#54 |
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Why loft vents for boiler and immersion cylinders?
On Sun, 5 Mar 2006 13:58:44 -0000 someone who may be "Doctor Drivel"
wrote this:- That is why on combined feed & expansion pipes it has to be 22mm minimum. Here you appear to be mixing up two pipes. The first pipe is the feed and expansion pipe, the second pipe is the vent pipe. This is strange as you got it right earlier in the thread. The one pipe has system water move up and down the pipe, The name feed and expansion pipe is something of a clue. In such a pipe water will/should indeed move up and down, as the system is warmed up or cools down. As it happens water will also move up and down the vent pipe, because the level of water in the vent pipe will/should be the same as the level of water in the F & E tank. -- David Hansen, Edinburgh I will *always* explain revoked encryption keys, unless RIP prevents me http://www.opsi.gov.uk/acts/acts2000/00023--e.htm#54 |
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Why loft vents for boiler and immersion cylinders?
"David Hansen" wrote in message ... On Sun, 5 Mar 2006 13:58:44 -0000 someone who may be "Doctor Drivel" wrote this:- That is why on combined feed & expansion pipes it has to be 22mm minimum. Here you appear to be mixing up two pipes. Nope. A combined feed and expansion pipe is one pipe. Legal on systems which sealed system compatible boilers may be fitted. And no need to have a blow-off valve either. The one pipe has system water move up and down the pipe, The name feed and expansion pipe is something of a clue. Yes it is. I have the clue and also explained. You should understand what it is. |
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Why loft vents for boiler and immersion cylinders?
On Sun, 5 Mar 2006 16:01:37 -0000 someone who may be "Doctor Drivel"
wrote this:- Here you appear to be mixing up two pipes. Nope. Yet you then go on to make precisely the same mistake again. A combined feed and expansion pipe is one pipe. A feed and expansion pipe is indeed one pipe. However, as I said and you snipped, you appear to be mixing up this one pipe with the vent pipe, which is another pipe. As I said, this is strange as you got it right earlier. Bluff and bluster on this again, if you wish. -- David Hansen, Edinburgh I will *always* explain revoked encryption keys, unless RIP prevents me http://www.opsi.gov.uk/acts/acts2000/00023--e.htm#54 |
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Why loft vents for boiler and immersion cylinders?
"David Hansen" wrote in message ... On Sun, 5 Mar 2006 16:01:37 -0000 someone who may be "Doctor Drivel" wrote this:- Here you appear to be mixing up two pipes. Nope. Yet you then go on to make precisely the same mistake again. A combined feed and expansion pipe is one pipe. A feed and expansion pipe is indeed one pipe. However, as I said and you snipped, you appear to be mixing up this one pipe with the vent pipe, which is another pipe. As I said, this is strange as you got it right earlier. Bluff and bluster on this again, if you wish. It is the vent pipe as air works its way up this pipe. Air doesn't care. It will go up any pipe. |
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Why loft vents for boiler and immersion cylinders?
A feed and expansion pipe is indeed one pipe. However, as I said and
you snipped, you appear to be mixing up this one pipe with the vent pipe, which is another pipe. As I said, this is strange as you got it right earlier. At the risk of agreeing with Drivel, a combined feed and expansion pipe also handles the venting. There is only one 22mm pipe from the system to the loft. This pipe handles feeding of the system with water, expansion from the system into the header tank and venting of air or steam to the loft space. It splits into 2 at the bottom of the tank and a vent only pipe then continues above the tank. Christian. |
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Why loft vents for boiler and immersion cylinders?
"Christian McArdle" wrote in message .. . A feed and expansion pipe is indeed one pipe. However, as I said and you snipped, you appear to be mixing up this one pipe with the vent pipe, which is another pipe. As I said, this is strange as you got it right earlier. At the risk of agreeing with Drivel, As I know more about it than anyone else just read and take heed. a combined feed and expansion pipe also handles the venting. There is only one 22mm pipe from the system to the loft. This pipe handles feeding of the system with water, expansion from the system into the header tank and venting of air or steam to the loft space. It splits into 2 at the bottom of the tank and a vent only pipe then continues above the tank. It doesn't split at all. It is one 22mm pipe to the bottom of the F&E tank. Been standard for years. As 95% of all boilers are sealed system compatible, doing it this way saves on pipe, time and no pump over or drawing of air in. Potterton/Baxi specify a air ejector when the combined Feed and expansion pipe meets the system. Works very well. With this method extremely low heads can be attained (200mm from top of boiler). |
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Why loft vents for boiler and immersion cylinders?
