Have PIV (VMI), what next? Humidity-sensitive ventilation? HRV?

[Garald]

Hi,

 

As some of you know, I'm wrapping up a rather long-winded renovation. I'm thinking of what I can do to improve energy efficiency further. Sure, solar panels are an important (and expensive) possibility, but I am also thinking of some other measures.

 

I have PIV (VMI), i.e., positive-input ventilation. According to the official energy diagnostic (which may make some sense or be useless, I can't tell), half of the heat lost in my house is lost through ventilation. There areas around the windows that are deliberately not airtight, as PIV needs an exit.

 

What can I do to improve matters?

(a) Install (humidity-regulated?) negative-input ventilation on top of the positive-input ventilation system; make things airtight. (How much efficiency would I gain?)

(b) more ambitiously, I could have MVHR installed (again, leaving the PIV in place, presumably; for one thing, it ought to help during the summer, as it draws air from the (cooler) courtyard). Is this a realistic goal? Would I have to rip everything apart? The attic has been turned into home offices (I'm typing from the attic), so it's not empty space I can exploit.

(c) off-beat idea: install a water-heater with its own little heat-pump (such models exist) to place in the attic bathroom (it does get hot during the summer), the idea being that I'd use it instead of the main PAC's own water-tank during the summer, in part so as to cool the attic. OTOH a plumber would probably ask for too much

 

Comments? Further possibilities? Reality check?

 

 

[SteamyTea]

7 hours ago, Garald said:

off-beat idea

May work, calculate how much energy you use for DHW and how much you would save using a HP based one.

 

7 hours ago, Garald said:

cooler) courtyard

Is the air really cooler, or is the courtyard just in shade.

My air temperature is currently 5.2°C, a piece of wood in the shade is currently 3.5° and another piece of wood in the sun is 8.5°C.

There is a reason that there are two standard methods for taking air temperature measurements, dry bulb and wet bulb, and a Stevenson Screen is used.

[JohnMo]

7 hours ago, Garald said:

What can I do to improve matters?

(a) Install (humidity-regulated?) negative-input ventilation on top of the positive-input ventilation system; make things airtight

Could you not control piv based on humidity? Low rate and higher rate when needed. Less ventilation is less heat loss. Or even configure as on or off? Use 1 or 2 Shelly H&T's as the trigger and Shelly relay to setback flow rate or boost it or even to start or stop. Low rate at below 55% humidity high rate (normal rate really) above 55%? Really depends on what wiring options your piv unit has.  Keep it simple.

[SteamyTea]

Paris is a relatively high humidity city.

 

 

 

 

London

 

 

 

[joe90]

20 minutes ago, JohnMo said:

Could you not control piv based on humidity?

I asked about this years ago when considering switching my MVHR off when not required (summer, doors and windows open) it already controlled the boost.

[Garald]

1 hour ago, JohnMo said:

Could you not control piv based on humidity? Low rate and higher rate when needed. Less ventilation is less heat loss. Or even configure as on or off? Use 1 or 2 Shelly H&T's as the trigger and Shelly relay to setback flow rate or boost it or even to start or stop. Low rate at below 55% humidity high rate (normal rate really) above 55%? Really depends on what wiring options your piv unit has.  Keep it simple.

 

Well, I have a manual remote control for the PIV: I have it on low or medium when I'm alone, on very low when I travel, and on high when I have a birthday party, say. (Sounds sensible?) As SteamyTea pointed out, humidity is always above 55% in Paris, except on those short periods when it's very hot - and then you want as much ventilation as possible!

 

I think that what the energy diagnostics guy was recommending was ventilation fans that would be sensitive to *interior* humidity.

 

Incidentally, there's a little fan that works all the time (the only non-PIV bit of the ventilation system) - the builder installed it on his own initiative in the tiny laundry room (really more of a laundry closet + coat room; 2 m^2 or so). His notion was that extra ventilation would be needed there. However, I have a modern heat-pump dryer that doesn't diffuse humidity into the air (it deposits it into a container) and doesn't produce much heat. Should I have that fan taken out, or replaced by, well, a humidity-sensitive fan?

