MVHR design review

[Joel]

Hi there.

I am planning on installing an MVHR system in my two-floor (ground and first floor) maisonette apartment, and I was hoping I could get some feedback on my design from the experts here before I proceed. Here is a link to my calculations, along with some images of my design. It's a small place so the design is not very complicated.

Some background: The motivation for installing the unit is that I have cigarette smoke and food smells entering the apartment through multiple party walls (see here for some more discussion of this). Between the ceiling and the upstairs floor boards there is exposed brickwork and holes in the wall which allows air to flow, which is the most likely source of the majority of the fumes. I plan to seal all of this up, along the entire perimeter of the apartment, as well as some other unplastered portions of wall. My hope is that this will stop all major sources of airflow between my apartment and my neighbours'. We don't have any damp or mold problems, likely due to good ventilation, so I want to supplement this loss of air flow with a mechanical ventilation system. My hope is that I can also affect some positive pressure in the apartment through the mechanical ventilation system to help keep the fumes out. An additional motivation is to improve air quality in general, as my partner is sensitive to alergens. I appreciate that MVHR may be considered an extreme approach, but my strategy here is overkill -- I am more concerned about good air quality than expense, and I'd rather have a solution that works the first time round.

An overview: I'm installing an upright Zehnder Comfoair in a closet that opens onto the landing on the second floor. I plan to run 7.5cm semi-flexible ducting under the floorboards -- supplying the living room, bedroom, and office, and extracting from two bathrooms and the kitchen. The back wall of the closet adjoins the bathroom, and I plan to have the intake and exhaust ducts, as well as the water condensation pipe, run through that wall and under the bathtub and out of the building (the water condensation pipe I plan to connect to the drain under the tub).

Some specific questions and concerns:
-- I still have to include baffles in my design. Since I have a very simple radial design is it possible that the flow can just be controlled at the grilles?

-- I am trying to fit the silencers and insulated ducting down the sides of the unit, all in the closet, with u-bends coming out the top to connect everything. I have calculated the size I need to fit everything and I think it will fit with space to spare, but please let me know if my design is not accounting for something that might foil my plans.

-- I am trying to figure out the design for the outdoor intake vent. I understand I might want to include some kind of filter for large particles, and also a preheater to prevent frost. I'm wondering if there is a standard design for this that I can copy?

-- Since the ducting is coming up under the floor on the second floor, I'd like to have the ducting connect to wall grilles near the floor. I have thin solid walls that I don't think I can just run pipes into, and so I'm trying to understand what the installation of this part of the system will look like. I expect I need to cut a hole in the wall and inset a piece of ducting with custom dimensions -- but I can't find good resources for how to do this. I'm happy to hire a builder to do this, but I want to understand what's required.

-- since the unit is right in the middle of the home, should I be worried about noise? Would it make sense to surround it with noise insulating foam?

Please let me know if there's anything you spot that I should account for. Thanks for your help!

Edited October 7 by Joel

[Mike]

1 hour ago, Joel said:

I plan to seal all of this up, along the entire perimeter of the apartment, as well as some other unplastered portions of wall.

A good plan. Also look at other ways of improving airtightness - plenty of threads on that already.

 

1 hour ago, Joel said:

I plan to have the intake and exhaust ducts, as well as the water condensation pipe, run through that wall and under the bathtub and out of the building (the water condensation pipe I plan to connect to the drain under the tub)

That could be a bit tight. Note that the extract duct will need to slope out towards the exhaust vent at a minimum of 2% incline, to allow condensation to drain out.

 

1 hour ago, Joel said:

I still have to include baffles in my design. Since I have a very simple radial design is it possible that the flow can just be controlled at the grilles?

Potentially. Zehnder 'Luna' S125 are adjustable that way, and there's a matching extract E125.

 

1 hour ago, Joel said:

-- I am trying to fit the silencers

If you've not already found them, take a look at the Zehnder ComfoWell system, which combines silencers and manifold in one. They may give you more space to play with.

 

1 hour ago, Joel said:

I understand I might want to include some kind of filter for large particles

The Comfowell system had a module that can accept filters.

