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| UK diy (uk.d-i-y) For the discussion of all topics related to diy (do-it-yourself) in the UK. All levels of experience and proficency are welcome to join in to ask questions or offer solutions. |
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Upgrade to a Condensing boiler - yes or no?
Aside from my other post re. repairing existing boiler. I am tempted
by the higher efficiencies of the condensing boilers but are there hidden problems in upgrading an existing installation. I do not need a combined boiler - I have HW cylinder and pump / valves. Concerns I have are -: Cleanliness of existing system - any prerequisites? Will existing rads be ok - presuming that water temp is lower???? TIA. Rob |
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Upgrade to a Condensing boiler - yes or no?
Thanks - very informative.
One point on the modulation - I have an external pump and valves .. should I go for a boiler with internal pump so the boiler can vary it as needed .. I presume that using the existing pump will not allow full control over the flow by the boiler other than on / off. So many boiler options .. Ideal Icos is on the short list |
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Upgrade to a Condensing boiler - yes or no?
"robf" wrote in message m... Aside from my other post re. repairing existing boiler. I am tempted by the higher efficiencies of the condensing boilers but are there hidden problems in upgrading an existing installation. I do not need a combined boiler - I have HW cylinder and pump / valves. Concerns I have are -: Cleanliness of existing system - any prerequisites? Have it flushed out. Put in flushing agent before scrapping it. Flush with fresh water about three times. Will existing rads be ok - presuming that water temp is lower???? Some modern modulating condensing boilers are designed for existing 80C temp installations. It modulates to suit. If it needs full 80C it gives it. Most of the time it will be on part load If you buy a boiler which modulates the internal pump, then just remove the existing remote pump. Simple. --- -- Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.507 / Virus Database: 304 - Release Date: 05/08/2003 |
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Upgrade to a Condensing boiler - yes or no?
Andy Hall wrote:
On Tue, 26 Aug 2003 18:44:55 +0100, Ed Sirett wrote: Andy Hall wrote: On 23 Aug 2003 05:46:20 -0700, (robf) wrote: Aside from my other post re. repairing existing boiler. I am tempted by the higher efficiencies of the condensing boilers but are there hidden problems in upgrading an existing installation. I do not need a combined boiler - I have HW cylinder and pump / valves. Concerns I have are -: Cleanliness of existing system - any prerequisites? Will existing rads be ok - presuming that water temp is lower???? TIA. Rob There are a few areas to be considered, but overall, I think it is worth the effort for the improved efficiency. Most boiler manufacturers will, in any case recommend ot make it a warranty condition that the system is thoroughly cleaned and ideally an in line strainer is put on the return to the boiler. If you do a Google search, I have a suggested a few times a very effective way of thoroughly cleaning a system involving flushing at each radiator and taking each radiator outside for a thorough flush through. A large proportion, though not all condensing boilers require to work on a sealed system. This is no big deal and it is very easy to convert an existing open vented system and to install the expansion vessel and filling and pressure relief equipment. One possible impact is that there may be seepage at the radiator valves. If these are of significant age then it is worth changing them and that is a cheap exercise. You do need to properly provision for the condensate drain. The condensate is acidic and must be delivered from the boiler through plastic pipe to a suitable drain inside the house or if outside making arrangements such that the condensate can't freeze. There is a myth and much confusion in the heating and plumbing supply industry (especially at the merchants) about the efficiency and behaviour of condensing boilers. The misinformation is that they must always operate below 52 to 54 degrees on the return side in order to realise efficiency, as though some nirvana is reached at this temperature and that the radiators must be organised to achieve this. It isn't the case. The main difference compared with a conventional boiler is that the heat exchanger is more substantial and the boiler is designed to operate with a flow/return temperature difference of 20 degrees instead of about 10-12 as for conventional systems. Conventional systems are (supposed to be) designed to work with 82 flow and 70 degree return temperatures and radiators sized accordingly. The reality of the efficiency of a condensing boiler is that it increases with reduction in return temperature. It is the *rate* of increase of efficiency with reduction of temperature that drops below the dew point (54 degrees) - there is not some Holy Grail that is discovered at this point. So...... to maximise boiler efficiency, it follows that the temperature should be made as low as possible. However..... condensing boilers are able to modulate their output (by controlling the fuel burning rate over a range. 