ASHP- struggling to warm house in the cold weather

[jfb]

Jude, I would second what Dave has been saying. Find out and give us details of what results you got for your air tightness test and what the specification for insulation values was. Without these figures it is hard to offer advice.

The air tightness test result should be in the form of  X m3/m2h @ 50 Pa. X being anywhere from 10 (terrible) to 0.6 (very air tight). 

[Jeremy Harris]

15 minutes ago, newhome said:

 

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? 

 

I don't think it relates to the heat source, so much as to the design and layout of the house.  For example, our primary heating is an ASHP running UFH in the ground floor slab only.  The effective heated area of that slab is about 75m².  We have no heating upstairs, apart from heated towel rails in the batrhooms, of which only one is used normally, and then only for a couple of hours in the early morning and again in the evening.

 

We have a central hallway that is about 2m wide, 5m long and 6m high so extends right up to the doors that lead to the bedrooms on either side.  The UFH in that hallway is undersized for the volume of space it's heating, deliberately so, as we didn't want the upstairs to get too warm.

 

With the ground floor surface running at around 23°C in the rooms either side of the hallway, and around 22°C to 22.5°C in the hallway itself, we find that we have a comfortable temperature in the living rooms (around 22°C to 22.5°C) and a temperature in the bedrooms of around 19°C to 19.5°C.   It's very much personal preference, but we like the bedrooms to be a bit cooler than the living rooms.

 

I did fit FCUs in the bedrooms, together with ply backing boards behind the plasterboard, so that it would be no more than an hours work to fit thermostatic panel heaters in the bedroom, if we every feel we need them.  I'm inclined to the view that we probably won't ever need them, but the cost of fitting the additional cable and outlets during the build was trivial, probably less than £10, so they are cheap insurance for things not working out as planned.

 

On the subject of MVHR, then I think it's important to reiterate that normal, passive, MVHR will always cool rooms down in cool or cold weather.  The air supplied by the fresh air feed terminal will always be colder that the room temperature, not by a lot, but still cooler.  During the cold spell recently we were seeing a MVHR fresh air supply temperature of around 18°C with the MVHR running in passive mode.  That certainly helps to keep the bedrooms cool, given that the only source of heat to them is whatever leaks up through the (insulated) floor from the rooms below, or comes up via the hallway and landing.

 

 

[ProDave]

A common theme here is like @JSHarris our house is built either side of a central stairwell. Downstairs rooms heated by UFH, minimal UFH in the actual hallway.

 

With all doors open there is a good convection path for heat from downstairs to get upstairs.  Currently the downstairs thermostats are set at 20 degrees and the bedrooms are at 18.5 degrees this morning,  The coldest it has got in the bedrooms was 16 degrees, and when that happens we fire up the WBS, which heats the kitchen / diner to about 25 (some would say overheats it) and that excess heat soon finds it's way up to boost the bedroom temperatures a little.

 

There is also an argument if relying on downstairs heat to get upstairs, not to go overboard with insulation between floors.

[newhome]

2 hours ago, JSHarris said:

 

I don't think it relates to the heat source, so much as to the design and layout of the house

 

I think ASHPs stand out here as they are less well understood and an undersized one may struggle to provide the heat demand needed. With a standard gas boiler you can just keep running it pretty consistently to provide the heat required as the performance doesn’t vary with the weather in the same way as an ASHP. Hence there are more issues with an ASHP. 

 

 

 

 

[TerryE]

+1 with Jeremy and Dave's comment. Our basic layout is a 3 × 2 block layout. The front centre block is an open hall which rises up all 3 stories.  The ground floor left and right are a through living room and kitchen diner.  We leave the lounge and kitchen doors open at night, so the UFH heated air also flows upstairs. 

 

(The central hall also has an opening roof light on the top floor, which gives us excellent summer cooling: open this and a window or two on the shaded side of the build dumps excess heat in the house.)

