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Mixing header and pumps
My understanding is that most domestic unvented heating systems use the
boiler's pump to circulate water and on/off valves to divert water to the hot water cylinder or heating zones. Under what circumstances should the zone valves be replaced by zone pumps with a mixing header between the pumps and the boiler? What's the function of the mixing header, and do you always need it if you have any heating circuit pumps or DHW pumps external to the boiler? Does a zone pump arrangement confer any control advantages over using a boiler pump + zone valves? (I'm currently considering buying a 38kW boiler which offers a vertical low velocity header as an accessory: http://www.mhsboilers.com/boilers/premix/strata1.htm) |
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"John Aston" wrote in message ... My understanding is that most domestic unvented heating systems use the boiler's pump to circulate water and on/off valves to divert water to the hot water cylinder or heating zones. Under what circumstances should the zone valves be replaced by zone pumps with a mixing header between the pumps and the boiler? What's the function of the mixing header, and do you always need it if you have any heating circuit pumps or DHW pumps external to the boiler? Does a zone pump arrangement confer any control advantages over using a boiler pump + zone valves? (I'm currently considering buying a 38kW boiler which offers a vertical low velocity header as an accessory: http://www.mhsboilers.com/boilers/premix/strata1.htm) If I was you I would go for: * A heat bank/thermal store. Off this you can have the UFH and rad circuits, each one taken directly off the herat bank, so influence from one to the other. The UFH is taken off the cooler bottom, the rads off the centre and the DHW off the hotter top It also provides instant mains pressure DHW. It provides a neutral point that solves many problems with mixed circuits too. See http://www.heatweb.com for an explanation. Other companies make heat banks too. The boiler only heats the heat bank and is best with two cylinder stats to eliminate inefficient boiler cycling. The mains pressure DHW means that power shower pumps are not required. Check out your mains pressure. It may be worth your while replacing the existing mains pipe with a new plastic larger bore pipe. * A simpler and much cheaper condensing boiler: Worcester Bosch Greenstar, Ideal Icos, Glow Worm, are three good candidates and can be had from £500-£750. The advantage of an heat bank is that cheaper and much simpler boiler can be used as they only heat the water in the heat bank as fast as possible. * A control system of a Landis & Staefa 2 stage controller and modulating valves. (see my other post on this) This would be a pretty cost effective solution and provide exactly what you need giving excellent efficiency and economy. The Landis & Staefa controller does most of the control, seamlessly controlling the two differing heating systems of UFH and rads brilliantly, rather than have a control system in an expensive boiler that only half does the job. |
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John Aston wrote:
My understanding is that most domestic unvented heating systems use the boiler's pump to circulate water and on/off valves to divert water to the hot water cylinder or heating zones. Under what circumstances should the zone valves be replaced by zone pumps with a mixing header between the pumps and the boiler? What's the function of the mixing header, and do you always need it if you have any heating circuit pumps or DHW pumps external to the boiler? According to the boiler installation instructions on mhs' web site you use the mixing header if the resistance of the heating system to be supplied is more than the boiler's built-in pump can handle. (I'm currently considering buying a 38kW boiler which offers a vertical low velocity header as an accessory: http://www.mhsboilers.com/boilers/premix/strata1.htm) Why this particular boiler? I haven't looked at the price but I probably don't need to ;-). Your house must be (a) ginormous (b) draughty and/or (c) badly insulated to warrant a 38kW non-combi boiler, but if you need the output for either of (b) or (c) then spending £x on dealing with these losses is likely to give a better return on investment than spending the same amount on a more sophisticated boiler. For smaller and/or more energy-efficient houses the energy savings from installing even a cheap condensing boiler probably won't actually repay the extra purchase cost of the beast (though hopefully the prices of condensing boilers will come down next year when the big builders start buying 1000s of them). |
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"John Stumbles" wrote in message ... John Aston wrote: My understanding is that most domestic unvented heating systems use the boiler's pump to circulate water and on/off valves to divert water to the hot water cylinder or heating zones. Under what circumstances should the zone valves be replaced by zone pumps with a mixing header between the pumps and the boiler? What's the function of the mixing header, and do you always need it if you have any heating circuit pumps or DHW pumps external to the boiler? According to the boiler installation instructions on mhs' web site you use the mixing header if the resistance of the heating system to be supplied is more than the boiler's built-in pump can handle. (I'm currently considering buying a 38kW boiler which offers a vertical low velocity header as an accessory: http://www.mhsboilers.com/boilers/premix/strata1.htm) Why this particular boiler? I haven't looked at the price but I probably don't need to ;-). Your house must be (a) ginormous (b) draughty and/or (c) badly insulated to warrant a 38kW non-combi boiler, but if you need the output for either of (b) or (c) then spending £x on dealing with these losses is likely to give a better return on investment than spending the same amount on a more sophisticated boiler. For smaller and/or more energy-efficient houses the energy savings from installing even a cheap condensing boiler probably won't actually repay the extra purchase cost of the beast Not so. By April you will have no option anyhow. |
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"John Aston" wrote in message ...
My understanding is that most domestic unvented heating systems use the boiler's pump to circulate water and on/off valves to divert water to the hot water cylinder or heating zones. The main advantage of this is cheapness. One pump costs less than several pumps and the associated controls. One pump is generally adequate for most UK domestic installations. Many UK 'heating engineers' cannot comprehend anything more complex than one pump and a 3-port mid-position valve. Shutting a zone-valve will cause an increase in the flow rates to all the other open zones. This may cause problems with intermittent noise, especially from TRVs. It will mess up any intelligent control systems, anything with sensors and modulating valves. Under what circumstances should the zone valves be replaced by zone pumps with a mixing header between the pumps and the boiler? What's the function of the mixing header, and do you always need it if you have any heating circuit pumps or DHW pumps external to the boiler? Does a zone pump arrangement confer any control advantages over using a boiler pump + zone valves? Yes. You can get a more consistent flow rate to each zone. Shutting off any one zone won't affect the others. It costs more. I'm not sure why they call it a mixing header, I don't have time to look at the link. It's more usually a low-loss header, with no mixing of the water taking place before the returns. A thermal store/buffer vessel would also perform this function, as mentioned in the post about the heating controls. Try also a Google search for primary/secondary pumping and "closely spaced tees". (I'm currently considering buying a 38kW boiler which offers a vertical low velocity header as an accessory: http://www.mhsboilers.com/boilers/premix/strata1.htm) |
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#6
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"John Aston" wrote in message ...
