Central heating pump sizing

[Reddwarf4ever]

The calc for KW is, KW= m3/hr*16.66*60*deltaT/860. = 0.85*16.66*60*12/860, 11.86KW.

This the ref I have to D.18. (1 is the default)

View attachment 47439

Does that mean the pump will run 24/7 ?

 

[John.g]

Only applies to pump in overrun and for the overrun period I would think but don't know how it (if on eco mode 3) can differentiate between overrun after a low heat demand vs a high heat demand, there seems to be no simple settings on these boilers, surely it's really not that difficult to heat a few litres of water.

 

[Reddwarf4ever]

Changed D17 to 1, set the temperature by the dial to 55oC ( should be the inlet temperature) took some readings while it was firing, but abandoned for now, as not sure quite what was happening....D41=37oC D40=47oC D05=36oC wasn’t firing very hard 🤔

I thought D05 was the target temperature, so if I am controlling the inlet temperature, I thought it would read 55oC ???

will try again tomorrow....

some of the descriptions leave a lot to be desired, especially as you say the Eco mode 3

 

[John.g]

One would think that it should control as you say, above.

Another often discussed item is the power output and duration during ignition sequence, some say its 80% for 60 secs, others say 80% for 20 secs. You can get a good feel for this by noting the (pump) flowrate, the deltaT and the fan speed, d.34, during normal operation, then sometime when you next start up the boiler just watch and note the fan speed d.34 at start up and the time it remains at this speed before changing, can then calculate the output as fan speed is almost directly proportional to power output.

 

[Reddwarf4ever]

One would think that it should control as you say, above.

Another often discussed item is the power output and duration during ignition sequence, some say its 80% for 60 secs, others say 80% for 20 secs. You can get a good feel for this by noting the (pump) flowrate, the deltaT and the fan speed, d.34, during normal operation, then sometime when you next start up the boiler just watch and note the fan speed d.34 at start up and the time it remains at this speed before changing, can then calculate the output as fan speed is almost directly proportional to power output.

Hi
did a single observation ( Wife was pressuring me to do lunch 😂 )
Fan speed initially 400, quickly dropped and stabilised at 277, stayed there for 1 minute exactly, then dropped to 150 for around 20 seconds then climbed back to 277 for 30 seconds then cut out.....not sure what that means, if anything 🤔

also have been running steadily @62oC (10oC DT) for past few days, very stable, although boiler does modulate up & down a lot....tried increasing to 64oC to help warm up the house quicker, but it then it increased firing, expected but continued to 67oC and cut out 🤯, seems unacceptable that a boiler can’t fire up just enough to give a 2oC raise in temperatur.e, of course a 5oC tolerance would, likely have made this possible.

UPDATE
on normal running@ DT 10oC 0.7m3/Hr target 64oC the fan speed modulates between 143 & 192, doesn’t sound a lot, but can be heard. With proper tuning, this differential should slowly decrease & the modulation should be minimal.

I wondered if the PP setting on the pump could be responsible for varying the pump flow, chasing the continual boiler modulation 🤔 so switched the pump to CP2, 0.6m3/Hr and lower Watts 👍 and immediately the modulation stopped 👍 the fan is now constant at 150, occasionally it goes up to 154, then falls back to 150......so much better than the constant noise of the boiler firing up and down, although being in the kitchen it cant really be heard in the lounge, although the modulation could be heard in the spare bedroom, which is immediately above the boiler, but not any longer 👍

wonder if this pump behaviour is normal, or just ‘ one of those things’ 🤔

Any thoughts on the room stat question ???

thanks

 

[John.g]

Will be able to put a few numbers together once you (if) can get a steady reading, even briefly, the fan/boiler output should be more or less rock steady normally, changing from PP setting may help but normally this also stays steady unless TRVs etc are operating.