10kW to 25kW is very typical; some will do 4kW to 30kW. During quite a bit of the heating season, a lower than maximum output is enough. The effect of this is that the radiators will warm up but perhaps only to 50 to 60 degrees flow and the return could be at 30 to 50. This is well down the curve of good efficiency. When it is really cold, and full power is needed, the radiators may have to warm up to their original design temperature of 80 degrees and then the boiler won't be running quite as efficiently. However it is for only part of the year and in spring and autumn it will be running very efficiently. You can improve the efficiency by increasing radiator sizes to provide the same amount of heat at lower water temperatures. Thus you could work with 70 degree flow and 50 return if you like. I did this when I converted my system and achieved most of what was needed by moving radiators around and replacing only three. It is not mandatory, however. I vote this goes in a condensing boilers FAQ. It has come up a few times, hasn't it. Maybe if Phil is reading, he could pick this up. Also, I think this is closely allied to your sealed system FAQ and it would be worth having that or a pointer to it as well. When yours is up, we can add xref links. The only thing I feel called to query in the above was... However..... condensing boilers are able to modulate their output (by controlling the fuel burning rate over a range. 10kW to 25kW is very typical; some will do 4kW to 30kW. This is not the province of condensing boilers per se. Firstly modern non-condensing boilers can and do modulate and there control systems exploit this. The difference is that by using forced premix burners (cf atmospheric burners), they can modulate over a deeper range. -- Ed Sirett - Property maintainer and registered gas fitter. The FAQ for uk.diy is at www.diyfaq.org.uk Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html |
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Upgrade to a Condensing boiler - yes or no?
"Ed Sirett" wrote in message ... Andy Hall wrote: On 23 Aug 2003 05:46:20 -0700, (robf) wrote: Aside from my other post re. repairing existing boiler. I am tempted by the higher efficiencies of the condensing boilers but are there hidden problems in upgrading an existing installation. I do not need a combined boiler - I have HW cylinder and pump / valves. Concerns I have are -: Cleanliness of existing system - any prerequisites? Will existing rads be ok - presuming that water temp is lower???? TIA. Rob There are a few areas to be considered, but overall, I think it is worth the effort for the improved efficiency. Most boiler manufacturers will, in any case recommend ot make it a warranty condition that the system is thoroughly cleaned and ideally an in line strainer is put on the return to the boiler. If you do a Google search, I have a suggested a few times a very effective way of thoroughly cleaning a system involving flushing at each radiator and taking each radiator outside for a thorough flush through. A large proportion, though not all condensing boilers require to work on a sealed system. This is no big deal and it is very easy to convert an existing open vented system and to install the expansion vessel and filling and pressure relief equipment. One possible impact is that there may be seepage at the radiator valves. If these are of significant age then it is worth changing them and that is a cheap exercise. You do need to properly provision for the condensate drain. The condensate is acidic and must be delivered from the boiler through plastic pipe to a suitable drain inside the house or if outside making arrangements such that the condensate can't freeze. There is a myth and much confusion in the heating and plumbing supply industry (especially at the merchants) about the efficiency and behaviour of condensing boilers. The misinformation is that they must always operate below 52 to 54 degrees on the return side in order to realise efficiency, as though some nirvana is reached at this temperature and that the radiators must be organised to achieve this. It isn't the case. The main difference compared with a conventional boiler is that the heat exchanger is more substantial and the boiler is designed to operate with a flow/return temperature difference of 20 degrees instead of about 10-12 as for conventional systems. Conventional systems are (supposed to be) designed to work with 82 flow and 70 degree return temperatures and radiators sized accordingly. The reality of the efficiency of a condensing boiler is that it increases with reduction in return temperature. It is the *rate* of increase of efficiency with reduction of temperature that drops below the dew point (54 degrees) - there is not some Holy Grail that is discovered at this point. So...... to maximise boiler efficiency, it follows that the temperature should be made as low as possible. However..... condensing boilers are able to modulate their output (by controlling the fuel burning rate over a range. 10kW to 25kW is very typical; some will do 4kW to 30kW. During quite a bit of the heating season, a lower than maximum output is enough. The effect of this is that the radiators will warm up but perhaps only to 50 to 60 degrees flow and the return could be at 30 to 50. This is well down the curve of good efficiency. When it is really cold, and full power is needed, the radiators may have to warm up to their original design temperature of 80 degrees and then the boiler won't be running quite as efficiently. However it is for only part of the year and in spring and autumn it will be running very efficiently. You can improve the efficiency by increasing radiator sizes to provide the same amount of heat at lower water temperatures. Thus you could work with 70 degree flow and 50 return if you like. I did this when I converted my system and achieved most of what was needed by moving radiators around and replacing only three. It is not mandatory, however. I vote this goes in a condensing boilers FAQ. I bit of work required though. --- -- Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.507 / Virus Database: 304 - Release Date: 04/08/2003 |
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Upgrade to a Condensing boiler - yes or no?
