Air source heat pump on very old stone cottage

[blankton]

I am currently renovating a very old stone cottage, dating (I believe) to the early 1600's.  The property is in a village with no gas, and until recently had storage heaters. 

 

The property is currently empty. It has a solid floor which has been "sealed" with bichumen, but is causing damp around the bottom of the walls. I am going to install a new limecrete slab, to try and counter any damp issues, so it makes sense to install UFH at the same time. I believe the more constant temperature from the UFH will benefit the old property . I also have the ground floor ceilings down, so could even fit wet UFH under the first floor. At the beginning of the project I was going to run this from a small oil boiler, but then the oil price went crazy! 

 

It is essentially a 2 up 2 down small cottage. the ground floor walls are 500mm thick stone, although this is unlikely to be solid. I believe it is an outer skin and inner skin and loose rubble / earth infil.  The first floor is oak timber frame with brick infill panels. The first floor has been "dot and dabbed" with insulating plasterboard. The roof has 300mm+ of loft insulation. The windows are double glazed. There is one chimney, which I am going to fit a log burner. 

 

My gut feeling is that it is quite well insulated, although the EPC gave it an "F" stating that it needs wall insulation on the downstairs walls. I am loath to do this both for aesthetic and damp reasons. I want the external stonework on show (and also some internally). I realise that running an ASHP non optimally can be expensive and cold, but I think the UFH and the fact that I am benchmarking (cost wise) against storage heaters or oil heating, will skew the sums in favor of the ASHP. 

 

I think I am at the stage where I need to get a better calculation of the losses from the building to determine the size of the ASHP I would need. (I have been offered a 10KW unit from my brother at a good price).I've had a quick look at working out heat losses. I am a bit confused because I have varying construction in different areas - stone, brick with dot and dab. Do I just work out losses for each room and add them up? To be honest I am very confused. Is there an idiots guide?

 

I would also like to try and get a grant, but I think this wont be possible while I haven't got my stonework insulated. I suspect I could probably get my cottage listed, but this would seem like an excessive step to take just to become eligible for a 5k grant 😁

 

I would appreciate any advice. 

 

 

 

[Radian]

Calculating the heat loss will be super-tricky if you're uncertain of the wall makeup. Even if you took a core sample it probably varies a lot anyway. Another approach is to temporarily use a thermostatically controlled electric heater and monitor power consumption vs. average outdoor temperatures over a period of time. If the heater (or possible more than one) does its job and maintains a fixed indoor temperature then the average daily outdoor temperature difference divided by the total kWh for each day will give you a slope from which you can read off the heating loss per degree difference indoor to outdoor. From this you can estimate your space heating demand for whatever worst case you require. Domestic hot water is a separate exercise that you can do with made-up figures.

[HughF]

I'd skip the grant bit altogether - you sound technically competent, buy the bits and install it yourself. Provided you get a monoblock (which nearly everything in the UK is), you don't need an F Gas ticket.

 

Treat yourself to a second hand press gun with some M and U jaws and you'll get the lot installed in no time.

[ReedRichards]

Heat pumps run most efficiently and therefore most cost-effectively when the leaving water temperature is as low as possible.  UFH generally requires a lower water temperature than radiators so with a mix of UFH and radiators you may not be able to run the heat pump as efficiently as if you had only UFH.  So use UFH on both floors.  

[Dillsue]

10 hours ago, blankton said:

I am a bit confused because I have varying construction in different areas - stone, brick with dot and dab. Do I just work out losses for each room and add them up? To be honest I am very confused. Is there an idiots guide?

Exactly as you say, work out loss for each room then add them up. Factor in ventilation/draught loss and thats it done. If you can use MS Excel its very easy to do, otherwise its long hand on paper with a calculator. Using Excel allows you to easily see the impact of changing materials/thickness.

 

A while ago Which produced some very good books on building and this one on Ebay 144467667935 explains the calculation process and gives U values for lots of differing materials in use up to the publication date. If youre planning on using newer insulation youll get U values from the manufacturer online.

[JohnMo]

There is a heat loss spreadsheet on here, think it's in the boffin corner.