 

[John.g]

Hi
did a single observation ( Wife was pressuring me to do lunch 😂 )
Fan speed initially 400, quickly dropped and stabilised at 277, stayed there for 1 minute exactly, then dropped to 150 for around 20 seconds then climbed back to 277 for 30 seconds then cut out.***.not sure what that means, if anything 🤔

also have been running steadily @62oC (10oC DT) for past few days, very stable, although boiler does modulate up & down a lot....tried increasing to 64oC to help warm up the house quicker, but it then it increased firing, expected but continued to 67oC and cut out 🤯, seems unacceptable that a boiler can’t fire up just enough to give a 2oC raise in temperatur.e, of course a 5oC tolerance would, likely have made this possible.

UPDATE
on normal running@ DT 10oC 0.7m3/Hr target 64oC the fan speed modulates between 143 & 192, doesn’t sound a lot, but can be heard. With proper tuning, this differential should slowly decrease & the modulation should be minimal.

I wondered if the PP setting on the pump could be responsible for varying the pump flow, chasing the continual boiler modulation 🤔 so switched the pump to CP2, 0.6m3/Hr and lower Watts 👍 and immediately the modulation stopped 👍 the fan is now constant at 150, occasionally it goes up to 154, then falls back to 150.***..so much better than the constant noise of the boiler firing up and down, although being in the kitchen it cant really be heard in the lounge, although the modulation could be heard in the spare bedroom, which is immediately above the boiler, but not any longer 👍

wonder if this pump behaviour is normal, or just ‘ one of those things’ 🤔

Any thoughts on the room stat question ???

thanks

No real thoughts on room stat, its switching in at SP-1C (should be SP-0.5C) and off at SP-0.3 but should be SP so 0.3C error at this end, maybe faulty controller but not a huge problem?.

PP mode would certainly seem to be a bit erratic, I wouldn't have thought it should behave like this.
Now that its settled down at 0.6 ms/hr and 1500 rpm, what are the flow/return temps??, I can then give some numbers.

 

[John.g]

At the moment the best I can come up with is that 5200 rpm = 18kw.
So at startup the boiler did a pre purge at 4000 rpm, probably followed by ignition at 77% output = 13.85kw but fell very rapidly to 2770 RPM = 53.35% output or 9.6kw for 60 secs and then reduced further to 1500 rpm or 5.2kw. The lowest (erratic) fan speed was 1430 rpm = 4.95kw.

 

[Reddwarf4ever]

No real thoughts on room stat, its switching in at SP-1C (should be SP-0.5C) and off at SP-0.3 but should be SP so 0.3C error at this end, maybe faulty controller but not a huge problem?.

PP mode would certainly seem to be a bit erratic, I wouldn't have thought it should behave like this.
Now that its settled down at 0.6 ms/hr and 1500 rpm, what are the flow/return temps??, I can then give some numbers.

re room stat, is the 0.5oC offset setting, ‘ shared’ either side of the target temperature?

i.e. 22.5oC +-0.5oC.....or is it meant to be only below the target temperature ? Presently, it doesn’t come back on again until it’s fallen to 21.5oC which is a Whole degree below the target temperature....which is too far really 🥶

will ask DAB about the PP mode causing the boiler to continually modulate And CP mode keeping it steady. The boiler ran virtually all day without cutting out, then in the evening it cut out, no obvious reason and continued starting and stopping until 1030pm when it shut down for the night....wish I could find out what causes this.🤔 have boiler set at 14KW to allow it to heat up quicker first thing in the morning, but feel of I reduced this to say 11KW maybe it would cope in the evening, but wouldn’t be suitable, if the cut out allowed +-5oC tolerance maybe this would prevent it cycling in this way.....can’t monitor the boiler to see why it cuts out......
DT 10oC return 54oC target 64oC.flow 0.6m3/Hr.....thanks

 

[John.g]

That changes things so, it might mean that the boiler is outputting 12.9 kw for 60 secs which is closer to what some users are finding, if correct it means that the deltaT for that 60 secs or so is 18.5C at a flow rate of 0.6m3/hr and means that the flow temp at start up or re firing is < 45.5C to avoid exceeding a target temp of 64C. I feel that a flow rate of 0.8/0.9 m3/hr is the optimum, unfortunately PP3 which gives that causes modulating, if the pump watts are not changing then it points to a very/over sensitive boiler controller bearing in mind that a change of 1 watt in PP3 mode only results in a flow change of 0.08 m3/hr.

