Service voids as MVHR ducts?

[markocosic]

Monopoly house. 

 

12m long. 6m wide. 3m to eaves. 5.5m to ridge.

 

Cathedral ceiling to 1/3rd of it. Mezzanine floor to 2/3rds of it.

 

12 mm OSB as the airtight layer. 45 mm battens as insulation space / service void. Then plasterboard.

 

 

The MHVR unit is going to be at the north end which is opposite the cathedral ceiling area.

 

Supply to the two rooms under the mezzanine, and extract from the bathroom under the mezzanine, is easy.

 

I also need to supply / extract from the cathedral ceiling area. This is the kitchen / living room.

 

 

I would like to extract from the mezzanine / cathedral ceiling area near the ridge.

 

I would like to supply fresh air to the cathedral ceiling area too but am not too bothered about supplying it to the mezzanine.

 

 

Silly idea time:

 

The service cavities are 500 x 45 mm. At the expense of sacrificing some insulation I could repurpose these as supply / extract ducts by leaving out the insulation. I could pop a hole or six through the plasterboard and let in extract inlet / supply outlet. Tada. Hidden supply / extract ducts that SWMBO won't complain about the visuals for.

 

 

What could go wrong here?

 

Ever seen it done?

 

 

The alternatives I can thin of are:

 

- ducts down either side of the mezzanine that stop at the end of the mezzanine, say supply on one side and extract n the other side, and try to "stir the air across" from the living room side (left) to the kitchen side (right) and out of the extract duct before it rises to the ridge

 

- filling in the top of the ridge and having the supplies either side at mezzanine level and the extract at the ridge

 

 

Assume downdraught recirc extractor for the hob. Assume that humidity isn't an issue. (dry here in winter)

 

 

 

[Marvin]

I would be concerned about condensation via bathroom and kitchen air. 

 

 

[markocosic]

The rooms under the mezzanine (bathroom) would be handled separately via ordinary ducts. This is just large open plan living space albeit with a kitchen too.

[MikeSharp01]

Did the designer not work duct routes out at the design stage? If not then looks like you may need to work through the 'boxing in' thread. That said your idea has merit but you might want to think about lining the sections including the inner of the plasterboard with ali foil and provide collection points for any liquid that does gather at the bottom of verticals.

[JohnMo]

Could you use coanda effect supply nozzles to throw the air from the mezzanine area to the other side of the cathedral area (will Google roof line for about 4 to 6m, this would need no ducts in the cathedral roof.

 

The two dots in the roof slope about 20% up in the photo are mine.

[ToughButterCup]

20 minutes ago, JohnMo said:

Could you use coanda effect supply nozzles to throw the air from the mezzanine area to ...

 

Thanks for that. A very interesting read over coffee this morning.  It bears some 'resemblance' to the Bernoulli effect doesn't it....

[JohnMo]

Think so.  I have used Coanda effect nozzles in all bedrooms, hall and living room, made duct runs real simple.  No drafts as the air is at room temperature by the time it descends.

 

I used the Zehnder Supply air valve, coanda effect, ⌀ 90mm SKU: 990326254.  Also used ComfoTube ⌀ 90mm, adjustable airflow regulator, to adjust flow rate.

 

About £9 each for the valve, and regulators about £25 each.