MVHR - New build with basement

[mike77]

Hi

 

We are project managing our own self build and MVHR is next on the list.

 

The house has a basement circa 1800 sqft, Ground floor 1000 sq ft and first floor 800 sq ft.

 

My understanding is that we will need more than one unit to service the sq footage of the house. The house is not passive house standard but is very well insulated with a warm room. It is South facing with 80 sqm of glazing at the front of the house. No windows or glazing at the rear.

 

We are also interested in adding a cooling element to the MVHR on-top of the summer bypass function, any recommendations?

 

Does anyone have recommendations of what companies / products to use/approach?

 

Any tips on basements etc...

 

Regards

 

Mehul

[ragg987]

Hi and welcome.

3 hours ago, mike77 said:

My understanding is that we will need more than one unit to service the sq footage of the house

I built a 330m2 with basement and use a single MVHR for the whole house. So unless you have some other constraints you can use a single unit, if you add another one you have the added complication of balancing between the 2 units. BPC ventilation were the place to go to for good prices when we built 4 years ago, they also offered us a free design service.

 

80m2 south facing glazing gives a risk for over-heating - you may need to consider shading externally.

 

Basement is tricky to heat / cool. It is an underground element so in winter requires less heat than the space above ground and in summer it can get a bit cool. But bear in mind it can easily over-heat down there at any time. E.g. I have a home cinema down there and a few people for a few hours with audio and video equipment raises the temperature quite a bit at any time of the year. When we were building I was advised of this by a company who suggested I fit a stand-alone air-con unit in there. I did not, but maybe should have.

[mvincentd]

I’ve An approx 1700sqf Basement with all south facing floor to ceiling windows (approx 30sqm).  It’s layout is long and thin as I’m taking a wild guess yours is too given the window configuration? I’ve an approx 450sqf upper floor.  My Zehnder Comfo350 is in a utility room at one end making for runs to room plenums ranging from 4m to 25m.  This doesn’t make it easy to balance (branch system, not radial).   My designers/suppliers were ADM Systems and they raised the prospects of 2 units for me at my size, but I was set against that.

It works ok and the lower floor is well regulated year round.  The upper floor getS problematically hot from solar gain, and I think the overall house ‘heat rising’.  I believe I need my currently fixed skylight at the house’ high point to become openable to draw this heat off.

I don’t believe (based on posts here[jsharris] and ADM advice) cooling inline via mvhr will contribute enough relative to the complexity it introduces.

The key thing from my experience is to accommodate the mvhr very early in the whole design stage and do not just assume duct runs will be achievable....establish that they actually are!

[Bitpipe]

Another basement owner here - 120m2, more or less square, with passive standard house on top - total of about 400m2. Suspended timber ground floor made it easy to fit the MVHR (and other services).

 

We have one Vent Axia Sentinel kinetic High Flow unit (from BPC) in plant room in basement and it's more than enough for the whole house - 13 supply points and 7 double ducted extracts. I didn't put any extract in the basement as there are no damp services in there, so all supply only. 

 

We also have our MVHR to one side of the house so balancing the system was fun but managed to get there ok. 

 

Basement is a comfortable temp year round, has no heating but is very well insulated externally (sits on 300mm EPS, 200MM EPS to the walls) as it ties into the passive structure above. It has a few fridges and the kids TVs etc, was getting a bit warm yesterday with a few teenagers in there but usually fine.

 

We also have a external door for fire regs which can be opened if more ventilation requires.

 

Per previous comments, MVHR is not effective for active heating or cooling as the airflows are designed to be low, I only notice ours when boost is activated. As air is a poor carrier of heat, this would be insufficient to noticeably heat/cool a space but can act as a trim in a highly efficient dwelling.

 

My suggestion is to make provision now for a split AC unit (i.e. ducting & power) when it's cheap and easy to do and then make a call later if you need to invest in the units. 

[Thorfun]

On 28/07/2020 at 11:10, Bitpipe said:

We have one Vent Axia Sentinel kinetic High Flow unit (from BPC) in plant room in basement...

 

I'm just starting my MVHR research and also obtaining quotes. I also have a basement planned with a plant room in the basement and one thing I can't get my head around is if the MVHR unit is in the basement where do the fresh air and exhaust vents enter/exit the building? do they go up to first floor height and then out through the wall? in which case aren't they a bit big to fit within the wall as they go up? or do the exit through the basement wall and then go up to the ground level and poke up like periscopes? which would look a bit odd and I'd need to cover with some kind of shrubbery.

