Improving efficiency

[Leopold1904]

Recently purchased a new house in France and just installed a couple of Hitach Yutaki 12kW ASHP. The house is large (340 sqm), old (1830s) and very poorly insulated. We can't do much about the walls or windows but will be insulating the attic. In any case, the pumps have been up and running and our latest electricity bill (for November-December) is more than 2000€. Yes. Now part of this is due to workmen being in the house and external doors open all day, etc., so we're not seriously concerned; but we are slightly concerned. Our engineer (who installed them) has us running the pump 24 hours a day at a steady temp of 19°, and I think that this is not necessary. I've suggested putting it on a timer. He says no, it's going to cost us just as much, if we turn the pump off at night then the cost of reheating the cooled house in the morning will be as much as keeping it warm all night. He says it's also not good for the pump to be switched on and off repeatedly. What's the consensus on this? If there is one?

Thanks!

Iain.

[joth]

3 minutes ago, Leopold1904 said:

What's the consensus on this?

Leave it on 24/7 while the house is occupied, but be sure weather compensation is in use. 

 

What emitters are you using? Depending on the property layout and draftyness it maybe beneficial to turn off "areas" that are unused for long periods. Especially if that allows one of the 2 ASHP to be turned off - effectively doubling your modulation ratio. But depends how quick the rooms are to heat back up when needed, and your patience to wait (or turn it on in advance)

 

French houses, especially older ones and in the south, tend to have very thick uninsulated walls. High thermal mass. This will take yonks (multiple days).to heat up with the ASHP running at an efficient (low) temperature, likely why the installer is well versed in leaving the things on all the time. 

[BotusBuild]

Iain. If you have people working in the property and doors open all day, get one of those mobile propane heaters, probably work out cheaper.

 

You might be able to then use the ASHP's overnight to keep the building warm, but as it is poorly insulated as you state, I am not surprised at the Nov/Dec elec bill

[Leopold1904]

3 hours ago, joth said:

Leave it on 24/7 while the house is occupied, but be sure weather compensation is in use. 

Thanks for the reply. I'd better google "weather compensation"...

3 hours ago, joth said:

What emitters are you using? Depending on the property layout and draftyness it maybe beneficial to turn off "areas" that are unused for long periods. Especially if that allows one of the 2 ASHP to be turned off - effectively doubling your modulation ratio. But depends how quick the rooms are to heat back up when needed, and your patience to wait (or turn it on in advance)

By emitters, I presume you mean radiators. These are very old big cast iron ones that probably date from when central heating was first installed in the house decades ago. We have bedrooms on the top floor that are only used a couple of months a year. Are you saying we can turn them off in these rooms? Will this not affect the flow of water through the whole system? That's what our engineer says.

3 hours ago, joth said:

French houses, especially older ones and in the south, tend to have very thick uninsulated walls. High thermal mass. This will take yonks (multiple days).to heat up with the ASHP running at an efficient (low) temperature, likely why the installer is well versed in leaving the things on all the time. 

Yep, 30 cm stone walls. So can we turn the heat down at night rather than off completely? It seems extragavant to have the temperature set at 19° all night and we're throwing off the bedclothes because we're too hot.

[Leopold1904]

3 hours ago, BotusBuild said:

Iain. If you have people working in the property and doors open all day, get one of those mobile propane heaters, probably work out cheaper.

 

You might be able to then use the ASHP's overnight to keep the building warm, but as it is poorly insulated as you state, I am not surprised at the Nov/Dec elec bill

Well, hopefully the builders will be gone soon. 😀

[Mike]

3 hours ago, Leopold1904 said:

The house is large (340 sqm), old (1830s) and very poorly insulated. We can't do much about the walls or windows

Why not - what's the problem?

[Leopold1904]

33 minutes ago, Mike said:

Why not - what's the problem?

Well I don't know, maybe there isn't one, in the rooms we're renovating we've put in cavity insulation behind plasterboard, but not sure about the whole house... That would cost a fair bit. Windows we don't want change - they're original blown glass which we'd like to keep. But if it comes down to it I suppose we could try double glazing. Not sure if the frames would take it though. Haven't really looked into it since people we've talked to said it would be a shame.

Edited January 23 by Leopold1904

[PhilT]

19 minutes ago, Leopold1904 said:

So can we turn the heat down at night rather than off completely? It seems extragavant to have the temperature set at 19° all night and we're throwing off the bedclothes because we're too hot.

Yes that's what I do, for the same reason, mine's set to 19 during the day and 17 at night

[Mike]

11 minutes ago, Leopold1904 said:

in the rooms we're renovating we've put in cavity insulation behind plasterboard, but not sure about the whole house... That would cost a fair bit.

If you use approved contractors, then it's worth knowing that there is potentially a lot of financial help for energy-related renovation in France - see https://www.maprimerenov.gouv.fr/    (in French, of course). Not much help if you're doing the work yourself though.

