MVHR - ensuring adequate ventilation in Irish weather

mrsWhippy

Hi all,

Can anyone tell me a little about MVHR systems and how sufficient they are for the humid Irish weather? I had a conversation with somebody in the industry and they were ranting about how most systems as they were designed for Germany, are not adequate for the Irish market, and only a very small percentage of MVHR units are sufficient. He claims to have seen black mold in a lot of houses with this type of ventilation.

How do we ensure what I'm buying is going to provide enough ventilation?

Thanks

mike_2009

Wow,

That's a bit gloomy?!! The only time I've heard about Black Mold and MHVR is when the owner turned OFF the unit and just opened windows as they "thought" that was better! Or if it was too "noisy" - turned off and yes you will get black mold everywhere around the bathroom as a result!

If the system is commissioned properly then it should not be noisy, even on boost, this should all be checked when commissioning. They should balance the system, i.e. use a device to measure the air flow at all inlet and outlets in the house and not leave things on defaults. They can adjust the valves to control flow and a good installer will go around a few times balancing things.

There are a lot of houses using MHVR successfully in Ireland - last weekend's NZEB open doors event would have offered you a chance to quiz owners directly and any I've visited worked great, no lingering smells after a big fry up that morning etc.

As always do your homework before purchasing, but focus more on the vendor than the product. There is an article in the latest passive house magazine on a recent study and their findings. It shows many were never commissioned properly so you need someone with a proven track record and good references. No reason it can't work here, if anything they have an easier time with the milder weather, we tend to be cool and wet rather than cold and dry but that's more of an issue for Air Source Heat Pumps and their defrost cycle than MHVR.

Hope this helps,
Michael.

mrsWhippy

That's extremely helpful Michael, thank you.

Does the supplier generally commission the system or the installer?

If you do have any recommended vendor, it would be much appreciated. I've contacted a few companies for quotes already, and it's very difficult to separate real information from sales pitches!

Cheers

mrsWhippy

That's extremely helpful Michael, thank you.

Does the supplier generally commission the system or the installer?

If you do have any recommended vendor, it would be much appreciated. I've contacted a few companies for quotes already, and it's very difficult to separate real information from sales pitches!

Cheers

mike_2009

I would expect any supplier to have fully trained installers who can set one up and commission. Make sure they seal the vents until the house renovation / build is completed so that no dust / particles get into the ducts and cause noise down the line. Also your cooker should have a good recirculation extract hood to prevent grease etc getting into the ducts.

I'll PM you some vendor ideas but not had any direct experience with their install expertise as I'm still in planning stages myself.

Good hunting!

_Brian

Poorly installed units cause trouble too. I know one estate where the builder bought the units direct and had his "lads" install them.

The result is a disaster with mould everywhere, one bathroom ceiling fell in with the weight of the damp mouldy boards.

Poor building integrity will cause problems where there are cold spots/bridges around windows etc.

mrsWhippy

Thanks.

Are there any guidelines around the type of ducting that is recommended, i.e plastic/metal, diameter, flat or cylindrical etc? Assuming that ducts that are too narrow would cause excessive noise etc too?

What are the minimum requirements regarding ideal humidity levels in a room (so it won't cause air that is too dry but also won't cause mold), and also how many air changes per hour is the ideal?

mike_2009

Bigger Ducts means the air can move slower and therefore with less noise. Rigid appears to be more recommended from what I've read. They are mostly plastic & round from what I've seen, in domestic installs anyway. Hope you're not planning a Bruce Willis excursion and expecting a rectangular one?! If you've limited cavity space you may be forced to use smaller diameter ducts?

Humidity should be around 40-50% max, if you're up around 70% you in trouble except just after a shower when boost should kick in for 30 minutes or so. Passive House standard is 0.6 ACH but a retrofit would be much higher, it depends on the air tightness levels of your house.

CO2 levels should be below 1000 ppm, getting to 3000 in a bedroom overnight means MHVR isn't up to the job.

mrsWhippy

mike_2009 wrote: »

CO2 levels should be below 1000 ppm, getting to 3000 in a bedroom overnight means MHVR isn't up to the job.

How is this tested?

Thanks again

mike_2009

I bought a CO2 measurement device on ebay last year and shocked myself with how stuffy my current bedroom is! I'll see if I can find the link and PM you with it.