 

1 hour ago, Joel said:

a preheater to prevent frost

The most space-saving method is to buy a variant of the Zehnder Comfoair that has one internally. In warmer parts of the UK it's often omitted - the unit will then regulate the airflow (or even cut it off) if necessary, which can be OK for short periods.

 

1 hour ago, Joel said:

Since the ducting is coming up under the floor on the second floor, I'd like to have the ducting connect to wall grilles near the floor

A sketch of the floor plan may help people come up with ideas.

 

1 hour ago, Joel said:

since the unit is right in the middle of the home, should I be worried about noise?

Fitting seals to the cupboard door will probably enough for airborne noise, if the door is fairly solid. Vibration could be another problem, depending on what you're fitting it to (floor / wall / material, etc).

 

 

Edited October 7 by Mike

[Joel]

Hi Mike, thanks so much for your reply -- sorry it has taken me a while to respond.
 

On 07/10/2024 at 15:20, Mike said:

If you've not already found them, take a look at the Zehnder ComfoWell system, which combines silencers and manifold in one. They may give you more space to play with.

 

Ah cool! I'll take a look and see if I can incorporate them into my design. I suppose with my radial design this would also help with muffling sound between roo

ms.

 

On 07/10/2024 at 15:20, Mike said:

The Comfowell system had a module that can accept filters.

 

I guess these would fit on the comfowell system after the air has come through the MVHR unit from the outside. Should I be worried about large dust particles coming into the MVHR system from outside or is that handled by the MVHRs own filters?

 

On 07/10/2024 at 15:20, Mike said:

A sketch of the floor plan may help people come up with ideas

 

In my spreedsheet I linked above there are some embedded images with floorplans. I'll include them here in followup posts. They're a bit crude but hopefully they're sufficient.

 

 

[Joel]

This is the layout of the upstairs (with the ducting overlay)

[Joel]

And this is the downstairs (with the same overlay)

[JohnMo]

On 07/10/2024 at 15:20, Mike said:

On 07/10/2024 at 14:14, Joel said:

a preheater to prevent frost

The most space-saving method is to buy a variant of the Zehnder Comfoair that has one internally. In warmer parts of the UK it's often omitted - the unit will then regulate the airflow (or even cut it off) if necessary, which can be OK for short periods.

We never bothered and we get -9 for days on end. Not sure preheat is really needed in the UK. The units just slow down the incoming air, which isn't a big deal, when its that cold your house air humidity drops like a stone.

 

On 07/10/2024 at 15:20, Mike said:

On 07/10/2024 at 14:14, Joel said:

since the unit is right in the middle of the home, should I be worried about noise?

Fitting seals to the cupboard door will probably enough for airborne noise, if the door is fairly solid. Vibration could be another problem, depending on what you're fitting it to (floor / wall / material, etc).

We have a unit in our hall between two bedroom, mounted on wooden stud walls that are lined with two layers of 18mm ply. Hear when you open the cupboard doors but only then.

 

15 minutes ago, Joel said:

Should I be worried about large dust particles coming into the MVHR system from outside or is that handled by the MVHRs own filters?

No worries the MVHR filter deal with this.

 

Not really understanding your sketches? Need some more detail

[Mike]

On 13/10/2024 at 19:30, Joel said:

I guess these [filters] would fit on the comfowell system after the air has come through the MVHR unit from the outside. Should I be worried about large dust particles coming into the MVHR system from outside or is that handled by the MVHRs own filters?

Domestic MVHR units have space for 1 intake filter and many people would just rely on that.

 

Adding a filter box before the MVHR unit allows 2-stage filtering. The additional filter is normally significantly bigger, so can last for longer without changing it (useful if the outside air is particularly dirty). You can then use a finer filter on the MVHR unit.

 

Alternatively filter boxes can be used hold a carbon filter - they can remove smells, VOCs and the like that regular filters can't - perhaps including cigarette smoke, if the main MVHR filter isn't cutting it (though feedback here is that they normally can). You'd want a regular filter before a carbon filter, so you'd install it either between a first filter in a filter box and the MVHR unit (in the same filter box, if it's an option), or else between the MVHR unit and the supply manifold.

 

Edited October 25 by Mike