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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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CH - alpha pumps
Hi all,
My CH upgrade is going well. Germans and Italians have some pretty fancy sealed system thingys. My pump is on its last legs, so will have to replace it soon. Has anyone any opinions (silly me, of course you have) about alpha pumps? I'm not quite sure how they work. What are their advantages over standard pumps? Francis |
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#2
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On Tue, 21 Sep 2004 11:48:21 +0100, "FrancisJK"
wrote: Hi all, My CH upgrade is going well. Germans and Italians have some pretty fancy sealed system thingys. My pump is on its last legs, so will have to replace it soon. Has anyone any opinions (silly me, of course you have) about alpha pumps? I'm not quite sure how they work. What are their advantages over standard pumps? Yes I do. Basically, they back off the power as flow restriction increases, so for example, if you have TRVs, the pump doesn't run its nuts off and become noisy. It has a peak pressure point at just below 0.5 m^3/hr. Above this it has a typical head/flow curve. Below it the power is reduced as restriction increases. I found that mine therefore runs a lot quieter than erstwhile models. There are a few other features such as a deblocking function. http://www.grundfos-www.com/alpha/frames_html.htm Nice product and well worth having. ..andy To email, substitute .nospam with .gl |
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#3
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"Andy Hall" wrote in message ... On Tue, 21 Sep 2004 11:48:21 +0100, "FrancisJK" wrote: Hi all, My CH upgrade is going well. Germans and Italians have some pretty fancy sealed system thingys. My pump is on its last legs, so will have to replace it soon. Has anyone any opinions (silly me, of course you have) about alpha pumps? I'm not quite sure how they work. What are their advantages over standard pumps? Yes I do. Basically, they back off the power as flow restriction increases, so for example, if you have TRVs, the pump doesn't run its nuts off and become noisy. It has a peak pressure point at just below 0.5 m^3/hr. Above this it has a typical head/flow curve. Below it the power is reduced as restriction increases. I found that mine therefore runs a lot quieter than erstwhile models. There are a few other features such as a deblocking function. http://www.grundfos-www.com/alpha/frames_html.htm Nice product and well worth having. .andy To email, substitute .nospam with .gl WOOOOOOOOOO HOOOOOOOOOOOOOOOOOOOOOOOOOOOO Thanks Andy. That installation team can install my pump right away! Francis |
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#4
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"FrancisJK" wrote in message ... "Andy Hall" wrote in message ... On Tue, 21 Sep 2004 11:48:21 +0100, "FrancisJK" wrote: Hi all, My CH upgrade is going well. Germans and Italians have some pretty fancy sealed system thingys. My pump is on its last legs, so will have to replace it soon. Has anyone any opinions (silly me, of course you have) about alpha pumps? I'm not quite sure how they work. What are their advantages over standard pumps? Yes I do. Basically, they back off the power as flow restriction increases, so for example, if you have TRVs, the pump doesn't run its nuts off and become noisy. It has a peak pressure point at just below 0.5 m^3/hr. Above this it has a typical head/flow curve. Below it the power is reduced as restriction increases. I found that mine therefore runs a lot quieter than erstwhile models. There are a few other features such as a deblocking function. http://www.grundfos-www.com/alpha/frames_html.htm Nice product and well worth having. .andy To email, substitute .nospam with .gl WOOOOOOOOOO HOOOOOOOOOOOOOOOOOOOOOOOOOOOO I assume you are woo-hooing the 4 birds in cat suits. Those birds go to trendy bars and pull out their Alphas while ordering a Martini. |
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#5
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"FrancisJK" wrote in message ... Hi all, My CH upgrade is going well. Germans and Italians have some pretty fancy sealed system thingys. My pump is on its last legs, so will have to replace it soon. Has anyone any opinions (silly me, of course you have) about alpha pumps? Yes - quite simply the Alpha pump is the biggest advance in plumbing in years and should be mandated to be put into every home thereby allowing us to close umpteen power stations. Okay bit over the top but once you've tried one you won't want to go back to anything else. |
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#6
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FrancisJK wrote:
Thanks Andy. That installation team can install my pump right away! Or better still, pump your install! -- Cheers, John. /================================================== ===============\ | Internode Ltd - http://www.internode.co.uk | |-----------------------------------------------------------------| | John Rumm - john(at)internode(dot)co(dot)uk | \================================================= ================/ |
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#7
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"FrancisJK" wrote in message ... Has anyone any opinions (silly me, of course you have) about alpha pumps? With an alpha, as TRVs close the flow falls but the head does not rise as in normal pumps. With a normal pump you need a bypass. So normal pump+bypass gives constant-ish flow rate and return temperature rises as TRVs close. Alpha gives reducing flow and a lower return temperature. Hence Alpha's are a good idea if you have a condensing boiler since those are more efficient with lower return temperature. But normal + bypass is probably better for a standard boiler since they do NOT want a lower return temperature due to the risk of condensing causing boiler corrosion. -- Malcolm Malcolm Reeves BSc CEng MIEE MIRSE, Full Circuit Ltd, Chippenham, UK , or ). Design Service for Analogue/Digital H/W & S/W Railway Signalling and Power electronics. More details plus freeware, Win95/98 DUN and Pspice tips, see: http://www.fullcircuit.com or http://www.fullcircuit.co.uk NEW - Desktop ToDo/Reminder program (free) |
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#8
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"Malcolm Reeves" wrote in message ... "FrancisJK" wrote in message ... Has anyone any opinions (silly me, of course you have) about alpha pumps? With an alpha, as TRVs close the flow falls but the head does not rise as in normal pumps. With a normal pump you need a bypass. So normal pump+bypass gives constant-ish flow rate and return temperature rises as TRVs close. Alpha gives reducing flow and a lower return temperature. Hence Alpha's are a good idea if you have a condensing boiler since those are more efficient with lower return temperature. But normal + bypass is probably better for a standard boiler since they do NOT want a lower return temperature due to the risk of condensing causing boiler corrosion. People use these having TVRs on all rads. Boilers require a minimum flow through the rads, using TRVs on all will reduce this flow. A flow switch that cuts out the burner is required when the flow gets below the boiler makers stated flow. Using a by-pass on a "modern" condensing boiler defeats much of its purpose. Older condensing boilers had the same design specs as regular boilers: the Ideal Minimiser stated 80C flow and 11C delta T on flow and return. The makers did say that you can stretch it to 15C. |
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#9
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On Wed, 22 Sep 2004 09:57:06 +0100, Malcolm Reeves
wrote: "FrancisJK" wrote in message ... Has anyone any opinions (silly me, of course you have) about alpha pumps? With an alpha, as TRVs close the flow falls but the head does not rise as in normal pumps. Not exactly. Between a certain range of flow/pressure, the Alpha behaves conventionally. When the flow falls below a certain point, that is detected and the power is reduced to reduce the head. With a normal pump you need a bypass. So normal pump+bypass gives constant-ish flow rate and return temperature rises as TRVs close. Alpha gives reducing flow and a lower return temperature. Only close to the point of total closure. Hence Alpha's are a good idea if you have a condensing boiler since those are more efficient with lower return temperature. But normal + bypass is probably better for a standard boiler since they do NOT want a lower return temperature due to the risk of condensing causing boiler corrosion. it's suitable for a normal boiler as well, since if the bypass opens, the flow increases anyway. ..andy To email, substitute .nospam with .gl |