 

can anyone post pictures or drawings as to how they've got their basement sited MVHR unit incoming/outgoing vents located?

[Conor]

@Thorfun we were in a similar position

Partial basement, but the logical place for the ASHP and mvhr ducts we're on a side of the house that was underground. Architect strongly argued against going though the basement wall (and therefore tanking) as it opens up a whole raft of problems and complications. There was talk of a service void coming up behind a kitchen cabinet and out through at ground level. I think that's what you'd have to do, either that or locate your mvhr at ground level and have everything else in basement.

 

We have ended up with plant "room" under the basement stairs and a 3m duct run to the south wall that isn't below ground.

[Thorfun]

4 minutes ago, Conor said:

@Thorfun we were in a similar position

Partial basement, but the logical place for the ASHP and mvhr ducts we're on a side of the house that was underground. Architect strongly argued against going though the basement wall (and therefore tanking) as it opens up a whole raft of problems and complications. There was talk of a service void coming up behind a kitchen cabinet and out through at ground level. I think that's what you'd have to do, either that or locate your mvhr at ground level and have everything else in basement.

 

We have ended up with plant "room" under the basement stairs and a 3m duct run to the south wall that isn't below ground.

thanks for the response. our basement is fully submerged so we don't have any side that isn't below ground. I was thinking about putting the MVHR in the loft space above the master bedroom dressing room and vent through the roof but it's a heavy bit of equipment to lug up a ladder in to the loft! but that might be the best solution. although I will see if it's possible to build a service void from the plant room to ground floor level. just another decision to add to a long list of decisions that need to be made.

[Bitpipe]

Our ducts go up into the utility room above the plant room and then exit the house about 500mm above ground level. They are obscured by the cupboards in the utility. Will get a few pictures.

[Bitpipe]

I have some nice external cowls to fit once the render gets replaced.

 

Despite being near ground level, the internal intake filter does not get that dirty.

[Thorfun]

6 minutes ago, Bitpipe said:

Our ducts go up into the utility room above the plant room and then exit the house about 500mm above ground level. They are obscured by the cupboards in the utility. Will get a few pictures.

 

this is the direction I'm now thinking of going. our larder is above the plant room so I can create a 300mm service void between the larder and exterior wall and run the vents up there and out the wall. the only potential issue is that the area external is not very wide (maybe 1200mm) so I wonder if the distance between the vents will be ok and also it's very sheltered so will it get the fresh air. here's a picture of it. what do you think? a suitable exit? would be around about where the RWPs are so they'd need to be moved.

 

[Bitpipe]

1m separation is fine, sheltered means you won't get unbalancing due to gusts of wind either.

 

My garage wall is directly opposite the vents (about 1m) away and it's fine, fresh air is fresh air

 

Good thing about having unit in basement is that its very easy to access and service -  check filters monthly, take out condensing unit for a clean every 6 months etc.

 

Also you never hear it, no vibration hum etc.

[Thorfun]

58 minutes ago, Bitpipe said:

1m separation is fine, sheltered means you won't get unbalancing due to gusts of wind either.

 

My garage wall is directly opposite the vents (about 1m) away and it's fine, fresh air is fresh air

 

Good thing about having unit in basement is that its very easy to access and service -  check filters monthly, take out condensing unit for a clean every 6 months etc.

 

Also you never hear it, no vibration hum etc.

 

perfect! sounds like the best solution all around as the vents will be pretty much hidden from normal view. I'll speak to the architect about moving increasing the larder size to accommodate a service void which I can use to run the radial ducting down through to the plant room as well as lots of other stuff!

[Thorfun]

@Bitpipe do you think a 300mm service void would be enough to get the ducts up and turned at 90o out through the external wall? from the photos it looks about what you have in that cupboard.

[Bitpipe]

Depends on your external duct size - mine were 180mm but it was slightly complicated by the way the basement wall sits in relation to the timber frame above - meant that even when the ducts were tight against the basement wall there was a 100mm gap between the duct and the internal utility wall that increased the space required. Also keep in mind that the duct  diameter increases by another 50-60mm due to the duct insulation.

 

I was not able to get a sharp 90 either as the floor joists dictated where the ducts could rise so I used a combination of 45 bends and eventually got there - was quite fiddly and I remember there was lots of swearing

 

I did get the TF team to fit two sections of 180 duct into the wall ahead of time to ensure these could be made airtight against the frame and be rendered up against, but it did mean I had zero flexibility in making the connections. 

 

However I think 300mm should be more than enough for you.