"Ed Sirett" wrote in message ... Andy Hall wrote: On Tue, 26 Aug 2003 18:44:55 +0100, Ed Sirett wrote: Andy Hall wrote: On 23 Aug 2003 05:46:20 -0700, (robf) wrote: Aside from my other post re. repairing existing boiler. I am tempted by the higher efficiencies of the condensing boilers but are there hidden problems in upgrading an existing installation. I do not need a combined boiler - I have HW cylinder and pump / valves. Concerns I have are -: Cleanliness of existing system - any prerequisites? Will existing rads be ok - presuming that water temp is lower???? TIA. Rob There are a few areas to be considered, but overall, I think it is worth the effort for the improved efficiency. Most boiler manufacturers will, in any case recommend ot make it a warranty condition that the system is thoroughly cleaned and ideally an in line strainer is put on the return to the boiler. If you do a Google search, I have a suggested a few times a very effective way of thoroughly cleaning a system involving flushing at each radiator and taking each radiator outside for a thorough flush through. A large proportion, though not all condensing boilers require to work on a sealed system. This is no big deal and it is very easy to convert an existing open vented system and to install the expansion vessel and filling and pressure relief equipment. One possible impact is that there may be seepage at the radiator valves. If these are of significant age then it is worth changing them and that is a cheap exercise. You do need to properly provision for the condensate drain. The condensate is acidic and must be delivered from the boiler through plastic pipe to a suitable drain inside the house or if outside making arrangements such that the condensate can't freeze. There is a myth and much confusion in the heating and plumbing supply industry (especially at the merchants) about the efficiency and behaviour of condensing boilers. The misinformation is that they must always operate below 52 to 54 degrees on the return side in order to realise efficiency, as though some nirvana is reached at this temperature and that the radiators must be organised to achieve this. It isn't the case. The main difference compared with a conventional boiler is that the heat exchanger is more substantial and the boiler is designed to operate with a flow/return temperature difference of 20 degrees instead of about 10-12 as for conventional systems. Conventional systems are (supposed to be) designed to work with 82 flow and 70 degree return temperatures and radiators sized accordingly. The reality of the efficiency of a condensing boiler is that it increases with reduction in return temperature. It is the *rate* of increase of efficiency with reduction of temperature that drops below the dew point (54 degrees) - there is not some Holy Grail that is discovered at this point. So...... to maximise boiler efficiency, it follows that the temperature should be made as low as possible. However..... condensing boilers are able to modulate their output (by controlling the fuel burning rate over a range. 10kW to 25kW is very typical; some will do 4kW to 30kW. During quite a bit of the heating season, a lower than maximum output is enough. The effect of this is that the radiators will warm up but perhaps only to 50 to 60 degrees flow and the return could be at 30 to 50. This is well down the curve of good efficiency. When it is really cold, and full power is needed, the radiators may have to warm up to their original design temperature of 80 degrees and then the boiler won't be running quite as efficiently. However it is for only part of the year and in spring and autumn it will be running very efficiently. You can improve the efficiency by increasing radiator sizes to provide the same amount of heat at lower water temperatures. Thus you could work with 70 degree flow and 50 return if you like. I did this when I converted my system and achieved most of what was needed by moving radiators around and replacing only three. It is not mandatory, however. I vote this goes in a condensing boilers FAQ. It has come up a few times, hasn't it. Maybe if Phil is reading, he could pick this up. Also, I think this is closely allied to your sealed system FAQ and it would be worth having that or a pointer to it as well. When yours is up, we can add xref links. The only thing I feel called to query in the above was... However..... condensing boilers are able to modulate their output (by controlling the fuel burning rate over a range. 10kW to 25kW is very typical; some will do 4kW to 30kW. This is not the province of condensing boilers per se. Firstly modern non-condensing boilers can and do modulate and there control systems exploit this. The difference is that by using forced premix burners (cf atmospheric burners), they can modulate over a deeper range. pre-mix burners are used in all boilers. --- -- Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.507 / Virus Database: 304 - Release Date: 04/08/2003 |
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#9
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Upgrade to a Condensing boiler - yes or no?
