ASHP- struggling to warm house in the cold weather

[Jude1234]

So we have an ASHP taht was chosen and fitted by our main contractor.  It heats our DHW and also our UFH.  However in this cold spell (and previously when it was nippy) it seemed to really struggle to get the house temperature up to the set thermostat temp (21C). Our builder says as it is our first winter in the house it takes a while for the slab to warm up.  So glad we have the WBS, at the moment it is the only room that it is warm.  So disappointed as we deliberately moved out of an old cold house and built this one and thought it would be snug whatever the temperature.  The upstairs has no heating as we were assured that the heat would rise and with the insulation we wouldn't need it.  But it is absolutely freezing.  Is there anything that I can check easily (I have no idea how the controls of the ASHP work). Is it possible that the pump isn't the right size for the house. 

 

On another point our electricity bill is massive.  Using about 1300 kwh per month is this normal for an 'energy efficient' house.

 

Any advice appreciated

[PeterW]

So you’re using about £200 in winter, that may even out in the summer so may not be far off. 

 

What is the spec of the ASHP and what is it programmed to do..?? If it’s 2-3 hours morning and evening then you may be disappointed. Get E7 and run the ASHP overnight to do the heating and then use ASHP and immersion timers to do the tank. Get as much on E7 as possible. 

 

What was the final EPC/SAP..??

[ProDave]

How well insulates is the house and how large?  How does it heat the house UFH?

 

We are heating our new house with a 5KW ASHP and UFH downstairs only.  In this cold snap (-14 here last night) we are using about 100KWh per week for just the heating so 400KWh per month.  When it is less cold than this present very cold period, the usage is a lot less.

 

Start by telling us the size of house, typical U values of wall and roof etc if you know them. Type of heating, and if under floor heating the flow temperature, and what make and size of ASHP.

[Jude1234]

10 minutes ago, ProDave said:

How well insulates is the house and how large?  How does it heat the house UFH?

 

We are heating our new house with a 5KW ASHP and UFH downstairs only.  In this cold snap (-14 here last night) we are using about 100KWh per week for just the heating so 400KWh per month.  When it is less cold than this present very cold period, the usage is a lot less.

 

Start by telling us the size of house, typical U values of wall and roof etc if you know them. Type of heating, and if under floor heating the flow temperature, and what make and size of ASHP.

It is supposed to be really well insulated, especially upstairs (to insulate against noise as well as the cold).  It is 200sqm but the ground floor is larger than the first floor.  WE still haven't got our EPC (long story). The only heating is water UFH on the whole of the ground floor.  We also have MVHR.  The ASHP is Master Therm BoxAir – BA26i. Not sure about the flow temperature.  I have been trying to get the contractor out to take a look but not getting much response.

[Inchbyinch]

Hi All,  

 

i came on here to ask the exact same question.

I have a 12 kw kingspan/carrier unit

walls and roof typically .1-.13 u-value

300m2 floor area

1400m of UFH across 15 zones

1.2 ACH air thightness

 

I have the NUI controller and I cannot get the water leaving the unit to get anywhere near the 40deg setpoint.....typically with the compressor running @ max frequency (and max pressure) the discharge of the compressor is getting up to 65-82Degrees but the temperature of the water leaving the heat pump is only getting to max 37 and normally 32-34. 

 

It it is also on almost full time at the moment. Something doesn’t add up here.....how can the compressor discharge be so high and not raise the heated water temp much? 

 

Interested in replies.

 

thnks

ed

[ProDave]

3 minutes ago, Jude1234 said:

It is supposed to be really well insulated, especially upstairs (to insulate against noise as well as the cold).  It is 200sqm but the ground floor is larger than the first floor.  WE still haven't got our EPC (long story). The only heating is water UFH on the whole of the ground floor.  We also have MVHR.  The ASHP is Master Therm BoxAir – BA26i. Not sure about the flow temperature.  I have been trying to get the contractor out to take a look but not getting much response.

That looks to be a 9KW heat pump, I would have thought that was enough, depending on the insulation levels etc.

 

Have a look at the under floor heating manifold, there is usually a thermometer on them to show the water flow temperature.  Post a picture of the manifold if you can.

[Roundtuit]

How about air tightness? If you're a bit leaky, it negates the insulation.  Might be worth a check round for draughts.  I assume mvhr will be feeding cool air into your bedrooms; might be worth checking it's not 'over performing' in terms of air flow.  The supply air temperature is going to be whatever the outdoor temperature is, tempered by whatever heat can be recovered from the exhaust air, so if its cold inside, it can't do much tempering...

