Central heating pump sizing

[John.g]

Even 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.

 

[Reddwarf4ever]

Even 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.

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 was

tried various pump settings today, settled on CP2, for now at least. Trying boiler on 66oC target, will give it ‘more to work on’ return temperature 53-55oC....but as it’s milder the room stat is switching it off for hours at a time....so have to catch it decided to be more sensible with room temperature, now set at 21.5oC....only increases to 23oC 0800-1100 & 2200-2230 as I heat the hot water during these periods also. Read another post that said Rads should be developed with a delta of 40oC & not the traditional 50 or 60oC.....will defo change my two lounge rads this summer for double fin....have others upstairs, but as most in bedrooms the TRV’s not set very high anyway, could do two more upstairs,, will see how changing the two on the ground floor helps Gas today 7pm 4759.17 does that look correct ? Gas is only used With the boiler thankfully

 

[John.g]

You will always see a plume from a high efficiency boiler even if its never in condensing mode as generally the flue gas temperature is never more than ~ 65/100C, the relatively cool gases then condense very soon after hitting the much colder air, a standard efficiency boiler with a flue gas temperature of ~ 230C will never show a plume because by the time the relatively hot gases cool to dew point all the water vapour (steam) has been diluted/absorbed and will never condense.

That meter looks to me to be reading 475,917 FT3 and when the counter on the right reaches "1" will read 475,920 FT3, I also base this on a meter life of 35 years which is a average gas consumption of 13598 FT3/annum or 13598x0.3, 4079 kwh/year, a very modest consumption if house in occupation during this 35 year period.
What were your exact readings to give you these 3 units?

 

[John.g]

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?)

 

[John.g]

deleted, double post.

 

[Reddwarf4ever]

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?)

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.

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

 

[ShaunCorbs]

Yep

 

[John.g]

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

View attachment 47612

That's fantastic, you can now use this to either get a new DAB pump or a new boiler or something in between!.
When you think your boiler is at minimum output get a stop watch and time in secs one complete revolution of the dial which is 0.1FT3?, calc then is
0.1x0.3X0.85X3600/(time in secs), KW. will be very interesting to see your findings.

Those 3 units you got for 24 hour period don't make sense as it means a consumption of less than 1 kwh.

 

[Reddwarf4ever]

what did you mean about getting a new DAB pump or boiler ? Was that a joke

I actually removed the radiator from the kitchen in 2008, the year before I got the valiant, so considering reinstating that, but with a 100x50cm double fin, together with replacing the two lounge rads with double fins should hopefully give the boiler more to work on & help the return temperature ......so frustrating this morning, trying to heat the house, but at 64oC target, inlet 54oC, it was only consuming 5KW...with the pump on CP3....just not enough heat being dissipated.....increased outlet to 68oC but now the inlet 58oC and not condensing.....looks like won’t win as things stand.

just put back to outlet 64oC ( inlet 54oC ) & see if it eventually warms the house up, fan 1600rpm

Gas Units ( ft3 ) conversion to KWh
units × 2.83 × 1.02264 × 38.9 ÷ 3.6 = kWh

therefore 3 units ( 24 Hrs ) = 94KWh

will do the consumption reading shortly

P.S. used 2845 KWh in January 2021 which is 92KWh / Day which ties up.

 

[John.g]

I can certainly assure you that 3 FT3 of natural gas does not contain 94 kwh but 300 FT3 does.
Just carry out that test I suggested and that will do a rough meter check as well.
Have you got before/after meter readings for any billing period or before/after for that 24 hour period?.

I wouldn't get too carried away with this condensing, the extra saving in running at a return temp of 58C as against 54C is the sq. root of nothing as IMO you have to get down to a water temperature of ~ 50C to even begin to condense.