On Tue, 26 Aug 2003 23:43:19 +0100, "IMM" wrote:
"IMM" wrote in message ... "Ed Sirett" wrote in message ... Andy Hall wrote: On 23 Aug 2003 05:46:20 -0700, (robf) wrote: Aside from my other post re. repairing existing boiler. I am tempted by the higher efficiencies of the condensing boilers but are there hidden problems in upgrading an existing installation. I do not need a combined boiler - I have HW cylinder and pump / valves. Concerns I have are -: Cleanliness of existing system - any prerequisites? Will existing rads be ok - presuming that water temp is lower???? TIA. Rob There are a few areas to be considered, but overall, I think it is worth the effort for the improved efficiency. Most boiler manufacturers will, in any case recommend ot make it a warranty condition that the system is thoroughly cleaned and ideally an in line strainer is put on the return to the boiler. If you do a Google search, I have a suggested a few times a very effective way of thoroughly cleaning a system involving flushing at each radiator and taking each radiator outside for a thorough flush through. A large proportion, though not all condensing boilers require to work on a sealed system. This is no big deal and it is very easy to convert an existing open vented system and to install the expansion vessel and filling and pressure relief equipment. One possible impact is that there may be seepage at the radiator valves. If these are of significant age then it is worth changing them and that is a cheap exercise. You do need to properly provision for the condensate drain. The condensate is acidic and must be delivered from the boiler through plastic pipe to a suitable drain inside the house or if outside making arrangements such that the condensate can't freeze. The acid level is that of Coca Cola. Approximately pH4, and metal pipe can't be used. There is a myth and much confusion in the heating and plumbing supply industry (especially at the merchants) about the efficiency and behaviour of condensing boilers. The misinformation is that they must always operate below 52 to 54 degrees on the return side in order to realise efficiency, as though some nirvana is reached at this temperature and that the radiators must be organised to achieve this. It isn't the case. The main difference compared with a conventional boiler is that the heat exchanger is more substantial and the boiler is designed to operate with a flow/return temperature difference of 20 degrees instead of about 10-12 as for conventional systems. Heat exchangers can be one piece downward or upward firing Some are boilers are conventional rail burners, some are basic system boilers with an extra condensing heat exchanger. Heat exchangers can also be cylindrical like the Econox/Spiranox burner/heat exchanger. One piece heat-exchanger downward firing burners are self cleaning. This does not necessarily mean that no cleaning is needed in the burner/heat exchanger chamber. The manufacturer's instructions should be followed. Conventional systems are (supposed to be) designed to work with 82 flow and 70 degree return temperatures and radiators sized accordingly. The reality of the efficiency of a condensing boiler is that it increases with reduction in return temperature. It is the *rate* of increase of efficiency with reduction of temperature that drops below the dew point (54 degrees) - there is not some Holy Grail that is discovered at this point. So...... to maximise boiler efficiency, it follows that the temperature should be made as low as possible. Without exceeding the flow/return delta T. However..... condensing boilers are able to modulate their output (by controlling the fuel burning rate over a range. 