ASHP performance and Heating System not achieving design temperatures.

[JamesPa]

1 hour ago, JohnMo said:

Nearly.

 

Set thermostats to 22. Ideal is to trim everything to get the room temperatures you want. But after a couple of days of settling. Set backs are serving to make the heat pump work harder than it needs too.

@DREG

 

Just to amplify what (I believe) @JohnMo is saying.

 

You want thermostats set well above the target temperature so they are constantly calling for heat.  You then operate your heat pump 24*7 and reduce the weather compensation curve to the lowest value possible consistent with the house reaching the target temperature.  You may need to balance radiators and/or ufh loops to get all rooms at precisely the design temp.

Edited February 16 by JamesPa

[JamesPa]

3 minutes ago, JamesPa said:

@DREG

@JohnMo

 

Edited February 16 by JamesPa
Duplicate post

[DREG]

11 minutes ago, JohnMo said:

Interesting the target rates are lower that the as built. Which is very poor. So built house is worse than minimum building regs.

 

I do not have an in-depth knowledge of SAP reports. I got it 2 days ago and it’s the first one I’ve seen.  Can you please explain what you mean about the built house being

 

14 minutes ago, JohnMo said:

Interesting the target rates are lower that the as built. Which is very poor. So built house is worse than minimum building regs.

 

I don’t have in-depth knowledge of SAP reports. This is the first one I’ve seen and it was sent by builder on Friday.  Can you please explain the built house being less than building regs and, if so, how it would be signed off.

My understanding is they work out the heat loss as per photo attached showing calculation.

[Andehh]

Your house is, on paper, noticeably better Insulated then ours, and not being a bungalow likely a more efficient design... Albeit it UFH at 35 degrees give us bigger heat emitters so more warmth at better efficiency (in theory).

 

Could just be under sized radiators?? I'm sure I've heard Tower rads are generally a lot less effective then normal twin or triple fin ones.

Edited February 16 by Andehh

[JohnMo]

HLP is per m² of the outside surface area not the floor area. It gets further calculations done to it, so not sure it's a good number to use. Just looked at the calculation behind the one posted and that's not that good either.

 

The heat loss parameter (HLP) is an intermediate result from the SAP calculation which describes the specific heat loss per unit of the dwelling’s external surface area, in W/m²K. It includes ventilation heat losses as well as conduction heat losses. It is in that respect a very pure measure of the thermal efficiency of the shell of the building. This is therefore another option for use as a fabric efficiency rating metric.

[John Carroll]

14 hours ago, DREG said:

Adjacent house (250m2) like us finds it costly to run and not particularly warm. They use a log burner to supplement the heating. The other (220m3) house occupants say they like to be cool 🤷🏻‍♂️.

Do not have a heat meter.  I think it would cost about £1200 (£600 for meter, £600 for labour) to install and nobody seems interested in doing the work.  Assuming the WATER INLET and WATER OUTLET temps shown on the controller (photos below) equate to RETURN and FLOW temps, I could estimate POWER as:

 

1.66/3.666 X 4.2 X (46-43)=5.70kW.
Is that correct?

 

Yes, the calcs are correct.

Its a bit strange though that the rad outputs were based on a T60 rating which was replaced well over 10 years ago by the T50 standard in the UK, if the rads are actually "T50" then any calculated output(s) based on T60 will be 20% or so lower, shouldn't affect the UFH though. Might also be worth checking the flow/return temps in the bathroom rad to get a proper dT, it may be far greater than 3C.

[Post and beam]

17 hours ago, Conor said:

The airtightness result will be mentioned in the SAP report. 

I would be suspicious of this bit. One because they cannot provide it and secondly because developers can apparently test one house and apply the figures globally to the rest of that type across the board. Are these 3 houses substantially the same design ?  Might they have 'virtually'  done your airtightness ?

[DREG]

1 hour ago, John Carroll said:

 

Yes, the calcs are correct.

Its a bit strange though that the rad outputs were based on a T60 rating which was replaced well over 10 years ago by the T50 standard in the UK, if the rads are actually "T50" then any calculated output(s) based on T60 will be 20% or so lower, shouldn't affect the UFH though. Might also be worth checking the flow/return temps in the bathroom rad to get a proper dT, it may be far greater than 3C.

Here’s the calculator, results and deltaT correction from the radiator manufacturer’s website….

 

34 minutes ago, Post and beam said:

I would be suspicious of this bit. One because they cannot provide it and secondly because developers can apparently test one house and apply the figures globally to the rest of that type across the board. Are these 3 houses substantially the same design ?  Might they have 'virtually'  done your airtightness ?