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#10
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"Malcolm Reeves" wrote in message ... "FrancisJK" wrote in message ... Has anyone any opinions (silly me, of course you have) about alpha pumps? With an alpha, as TRVs close the flow falls but the head does not rise as in normal pumps. With a normal pump you need a bypass. So normal pump+bypass gives constant-ish flow rate and return temperature rises as TRVs close. Alpha gives reducing flow and a lower return temperature. Hence Alpha's are a good idea if you have a condensing boiler since those are more efficient with lower return temperature. But normal + bypass is probably better for a standard boiler since they do NOT want a lower return temperature due to the risk of condensing causing boiler corrosion. -- Malcolm Malcolm Reeves BSc CEng MIEE MIRSE, Full Circuit Ltd, Chippenham, UK , or ). Design Service for Analogue/Digital H/W & S/W Railway Signalling and Power electronics. More details plus freeware, Win95/98 DUN and Pspice tips, see: http://www.fullcircuit.com or http://www.fullcircuit.co.uk NEW - Desktop ToDo/Reminder program (free) Hi Malcom, Great site. I have not heard BESPOKE since that TV show "Never mind the quality, feel the width". I'll have a look in detail later. We have a back boiler unit at the moment, which is coming to the end of its life. I have an automatic by-pass valve in the circuit, but I'm not sure how to set it. Any guidance on this appreciated. Francis |
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#11
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Yes I do. Basically, they back off the power as flow restriction increases, so for example, if you have TRVs, the pump doesn't run its nuts off and become noisy. It has a peak pressure point at just below 0.5 m^3/hr. Above this it has a typical head/flow curve. Below it the power is reduced as restriction increases. I found that mine therefore runs a lot quieter than erstwhile models. There are a few other features such as a deblocking function. http://www.grundfos-www.com/alpha/frames_html.htm Nice product and well worth having. Would it work as well on a microbore system ? My installation consists of 22mm (may be 28) pipe which does a circuit under the 1st floor. From this, each rad has a tee down to microbore (probably 10mm). Only a short distance for the upstairs rads and down behind the plasterboard walls for the downstairs rads. I guess there is more resistance in this setup than an 'ordinary' setup. Alan |
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#12
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In an earlier contribution to this discussion,
Andy Hall wrote: it's suitable for a normal boiler as well, since if the bypass opens, the flow increases anyway. The thing that worries me about this discussion, though, is that if the Alpha has reduced its power/speed/head because the flow has reduced, there may not be enough head to open the by-pass. There may not then be enough flow through the boiler to remove the residual heat after it stops firing. How do you ensure that this doesn't happen? -- Cheers, Set Square ______ Please reply to newsgroup. Reply address is invalid. |
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#13
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On Wed, 22 Sep 2004 13:09:32 +0100, "Set Square"
wrote: In an earlier contribution to this discussion, Andy Hall wrote: it's suitable for a normal boiler as well, since if the bypass opens, the flow increases anyway. The thing that worries me about this discussion, though, is that if the Alpha has reduced its power/speed/head because the flow has reduced, there may not be enough head to open the by-pass. There may not then be enough flow through the boiler to remove the residual heat after it stops firing. How do you ensure that this doesn't happen? By setting the bypass appropriately. You can also adjust the pump. ..andy To email, substitute .nospam with .gl |
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#14
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"Alan Campbell" wrote in message om... Yes I do. Basically, they back off the power as flow restriction increases, so for example, if you have TRVs, the pump doesn't run its nuts off and become noisy. It has a peak pressure point at just below 0.5 m^3/hr. Above this it has a typical head/flow curve. Below it the power is reduced as restriction increases. I found that mine therefore runs a lot quieter than erstwhile models. There are a few other features such as a deblocking function. http://www.grundfos-www.com/alpha/frames_html.htm Nice product and well worth having. Would it work as well on a microbore system ? My installation consists of 22mm (may be 28) pipe which does a circuit under the 1st floor. From this, each rad has a tee down to microbore (probably 10mm). Only a short distance for the upstairs rads and down behind the plasterboard walls for the downstairs rads. I guess there is more resistance in this setup than an 'ordinary' setup. It will work just as well on Microbore. |
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#15
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"Alan Campbell" wrote in message om... Yes I do. Basically, they back off the power as flow restriction increases, so for example, if you have TRVs, the pump doesn't run its nuts off and become noisy. It has a peak pressure point at just below 0.5 m^3/hr. Above this it has a typical head/flow curve. Below it the power is reduced as restriction increases. I found that mine therefore runs a lot quieter than erstwhile models. There are a few other features such as a deblocking function. http://www.grundfos-www.com/alpha/frames_html.htm Nice product and well worth having. Would it work as well on a microbore system ? My installation consists of 22mm (may be 28) pipe which does a circuit under the 1st floor. From this, each rad has a tee down to microbore (probably 10mm). Only a short distance for the upstairs rads and down behind the plasterboard walls for the downstairs rads. My installation, heating loop, conists of a two-floor teeoff with, on each floor, the distribution pipes stepping down to each rad. Every rad is fed by 10mm pipes but the distribution pipe steps down at each stage; - =22==22-10-15==15==15-10-10===10== | | | Rad Rad Rad | | | =22==22-10-15==15==15-10-10===10== each floor has a minimum of copper although it uses several sizes of piping. The design/installation was at a time when copper prices were going through the roof -and Belgian paratroopers were dropping onto the coppermines in Zaire (or was it the Congo.?) I guess there is more resistance in this setup than an 'ordinary' setup. Alan -- Brian |
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#17
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"Andy Hall" wrote in message ... On Wed, 22 Sep 2004 09:57:06 +0100, Malcolm Reeves wrote: "FrancisJK" wrote in message ... Has anyone any opinions (silly me, of course you have) about alpha pumps? With an alpha, as TRVs close the flow falls but the head does not rise as in normal pumps. Not exactly. Between a certain range of flow/pressure, the Alpha behaves conventionally. When the flow falls below a certain point, that is detected and the power is reduced to reduce the head. With a normal pump you need a bypass. So normal pump+bypass gives constant-ish flow rate and return temperature rises as TRVs close. Alpha gives reducing flow and a lower return temperature. Only close to the point of total closure. Hence Alpha's are a good idea if you have a condensing boiler since those are more efficient with lower return temperature. But normal + bypass is probably better for a standard boiler since they do NOT want a lower return temperature due to the risk of condensing causing boiler corrosion. it's suitable for a normal boiler as well, since if the bypass opens, the flow increases anyway. .andy To email, substitute .nospam with .gl Andy, I'm now puzzled. Is it a choice between Standard pump AND automativ by-pass against Alpha Pump AND no by-pass Francis |
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#18
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On Wed, 22 Sep 2004 13:38:42 +0100, "FrancisJK"