On 9 Mar 2006 10:21:06 -0800, "legin"
wrote: I went to the recent Homebuilding show at the Nec. The reason was that having googled and followed recent threads I was thinking that the best probable solution would indeed be to fit a heatbank in my self build. I went with the specific question in mind. How do you keep the condednsing boiler condensing if a temperature of circa 75 degrees is required for the heatbank. I even suggested mixing the return from the heatbank with the return from the underfloor heating to get the return temp down enough to get lull the boiler into condensing mode. Apart from some exhibitors being unsure of how a system could be piped, the overall conclusion was to fit an unvented cylinder. This would take better advantage of a condensing boiler. Anyone any better advice to offer. Regards Legin One thing to bear in mind is that a boiler does not reach Nirvana or orgasm when it "goes into condensing mode". What actually happens for boilers designed for condensing is that there is an efficient heat exchanger able to work with a temperature differential between return and flow of 20 degrees and possible more. The lower the return temperature, the more efficiently the boiler is running. This happens regardless of whether it is condensing or not. What happens at the dew point - around 54 degrees - below which condensing takes place, is that the *rate of change* of efficiency with return temperature increases below this point. This is as a result of the contribution of the latent heat that is released from the phase change of water from gas (i.e. steam from combustion) to liquid. Note that I am talking about steam in the true and invisible sense here and not "steam" that is visible and is in fact, water vapour. There isn't a step change of efficiency at the dew point - just a knee in the curve. In terms of optimising overall efficiency, anything that can be done to reduce the temperature of the return water to the boiler will help. UFH is possibly one aspect for this. Another, if you are going to use radiators, is to make sure that these give the heat required when you run them at 70 degree flow and 50 return. Conventionally, radiators are sized based on 82 and 70. To achieve 70/50 requires them to be approximately a third higher nominal output when choosing from the manufacturer datasheet. The effect of doing this is to run the boiler at a lower temperature overall for more of the heating season. Where a heatbank is used for water heating, normally the objective is to maintain it at as high a temperature as is reasonably practicable - i.e. 82 degrees. THe implication is that the return would be at around 60 degrees and you are out of condensing range. This is not really a problem for several reasons: - The cylinder will cool as HW is run with cool water replacing hot at the bottom. The plate heat exchangers used are able to trasnfer heat very efficently to the cold water (100-200kW equivalent is typical), so quite a drop in temperature in water returned to the cylinder. - The point at which the boiler fires can be arranged to be when the water is quite a bit cooler such that in any case there is a low return temperature to the boiler. It is only going to reach the 62 degree point relatively late in the reheat cycle if adjusted correctly. There is not really a lot of point, therefore, in striving to achieve 55 return by reducing the flow to 75 max. because also you will lose heat storage capacity in the heatbank -- ..andy |
#33
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Why loft vents for boiler and immersion cylinders?