10kW to 25kW is very typical; some will do 4kW to 30kW. Some are fixed rate burners. "most" modulating burners have load compensation control. In some boilers this can be disabled to give a fixed rate output. Fixed rate outputs are beneficial to some thermal store and UFH applications. Some boilers have a DHW mode which give full unmodulated power when DHW is calling and modulation on CH. Some boilers have a high temp output for DHW and rads, and a low temp UFH output. During quite a bit of the heating season, a lower than maximum output is enough. The effect of this is that the radiators will warm up but perhaps only to 50 to 60 degrees flow and the return could be at 30 to 50. This is well down the curve of good efficiency. Known as part load. When it is really cold, and full power is needed, the radiators may have to warm up to their original design temperature of 80 degrees and then the boiler won't be running quite as efficiently. However it is for only part of the year and in spring and autumn it will be running very efficiently. Once a house is up to temperature the burner will modulate to the more efficient lower temp part load. With weather compensation it may well also start at part load. You can improve the efficiency by increasing radiator sizes to provide the same amount of heat at lower water temperatures. Thus you could work with 70 degree flow and 50 return if you like. I did this when I converted my system and achieved most of what was needed by moving radiators around and replacing only three. It is not mandatory, however. It is madatory in Sweden and Denmark since 1980 to have 60 flow 40 return. That is irrelevant since this is a UK group. No mention that super long flue lengths can be obtained using cheap plastic drain pipe. This means boiler may be fitted anywhere in the house, not just on outside walls. That depends on what the manufacturer offers or specifies. I vote this goes in a condensing boilers FAQ. I bit of work required though. Correction. A hell of lot of work required. The objective was a simple and concise piece which covers most of the salient points without introducing irrelevancies. One or two of your points may be useful, once the spelling and grammar are corrected, but that is all. The intent was not to make this into a diatribe about peripheral issues. --- ..andy To email, substitute .nospam with .gl |
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#10
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Upgrade to a Condensing boiler - yes or no?
"Andy Hall" wrote in message news  On Tue, 26 Aug 2003 23:43:19 +0100, "IMM" wrote: "IMM" wrote in message ... "Ed Sirett" wrote in message ... Andy Hall wrote: On 23 Aug 2003 05:46:20 -0700, (robf) wrote: Aside from my other post re. repairing existing boiler. I am tempted by the higher efficiencies of the condensing boilers but are there hidden problems in upgrading an existing installation. I do not need a combined boiler - I have HW cylinder and pump / valves. Concerns I have are -: Cleanliness of existing system - any prerequisites? Will existing rads be ok - presuming that water temp is lower???? TIA. Rob There are a few areas to be considered, but overall, I think it is worth the effort for the improved efficiency. Most boiler manufacturers will, in any case recommend ot make it a warranty condition that the system is thoroughly cleaned and ideally an in line strainer is put on the return to the boiler. If you do a Google search, I have a suggested a few times a very effective way of thoroughly cleaning a system involving flushing at each radiator and taking each radiator outside for a thorough flush through. A large proportion, though not all condensing boilers require to work on a sealed system. This is no big deal and it is very easy to convert an existing open vented system and to install the expansion vessel and filling and pressure relief equipment. One possible impact is that there may be seepage at the radiator valves. If these are of significant age then it is worth changing them and that is a cheap exercise. You do need to properly provision for the condensate drain. The condensate is acidic and must be delivered from the boiler through plastic pipe to a suitable drain inside the house or if outside making arrangements such that the condensate can't freeze. The acid level is that of Coca Cola. Approximately pH4, and metal pipe can't be used. There is a myth and much confusion in the heating and plumbing supply industry (especially at the merchants) about the efficiency and behaviour of condensing boilers. The misinformation is that they must always operate below 52 to 54 degrees on the return side in order to realise efficiency, as though some nirvana is reached at this temperature and that the radiators must be organised to achieve this. It isn't the case. The main difference compared with a conventional boiler is that the heat exchanger is more substantial and the boiler is designed to operate with a flow/return