PIV + Canadian well?

[Garald]

As has already been discussed, I have a PIV system. I should probably look seriously into the possibility of getting MVHR, but, according to the contractor, it's now too late: it was a possibility to be considered at the beginning of the renovation (back when I was having poor decisions done for me by someone pretending to be an architect) rather than now.

 

What about what is called a "Canadian well" (puits canadien), though? That would seem to combine well with a PIV (unless there are real arguments in the "PIV is bogus" camp, that is). If I understand correctly, it's just a long pipe that goes in the ground and circles about before going into the ventilation input (MVHR or PIV). Of course that means the air is being heated by the ground during winter and cooled by it during summer, all essentially for free. (Well, running it costs no extra money; the installation costs are not huge but not trivial.) In fact, some people call it a "puits provençal" if the main idea is cooling, but it's the same device playing two roles.

 

What energy efficiency gains should I expect? What experiences do people here have with this sort of system?

Edited May 28 by Garald

[ProDave]

I think this has been discussed before.  To work, it has to be some exotic pipe coated with something like silver.  Any normal pipe used for that is likely to get cold, condensation and mould then all sorts of horror stories about what it draws into your house and people have had to cap it off and abandon it.

[Garald]

1 hour ago, ProDave said:

I think this has been discussed before.  To work, it has to be some exotic pipe coated with something like silver.  Any normal pipe used for that is likely to get cold, condensation and mould then all sorts of horror stories about what it draws into your house and people have had to cap it off and abandon it.

 

I can take a look at what is done here; a puits canadien/puits provençal is a known quantity in France, with (insured) specialists who install that sort of thing for a living, I take, not something I just dreamed up. Thanks for the heads-up. I take it's not common in the UK except as an apparently ill-fated DIY project?

 

Update: I just came across a place that does the piping in clay, and claims that solves condensation issues - is that plausible? https://lepuitscanadien.fr/

Edited May 28 by Garald

[JohnMo]

If you want MVHR instead of PIV, look into cascade MVHR.  Supply is pretty much the same as the PIV - one supply, possible some through (internal) wall vent fans to move air towards the extract points as you require.  The only difficulty comes in getting ducts to all wet rooms. But you would be better spending your time getting you your existing system to work more efficiently on an as required basis instead of set speed.

 

 

[Garald]

56 minutes ago, JohnMo said:

If you want MVHR instead of PIV, look into cascade MVHR.  Supply is pretty much the same as the PIV - one supply, possible some through (internal) wall vent fans to move air towards the extract points as you require.  The only difficulty comes in getting ducts to all wet rooms. But you would be better spending your time getting you your existing system to work more efficiently on an as required basis instead of set speed.

 

 

 

Oh, I'd love MVHR, but the contractor says it's too late by now - his opinion is roughly that I'll have to wait for the next major renovation (whenever that is). Right, the difficulty is in the ducting. Not sure he is right; I'll ask a specialist to come and give me his own assessment, but I am not too optimistic.

 

At any rate, if I am stuck with PIV, then a Canadian well makes more sense if anything - the increase of efficiency will be higher (in that there will be more to work on), whereas with MVHR a Canadian well plays just an ancillary role.

 

> But you would be better spending your time getting you your existing system to work more efficiently on an as required basis instead of set speed.

 

True, that should be the first order of business. On the other things - I want to get an idea of how worthwhile they are so that I can ask for quotes and decide what to do in the future.

Edited May 28 by Garald

[JohnMo]

15 minutes ago, Garald said:

want to get an idea of how worthwhile they are so that I can ask for quotes and decide what to do in the future.

Do you have the land for it, thought you needed quite along run to get the benefits bit like a GSHP. A short run (a few metres) is zero benefits 

[Garald]

4 minutes ago, JohnMo said:

Do you have the land for it, thought you needed quite along run to get the benefits bit like a GSHP. A short run (a few metres) is zero benefits 

 

I'd have to talk to the co-op to see whether it can be run under our shared courtyard (which is in less than optimal condition, and which I have fantasized about redoing at my cost). Alternatively - can the pipes go under the house? I haven't got a basement, and I have long been curious about what hides under the house (Cthulhu?). (There might be something interesting - I know from a plan from townhall that there is a quarry tunnel under the sidewalk in front of my place; it is connected to the catacombs).

Edited May 28 by Garald

[JohnMo]

15 minutes ago, Garald said:

 

I'd have to talk to the co-op to see whether it can be run under our shared courtyard (which is in less than optimal condition, and which I have fantasized about redoing at my cost). Alternatively - can the pipes go under the house? I haven't got a basement, and I have long been curious about what hides under the house (Cthulhu?). (There might be something interesting - I know from a plan from townhall that there is a quarry tunnel under the sidewalk in front of my place; it is connected to the catacombs).

Not sure you are being realistic on the cost v reward

[Garald]

53 minutes ago, JohnMo said:

Not sure you are being realistic on the cost v reward

 

Right - I'll have to get a quote (elsewhere) and learn how to calculate the reward (here).