"legin" wrote in message ups.com... I went to the recent Homebuilding show at the Nec. The reason was that having googled and followed recent threads I was thinking that the best probable solution would indeed be to fit a heatbank in my self build. I went with the specific question in mind. How do you keep the condednsing boiler condensing if a temperature of circa 75 degrees is required for the heatbank. I even suggested mixing the return from the heatbank with the return from the underfloor heating to get the return temp down enough to get lull the boiler into condensing mode. A plate heat exchanger is "highly" efficient. It can take in 80C primary water from the store and have 25C coming out of the plate, transferring all the heat to the incoming cold mains. This 25C water is pumped directly into the bottom of the store, where the return pipe to the condensing boiler is. So, very cool water at the bottom. Water baffles prevent de-stratification. Look at: http://www.heatweb.com/products/cyli...operation.html Ignore the solar and gravity circulation. Dedicated UFH heat banks have a cooler lower section for UFH. Look at the return from the plate heat ex, it goes into the bottom of the store. Also the UFH blend cool water the bottom with warmer water a bout 1/4 to 1/3 of the way up. The boiler return is right at the bottom where all the cool water returns promoting condensing. A store may be 75C at the top, but stratification will ensure that the lower section may be around 25 to 30C. All looking good. With two cylinder stats to eliminate inefficient boiler cycling, the boiler is only called in to reheat the whole store with one long efficient burn. The return water is a very low temperature and promotes condensing efficiency. The ignorant salesmen who spoke to you think, oh run temp of 75C, dew-point 54C, so no condensing. Total tripe. You need to understand the operation. Look at http://www.sedbuk.com Look at the ACV HeatMaster, a combined boiler/thermal store. It is one of the most efficient boilers there. "Direct" boiler heated heat banks (using a plate) are very efficient. Thermal stores use an inefficient (to the plate) coil for DHW take off. These do not promote a lower return temp as much. Apart from some exhibitors being unsure of how a system could be piped, the overall conclusion was to fit an unvented cylinder. That is tripe. http://www.waterheaterblast.com And an annual service charge for one too. Say it lasts 20 years that is £1600 minimum just to service it at today's rates; that is to have a cylinder of hot water standing there. In reality it will be much, much, more. At that price you could afford to replace a thermal store every 10 years and still ahead of the game. Many stores are guaranteed 20 years for the cylinder anyway. This would take better advantage of a condensing boiler. It would not. Most unvented cylinders do not have a quick recovery coil. Better than Part L, not quick recovery. Anyone any better advice to offer. Regards Legin |
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Why loft vents for boiler and immersion cylinders?
"Andy Hall" wrote in message ... On 9 Mar 2006 10:21:06 -0800, "legin" wrote: I went to the recent Homebuilding show at the Nec. The reason was that having googled and followed recent threads I was thinking that the best probable solution would indeed be to fit a heatbank in my self build. I went with the specific question in mind. How do you keep the condednsing boiler condensing if a temperature of circa 75 degrees is required for the heatbank. I even suggested mixing the return from the heatbank with the return from the underfloor heating to get the return temp down enough to get lull the boiler into condensing mode. Apart from some exhibitors being unsure of how a system could be piped, the overall conclusion was to fit an unvented cylinder. This would take better advantage of a condensing boiler. Anyone any better advice to offer. Regards Legin One thing to bear in mind is that a boiler does not reach Nirvana or orgasm when it "goes into condensing mode". What actually happens for boilers designed for condensing is that there is an efficient heat exchanger able to work with a temperature differential between return and flow of 20 degrees and possible more. The lower the return temperature, the more efficiently the boiler is running. This happens regardless of whether it is condensing or not. What happens at the dew point - around 54 degrees - below which condensing takes place, is that the *rate of change* of efficiency with return temperature increases below this point. This is as a result of the contribution of the latent heat that is released from the phase change of water from gas (i.e. steam from combustion) to liquid. Note that I am talking about steam in the true and invisible sense here and not "steam" that is visible and is in fact, water vapour. There isn't a step change of efficiency at the dew point - just a knee in the curve. In terms of optimising overall efficiency, anything that can be done to reduce the temperature of the return water to the boiler will help. UFH is possibly one aspect for this. Another, if you are going to use radiators, is to make sure that these give the heat required when you run them at 70 degree flow and 50 return. Conventionally, radiators are sized based on 82 and 70. To achieve 70/50 requires them to be approximately a third higher nominal output when choosing from the manufacturer datasheet. The effect of doing this is to run the boiler at a lower temperature overall for more of the heating season. Where a heatbank is used for water heating, normally the objective is to maintain it at as high a temperature as is reasonably practicable - i.e. 82 degrees. Wrong. Modern banks are 75C THe implication is that the return would be at around 60 degrees and you are out of condensing range. Wrong. See my explanation. This is not really a problem for several reasons: - The cylinder will cool as HW is run with cool water replacing hot at the bottom. The plate heat exchangers used are able to trasnfer heat very efficently to the cold water (100-200kW equivalent is typical), so quite a drop in temperature in water returned to the cylinder. - The point at which the boiler fires can be arranged to be when the water is quite a bit cooler such that in any case there is a low return temperature to the boiler. It is only going to reach the 62 degree point relatively late in the reheat cycle if adjusted correctly. There is not really a lot of point, therefore, in striving to achieve 55 return by reducing the flow to 75 max. because also you will lose heat storage capacity in the heatbank You size to suit. |
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Why loft vents for boiler and immersion cylinders?