PS to the above. If you're using a mixing device, for UFH for example, and are not using a boiler-reset type system, then you have to have a second circulator. The mixing valve might, for example, require 90% return water mixed with 10% hotter flow water. There will be 10% of the return from the mixed circuit returning to the boiler and this will probably be inadequate for proper boiler operation. I've seen mixing valves piped like this, though. They worked ok, unless they started mixing. In the above case you might have a primary pump circulating water from the boiler around a low-loss header and to the DHWS. You'd then have one or more secondary circuits, with their own pumps drawing water as required from the primary circuit. The secondary circuits would all return the same volume of return water to the primary as they draw off, so they won't affect the primary flow rate. |
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#7
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John Stumbles wrote in message ... John Aston wrote: My understanding is that most domestic unvented heating systems use the boiler's pump to circulate water and on/off valves to divert water to the hot water cylinder or heating zones. Under what circumstances should the zone valves be replaced by zone pumps with a mixing header between the pumps and the boiler? What's the function of the mixing header, and do you always need it if you have any heating circuit pumps or DHW pumps external to the boiler? According to the boiler installation instructions on mhs' web site you use the mixing header if the resistance of the heating system to be supplied is more than the boiler's built-in pump can handle. OK, but why not simply put another primary pump in series with the boiler? (I'm currently considering buying a 38kW boiler which offers a vertical low velocity header as an accessory: http://www.mhsboilers.com/boilers/premix/strata1.htm) Why this particular boiler? I haven't looked at the price but I probably don't need to ;-). Your house must be (a) ginormous (b) draughty and/or (c) badly insulated to warrant a 38kW non-combi boiler, but if you need the output for either of (b) or (c) then spending £x on dealing with these losses is likely to give a better return on investment than spending the same amount on a more sophisticated boiler. snip (a) 890 cu.m. and 'yes' to (b) and (c). The property is an old listed building and I can't change 20 large single-glazed sash windows for double-glazed ones...but that's a topic for a whole new thread. I'm doing what the Conservation Officer will allow me in terms of insulation. |
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#8
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Aidan wrote in message om... "John Aston" wrote in message ... Under what circumstances should the zone valves be replaced by zone pumps with a mixing header between the pumps and the boiler? What's the function of the mixing header, and do you always need it if you have any heating circuit pumps or DHW pumps external to the boiler? Does a zone pump arrangement confer any control advantages over using a boiler pump + zone valves? Yes. You can get a more consistent flow rate to each zone. Shutting off any one zone won't affect the others. It costs more. I'm not sure why they call it a mixing header, I don't have time to look at the link. It's more usually a low-loss header, with no mixing of the water taking place before the returns. A thermal store/buffer vessel would also perform this function, as mentioned in the post about the heating controls. Try also a Google search for primary/secondary pumping and "closely spaced tees". I did the Google search, and in doing so realised that the "low velocity mixing header" actually forms a primary loop, with the secondary pumped heating loops teed off primary loop. Contrast this with the normal domestic single pump and multiple zone valve arrangement, which is more like a radial circuit (sort of). It seems that primary/secondary pumping is used predominantly in larger (commercial) heating installations whereas domestic heating systems just have a primary pump and zone valves. I don't know at what point you should change from zone valves to p/s pumping. Perhaps, when you want more control than the 'crude' on/off systems provided by Danfoss Randall. |
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#9
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Pandora wrote in message
... (a) 890 cu.m. and 'yes' to (b) and (c). The property is an old listed building and I can't change 20 large single-glazed sash windows for double-glazed ones...but that's a topic for a whole new thread. I'm doing what the Conservation Officer will allow me in terms of insulation. That was actually my post, sent using my wife's newsreader by mistake. John |
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#10
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Aidan wrote in message
om... "John Aston" wrote in message ... If you're using a mixing device, for UFH for example, and are not using a boiler-reset type system, then you have to have a second circulator. The mixing valve might, for example, require 90% return water mixed with 10% hotter flow water. There will be 10% of the return from the mixed circuit returning to the boiler and this will probably be inadequate for proper boiler operation. Doesn't an automatic bypass valve stop this problem? I've seen mixing valves piped like this, though. They worked ok, unless they started mixing. In the above case you might have a primary pump circulating water from the boiler around a low-loss header and to the DHWS. With the DHWS controlled by a zone valve, I guess. You'd then have one or more secondary circuits, with their own pumps drawing water as required from the primary circuit. The secondary circuits would all return the same volume of return water to the primary as they draw off, so they won't affect the primary flow rate. That sounds so reasonable. Unfortunately, none of the domestic heating design books I've read refer to anything other than one primary pump plus zone valves. Being a beginner, I don't know if I'd have the confidence to go for pumps instead of valves. |
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#11
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"John Aston" wrote in message ... (I'm currently considering buying a 38kW boiler which offers a vertical low velocity header as an accessory: http://www.mhsboilers.com/boilers/premix/strata1.htm) Don't go that exspensive route. Another cost effective approach for you is: * Use a Landis & Steafa RWC82 controller. Two stage with "switching in each stage, no modulation. * use a load compensating control combi for UFH only. * Use a cheapish combi, not even a condensing model for the rads, as it will not be used as often as the UFH. * Have the condensing combi (UFH) do the DHW kitchen tap and other most used taps in the house. Have the other combi do the other taps. Combine the two hot outlets using non-return valves and a small shock arrestor, just before the high flow tap, which is the bath. The two combined should give over 20 litres per minute. Have one combi do one shower, one combi do the other, so no interference from one to the other. The RWC82 controller will switch in the UFH combi which is set to no more than 55C and it will modulate accordingly, so lowering the UFH temp to suit. The UFH is now sorted. When the UFH can't cope the rads combi will be switched in on the 2nd stage. This is boost so no real need for sophisticated modulation. This is a very cheap and effective solution to your needs. Seemless control of the UFH and rads to maintain the room temperatures. No expensive boilers, No expensive modulating valves. DHW instantly and to high flowrates by combining the two combi outlets. The set up is simple: one two stage controller and two combi's. The two combi's may set you back no more than £1400-1500. The 2nd stage rads combi can be had for under £400, The controller is £250. You may want to have a high limit pipe stat on the UFH flow set to 56C. When over 56C the UFH combi cuts out to protect the UFH circuits. You also have eredundancy. If one boiler is down you have have another. So, one controller, controlling two boilers to maintain a room temperature setpoint. The controllers are highly accurate and will maintain the room temp to what you set it to. NB: 4 room temperature sensors located around the house can be wired up to "average" between them. This gives a more realistic house temperature. I would not have them on rads in rooms where the sensors are. If the DHW flowrate is fine, 20 l/min will do even two bathrooms at a push, then I would go this route for cost effectiveness. |
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#12
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John Aston wrote:
Pandora wrote in message ... (a) 890 cu.m. and 'yes' to (b) and (c). The property is an old listed building and I can't change 20 large single-glazed sash windows for double-glazed ones...but that's a topic for a whole new thread. I'm doing what the Conservation Officer will allow me in terms of insulation. That was actually my post, sent using my wife's newsreader by mistake. Had me scratching my head! Looks like an ultra-efficient condensing boiler _is_ what you need then! Other makes/models you might look at (if you haven't already done so) are Keston and MAN or whatever they're called now. I daresay Andy H will be along in a few milliseconds to tell you all about his, though you could always ask that nice Mr Google :-) http://groups.google.com/groups?as_q...rs=Andy%20Hall |
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#13
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"John Aston" wrote in message t...
Doesn't an automatic bypass valve stop this problem? No. I don't think I was clear. The first paragraph referred to a heating system with a mixing valve, but only one pump, i.e., the way NOT to do it. The mixing valve was between the pump and the boiler. At low loads, most of the flow produced by the pump was re-circulated around the heating circuit leaving only a small amount to return to the boiler. The boiler did not like this. The second paragraph ( "In the above case you might have a primary pump………etc..") described how the system should have been set up, with primary boiler pump and a secondary (variable temperature) pump downstream of the mixing valve. On a conventional 1-pump system, an automatic by-pass valve might be connected between the pump's flow and return pipes, to maintain a minimum flow through the boiler if TRVs are mostly shut down. It's operated by the increase in the pump delivery pressure as the flow rate reduces. With the DHWS controlled by a zone valve, I guess. Yes. You'd probably need a regulating valve in the heating return to the boiler, which would be a straight pipe with little hydraulic resistance. The water would otherwise by-pass the DHWS branch, which would have a higher resistance. It could also be controlled by another secondary pump but generally the domestic DHWS flow rate is too small. My one's got a 3-port mid-position valve. That sounds so reasonable. Unfortunately, none of the domestic heating design books I've read refer to anything other than one primary pump plus zone valves. Being a beginner, I don't know if I'd have the confidence to go for pumps instead of valves. It (primary/secondary pumping) is very rare on UK domestic installations, mainly because of the costs. IMM has mentioned a £250 controller; most domestic customers cringe at £50 for a replacement heating timeswitch/on-off controller. Whether IMM's recommended controller is applicable to this is another convoluted question, but £250 is probably on the low side. With commercial stuff it's tax-deductible, so they're less price-sensitive and are prepared to pay for effective control. You would be very fortunate to find a UK ‘heating engineer' who understood such a system. Also, the Americans generally have bigger houses, so it's more common in the US. See ‘ Primary-Secondary Pumping made Easy' by Dan Holohan, available from HeatingHelp.com. It's written for home owners, so it's fairly free from techno-jargon. It's in US/Imperial units (gpm, BTU/hr, degF) but it's easy to grasp. |
