ASHP performance and Heating System not achieving design temperatures.

[DREG]

Hi All

I am new here and am looking for information and advice regarding my ASHP.  I have posted this in the ASHP area; but it is quite technical; so I thought it might be appropriate to post it here as well.

 

It is an Hitachi Mono 4 HP RASM4 [Yutaki RASM-4VNE] with a nominal output of 11kW.  It was manufactured in 2019 and was installed in a new build house in 2022.The heat pump supplies a three storey 280m2 detached house with UFH on the ground floor and radiators on the upper floors.  The outside design temperature is -3.4C [central UK].

Various heat loss calculations have been made which estimate the heat loss of the building to be 10.3kW.  There does not appear to be an amount quoted for heating domestic hot water [300L DHW tank installed], or for defrost cycles included in that figure.

Qualitatively speaking, the heat pump appears to struggle at lower ambient temperatures, particularly if it is windy, leading to a fall in room temperatures.  More specifically, we have issues with two rooms. 

The main bathroom, which has a room volume of 25m3 is fitted with a vertical panel radiator rated at 5668BTU at deltaT 60C.  However, the water going into the radiator is only about 38-40C; giving a deltaT of 20C. Weather compensation is set so that the heat pump should produce water at 48C, when air temp. is close to 0C. Applying the radiator manufacturer’s deltaT correction factor means a corrected output of approx. 1400BTU. The design temperature of the bathroom is 22C and to date, the developer’s plumber has not been able to achieve a temperature higher than 20C, by balancing the upstairs radiators.  Usually, the bathroom temperature hovers around 17-19C dependent on outside air temperature.  A lack of adequate insulation was identified in the bathroom ceiling.  It was underdrawn with thermal plasterboard recently; but this has made no discernible difference.  There was a discussion about putting a larger rad [higher BTU output] in the bathroom. However, the heat pump manufacturer/supplier advised against this as it would “result in the heat pump becoming over worked and running more defrost cycles, taking heat away from the primary circuit”.

The dining room has a volume of about 180m3 and has total glass surface area of 40m2 [bifold doors and roof skylight].  It has its own UFH manifold.  Over recent weeks, with outside temperatures a couple of degrees above zero, the heat pump must run overnight to keep the room temperature acceptable and avoid it, otherwise, having to warm the room from about 16C in the early morning [i.e. reduce the warm up load].  I think the dining room is responsible for roughly a third of the total house heat loss.

The water pump runs at 100%, when I check it, and during cold periods we appear to be using about 80kW of electricity in 24 hours for the heat pump.

I have looked at various documents including MCS MIS 3005, MCS 021, MCS Best Practice Guide etc.  They state the heat pump should be able to cover 100% of the output; and to achieve a satisfactory installation the heat pump specification should take into account the heat emitters and room design temperatures.  I was told by one expert that the heat pump can only cover 96% of the heating requirements of the house at design condition.

I’m getting conflicting information from various sources: heat pump too small, heat pump borderline; or it should be possible to balance the rads to get 22C in the bathroom.  The developer is sticking with the heat pump manufacturer/supplier who say it is the correct size.  As an aside, two other properties on the same development have the same 11kW heat pump; but they are 220m2 and 250m2 respectively.

Any advice or opinion appreciated.

[John Carroll]

17 minutes ago, DREG said:

 

The main bathroom, which has a room volume of 25m3 is fitted with a vertical panel radiator rated at 5668BTU at deltaT 60C.  However, the water going into the radiator is only about 38-40C; giving a deltaT of 20C. Weather compensation is set so that the heat pump should produce water at 48C, when air temp. is close to 0C. Applying the radiator manufacturer’s deltaT correction factor means a corrected output of approx. 1400BTU. The design temperature of the bathroom is 22C and to date, the developer’s plumber has not been able to achieve a temperature higher than 20C, by balancing the upstairs radiators.  Usually, the bathroom temperature hovers around 17-19C dependent on outside air temperature.  A lack of adequate insulation was identified in the bathroom ceiling.  It was underdrawn with thermal plasterboard recently; but this has made no discernible difference.  There was a discussion about putting a larger rad [higher BTU output] in the bathroom. However, the heat pump manufacturer/supplier advised against this as it would “result in the heat pump becoming over worked and running more defrost cycles, taking heat away from the primary circuit”.

