my system doesn't need or want a by pass. Balls to part L. Written by monkeys.
Bypass when using Grundfos Alpha2 pump
- Thread starter smokebox
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J
JonasX
I have not read this in Part L, but never looked in to it in detail. I am not sure if Part L would state "you must fit an auto by-pass valve" They word things in an open way so many angles can be used.
Smokebox, the problem of auto by-pass valves also hit me when looking at efficiencies of return temperatures. As you have pointed out, raising the return temperature can reduce efficiency greatly. Using a weather compensator ensures the return temperature is as low as possible enhancing efficiency. WC does not prevent the return temperature rising greatly when an auto by-pass valve opens. I suspect most of these valves are never set properly reducing the efficiency of condensing boilers or accelerating heat exchanger wear. They seem like a cludge to me to get out of a problem when small water capacity boilers came about.
I have found that Opentherm protocol controllers modulate the burner down to the room temperature. That is, if the room is near to the set room temperature the burner will be wrung down to minimum. The boiler has to be compatible with Opentherm. Not all are. Open therm are simple to fit devices like stats, clock, weather compensation etc. Check Opentherm stuff and boiler compatibility.
When first looking into UFH I found many makers use thermal stores. What stood out was that the boiler was on full flow all the time with no TRVs restricting flow as they close down. The boiler was disconnected from the heating loops and operated independently. The stored water is a large buffer. I have homed in on the Geminox 1 to 10kW boiler set to 40-45C or on a weather compensator only heating the UFH zones to eliminate a thermal store. One UFH zone will be enough flow for the heat exchanger. The boiler is simple, cheap and efficient an no need for a an auto by-pass. Mysteryman has directed me to look at the Viessmann Vitodens 200-W with weather compensation. Does this really have six pipe connections, one pair each for the cyl, rads and UFH? It sounds like a normal boiler adapted using complex internal controls which will be expensive to replace when faulty. It still only modulates down to pretty high kilowatt rate, unlike the Geminox's 1 kilowatt, so I would expect burner cycling from the Viessmann.
Back to the problem of the auto by-pass. I struck me that putting a small thermal store as a buffer would prevent having an auto-by-pass. This could be a cheap 40 litre cylinder. The boiler heats it with a normal pump always on full flow when pumping.. The Alpha pump is on the other side, with both flow & return pipes of the heating loops are connected to the buffer. The Alpha pump takes out what heat it needs, even if only the smallest radiator's TRV is slightly open in the house. If all rads close down there is no problem. The weather compensator keeps the small buffer vessel to the temperature it dictates. These buffer vessels may be a standard item if you look around. On commercial installations they are common. The guys here may have come across them. Rigging one up from a small cylinder cannot be difficult.
Smokebox, the problem of auto by-pass valves also hit me when looking at efficiencies of return temperatures. As you have pointed out, raising the return temperature can reduce efficiency greatly. Using a weather compensator ensures the return temperature is as low as possible enhancing efficiency. WC does not prevent the return temperature rising greatly when an auto by-pass valve opens. I suspect most of these valves are never set properly reducing the efficiency of condensing boilers or accelerating heat exchanger wear. They seem like a cludge to me to get out of a problem when small water capacity boilers came about.
I have found that Opentherm protocol controllers modulate the burner down to the room temperature. That is, if the room is near to the set room temperature the burner will be wrung down to minimum. The boiler has to be compatible with Opentherm. Not all are. Open therm are simple to fit devices like stats, clock, weather compensation etc. Check Opentherm stuff and boiler compatibility.
When first looking into UFH I found many makers use thermal stores. What stood out was that the boiler was on full flow all the time with no TRVs restricting flow as they close down. The boiler was disconnected from the heating loops and operated independently. The stored water is a large buffer. I have homed in on the Geminox 1 to 10kW boiler set to 40-45C or on a weather compensator only heating the UFH zones to eliminate a thermal store. One UFH zone will be enough flow for the heat exchanger. The boiler is simple, cheap and efficient an no need for a an auto by-pass. Mysteryman has directed me to look at the Viessmann Vitodens 200-W with weather compensation. Does this really have six pipe connections, one pair each for the cyl, rads and UFH? It sounds like a normal boiler adapted using complex internal controls which will be expensive to replace when faulty. It still only modulates down to pretty high kilowatt rate, unlike the Geminox's 1 kilowatt, so I would expect burner cycling from the Viessmann.