wrote: "Andy Hall" wrote in message .. . On Wed, 22 Sep 2004 09:57:06 +0100, Malcolm Reeves wrote: "FrancisJK" wrote in message ... Has anyone any opinions (silly me, of course you have) about alpha pumps? With an alpha, as TRVs close the flow falls but the head does not rise as in normal pumps. Not exactly. Between a certain range of flow/pressure, the Alpha behaves conventionally. When the flow falls below a certain point, that is detected and the power is reduced to reduce the head. With a normal pump you need a bypass. So normal pump+bypass gives constant-ish flow rate and return temperature rises as TRVs close. Alpha gives reducing flow and a lower return temperature. Only close to the point of total closure. Hence Alpha's are a good idea if you have a condensing boiler since those are more efficient with lower return temperature. But normal + bypass is probably better for a standard boiler since they do NOT want a lower return temperature due to the risk of condensing causing boiler corrosion. it's suitable for a normal boiler as well, since if the bypass opens, the flow increases anyway. .andy To email, substitute .nospam with .gl Andy, I'm now puzzled. Is it a choice between Standard pump AND automativ by-pass against Alpha Pump AND no by-pass Francis Not as far as I am concerned. You can use an Alpha pump either way. The point comes back to the earlier one of what do you want the boiler to do when the flow becomes low as the result of the TRVs beginning to close. If it;s a conventional boiler, you want it to be locked off by the room thermostat when the flow becomes so low that the boiler begins to short cycle as a result of the high boiler output vs. low demand.. That will happen if if the flow rate is low because the TRVs have reduced it or if the return temperature is high because there is a substantial amount of bypass. Therefore you have the room thermostat in a room without TRV to put that additional control in place and stop the boiler shortly after the TRVs have reduced the load. With a condensing boiler, you still want to detect this case, but because the boiler will have modulated down adjustment will be easier. It's useful to have a bypass anyway, to cover the case where the boiler has been in full burn and the heat demand is suddenly satisfied - this is the pump over-run case. Some boilers have very low water content and if they have an integral pump can live with an internal bypass as well. If you have an external pump, then an external bypass is normally used anyway - in the form of a lockshield valve across flow and return. Using an automatic bypass instead is a better idea just for that since you are not shunting the flow back to the return until either the CH has reached low demand or turned off altogether. ..andy To email, substitute .nospam with .gl |
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#19
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"Andy Hall" wrote in message ... On Wed, 22 Sep 2004 13:38:42 +0100, "FrancisJK" wrote: "Andy Hall" wrote in message .. . On Wed, 22 Sep 2004 09:57:06 +0100, Malcolm Reeves wrote: "FrancisJK" wrote in message ... Has anyone any opinions (silly me, of course you have) about alpha pumps? With an alpha, as TRVs close the flow falls but the head does not rise as in normal pumps. Not exactly. Between a certain range of flow/pressure, the Alpha behaves conventionally. When the flow falls below a certain point, that is detected and the power is reduced to reduce the head. With a normal pump you need a bypass. So normal pump+bypass gives constant-ish flow rate and return temperature rises as TRVs close. Alpha gives reducing flow and a lower return temperature. Only close to the point of total closure. Hence Alpha's are a good idea if you have a condensing boiler since those are more efficient with lower return temperature. But normal + bypass is probably better for a standard boiler since they do NOT want a lower return temperature due to the risk of condensing causing boiler corrosion. it's suitable for a normal boiler as well, since if the bypass opens, the flow increases anyway. .andy To email, substitute .nospam with .gl Andy, I'm now puzzled. Is it a choice between Standard pump AND automativ by-pass against Alpha Pump AND no by-pass Francis Not as far as I am concerned. You can use an Alpha pump either way. The point comes back to the earlier one of what do you want the boiler to do when the flow becomes low as the result of the TRVs beginning to close. If it;s a conventional boiler, you want it to be locked off by the room thermostat when the flow becomes so low that the boiler begins to short cycle as a result of the high boiler output vs. low demand.. That will happen if if the flow rate is low because the TRVs have reduced it or if the return temperature is high because there is a substantial amount of bypass. Therefore you have the room thermostat in a room without TRV to put that additional control in place and stop the boiler shortly after the TRVs have reduced the load. With a condensing boiler, you still want to detect this case, but because the boiler will have modulated down adjustment will be easier. It's useful to have a bypass anyway, to cover the case where the boiler has been in full burn and the heat demand is suddenly satisfied - this is the pump over-run case. Some boilers have very low water content and if they have an integral pump can live with an internal bypass as well. If you have an external pump, then an external bypass is normally used anyway - in the form of a lockshield valve across flow and return. Using an automatic bypass instead is a better idea just for that since you are not shunting the flow back to the return until either the CH has reached low demand or turned off altogether. .andy To email, substitute .nospam with .gl Well, I'll read all that later. I have to go and paint a door now. I'm leaning towards the alpha and it's installation team! Which one is you and wich one is Ed?! ;-) Francis |
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#20
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On Wed, 22 Sep 2004 12:53:55 +0100, "FrancisJK"
wrote: I have an automatic by-pass valve in the circuit, but I'm not sure how to set it. Any guidance on this appreciated. The one I have just says set it 20% above the on state head so what I'd do is first balance the system with all TRVs open and bypass set to off. Then reduce bypass until there was some flow (pipe gets hot) then turn bypass up a bit so there was no flow. -- Malcolm Malcolm Reeves BSc CEng MIEE MIRSE, Full Circuit Ltd, Chippenham, UK , or ). Design Service for Analogue/Digital H/W & S/W Railway Signalling and Power electronics. More details plus freeware, Win95/98 DUN and Pspice tips, see: http://www.fullcircuit.com or http://www.fullcircuit.co.uk NEW - Desktop ToDo/Reminder program (free) |
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#21
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On Wed, 22 Sep 2004 13:09:32 +0100, "Set Square"
wrote: In an earlier contribution to this discussion, Andy Hall wrote: it's suitable for a normal boiler as well, since if the bypass opens, the flow increases anyway. The thing that worries me about this discussion, though, is that if the Alpha has reduced its power/speed/head because the flow has reduced, there may not be enough head to open the by-pass. True, or if the bypass opens before the alpha "effect" kicks in what is the point of an alpha? Basically they both do similar things so its debatable which you need. There may not then be enough flow through the boiler to remove the residual heat after it stops firing. How do you ensure that this doesn't happen? How does a bypass remove residual heat? For that the pump has to run so you need pump overrun not bypass. However, you may need a bypass and pump overrun to cover the situation of all rads with TRVs (which you shouldn't have) and needing to get rid of some heat (to the pipe work presumably). -- Malcolm Malcolm Reeves BSc CEng MIEE MIRSE, Full Circuit Ltd, Chippenham, UK , or ). Design Service for Analogue/Digital H/W & S/W Railway Signalling and Power electronics. More details plus freeware, Win95/98 DUN and Pspice tips, see: http://www.fullcircuit.com or http://www.fullcircuit.co.uk NEW - Desktop ToDo/Reminder program (free) |
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#22
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On Wed, 22 Sep 2004 21:34:25 +0100, Malcolm Reeves
wrote: On Wed, 22 Sep 2004 13:09:32 +0100, "Set Square" wrote: In an earlier contribution to this discussion, Andy Hall wrote: it's suitable for a normal boiler as well, since if the bypass opens, the flow increases anyway. The thing that worries me about this discussion, though, is that if the Alpha has reduced its power/speed/head because the flow has reduced, there may not be enough head to open the by-pass. True, or if the bypass opens before the alpha "effect" kicks in what is the point of an alpha? Basically they both do similar things so its debatable which you need. There may not then be enough flow through the boiler to remove the residual heat after it stops firing. How do you ensure that this doesn't happen? How does a bypass remove residual heat? For that the pump has to run so you need pump overrun not bypass. However, you may need a bypass and pump overrun to cover the situation of all rads with TRVs (which you shouldn't have) and needing to get rid of some heat (to the pipe work presumably). How would the bypass operate without a pump? ..andy To email, substitute .nospam with .gl |
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#23