 

Just looking at the figures for the bathroom, flowtemp of say 39C with dT of 20C? gives a return temp of 19C, a mean rad temperature of, (39+20)/2, 29C, giving a output (T60 based) of ((29-20)/60)1.3, (9/60)^1.3, 8.5%, rad output, 5668*8.5%, 482BTU by my calcs or 141W (not a lot), if the room temp is 18C then the output is (11/60)^1.3, 11.02%, actual rad output 5668*11.02%, 625BTU, 183W?.

That dT seems very high for a flowtemp of 39C, would have expected ~ maybe around 8C or so which would increase the rad output due to the higher mean rad temp so ~ rad output of 16.49% to give a output of 935BTU, 274W assuming the room temp rose to 20C.

[JohnMo]

Couple of things jump out of your description

 

3 hours ago, DREG said:

heat pump must run overnight to keep the room temperature acceptable

 

3 hours ago, DREG said:

new build house in 2022.

 

3 hours ago, DREG said:

nominal output of 11kW

 

3 hours ago, DREG said:

80kW of electricity in 24 hours

So 80kWh divided by 24 hrs, is just over 3kW electric input. Your either running 24/7 and getting a CoP of 3.3 or you are running on a timer for short periods and getting a piss poor CoP for the hours run.

 

New build in 2022 should be nearer 3 to 8kW for your size house. So something doesn't add up. I suspect how you are running the system is the bit that's amiss. And or how it's set up.

3 hours ago, DREG said:

having to warm the room from about 16C

 

So are you running on a time based and thermostat regime or running on weather compensation 24/7?

 

How many thermostats do you have?

 

 

[Beelbeebub]

You also mention the performance is worse on windy days

 

This would point to a potential air tightness issue. If your airtightness is less than designed/estimated then your heat demand will be higher due to more airchanges per hour than expected. 

 

Do you have any drafts in windy weather?ie around windows or light fittings? 

[DREG]

Hi JohnMo

 

There are 6 Heatmiser thermostats on the ground floor which has UFH.  The schedule is:

06-0900 21C

09-1600 20C

16-2200 21C

22-0600 20C

 

That is to have the heat pump running 24/7 and to reduce the warm up load, based on the advice I was given.  Weather compensation is set on the YUTAKI controller, photo below.

 

Upstairs radiators controlled by a single Honeywell thermostat located on the landing. Schedule is very similar to that of the ground floor.

[DREG]

5 minutes ago, Beelbeebub said:

You also mention the performance is worse on windy days

 

This would point to a potential air tightness issue. If your airtightness is less than designed/estimated then your heat demand will be higher due to more airchanges per hour than expected. 

 

Do you have any drafts in windy weather?ie around windows or light fittings? 

I asked developer for SAP report and air leak/test report.  Got the SAP but they said “cannot locate air test at this point but house would not have been able to get CML if it had failed an air test”.  There is a large 4 pane double glazed window with no opening lights in the dining room.  I did a test with a small candle and there appeared to be a draught.  That’s the room with bifold doors and about 40m2 of glass.

[Conor]

It sounds more like an issue with poor build quality (insulation detailing and airtightness) than heat pump performance.

 

Heat pump sizing is borderline for the design heat loss. If heat loss is higher than design, then the heatpump won't keep the building warm enough.

 

Is this a one-off build or part of a development? The airtightness result will be mentioned in the SAP report. 

 

Fyi our house is 253m², A93, airtightness test result of 1.5, all triple glazed, 9kW heatpump.

 

40m² of glazing is huge, and if only double glazed, then you'll have massive heat loss. Add in bi-folds and it'll always struggle. Go through the SAP report in detail and make sure the assumptions match the actual build.

[DREG]

4 hours ago, John Carroll said:

 

Just looking at the figures for the bathroom, flowtemp of say 39C with dT of 20C? gives a return temp of 19C, a mean rad temperature of, (39+20)/2, 29C, giving a output (T60 based) of ((29-20)/60)1.3, (9/60)^1.3, 8.5%, rad output, 5668*8.5%, 482BTU by my calcs or 141W (not a lot), if the room temp is 18C then the output is (11/60)^1.3, 11.02%, actual rad output 5668*11.02%, 625BTU, 183W?.