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#14
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"Aidan" wrote in message om... It (primary/secondary pumping) is very rare on UK domestic installations, mainly because of the costs. IMM has mentioned a £250 controller; most domestic customers cringe at £50 for a replacement heating timeswitch/on-off controller. Whether IMM's recommended controller is applicable to this is another convoluted question, Oh it is, you had better believe me. but £250 is probably on the low side. Not really, I did also mention a £160 controller with limited weather compensation. The £250 "two stage switched" controller plus the room sensor, or 4 of them if you want to average temps, would be the only extra cost when using two combi's. NO valves of any description to buy. NO tanks or cylinders. NO pumps to buy as the boilers come with them. Just a Honeywell CM67, or better still a Landis & Staefa equiv. Each stage of the controller switches a combi. The 1st UFH stage a condensing combi set to 55C and it will also modulate. The seconds stage will also modulate, but supplies the rads. Seamless control.. Cost: Two Biasi Riva condensing combi's can be had for just over £500 each. OK these are at the lower end. Or more upmarket. An Ideal Icos condensing combi for £750 and a regular non-condensing Worcester Bosch Junior for around £560. So, for £1300 for two combi's. The controls, let's say £320 in all. A total of just over £1600 and then the rads and pipes on top. That is very, very good and a top rated commercial controller thrown in.. If you want to save on the boilers then A condensing Biasi at £500 plus a £381 regular Biasi. that works out at: £1200 all in plus pipes. NB: I would not go for the condensing Biasi. The regular is fine, just making a point. With commercial stuff it's tax-deductible, so they're less price-sensitive and are prepared to pay for effective control. You would be very fortunate to find a UK 'heating engineer' who understood such a system. Once understood it is quite easy. The £160 controller I mentioned is quite easy to understand. |
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#15
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"Aidan" wrote in message om... It (primary/secondary pumping) is very rare on UK domestic installations, mainly because of the costs. Interestingly, having spoken to their technical departments, both Viessman and MHS *require* the installation of low loss headers if any pumps are installed in the heating system (other than the boiler's pump, of course) running off their modulated boilers. MHS supply a Strata 1 boiler. It is a re-badged version of the Eco Hometec Micromat EC. The Eco Hometec literature shows a Y-plan zone valve installation with a supplementary pump in the radiator circuit. The MHS literature shows almost the same arrangement as an example of an incorrect installation! (For flow control, Viessman Vitodens can be connected to a sensor that monitors the header temperature. The Strata 1 just monitors the temperature within the boiler.) I think that I've got enough information to come up with a draft heating system design. I'll probably post it on the web and invite comments. This newsgroup has been an excellent source of help in that respect. |
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#16
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"IMM" wrote in message
... "John Aston" wrote in message ... (I'm currently considering buying a 38kW boiler which offers a vertical low velocity header as an accessory: http://www.mhsboilers.com/boilers/premix/strata1.htm) Don't go that exspensive route. Another cost effective approach for you is: * Use a Landis & Steafa RWC82 controller. Two stage with "switching in each stage, no modulation. * use a load compensating control combi for UFH only. * Use a cheapish combi, not even a condensing model for the rads, as it will not be used as often as the UFH. * Have the condensing combi (UFH) do the DHW kitchen tap and other most used taps in the house. Have the other combi do the other taps. Combine the two hot outlets using non-return valves and a small shock arrestor, just before the high flow tap, which is the bath. The two combined should give over 20 litres per minute. Have one combi do one shower, one combi do the other, so no interference from one to the other. The RWC82 controller will switch in the UFH combi which is set to no more than 55C and it will modulate accordingly, so lowering the UFH temp to suit. The UFH is now sorted. When the UFH can't cope the rads combi will be switched in on the 2nd stage. This is boost so no real need for sophisticated modulation. This is a very cheap and effective solution to your needs. Seemless control of the UFH and rads to maintain the room temperatures. No expensive boilers, No expensive modulating valves. DHW instantly and to high flowrates by combining the two combi outlets. The set up is simple: one two stage controller and two combi's. The two combi's may set you back no more than £1400-1500. The 2nd stage rads combi can be had for under £400, The controller is £250. You may want to have a high limit pipe stat on the UFH flow set to 56C. When over 56C the UFH combi cuts out to protect the UFH circuits. You also have eredundancy. If one boiler is down you have have another. So, one controller, controlling two boilers to maintain a room temperature setpoint. The controllers are highly accurate and will maintain the room temp to what you set it to. NB: 4 room temperature sensors located around the house can be wired up to "average" between them. This gives a more realistic house temperature. I would not have them on rads in rooms where the sensors are. If the DHW flowrate is fine, 20 l/min will do even two bathrooms at a push, then I would go this route for cost effectiveness. Thanks. Actually, cost isn't a major factor. Not because I'm loaded but because my renovated house will be a family home for a considerable time so I've got time to "enjoy" the capital outlay. Something that is clear for me to understand is one of the key requirements for the new heating system. Unfortunately, I'm a plumbing novice with that very dangerous thing: a little bit of knowledge. |
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#17
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"John Aston" wrote in message ... "Aidan" wrote in message om... It (primary/secondary pumping) is very rare on UK domestic installations, mainly because of the costs. Interestingly, having spoken to their technical departments, both Viessman and MHS *require* the installation of low loss headers if any pumps are installed in the heating system (other than the boiler's pump, of course) running off their modulated boilers. MHS supply a Strata 1 boiler. It is a re-badged version of the Eco Hometec Micromat EC. The Eco Hometec literature shows a Y-plan zone valve installation with a supplementary pump in the radiator circuit. The MHS literature shows almost the same arrangement as an example of an incorrect installation! (For flow control, Viessman Vitodens can be connected to a sensor that monitors the header temperature. The Strata 1 just monitors the temperature within the boiler.) I think that I've got enough information to come up with a draft heating system design. I'll probably post it on the web and invite comments. This newsgroup has been an excellent source of help in that respect. With condensing boilers headers reduce efficiency. With a condenser you don't want very hot water feeding right back into the return. This raises the return temp which reduces efficiency. You want the return temp as low as possible. Best use a heat bank or thermal store, which is a great neutral point, and have the boiler heat that directly. For most of the re-heat the return temp will be low. All headers are neutral points for circuiots to tee into. A heat bank gives you that and a DHW store with instant high pressure DHW. You only need cheap simple boilers with a heat bank, one of its selling points. I'll try and come up with some alternative systems. |
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#18
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On Fri, 12 Nov 2004 00:39:49 -0000, "IMM" wrote:
"John Aston" wrote in message ... "Aidan" wrote in message om... It (primary/secondary pumping) is very rare on UK domestic installations, mainly because of the costs. Interestingly, having spoken to their technical departments, both Viessman and MHS *require* the installation of low loss headers if any pumps are installed in the heating system (other than the boiler's pump, of course) running off their modulated boilers. MHS supply a Strata 1 boiler. It is a re-badged version of the Eco Hometec Micromat EC. The Eco Hometec literature shows a Y-plan zone valve installation with a supplementary pump in the radiator circuit. The MHS literature shows almost the same arrangement as an example of an incorrect installation! (For flow control, Viessman Vitodens can be connected to a sensor that monitors the header temperature. The Strata 1 just monitors the temperature within the boiler.) I think that I've got enough information to come up with a draft heating system design. I'll probably post it on the web and invite comments. This newsgroup has been an excellent source of help in that respect. With condensing boilers headers reduce efficiency. With a condenser you don't want very hot water feeding right back into the return. This raises the return temp which reduces efficiency. You want the return temp as low as possible. Best use a heat bank or thermal store, which is a great neutral point, and have the boiler heat that directly. For most of the re-heat the return temp will be low. Not if you are using a condensing boiler with wide modulating range such as the MAN Micromat or Viessmann. Putting a heat bank in the middle will do one of two things. a) If the heatbank is used for HW as well as CH, and there is a thermostat arrangement on the heatbank, the effect will be to prevent the boiler from operating at the lower end of its temperature range and will cause it to cycle on and off. The whole point of this type of boiler is to have high output for a short period to heat the heatbank/cylinder quickly for DHW use, and to drive the heating system directly to allow modulation down to low output levels. or b) If the heatbank is used solely for CH and no thermostat, it will effectively create an equilibrium situation with heat in and out and no real advantage over a much smaller header. It is far more efficient to run this type of boiler continuously at lower output than in bursts of high output. All headers are neutral points for circuiots to tee into. A heat bank gives you that and a DHW store with instant high pressure DHW. You only need cheap simple boilers with a heat bank, one of its selling points. I'll try and come up with some alternative systems. This could be entertaining..... -- ..andy To email, substitute .nospam with .gl |
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#19
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"IMM" wrote in message
... snip With condensing boilers headers reduce efficiency. With a condenser you don't want very hot water feeding right back into the return. This raises the return temp which reduces efficiency. You want the return temp as low as possible. snip Won't a modulating boiler adjust its flow temperature and velocity to reduce the return temperature though? I thought that that was the purpose of the modulating control. |