[joe90]

I also have a 5Kw ASHP Running UFH downstairs only and electric towel radiators upstairs. We found the MVHR was cooling the bedrooms because it is not yet balanced so I only turn it on when cooking and showering (no noticeable bad air recognised). Our house is a constant 21 - 22 degrees. I do not know the lecky usage yet and our house is on its first winter. 

 

[Nickfromwales]

Flow temp of the manifold is a critical bit of info here. Need to find out if the ASHP is getting useful heat to the manifold and then the manifold is conveying that to the UFH loops. Does your manifold have temp gauges? If not can you get 'baby head' thermometer strips and fix them on to get a yardstick? UFH needs surprisingly little to get it all warmed through, so how thick is your slab?

[Inchbyinch]

My UFH,

 

Both manifolds previously were 26-27 on the flow maybe 22-24 on the return.

 

Circulation pump and two manifold pumps were going at a high speed up to tonight and I slowed all of these down to their lowest setting. 

 

This has increased the temperature across all gauges by about 2-3 Deg but the ASHP is still operating at max frequency most of the time. It’s looking to achieve 40 DegC on the outlet and as it’s falling short it’s continually looking for a maxcompressor output. 

 

My Slab is a mix of 100 & 200 in some areas where my passive slab is thickened for a retaining wall (one bedroom really) 

 

What do you think Nick?

 

[Jeremy Harris]

Just to second what @PeterW has said, run the ASHP for as long as you can, ideally on E7.  Last night was the coldest we've seen in a long time, and our ASHP ticked over all night on E7 at around 800 W consumption, and turned off around 06:00 this morning.  Our slab is currently at 23 deg C, with the rooms around 22 deg C.  Flow temperature into the UFH was around 26 deg C, return temperature around 21 to 22 deg C.  Our ASHP is rated at 7 kW output, but it never runs that high.  I doubt we ever run it at more than around 3 kW output.

 

I'm going to hazard a guess that we will get a bit of solar gain today, as the sky is very clear this morning, so in all probability we won't need any more heating until the E7 period this evening.  Our ASHP used about 5.5 kWh last night, and probably delivered around 15 kWh of heat to the house, which is a lot for us.  I can't complain about the running cost though, as even in this cold weather the electricity consumption of everything else in the house is significantly greater than that consumed by the heating.  At E7 rates I would guess that our heating cost for this 24 hour period will be around £0.50 at the most, which seems pretty reasonable.

 

We have frost on the outside of all the windows this morning, too, first time this year.  We've had condensation on the outside of the windows a fair bit, but it's not frozen before now.  Shows how good the glazing is, though, as the inner pane of glass is around 18 deg C, with the outer pane below zero.

[Nickfromwales]

8 hours ago, Inchbyinch said:

What do you think Nick?

The temp delivered by the ASHP is dictated at the point of commissioning, so if your using more energy at the mo then it wouldn’t be unreasonable to see the ASHP running more than normal. 

If it’s performing ‘admirably’ at all other times then I’d not worry. What does it do in ‘better’ weather ?

[Gone West]

12 hours ago, ProDave said:

In this cold snap (-14 here last night)

Strewth, it was -3.1C here this morning, the coldest this winter by a long way and I thought that was cold.

[newhome]

8 minutes ago, PeterStarck said:

Strewth, it was -3.1C here this morning, the coldest this winter by a long way and I thought that was cold.

 

We were only -5 so not that much different from England. 

 

[Stones]

I've not had any issues at all in respect of our ASHP (either heating or DHW).  We opted for a pre-plumbed package which meant on site, the plumber and electrician had simple connections to make (flow/return to ASHP, flow/return to UFH manifold, mains cold in, hot out, and electrically, power to ASHP, control cable between ASHP and control module on cylinder). The cost of getting a pre-plumb system was of course more than buying an ASHP, cylinder and all the various component parts, but there was a labour saving which I think pretty much balanced things out.  Given that some of the problems we see described on the forum seem to be down to complicated installation issues, this may be something worth bearing in mind for future readers.

 

It's probably also worth noting that not all of us are going to be able to achieve the type of heating performance detailed by some members, due to differences in design, orientations, microclimate and so forth.

 

@Jude1234 Hopefully others more knowledgeable will be able to assist if you post some pics of your set up.  Electricity consumption wise, it does seem a little high.  Your ASHP will probably have some form of on board metering - any way you can check to see?

[Nickfromwales]

23 hours ago, Stones said:

It's probably also worth noting that not all of us are going to be able to achieve the type of heating performance detailed by some members, due to differences in design, orientations, microclimate and so forth.

Agreed, and a very important point to reiterate. 

Not everyone achieves perfection, but anything above the usual Uk BRegs is a welcome improvement tbh. 

