MVHR ~ extract from bedrooms??

[Cognis0]

Although I spent years planning for a Passivhaus new build, having failed to find a suitable site we have ended up in a 16th century origins thatched house!!

 

With an old house I had abandoned the idea of MVHR, but with the amount of condensation and mold we are seeing this is now back on the table. Before I get started on working out what is needed, there is a fundamental issue it would be good to get feedback on. Most of the condensation and mold we see is on and around bedroom windows over-night/morning. Bedrooms also have lots of dust and who knows what else in the air which needs to be extracted. So to my small brain we need to see extract vents in the bedrooms rather than supply vents. In fact my limited brain power tells that the best whole house ventilation solution would be to have air extracted from all of the first floor rooms with heat-recovery fresh air then being supplied back to the ground floor reception rooms (open plan arrangements). Fresh/warm air would then rise up the central staircase and back to the bedrooms...

 

Please let me know what is wrong with my logic here.

 

Many thanks

[JohnMo]

For MVHR to work you need a flow path for supply and extract. Your wet rooms will generate lots of condensation, if you pull air out of the bedrooms that air could be pulled out of the wet room towards the bedroom. That's the main reason you supply dry rooms and extract from wet.

 

Flow rates from MVHR are such that they are rubbish at moving heat from A to B.

[Cognis0]

Yes, a simple flow path from supply to extract is what I have suggested (extracting air from the bathrooms as well as the bedrooms), and the flow path from ground to first floors seems more logical than the complex air movements produced with wet room only extract.

The standard methodology doesn't make much sense to me ~ a bathroom produces water vapour for half an hour so in the mornings and I read somewhere the average shower puts about 250ml water into the air, so a lot of air/vapour needs to be extracted relatively quickly. Whilst sleeping a person puts about the same amount of water into the air overnight, but this needs to be done at a slower rate extending over the whole night.

I am sure I will end up with a standard installation, but I do have doubts about the current methods used...

[JohnMo]

Sounds a little like you are trying to reinvent the wheel, when nothing wrong with the one we have.

[Cognis0]

6 hours ago, JohnMo said:

Sounds a little like you are trying to reinvent the wheel, when nothing wrong with the one we have.

Yes, that sounds about right. I'm sure there are better ways to do most things...!

[JohnMo]

On 09/10/2023 at 19:09, Cognis0 said:

Yes, that sounds about right. I'm sure there are better ways to do most things...!

 

Take a look at cascade ventilation strategies with MVHR. Do a Google or similar search.