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#20
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"Andy Hall" wrote in message
... On Fri, 12 Nov 2004 00:39:49 -0000, "IMM" wrote: With condensing boilers headers reduce efficiency. With a condenser you don't want very hot water feeding right back into the return. This raises the return temp which reduces efficiency. You want the return temp as low as possible. Best use a heat bank or thermal store, which is a great neutral point, and have the boiler heat that directly. For most of the re-heat the return temp will be low. Here is Andy still attempting to justify an expensive purchase. He goes on.... Not if you are using a condensing boiler with wide modulating range such as the MAN Micromat or Viessmann. All that does is lower the flow temp in the header. If a secondary circuit kicks in it may require hotter water than what is in the header, then the boiler has to react, which can take far too much time. Fan coil units require high temps of around 80C pretty instantly, so having a header stting there at 40C is no use. Also the primary and secondary pumping has to be setup correctly. If not you may have problems. Putting a heat bank in the middle will do one of two things. a) If the heatbank is used for HW as well as CH, and there is a thermostat arrangement on the heatbank, the effect will be to prevent the boiler from operating at the lower end of its temperature range and will cause it to cycle on and off. Not if anti-cycle stats are fitted. Simple thing to do. Putting a MAN boiler on a heat bank will do the same thing as if it is on a header, except the return temp will be cooler most of run time as speaders are inside the heat bank to ensure hot water goes to the top and stays there, preventing mixing of the store, and the heat bank heats up top down. It is possible for the water at the top of the heat bank to be 80C and 20C at the bottom. Which is not the case with a header which sends heated water from the boiler directly back to the return. In commercial systems cylinders are used as neutral points to replace headers, similar to Dunsley neutralisers and heat banks. The Germans tend to use these. Cylinder neutral points, similar to a heat bank, are better when using condensing boilers. The cylinder water is stratified with say hot water for fan coil units and DHW at the top and cooler water at the bottom for background rads circuits controlled weather compensators. When the boiler reheats the neutral point cylinder, the return temp is invariable lower than using a header promoting efficiency. Also not having to set the primary and secondary pumps up is great bonus. In is usually better to divide and rule and have dedicated boilers heating to the temperatures of the various circuits. One boiler heating only high temp DHW, one high efficiency condensing boiler only heating a low temp background rad circuit etc. Boilers can then be matched for maximum efficiency. I have seen one demostic boioer heat only the fan coilo battery on an air handfling unit. There misy have been 20 or 30 of these in the place. They had a cuborad of spare for the bopioer type and they were never down for long if part were replaced. No expensive mixing valves were used and large harders and long large expensive pipes. Quite cheap to do they told me. The problem is redundancy in commercial systems, that is why boilers are sequenced together. If open drops out the other(s) will cope. Then headers, neutral points, mixing circuits etc, are incorporated to make it all work. Many commercial boilers are frames with smaller boilers on the frame, called modules, each with its own burner. The size of the whole "boiler" can be specified by adding modules. Having many modules reduces large boiler cycling as smaller burners (boilers in effect) are brought in to match the heat demand. If one module drops out the others are still operative. The "modules" are switched in to demand by a controller similar in operation to the two stage Landis & Staefa one I mentioned, only it will have stages to suit the number of burners. So, dividing and ruling when boilers are cheap enough makes a lot of sense in a small comercial large domestic setup. The whole point of this type of boiler is to have high output for a short period to heat the heatbank/cylinder quickly for DHW use, and to drive the heating system directly to allow modulation down to low output levels. Is it? Look at what I write and take note. Nah, don't bother. or b) If the heatbank is used solely for CH No DHW? and no thermostat, it will effectively create an equilibrium situation with heat in and out and no real advantage over a much smaller header. There is. The return is cooler most of the run time compared to a straight through header. It is far more efficient to run this type of boiler continuously at lower output than in bursts of high output. So, you use a cheaper and simpler boiler. The MAN type of boilers will be more efficient on a heat bank rather than on a straight through header, because of the top down heating of the heat bank. Most commercial system are still non-condensing and use headers. Where commerical condesners are used they still use the same temps as in non condensers, and gain about 5-7% because of the larger heat exchangers. Headers are commercial and are intended as: 1. A neutral point where different circuits may take off hot water to suit. The different circuits then mix to lower temps to suit. 2. Headers also are used to keep the return temp up on the boiler to prevent back end condensation. 3. A central point for all circuits. All headers are neutral points for circuiots to tee into. A heat bank gives you that and a DHW store with instant high pressure DHW. You only need cheap simple boilers with a heat bank, one of its selling points. I'll try and come up with some alternative systems. This could be entertaining..... It will be and you will be educated somewhat. Imagine allowing people like you to design a system? The thought of it..... |
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"John Aston" wrote in message
... "IMM" wrote in message ... snip With condensing boilers headers reduce efficiency. With a condenser you don't want very hot water feeding right back into the return. This raises the return temp which reduces efficiency. You want the return temp as low as possible. snip Won't a modulating boiler adjust its flow temperature and velocity to reduce the return temperature though? I thought that that was the purpose of the modulating control. Firstly there is two types of modulating control. Modulation to maintain a flow set point, as on most combi's. If set to 70C when approaching 70C the burner lowers to keep the heat moving out. The second is load compensation, which senses the flow and return temps. When the temps close up it sees the building is getting up to temp and lowers the flow temp and hence the return temp. They are very different. The Siemens BLC1.A controller I gave details can be set from load compensation to weather compensation. It does it externally to the boiler by switching with integral boiler anti-cycle control. Velocity? Pump speed. Some do, but these are on very expensive boilers. In some cases this may be a disadvantage as the pump when modulated down may not reach the far points of a largish system. |
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Aidan wrote in message om... It (primary/secondary pumping) is very rare on UK domestic installations, mainly because of the costs. snip You would be very fortunate to find a UK 'heating engineer' who understood such a system. Also, the Americans generally have bigger houses, so it's more common in the US. See ' Primary-Secondary Pumping made Easy' by Dan Holohan, available from HeatingHelp.com. It's written for home owners, so it's fairly free from techno-jargon. It's in US/Imperial units (gpm, BTU/hr, degF) but it's easy to grasp. If anyone else is reading this thread and wants some background information, I came across Warmrite's "Manual Of Modern Hydronics" at http://www.heatinghelp.com/pdfs/156.pdf It gives loads of examples of different boiler/heating arrangements. |
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"John Aston" wrote in message .. . Aidan wrote in message om... It (primary/secondary pumping) is very rare on UK domestic installations, mainly because of the costs. snip You would be very fortunate to find a UK 'heating engineer' who understood such a system. Also, the Americans generally have bigger houses, so it's more common in the US. See ' Primary-Secondary Pumping made Easy' by Dan Holohan, available from HeatingHelp.com. It's written for home owners, so it's fairly free from techno-jargon. It's in US/Imperial units (gpm, BTU/hr, degF) but it's easy to grasp. If anyone else is reading this thread and wants some background information, I came across Warmrite's "Manual Of Modern Hydronics" at http://www.heatinghelp.com/pdfs/156.pdf It gives loads of examples of different boiler/heating arrangements. Remember this USA/Canda, where things are done a little different. There is a diagram of a UFH system taken of the fresh water of a cylinder. Potable water running through the heat emitters. Not allowed here. |
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"John Aston" wrote in message .. . Aidan wrote in message om... It (primary/secondary pumping) is very rare on UK domestic installations, mainly because of the costs. snip You would be very fortunate to find a UK 'heating engineer' who understood such a system. Also, the Americans generally have bigger houses, so it's more common in the US. See ' Primary-Secondary Pumping made Easy' by Dan Holohan, available from HeatingHelp.com. It's written for home owners, so it's fairly free from techno-jargon. It's in US/Imperial units (gpm, BTU/hr, degF) but it's easy to grasp. If anyone else is reading this thread and wants some background information, I came across Warmrite's "Manual Of Modern Hydronics" at http://www.heatinghelp.com/pdfs/156.pdf It gives loads of examples of different boiler/heating arrangements. I had a look. The document is specific to UFH and the USA/Canada variantions and heavily leans towards the makers solutions. Look at figs. 2.1, regular boiler & 2.2, condensing boiler. Condensing biolers should not mix return water that woudl raise its temperature. That is why a thermal store/heat bank is the best alternative when using a condesning boiler, which is what I have been trying to get you to understand. The North Americans are way ahead of us in dosmestic forced air and vent, to the point we are hardly in the race. |
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"IMM" wrote in message
... "John Aston" wrote in message .. . If anyone else is reading this thread and wants some background information, I came across Warmrite's "Manual Of Modern Hydronics" at http://www.heatinghelp.com/pdfs/156.pdf It gives loads of examples of different boiler/heating arrangements. I had a look. The document is specific to UFH and the USA/Canada variantions and heavily leans towards the makers solutions. Look at figs. 2.1, regular boiler & 2.2, condensing boiler. Condensing biolers should not mix return water that woudl raise its temperature. That is why a thermal store/heat bank is the best alternative when using a condesning boiler, which is what I have been trying to get you to understand. Sorry if I've missed the point about a heat store. I've spoken to technical engineers at Keston, Viessman, MAN Heiztechnik and Geminox, and they have all recommended that a low loss header should be used for my application. It's difficult to argue against that weight of opinion.; |