 

[JohnMo]

28 minutes ago, Garald said:

always above 55% in Paris, except on those short periods when it's very hot

It is just about everywhere.

 

But the relative humidity drops with temperature rise. We are currently at 7 degrees outside and 74% humidity outside.

 

Our summer house for example with a simple dMEV fan is at 19.5 degrees with a humidity of 35%. Our house with MVHR 20.5 is at 40%.

 

28 minutes ago, Garald said:

energy diagnostics guy was recommending was ventilation fans that would be sensitive to *interior* humidity

That is exactly what I was recommending, but to make the piv responsive to internal humidity. The shelly H&T sits in room or two, it then uses a shelly relay to move the speed up or down on the piv unit. You now have closed loop control of the piv responding to internal humidity. No extra fan etc or upheaval.

Edited April 28 by JohnMo

[SteamyTea]

33 minutes ago, JohnMo said:

relative humidity drops with temperature rise.

Paris is quite warm in the summer, mean is above 20⁰C from end of April to almost beginning of October.

So just ventilation is not much use. 

Maybe duct in a dehumidifier.

[JohnMo]

33 minutes ago, SteamyTea said:

Paris is quite warm in the summer, mean is above 20⁰C from end of April to almost beginning of October.

So just ventilation is not much use. 

Maybe duct in a dehumidifier.

Trouble when the op tries to talk about two subjects in the same thread - summer cooling and ventilation heat loss, you get random answers

[Mike]

11 hours ago, Garald said:

According to the official energy diagnostic (which may make some sense or be useless, I can't tell), half of the heat lost in my house is lost through ventilation.

If it's since July 2021 - the last (major) update - it should be fairly good. From then, if they are inaccurate you can seek damages from the landlord / seller / assessor (as appropriate), which is a definite incentive to get them right.

 

Before my current French renovation I commissioned an assessor to model several scenarios. According to them, for me adding MVHR cuts heat lost through ventilation from 43% to 34%. In your case I imagine the result would be more dramatic if the airtightness of the windows is upgraded and taken into account.

 

12 hours ago, Garald said:

I could have MVHR installed ... Would I have to rip everything apart? The attic has been turned into home offices (I'm typing from the attic), so it's not empty space I can exploit.

You'd need space for ducts, which come in various sizes and shapes. You don't need an attic, just a big enough space to put the unit and something firm enough to attach it to. Mine's hung from the ceiling joists.

 

12 hours ago, Garald said:

leaving the PIV in place, presumably; for one thing, it ought to help during the summer, as it draws air from the (cooler) courtyard)

You want MVHR or PIV, not both. But you could potentially have the inlet and exhaust in the courtyard (you want them on the same wall) to take advantage of the cooler air.

 

12 hours ago, Garald said:

What can I do to improve matters?

(a)

(b)

(c)

You could get all 3 modelled by an assessor and then decide.

[Garald]

1 hour ago, SteamyTea said:

Paris is quite warm in the summer, mean is above 20⁰C from end of April to almost beginning of October.

So just ventilation is not much use. 

Maybe duct in a dehumidifier.

 

I've been doing the exact opposite in the hottest weeks (which are the only ones with low relative humidity) - I'm using a column fan/humidifier (direct diabatic cooling). Of course if I install a dehumidifer in the PIV (how?) the column fan/humidifier will become more effective - that's a thought, thanks. (Remove hot water, mix in cold water.)

[Garald]

1 hour ago, JohnMo said:

Trouble when the op tries to talk about two subjects in the same thread - summer cooling and ventilation heat loss, you get random answers

 

I (OP) was thinking in terma of ventilation heat loss; summer cooling is a bit of a tangent that has come up (and is useful to think about).

[Garald]

18 minutes ago, Mike said:

If it's since July 2021 - the last (major) update - it should be fairly good. From then, if they are inaccurate you can seek damages from the landlord / seller / assessor (as appropriate), which is a definite incentive to get them right.

 

The assessment was done in July 2023 - I (new owner) paid for it, just to double-check that everything had been done correctly. I've already boasted plenty of how the place went from a B to an F.

 

18 minutes ago, Mike said:

 

Before my current French renovation I commissioned an assessor to model several scenarios. According to them, for me adding MVHR cuts heat lost through ventilation from 43% to 34%. In your case I imagine the result would be more dramatic if the airtightness of the windows is upgraded and taken into account.