 

25 minutes ago, newhome said:

an undersized one may struggle to provide the heat demand needed

 

Karen, I think that your emphasis here is wrong. The design heat losses in a build are in essence very simple: a set of surfaces with known area, U-value and delta T; an air change rate with given % heat recovery and specific heat.  With a well designed house, the thermal bridging and linear psi components are minimal.  So the heat demand for a given outside temp would be well determined. If your house is losing 40 kWh/day at the target internal temperature, then you can maintain overall heat balance with a single 2kW oil heater or a 5kW ASHP on a 3 CoP at a 30% duty cycle even at a 30% output.

 

If your as-built house is losing 120 kWh / day instead of a designed 40, this isn't the fault of the ASHP, it is because of design flaws or poor quality control during construction.

 

I could understand and accept a 20% as-built variance, but much more than that is just crap workmanship, IMO.  Fixing it is more one of understanding and mitigating these built flaws.  

Edited February 4, 2019 by TerryE

[Roundtuit]

45 minutes ago, TerryE said:

If your as-built house is losing 120 kWh / day instead of a designed 40, this isn't the fault of the ASHP, it is because of design flaws or poor quality control during construction.

 

I could understand and accept a 20% as-built variance, but much more than that is just crap workmanship, IMO.  Fixing it is more one of understanding and mitigating these built flaws.  

Agreed, hence my question about whether there are trickle vents in the windows.  If there is, that may explain some heat loss, but more significantly, it will give an indication on whether the builder has got a grip on the principles of an energy efficent build.

 

FWIW,  my build (270 sq m) is well insulated, fairly airtight (approx 1) and triple glazed, with UFH downstairs and rads up.  No heating upstairs would have been a bad mistake.  Downstairs sits comfortably at 21-22C at the moment with maybe 4-6  hours a day of UFH from the ASHP, and I can get the open plan living room/kitchen/diner up to about 25-26C with a couple of hours of the wood burner running (4.5kw output), but even with double doors open into a full height hallway, not enough heat would reach the bedrooms.

 

 

[Jude1234]

So unfortunately I have very little information to provide.  No trickle vents, MVHR.  Airtightness result of around 4.5.  Still not got EPC so don't know what any of the SAP calculations are. It is a timber frame house, with dg downstairs and triple glazing upstairs (for noise rather then insulation primarily).

Someone has been here today and changed heat flow curve????  The expert from the ASHP manufacturer says run it at a constant temperature 24 hours a day, but that seems a bit wasteful as during the week we are only up and in the house from 6.30 - 8am and the 5-10.30ish.  I just don't know who to believe.

[Declan52]

4.5 ain't a good score for a timber frame. 

Did you see it being built and take pictures of the walls so we can even what's there.  

[Cpd]

4 minutes ago, Jude1234 said:

Airtightness result of around 4.5. 

That’s a worry I think..... if this was the result after several attempts of bogging up gaps and cracks  it could mean some seriously poor workmanship, especially in regards to the installation of the insulation. The mvhr could well be sucking in lots of cold air from these gaps and therefore rapidly cooling the house. 

[Jeremy Harris]

I agree with @Declan52 and @Cpd, it doesn't sound as if you don't have a particularly well-sealed build, and that will impact pretty heavily on your heating requirement, unfortunately.  I also think that the DG, rather than TG, will also have a negative impact on the overall heating requirement, and if the overall house insulation level matches the airtightness performance then you could be looking at having relatively high energy bills in cold weather.

 

Knowing the EPC details should help us see whether or not your heating requirements can be met OK with the system you have, so getting that would be very useful.

[ProDave]

Can you not at least get hold of the design SAP document?

[Declan52]

Could you please give some information on how you have went about the build.  Did you get your plans done by an architect with the brief to design you a super insulated house which you then gave to your chosen builder to build.  I'm trying to figure out was the house not designed at the start to match your brief or has the builder not  followed the plans and you have ended up with a super insulated house on paper but not in the real world.  

As for the  airtightness test where you present and if so did the company give you any indication of some remedies to improve your score.  The insulation built in is what it is so the only real aspect you can change is that score which will have a massive impact on your heating bill. It might be worth while to get them back and go round the house and mark and fix where possible any leaks. Some things like mastic in the electrical conduits, tighten window and door seals are easily done by yourself.  Things like downlights lose a lot of heat if not done correctly.  It will cost you a few hundred quid but in the long run should save you money if the leaks can be sorted.  