Might also be worth talking to DAB re a replacement pump as it was stopping on full speed originally which it certainly shouldn't have been so faulty?.

Your old pump I think gives almost your exact requirement (will look at pump curves again), so maybe take the top off it and see if its sludged up.

 

[Reddwarf4ever]

That changes things so, it might mean that the boiler is outputting 12.9 kw for 60 secs which is closer to what some users are finding, if correct it means that the deltaT for that 60 secs or so is 18.5C at a flow rate of 0.6m3/hr and means that the flow temp at start up or re firing is < 45.5C to avoid exceeding a target temp of 64C. I feel that a flow rate of 0.8/0.9 m3/hr is the optimum, unfortunately PP3 which gives that causes modulating, if the pump watts are not changing then it points to a very/over sensitive boiler controller bearing in mind that a change of 1 watt in PP3 mode only results in a flow change of 0.08 m3/hr.

Might also be worth talking to DAB re a replacement pump as it was stopping on full speed originally which it certainly shouldn't have been so faulty?.

Your old pump I think gives almost your exact requirement (will look at pump curves again), so maybe take the top off it and see if its sludged up.

Hi
don't remember it stopping in high speed, assume CP3 ?...the inlet temperature was excessive, but that’s all I remember ....will see what DAB say, thanks

 

[John.g]

The pump was running at its maximum setting of constant curve 3 which shouldn't have caused the below.
See post 126 on page 11, also post 123 on page 11.
I would watch the watts on PP3 again and if no deviation then difficult not to conclude that you have a hyper sensitive (or faulty) boiler PID controller.
But if the DAB is displaying LOW FLOW again on full speed 3, I wouldn't be too happy and would contact DAB.

"UPDATE
1- I have set the boiler to 18KW, first time ever....its modulating ok, but have had to reduce the target temperature to 68oC to keep the inlet below 55oC.***.so quite a low DT
2-occasionally the pump declares ‘LO FLOW’ then shortly after shuts off, restarts with the same message, then after a few minutes reverts to the previous readings I.e. 0.7m3/Hr etc....set it to heating only for now to establish that works ok."

 

[Reddwarf4ever]

The pump was running at its maximum setting of constant curve 3 which shouldn't have caused the below.
See post 126 on page 11, also post 123 on page 11.
I would watch the watts on PP3 again and if no deviation then difficult not to conclude that you have a hyper sensitive (or faulty) boiler PID controller.
But if the DAB is displaying LOW FLOW again on full speed 3, I wouldn't be too happy and would contact DAB.

"UPDATE
1- I have set the boiler to 18KW, first time ever....its modulating ok, but have had to reduce the target temperature to 68oC to keep the inlet below 55oC.***.so quite a low DT
2-occasionally the pump declares ‘LO FLOW’ then shortly after shuts off, restarts with the same message, then after a few minutes reverts to the previous readings I.e. 0.7m3/Hr etc....set it to heating only for now to establish that works ok."

Thanks, completely forgot about that, your memory is better than mine 😂 have emailed DAB & will check other settings again......

 

[John.g]

Maybe no harm to check that full speed setting again as there may have been some air in the pump after installation, if "no flow "not annunciating now then pump OK IMO.

 

[Reddwarf4ever]

Maybe no harm to check that full speed setting again as there may have been some air in the pump after installation, if "no flow "not annunciating now then pump OK IMO.

Exactly my thoughts 😎CP3 30W 4.5m 0.9m3/Hr....will leave as is amd see how the boiler performs

 

[John.g]

CP3 wasn't the problem No Flow, it was fixed speed 3 @ 36W AFAIK, even if you never use this mode, the pump should run at this setting with no problems.

 

[Reddwarf4ever]

CP3 wasn't the problem No Flow, it was fixed speed 3 @ 36W AFAIK, even if you never use this mode, the pump should run at this setting with no problems.

I thought CP3 is fixed speed 3 🤔 there is CP PP and the other one which AFAIK is for underfloor heating, does that make sense ?

had a reply from DAB, they said the pump can’t be faulty as no error codes are shown....this is crazy, I explained that although internal diagnostics will capture virtually all faults, this should not be relied on 100% as there could be a fault , not actually recognised as a designated fault.....seems the way of the world, relying 100% on technology, without any understanding of science principals and common sense.