 

The windows themselves are mostly new; it's just that the builder left some well-concealed ventilation outlets somewhere around the frame on the advice of the PIV installer.

 

18 minutes ago, Mike said:

 

You'd need space for ducts, which come in various sizes and shapes. You don't need an attic, just a big enough space to put the unit and something firm enough to attach it to. Mine's hung from the ceiling joists.

 

How noisy and bulky is it? My current PIV unit is hidden above the false ceiling above the kitchenette in the ground-floor guest room. The advantage of that spot is that it's close to the (cool) courtyard, but obviously I can't have a noisy machine there. Other possible spots for the unit: garage, space behind the attic WC.

 

18 minutes ago, Mike said:

 

You want MVHR or PIV, not both. But you could potentially have the inlet and exhaust in the courtyard (you want them on the same wall) to take advantage of the cooler air.

 

You could get all 3 modelled by an assessor and then decide.

 

Can you recommend a specialized assesor who does a good job and charges reasonable prices? The assesor I used for the DPE gave "VMC type B hydroreglable" as one of his suggestions, but he's an all rounder who keys things into a program. The guy who did the audit energetique at the beginning of the renovation (required for MaPrimeRenov) was useless - he barely spent any time on the spot.

[Mike]

6 minutes ago, Garald said:

How noisy and bulky is it? My current PIV unit is hidden above the false ceiling above the kitchenette in the ground-floor guest room. The advantage of that spot is that it's close to the (cool) courtyard, but obviously I can't have a noisy machine there. Other possible spots for the unit: garage, space behind the attic WC.

I've got a Zehnder CA 225, which hits 49dB at 150m³ (about the same as a kitchen extractor hood on low) but I'll eventually be shutting it away behind an acoustically-sealed ceiling trap. I wouldn't put it above a bedroom.

 

The unit + ComfoWell silencers / manifolds + a diabatic HomEvap cooler (on the extract) are squeezed into a space about 750 x 2500 x 400 deep. There are shallower and quieter units available, but it's a matter of juggling size, noise, efficiency and having the pipe connections pointing where you need them (some, like the CA 225, go in one end and out the other, others have all 4 connections on the top). A good place to compare is the Passivhaus list at https://database.passivehouse.com/en/components/list/ventilation_small

 

41 minutes ago, Garald said:

Can you recommend a specialized assesor who does a good job and charges reasonable prices?

Not in the Paris area :(

I sent enquires to a few I found online, chatted to a couple to make sure they know what I was after, then picked the one I felt happiest with.

[Garald]

1 hour ago, Mike said:

I

Not in the Paris area

I sent enquires to a few I found online, chatted to a couple to make sure they know what I was after, then picked the one I felt happiest with.

 

But how *do* you find a specialized assessor for ventilation? All I know is how to find people who do DPEs (and audits energetiques, but those are crap).

[JohnMo]

1 hour ago, Garald said:

specialized assessor for ventilation?

PIV wouldn't be my first option, my options would be

1. MEV operating demand basis.  With either humidity operated trickle vents or self regulated. Very low losses only ventilating when required.

2. As above but dMEV fans, slightly more losses as always some background ventilation happens.

3. MVHR cascade system such as Fresh-R or self built system.

 

Or get an assessor spend 1000 euro, get told to spend 5k more, gain 1 to 0.5 euro a day for 5 months a year. You really need to put your losses into financial numbers.  Electric at 0.3 euro, is only about 0.08 after its been through a heat pump.

 

The energy required to raise one cubic metre of air through one kelvin is 0.33 watt-hours, i.e. its heat capacity per cubic metre is 0.33 Wh m–3 K−1. Thus the total ventilation heat loss, Qv , will be:

 

Qv = 0.33 × n × V × ΔT watts

 

0.33 x 0.3 x 300 x 23 = 683W

 

So 100m2, 3m tall room, 0.3 ACH, by 23 delta T, looses 683W or 16kWh a day on the typical coldest day. Your heat pump generate that heat at about 3.5:1,  so about Euro 1.28 ventilation losses on the coldest day - half that on a typical 7 deg day.