Back to the problem of the auto by-pass. I struck me that putting a small thermal store as a buffer would prevent having an auto-by-pass. This could be a cheap 40 litre cylinder. The boiler heats it with a normal pump always on full flow when pumping.. The Alpha pump is on the other side, with both flow & return pipes of the heating loops are connected to the buffer. The Alpha pump takes out what heat it needs, even if only the smallest radiator's TRV is slightly open in the house. If all rads close down there is no problem. The weather compensator keeps the small buffer vessel to the temperature it dictates. These buffer vessels may be a standard item if you look around. On commercial installations they are common. The guys here may have come across them. Rigging one up from a small cylinder cannot be difficult.
J
JonasX
Mysteryman,thanks for that. I will check it out. It appears the complexity of the external control for UFH, etc, are incorporated into one unit, aka combi, when the submounting kit is used. Whether the controls are external and installer fitted via his discretion, or chosen by Veissmann and packaged into the boiler, they still add complexity and hence expense and hassle if they go wrong.
I still like the idea of the simplicity of the one boiler running down to 1 kilowatt heating only UFH. To my knowledge only the Geminox does that.
Simplicity of equipment appeals to me that is why I like the low modulating Geminox only heating UFH and the simple Intergas combi only heating DHW acting like an open vented condensing multi-point. 13 litres a minute in flow does me fine. For way under £2K, more near to £1.6K, I can get the two boilers and prob' W Comp for the Geminox as well (WC would a bonus and no more than that and Would think hard about that). The UFH side would be a doddle using simple off the shelf zone valves, stat/timers and no complex, expensive temperature reduction controls.
And with my current idea no auto by-passes reducing efficiency.
OP
I am impressed with your research and understanding of these aspects. I largely agree with the conclusions that you havce come to.
MM has given advice which is amusingly contrary to his employer's advice. He also specialises in his employer's boilers.
You seem to be lucky because your particular boiler model is very sensitive to a lack of flow through it. Consequently an ABV is usually required to prevent boiler problems which we see as caused by less than ideal software. on the system and combi versions it is not a problem and just on the heat only.
All the advice, CHESS, good practice etc. is that an ABV is fitted to all installations. Many installers now do this but there are still many who dont because they dont like paying the cost when their customer does not know that its required.
You should note that the smart pumps have not been very popular. Boiler makers have not used them and are trying to get more efficient pumps using permanent magnet motors. In due course those are likely to be used with the equivalent of an inverter drive. A very few makers use stepped output pumps but only 2 or 3 steps and not totally variable.
I have not studied smart pumps in any detail but they seem to be most effectively used as a constant head device. That does not solve the minimum flow rate through the boiler which is expected by its software.
Many installers familiar with the Vaillant 400 series problems take the view that with a 28 kW or larger model a more powerful pump is needed than the 15-60 series.
Your research has apparently not noted or heeded that the advice is to only allow 2 kW for water heating in addition to the heat loss of the house. This largely arises because the water heating should be started before the heating comes on in the morning when the whole boiler output will be available.
Congratulations on having such a well insulated house! But based on the info you have given your boiler is oversized and this compounds the minimum flow problems.
Tony Glazier
I am impressed with your research and understanding of these aspects. I largely agree with the conclusions that you havce come to.
MM has given advice which is amusingly contrary to his employer's advice. He also specialises in his employer's boilers.
You seem to be lucky because your particular boiler model is very sensitive to a lack of flow through it. Consequently an ABV is usually required to prevent boiler problems which we see as caused by less than ideal software. on the system and combi versions it is not a problem and just on the heat only.
All the advice, CHESS, good practice etc. is that an ABV is fitted to all installations. Many installers now do this but there are still many who dont because they dont like paying the cost when their customer does not know that its required.
You should note that the smart pumps have not been very popular. Boiler makers have not used them and are trying to get more efficient pumps using permanent magnet motors. In due course those are likely to be used with the equivalent of an inverter drive. A very few makers use stepped output pumps but only 2 or 3 steps and not totally variable.
I have not studied smart pumps in any detail but they seem to be most effectively used as a constant head device. That does not solve the minimum flow rate through the boiler which is expected by its software.
Many installers familiar with the Vaillant 400 series problems take the view that with a 28 kW or larger model a more powerful pump is needed than the 15-60 series.
Your research has apparently not noted or heeded that the advice is to only allow 2 kW for water heating in addition to the heat loss of the house. This largely arises because the water heating should be started before the heating comes on in the morning when the whole boiler output will be available.
Congratulations on having such a well insulated house! But based on the info you have given your boiler is oversized and this compounds the minimum flow problems.
Tony Glazier
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The Domestic Building Compliance Guide (October 2010) makes it clear that a bypass is only required if the boiler manufacturer's instructions so advise. In which case, it must be an auto bypass.
I often wonder why so few manufacturers make boilers which modulate below 5kW. Modern houses are very well insulated and will only need about 7 or 8 kW to heat them in very cold weather, so logically the boiler should be modulating down to about 2kW.