 

[newhome]

6 hours ago, ProDave said:

With all doors open there is a good convection path for heat from downstairs to get upstairs.

 

Ah I didn’t realise that the heat got upstairs by leaving the bedroom doors open. I always keep mine shut as I don’t heat the whole house. 

 

So I get that heat requirements can be low if insulation, airtightness etc is very good but what about someone who claims that there will be no heating installed at all, but then says that there will be a small heat pump on the MVHR intake and electric radiators in the bathrooms? Or is that as good as saying ‘we will have minimal heating’ rather than claiming that there will be none installed at all? 

[Jeremy Harris]

The Passivhaus standard isn't for a house that needs no heating at all, although some do tend to make the mistake in assuming that's what it is.  A house that needs minimal, or modest, amount of heat in the heating season probably best describes it.

 

We could heat our house using the heat pump in the MVHR coupled with heated towel rails I think (it useful to have this as a backup heating system if we ever need it) but we prefer to heat the ground floor slab, just from a personal preference.  We both find the air from the MVHR with the heat pump turned on a bit dry, but I guess that could be resolved with some sort of humidifier easily enough.

[newhome]

6 minutes ago, JSHarris said:

The Passivhaus standard isn't for a house that needs no heating at all, although some do tend to make the mistake in assuming that's what it is.  A house that needs minimal, or modest, amount of heat in the heating season probably best describes it.

 

We could heat our house using the heat pump in the MVHR coupled with heated towel rails I think (it useful to have this as a backup heating system if we ever need it) but we prefer to heat the ground floor slab, just from a personal preference.  We both find the air from the MVHR with the heat pump turned on a bit dry, but I guess that could be resolved with some sort of humidifier easily enough.

 

Thanks. This was a quote from someone making a video of building a PassivHaus. Was a bit surprised to see 'none installed' when asked about heating and then a heat pump and electric rads in the bathrooms mentioned. Modest heat requirement covers it and of course that requires some form of heating to be installed.  

[Nickfromwales]

10 hours ago, newhome said:

 

Thanks. This was a quote from someone making a video of building a PassivHaus. Was a bit surprised to see 'none installed' when asked about heating and then a heat pump and electric rads in the bathrooms mentioned. Modest heat requirement covers it and of course that requires some form of heating to be installed.  

There are many people out there blabbering on about super-insulated / eco-friendly / low energy build approaches, but most are talking out of their arsehole I'm finding of late.

One client stated "near passive build standard" and then showed me their plans for 70mm of PIR over cold ventilated block and beam with UFH pipes atop in 80mm of screed.....WTF?!?

Another building a low energy home in block, but not even approached by either the architect or the builder about parge-coating or using wall plates instead of sockets into the cavity.

12 hours ago, Declan52 said:

the brief to design you a super insulated house which you then gave to your chosen builder to build.

That's the money shot.  

With no accurate direction most builders will just revert to the same standard they pedalled out for the last 20 years. I have actually caught one builder purposefully dissuading a client from putting 200mm of PIR under the heated screed in a summer room, 10 minutes after I told the client to order it for the builder to install. Idiot. 

 

The terms get banded about too loosely, and as BR don't 'go that high' nothing gets enforced. BCO's are overjoyed to see 5mm more insulation, 

[Gone West]

11 hours ago, newhome said:

 

Thanks. This was a quote from someone making a video of building a PassivHaus. Was a bit surprised to see 'none installed' when asked about heating and then a heat pump and electric rads in the bathrooms mentioned. Modest heat requirement covers it and of course that requires some form of heating to be installed.  

The maximum U factor for PH walls is 0.15W/m2K and I would guess that a house constructed like that, anywhere in the UK, would probably need central heating if only at low level. Our house has walls with U factor of 0.095W/m2K and is heated with residual heat from bathroom towel rails and supplemented with warm air through the MVHR. Most people seem to think we don't have heating because we don't have conventional central heating such as UFH or radiators.