On Thu, 9 Mar 2006 17:00:52 -0000 someone who may be "Christian
McArdle" wrote this:- At the risk of agreeing with Drivel, a combined feed and expansion pipe also handles the venting. There is only one 22mm pipe from the system to the loft. This pipe handles feeding of the system with water, expansion from the system into the header tank and venting of air or steam to the loft space. It splits into 2 at the bottom of the tank and a vent only pipe then continues above the tank. You appear to be describing a particular system. If so then it is far more dangerous than one with separate feed & expansion and vent pipes. Unless, of course, other precautions are taken that are roughly equivalent. -- David Hansen, Edinburgh I will *always* explain revoked encryption keys, unless RIP prevents me http://www.opsi.gov.uk/acts/acts2000/00023--e.htm#54 |
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Why loft vents for boiler and immersion cylinders?
How do you keep the condednsing boiler condensing if a
temperature of circa 75 degrees is required for the heatbank. It is the return temperature that determines condensing efficiency, not the flow temperature. The temperature at the bottom of the heatbank, provided the thermostatic control is good, should actually be quite low. Christian. |
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Why loft vents for boiler and immersion cylinders?
On 10 Mar 2006 23:45:17 -0800, "legin"
wrote: It is the return temperature that determines condensing efficiency, not the flow temperature. The temperature at the bottom of the heatbank, provided the thermostatic control is good, should actually be quite low. Christian. If that is the case, what will be the flow temp. Assuming that the boiler will lift the temp say 20 degrees. If the return temp is say 45 then the flow temp will be 65. Going through a heat bank previously heated to say 75, then it will have a cooling effect on the heatbank. Thanks to Andy for the detailed response. I understand what you are saying about the knee in the curve. However at this stage it would be nice to get it right and have the most efficient system. That to me means making sure that the condensing boiler actually condenses. The heat bank technology is completely new to me. Is there not a boiler out there that could supply heating to the heatbank at say 75 degrees until it is totally satisfied then reduce its temp down to say 65, to ensure that the return is well within the condensing range. I know that this would mean using a S plan to supply the heatbank and not actually use it to feed the rad circuits and underfloor circuits. Or could it be plumbed as a heatbank supplying the rad/ ufh circuits, with a low return as Christian suggests. Would the boiler then be capable of lifting the temp say 25 degrees. Also dare i say thanks to drivel. I know his ramblings have been the source of a lot of banter, but I have got to admit that it does amuse me. More importantly he has raised my awareness of heatbanks to the point where I am now seriously considering using one. Legin Yes. I have the MAN (now MHG) Micromat EC and it will do precisely that. http://www.mhg.de/en/products/gas_un...cromat_ec.html In the UK, this unit is sold by Eco Hometec and targetted (among other places) for the homebuild market. MHS boilers sell it as the Strata 1 more for commercial applications where several can be clustered for more output. http://www.mhsboilers.com/boilers/premix/strata1.htm http://www.eco-hometec.co.uk/EC30.htm I mention the MHS site because it has much better brochures and technical manuals and the product is the same. This boiler has a wide modulating range - down to 3kW on some models - and a very good build quality. Servicability is also good in that all major components push fit and clip onto the back plate and can be swapped very quickly. The internal controller has - Weather compensation. A sensor located outside provides the temperature and the boiler will adjust output as that changes. For UFH this can be helpful because heat output from the floor can't be quickly adjusted. Because of the insulating effect of the house an inside sensor knows about outside temperature change much later than if it is measured directly - Analogue sensing of HW cylinder/store temperature. There is a sensor which fits into a pocket in the cylinder which places it in the middle rather than the surface. The boiler knows the store temperature and a reheat cycle can be triggered at a programmable temperature. - Optionally, analogue sensing of room temperature. There is a programmer made by Siemens for this boiler which gives it the actual room temperature to use rather than just a controller telling the boiler to switch on and off. This provides better results when combined with the weather compensator. - Analogue