[Jude1234]

Well apparently the reason the downstairs is not getting up to temp is because we don't have any heating upstairs so a lot of the heat is going upstairs.  So much for our builder saying we won't need any heating upstairs as it will be so well insulated.  A heating engineer is coming in a  week to assess what additional heating is required, sounds costly.  We did have electric points fitted in all the bedrooms upstairs just in case but we had an electrician quote to supply and fit to 3 of the bedrooms and they said it would be £1500.  So currently we are just using convector heaters to warm up just before bed and when getting dressed in the morning.  Not exactly what I envisaged for our ultra modern super insulated house.

 

Regarding using UFH throughout the night unfortunately I am not on E7, locked in now for 12 months.  Something to think about for the future though

[Roundtuit]

Sorry to hear you're still having problems, but if all the heat is going upstairs, wouldn't the upstairs be warm? Something feels wrong somehow;  you seem to be putting a fair bit of heat into the house, but not hanging on to it like you should in a well insulated house.  Are you able to share any details on insulation specs or air tightness strategy? Do your windows have trickle vents perhaps?

Edited February 3, 2019 by Roundtuit

[Declan52]

What does your as built SAP give for your heating demand??? 

As above When you say super insulated what exactly do you mean??? 

You  need to give a bit more detail on how your house is constructed.  

[ProDave]

1 hour ago, Jude1234 said:

We did have electric points fitted in all the bedrooms upstairs just in case but we had an electrician quote to supply and fit to 3 of the bedrooms and they said it would be £1500.  So currently we are just using convector heaters to warm up just before bed and when getting dressed in the morning.  Not exactly what I envisaged for our ultra modern super insulated house.

That does annoy me.  you have the wiring and the heater points, a really good electric heater will be under £200 and an hour to fit.  No way on earth should it be £1500, that's £300 labour per heater.

 

But before you do anything more, leave your plug in heaters on for a whole day, so they are keeping the bedrooms warm (I assume they have thermostats)  Then with the bedrooms warm, and not sucking heat from the rest of the house, see if downstairs is now warm and cosy or not.  This will prove or disprove it the cold upstairs theory is true or just an excuse.

[PeterW]

@Jude1234 

 

Do you have your air tightness and as built SAP scores ..?

 

Even in cold weather, a minimum building regs build wouldn’t need more than 9kw which is what the heat pump will give. 

 

I think there is something amiss - from memory, you have a timber frame ..? Insulation in this should have been pretty good, I’m wondering if the manifolds are shutting down as the thermostat is in the wrong place. 

 

Pictures, info on the build spec etc would be useful if you have it ..?

[newhome]

11 minutes ago, ProDave said:

This will prove or disprove it the cold upstairs theory is true or just an excuse.

 

Sounds like an excuse to me. If I don’t have the heating on upstairs it’s cold upstairs. I don’t see that heat escaping upstairs thus cooling the ground floor. Not the same spec house clearly but even so I don’t see how having no heat at all upstairs works tbh unless the MVHR has some way of providing warm air. 

[ProDave]

If it really is an ultra modern super insulated house, then you can manage without upstairs heating.We don't have any.

 

But we need more information about the building, insulation levels etc.

[TerryE]

14 hours ago, newhome said:

but even so I don’t see how having no heat at all upstairs works

 

It's about 21½°C throughout our upstairs in our house and 22½°C downstairs, so "no heat at all upstairs" definitely can work with a correctly designed and built energy-efficient house.

 

On 30/01/2019 at 21:01, Jude1234 said:

On another point our electricity bill is massive.  Using about 1300 kWh per month is this normal for an 'energy efficient' house.

 

On Jude's original post we actually use slightly more than this in this weather in a smaller house (4 double bedrooms) than Jude's.

 

However, about 75% of our use is at E7 cheap rate, which mitigates this cost.  We also haven't got an ASHP installed yet, so our heating is at a CoP of 1 rather than 3-4.    1300kWh suggests to me that the heating element is probably more than 1000kWh + at a CoP of 3 say means that the house is leaking about 100+ kWh of heat / day.  Something is wrong with the as-built performance of Jude's house.

Edited February 4, 2019 by TerryE

[newhome]

1 hour ago, TerryE said:

It's about 21½°C throughout our upstairs in our house and 22½°C downstairs, so "no heat at all upstairs" definitely can work with a correctly designed and built energy-efficient house.

 

It’s just that I have seen quite a few people (not just on here) who have reported that their upstairs is too cold having planned for minimal or no heating upstairs. In all cases their main heat source has been via an ASHP alongside MVHR. I think the ‘correctly designed and built’ statement is certainly key but clearly there is a general issue if people from all over are reporting issues. Is it the basic design / specification / calcs that are wrong or how the houses have been built?