VMCs and heat extraction

[f1steveuk]

Just a question for the hell of it really! The VMC, although primarily for the extraction of damp air, and to ensure air circulation, logic would suggest that as warm air rises, and the VMC vents are in the ceilings, it would make sense to run the VMC all through the summer as well, in conjunction with having windows and doors open?

[NormanH]

A few thoughts on that.

1) Down here in the South we leave windows, patio doors etc open at night if secure, then close them, and even the shutters during the hot part of the day to keep the cool in. I certainly wouldn't have doors and windows open when it is hot.

2) I have certainly noticed unwanted heat extraction in my recent flat, which is in a cooler climate, and I am wondering how to avoid heat loss in the winter. My VMC has a fast and slow setting, but no 'off'...

[nomoss]

If the building has modern doors and windows it is on the way to hermetically sealing you in [:(] and unlike UK products, French windows I have seen don't even have an adjustable ventilator built into them.

I assume the VMC is designed to alleviate this problem, so it may be a bit unhealthy to turn it off..

Presumably there has also to be some provision for fresh air to enter the building, which makes the process of carefully sealing the doors and windows rather superfluous.

[woolybanana]

Norman, getting a switch installed on the system may not be impossible, but probably not advisable.

What by the way is a 'recent flat' - it is akin to a 'dead parrot'?

[idun]

I have a few thoughts about this and I did ask questions when our house was being built and this is what we had. They may have changed things, but this system worked very very well.

Firstly certain windows in 'modern' french houses have trickle vents, OK one cannot shut them off, but they are there and they do not face down, as they do in the UK............ they face upwards on the windows, so that cool air coming in is directed 'up' and not down as in the UK, which I personally find stupid beyond words, as the 'covers' in reality hardly work and closed or open direct the cold air 'down' into the room.

In the rooms where the VMC pulls the air from, ie kitchen, bathroom and toilet, there should be no trickle vent on those windows, the air current coming through from other rooms and a sufficient gap under the doors to allow the air to circulate.

And yes, we had ours on all the year round, VMC's are, IMO wonderful things.

I decided to get it in this house and our plumber suggested we get it with an air recouperation system. At long last M. Idun is sorting it out. It will pull the air from the bathrooms and kitchen and this air will be filtered and the warm air will go into a small sitting room we have when necessary. We can turn the heat recouperation system off and just have the VMC working.

We currently have friends in France who have been doing everything they can in their old house to make it warm and well 'sealed'. They are currently having problems with damp, as the house has never had a VMC system and they never thought of installing one. Their heating bills have dropped and it is cosy and warm, but I reckon that they will have to get a VMC system installed, as I cannot see how they can deal with the damp otherwise.

[pip24]

If you switch on the VMC then the air that is extracted will most probably be replaced by air from outside. So get an inside/outside thermometer with remote outside sensor. If the outside temperature is lower than the inside temp then the air that you are replaceing will be cooler. If the outside temp is hotter than inside then dont switch it on because you will be drawing warmer air into the house.

Another food for thought is does a ceiling fan cool the room down or does the energy used warm the room up?

[Théière]

[quote user="pip24"]

Another food for thought is does a ceiling fan cool the room down or does the energy used warm the room up?[/quote]

It just stirs up the air, as we are nearly all warm blooded we feel the effect of the movement as cooling us. very low power ulikely to notice any heat from the motor.

VMC's have some extraction and some inlets to balance the flow it's a controlled draft but necessary to remove the water vapor to prevent mould etc.

Idun, upward ducts would surely interfere with the convection currents around a room, by feeding in cold air downwards hot air will circulate and create no cold or hotspots, the same reason why radiators are put under windows.  A friend di the opposite believing it to be true only to have it hot around the sofa by the wall and cold on the other side of the room by blocking the convection current.

[PaulT]

WB why is installing an on/off switch inadvisable - I have done just that.

[idun]

Teapot, what can I say is that I lived in a house for 25 full years, with some very hot summers and cold winters, which could be  cold winters in the extreme, and there was never a cold draft in my house at all. No mould problems, no damp problems, a well aired, but lovely warm house in the winter.

I find the down facing trickle vents put cold drafts into rooms, and as the covers never fit that well, there is a noticeable cold draft.

The science of how my trickle vents in France worked, I don't know, I just know that they did.

