Heating and cooling: air source heat pump and open windows

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- CommentAuthorFairynuff
- CommentTimeNov 25th 2020
Long story short.
We are fully renovating Devon cottage constructed of local stone (more like slate), cob to hold it together, and lime which had been badly renovated and overmaintained since the 60's so its a complete gut job with reinstatement of walls, roof, floor and windows.
I would have liked a ground source system but we have had to locate the new septic tank drainage field across most of the ground and I dont think we have sufficient area remaining so I'm investigating air to water heat pumps but we like open windows, winter and summer and from my investigations this doesnt appear to match well. We have mains gas, but I was hoping for a greener solution
Any comments would be greatly appreciated.
- CommentAuthordereke
- CommentTimeNov 25th 2020
hmm
I think you can do it you would just need a heatpump matched to the heatloss of having all the windows open.
It is not going to be very efficient, just like burning all that GAS to send the heat out the windows is not very efficient.

Sounds like you would be better off not having central heating and instead retrofit a jumper with an electric blanket.
- CommentAuthortony
- CommentTimeNov 25th 2020
No problem opening windows, as Derek says it just increases heat losses
- CommentAuthordjh
- CommentTimeNov 25th 2020
I don't suppose it's worth suggesting but an MVHR will give much the same effect as having windows open without the large heat loss. You can open windows as well pretty much as you like during spring, summer and autumn except for a few hot days in summer.
- CommentAuthorjms452
- CommentTimeNov 25th 2020
Posted By: djhI don't suppose it's worth suggesting but an MVHR will give much the same effect as having windows open without the large heat loss. You can open windows as well pretty much as you like during spring, summer and autumn except for a few hot days in summer.

We used to love having windows open and though it seemed stuffy if they were closed.

Now (with MVHR) all winter they are closed, it's fresh, quiet and no drafts.
- CommentAuthorphiledge
- CommentTimeNov 25th 2020
If youve not already laid youre leachfield, I cant see any reason why you cant have the GSHP under the leachfield. A flow of liquid in the soil round the collector pipe helps with heat transfer:)
- CommentAuthorWillInAberdeen
- CommentTimeNov 25th 2020
And Waste Water Heat Recovery scores extra SAP points! Have you got a SAP assessment yet for your proposed design? You'll need one to show how the refurbishment is going to comply with Building Standards for heat conservation.

More seriously, if you're going to run the heating with the windows open, the 'Green' Building Forum might not be a good place to ask about it, but wasting heat from a heat pump is less bad than wasting heat from most other heating systems.

Have you tried this: turn off the heating and open all the windows for 20minutes, just before you go out for the day. The house will get aired out, and get cold, but it would have cooled down anyway while you're out. Heat the house up again when you get back. We did that with an air-to-water heat pump in our last house, but any heat source would work, so long as there isn't a big thermal inertia such as a heated floor slab which wouldn't have cooled down in the time.
- CommentAuthordickster
- CommentTimeNov 26th 2020
Some 9 years too late, I realised we could have put heat pump coils in the required 65 metres of drainage field trench. Even if we didn't know we might want it at the time, what a missed trick that was. Ah well.
- CommentAuthorFairynuff
- CommentTimeNov 27th 2020
Thank you Dereke and Tony - thats what I thought, and I feel wasting energy from a heat pump is less bad than wasting energy from burning fossil fuel
thank you DJH and JMS452 - I've been told we cant achieve required air tightness for MVHR as it is a renovation not a rebuild
thank you Philedge and Dickster - sadly I only discovered too late we could lay beneath the leachfield as the leachfield was complete and being covered over
thank you WillinAberdeen - we are looking at an air to water pump with underfloor heating at groundfloor level and radiators for bedrooms and bathrooms on the first floor. Its our bedroom where we sleep with the windows open all year round, but I suppose we could have smaller radiators upstairs than would normally be the case as although we like to be warm when sitting around, we sleep better with open windows
- CommentAuthorrevor
- CommentTimeNov 27th 2020
Who says you cant have MVHR on a renovation. As long as you can get a good airtightness there is no reason why you can't. Our main structure was built about 1750 and we fitted one. Even if it is not that efficient it is also useful if you have several en-suites or bathrooms or utility rooms etc one unit rather than several individual fans.
You look to be gutting the place just pay attention to cold bridges and potential places for air leaks. A few years ago I asked a consultant who did air tightness test as to where were the places he tended to find leaks. His answer was where the trades have been, joiners plumbers electricians never think of air sealing the holes they make.
- CommentAuthordereke
- CommentTimeNov 27th 2020
MVHR with poor air tightness is still going to perform better than windows wide open.
It will be much much more comfortable to live in too! I've had a leaky house with MVHR and it was transformed overnight from condensation everywhere one day to clear windows and pleasant environment the next.
I think you will find it easier to convince someone to install MVHR than to install a heatpump that is speced to keep you warm with the windows open!
- CommentAuthorjms452
- CommentTimeNov 27th 2020 edited
Posted By: derekeMVHR with poor air tightness is still going to perform better than windows wide open.
It will be much much more comfortable to live in too! I've had a leaky house with MVHR and it was transformed overnight from condensation everywhere one day to clear windows and pleasant environment the next.

+1

our house is a renovation, victorian with some suspended floors.

Design your renovation for where you are going - not where you are starting from.
That logic will stop you ever doing anything - after all why insulate if the windows are open!

MVHR enables you to largely decouple ventilation from heat loss and go to town on air tightness without creating problems. It sounds like you prefer more ventilation than typical, making MVHR a better investment.
- CommentAuthordjh
- CommentTimeNov 27th 2020
Posted By: FairynuffI've been told we cant achieve required air tightness for MVHR as it is a renovation not a rebuild

Hmm ...
(1) there is no airtightness requirement for MVHR
(2) it's perfectly possible to achieve an excellent airtightness on a renovation

The key is knowing what you're doing (or employing somebody who actually knows what they're doing)
- CommentAuthorrevor
- CommentTimeNov 28th 2020
How much if anything you are doing yourself. There is no reason why you cannot make a real good job of the renovation. If a builder has told you that you cannot have MVHR then find someone else who understands. Many builders are not up to speed with the advances made in building quality houses. When I was renovating / extending my BCO spotted my MHVR and said it was first he had come across. when he came on a later visit he said when he left me last time he went on his next inspection and coincidentally there was another build with MVHR but in his ignorance the builder had done it wrong all the windows had trickle vents.
- CommentAuthorDominic Cooney
- CommentTimeNov 28th 2020
Also have put MVHR in the barn conversion that we are doing. Trying to keep things as airtight as possible.

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