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"John Aston" wrote in message ... "IMM" wrote in message ... "John Aston" wrote in message .. . If anyone else is reading this thread and wants some background information, I came across Warmrite's "Manual Of Modern Hydronics" at http://www.heatinghelp.com/pdfs/156.pdf It gives loads of examples of different boiler/heating arrangements. I had a look. The document is specific to UFH and the USA/Canada variantions and heavily leans towards the makers solutions. Look at figs. 2.1, regular boiler & 2.2, condensing boiler. Condensing biolers should not mix return water that woudl raise its temperature. That is why a thermal store/heat bank is the best alternative when using a condesning boiler, which is what I have been trying to get you to understand. Sorry if I've missed the point about a heat store. I've spoken to technical engineers at Keston, Viessman, MAN Heiztechnik and Geminox, and they have all recommended that a low loss header should be used for my application. It's difficult to argue against that weight of opinion.; These people mainly deal with commercial applications, where headers are the norm. You intend to use UFH, contact the UFH people and just about everyone of them will say use a thermal store. So their weight of opinion would be greater, as there are more of them. Using a header will lower a condensing boilers efficiency, that is certain. Ask the boiler people about connecting the boiler to an integrated thermal store with the UFH and rads taken off the store. Not one will say no. You also have to take into account that the tech depts have people who read from crib sheets. Did you ask them about a header specifically? Or did you ask them about running a UFH and rad system off the boiler? Look at this: http://www.heatweb.com/techtips/unde...orheating.html Then scroll down to Twin Zone Thermal Store Injection System A dedicated UFH thermal store shown with the old fashioned type of waether compensation of stats. Cheap and effective. Of course an outsise weather compensator can be fitted to maintain the UFH section to what the outside temp dictates. Rads can be taken off the top of the store. Also go to: http://www.heatweb.com scroll down to underfloor heating and see the solutions to underfloor heating. |
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On Sat, 13 Nov 2004 22:19:34 -0000, "IMM" wrote:
These people mainly deal with commercial applications, where headers are the norm. You intend to use UFH, contact the UFH people and just about everyone of them will say use a thermal store. So their weight of opinion would be greater, as there are more of them. That is not a sound argument. Using a header will lower a condensing boilers efficiency, that is certain. Ask the boiler people about connecting the boiler to an integrated thermal store with the UFH and rads taken off the store. Not one will say no. You also have to take into account that the tech depts have people who read from crib sheets. Did you ask them about a header specifically? Or did you ask them about running a UFH and rad system off the boiler? Look at this: http://www.heatweb.com/techtips/unde...orheating.html Then scroll down to Twin Zone Thermal Store Injection System A dedicated UFH thermal store shown with the old fashioned type of waether compensation of stats. Cheap and effective. Of course an outsise weather compensator can be fitted to maintain the UFH section to what the outside temp dictates. Rads can be taken off the top of the store. Also go to: http://www.heatweb.com scroll down to underfloor heating and see the solutions to underfloor heating. There are quite a number of muddled points on their underfloor heating page. For example, they say: "Reducing cycling in itself will improve efficiency, however gains are also to be achieved by keeping return temperatures to the boiler low at all times. Without a thermal store this is very difficult to achieve, unless the boiler has built in electronics. " This is erroneous. If you have a modulating, condensing boiler, which most are nowadays, they have temperature sensing and electroniics to optimise behaviour. Obviously a simple boiler with on/off burner control will operate more effciently with a buffer. They don't present a convincing argument for the case of most new boilers which modulate. Their whole "buffer store" argment is based on the idea that the boiler will otherwise cycle when driving the load, and this argument is flawed with a modulating boiler. I get the distinct impression, that as a vendor of thermal stores, they are bending the situation to justify buying their product. -- ..andy To email, substitute .nospam with .gl |
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"Andy Hall" wrote in message ... On Sat, 13 Nov 2004 22:19:34 -0000, "IMM" wrote: These people mainly deal with commercial applications, where headers are the norm. You intend to use UFH, contact the UFH people and just about everyone of them will say use a thermal store. So their weight of opinion would be greater, as there are more of them. That is not a sound argument. It is. You have never dealt with boiler manufacturers. At times their knowledge of systems is minimal. They after all only make a water heater, which is the new name for a boiler. Say boiler and you fail the corgi test. Headers with a condensing boiler, UFH and rads in a domestic system is ludicrous. I can them suggesting that if two boilers are used, or a regular boiler, but a header which raises the return temp is ludicrous. I contacted Ferroli about combining the output of two combi's. They said no. I rang their top techie, who wasn't very good at all, and he was going on about back pressure to the heat exchanger. I said a non-return valve would be fitted on each and one also on the main in, so it highly unlikely this would ever occur. I told him I had seen two Ferroli's connect this way in France. He murmured and said no. They want people to fit them as per the instructions as they can deal with that. Any deviation and they are screwed. I rang Worcester Bosch about doing the same. They said yes sir, and sent a coloured diagram on how to do it. I mentioned what Ferroli said and they confirmed my view that there is no reason at all why any two combi's of any make cannot have their draw-offs combined as long as non-return valves are used and there is enough flow. Even the makers can't agree. Using a header will lower a condensing boilers efficiency, that is certain. Ask the boiler people about connecting the boiler to an integrated thermal store with the UFH and rads taken off the store. Not one will say no. You also have to take into account that the tech depts have people who read from crib sheets. Did you ask them about a header specifically? Or did you ask them about running a UFH and rad system off the boiler? Look at this: http://www.heatweb.com/techtips/unde...orheating.html Then scroll down to Twin Zone Thermal Store Injection System A dedicated UFH thermal store shown with the old fashioned type of waether compensation of stats. Cheap and effective. Of course an outsise weather compensator can be fitted to maintain the UFH section to what the outside temp dictates. Rads can be taken off the top of the store. Also go to: http://www.heatweb.com scroll down to underfloor heating and see the solutions to underfloor heating. There are quite a number of muddled points on their underfloor heating page. For example, they say: "Reducing cycling in itself will improve efficiency, however gains are also to be achieved by keeping return temperatures to the boiler low at all times. That is so. Without a thermal store this is very difficult to achieve, unless the boiler has built in electronics. " That is so. This is erroneous. If you have a modulating, condensing boiler, which most are nowadays, What sort of modulation? Load compensation as yours is. Few have that. Most modulation is maintaining the boiler temp setpoint. The burner lowers when reaching setpoint. Very different. they have temperature sensing and electroniics to optimise behaviour. Only the up market expensive boilers. Obviously a simple boiler with on/off burner control will operate more effciently with a buffer. And one with flow setpoint burner modulation. They don't present a convincing argument for the case of most new boilers which modulate. They do. Their whole "buffer store" argment is based on the idea that the boiler will otherwise cycle when driving the load, and this argument is flawed with a modulating boiler. Not so. They say that a low temperature will be maintained from a heat bank/thermal store. This because of stratification and re-heating in one pass of the water through the boiler. A tall heat bank that has dropped to say 25C at the bottom and 55C at the top, and most of the centre 30C will be reheated in "one pass" of the stores water. This is important. The boiler will dump heat into the top of the heat bank, without mixing the stores water, heating it up from top down. It may be 75C at the top and 25C at the bottom. For most of the reheat the stores return temp to the boiler will be very low and high efficiency follows. They also say once the heat bank water starts a second pass the return temp is substantially higher. So, the secret is: - Have a tall thin cylinder to aid stratification. - Controls to ensure store water is heat in only one pass through the boiler - Stats to ensure the store is re-heated when most of water has cooled. This also prevents boiler cycling. I get the distinct impression, that as a vendor of thermal stores, they are bending the situation to justify buying their product. They are telling it as it is. Also with thermal stores/heat banks, a cheaper simpler boiler can be purchased. Their Twin Zone Thermal Store Injection System, is not as good as the sectioned temperature store I described to you some time back, where a weather compensator maintains the bottom section (UFH) of the store to the desired temp the FUN needs. |
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"John Aston" wrote in message
.. . If anyone else is reading this thread and wants some background information, I came across Warmrite's "Manual Of Modern Hydronics" at http://www.heatinghelp.com/pdfs/156.pdf I didn't know that was on the Heatinghelp website, thanks for that. Remember this USA/Canda, where things are done a little different. There is a diagram of a UFH system taken of the fresh water of a cylinder. Potable water running through the heat emitters. Not allowed here. The majority of US houses have a direct fired water heater. There are companies in the US who are aggresively selling systems which use hot water from a DHWS heater to supply UFH (e.g., Radiantec). I think that the wording of the Warmrite manual was probably chosen to avoid any legal action from such companies. They do say that the preferred approach to such "dual use" systems is to separate the space heating from those containing domestic water using a small stainless steel heat exchanger. This 'dual-use' system is banned in some states and there are many US heating professionals who are vigourously opposing it's use. |