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On Wed, 22 Sep 2004 14:00:09 +0100, Andy Hall
wrote: With an alpha, as TRVs close the flow falls but the head does not rise as in normal pumps. Not exactly. Between a certain range of flow/pressure, the Alpha behaves conventionally. When the flow falls below a certain point, that is detected and the power is reduced to reduce the head. OK. Nothing is perfect but the TRVs will close enough to reduce the flow otherwise what are they doing, nothing. The flow has to reduce to lower the average radiator temperature and so lower its output. So at the bit of the alpha curve where the head rises to keep the flow up then all that will happen is the TRVs close more. They must reduce the flow. With a normal pump you need a bypass. So normal pump+bypass gives constant-ish flow rate and return temperature rises as TRVs close. Alpha gives reducing flow and a lower return temperature. Only close to the point of total closure. The heat flow from the boiler is the flow, kg/s, and the difference across the boiler. The heat output from the rads is the temperature difference. Since the input water temperature is fixed then TRVs must slow the flow down so the output temperature is lower and thus the average water temperature lower. Ergo TRVs must reduce the flow AT any time they are having an effect. NOT just when they are about to shut the rad off completely. Hence Alpha's are a good idea if you have a condensing boiler since those are more efficient with lower return temperature. But normal + bypass is probably better for a standard boiler since they do NOT want a lower return temperature due to the risk of condensing causing boiler corrosion. it's suitable for a normal boiler as well, since if the bypass opens, the flow increases anyway. So what is the point of an alpha? If the bypass is kicking in before the alpha "effect" why not use a normal cheaper pump! If the alpha "effect" kicks in the bypass won't open. Both effects are driven by pressure, ones got to happen first then the other won't. An alpha would suit something like a coal fired room heater where the best way to run it is slow continuous release of heat, not super-burn/off/super-burn/off as you get with normal pump + stat (no bypass). Also a condensing modulating gas boiler (as long as it could cope with low flow (coal fires can). -- Malcolm Malcolm Reeves BSc CEng MIEE MIRSE, Full Circuit Ltd, Chippenham, UK , or ). Design Service for Analogue/Digital H/W & S/W Railway Signalling and Power electronics. More details plus freeware, Win95/98 DUN and Pspice tips, see: http://www.fullcircuit.com or http://www.fullcircuit.co.uk NEW - Desktop ToDo/Reminder program (free) |
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#24
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On Wed, 22 Sep 2004 21:52:50 +0100, Malcolm Reeves
wrote: On Wed, 22 Sep 2004 14:00:09 +0100, Andy Hall wrote: With an alpha, as TRVs close the flow falls but the head does not rise as in normal pumps. Not exactly. Between a certain range of flow/pressure, the Alpha behaves conventionally. When the flow falls below a certain point, that is detected and the power is reduced to reduce the head. OK. Nothing is perfect but the TRVs will close enough to reduce the flow otherwise what are they doing, nothing. The flow has to reduce to lower the average radiator temperature and so lower its output. So at the bit of the alpha curve where the head rises to keep the flow up then all that will happen is the TRVs close more. They must reduce the flow. The flow reduces naturally as a result of the increased restriction. The point is to reduce the power to the pump to stop it from screaming its nuts off. With a normal pump you need a bypass. So normal pump+bypass gives constant-ish flow rate and return temperature rises as TRVs close. Alpha gives reducing flow and a lower return temperature. Only close to the point of total closure. The heat flow from the boiler is the flow, kg/s, and the difference across the boiler. Only while the boiler is firing. At the point where the heat used is less than that produced it will begin to cycle. The heat output from the rads is the temperature difference. It is proportional to the temperature difference and flow. Since the input water temperature is fixed It isn't. It will move up and down as the boiler cycles. then TRVs must slow the flow down so the output temperature is lower and thus the average water temperature lower. Ergo TRVs must reduce the flow AT any time they are having an effect. NOT just when they are about to shut the rad off completely. That wasn't my point. Hence Alpha's are a good idea if you have a condensing boiler since those are more efficient with lower return temperature. But normal + bypass is probably better for a standard boiler since they do NOT want a lower return temperature due to the risk of condensing causing boiler corrosion. it's suitable for a normal boiler as well, since if the bypass opens, the flow increases anyway. So what is the point of an alpha? If the bypass is kicking in before the alpha "effect" why not use a normal cheaper pump! If the alpha "effect" kicks in the bypass won't open. That would depend on how the bypass is set. Have you read through the Alpha datasheet? Both effects are driven by pressure, ones got to happen first then the other won't. You're missing the point. It is far better to have the pump reduce output as the heat flow reduces rather than shortcircuiting it back to the boiler with the pump on full power. An alpha would suit something like a coal fired room heater where the best way to run it is slow continuous release of heat, not super-burn/off/super-burn/off as you get with normal pump + stat (no bypass). Also a condensing modulating gas boiler (as long as it could cope with low flow (coal fires can). This misses the point completely. ..andy To email, substitute .nospam with .gl |
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#25
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In an earlier contribution to this discussion,
Malcolm Reeves wrote: How does a bypass remove residual heat? For that the pump has to run so you need pump overrun not bypass. However, you may need a bypass and pump overrun to cover the situation of all rads with TRVs (which you shouldn't have) and needing to get rid of some heat (to the pipe work presumably). By providing a flow path for the water when the pump is over-running and all the TRVs and/or zone valves are shut. The residual heat is actually dissipated by the pipework as the water flows round the by-pass circuit. If the residual heat can't be carried away from the boiler, the boiler temperature continues to rise to the point where its overheat stat trips - which requires manual resetting. -- Cheers, Set Square ______ Please reply to newsgroup. Reply address is invalid. |
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#26
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"Andy Hall" wrote in message ... On Wed, 22 Sep 2004 21:52:50 +0100, Malcolm Reeves wrote: On Wed, 22 Sep 2004 14:00:09 +0100, Andy Hall wrote: With an alpha, as TRVs close the flow falls but the head does not rise as in normal pumps. Not exactly. Between a certain range of flow/pressure, the Alpha behaves conventionally. When the flow falls below a certain point, that is detected and the power is reduced to reduce the head. OK. Nothing is perfect but the TRVs will close enough to reduce the flow otherwise what are they doing, nothing. The flow has to reduce to lower the average radiator temperature and so lower its output. So at the bit of the alpha curve where the head rises to keep the flow up then all that will happen is the TRVs close more. They must reduce the flow. The flow reduces naturally as a result of the increased restriction. The point is to reduce the power to the pump to stop it from screaming its nuts off. With a normal pump you need a bypass. So normal pump+bypass gives constant-ish flow rate and return temperature rises as TRVs close. Alpha gives reducing flow and a lower return temperature. Only close to the point of total closure. The heat flow from the boiler is the flow, kg/s, and the difference across the boiler. Only while the boiler is firing. At the point where the heat used is less than that produced it will begin to cycle. The heat output from the rads is the temperature difference. It is proportional to the temperature difference and flow. Since the input water temperature is fixed It isn't. It will move up and down as the boiler cycles. then TRVs must slow the flow down so the output temperature is lower and thus the average water temperature lower. Ergo TRVs must reduce the flow AT any time they are having an effect. NOT just when they are about to shut the rad off completely. That wasn't my point. Hence Alpha's are a good idea if you have a condensing boiler since those are more efficient with lower return temperature. But