I suspect it's psychological. Customers like radiators to feel hot when they touch them. If they are not, they immediately say: " No wonder I feel cold - the radiators are not on."
Did you find out the price of a Geminox boiler?
Jonas - a LLH would do pretty much what your 40l cylinder would.
JonasX";p="2138021 said:
Lord Hailsham
I totally concur all you say.
I now have a boiler which is I hope going to be OK for my house though it still only modulates down to 5kW, so I am not totally confident.
I did look up Geminox on Google - not a very informative website. I think it is a French manufacture. Haven't seen prices or UK stockists but have not really chased. Too late for my case!
I now recall you have already at the faltering start of the thread put us all right about the true timing of forced introduction of auto pressure set bypasses. Part L is indeed a bit of a dogs breakfast, though they are certainly pushing the auto bypass now.
I totally concur all you say.
I now have a boiler which is I hope going to be OK for my house though it still only modulates down to 5kW, so I am not totally confident.
I did look up Geminox on Google - not a very informative website. I think it is a French manufacture. Haven't seen prices or UK stockists but have not really chased. Too late for my case!
I now recall you have already at the faltering start of the thread put us all right about the true timing of forced introduction of auto pressure set bypasses. Part L is indeed a bit of a dogs breakfast, though they are certainly pushing the auto bypass now.
Agile thanks for remarks!
I think you are quite right about poor software. Surely on an eBUS system you could anticpate actual zone closure and put out the flame a minute earlier! Might be difficult with older fashioned type of "on" "off" controls, but not impossible.
I do think the eco TEC Plus Vallants are very sensitive to these shut down bangs - I agree. Mine actually is an open vent boiler - not combi or system.
As discussed, at max down regulation of 5.3kW, I like you fear inevitable boiler cycling even in the larger size house - especially if well insulated.
I am already suspicious that my smart pump is too small at Alpha2 15 50 130 max head of 4m. on fixed speed III at that, and if I get even more fanatical might have to change it. But whole system not yet properly balanced. Still studying behaviour! The boiler itself at full output flow of 1220 l/hr at 20*k flow return differential doing 30 kW has a high resistance of 2.4 metres on its own consuming a vast amount of pump energy just to get the water through the boiler!! I expect this is part of the contribution to the shut off explosions I had.
I have a growing uneasy feeling about persisting with a smart pump, but it should be doable. I am beginning to see why some fitters are cautious about them!
smokebox
It does not quite work like that ! The flow resistance of the boiler and rads are in series. The net result of this is that with an inadequate pump pressure the flow rate falls below what the boiler is programmed to expect.
An ABV will assist a little by reducing the flow resistance of the heating ( and ABV ) circuit but at the expense of raising the return temperature which causes the boiler to modulate back and reduce its heat output.
Its difficult to design a boiler which maintains the combustion conditions over a wide modulation range. About 3:1 tends to be usual. Bearing in mind this limitation of practical boilers makes it all the more important NOT to specify an over powered boiler like yours. It would seen that a 15 kW or 18 kW would have been quite adequate for you.
Tony
Why do you imagine that the Viessmann has "complex internal controls"?
They are standard boiler type bits and should be very reliable. Viessmann spares are certainly very expensive, a temp sensor at almost £50 ! but as they have a five year warrantee so the manufacturers dont expect to repair many under warrantee.
You dont seem to have a very good appreciation of Geminox boilers in the UK.
The reality is that they are an odd French design, they have a single service agent whose staff are seen as pretty clueless and very expensive by customers.
I used to maintain one but to be honest I did not relish that work as it was a very high earning customer in a very posh area who although having experience of Geminox problems frightened me that had anything serious gone wrong when with the non availability of UK spares it could have been out of action for weeks.
He was very keen for me to look after it but it was in a difficult area for me to cover and his lifestyle would have expected me to be there at 8 am on a Sunday morning if it had failed.
Furthermore his technical understanding was almost nil so no chance of asking him to check or adjust anything by phone. So I seem to have managed to wriggle out of dealing with his problems. At least I think so! Or perhaps my last repair is still holding up?
Tony
Now the NUB of the matter!
We have all done our homework and understand what a smart pump is. (see my earlier links), I am sure!!!
http://www.grundfos.pt/web/homept.n...d003071c2/$FILE/Grundfosliterature-815904.pdf
You cannot logically use an auto bypass in smart mode. Even though Vaillant say their boiler ecoTEC plus series needs to have them. The manual may have been written before there were smart pumps for domestic use.
My Alpha2 15-50-130, in its "smart operating triangle" produces Max 3m head, AND could choose to go there any time it wanted. The auto bypass therefore should have to have opening pressure set slightly higher than this to prevent wasteful bypassing effects on condensing during ordinary running.