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"Aidan" wrote in message om... "John Aston" wrote in message .. . If anyone else is reading this thread and wants some background information, I came across Warmrite's "Manual Of Modern Hydronics" at http://www.heatinghelp.com/pdfs/156.pdf I didn't know that was on the Heatinghelp website, thanks for that. Remember this USA/Canda, where things are done a little different. There is a diagram of a UFH system taken of the fresh water of a cylinder. Potable water running through the heat emitters. Not allowed here. The majority of US houses have a direct fired water heater. There are companies in the US who are aggresively selling systems which use hot water from a DHWS heater to supply UFH (e.g., Radiantec). I think that the wording of the Warmrite manual was probably chosen to avoid any legal action from such companies. They do say that the preferred approach to such "dual use" systems is to separate the space heating from those containing domestic water using a small stainless steel heat exchanger. This 'dual-use' system is banned in some states and there are many US heating professionals who are vigourously opposing it's use. They also have a large section on external drive heating. Some nice UFH layouts, but primary loops everywhere raising the return temperature, and we are going over to full condensing boilers in April. Overall the manual is of limited use to the UK market. |
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On Sat, 13 Nov 2004 23:36:44 -0000, "IMM" wrote:
"Andy Hall" wrote in message .. . On Sat, 13 Nov 2004 22:19:34 -0000, "IMM" wrote: These people mainly deal with commercial applications, where headers are the norm. You intend to use UFH, contact the UFH people and just about everyone of them will say use a thermal store. So their weight of opinion would be greater, as there are more of them. That is not a sound argument. It is. You have never dealt with boiler manufacturers. I have actually - several - and thoroughly tested their technical departments. At times their knowledge of systems is minimal. They after all only make a water heater, which is the new name for a boiler. Say boiler and you fail the corgi test. Headers with a condensing boiler, UFH and rads in a domestic system is ludicrous. I can them suggesting that if two boilers are used, or a regular boiler, but a header which raises the return temp is ludicrous. I contacted Ferroli about combining the output of two combi's. They said no. I rang their top techie, who wasn't very good at all, and he was going on about back pressure to the heat exchanger. I said a non-return valve would be fitted on each and one also on the main in, so it highly unlikely this would ever occur. I told him I had seen two Ferroli's connect this way in France. He murmured and said no. They want people to fit them as per the instructions as they can deal with that. Any deviation and they are screwed. I rang Worcester Bosch about doing the same. They said yes sir, and sent a coloured diagram on how to do it. I mentioned what Ferroli said and they confirmed my view that there is no reason at all why any two combi's of any make cannot have their draw-offs combined as long as non-return valves are used and there is enough flow. Even the makers can't agree. I'm not surprised. If I find an issue like this and there are signs of disagreement or I am not convinced of the soundness of the argument, I would probe deeper. However, to be fair to them, what proportion of Ferroli's target customer base is likely to combine two combis in the way you describe? One in a thousand? It's not going to be one in ten. Using a header will lower a condensing boilers efficiency, that is certain. Ask the boiler people about connecting the boiler to an integrated thermal store with the UFH and rads taken off the store. Not one will say no. You also have to take into account that the tech depts have people who read from crib sheets. Did you ask them about a header specifically? Or did you ask them about running a UFH and rad system off the boiler? Look at this: http://www.heatweb.com/techtips/unde...orheating.html Then scroll down to Twin Zone Thermal Store Injection System A dedicated UFH thermal store shown with the old fashioned type of waether compensation of stats. Cheap and effective. Of course an outsise weather compensator can be fitted to maintain the UFH section to what the outside temp dictates. Rads can be taken off the top of the store. Also go to: http://www.heatweb.com scroll down to underfloor heating and see the solutions to underfloor heating. There are quite a number of muddled points on their underfloor heating page. For example, they say: "Reducing cycling in itself will improve efficiency, however gains are also to be achieved by keeping return temperatures to the boiler low at all times. That is so. Without a thermal store this is very difficult to achieve, unless the boiler has built in electronics. " That is so. This is erroneous. If you have a modulating, condensing boiler, which most are nowadays, What sort of modulation? Load compensation as yours is. Few have that. Most modulation is maintaining the boiler temp setpoint. The burner lowers when reaching setpoint. Very different. Their description and justification is based on boilers running in on/off mode between 60 and 80 degrees, and the argument is that a heatstore is needed to smooth out that effect and keep the boiler running for longer periods. I don't have any argument with that. I also realise that there are different algorithms used in modulating, condensing boilers, but the effect is still that the output is reduced as the load requirement falls simply because the temperatures will be maintained if that happens. It may not be the same mechanism as load compensation, but the effect is crudely the same - the boiler does not cycle in the same way as one with full power on/off would. they have temperature sensing and electroniics to optimise behaviour. Only the up market expensive boilers. Modulation is still based on sensing *a* temperature somewhere and modulating on the basis of it. My point was that the argument that a heatstore is needed to stop cycling is really not true for this type of boiler. DPS are intimating that cycling is going to be a big issue needing a thermal store *unless* there are some electronics and modulation. Most condensing boilers are modulating types so they are really trying to make a selling point out of what has become a corner case. Obviously a simple boiler with on/off burner control will operate more effciently with a buffer. And one with flow setpoint burner modulation. Are you saying that this form of modulation would cause the burner to cycle on and off rather than up and down? I'd find that hard to believe. They don't present a convincing argument for the case of most new boilers which modulate. They do. It doesn't convince me. Once somebody does this kind of thing, then I go through the rest of their claims with a degree of scepticism. Their whole "buffer store" argment is based on the idea that the boiler will otherwise cycle when driving the load, and this argument is flawed with a modulating boiler. Not so. They say that a low temperature will be maintained from a heat bank/thermal store. This because of stratification and re-heating in one pass of the water through the boiler. A tall heat bank that has dropped to say 25C at the bottom and 55C at the top, and most of the centre 30C will be reheated in "one pass" of the stores water. This is important. The boiler will dump heat into the top of the heat bank, without mixing the stores water, heating it up from top down. It may be 75C at the top and 25C at the bottom. For most of the reheat the stores return temp to the boiler will be very low and high efficiency follows. They also say once the heat bank water starts a second pass the return temp is substantially higher. How can that happen? If you are taking water from the cylinder at 25 degrees and passing it through a heat exchanger that can manage a dT of typically 20 degrees or 25 if you're lucky, then the flow temperature can't be more than 45- 50 degrees. I assume that you are talking about a directly heated store where the bulk water goes through the boiler. This means that the water will need to go several times through the boiler to reach 75 at the top. So, the secret is: - Have a tall thin cylinder to aid stratification. - Controls to ensure store water is heat in only one pass through the boiler - Stats to ensure the store is re-heated when most of water has cooled. This also prevents boiler cycling. If the boiler is a modulating type, what is the mechanism for it cycling? This will only happen if the rate of heat production by the boiler exceeds the rate of use. If the burner has modulated down and stays lit, then it will be running in an efficient range. I get the distinct impression, that as a vendor of thermal stores, they are bending the situation to justify buying their product. They are telling it as it is. Also with thermal stores/heat banks, a cheaper simpler boiler can be purchased. They are selling a thermal store, partly on this argument. There are cases where a simpler non-modulating boiler may be what has to be used (e.g. oil). However, most modern condensing boilers are at least modulating types and this effectively knocks that argment on the head. The sales argument is a reasonable one as a sales pitch, and results in the customer buying a heatstore to make a simple boiler more efficient - revenue for DPS. What I believe not to be reasonable is the impression given that condensing boilers *need* this unless they are in some way sophisticated when the reality is that it's nowadays teh exception that condensing boilers are not modulating. While not untrue it's at least misleading. -- ..andy To email, substitute .nospam with .gl |
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"Andy Hall" wrote in message ... On Sat, 13 Nov 2004 23:36:44 -0000, "IMM" wrote: "Andy Hall" wrote in message .. . On Sat, 13 Nov 2004 22:19:34 -0000, "IMM" wrote: These people mainly deal with commercial applications, where headers are the norm. You intend to use UFH, contact the UFH people and just about everyone of them will say use a thermal store. So their weight of opinion would be greater, as there are more of them. That is not a sound argument. It is. You have never dealt with boiler manufacturers. I have actually - several - and thoroughly tested their technical departments. Once. At times their knowledge of systems is minimal. They after all only make a water heater, which is the new name for a boiler. Say boiler and you fail the corgi test. Headers with a condensing boiler, UFH and rads in a domestic system is ludicrous. I can them suggesting that if two boilers are used, or a regular boiler, but a header which raises the return temp is ludicrous. I contacted Ferroli about combining the output of two combi's. They said no. I rang their top techie, who wasn't very good at all, and he was going on about back pressure to the heat exchanger. I said a non-return valve would be fitted on each and one also on the main in, so it highly unlikely this would ever occur. I told him I had seen two Ferroli's connect this way in France. He murmured and said no. They want people to fit them as per the instructions as they can deal with that. Any deviation and they are screwed. I rang Worcester Bosch about doing the same. They said yes sir, and sent a coloured diagram on how to do it. I mentioned what Ferroli said and they confirmed my view that there is no reason at all why any two combi's of any make cannot have their draw-offs combined as long as non-return valves are used and there is enough flow. Even the makers can't agree. I'm not surprised. If I find an issue like this and there are signs of disagreement or I am not convinced of the soundness of the argument, I would probe deeper. However, to be fair to them, what proportion of Ferroli's target customer base is likely to combine two combis in the way you describe? One in a thousand? It's not going to be one in ten. Not the point. They are supposed to know their product and systems in general. They don't. Using a header will lower a condensing boilers efficiency, that is certain. Ask the boiler people about connecting the boiler to an integrated thermal store with the UFH and rads taken off the store. Not one will say no. You also have to take into account that the tech depts have people