normal + bypass is probably better for a standard boiler since they do NOT want a lower return temperature due to the risk of condensing causing boiler corrosion. it's suitable for a normal boiler as well, since if the bypass opens, the flow increases anyway. So what is the point of an alpha? If the bypass is kicking in before the alpha "effect" why not use a normal cheaper pump! If the alpha "effect" kicks in the bypass won't open. That would depend on how the bypass is set. Have you read through the Alpha datasheet? Both effects are driven by pressure, ones got to happen first then the other won't. You're missing the point. It is far better to have the pump reduce output as the heat flow reduces rather than shortcircuiting it back to the boiler with the pump on full power. An alpha would suit something like a coal fired room heater where the best way to run it is slow continuous release of heat, not super-burn/off/super-burn/off as you get with normal pump + stat (no bypass). Also a condensing modulating gas boiler (as long as it could cope with low flow (coal fires can). This misses the point completely. .andy To email, substitute .nospam with .gl Well, the door is painted, a nice grey. Gunmetal, actually. You guys seemed to be enjoying yourselves while I was away. I have upstairs on a separate zone, with TRV's on all but one Rad. I've just installed a wireless stat in that room. Don't know about the pump yet. I'll probably go for the alpha and i can always close the abv fully if necessary. Francis |
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#27
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"Set Square" wrote in message ... In an earlier contribution to this discussion, Malcolm Reeves wrote: How does a bypass remove residual heat? For that the pump has to run so you need pump overrun not bypass. However, you may need a bypass and pump overrun to cover the situation of all rads with TRVs (which you shouldn't have) and needing to get rid of some heat (to the pipe work presumably). By providing a flow path for the water when the pump is over-running and all the TRVs and/or zone valves are shut. The residual heat is actually dissipated by the pipework as the water flows round the by-pass circuit. If the residual heat can't be carried away from the boiler, the boiler temperature continues to rise to the point where its overheat stat trips - which requires manual resetting. In this scenario the boiler is required by the regs to turn off so the bypass is only in operation for a very short while |
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#28
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"FrancisJK" wrote in message ... I'm now puzzled. Is it a choice between Standard pump AND automativ by-pass against Alpha Pump AND no by-pass No. I have a conventional boiler, Alpha pump and an automatic bypass. Plus 4 zones valves run from room thermostats and only a couple of TRVs. This gives lots of degrees of freedom in setting up the system to operate efficiently - or in getting it wrong if you don't set it up well. |
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#29
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In an earlier contribution to this discussion,
G&M wrote: "Set Square" wrote in message ... In an earlier contribution to this discussion, Malcolm Reeves wrote: How does a bypass remove residual heat? For that the pump has to run so you need pump overrun not bypass. However, you may need a bypass and pump overrun to cover the situation of all rads with TRVs (which you shouldn't have) and needing to get rid of some heat (to the pipe work presumably). By providing a flow path for the water when the pump is over-running and all the TRVs and/or zone valves are shut. The residual heat is actually dissipated by the pipework as the water flows round the by-pass circuit. If the residual heat can't be carried away from the boiler, the boiler temperature continues to rise to the point where its overheat stat trips - which requires manual resetting. In this scenario the boiler is required by the regs to turn off so the bypass is only in operation for a very short while This is true - but the by-pass *must* operate under these conditions, albeit for a short period - otherwise the boiler trips. But the by-pass *shouldn't* operate at any other time. I don't have any direct experience of this, but I was speculating that - with an Alpha pump - it may be difficult (or perhaps even impossible?) to adjust everything so that the by-pass *only* operates during pump over-run conditions. -- Cheers, Set Square ______ Please reply to newsgroup. Reply address is invalid. |
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#30
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"Set Square" wrote in message ... How does a bypass remove residual heat? For that the pump has to run so you need pump overrun not bypass. However, you may need a bypass and pump overrun to cover the situation of all rads with TRVs (which you shouldn't have) and needing to get rid of some heat (to the pipe work presumably). By providing a flow path for the water when the pump is over-running and all the TRVs and/or zone valves are shut. The residual heat is actually dissipated by the pipework as the water flows round the by-pass circuit. If the residual heat can't be carried away from the boiler, the boiler temperature continues to rise to the point where its overheat stat trips - which requires manual resetting. In this scenario the boiler is required by the regs to turn off so the bypass is only in operation for a very short while This is true - but the by-pass *must* operate under these conditions, albeit for a short period - otherwise the boiler trips. But the by-pass *shouldn't* operate at any other time. I don't have any direct experience of this, but I was speculating that - with an Alpha pump - it may be difficult (or perhaps even impossible?) to adjust everything so that the by-pass *only* operates during pump over-run conditions. Oh you can adjust an Alpha to do almost anything. You can even make it run like a normal pump if you want though it gets a lot louder then. But I found that by setting it a 'bit of a turn' more clockwise than is really required then I can make the by-pass operate. |
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#31
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On Thu, 23 Sep 2004 00:21:08 +0100, "G&M"
wrote: I don't have any direct experience of this, but I was speculating that - with an Alpha pump - it may be difficult (or perhaps even impossible?) to adjust everything so that the by-pass *only* operates during pump over-run conditions. Oh you can adjust an Alpha to do almost anything. You can even make it run like a normal pump if you want though it gets a lot louder then. But I found that by setting it a 'bit of a turn' more clockwise than is really required then I can make the by-pass operate. At last an interesting comment of practical experience. However, I think the alpha is now operating in almost standard pump mode. The alpha data sheet curves show for a normal pump change of flow from Q1 DOWN to Q2 gives INCREASE of head from A1 to A2. As expected. But for alpha Q1 down to Q2 gives DECREASE of head from A2 DOWN to A3. Which is what you want if don't have an auto bypass. With an alpha and an auto bypass you have to adjust the alpha to behave like a normal pump for the bypass to operate, that is flow down, head up. OK, an alpha has more adjustment than a normal pump but is the extra cost worth it? For standard boiler I'd say no as you don't want flow reduction and low return temperatures with a standard due to the risk of condensation. For a condensing boiler I would be tempted by an alpha as with the better adjustment you are more likely to be able to delay the operation of the bypass and so work sometimes with a lower flow, lower return temperature, which makes a condenser more efficient. However I wouldn't like to say for sure that you would recover the extra GBP35 and alpha costs in the lifetime of the pump. -- Malcolm Malcolm Reeves BSc CEng MIEE MIRSE, Full Circuit Ltd, Chippenham, UK , or ). Design Service for Analogue/Digital H/W & S/W Railway Signalling and Power electronics. More details plus freeware, Win95/98 DUN and Pspice tips, see: http://www.fullcircuit.com or http://www.fullcircuit.co.uk NEW - Desktop ToDo/Reminder program (free) |
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#32
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On Wed, 22 Sep 2004 21:46:23 +0100, Andy Hall