 

Unless the ground floor is insulated I would not fit UFH, as so much heat will go downwards to heat the earth below the building, your heating bills will huge.  You will have oversized rads so you would run them the same as UFH at low temp for long periods.

 

Our last property was circa 1830, the downstairs walls were battened out and rock wool insulation used then plasterboard.  But you will remove around 100 to 115mm from each wall floor space.  The other two floors had no additional insulation in the walls, the heating bills weren't that bad really. 

 

Look to minimise drafts and air leakage.  When you install the log burner have the chimney sealed around the flue pipe, I think they vermiculite fill it afterwards.

 

If you make a good job of draft proofing you may may need to consider ventilation afterwards, dMEV fans install in the same holes as normal intermittent fans, but provide slow and quiet controlled ventilation continuously. 

 

 

[CotswoldDoItUpper]

Have you considered LPG? With the price of electricity so high it might make sense. You can burry the tank outside as well so there is nothing to see. Then it’s just a simple (cheep!)  combi boiler for unlimited hot water and you can have either UFH or rads of both. We fixed our LPG cost about 6 weeks ago at a shade over 5p per kWh. An air source heat pump would need a COP over 6 to match this at current prices, regardless of increases in the future. Or some big solar panels. 

[SteamyTea]

Is your damp being caused by condensation, rather than something penetrations the wall.

A lime slab is not going to help any really. A lot if insulation will though.

 

To add to @Radiansuggestion about using heater to calculate heat loss, all you need to do is log external and internal temperature difference, then chart and calculate the slope, which will become power (W) per degree (⁰c or K). That way you do not have to try and keep the house at a constant temperature.

Worth making a Raspberry Pi based logger, only cost a few quid and you can see what the RH is as well.

[blankton]

Lots of points raised above - I'll try and cover them all. 

 

Damp - the house was empty for 2 years. The guttering at the front was leaking and there is a back wall which is below the ground level of my neighbors garden. Some of the damp is localised to these areas, however  all skirting boards were rotting at the base, where moisture was getting around the edge of the bitchumen floor, even those in the middle of the house. Its a little difficult to isolate how much of the damp has come about due to it being unoccupied (heating off and no ventilation) and how much is intrinsically to do with the construction. I am hoping that by addressing the aspects which are in my control, the finished house wont have any damp. Guttering is fixed and I plan to install a heated and breathable floor. The outstanding item that isn't within my control is ground level on the back wall.  

The new floor would be insulated beneath with 100-200mm foamed glass. Do people fit heated slabs with no insulation, I haven't heard of that before?

 

Currently the house is a bit of a building site (ceilings down, loft insulation peeled back) so I don't think I'll be able to run the heat loss experiment, as its not representative. I can do excel, so I'll have a go with that. 

 

Here is an example of one of my stone walls. I have been repointing today with an NHL 2 lime. I am loath to box in  something as old as this with rockwool / kingspan, I appreciate this might mean a compromise on the heating bills 😊

 

Before

[img]https://i.ibb.co/zSpRPS2/IMG-20220329-083633.jpg[/img]

 

After

[img]https://i.ibb.co/b5Km3kx/IMG-20220409-164851.jpg[/img]

 

Looks like my links aren't working. 

 

 

 

 

 

  

Edited April 9, 2022 by blankton
photos

[TonyT]

Can’t you dig the soil away from the wall?

 

if not can’t you dig a French drain and install perforated pipe to get the water away from the house? And reinstall the soil?

 

 

 

 

[blankton]

1 hour ago, TonyT said:

Can’t you dig the soil away from the wall?

 

if not can’t you dig a French drain and install perforated pipe to get the water away from the house? And reinstall the soil?

 

 

 

 

It's not my soil, its my neighbors. Its not like they have built a muck heap against my house, its just the general ground level on that side of the property. Both are 400+ years old and I assume the ground level has built up over the years.

 

French drain is something I have thought about, but I think will need their agreement. I don't think I can just march into their back garden and start digging. 

 

To complicate matters, the house is currently for sale and under offer. So I doubt they want me digging up the garden and potentially disrupting their sale. I plan to speak to he new owners. I suspect ground level is also high against their wall as well.