control of the pump. Water flow is optimised to match the boiler output and thus the temperature difference across the heat exchanger is optimised. - Control of motorised valves. There is an option on the boiler to have an internal diverter valve, but a better solution is to use either an external diverter valve or zone valves (S plan). There are installer settings on the controller which allow the boiler to control either scenario directly - i.e. you don't need an external controller. The controller has about 40 different combinations of operational settings for different max flow temperatures, valve operations, external controls. You can set the weather compensation curve, which basically means the weather compensated flow temperatures at 20 and -1 degrees outside. Max. flow temperatures in CH mode can be set for systems with radiator outputs designed for conventional boilers (85), condensing (70) and UFH (55). My system had a conventional boiler originally and I changed radiators where needed to give enough output at 70. If you want to run radiators and UFH, then the normal way is to run either a separate zone or one derived from the main CH with a separate pump and mixing valve which will blend some of the UFH return water with flow at 70 degrees to provide a low flow temperature for the UFH. In CH operation, I find that the boiler will modulate down to a flow temperature of about 40 degrees or so when the weather is relatively warm and will sit all day doing that. In colder weather, it's rare that it goes over 60 degrees. There can be as much as a 25 degree difference across the heat exchanger. The pump speed drops to as low as 35% of max output. HW reheat operation depends on one of two things. The cylinder temperature has dropped below the low set point (in my case 55 degrees and a storage temperature of 60 degrees) - it would probably be 85 and 80 or possibly 85 and 75 for a store depending on size. If the boiler detects the cylinder temperature dropping rapidly - i.e you just started running a bath and a shower, then it will start much earlier. This prevents regular reheats when small amounts of water are being used, but begins reheat earlier when there are large amounts. The boiler controller switches over the zone valves and winds the boiler and pump up to full power. The return temperature is low until the last couple of minutes of the cycle, whereupon the power level and pump speeds are gradually reduced. This prevents the cylinder temperature from overshooting and maintains the boiler return temperature as low as possible. In practice all of this works very well. However the boiler does cost around 60-100% more than other good quality boilers. -- ..andy |
#38
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Why loft vents for boiler and immersion cylinders?
"legin" wrote in message oups.com... It is the return temperature that determines condensing efficiency, not the flow temperature. The temperature at the bottom of the heatbank, provided the thermostatic control is good, should actually be quite low. Christian. If that is the case, what will be the flow temp. Assuming that the boiler will lift the temp say 20 degrees. If the return temp is say 45 then the flow temp will be 65. Going through a heat bank previously heated to say 75, then it will have a cooling effect on the heatbank. Thanks to Andy for the detailed response. I understand what you are saying about the knee in the curve. However at this stage it would be nice to get it right and have the most efficient system. That to me means making sure that the condensing boiler actually condenses. The heat bank technology is completely new to me. Is there not a boiler out there that could supply heating to the heatbank at say 75 degrees until it is totally satisfied then reduce its temp down to say 65, to ensure that the return is well within the condensing range. I know that this would mean using a S plan to supply the heatbank and not actually use it to feed the rad circuits and underfloor circuits. Or could it be plumbed as a heatbank supplying the rad/ ufh circuits, with a low return as Christian suggests. Would the boiler then be capable of lifting the temp say 25 degrees. Also dare i say thanks to drivel. I know his ramblings have been the source of a lot of banter, but I have got to admit that it does amuse me. More importantly he has raised my awareness of heatbanks to the point where I am now seriously considering using one. Legin Please use paragraphs The great thing about a heat bank is that a simpler, cheaper, less complicated boiler can be fitted. The way the cylinder is arranged ensures stratification has low temperatures at the bottom of the cylinder. The 75C is only at the top section of the cylinder, for DHW purposes. The lower section will always be