MHVR location - utility room or garage?

[Happy Valley]

Plan to fit a Vent Axia MHVR and we have the option of fitting the unit either in the attached garage or in the utility/plant room which is immediately next door. Inlet and exhaust pipes will be in the flat roof of the garage. 

 

Ducting will run to both ground floor and up to the top floor. 

 

 

[joth]

Is the garage inside the airtightness & thermal envelope? Normally they're not as an airtight garage door is borderline impossible.

But putting the MVHR unit outside the airtight boundary will be awkward as it's (potentially) a lot of pipework to detail airtightness for (depending on manifold locations etc), and also the unit is more efficient if inside the thermal envelope and any warm-side ducting outside the thermal envelope would need to be insulated.

 

tl;dr: Utility room is likely the better choice. 

 

[Happy Valley]

Thanks for the information.

 

I have space in the utility room and the runs up through the floors are easier from here. It does however create an issue with the drain off the unit as we will find it difficult to connect to the current system. How much moisture an average do these things pull out in a 3 bedroom 3 person 160 sq m home? Could we have a smallish drain tank underneath on the floor that we empty once a week or so?

[Marvin]

Someone will know but I think it's a calculation about the following:

 

Volume of air exchanged times the weight difference between the humidity level of the warm moist air before going into the MVHR and the lower temprature air's dew point coming out of the MVHR after losing any heat.

 

So:

Temprature and humidity level of the air beforegoing into MVHR will give you the weight of the air at start.

 

Temprature and dewpoint of the air leaving the MVHR will give you the weight of the air at end.

 

Start weight minus end weight will give you condensation weight. 

 

Times this by volume of air passing through MVHR per hour and you have the amount of condensation produced per hour.

 

Then someone boils a kettle or has a bath or shower and all your calculations go to pot!

 

Sometimes ours is nothing sometimes a trickle.

 

I don't think it's poisonous. Can't you get it out to a soak away?

 

I await the flood of corrections to my thinking...

 

Marvin

[Marvin]

MHVR location - utility room or garage?

Can't say except that more pipe = more insulation= more cost.

 

As commented by joth: as a yard stick not good positioning outside thermal envelope because of heat loss/gain. We have found a MVHR very good (but I'm not saying perfect) but the further away from perfect the further away from perfect the results.

 

I would check carefully the installation instructions for guidance.

 

Good luck.

[joth]

2 hours ago, Happy Valley said:

Thanks for the information.

 

I have space in the utility room and the runs up through the floors are easier from here. It does however create an issue with the drain off the unit as we will find it difficult to connect to the current system. How much moisture an average do these things pull out in a 3 bedroom 3 person 160 sq m home? Could we have a smallish drain tank underneath on the floor that we empty once a week or so?

 

An alternative approach is to use an enthalpy heat exchanger (So "energy recovery" rather than heat recovery) and then you don't need a condensate drain.

 

BTW depending what other things you have in the utility room, you may need more drainage anyway? I was surprised by the number of tundish and overflows needed for heating system, water softener, etc, and with condensate dripping off basically everything when using active cooling I kinda wish I'd just tanked the room and set a drain into the tiled floor.

 

 

 

[Happy Valley]

Thanks everyone for your input.

 

We have found a solution that can tap into a foul water drain once we take it through to the garage. That's eleven holes in total that we have to drill through the ICF and sleeve before we pour the concrete next week!