who read from crib sheets. Did you ask them about a header specifically? Or did you ask them about running a UFH and rad system off the boiler? Look at this: http://www.heatweb.com/techtips/unde...orheating.html Then scroll down to Twin Zone Thermal Store Injection System A dedicated UFH thermal store shown with the old fashioned type of waether compensation of stats. Cheap and effective. Of course an outsise weather compensator can be fitted to maintain the UFH section to what the outside temp dictates. Rads can be taken off the top of the store. Also go to: http://www.heatweb.com scroll down to underfloor heating and see the solutions to underfloor heating. There are quite a number of muddled points on their underfloor heating page. For example, they say: "Reducing cycling in itself will improve efficiency, however gains are also to be achieved by keeping return temperatures to the boiler low at all times. That is so. Without a thermal store this is very difficult to achieve, unless the boiler has built in electronics. " That is so. This is erroneous. If you have a modulating, condensing boiler, which most are nowadays, What sort of modulation? Load compensation as yours is. Few have that. Most modulation is maintaining the boiler temp setpoint. The burner lowers when reaching setpoint. Very different. Their description and justification is based on boilers running in on/off mode between 60 and 80 degrees, and the argument is that a heatstore is needed to smooth out that effect and keep the boiler running for longer periods. I don't have any argument with that. I also realise that there are different algorithms used in modulating, condensing boilers, but the effect is still that the output is reduced as the load requirement falls simply because the temperatures will be maintained if that happens. The ouput of the boiler falls, not the temperature given to the building. It may not be the same mechanism as load compensation, but the effect is crudely the same - the boiler does not cycle in the same way as one with full power on/off would. You have lost it. It reduces cycling. they have temperature sensing and electroniics to optimise behaviour. Only the up market expensive boilers. Modulation is still based on sensing *a* temperature somewhere and modulating on the basis of it. My point was that the argument that a heatstore is needed to stop cycling is really not true for this type of boiler. An expensive load compensation boiler, not flow setpoint modulation. DPS are intimating that cycling is going to be a big issue needing a thermal store *unless* there are some electronics and modulation. Correct. Most condensing boilers are modulating types so they are really trying to make a selling point out of what has become a corner case. You don't understand the various types of modulation. With a heat bank high efficiencies can gained from a very simple cheap condensing boiler. A great bonus. Obviously a simple boiler with on/off burner control will operate more effciently with a buffer. And one with flow setpoint burner modulation. Are you saying that this form of modulation would cause the burner to cycle on and off rather than up and down? I'd find that hard to believe. The burner modulates down when approaching setpoint reducing, not eliminating, cycling. A heat bank can eliminate cycling and produce high efficiencies. They don't present a convincing argument for the case of most new boilers which modulate. They do. It doesn't convince me. because you don't know much. Once somebody does this kind of thing, then I go through the rest of their claims with a degree of scepticism. Their whole "buffer store" argment is based on the idea that the boiler will otherwise cycle when driving the load, and this argument is flawed with a modulating boiler. Not so. They say that a low temperature will be maintained from a heat bank/thermal store. This because of stratification and re-heating in one pass of the water through the boiler. A tall heat bank that has dropped to say 25C at the bottom and 55C at the top, and most of the centre 30C will be reheated in "one pass" of the stores water. This is important. The boiler will dump heat into the top of the heat bank, without mixing the stores water, heating it up from top down. It may be 75C at the top and 25C at the bottom. For most of the reheat the stores return temp to the boiler will be very low and high efficiency follows. They also say once the heat bank water starts a second pass the return temp is substantially higher. How can that happen? If you are taking water from the cylinder at 25 degrees and passing it through a heat exchanger No direct. I assume that you are talking about a directly heated store where the bulk water goes through the boiler. Yes, and so are they. This means that the water will need to go several times through the boiler to reach 75 at the top. No. One pass and it heats up top down and the heated water from the boiler does not mix with the water already in the store. So, the secret is: - Have a tall thin cylinder to aid stratification. - Controls to ensure store water is heat in only one pass through the boiler - Stats to ensure the store is re-heated when most of water has cooled. This also prevents boiler cycling. If the boiler is a modulating type, what is the mechanism for it cycling? uh! ??? This will only happen if the rate of heat production by the boiler exceeds the rate of use. If the burner has modulated down and stays lit, then it will be running in an efficient range. If it has load compensation control, it may drop the flow temp tom unacceptable levels. I get the distinct impression, that as a vendor of thermal stores, they are bending the situation to justify buying their product. They are telling it as it is. Also with thermal stores/heat banks, a cheaper simpler boiler can be purchased. They are selling a thermal store, partly on this argument. Only one of the benefits. There are cases where a simpler non-modulating boiler may be what has to be used (e.g. oil). However, most modern condensing boilers are at least modulating types Depends on what type of modulation. and this effectively knocks that argment on the head. You fail to grasp. The sales argument is a reasonable one as a sales pitch, and results in the customer buying a heatstore to make a simple boiler more efficient - revenue for DPS. Heat banks are not big sellers, but getting better, as most plumbers fail to understand them. What I believe not to be reasonable is the impression given that condensing boilers *need* this unless they are in some way sophisticated when the reality is that it's nowadays teh exception that condensing boilers are not modulating. While not untrue it's at least misleading. Nothing misleading, you just fail to understand. That is sad. |
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On Sun, 14 Nov 2004 02:28:55 -0000, "IMM" wrote:
It is. You have never dealt with boiler manufacturers. I have actually - several - and thoroughly tested their technical departments. Once. Actually several times for myself and for others as well. However, to be fair to them, what proportion of Ferroli's target customer base is likely to combine two combis in the way you describe? One in a thousand? It's not going to be one in ten. Not the point. They are supposed to know their product and systems in general. They don't. Why? They are there to support the requirements of the vast majority of their customer base. For a domestic boiler, this is going to mainly be installers of single boilers in houses. How often do you imagine they get questions on how to hook two of them together? Once a year? Twice? .. The ouput of the boiler falls, not the temperature given to the building. If the output falls it's as a direct or indirect consequence of the building requiring less heat and does not imply that the burner is cycling to do it. It may not be the same mechanism as load compensation, but the effect is crudely the same - the boiler does not cycle in the same way as one with full power on/off would. You have lost it. It reduces cycling. That makes no sense. If the output is reduced, it results in less heat transfer. If the heat requirement of the load is matched by the boiler running at lower output, why would the boiler cycle. Your argument only holds true if the boiler output exceeds the load requirement. they have temperature sensing and electroniics to optimise behaviour. Only the up market expensive boilers. Modulation is still based on sensing *a* temperature somewhere and modulating on the basis of it. My point was that the argument that a heatstore is needed to stop cycling is really not true for this type of boiler. An expensive load compensation boiler, not flow setpoint modulation. The issue is that the output is reduced - the boiler modulates down, not off. If the monitored point is maintaining the flow temperature set point, then inevitably if the load reduces, the burn rate will be reduced to match it - otherwise why have modulation? DPS are intimating that cycling is going to be a big issue needing a thermal store *unless* there are some electronics and modulation. Correct. Most condensing boilers are modulating types so they are really trying to make a selling point out of what has become a corner case. You don't understand the various types of modulation. Actually I do. However the point is that the power output is being reduced. Their argument and yours is based on an assumption of cycling. Where does this arise unless the heat required is less than the minimum that the boiler can do? With a heat bank high efficiencies can gained from a very simple cheap condensing boiler. A great bonus. It becomes an equation between a) simple boiler (and there seem to be few new ones coming onto the market like that) plus heatbank, or b) boiler with modulation. The only bonus in a) for the customer is if he has to use a simple boiler for other reasons or is the cost of a) is less than b) Obviously a simple boiler with on/off burner control will operate more effciently with a buffer. And one with flow setpoint burner modulation. Are you saying that this form of modulation would cause the burner to cycle on and off rather than up and down? I'd find that hard to believe. The burner modulates down when approaching setpoint reducing, not eliminating, cycling. If the burner is turned down and not off, then cycling hasn't happened. A heat bank can eliminate cycling and produce high efficiencies. If the boiler would otherwise cycle. Where is the mechanism for that if the boiler modulates down such that it is producing heat at the rate required by the load? They don't present a convincing argument for the case of most new boilers which modulate. They do. It doesn't convince me. because you don't know much. So you believe that this can help a modulating boiler that is not cycling off because its output matches the load? How can that happen? If you are taking water from the cylinder at 25 degrees and passing it through a heat exchanger No direct. I assume that you are talking about a directly heated store where the bulk water goes through the boiler. Yes, and so are they. This means that the water will need to go several times through the boiler to reach 75 at the top. No. One pass and it heats up top down and the heated water from the boiler does not mix with the water already in the store. How can that happen? You can't have water entering the heat exchanger at 25 degrees from the bottom of the store, going through a heat exchanger with dT of 25 degrees max and delivering water into the top of the store at 75 degrees. That can only happen when the return temperature reaches 50 and that won't be in one pass. So, the secret is: - Have a tall thin cylinder to aid stratification. - Controls to ensure store water is heat in only one pass through the boiler - Stats to