wrote: There may not then be enough flow through the boiler to remove the residual heat after it stops firing. How do you ensure that this doesn't happen? How does a bypass remove residual heat? For that the pump has to run so you need pump overrun not bypass. However, you may need a bypass and pump overrun to cover the situation of all rads with TRVs (which you shouldn't have) and needing to get rid of some heat (to the pipe work presumably). How would the bypass operate without a pump? That's not my point, which was pump overrun is what you need to get rid of boiler excess heat. Bypass does not figure, except that you need to allow flow. You could have an always on rad for that. You always need to allow some flow, during normal firing primarily so if you have that you have it during overrun to. -- Malcolm Malcolm Reeves BSc CEng MIEE MIRSE, Full Circuit Ltd, Chippenham, UK , or ). Design Service for Analogue/Digital H/W & S/W Railway Signalling and Power electronics. More details plus freeware, Win95/98 DUN and Pspice tips, see: http://www.fullcircuit.com or http://www.fullcircuit.co.uk NEW - Desktop ToDo/Reminder program (free) |
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#33
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On Thu, 23 Sep 2004 08:48:41 +0100, Malcolm Reeves
wrote: On Wed, 22 Sep 2004 21:46:23 +0100, Andy Hall wrote: There may not then be enough flow through the boiler to remove the residual heat after it stops firing. How do you ensure that this doesn't happen? How does a bypass remove residual heat? For that the pump has to run so you need pump overrun not bypass. However, you may need a bypass and pump overrun to cover the situation of all rads with TRVs (which you shouldn't have) and needing to get rid of some heat (to the pipe work presumably). How would the bypass operate without a pump? That's not my point, which was pump overrun is what you need to get rid of boiler excess heat. Bypass does not figure, except that you need to allow flow. You could have an always on rad for that. You always need to allow some flow, during normal firing primarily so if you have that you have it during overrun to. You can use an automatic bypass purely to take care of the over-run case. ..andy To email, substitute .nospam with .gl |
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#34
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On Thu, 23 Sep 2004 08:42:08 +0100, Malcolm Reeves
wrote: On Thu, 23 Sep 2004 00:21:08 +0100, "G&M" wrote: I don't have any direct experience of this, but I was speculating that - with an Alpha pump - it may be difficult (or perhaps even impossible?) to adjust everything so that the by-pass *only* operates during pump over-run conditions. Oh you can adjust an Alpha to do almost anything. You can even make it run like a normal pump if you want though it gets a lot louder then. But I found that by setting it a 'bit of a turn' more clockwise than is really required then I can make the by-pass operate. At last an interesting comment of practical experience. However, I think the alpha is now operating in almost standard pump mode. The alpha data sheet curves show for a normal pump change of flow from Q1 DOWN to Q2 gives INCREASE of head from A1 to A2. As expected. But for alpha Q1 down to Q2 gives DECREASE of head from A2 DOWN to A3. Which is what you want if don't have an auto bypass. This ignores the issue of the effect of short circuiting the flow back to the return if a bypass is used for the low flow rate case. With an alpha and an auto bypass you have to adjust the alpha to behave like a normal pump for the bypass to operate, that is flow down, head up. OK, an alpha has more adjustment than a normal pump but is the extra cost worth it? Obviously. The bypass is simply set to the appropriate opening point, if one is used at all. For standard boiler I'd say no as you don't want flow reduction and low return temperatures with a standard due to the risk of condensation. That's a red herring, because if the flow has reduced (which it will have done), then relatively little low temperature water will be being introduced into the heat exchanger. In a conventional boiler, the heat exchanger is not designed to allow condensation anyway and so the low flow will simply cause the boiler to cycle off as the heat load falls. For a condensing boiler I would be tempted by an alpha as with the better adjustment you are more likely to be able to delay the operation of the bypass and so work sometimes with a lower flow, lower return temperature, which makes a condenser more efficient. This misses the point. A condensing boiler typically modulates as well, so there is much less of an issue of mismatch between the rate of heat production and use. However I wouldn't like to say for sure that you would recover the extra GBP35 and alpha costs in the lifetime of the pump. That depends on the lifetime of the pump, but it certainly improves system behaviour as regards noise. If it saves the cost of an ABV, then it's a no-brainer, although the latter may be useful as a better alternative than a simple lockshield. ..andy To email, substitute .nospam with .gl |
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#35
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On Wed, 22 Sep 2004 22:08:16 +0100, Andy Hall
wrote: On Wed, 22 Sep 2004 21:52:50 +0100, Malcolm Reeves wrote: On Wed, 22 Sep 2004 14:00:09 +0100, Andy Hall wrote: With an alpha, as TRVs close the flow falls but the head does not rise as in normal pumps. Not exactly. Between a certain range of flow/pressure, the Alpha behaves conventionally. When the flow falls below a certain point, that is detected and the power is reduced to reduce the head. Not according to the alpha data sheet which says: Electronically controlled, the pump can, by means of a selector switch located on the terminal box, be set to: • 2 constant pressure curves • 2 proportional pressure curves • 3 fixed speed curves. So either constant head (I think I said that), proportional head (head goes down with lower flow), or 3 normal pump modes. OK. Nothing is perfect but the TRVs will close enough to reduce the flow otherwise what are they doing, nothing. The flow has to reduce to lower the average radiator temperature and so lower its output. So at the bit of the alpha curve where the head rises to keep the flow up then all that will happen is the TRVs close more. They must reduce the flow. The flow reduces naturally as a result of the increased restriction. The point is to reduce the power to the pump to stop it from screaming its nuts off. I'm glad we agree it seemed to me before that you said the flow did not reduce until the TRVs almost closed, which is of course not the case. Protection of standard pump nuts can be achieved by a bypass. With a normal pump you need a bypass. So normal pump+bypass gives constant-ish flow rate and return temperature rises as TRVs close. Alpha gives reducing flow and a lower return temperature. Only close to the point of total closure. No. If alpha is in constant or proportion head mode flow decreases. Otherwise it is in normal pump mode. The heat flow from the boiler is the flow, kg/s, and the difference across the boiler. Only while the boiler is firing. At the point where the heat used is less than that produced it will begin to cycle. Of course but what is the relevance of that. It will always cycle when Watts in Watts out. We are discussing TRVs and pumps. The heat output from the rads is the temperature difference. It is proportional to the temperature difference and flow. No it isn't. Temperature output from a rad is proportional to the average rad temperature (or rather difference to the room). The flow does not come into the rad output. What happens is that as you restrict the flow the output temperature drops so the average rad temperature making its output less. Since the input water temperature is fixed It isn't. It will move up and down as the boiler cycles. We aren't talking about the boiler cycling but in any case at any point in time the temperature in to the rads is fixed. It is the output temperature that decreases, as the TRVS control it, in order to lower the rad output. My point is that the flow varies since you seem to be saying that TRVs only reduce the flow as the close completely. then TRVs must slow the flow down so the output temperature is lower and thus the average water temperature lower. Ergo TRVs must reduce the flow AT any time they are having an effect. NOT just when they are about to shut the rad off completely. That wasn't my point. I'm glad we agree on that then as I read your post differently. Hence Alpha's are a good idea if you have a condensing boiler since those are more efficient with lower return temperature. But normal + bypass is probably better for a standard boiler since they do NOT want a lower return temperature due to the risk of condensing causing boiler corrosion. it's suitable for a normal boiler as well, since if the bypass opens, the flow increases anyway. So what is the point of an alpha? If the bypass is kicking in before the alpha "effect" why not use a normal cheaper pump! If the alpha "effect" kicks in the bypass won't open. That would depend on how the bypass is set. Have you read through the Alpha datasheet? Yes, have you? Both effects are driven by pressure, ones got to happen