 

According to the (dumb software of) the diagnostician who came here last summer, 50% of heat losses at my place are through ventilation, so it does seem like ventilation is the right thing to obsess about at this point.

[JohnMo]

1 hour ago, Garald said:

 

Right - I'll have to get a quote (elsewhere) and learn how to calculate the reward (here).

 

According to the (dumb software of) the diagnostician who came here last summer, 50% of heat losses at my place are through ventilation, so it does seem like ventilation is the right thing to obsess about at this point.

I would calculate it yourself as that sounds big, 30% of the heat loss sounds better - unless you have an extremely leaky house or you are flowing way too much through the piv system. Then adding MVHR would just make heat loss higher due to the additional ventilation.

 

Having a ducted pre heat will only preheat to 7 degs at best (if very long and a reasonable depth) but possibly closer to a couple of degrees above ambient.

 

Spend a couple of days optimising the flow settings of the piv. Get a CO2 monitor, set it the bedroom first and get so you hit a max of just under 1000 ppm overnight with the bedroom window closed. Don't worry to much about humidity levels as they will be all over the place at the moment.

 

 

[Garald]

2 minutes ago, JohnMo said:

I would calculate it yourself as that sounds big, 30% of the heat loss sounds better - unless you have an extremely leaky house or you are flowing way too much through the piv system. Then adding MVHR would just make heat loss higher due to the additional ventilation.

 

How do I calculate it myself? I don't think the diagnostician looked at my PIV settings - he was just keying data into his system for a couple of hours. I don't think the house is very leaky either, just well-insulated (R>=3.8 on all walls, new high-spec double-glazing, etc.).

 

I have pre-heating (basically a radiator on the PIV, fed by the heat-pump) but that does nothing for efficiency; the point is that a Canadian well would heat the incoming air in winter (and cool it in summer) using essentially no energy.

 

I have a CO2 monitor and I am currently trying to get an automatic controller for the PIV linked to humidity and CO2 readings.

[JohnMo]

The basics are here

https://www.open.edu/openlearn/nature-environment/energy-buildings/content-section-2.4.1

[SteamyTea]

Ground temperature lags air temperature, as does ocean temperature (which is why it was only 13°C yesterday).

Like using the thermal inertia in a house to stabilise ambient temperature, it is only 'right' under very specific circumstances i.e. right ∆T, right, solar gains, right temperature variation.

 

As @JohnMo says, probably not worth the effort, or expense.

 

If pipes in the ground really did make a difference, they would have been used for centuries.

 

[Garald]

20 minutes ago, SteamyTea said:

If pipes in the ground really did make a difference, they would have been used for centuries.

 

 

Well, the story here is that they *have* been used for centuries, for cooling, by technically minded people in the south of France (hence "puits provençal"). And that folks in some parts of Canada do this routinely. Will have to check on both stories.

[JohnMo]

9 hours ago, Garald said:

that plausible? https://lepuitscanadien.fr/

Edited 8 hours ago by Garald

Just translated the text

 

Depth between 2 and 6m, Length between 30 and 60m.  

 

That's long and deep!

[SteamyTea]

Just skimmed, may be useful, of only for the MET Office links.

 

https://core.ac.uk/download/pdf/33453718.pdf

[Garald]

Turns out I already calculated the ventilation loss myself a while back, or rather the spreadsheet from here did. It gives me that 31% of the heat is lost through ventilation, not 50%; I'd rather trust that than the diagnostician's software.

 

Here are some links that might be useful (modulo French skills or automatic translation):

https://www.fiabitat.com/le-principe-du-puits-canadien/

https://conseils-thermiques.org/contenu/puits-canadien.php

- apparently, it is recommended to clean a puits canadien at least once every 2 years (the filters and air intakes must be cleaned much more often).

 

https://passivact.fr/Concepts/files/PuitsClimatique-Limites-PuitsCanadien.html

  claims that a puits canadien is worth it only in a passive house - but the calculation is based on the assumption that MVHR has been installed. Obviously, as I was saying, the difference can be much greater if it hasn't been (but then one has to double-check that MVHR cannot be installed.

[Garald]

Just a sanity check: the spreadsheets gives me the following percentage estimates for heat loss -

19% external walls, 14% windows, 25% roof/ceiling, 11% floor, 31% ventilation.

I think the percentages of roof/floor loss are a bit higher than typical, but that makes sense, as the roof insulation is basically that put by the previous owners, and the floor insulation is new but thin (should have added a significant floor height, Japanese-style - a missed opportunity).

The diagnostician's percentages are:

11% walls, 22% windows and doors, 7% roof/ceiling, 5% floor, 5% thermal bridging, 50% ventilation.

This somehow seems odder (except for the thermal bridging, which is actually there, where the foundations end), or am I wrong?

Edited May 29 by Garald