ensure the store is re-heated when most of water has cooled. This also prevents boiler cycling. If the boiler is a modulating type, what is the mechanism for it cycling? uh! ??? It was a simple question. What is the reason that a modulating boiler would cycle without the store if the production rate matches the load? This will only happen if the rate of heat production by the boiler exceeds the rate of use. If the burner has modulated down and stays lit, then it will be running in an efficient range. If it has load compensation control, it may drop the flow temp tom unacceptable levels. That's only an issue if you put the store there. If you are driving the heating load of radiators directly and the UFH via a blending valve, the issue doesn't arise. There is only a need to heat the store to 75 degrees if it's driving radiators and they need this temperature to give required output or if it's running a DHW exchanger as well. If it's only driving a DHW exchanger and that is handled by a priority arrangement and motorised valve, then the whole thing is simple. I get the distinct impression, that as a vendor of thermal stores, they are bending the situation to justify buying their product. They are telling it as it is. Also with thermal stores/heat banks, a cheaper simpler boiler can be purchased. They are selling a thermal store, partly on this argument. Only one of the benefits. It would be on boilers that exhibit cycling. Other than that it's a hollow argument. There are cases where a simpler non-modulating boiler may be what has to be used (e.g. oil). However, most modern condensing boilers are at least modulating types Depends on what type of modulation. Why do you believe that that affects whether or not it will cycle if driving a heating load directly and matching the requirement with lower burn rate? and this effectively knocks that argment on the head. You fail to grasp. Then please explain. I want the mechanism by which you believe that a boiler modulating on flow set point and running with output at or below load requirement will cycle the burner on and off. The sales argument is a reasonable one as a sales pitch, and results in the customer buying a heatstore to make a simple boiler more efficient - revenue for DPS. Heat banks are not big sellers, but getting better, as most plumbers fail to understand them. With embellishments and claims that are stretching reality it's not surprising. What I believe not to be reasonable is the impression given that condensing boilers *need* this unless they are in some way sophisticated when the reality is that it's nowadays teh exception that condensing boilers are not modulating. While not untrue it's at least misleading. Nothing misleading, you just fail to understand. That is sad. Then please explain the mechanisms as requested I am specifically asking why you believe that the method of modulation has an impact on whether a boiler will cycle when running at or below the heat load requirement when directly connected to the load -i.e. radiators and via a blender valve to UFH. -- ..andy To email, substitute .nospam with .gl |
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John Aston wrote:
Unfortunately, I'm a plumbing novice with that very dangerous thing: a little bit of knowledge. You are IMM, and I claim my five pounds ;-) -- Cheers, John. /================================================== ===============\ | Internode Ltd - http://www.internode.co.uk | |-----------------------------------------------------------------| | John Rumm - john(at)internode(dot)co(dot)uk | \================================================= ================/ |
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On Sun, 14 Nov 2004 03:56:21 +0000, John Rumm
wrote: John Aston wrote: Unfortunately, I'm a plumbing novice with that very dangerous thing: a little bit of knowledge. You are IMM, and I claim my five pounds ;-) Can't be. This John can write coherent sentences, spell his own name (Wol) and almost certainly do joined up hand writing (as well as joined up logic). -- ..andy To email, substitute .nospam with .gl |
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"IMM" wrote in message
... snip Headers with a condensing boiler, UFH and rads in a domestic system is ludicrous. I can them suggesting that if two boilers are used, or a regular boiler, but a header which raises the return temp is ludicrous. Doesn't the design of the header and control of the water temperature inside it mean that the return temperature is low? I found a Viessman manual on their domestic Vitodens 200 boiler which says a bit more about this http://tinyurl.com/6cqtt (page 35). For my application, it seems like the options a (a) Rely on the condensing boiler pump and zones valves if the load has sufficiently low resistance. As soon as any external circulation pumps are required, however, it appears that zones valves cannot be used and a means of hydraulically separating the boiler from the rest of the circuit is required. (Heating system suppliers give conflicting advice on this, however.) (b) Use a low loss header and circulation pumps in each heating zone. (c) Use some other means of separating the boiler flow from the secondary circulation (such as IMM's method). All UFH suppliers provide a circuit manifold with a secondary pump on the load side of a thermostatic mixing valve. That would seem to rule option out (a). However, I bet that a simple zone valve system is (erroneously) used with these manifold/pump arrangements in most UFH installations. The UFH suppliers don't seem to specify headers or heat banks. |
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"Aidan" wrote in message
om... "John Aston" wrote in message t... Doesn't an automatic bypass valve stop this problem? No. I don't think I was clear. The first paragraph referred to a heating system with a mixing valve, but only one pump, i.e., the way NOT to do it. The mixing valve was between the pump and the boiler. At low loads, most of the flow produced by the pump was re-circulated around the heating circuit leaving only a small amount to return to the boiler. The boiler did not like this. Page 39 in Viessmann's Vitodens 200 manual http://tinyurl.com/6cqtt shows a mixing valve between the pump and the boiler. With a low load, the rads could be off and the flow from the boiler could be very low. Why would this arrangement be acceptable without a low loss header? |
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"John Aston" wrote in message
... Page 39 in Viessmann's Vitodens 200 manual http://tinyurl.com/6cqtt shows a mixing valve between the pump and the boiler. With a low load, the rads could be off and the flow from the boiler could be very low. Why would this arrangement be acceptable without a low loss header? Re-reading that manual page, the design assumes that the flow though the radiators will be greater than the flow through the UFH. |
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"Andy Hall" wrote in message ... On Sun, 14 Nov 2004 02:28:55 -0000, "IMM" wrote: It is. You have never dealt with boiler manufacturers. I have actually - several - and thoroughly tested their technical departments. Once. Actually several times for myself and for others as well. You can count on one hand and have fingers to spare. On some commercial boilers, the company I once worked for knew more about their boilers than they did. We were maintaining them on a daily basis, they were not. However, to be fair to them, what proportion of Ferroli's target customer base is likely to combine two combis in the way you describe? One in a thousand? It's not going to be one in ten. Not the point. They are supposed to know their product and systems in general. They don't. Why? They are there to support the requirements of the vast majority of their customer base. They are supposed to know their product and systems in general, they do not. For a domestic boiler, this is going to mainly be installers of single boilers in houses. How often do you imagine they get questions on how to hook two of them together? Once a year? Twice? Probably more than you think. Not the point, they are supposed to know their product and systems in general, they do not. The ouput of the boiler falls, not the temperature given to the building. If the output falls it's as a direct or indirect consequence of the building requiring less heat and does not imply that the burner is cycling to do it. But will cycle and sooner than load compensation. It may not be the same mechanism as load compensation, but the effect is crudely the same - the boiler does not cycle in the same way as one with full power on/off would. You have lost it. It reduces cycling. That makes no sense. If the output is reduced, it results in less heat transfer. If the heat requirement of the load is matched by the boiler running at lower output, why would the boiler cycle. Your argument only holds true if the boiler output exceeds the load requirement. they have temperature sensing and electroniics to optimise behaviour. Only the up market expensive boilers. Modulation is still based on sensing *a* temperature somewhere and modulating on the basis of it. My point was that the argument that a heatstore is needed to stop cycling is really not true for this type of boiler. An expensive load compensation boiler, not flow setpoint modulation. The issue is that the output is reduced - the boiler modulates down, not off. I recently fitted a W-B Greenstar heating boiler coupled to a heat bank. It modulates on flow setpoint. Fine for a heat bank. More expensive load compensation would lower the flow temp. Not what I want. If the monitored point is maintaining the flow temperature set point, then inevitably if the load reduces, the burn rate will be reduced to match it - otherwise why have modulation? They all eventually cyclcle. With aheat bank, correctly wired, they do NOT. DPS are intimating that cycling is going to be a big issue needing a thermal store *unless* there are some electronics and modulation. Correct. Most condensing boilers are modulating types so they are really trying to make a selling point out of what has become a corner case. You don't understand the various types of modulation. Actually I do. You don't. However the point is that the power output is being reduced. Their argument and yours is based on an assumption of cycling. Where does this arise unless the heat required is less than the minimum that the boiler can do? Cycling will occur. With a heat bank high efficiencies can gained from a very simple cheap condensing boiler. A great bonus. It becomes an equation between a) simple boiler (and there seem to be few new ones coming onto the market like that) I just mentioned one. I can name a few more too. plus heatbank, or b) boiler with modulation. The only bonus in a) for the customer is if he has to use a simple boiler for other reasons or is the cost of a) is less than b) A heat bank plus simple boiler is cheaper than an expensive load compensation model plus a heat bank or unvented cylinder. AND... the heat bank creates a brilliant - buffer-store - neutral-point - anti-boiler-cycle - instant mains pressure hot water - all the benefits of using plate heat exchanger, etc,etc. - no expensive high tech boiler to expensively go wrong. Nothing wrong with high tech boilers when the need dictates, but why bother when you can get the same plus more and a simple cheaper more reliable boiler. NO contest. snip babble about attempting to justify an expensive purchase |
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"John Rumm" wrote in message ... John Aston wrote: Unfortunately, I'm a plumbing novice with that very dangerous thing: a little bit of knowledge. You are IMM, and I claim my five pounds ;-) And they let him near a keyboard. |
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