Farmhouse refurb heating system

[Wil]

Hi all,

 

I've been lurking for a while as our potential dream of a move to a smallholding has done the hokey-cokey with banks, kids and CV19 all throwing various spanners in the works, but it looks like we're really on this time and should be collecting the keys soon.

 

The farmhouse is a beautiful stone building, but has an EPC energy rating somewhere off the bottom of the chart. It may have got a point for effort. EWI would ruin the setting, IWI would ruin the features. It has secondary glazing throughout but plenty of chimneys etc so air tightness is probably fairly poor. I've had a stab at Jeremy's heat loss calculator but it all seems to depend on the MVHR and air changes which I don't yet know. I set air changes to 1 and MVHR to 100% efficient (there isn't one- yet) and came out with a heat loss of 16.5kW. (2 ACH and 0% efficient gives 27kW total heat loss. It's ~310m2, heated by an ancient oil burner with radiators throughout. The EPC says space heating of 52,430kWh (!) with 2109kWh to be reduced by loft insulation and a 22kWh reduction for solid wall insulation (unlikely to be able to achieve), Water heating 3240kWh. There are some currently unheated rooms and the potential for woodburners for room point heating.

 

My intent would be to do all of the loft insulation possible, then install UFH in the unheated rooms and manifolds to fan convectors throughout to replace the radiators. But how to get heat into the house and do hot water? I was originally convinced that a GSHP (there's room) with some solar HW and solar PV (there's a lot of roof space for solar of any type in a good SSW orientation) all feeding into a large thermal store or two. But having read all of the posts here on 'don't do GSHP just go ASHP' and 'get a sunamp' not a thermal store, it's all gotten a bit confusing. There's a decent sized single garage that would do as a plantroom although technically outside the thermal line of the house.  3phase electricity is available, but not sure of capacity yet.

 

For DHW, there's currently a bathroom  (small immersion-heated, open vented HW tank) and en-suite (hateful electric shower)and we'd probably add another en-suite at some stage. We're a family of 4 but relatively regularly have a full house stuffed with people, so I'd definitely want capacity and response time on the DHW side. Showers are usually in the morning pre-work/ school before the sun's up.

 

So, over to you- what on earth do I do to keep the kiddies warm (except move them into one of the chicken sheds)...

 

Many thanks in advance...

 

W

[PeterW]

I take it that you want something cost effective and not capex hungry..?

 

If you're in the middle of nowhere then what about a pellet boiler in the garage..? Insulated pipes into the thermal stores and run it as traditional rads. RHI would be OK as long as you have the insulation sorted in the attic I expect

 

 

[ProDave]

How water first.  Thermal store is the very last thing you want.  A thermal store has to store water and a much higher temperature than the delivered water temperature otherwise it's capacity will be very low.  So if choosing a water tank, choose an unvented cylinder (UVC)  that only has to store water at the required use temperture and several of us have found about 48 degrees to be plenty. that is low enough for an ASHP to heat okay.

 

The Sun Amp is a different animal. It does what it does very well.  It's main selling point is the way it stores heat it packs a lot of storage into a small space and with it's vacuum panel insulation the standing heat losses are very low.  However you won't heat them with an ASHP.   That's too much of a limitation for me.

 

Do your sums carefully before going for UFH in an old leaky building. You will require a lot more heat per square metre than a modern house so you really really need to make sure you have a LOT of insulation under the floors.  That is likely to be a lot of work.

[jfb]

Are you moving in to the house straight away or is there a period of building when nobody is in the house?

If the latter then you have a better chance of digging up floors so that you can get insulation under UFH.

If you are not going to address the air tightness of the building then I would suggest MVHR is not suitable. If you do a thorough refurb then you have every opportunity to concentrate on air tightness detailing. This is much harder to do if you plan on doing things bit by bit if you have to live in the house while works are going on.

I originally planned on a pellet boiler to power my farmhouse but I am glad I didn't go for it in the end. Many arguments against them from an ecological/maintenance point of view.

If you can get your heat demand down I would say an ASHP would be best way.