much lower temperature than this. There are baffles in the cylinder to prevent water mixing. The plate heat exchanger can ensure that water fed back into the bottom of the heat bank is around 25C. You could insist on a double pass plate heat exchanger be fitted which would ensure this sort of return temperature and high flowrates in DHW on full load. Another point about a heat banks is that a smaller boiler can be used. Boilers operating directly on heating systems are sized for "peak" use. On heat banks/thermal stores only "average" use is required. The thermal storage fills the peaks. But also when fitting a boiler "directly" to a heat bank, not via a coil, a "very large" boiler can be fitted too. This will give pronto DHW recovery. So you have the best of both to choose from. Most boilers modulate their output these days, and the most cost effective boilers are in the 25 - 30kW range. So getting the largest you can at a good price is worth it as the heat bank will not complain and still no cycling. I personally would consider a Glow HXi30, 30kW, boiler mated to a heat bank. It is a Vaillant underneath, stainless heat exchanger, cheap enough, quiet and very, very good. They do have different sizes and the boiler keeps a constant output modulating along the way. Going over in kW size is not a problem http://www.uselessenergy.org.uk/boilers_prices.asp Do not use S plans and the likes. Take everything off the heat bank using pumps which don't restrict flow. It is a wonderful central neutral spot. Insist on "two" cylinder anti-cycle stats on the heat bank. This prevents anti-cycling. When heating, the store is heated to 75C, then it cools to 60C before the boiler cuts in. So no on-off, on-off of the boiler on the one cylinder stat. The stats are placed so that the bottom of the store still remains very, very cool. Look at the DPS diagrams http://www.heatweb.com So-called professional people who say a condensing boiler will not condense when mated to a thermal store/heat bank are just plainly thick. |
#39
Posted to uk.d-i-y
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Why loft vents for boiler and immersion cylinders?
"Christian McArdle" wrote in message ... If that is the case, what will be the flow temp. Assuming that the boiler will lift the temp say 20 degrees. If the return temp is say 45 then the flow temp will be 65. Going through a heat bank previously heated to say 75, then it will have a cooling effect on the heatbank. Nope. If you take water out at 25C and return it at 45C, then it will heat the heatbank, even if most of it was previously at 75C and the hot water is deposited at the top. Is there not a boiler out there that could supply heating to the heatbank at say 75 degrees until it is totally satisfied then reduce its temp down to say 65, to ensure that the return is well within the condensing range. Worcester Bosch Greenstar System with the optional diverter valve allows separate setting of water and CH temperatures. You can further subzone the heating side with S-Plan if you have multiple zones. I have the boiler without the diverter and was only aware of it from reading the instructions. I seriously wish I had bought the option, as it would have enabled me to run the heating at a much lower temp. The W-Bosch setup. Do they extra controls for DHW and CH and it diverts to suit? I can't remember now. IIRC, the W-B maintains a constant flow temp and modulates to maintain that. You can install your own diverter valve and fit a weather compensator. It will switch in and out the boiler to maintain the compensator setpoint, which will be low most of the time. Compensators have anti-cycle control on them. |
#40
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Why loft vents for boiler and immersion cylinders?
The W-Bosch setup. Do they extra controls for DHW and CH and it diverts
to suit? I can't remember now. It's a diverter, rather than a 3 way. DHW priority and separate flow temp controls. The DHW side is limited to 75C. The CH side to 85C. I would have preferred it the other way round as I have indirect heat bank heating and would have liked 82-85C for the hot water and 70C for the heating, but it should be possible to swap the sides (possibly with a relay to invert the priority). IIRC, the W-B maintains a constant flow temp and modulates to maintain that. That is my understanding and why I think it would be possible to run the hot water from the CH side. You can install your own diverter valve and fit a weather compensator. It will switch in and out the boiler to maintain the compensator setpoint, which will be low most of the time. Compensators have anti-cycle control on them. How would you get it to go hotter for the water with an external diverter? Christian. |
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