 

34 minutes ago, Post and beam said:

I would be suspicious of this bit. One because they cannot provide it and secondly because developers can apparently test one house and apply the figures globally to the rest of that type across the board. Are these 3 houses substantially the same design ?  Might they have 'virtually'  done your airtightness ?

Yes, made me suspicious too.  The three houses are similar design, yes.

[DREG]

16 hours ago, Beelbeebub said:

What are your bills like? 

Used 93kW in last 24 hours.  Vast majority of that will have been heat pump; apart from lights, TV for a few hours, oven 1 hour, small electronic devices recharge.

Outside air temperature between 0 and +4C.

[MikeSharp01]

15 minutes ago, DREG said:

93kW

Cripes - @ 24.5p per kWh that is approximately £24 a day or close to £700 a month. Something is wrong somewhere - but I guess you know that.

[JohnMo]

31 minutes ago, DREG said:

Used 93kW in last 24 hours

So if your design load is 10kW+ at -3 the demand at an average of about 2 degs will be about 75% of 10kW. So 7.5kW. 24 x 7.5 is 180kWh. So you are getting a CoP of about 2, assuming everything is going into the heat pump.

 

Your trouble is your flowing at 45+ degs.

 

So what temperature do you have into UFH and out and from heat pump and back.

 

Are your radiators only in bathrooms? If so I would look to dual fuel with an electric element and reduce the flow temp of the heat pump down to max mid 30s. This will knock 30% off your electric consumption. 

 

Not seen asked but does your heat pump feed a buffer then heating system?

[DREG]

2 hours ago, JohnMo said:

So if your design load is 10kW+ at -3 the demand at an average of about 2 degs will be about 75% of 10kW. So 7.5kW. 24 x 7.5 is 180kWh. So you are getting a CoP of about 2, assuming everything is going into the heat pump.

 

Your trouble is your flowing at 45+ degs.

 

So what temperature do you have into UFH and out and from heat pump and back.

 

Are your radiators only in bathrooms? If so I would look to dual fuel with an electric element and reduce the flow temp of the heat pump down to max mid 30s. This will knock 30% off your electric consumption. 

 

Not seen asked but does your heat pump feed a buffer then heating system?

House has UFH on ground floor. Rads in bathroom, bedrooms and en-suites on upper floors. Flow temp into bathroom rad is about 37-40C.

 

Screenshots of temp gauge on dining room (bifold doors) UFH manifold and the outlet/inlet temps on heat pump controller from yesterday.

[DREG]

2 hours ago, JohnMo said:

So if your design load is 10kW+ at -3 the demand at an average of about 2 degs will be about 75% of 10kW. So 7.5kW. 24 x 7.5 is 180kWh. So you are getting a CoP of about 2, assuming everything is going into the heat pump.

 

Your trouble is your flowing at 45+ degs.

 

So what temperature do you have into UFH and out and from heat pump and back.

 

Are your radiators only in bathrooms? If so I would look to dual fuel with an electric element and reduce the flow temp of the heat pump down to max mid 30s. This will knock 30% off your electric consumption. 

 

Not seen asked but does your heat pump feed a buffer then heating system?

 

[JohnMo]

Buffer?

[DREG]

5 minutes ago, JohnMo said:

Buffer?

Top to bottom. 60L buffer.

[DREG]

Why would the inlet temperature be higher than the output temperature?

That would give a negative answer to the Q (power) = Flow x SHC x (Flow-Rtn Temp)

[JamesPa]

Is it doing a defrost?

[Conor]

Do as the others have said and set all your stats to something like 24c, so constantly call for heat. Reduce your flow temp to 35c and just leave the thing alone for a few days, keeping an eye on your electric consumption. Adjust each room temp by the flow rate. 

[ReedRichards]

On 16/02/2025 at 16:27, DREG said:

The plumber found the temp of the water entering the rad to be 37C. The design temp of bathroom is 22C. Based on rad manufacturer’s table (see photo) the deltaT is 15C, I think-perhaps less if you allow for the temp drop across the rad.

 

You should always take the average temperature of the radiator, so measure the inlet and outlet water temperatures and take the average of the two.  The temperature of the water entering the bathroom radiator should be the same as the water temperature entering every other radiator.  Your weather compensation curve would give you an output water temperature of 39 C when it's 10 C outside and 30 C when it's 20 C outside.  The temperature of the water entering the rad should be almost the same as that of the water leaving the heat pump so the implication is that it was about 12 C outside when your plumber made his measurement.  Does that sound right?  If the plumber had come when the outside temperature was below 0 C then he should have fond that the water entering the rad was at about 48 C.