 

14 minutes ago, Leopold1904 said:

Windows we don't want change - they're original blown glass which we'd like to keep

Yes historic glass is certainly worth keeping if you can. Sounds like adding a secondary window (double fenêtre) might be worth considering, even if only in certain rooms.

[SteamyTea]

@Garald has recently finished his renovation, he may know a trick or two.

[Garald]

1. In order to get Ma Prime Renov, you need to have been a French taxpayer the previous year (I'm not sure this was intended, but that's how it works out because of how their arcane website is set up). If you weren't, there's an alternative - less generous but still not a completely trivial amount - the Certificats d'Économie d'Énergie (which I should get as soon as the contractor sends me the remaining technical specifications! grrrr). 

2. I hope you had the ASHP installer get rid of the old boiler himself? Otherwise the CEEs you can get for the heat-pump will be drastically reduced.

3. Right, my electricity bills were huge when the workmen were using machines - and space-heaters to heat themselves (the heat-pump went into operation fairly late; early in the renovation, I had the "help" of a supposed professional about whom the less said, the better - I had to take charge at that point, with the help of the good people of this forum).

4. Of course insulating is worthwhile. I mean, do your own budgeting, but, unlike a heat-pump, it should last for many decades, if properly done. Insulating walls is particularly cost-effective - what you have to worry about there is not so much the cost of insulation or even the cost of labor, but rather the fact that losing m^2 means losing property value (though obviously the extent depends on the area). If I had to do things again, I would seriously consider insulating on the outside on the courtyard side. (Didn't happen because of what I mentioned in point 3.) 

5. New windows are expensive, but getting them on the street-side was a no-brainer, since I am rather sensitive to noise. On the courtyard side, I mostly left the old windows, which are double-glazing and less than 10 years old. Their performance seems to be very reasonable.

6. Take advantage of cold waves to measure current performance. Get a thermal camera now! Less than 200eur on Amazon. Hunt for defects in the insulation - thermal bridges and so forth.

Edited January 23 by Garald

[Garald]

And yes, the contractor/head builder should have RGE certification for you to get any subsidies. Mine got it at the beginning of work because I insisted - it's a symbolic one-week course (partly deontology, I'd imagine) that he needed to take sooner or later at any event.

[Garald]

Used BioFib Trio on some walls (seems to be working well; the conductivity is similar to that of rockwool), a thinner layer of BioFib Trio combined with reflective insulation in walls where I had less space to spare (seems to work very decently, considering it's mostly north walls - but, as I said, insulating on the outside would have been a good option) and cellulose insulation in the combles perdues (I'm a bit unhappy (see other threads) - I think it has settled). In the roof, the contractors just opened things up and replaced insulation that had gone bad by new rock wool. I'll do a more thorough job on the roof if we ever raise it.

 

Another thing I would do differently: I would add a thick layer of insulation on the floor of the groundfloor (as opposed to 1-2cm polyurethane, which is what we did). Of course that would mean a Japanese-style entrance, but surely that's a good thing if you don't wear shoes at home.

 

The DPE was F at the start; it is B now.

[Garald]

1 hour ago, Mike said:

 

 

Yes historic glass is certainly worth keeping if you can. Sounds like adding a secondary window (double fenêtre) might be worth considering, even if only in certain rooms.

 

Yes, did that with stained glass. The secondary windows (on the outside) are really not great, though (just a couple of degrees warmer than the outside) - I wasn't keeping tabs on every single detail at that point. Still, it helps.

 

 

 

Outside temperature = - 2C.

 

Of course, because of the secondary windows, the stained glass is now less visible from the outside.

 

Edited January 23 by Garald

[Leopold1904]

Thanks everyone, I'll have to digest all that. Yes, les primes, we're not (or weren't) tax resident so didn't qualify. Hopefully for future work.

[Garald]

You should still be able to get CEEs. They'll be in the low thousands for a major renovation, though - not counting 3k for replacing a boiler by a heat-pump, but for that, as I said, the installer must have been there when the boiler was removed.

[Mike]

42 minutes ago, Garald said:

losing m^2 means losing property value

However, in France, having a higher DPE increases the property value, so there may be a gain rather than a loss.

 

30 minutes ago, Garald said:

Used BioFib Trio

I'm using the same - it seems good stuff.

[Garald]

1 minute ago, Mike said:

However, in France, having a higher DPE increases the property value, so there may be a gain rather than a loss.

 

Well, obviously. Prices (particularly in the Paris area) do not yet reflect DPEs enough, but that ought to gradually change as people realize how much it costs to raise a DPE even by one single grade.

 

The point is that you want to lose as few m^2 as possible for a given insulation performance. 

 

 

1 minute ago, Mike said:

 

I'm using the same - it seems good stuff.