Update, 2nd reply from DAB

“Hi,
There appears to be something within your system which is causing the pump to ramp up and down due to high resistance , which the pump is designed to do in PP setting, we suggest then that in regards to your system to be set and operated in CP setting to overcome this issue”

 

[John.g]

CP3 is fixed pressure, the pump changes speed to maintain a constant pressure, the one you had it on was constant curve or fixed speed (3) where the pressure will decrease with increasing flow and increase with reducing flow, this is the way all the old circ pumps ran, so c/o to CC 3 and ensure its not flagging up NO FLOW.

 

[Reddwarf4ever]

Trying CP3 28W 4.5m 0.8m3/Hr 62oC target DT 19oC Boiler started modulating fan speed 145<>177 consistent. Then later when I checked, it was 150 and steady, no modulation ??? Then within seconds of me looking at it, it cut out ??? Can’t see why though 🤔 took 3 restarts and stayed running, started modulating again 145<>180

it seems, sometimes at least, that the boiler decreases it’s firing with each successive restart, which allows it to eventually stay running, is that how it works, or am I imagining it ???

 

[Reddwarf4ever]

After only 1/2 Hr it stopped ‘ continually modulating‘ and is steady at a fan speed of 150

 

[John.g]

The whole thing is baffling, even though its highly unlikely that the pump would fluctuate on both CP and PP, it might be worth trying it on a "true" fixed speed or constant curve setting ie CC3 as shown above, if the boiler is still fluctuating then I think you can rule out the pump as the cause.

 

[John.g]

Trying CP3 28W 4.5m 0.8m3/Hr 62oC target DT 19oC Boiler started modulating fan speed 145<>177 consistent. Then later when I checked, it was 150 and steady, no modulation ??? Then within seconds of me looking at it, it cut out ??? Can’t see why though 🤔 took 3 restarts and stayed running, started modulating again 145<>180

it seems, sometimes at least, that the boiler decreases it’s firing with each successive restart, which allows it to eventually stay running, is that how it works, or am I imagining it ???

Nothing really adds up from the above numbers, wonder if the thermistors are faulty or improperly attached to the flow/return pipes.
A deltaT of 19C&0.8m3/hr = boiler output of 17.67kw, clearly not correct. Fan speed of 145/177 = ~ 5.57kw output = deltaT of 6C, more believable but seems too low except restricted by d.00?.

 

[Reddwarf4ever]

Running very well today CC3 35W 5.0m 1.0m3/Hr boiler 63oC DT 19oC fan 150 running steady....been off a couple of times as room stat satisfied, so thats good, but been milder today.....only cut out once today for no apparent reason, but normalised fairly quickly, but wasn’t able to observe. Obviously CC3 uses a little more power than PP3, but maybe there are benefits.....(it did show lo flow just once after reinstalling the pump, but think it was due to being on hot water only and a lot of air in the system) tried to fit the insulation shroud, but typist for a 180 version and doesn’t fit mine, so it’s back to hessian wrap....dont Need the shroud now 😩

Air noise has disappeared now completely, hiding in a radiator somewhere 🤯 wonder if I should connect a valve to the vent, ( currently return and feed linked together ) to occasionally vent to the F&E tank ???

 

[John.g]

Something not adding up there, you have a deltaT of 19C ie flow of 63c & return of 44C? which at a flow rate of 1M3/hr equals to a boiler output of 22.1kw, no way.
The fan speed would indicate a boiler output of ~ 5.2kw so something has changed dramatically from your original readings. If you keep slowly reducing d.00 until the flow or/and return temps start falling then you will get a good feel for the real boiler/rad output, can then start trouble shooting.

Can you give a sketch of your combined vent & cold feed, mine has the vent carrying on up as per normal with the cold feed teed into it.

 

[Reddwarf4ever]

Sorry I meant DT 9oC......hope that makes more sense....🤞will have. look at the F&E tank, a plumber did this for me and I insulated it all, so can’t see where / how it joins.....will jot down how it’s connected.