first then the other won't. You're missing the point. It is far better to have the pump reduce output as the heat flow reduces rather than shortcircuiting it back to the boiler with the pump on full power. I'd agree that the fine adjustment on the alpha is nice. But you still have to operate the alpha in normal pump mode to use it with a bypass. If the fine adjustment necessary, or worth the money? I think we'll have to disagree on that. An alpha would suit something like a coal fired room heater where the best way to run it is slow continuous release of heat, not super-burn/off/super-burn/off as you get with normal pump + stat (no bypass). Also a condensing modulating gas boiler (as long as it could cope with low flow (coal fires can). This misses the point completely. Why? The alpha's modes of constant and proportional head are designed for system that work best with a variable flow. That has to be boilers that modulate their output. Also, those boilers that are happy with a low return temperature, which is another effect of low flow. Set it any differently and it's just a fine adjustment standard pump. -- Malcolm Malcolm Reeves BSc CEng MIEE MIRSE, Full Circuit Ltd, Chippenham, UK , or ). Design Service for Analogue/Digital H/W & S/W Railway Signalling and Power electronics. More details plus freeware, Win95/98 DUN and Pspice tips, see: http://www.fullcircuit.com or http://www.fullcircuit.co.uk NEW - Desktop ToDo/Reminder program (free) |
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#36
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On Thu, 23 Sep 2004 09:18:51 +0100, Malcolm Reeves
wrote: Between a certain range of flow/pressure, the Alpha behaves conventionally. When the flow falls below a certain point, that is detected and the power is reduced to reduce the head. Not according to the alpha data sheet which says: Electronically controlled, the pump can, by means of a selector switch located on the terminal box, be set to: • 2 constant pressure curves • 2 proportional pressure curves • 3 fixed speed curves. So either constant head (I think I said that), proportional head (head goes down with lower flow), or 3 normal pump modes. You need to look at the technical manual for the Alpha. They have some other products which have different selectable operating modes. OK. Nothing is perfect but the TRVs will close enough to reduce the flow otherwise what are they doing, nothing. The flow has to reduce to lower the average radiator temperature and so lower its output. So at the bit of the alpha curve where the head rises to keep the flow up then all that will happen is the TRVs close more. They must reduce the flow. The flow reduces naturally as a result of the increased restriction. The point is to reduce the power to the pump to stop it from screaming its nuts off. I'm glad we agree it seemed to me before that you said the flow did not reduce until the TRVs almost closed, which is of course not the case. No I didn't say that. Protection of standard pump nuts can be achieved by a bypass. Possibly, but there's no point. With a normal pump you need a bypass. So normal pump+bypass gives constant-ish flow rate and return temperature rises as TRVs close. Alpha gives reducing flow and a lower return temperature. Only close to the point of total closure. No. If alpha is in constant or proportion head mode flow decreases. Otherwise it is in normal pump mode. Have a look at the technical manual. The heat flow from the boiler is the flow, kg/s, and the difference across the boiler. Only while the boiler is firing. At the point where the heat used is less than that produced it will begin to cycle. Of course but what is the relevance of that. It will always cycle when Watts in Watts out. We are discussing TRVs and pumps. I know. The point was that the behaviour is not simple because the burner is being fired on and off. This has a substantial effect on the temperatures. The heat output from the rads is the temperature difference. It is proportional to the temperature difference and flow. No it isn't. Temperature output from a rad is proportional to the average rad temperature (or rather difference to the room). The flow does not come into the rad output. From the perspective of heat output to the room, it is approximately proportional to the Mean Water to Air Temperature. From the perspective of heat delivery to the radiator (which will be the same since none of it disappears) it will be proportional to the flow and temperature difference across the radiator. What happens is that as you restrict the flow the output temperature drops so the average rad temperature making its output less. That is because the rate of heat delivery to the radiator reduces. Since the input water temperature is fixed It isn't. It will move up and down as the boiler cycles. We aren't talking about the boiler cycling but in any case at any point in time the temperature in to the rads is fixed. It is the output temperature that decreases, as the TRVS control it, in order to lower the rad output. You can't treat them in isolation though. If the boiler is cycling, the output temperature is far from being fixed, My point is that the flow varies since you seem to be saying that TRVs only reduce the flow as the close completely. I didn't say that at all. then TRVs must slow the flow down so the output temperature is lower and thus the average water temperature lower. Ergo TRVs must reduce the flow AT any time they are having an effect. NOT just when they are about to shut the rad off completely. That wasn't my point. I'm glad we agree on that then as I read your post differently. Hence Alpha's are a good idea if you have a condensing boiler since those are more efficient with lower return temperature. But normal + bypass is probably better for a standard boiler since they do NOT want a lower return temperature due to the risk of condensing causing boiler corrosion. it's suitable for a normal boiler as well, since if the bypass opens, the flow increases anyway. So what is the point of an alpha? If the bypass is kicking in before the alpha "effect" why not use a normal cheaper pump! If the alpha "effect" kicks in the bypass won't open. That would depend on how the bypass is set. Have you read through the Alpha datasheet? Yes, have you? Yep, and the technical manual. Plus I have one of these and know how it behaves. Both effects are driven by pressure, ones got to happen first then the other won't. You're missing the point. It is far better to have the pump reduce output as the heat flow reduces rather than shortcircuiting it back to the boiler with the pump on full power. I'd agree that the fine adjustment on the alpha is nice. But you still have to operate the alpha in normal pump mode to use it with a bypass. If the fine adjustment necessary, or worth the money? I think we'll have to disagree on that. Up to you. You can effectively replace the need for a bypass and have quieter and better controlled operation. An alpha would suit something like a coal fired room heater where the best way to run it is slow continuous release of heat, not super-burn/off/super-burn/off as you get with normal pump + stat (no bypass). Also a condensing modulating gas boiler (as long as it could cope with low flow (coal fires can). This misses the point completely. Why? The alpha's modes of constant and proportional head are designed for system that work best with a variable flow. That has to be boilers that modulate their output. Also, those boilers that are happy with a low return temperature, which is another effect of low flow. Set it any differently and it's just a fine adjustment standard pump. Even a fixed boiler has varying output temperature as the burner cycles. There isn't going to be an issue with the return temperature being low at low flow rates anyway. ..andy To email, substitute .nospam with .gl |
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#37