[Théière]

Thanks Idun,  I will take more notice now I know the french do it a different way, it's interesting, well to me at least. I have a thermal imaging camera so can take photos of changes in temperature to see how that works. Thank you for highlighting it, obviously there is reasoning behind the change and it doesn't mean the original way was correct/best either. Usually easy to change anyway, just undo the screws and turn round the trickle vents

[Chancer]

Re the on/off switch, they should be used 24/7

I am a great fan of VMC's,   I live between two seriously compromised properties, one a wooden shed, the other with the rear walls 1 metre underground and not tanked, they both are left unnocupied for several months a year, both had severe damp problems which were completely resolved by the use of a VMC running 24/7 as it should.

A couple of anecdotes to show how effective they are.

The rear wall in question runs the length of my salon, cuisine and salle de bain, they were black with mould from top to bottom when I bought the property, the insulated placo fell off the walls and the polystyrene backing had decomposed into millions of billes, I replaced it with hygrofuge placo on rails with 4.5cm insulation and pretty much no air gap, with the VMC there is no dampness anywhere but recently I removed a socket and backbox to run an aerial cable, the Inside surface of the wall was running with water and the insulation saturated. I also have a tole bac acier roof which I know runs with condensation on the Inside in summer.

The VMC sucks from the kitchen and the bathroom, the salon is open plan to the kitchen and the bedroom seperate without an outlet although it only has one external wall, I have no trickle vents relying instead on the gaps around the volet roulants. Last summer I spent 3 months in the UK in my now no longer damp shed, I had accidentally closed the bedroom door in France with the result that there was no air circulation, on my return there were mould patches on walls, my wooden units and my leather shoes were covered in mould, when the door is left open there is never a problem, indeed I had always thought this was my only dry room but I had overlooked that my tiles are laid over the original tiles which are direct on a terre battu floor. It should be noted that with the door open and no damp problems the nearest VMC exit in the kitchen is some 7 meters away and round a corner.

I have seen several rented houses that have had to be completely gutted, stripped and repainted where the tenants switch off the VMC's.

[idun]

Teapot, I shall be curious as to what your thermal imaging finds. Skin, is rather sensitive to drafts, and that is the only thing we have thus far used.

I'm with Chancer, I believe VMC's to be the 'great'!

[Théière]

Chancer your description of the french property with back wall 1 metre into soil sounds just like ours, used to get mold when first owned but put a std bathroom extractor in the bathroom and cut a hole for another in what maybe another sitting room and also leave all doors open and no growth since. mind you with naff all insulation on the inside of the roof we do have a fair draft but that roof is to be replaced and insulated so I hope to then fit a VMC which are very cheap to run and I find the hydro switches to be really poor quality so will build my own to switch it on and off if required with the humidity.

[Chancer]

I am happy for all mine including the rental apartments to run 24/7 on the low speed with the option to use the high speed as and when. I have given up on the hygrostat ones now.

I have also had to replace the capacitors on all the units within a couple of years, I have since mucked around with the values to arrive at a satisfactory 1st speed low enough to not be disturbing but just enough to function.

Visited some friends in their new rental property, they had switched off the VMC because of noise, had all the Windows closed to keep out bêtes and already had significant damp after a fortnight in the height of summer[:(]

On inspection it was a hygroréglable unit and it is horrendously Noisy as it runs at a permanent fast speed with the inlets doing the regulation making even more noise, it was so powerfull I estimate it must have been pulling 500 watts so they have done themselves a favour in turning it off but not the landlord.

The €30-40 cheapies are a Wise choice if you accept the inevitable £1 capacitor change which never needs re-doing.

[Théière]

Thanks Chancer, What type of motors have they got? I already have it my mind to change the motor for something more efficient/controllable

[NormanH]

What worries me is that the one in the kitchen is directly over the electric convector heater, so I would imagine when winter comes it will simply suck any heat from that straight out of the room..

[Gardengirl]

Norman, when we moved into our apartment 5+ years ago, we were uhappy

with the system of trickle vents as there were draughts, particularly in

the living room, and VMC as it was noisy and seemed too powerful. As it was a new apartment

block, we had the technical people round to try to sort the problem out.

The plumber with them suggested putting a foam shape in the noisiest

VMC, in the kitchen; he put one in and it has worked quietly and

efficiently since then. Maybe you could have that done too, so that your heat isn't sucked out. The convector heater in our kitchen was behind the door, so we removed it.

We put a piece of foam in half of the

draughtiest trickle vent, and in the autumn we cover them all with masking tape, which we remove when we return to UK and replace on our arrival

for another few weeks for as long as the weather is cold. When the technical people visited again because

of other problems they were appalled, insisted that we would have a very

damp apartment, but that has never happened and it always smells fine,

no sign of damp at all.

