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Does that mean the pump will run 24/7 ?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
Discuss Central heating pump sizing in the USA area at PlumbersForums.net
Does that mean the pump will run 24/7 ?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
HiOne 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.
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?.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
re room stat, is the 0.5oC offset setting, ‘ shared’ either side of the target temperature?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.
HiThat 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.
Thanks, completely forgot about that, your memory is better than mine have emailed DAB & will check other settings again......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."
Exactly my thoughts CP3 30W 4.5m 0.9m3/Hr....will leave as is amd see how the boiler performsMaybe 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.
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 ?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.
Nothing really adds up from the above numbers, wonder if the thermistors are faulty or improperly attached to the flow/return pipes.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 ???
Could it be the f,ow isn’t 1.0m3/Hr ? As this is a calculated flow, not sure how accurate that is....A deltaT of 9c = 10.47kw, more like it but the fan speed is a mystery as IMO it should be ~ 3024, as I said above, progressively reducing the output will tell alot, ie if deltaT still remains the same at a d.00 of 6kw as at 12kw then the boiler isn't outputting 10.47kw.
DT 6oC fan steady 150 assume boiler limited to 5KW Target 62oC, actual 62-63oCWill do the calcs in a minute, is the flowrate still indicating 1.0M3/hr?, this is important.
Will take 24 hr gas readings over next 3 days, last week I used exactly 3 units in 24 hours, but will compare in a few days. Talking about plumes, so is it possible to see a plume if no condensing is taking place ?, hoped that was a sign that it wasEven though I am reasonably happy that a fan speed of 1500 RPM is min output of ~ 5.2kw, this is not borne out by using the flowrate of 1M3/hr and a deltaT of 9C which gives a output of 10.46kw, if the deltaT is correct then the actual flowrate is only 0.5 m3/hr for a output of 5.2kw, if the flowrate is correct then the deltaT is only 4.5C. Would like to monitor the gas meter.
Condensing: Achieving the utopia of 100% condensing requires a flue gas temperature of down around 30C which requires a return water temp still lower of ~ 20/25C, so you will always see a plume from the boiler unless these conditions are met, IMO to achieve ~ 3/4% condensing benefit requires a return temp of ~ 45C, the big advantage of condensing vs non condensing is that even when not condensing there is a big benefit, a non condensing boiler might have a flue gas temp of 230C (like my own) but a condensing boiler will easily achieve ~ 80C (non condensing) with a gain of ~ 7%,
I would definitely try and run on the return target temp of say 40/45C, you can then adjust flow rates etc to give optimum comfort and performance.
Think you are correct re the reading, the silent red 0 at the end confused me.
I also think there is a little rotating mechanical device (outlined with red oval) that you can get a very accurate boiler consumption number from, time it exactly for say 5 revolutions, if it takes say 70secs then the boiler consumption is 5.5 kw.
Or maybe time the red counter for exactly one revolution (1 FT3?)
Thanks, at least that dispels what I was told about the plume being a sign that the boiler is in condensing mode.....would measure the condensate, but it’s all piped in quite secure and insulated, so won’t disturb that.Think you are correct re the reading, the silent red 0 at the end confused me.
I also think there is a little rotating mechanical device (outlined with red oval) that you can get a very accurate boiler consumption number from, time it exactly for say 5 revolutions, if it takes say 70secs then the boiler consumption is 5.5 kw.
Or maybe time the red counter for exactly one revolution (1 FT3?)
That's fantastic, you can now use this to either get a new DAB pump or a new boiler or something in between!.Thanks, at least that dispels what I was told about the plume being a sign that the boiler is in condensing mode.***.would measure the condensate, but it’s all piped in quite secure and insulated, so won’t disturb that.
Re the gas meter, I think the dial marked in orange, is 1/10th of a unit, so each full rotation of the dial circled in green would increase the digit ‘ circled in orange’ by One, IMO
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Reply to Central heating pump sizing in the USA area at PlumbersForums.net
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