Effectively, on pump overrun there will be no flow ie useless...we are already above max head of smart pump mode.
So reduce opening pressure to a smaller figure. But the pump can deliver output right down to just below one metre head. To avoid wasteful bypass the opening pressure should be set ideally below this to maximise condensation. Again NO OPENING, useless.... edit I got this wrong .the bypass would be open virtually ALL the time on a low, say 1 meter opening pressure. This would REMOVE effectively any condensation to speak of even in ordinary running..... useless again!
Where should it be set, or should we have a small standing bypass flow set at say 1.5 l/min?[90 litres per hr.] this would be a small percentage of boiler full load out put [1220l/hr], but maybe a substantial proportion when TRVs are nearing closure. Also would this be enough to prevent bangs on shut down? Only Vaillant can advise a satisfactory MINIMAL ACCEPTABLE FLOW IN LITRES PER MINUTE. for thispurpose....... only they don't understand or refuse to specify, and eventually get rather rude to emails until you write to the UK Managing director. but they still don't know. One technician said the boiler flow must never fall below 1220 l/hr - a real jester! and I suppose he is paid!
In the absence of facts and advice is it really a suck it and see? Are there any other thoughts or approaches from the experts out there? apart from expensive additional buffer schemes. Or should an auto bypass be set at about midway between 1 and 3 metres - potentially very wasteful of condensing mode!
This small fixed pre-set bypass will be open all the time and will inevitably allow some warming of the return to the boiler and reduce condensing efficiency.
You could argue I am fussing too much about too little, but much gas could be lost in a winter!
smokebox
PS Grundfos have actually told me not to use auto bypass in smart mode because of waste energy. or zero function of bypass. Much more helpful to the foolish ignorant layman than Vaillant and their shut out of all except well trained Gas Numpties. I shudder for the industry
We have all done our homework and understand what a smart pump is. (see my earlier links), I am sure!!!
http://www.grundfos.pt/web/homept.n...d003071c2/$FILE/Grundfosliterature-815904.pdf
You cannot logically use an auto bypass in smart mode. Even though Vaillant say their boiler ecoTEC plus series needs to have them. The manual may have been written before there were smart pumps for domestic use.
My Alpha2 15-50-130, in its "smart operating triangle" produces Max 3m head, AND could choose to go there any time it wanted. The auto bypass therefore should have to have opening pressure set slightly higher than this to prevent wasteful bypassing effects on condensing during ordinary running.
Effectively, on pump overrun there will be no flow ie useless...we are already above max head of smart pump mode.
So reduce opening pressure to a smaller figure. But the pump can deliver output right down to just below one metre head. To avoid wasteful bypass the opening pressure should be set ideally below this to maximise condensation. Again NO OPENING, useless.... edit I got this wrong .the bypass would be open virtually ALL the time on a low, say 1 meter opening pressure. This would REMOVE effectively any condensation to speak of even in ordinary running..... useless again!
Where should it be set, or should we have a small standing bypass flow set at say 1.5 l/min?[90 litres per hr.] this would be a small percentage of boiler full load out put [1220l/hr], but maybe a substantial proportion when TRVs are nearing closure. Also would this be enough to prevent bangs on shut down? Only Vaillant can advise a satisfactory MINIMAL ACCEPTABLE FLOW IN LITRES PER MINUTE. for thispurpose....... only they don't understand or refuse to specify, and eventually get rather rude to emails until you write to the UK Managing director. but they still don't know. One technician said the boiler flow must never fall below 1220 l/hr - a real jester! and I suppose he is paid!
In the absence of facts and advice is it really a suck it and see? Are there any other thoughts or approaches from the experts out there? apart from expensive additional buffer schemes. Or should an auto bypass be set at about midway between 1 and 3 metres - potentially very wasteful of condensing mode!
This small fixed pre-set bypass will be open all the time and will inevitably allow some warming of the return to the boiler and reduce condensing efficiency.
You could argue I am fussing too much about too little, but much gas could be lost in a winter!
smokebox
PS Grundfos have actually told me not to use auto bypass in smart mode because of waste energy. or zero function of bypass. Much more helpful to the foolish ignorant layman than Vaillant and their shut out of all except well trained Gas Numpties. I shudder for the industry
'tis why I don't fit Vaillant.
If you are concerned about HE strain have you not looked at thermal stores and LLH as alternatives?
If you are concerned about HE strain have you not looked at thermal stores and LLH as alternatives?
Dan
I need help LLH? thermal stores?
smokebox
I need help LLH? thermal stores?
'tis why I don't fit Vaillant.
If you are concerned about HE strain have you not looked at thermal stores and LLH as alternatives?
smokebox
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