 

Right - similar performance to rock wool, fully "natural" (whether rock wool really poses any sort of danger or not is up for debate - no doubt it's a lot better than fiberglass, and any fibrous material, natural or not, poses *some* risk if not properly sealed - but better safe than sorry), moderate cost. The only downside I can see is its fire rating of F. I guess it's fine behind fireproof plasterboard?

 

Good sound absorber too (so is rockwool), for what that's worth.

[Garald]

PS. If you look at the thermal-camera picture of the stained glass closely, you will see some sort of frame within the wall. That's one of the walls where I have 5cm of BioFib + reflective insulation (which comes with its own insulating backing). As you can see, it works well enough (surprisingly so given @SteamyTea's experiments), but you do see the metal grid there, whereas I don't think I ever spotted it in the thermal-camera pictures of the walls where I have a thick layer of BioFib. Not sure how to interpret that.

Edited January 23 by Garald

[Mike]

33 minutes ago, Garald said:

Prices (particularly in the Paris area) do not yet reflect DPEs enough

Just checked and the price variance in Paris is fairly modest compared to other regions. For those in the UK, where the EPC rating still seems to be a minor factor, here's a map from the Notaires de France showing the difference the rating made to 2022 sales prices in France:

 

 

47 minutes ago, Garald said:

BioFib Trio... ...I guess it's fine behind fireproof plasterboard?

 

AFAIK it's fine behind any plasterboard, though I am using fireproof board throughout (GypsoLignum / GypsoOmnia) - for its other properties, rather than as a fire board.

[ReedRichards]

4 hours ago, Leopold1904 said:

So can we turn the heat down at night rather than off completely?

That's also what I do, 18 C overnight then gradually ramped up to 20.5 C by mid afternoon.  In the 6 hours that my set temperature is 18 C the actual temperature rarely gets that low so effectively my heat pump is off for 6 hours overnight.  I very much doubt that this has a significant adverse impact on my efficiency - and if it does it would be worth it not to get overheated in bed when trying to sleep. 

[Leopold1904]

10 hours ago, Mike said:

AFAIK it's fine behind any plasterboard, though I am using fireproof board throughout (GypsoLignum / GypsoOmnia) - for its other properties, rather than as a fire board.

Is this better insulation than polyurethane? I'm not worried about noise, there is none where we are.

Edited January 24 by Leopold1904

[Garald]

2 hours ago, Leopold1904 said:

Is this better insulation than polyurethane? I'm not worried about noise, there is none where we are.

 

Polyurethane is great (lower heat conductivity than BioFib Trio or rockwool), but I've had it used mostly for details - polyurethane sealant and so forth; I will also use it if I have a door padded. 

I did discuss possible large-scale usage of polyurethane (PIR) with more experienced users in this forum. The impression that I got is that it's not a product loved by firemen (even compared to some products rated F). It may be that my fears were exaggerated; discuss the matter with people with more technical experience and/or with those who have actually insulated their houses using mainly polyurethane. I no longer recall how it compares in terms of cost with other insulation materials.

 

BioFib Trio or Rockwool is what you use if you have at least 15cm to spare (ideally more like 20cm). Recall that the current standard in France (for new construction or a truly succesful renovation) is R=4.

[SteamyTea]

19 minutes ago, Garald said:

R=4

U = 1 / R

 

U = 0.25 W.m^-2.K^-1

 

Edited January 24 by SteamyTea

[Mike]

8 hours ago, Garald said:

  11 hours ago, Leopold1904 said:

Is this better insulation than polyurethane?

That depends what you mean by 'better'. As above, the thermal conductivity of BioFib Trio (0.038 W/m.K) is is higher than PU foam (0.023–0.026 W/m.K) so it's less good at retaining heat. So, as Garald says, PU foam is useful in a tight space. It's also useful if you need load-bearing insulation. In other circumstances, a natural insulation (but not sheep's wool) may be better.

 

For example, BioFib Trio contains 92% natural fibres - a blend of hemp, cotton & linseed fibre. Unlike PU foams, mineral wool & other similar products, many natural fibres - particularly hemp and linseed - are very good at moisture sorption and desorption - that is taking water vapour from the air into the fibre's cell walls, and releasing it again. There are several technical benefits to that, provided you have a construction that's vapour-open ('breathable') to take advantage of those properties:

• it reduces the risk of condensation
• improves thermal comfort by keeping the air within a comfortable relative humidity range for longer
• improves air quality by keeping the air within a healthy relative humidity range for longer (at <40% RH respiratory infections are more likely; at >60% bacteria and mould thrive)
• tends to reduce heating and cooling requirements (adsorption of moisture releases heat, desorption takes heat, though research into quantifying this in buildings is limited)

There are also non-technical benefits - it uses renewable materials, has low carbon emissions, supports (potentially local) agriculture, and It's also a pleasant product to work with.