 

A good MVHR would drop that by 90%, assuming the rest of the house is airtight. If it's not it may not change anything by much. So care should be taken 

 

16 hours ago, Garald said:

What can I do to improve matters?

(a) Install (humidity-regulated?) negative-input ventilation on top of the positive-input ventilation system; make things airtight. (How much efficiency would I gain?)

(b) more ambitiously, I could have MVHR installed (again, leaving the PIV in place, presumably; for one thing, it ought to help during the summer, as it draws air from the (cooler) courtyard). Is this a realistic goal? Would I have to rip everything apart? The attic has been turned into home offices (I'm typing from the attic), so it's not empty space I can exploit.

(c) off-beat idea: install a water-heater with its own little heat-pump (such models exist) to place in the attic bathroom (it does get hot during the summer), the idea being that I'd use it instead of the main PAC's own water-tank during the summer, in part so as to cool the attic. OTOH a plumber would probably ask for too much

a) none

b)best option would be not bother with PIV at all if you go MVHR. Do a cascade MVHR system, only need ducts in wet rooms. The supply works similar to PIV, depending on layout you may need an addition fan between rooms to move air around difficult rooms.

c) your starting to expensive and over thinking things.

 

Based on what you have and least spend, biggest gain for least effort. Shelly bits as mentioned earlier. 100 euros, 1 to 2 hours, done. 

[Garald]

9 hours ago, JohnMo said:

That is exactly what I was recommending, but to make the piv responsive to internal humidity. The shelly H&T sits in room or two, it then uses a shelly relay to move the speed up or down on the piv unit. You now have closed loop control of the piv responding to internal humidity. No extra fan etc or upheaval.

 

This sounds like a good, simple idea with minimal cost. Since the PIV unit has a remote control, there has to be a way to do this all on software - but I'll have to see whether the PIV manufacturers made it easy.

1 hour ago, JohnMo said:

PIV wouldn't be my first option, my options would be

1. MEV operating demand basis.  With either humidity operated trickle vents or self regulated. Very low losses only ventilating when required.

2. As above but dMEV fans, slightly more losses as always some background ventilation happens.

3. MVHR cascade system such as Fresh-R or self built system.

 

Right, but the reality is that I *have* PIV (because I was very poorly advised IRL - that's a story for another day). So, even though the diagnostics guy recommended 1, the real options may be

0. existing PIV with minor improvements ((a) shelly H&T as above, (b) dehumidifier (how?) as SteamyTea suggested, in part to make direct adiabatic cooling more effective during summer - I know, I know, let's keep on the subject of heating)

3. MVHR as above.

 

I'd be willing to pay 500 eur for a professional assessment of ventilation, or 1000 eur, say, if it includes a blow door test, a good look at the insulation (I may want to insulate the north wall from the outside eventually; the inside insulation on that side is not to the same standard as the insulation on the south wall) and so forth. Is that realistic?

 

Of course this is not the right season for a good look at the insulation (took lots of thermal-camera pictures myself, but that it was in January). But then it seems that MVHR is more of thing to do on the next renovation (if at all), together with insulating the heating ducts (and above all the DHW pipes), *possibly* insulation the north side, etc. Or am I wrong?

[JohnMo]

1 hour ago, Garald said:

Right, but the reality is that I *have* PIV

Did you end up installing 

vmi unit? As they seem to have humidity sensing as an option?

 

[Garald]

14 minutes ago, JohnMo said:

Did you end up installing 

vmi unit? As they seem to have humidity sensing as an option?

 

Right: I have a VMI unit, with a Hydro'R module (pre-heating only; incidentally, their more ambitious claims as to how much that can help with heating efficiency can't possibly be right -

it's just like having an extra radiator there where the air comes in).

 

I will ask the builder whether it comes with a humidity sensor (he hasn't been giving me the receipts; there was a third person involved in all of this, thankfully no longer involved - more about that juicy disaster story at some point). I imagine not, as I do not have it in writer. I better rig my own feedback system using the remote control in the way you suggested. Or I can contact the VMI company to see whether the optional sensors can be installed post facto.

 

 

Edited April 28 by Garald