What are the internal features that discount IWI?

[Wil]

Thanks all for the replies so far. I have a reasonable line in CAPEX available for the right solution (this one is going to be a forever home- no really- that's not what I said about the current house, but this one is). So realistically OPEX more of a consideration within reason. GSHPs look good for the RHI to cover install costs.

 

We will have our existing place available til it sells, but realistically will be moving over fairly soon, so piecemeal improvements rather than a complete refurb. The rooms I'd consider UFH are currently unheated and have much lower floors for some reason already, so there's easily 100-150mm of space for insulation and UFH by just going directly onto the existing floor coverings. You're right about the heat loss being high though.

 

I'd certainly look to deal with some of the leakage via chimneys where we're not using them for woodburners. no issue with blocking them up as needed, but it feels unlikely the whole place will reach decent air tightness without major work.

 

DHW through a UVC is a good call (except I'll need a person with quals to install it) I wonder if a thermal store for collecting various heating systems and a separate UVC for DHW is overkill?

 

I could go down the pellet boiler route, but for the horror stories around blocked augers etc. I'd rather go a gasification boiler with some of the wood we have available on site?

 

Then again, I'd prefer to use some sort of heat pump covered by PV/ economy tariffs to have a system that didn't need feeding and meets the WAF. Could I 'stack' ASHPs or have an upstairs/ downstairs arrangement?

[Wil]

Internal features are coving details and multiple wall angles/ returns that would mean internal studwork frames being very complicated and eating a lot of the space. Also means every skirting board, picture rail and socket/ switch need redone.

 

Given it's a farmhouse- in the summer it's likely to live with the back door open most of the time, so mainly winter heat losses to deal with.

[PeterW]

26 minutes ago, Wil said:

DHW through a UVC is a good call (except I'll need a person with quals to install it) I wonder if a thermal store for collecting various heating systems and a separate UVC for DHW is overkill?

 

So you need the TS to get hot, and I would suggest using some sort of high heat source for that and then potentially go ASHP to do the grunt  work getting it up to 45c. Log gasification or pellet are fine - pellet boilers have got much better over time and they are much more controllable. You could slave a UVC off the TS during the winter, and then just use the ASHP for the summer with an immersion backup.

[Miek]

The long and short of it is that however you heat it the house is going to use a ton of energy. Most old farmhouses are like colanders in terms of air tightness , and at 300sqm you will need a large heating system. 

 

If it's a cold roof then before you insulate the loft spend a lot of effort trying to seal up all the gaps in the upstairs ceiling, there will be hundreds! No point insulating a leaky ceiling IMO. Foam gun & tapes will be best for that.

[Wil]

28 minutes ago, Miek said:

The long and short of it is that however you heat it the house is going to use a ton of energy. Most old farmhouses are like colanders in terms of air tightness , and at 300sqm you will need a large heating system. 

 

If it's a cold roof then before you insulate the loft spend a lot of effort trying to seal up all the gaps in the upstairs ceiling, there will be hundreds! No point insulating a leaky ceiling IMO. Foam gun & tapes will be best for that.

Ain't that the truth ?ton of energy indeed, hence the desire to combine sources. Yes, you're right in trying to get the ceiling airtight. The cold roof is indeed cold and when I stuck my head up there in February, the howling gale almost took it off. It does have impermeable felt under the roof tiles, but appears to have some fairly major daylight gaps which may need dealing with swiftly. Particularly as I'd like to put the heating manifolds up there and any other plant in place of the large pair of cold water/ expansion tanks currently occupying it. The worst offenders are likely the light fittings and pipe penetrations between the 'warm' house and cold loft.

 

Peter- Slaving the UVC off a thermal store sounds interesting- effectively the ASHP feeds both and when the UVC is satisfied it runs into the TS? In the summer, just run the ASHP into the cooling manifold for the fan convectors?

 

As mentioned I'd have plenty of room to divert solar into immersion heaters for either TS or UVC. Possibly some solar HW to pre-heat the TS or do the UVC in summer? Or is that just overcomplicating things? It feels like Solar HW would always have somewhere to put the heat!