[DerekJ]

An interesting thread... I hadn't given the VMC a second thought before.

I guess we must be going against the recommended practice by turning off our electrical power when we aren't at the house (we spend about a third of the year there over around 4 visits/year).

We haven't seen any signs of damp as a result and there is no musty spell when we return to the house.

[Théière]

This all depends on the air inside and it's humidity. Modern well insulated buildings also have very low air leakage by design so benefit from mechanical ventilation to remove excess moisture, no excess moisture very little issue.  Norman has a vent above a heater but most vets will close by rotating the centre so you can adjust the amount of flow or shut off completely in any given space.

Gardengirl, there is a big difference between technical people and actual technicians, the ones who carry moisture metres and thermometers and actually test the air rather than carry a clipboard and talk ballcocks!  Because warm air carries more moisture ventilation is necessary but as it turns cooler and dryer ventilation is less necessary which may explain why mold doesn't always grow.  A simple and cheap humidity meter would, I have no doubt out teckie'd your teckies and keeping the humidity below 65% would be sufficient to prevent mold at normal temperatures.

I have to visit modern blocks of flats all fitted with VMC's as they are nearly hermetically sealed and mold grows on the window reveals as the moisture condenses onto the coldest part of the room.  I usually buy the humidity meters shown below and tell residents to keep the humidity in the range shown or preferably a bit lower at 65%.  The cause is always the VMC's are switched off because of the perceived cost of running them or noise (they are not noisy) and cannot be heard above the TV/radio but with walls that are thin and at night maybe it is enough to keep someone awake but I really doubt it.

The temperature in these flats is usually quite high 22deg and the humidity varies between 75-85% so they feel clammy to stay in but that confused as comfort by some so then I have to explain it's not healthy for their baby and that gets their attention.

[davidb5964]

My first post as only joined yesterday but this thread has given me some food for thought.I always turn the power off when I leave the house to return to England to work, thinking now this may not be such a good idea!

Dave

[Chancer]

They are all (the cheap ones) brushless what I would describe as pancake motors, they have two capacitors, one is shorted out for either the low or high speed I cannot recall, now that I have changed the capacitors on them all I havnt done the job for several years, its always the one capacitor that fails for the low speed, it gets slower and quieter until eventually it wont run.

Just checked my stock, I am now using 1.5 microfarad instead of the 2's.

Where do you get the humidity meters from?

[davidb5964]

Just looked on that well known auction site and plenty to choose from .

[f1steveuk]

Well. answered my question re removing heat from ceiling height during the summer, so I'll up the ante with a second poser.

We have one of these houses, a bungalow, but built on the side of a slope, so the cellar area is as big as the living space, but partially submerged, so single storey at the back, two storey at the front. Usual French practice, no damp course, no tanking etc

So, is the draw on the VMC enough when we aren't here, to extract from down stairs, from the cellar via the upstairs vents, or would it be worth opening one of the blanked off VMC points, and taking a hose down to a vent in the cellar, or even have a downstairs/cellar VMC?

[Chancer]

I take it there is no other ventilation in the sous sol?

Normally a partially submerged one would have two Windows in adjacent, not opposite walls for cross ventilation, that would normally be adequate.

If you have spare inlet to the VMC then it wont do any harm to use it, if its a hygrostat one though the more humid air in the cellar will enclench the high speed even when the humidity is low in the house.

The cellar in my ex's mitoyenne had no ventilation whtasoever and someone had previously run piping for a VMC but never fitted one, it was a really really damp cellar compared to my cross ventilated one, I doubt somehow that a VMC would have made a great deal of difference.

In the good old days of non hermetically sealed houses without central heating there was never a need for a VMC, houses with damp were usually a result of neglecting to open Windows.

I know a Young couple who have been in their rented property less than one month and its already running with damp, they are there 24/7, cook, dry clothes, shower and have switched off the VMC, they think that I am mad to suggest they open a window, its as if they think that fresh air will kill them, yet they love doing randonées with me [8-)]

[suein56]

[quote user="Chancer"]... they think that I am mad to suggest they open a window, its as if they think that fresh air will kill them, yet they love doing randonées with me [8-)][/quote]

Ahh, but walks are taken outside in the fresh air and that's good but 'fresh' air should most definitely be kept outside and not allowed to enter a house/home ! So I have discovered whilst living here.

Sue [:)]