That dT seems very high for a flowtemp of 39C, would have expected ~ maybe around 8C or so which would increase the rad output due to the higher mean rad temp so ~ rad output of 16.49% to give a output of 935BTU, 274W assuming the room temp rose to 20C.

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. It’s a big rad (1800x575mm) with output of 5668BTU/1662W. I’m assuming the reduced heat output and less than design temperature in the bathroom is down to the temp of the water entering the rad.  This is the second rad that’s been put in the bathroom. Previously it was a chrome type towel rad.  When developer changed it they said the aluminium column rad would be more than adequate but  they don’t appear to have taken account of the temp of the water in the rad.

[DREG]

20 minutes ago, Conor said:

It sounds more like an issue with poor build quality (insulation detailing and airtightness) than heat pump performance.

 

Heat pump sizing is borderline for the design heat loss. If heat loss is higher than design, then the heatpump won't keep the building warm enough.

 

Is this a one-off build or part of a development? The airtightness result will be mentioned in the SAP report. 

 

Fyi our house is 253m², A93, airtightness test result of 1.5, all triple glazed, 9kW heatpump.

 

40m² of glazing is huge, and if only double glazed, then you'll have massive heat loss. Add in bi-folds and it'll always struggle. Go through the SAP report in detail and make sure the assumptions match the actual build.

It’s a development of 3 houses (280m2; 250m2; 220m2-all with same 11kW heat pump). Unfortunately, the glass in that room is only double-glazed.

[JohnMo]

39 minutes ago, DREG said:

That is to have the heat pump running 24/7 and to reduce the warm up load,

The basics on how a heat pump works.

 

It will start and basically ramp up to full load. It will first try and get it's running delta T (difference between flow and return temperature) to within a defined pont controlled by the controller. It then only as Delta T reduces add more heat to the flow temperature. With UFH this can take hours. I would set all thermostats to 22, and let the system stabilise. Leave a couple of days. Do not do any setbacks, just let weather compensation do it's thing.

 

You are making the heat pump run full load most the time. Doing yourself no favours. If I let my house temp drop by a full degree, heat pump or boiler would take around 24 hrs to recover.

 

Room temperature setup, if a room is too hot, reduce the flow rate to those loops by 0.5L/min, leave again for 12 hours. Opposite for cool rooms.

 

Use the heatmiser as a monitor system do not use for control. That is the heat pumps job. 

 

This will take some time.

[JohnMo]

A thing I forgot to mention 

 

With a mixed radiator and UFH, the flow coming out of the UFH (cool) will dominate how the heat pump runs, until the floor temp stabilises.

[Beelbeebub]

48 minutes ago, DREG said:

It’s a development of 3 houses (280m2; 250m2; 220m2-all with same 11kW heat pump). Unfortunately, the glass in that room is only double-glazed.

How are the other houses getting on? 

 

So you have any monitoring hardware eg heat meter, elec consumption for HP only? 

 

Is it possible your HP isn't going flat out? I know some have "eco" modes that restrict output to the most efficient range at the cost of absolute power output.  If your HP is set in that regime you might be getting less than 11kw 

[DREG]

22 minutes ago, Beelbeebub said:

How are the other houses getting on? 

 

So you have any monitoring hardware eg heat meter, elec consumption for HP only? 

 

Is it possible your HP isn't going flat out? I know some have "eco" modes that restrict output to the most efficient range at the cost of absolute power output.  If your HP is set in that regime you might be getting less than 11kw 

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?

[JohnMo]

19 minutes ago, Beelbeebub said:

11kw

There isn't a reason why a house completed in 2022 should need anywhere near 11kW. I'm at nearly 200m² 6m high ceiling in one room, which also floor to ceiling glass, all other average 3m tall. At -9 the house needs around 3kW. Taking away heat recovery ventilation would double the heat load

 

Floors take lots of energy, take a huge amount of time to recover from being cool. Letting house cool takes an age to recover.

 

If house heat loss is say 10kW, an 11kW heat pump needs to run 24/7 to just stand still. Let alone recover from 14 hrs effective off due to thermostat timings.

[JohnMo]

4 minutes ago, DREG said:

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:

Sounds about correct.

 

But your target flow temp has been met, dT is small, so heat pump is modulating output down.

 

At that time you have the UFH switched down to 20 degs, so most likely the heat pump is just doing radiators.