 

One other point- the current owner mentioned an abandoned well outside the backdoor which her late husband had been considering for some sort of water-water heat pump, but had never gotten around to. Is this so niche it's unlikely to be an option? Thanks

Edited May 19, 2020 by Wil

[Miek]

The sums for a GSHP might work out if you have a big heating load. Most folk on here discount it and go for ASHP but they tend to be building well insulated houses and the capital cost of a GSHP is too high for the relatively small gain in COP. Also space is a big issue of course. 

 

Tapping in to an old well .... If the water in the well is not flowing then once you have pulled the heat out it will take a long time to replenish. I think you need flowing water for decent heat extraction. It might be a huge well though.

[Wil]

thanks Miek, I have calls in with Kensa and ThermalEarth to discuss GSHP options, so will see what they have to say. I did wonder if my lack of air tightness would preclude a ASHP option, or I may need two in series.

 

Good point on the replenishment of the water needed. There is a pond at the property too but I'm not sure it's big enough and I haven't seen what it looks like in summer to see if there's any water in it all year round.

 

I suppose there's no reason to completely scrap the oil burner and this could be used as 'top up' on any lower temp heat sources. But it can't have long left in it being at least 15 years old.

[PeterW]

13 minutes ago, Wil said:

thanks Miek, I have calls in with Kensa and ThermalEarth to discuss GSHP options, so will see what they have to say. I did wonder if my lack of air tightness would preclude a ASHP option, or I may need two in series.

 

Don't understand your logic..? You will have an even bigger issue with GSHP as that will need a bigger loop for higher output..?? I would probably go with a 14Kw (max single phase usually) ASHP for the heating, and a smaller 6Kw for the hot water if you're going that route but will need to go to a HP cylinder (min 300 litre, 400 better) and run that at night on E7. Heating then using the 14Kw into oversize rads or UFH if you are doing this sort of rebuild/refit and can get decent insulation under the floor.

[Wil]

Thanks Peter, I have 3phase available, so not limited to single except on the complications of using solar to offset it. Will probably end up with 3 single phase solar arrays though so again can offset daytime heat pump use to a degree. 14kW doesn't sound like it'd cover my peak losses though?

 

I was looking GSHP over ASHP only due to capacity/ efficiency for the size I'd need. I do have a friendly MCS certified installer and digging holes to put pipe in shouldn't be too much of an issue.

 

HP = Heat Pump Cylinder right? Where does this differ from a UVC cylinder? (will google shortly). Out of interest, why 400lt? Is that to give cover for the recovery time using a ASHP? There's a large airing cupboard in the bathroom so a DHW tank in the middle of the house isn't an issue.

 

Appreciate this is a heating conversation but is Icynene a reasonable idea for insulating and sealing up a leaky old building? Looking for breathable and minimum impact on depth, but afraid of a sticky mess requiring a new roof!

[Gone West]

2 hours ago, Wil said:

Appreciate this is a heating conversation but is Icynene a reasonable idea for insulating and sealing up a leaky old building?

We used 350mm Icynene to insulate our house (PH) and got an airtightness of 0.47ACH without any membranes or tapes. According to the manufacturers 100mm is supposed to be enough for good airtightness.

[Wil]

Thanks PeterStarck, I think I read your postings on it. Yours was newbuild and designed with Icynene in mind though right? I'm concerned about the application to an old existing building. It certainly sounds like a great option, even if only used as posh cold roof insulation to ensure all the air leakage is stopped there.

 

So many different things to think about, but for now, it's going and getting the keys tomorrow that'll keep me up tonight..

[Gone West]

37 minutes ago, Wil said:

Yours was newbuild and designed with Icynene in mind though right?

That's right, although some friends who built a self build also renovated an old outbuilding on the site and had 100mm Icynene sprayed onto the inside of the walls as IWI and draughtproofing. The only problem was it was done in the winter and apparently Icynene doesn't stick that well to cold surfaces and it pulled back slightly in places which had to be rectified but other than that it worked well. It was done about nine years ago and the building used as a artists studio.