[ProDave]

13 minutes ago, PeterStarck said:

The maximum U factor for PH walls is 0.15W/m2K and I would guess that a house constructed like that, anywhere in the UK, would probably need central heating if only at low level. Our house has walls with U factor of 0.095W/m2K and is heated with residual heat from bathroom towel rails and supplemented with warm air through the MVHR. Most people seem to think we don't have heating because we don't have conventional central heating such as UFH or radiators.

Most of our walls etc have a U value of 0.14, and the calculated heat loss when it's +20 inside and -10 outside, is just a shade over 2KW, which is comfortably delivered by a 5KW ASHP

[scottishjohn]

ok --so what in reality is the insulation level that is needed in uk --

walls 

roofs 

floor 

windows 

maybe too much is causing more over heating problems  as is being talked about all the time on these threads

one for you boffins.

trying to build with no heating -to me should not be the goal ,but a comfortable and economical build that most can afford 

[Gone West]

2 minutes ago, ProDave said:

Most of our walls etc have a U value of 0.14, and the calculated heat loss when it's +20 inside and -10 outside, is just a shade over 2KW, which is comfortably delivered by a 5KW ASHP

The weather down here is a lot kinder to us than you. My life wouldn't be worth living if the bedroom temperature went below 21C let alone 16C .

[Gone West]

1 minute ago, scottishjohn said:

ok --so what in reality is the insulation level that is needed in uk --

Depends where you live in the UK. Huge difference between NE Scotland and SW England.

 

2 minutes ago, scottishjohn said:

trying to build with no heating -to me should not be the goal ,but a comfortable and economical build that most can afford 

It's a personal thing. Again, big difference in what people can afford and want.

[scottishjohn]

what is your aevrage winter temp that is used for heat calculations  for energy  cert (EPC)

here it is +3c

Edited February 5, 2019 by scottishjohn

[Jeremy Harris]

Just a quick observation about the idea of building a house that needs no heating.  This is not a good idea at all, because if you were to build a house that needed no heating system, and just relied on the heat given off by the occupants and appliances to keep it warm in winter, then it would probably be unbearably hot in summer.

 

A heating system can be controlled, turned up and down to regulate the house temperature in winter.  The heat output from occupants and appliances can't really be controlled at all, so the heat input to the house will be much the same on the hottest day of the year as it is on the coldest day of the year.

 

Take a typical winter day, with an outside air temperature of around 6°C.  If a house needs no heating in order to stay at 21°C, then that implies that the heat from the occupants and appliances is enough to raise the house temperature by about 15°C.  Now take a typical summer day, with an outside temperature of 20°C.  The heat from the occupants and appliances will still increase the house temperature by about 15°C *, so now the house will be at around 35°C *.

 

So, what's needed is a specification for a house where the insulation and airtightness is good enough to reduce the heating requirement to the point where the house is comfortable all year around, with a minimal amount of heating in winter and little or no active cooling in summer.  The Passivhaus requirements are just about spot on in hitting that sweet spot, so arguably there is little or no merit in trying to build a house that exceeds them by much, unless you live in a much colder all year around region, perhaps.

 

 

 

* Actually it won't quite do this, as the heating output of the occupants will probably reduce a bit as the indoor temperature increases relative to their temperature, but this rough approximation does just illustrate the point.

[Onoff]

25 minutes ago, scottishjohn said:

trying to build with no heating -to me should not be the goal ,but a comfortable and economical build that most can afford 

 

That when I retire my annual oil bill will probably eclipse my pi$$ poor pension makes me wish I lived in a passive spec house.

 

You only pay for insulation ONCE. You are at the mercy of A N other whatever energy source you consume.

[scottishjohn]

5 hours ago, Onoff said:

 

That when I retire my annual oil bill will probably eclipse my pi$$ poor pension makes me wish I lived in a passive spec house.

 

You only pay for insulation ONCE. You are at the mercy of A N other whatever energy source you consume.

absolutely no argument there  at all --,but has to a balancing factor .

like the kingspan  man told me when speccing insulation for my solar store 

anything over 6" of phonelic  is probably too much cos extra cost verus extra insulation never works out.

which is probably 10-12" of polystyrene as a comparsion .

Edited February 5, 2019 by scottishjohn