[DREG]

1 hour ago, JohnMo said:

There isn't a reason why a house completed in 2022 should need anywhere near 11kW. I'm at nearly 200m² 6m high ceiling in one room, which also floor to ceiling glass, all other average 3m tall. At -9 the house needs around 3kW. Taking away heat recovery ventilation would double the heat load

 

Floors take lots of energy, take a huge amount of time to recover from being cool. Letting house cool takes an age to recover.

 

If house heat loss is say 10kW, an 11kW heat pump needs to run 24/7 to just stand still. Let alone recover from 14 hrs effective off due to thermostat timings.

Several different heat loss calcs done and all give heat loss of approx 10.3kW.

I assume 11kW heat pump specified on that basis. But there’s no allowance for DHW heating or defrosting. Should there be?

 

You recommend setting everything to 21C for 24hrs daily with no set-backs.  Is that right?

 

[JohnMo]

15 minutes ago, DREG said:

You recommend setting everything to 21C for 24hrs daily with no set-backs.  Is that right?

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.

[MikeSharp01]

3 hours ago, DREG said:

bifold doors

Very hard to get anything like airtight.

[MikeSharp01]

34 minutes ago, DREG said:

I assume 11kW heat pump specified on that basis. But there’s no allowance for DHW heating or defrosting. Should there be?

Yes - assuming it was done in some way under the MCS scheme as that requires the installers to account for DHW.

[Beelbeebub]

1 hour ago, DREG said:

1.66/3.666 X 4.2 X (46-43)=5.70kW.

With an outside temp of 3 you have a 17C temp difference to inside. 

 

You said your design temp was - 3.4C so design temp diff wouod be 24C

 

So at 3C your power should be roughly 17/24 x11 which is close to 8kw. 

 

I'll assume your UFH isnt under powered, so are your rads too small? Do you need to up your flow temps a bit?

 

What are your bills like? 

 

(as an aside, how is your UFH plumbed in? Is it direct or does it mix down to a lower temp? Can you get a reading of the floor temperature?) 

[Andehh]

• Something not right. We're 250sqm ish bungalow, with 3.5 to 4.5m ceilings, lots of glazing (albeit it 45 sqm kitchen floor have around 25sqm of glazing.... Which is a lot in its own right) and our 12kw Samsung ASHP has no real issues keeping us around 21 degrees with around 12 hours run time even on the coldest of sub zero days. Ufh throughout though and we upgraded all our insulation.

 

Can you post up your Sap report? What insulation is detailed?

 

 

[DREG]

ABSAPD_1.pdf

27 minutes ago, Andehh said:

• Something not right. We're 250sqm ish bungalow, with 3.5 to 4.5m ceilings, lots of glazing (albeit it 45 sqm kitchen floor have around 25sqm of glazing.... Which is a lot in its own right) and our 12kw Samsung ASHP has no real issues keeping us around 21 degrees with around 12 hours run time even on the coldest of sub zero days. Ufh throughout though and we upgraded all our insulation.

 

Can you post up your Sap report? What insulation is detailed?

 

 

Here’s the SAP report

 

[JohnMo]

As said earlier the 11kW sounded high.

 

Your SAP report says the January heat demand is 5171W.

 

 

[JohnMo]

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

 

[DREG]

1 hour ago, Beelbeebub said:

With an outside temp of 3 you have a 17C temp difference to inside. 

 

You said your design temp was - 3.4C so design temp diff wouod be 24C

 

So at 3C your power should be roughly 17/24 x11 which is close to 8kw. 

 

I'll assume your UFH isnt under powered, so are your rads too small? Do you need to up your flow temps a bit?

 

What are your bills like? 

 

(as an aside, how is your UFH plumbed in? Is it direct or does it mix down to a lower temp? Can you get a reading of the floor temperature?) 

The rooms with rads are ok in terms of temperature, except for the main bathroom. That’s always been cold as detailed in original post.

It’s a vertical panel aluminium rad. It’s rated at 5668 BTU but it can’t be emitting anything like that as the water going into it is about 37-39C.  When the other rooms heated by rads are at 21C, the bathroom is 19C maximum. Its design temperature is 22C.

 

The dining room with all the glass has its own UFH manifold.  Appears to have a mixer valve. Photos attached.