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"Malcolm Reeves" wrote in message ... On Thu, 23 Sep 2004 00:21:08 +0100, "G&M" wrote: I don't have any direct experience of this, but I was speculating that - with an Alpha pump - it may be difficult (or perhaps even impossible?) to adjust everything so that the by-pass *only* operates during pump over-run conditions. Oh you can adjust an Alpha to do almost anything. You can even make it run like a normal pump if you want though it gets a lot louder then. But I found that by setting it a 'bit of a turn' more clockwise than is really required then I can make the by-pass operate. At last an interesting comment of practical experience. However, I think the alpha is now operating in almost standard pump mode. The alpha data sheet curves show for a normal pump change of flow from Q1 DOWN to Q2 gives INCREASE of head from A1 to A2. As expected. But for alpha Q1 down to Q2 gives DECREASE of head from A2 DOWN to A3. Which is what you want if don't have an auto bypass. With an alpha and an auto bypass you have to adjust the alpha to behave like a normal pump for the bypass to operate, that is flow down, head up. OK, an alpha has more adjustment than a normal pump but is the extra cost worth it? For standard boiler I'd say no as you don't want flow reduction and low return temperatures with a standard due to the risk of condensation. For a condensing boiler I would be tempted by an alpha as with the better adjustment you are more likely to be able to delay the operation of the bypass and so work sometimes with a lower flow, lower return temperature, which makes a condenser more efficient. The efficiency of a condenser is not determined by the return flow, only the temperature. You can get a lower return temp by having the flow faster, or in some instances slower. However I wouldn't like to say for sure that you would recover the extra GBP35 and alpha costs in the lifetime of the pump. They are quieter. Nevertheless, if a system is installed properly and the odd bit of vibration absorbing flexible pipe or plastic pipe is used, a pump should not be noisy, even if the TRVs are nearly all closed. Malcolm Malcolm Reeves BSc CEng MIEE MIRSE, Full Circuit Ltd, Chippenham, UK , or ). Design Service for Analogue/Digital H/W & S/W Railway Signalling and Power electronics. More details plus freeware, Win95/98 DUN and Pspice tips, see: http://www.fullcircuit.com or http://www.fullcircuit.co.uk NEW - Desktop ToDo/Reminder program (free) |
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On Thu, 23 Sep 2004 08:58:21 +0100, Andy Hall
wrote: On Thu, 23 Sep 2004 08:48:41 +0100, Malcolm Reeves wrote: On Wed, 22 Sep 2004 21:46:23 +0100, Andy Hall wrote: There may not then be enough flow through the boiler to remove the residual heat after it stops firing. How do you ensure that this doesn't happen? How does a bypass remove residual heat? For that the pump has to run so you need pump overrun not bypass. However, you may need a bypass and pump overrun to cover the situation of all rads with TRVs (which you shouldn't have) and needing to get rid of some heat (to the pipe work presumably). How would the bypass operate without a pump? That's not my point, which was pump overrun is what you need to get rid of boiler excess heat. Bypass does not figure, except that you need to allow flow. You could have an always on rad for that. You always need to allow some flow, during normal firing primarily so if you have that you have it during overrun to. You can use an automatic bypass purely to take care of the over-run case. Are we taking about the same sort of automatic bypass, i.e. pressure driven or is this an electric bypass? As I fail to see how a pressure bypass can handle overrun without first handling the run into closed TRVs first. If TRVs are open, stat goes off, boiler goes off, pump goes to over run then water will go to rads (or cylinder). -- Malcolm Malcolm Reeves BSc CEng MIEE MIRSE, Full Circuit Ltd, Chippenham, UK , or ). Design Service for Analogue/Digital H/W & S/W Railway Signalling and Power electronics. More details plus freeware, Win95/98 DUN and Pspice tips, see: http://www.fullcircuit.com or http://www.fullcircuit.co.uk NEW - Desktop ToDo/Reminder program (free) |
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#39
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In an earlier contribution to this discussion,
Malcolm Reeves wrote: That's not my point, which was pump overrun is what you need to get rid of boiler excess heat. Bypass does not figure, except that you need to allow flow. You could have an always on rad for that. You may not want this in the summer! Consider an S-Plan system with the heating zone valve firmly shut, and the boiler running to heat the hot water. When this is satisfied, the HW zone valve closes and the boiler stops firing. BUT you still need some flow during the pump over-run period to stop the boiler from tripping. Where can this flow go if you don't have a by-pass? -- Cheers, Set Square ______ Please reply to newsgroup. Reply address is invalid. |
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#40
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On Thu, 23 Sep 2004 09:33:06 +0100, Andy Hall
wrote: On Thu, 23 Sep 2004 09:18:51 +0100, Malcolm Reeves wrote: Between a certain range of flow/pressure, the Alpha behaves conventionally. When the flow falls below a certain point, that is detected and the power is reduced to reduce the head. Not according to the alpha data sheet which says: Electronically controlled, the pump can, by means of a selector switch located on the terminal box, be set to: • 2 constant pressure curves • 2 proportional pressure curves • 3 fixed speed curves. So either constant head (I think I said that), proportional head (head goes down with lower flow), or 3 normal pump modes. You need to look at the technical manual for the Alpha. I am looking at the pdf from the grundfos website alpha_data_booklet.pdf, 16 pages with graphs etc. from which the quote above is taken - page 6. Protection of standard pump nuts can be achieved by a bypass. Possibly, but there's no point. You need auto bypass for standard pump - I was being humorous referring to your comment it would scream its nuts off. The heat flow from the boiler is the flow, kg/s, and the difference across the boiler. Only while the boiler is firing. At the point where the heat used is less than that produced it will begin to cycle. Of course but what is the relevance of that. It will always cycle when Watts in Watts out. We are discussing TRVs and pumps. I know. The point was that the behaviour is not simple because the burner is being fired on and off. This has a substantial effect on the temperatures. If the boiler is short cycling yes but if it is doing that you need to fix it since that is very wasteful. If it is on a long cycle then you can consider it as being in almost steady state. There will be a steady climb in temperatures but relative temperatures will be similar during this time. From the perspective of heat output to the room, it is approximately proportional to the Mean Water to Air Temperature. From the perspective of heat delivery to the radiator (which will be the same since none of it disappears) it will be proportional to the flow and temperature difference across the radiator. Agreed (I think I said that). You can't treat them in isolation though. If the boiler is cycling, the output temperature is far from being fixed, Short cycling is a different problem and needs to be fixed. Normal long cycling is relatively stable temperature difference on an overall rising base line. Both effects are driven by pressure, ones got to happen first then the other won't. You're missing the point. It is far better to have the pump reduce output as the heat flow reduces rather than shortcircuiting it back to the boiler with the pump on full power. Why? Assuming you have a normal pump set to the right setting. In fact since there is a recommend minimum speed to stop sludging it could be argued that a bypass, which keeps the boiler flow constant is better as it stops the sludge settling in the boiler. Of course if you correctly treat the water then sludge is not an issue, hopefully. An alpha would suit something like a coal fired room heater where the best way to run it is slow continuous release of heat, not super-burn/off/super-burn/off as you get with normal pump + stat (no bypass). Also a condensing modulating gas boiler (as long as it could cope with low flow (coal fires can). This misses the point completely. Why? The alpha's modes of constant and proportional head are designed for system that work best with a variable flow. That has to be boilers that modulate their output. Also, those boilers that are happy with a low return temperature, which is another effect of low flow. Set it any differently and it's just a fine adjustment standard pump. Even a fixed boiler has varying output temperature as the burner cycles. There isn't going to be an issue with the return temperature being low at low flow rates anyway. I would tend to agree with you as it would seem reasonable that a low flow low temperature return is going to quickly warm up in the heat exchange. However, I'd want to check with the boiler manufacturer that he was happy with that. I suspect most might prefer the constant flow arrangement so as to avoid even the only perceived risk of condensation. So I'd reckon most would recommend normal + bypass (that's the result I had when talking to HRM). Of course, assuming this is a standard boiler, not a condensing. -- Malcolm Malcolm Reeves BSc CEng MIEE MIRSE, Full Circuit Ltd, Chippenham, UK , or ). Design Service for Analogue/Digital H/W & S/W Railway Signalling and Power electronics. More details plus freeware, Win95/98 DUN and Pspice tips, see: http://www.fullcircuit.com or http://www.fullcircuit.co.uk NEW - Desktop ToDo/Reminder program (free) |
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