temperature difference of 20 degrees instead of about 10-12 as for conventional systems. Heat exchangers can be one piece downward or upward firing Some are boilers are conventional rail burners, some are basic system boilers with an extra condensing heat exchanger. Heat exchangers can also be cylindrical like the Econox/Spiranox burner/heat exchanger. One piece heat-exchanger downward firing burners are self cleaning. This does not necessarily mean that no cleaning is needed in the burner/heat exchanger chamber. That was not implied. The heat exchanger does not require cleaning as stated. The manufacturer's instructions should be followed. As always. Conventional systems are (supposed to be) designed to work with 82 flow and 70 degree return temperatures and radiators sized accordingly. The reality of the efficiency of a condensing boiler is that it increases with reduction in return temperature. It is the *rate* of increase of efficiency with reduction of temperature that drops below the dew point (54 degrees) - there is not some Holy Grail that is discovered at this point. So...... to maximise boiler efficiency, it follows that the temperature should be made as low as possible. Without exceeding the flow/return delta T. However..... condensing boilers are able to modulate their output (by controlling the fuel burning rate over a range. 10kW to 25kW is very typical; some will do 4kW to 30kW. Some are fixed rate burners. "most" modulating burners have load compensation control. In some boilers this can be disabled to give a fixed rate output. Fixed rate outputs are beneficial to some thermal store and UFH applications. Some boilers have a DHW mode which give full unmodulated power when DHW is calling and modulation on CH. Some boilers have a high temp output for DHW and rads, and a low temp UFH output. During quite a bit of the heating season, a lower than maximum output is enough. The effect of this is that the radiators will warm up but perhaps only to 50 to 60 degrees flow and the return could be at 30 to 50. This is well down the curve of good efficiency. Known as part load. When it is really cold, and full power is needed, the radiators may have to warm up to their original design temperature of 80 degrees and then the boiler won't be running quite as efficiently. However it is for only part of the year and in spring and autumn it will be running very efficiently. Once a house is up to temperature the burner will modulate to the more efficient lower temp part load. With weather compensation it may well also start at part load. That is merely another level of control and not necessarily directly aplicable to a condesning boiler. A good compensator will start on full heat until the building is up to temp. A boost function. You can improve the efficiency by increasing radiator sizes to provide the same amount of heat at lower water temperatures. Thus you could work with 70 degree flow and 50 return if you like. I did this when I converted my system and achieved most of what was needed by moving radiators around and replacing only three. It is not mandatory, however. It is madatory in Sweden and Denmark since 1980 to have 60 flow 40 return. That is irrelevant since this is a UK group. It gives a good indication of the way matters are moving. No mention that super long flue lengths can be obtained using cheap plastic drain pipe. This means boiler may be fitted anywhere in the house, not just on outside walls. That depends on what the manufacturer offers or specifies. This is great advantage and it was not mentioned at all. I vote this goes in a condensing boilers FAQ. I bit of work required though. Correction. A hell of lot of work required. The objective was a simple and concise piece which covers most of the salient points without introducing irrelevancies. One or two of your points may be useful, once the spelling and grammar are corrected, but that is all. Your so-called FAQable piece was sadly lacking. Now you know. The intent was not to make this into a diatribe about peripheral issues. Like compensators? --- -- Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.507 / Virus Database: 304 - Release Date: 04/08/2003 |
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#11
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Upgrade to a Condensing boiler - yes or no?
"Ed Sirett" wrote in message ... IMM wrote: "Ed Sirett" wrote in message ... Andy Hall wrote: On Tue, 26 Aug 2003 18:44:55 +0100, Ed Sirett wrote: Andy Hall wrote: On 23 Aug 2003 05:46:20 -0700, (robf) wrote: Aside from my other post re. repairing existing boiler. I am tempted by the higher efficiencies of the condensing boilers but are there hidden problems in upgrading an existing installation. I do not need a combined boiler - I have HW cylinder and pump / valves. Concerns I have are -: Cleanliness of existing system - any prerequisites? Will existing rads be ok - presuming that water temp is lower???? TIA. Rob There are a few areas to be considered, but overall, I think it is worth the effort for the improved efficiency. Most boiler manufacturers will, in any case recommend ot make it a warranty condition that the system is thoroughly cleaned and ideally an in line strainer is put on the return to the boiler. If you do a Google search, I have a suggested a few times a very effective way of thoroughly cleaning a system involving flushing at each radiator and taking each radiator outside for a thorough flush through. A large proportion, though not all condensing boilers require to work on a sealed system. This is no big deal and it is very easy to convert an existing open vented system and to install the expansion vessel and filling and pressure relief equipment. One possible impact is that there may be seepage at the radiator valves. If these are of significant age then it is worth changing them and that is a cheap exercise. You do need to properly provision for the condensate drain. The condensate is acidic and must be delivered from the boiler through plastic pipe to a suitable drain inside the house or if outside making arrangements such that the condensate can't freeze. There is a myth and much confusion in the heating and plumbing supply industry (especially at the merchants) about the efficiency and behaviour of condensing boilers. The misinformation is that they must always operate below 52 to 54 degrees on the return side in order to realise efficiency, as though some nirvana is reached at this temperature and that the radiators must be organised to achieve this. It isn't the case. The main difference compared with a conventional boiler is that the heat exchanger is more substantial and the boiler is designed to operate with a flow/return temperature difference of 20 degrees instead of about 10-12 as for conventional systems. Conventional systems are (supposed to be) designed to work with 82 flow and 70 degree return temperatures and radiators sized accordingly. The reality of the efficiency of a condensing boiler is that it increases with reduction in return temperature. It is the *rate* of increase of efficiency with reduction of temperature that drops below the dew point (54 degrees) - there is not some Holy Grail that is discovered at this point. So...... to maximise boiler efficiency, it follows that the temperature should be made as low as possible. However..... condensing boilers are able to modulate their output (by controlling the fuel burning rate over a range. 10kW to 25kW is very typical; some will do 4kW to 30kW. During quite a bit of the heating season, a lower than maximum output is enough. The effect of this is that the radiators will warm up but perhaps only to 50 to 60 degrees flow and the return could be at 30 to 50. This is well down the curve of good efficiency. When it is really cold, and full power is needed, the radiators may have to warm up to their original design temperature of 80 degrees and then the boiler won't be running quite as efficiently. However it is for only part of the year and in spring and autumn it will be running very efficiently. You can improve the efficiency by increasing radiator sizes to provide the same amount of heat at lower water temperatures. Thus you could work with 70 degree flow and 50 return if you like. I did this when I converted my system and achieved most of what was needed by moving radiators around and replacing only three. It is not mandatory, however. I vote this goes in a condensing boilers FAQ. It has come up a few times, hasn't it. Maybe if Phil is reading, he could pick this up. Also, I think this is closely allied to your sealed system FAQ and it would be worth having that or a pointer to it as well. When yours is up, we can add xref links. The only thing I feel called to query in the above was... However..... condensing boilers are able to modulate their output (by controlling the fuel burning rate over a range. 10kW to 25kW is very typical; some will do 4kW to 30kW. This is not the province of condensing boilers per se. Firstly modern non-condensing boilers can and do modulate and there control systems exploit this. The difference is that by using forced premix burners (cf atmospheric burners), they can modulate over a deeper range. pre-mix burners are used in all boilers. That's casuistry IMHO. I.e. a bit like the games lawyers play to get guilty client off on technicalities. Clearly all gas applinaces mix the air and gas - the relevant point being that forced premix burners do so by a different mechanism. My point is that they are not particular to condensing boilers, although most are in condensing boilers. The Ideal Response has a pre-mix burners yet is not a condenser. --- -- Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.507 / Virus Database: 304 - Release Date: 04/08/2003 |
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Upgrade to a Condensing boiler - yes or no?
On Wed, 27 Aug 2003 15:55:15 +0100, "IMM" wrote:
The intent was not to make this into a diatribe about peripheral issues. Is there anything else that is sensible and relevant that you want to add? I've included some of your points (e.g. flexibility of flue systems and modes of operation) as well as Ed's. ..andy To email, substitute .nospam with .gl |
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#13
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Upgrade to a Condensing boiler - yes or no?
"Andy Hall" wrote in message ... On Wed, 27 Aug 2003 15:55:15 +0100, "IMM" wrote: The intent was not to make this into a diatribe about peripheral issues. Is there anything else that is sensible and relevant that you want to add? I've included some of your points (e.g. flexibility of flue systems and modes of operation) as well as Ed's. Show us the draft. --- -- Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.507 / Virus Database: 304 - Release Date: 04/08/2003 |
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