MVHR design help / feedback

[Ola]

Any help/comments on the MVHR design greatly appreciated

 

We have just ordered Zehnder Comfoair Q350, 90mm radial ducts, 160mm spiral and insulated ducts (split order: 80% BPC / 20% VentilationLand & phstore).

MVHR unit will be located at the ground floor utility/laundry room.

I received two quite different Location Guides from BPC. The first one was initially done for the 75mm radial ducting by an error but then no change in the guide when we pointed this out; the second one for the 90mm ducting after asking some additional questions regarding the number of double duct valves (in return they changed the design). Both guides show two separate exhaust/supply external terminals but this will be changed to Zehnder 160mm combo-grille (drilling openings vs building construction issues, plus wouldn't want the terminals on two different walls anyway).

I also received some calculations from PAUL for the Zehnder unit and 90mm system, with the number of supply/extract points indicated in the table below (the quote was well out of our budget though so have not got the full design from them).

 

Which one out of the three would you describe as the most suited? Can any obvious errors be seen in the valves placement, folks? 

 

1. BPC

Ground floor (left hand side drawing) has red extract points in 2x utility, 2x shower room, 2x kitchen; green supply points in 2x living area (dining area via cascade effect?), 1x bed/study

Upper floor extracts: 2x bathroom, 1x in each bedroom

 

2. BPC re-designed

Ground floor: extracts - 1x utility, 1x shower room, 2x kitchen; supply valves - 2x living area, 1x bed/study, 1x hallway

Upper floor: extracts - 1x bathroom, 1x hallway; supply valves - 1x in each bedroom

 

3. PAUL calcs for 90mm ducting system and a different approach to the valves' number/ location (see the right hand side column for this) - no valves in the hallways at all, 2x extract valves in the upper (main) bathroom, and 2x supply point in the "master" bedroom (although it is slightly smaller in area than the other two upper floor bedrooms and much closer to the unit).

 

 

Edited May 8, 2023 by Ola
some details added to the description

[Johnny Jekyll]

Design one with two ducts per valve in larger (or multiple occupancy) areas seems to be common with 75mm ducting.

 

Design two which I’m presuming will be your approach because you have purchased 90mm ducting seems good. I’ve read that 90mm ducting enables a lot more airflow, which is why only one duct is needed to most valves. The valves are on the opposite sides of the rooms to the doors (near to windows), which is great.

 

The only question I would ask BPC is why are valves being used in the hallways? I was under the impression valves aren’t needed in hallways because they are not habitable rooms? Maybe a Build Hub colleague with more knowledge can jump in and explain?

 

Also I will follow with interest (to try and learn and bit) what others on here will say about the PAUL calcs.
 

[Ola]

3 hours ago, Johnny Jekyll said:

The only question I would ask BPC is why are valves being used in the hallways? I was under the impression valves aren’t needed in hallways because they are not habitable rooms? Maybe a Build Hub colleague with more knowledge can jump in and explain?

 

Thank you for your response @Johnny Jekyll

 

I have inquired this and got an email from BPC explaining that the vales in the hallway would let them balance the machine. They also like to have an extract in the upstairs hall for heat grab. (As heat rises, there is usually a good source of heat there.)

 

I really don't know.

My another guess was, they added the supply valve in the downstairs hallway, to allow more air in the living room? The location of the living area supply valve would perhaps cause the fresh air making a shortcut to the kitchen extract point, creating a stale air zone when the sitting area is? 

[Ola]

On 08/05/2023 at 15:38, Ola said:

Upper floor extracts: 2x bathroom, 1x in each bedroom

Re- BPC 1 design - somehow I missed out 'supply valves' in the original post description (this should read "uper floor extracts: 2x bathroom,  supply valves: 1x in each bedroom") 

[MikeSharp01]

On 09/05/2023 at 20:26, Ola said:

I have inquired this and got an email from BPC explaining that the vales in the hallway would let them balance the machine. They also like to have an extract in the upstairs hall for heat grab. (As heat rises, there is usually a good source of heat there.)

I have not heard that heat grab idea before - I wonder how it really works as apart from the immediately obvious it will have the effect of extracting in a place where you would naturally want to be supplying  so the air from the bedrooms will now go out of the hallway and bathroom extracts and it may suck air up the stairs feels odd but has the whiff of right about it.

[MikeGrahamT21]

12 minutes ago, MikeSharp01 said:

I have not heard that heat grab idea before - I wonder how it really works as apart from the immediately obvious it will have the effect of extracting in a place where you would naturally want to be supplying  so the air from the bedrooms will now go out of the hallway and bathroom extracts and it may suck air up the stairs feels odd but has the whiff of right about it.

 

Sucking up warm air and passing it through a heat exchanger which isn't 100% efficient, surely leaving the warm air where it is, displace it with filtered cool air with recovered heat would be more efficient overall? The humidity helps with the heat exchange too, so by pulling from hallway you would be drying that air somewhat, and reducing efficiency?

 

Maybe i'm wrong here, i'm no expert, just doesn't necessarily seem sensible

[jack]

On 09/05/2023 at 20:26, Ola said:

They also like to have an extract in the upstairs hall for heat grab. (As heat rises, there is usually a good source of heat there.)

Admittedly I don't have any heating upstairs, but this is very much not my experience in winter. It's always 2-3 degrees cooler upstairs than down in winter.

 

We're just at the time of year where that changes. In summer it's a lot warmer upstairs, and maybe a central extract upstairs would help when the MVHR is in summer bypass mode.

[Ola]

Thank you for all the comments.

I now have also received the calcs from BPC relating to the 2nd design. 

The height of the ground floor has been incorrect though, it should be 2.60m (it looks grey used 2.4m). 

Edited May 12, 2023 by Ola

[LeeJon]

Hello,

Maybe a few comments on exhaust positions?

 

[jon3]

On 12/05/2023 at 15:19, jack said:

Admittedly I don't have any heating upstairs, but this is very much not my experience in winter. It's always 2-3 degrees cooler upstairs than down in winter.

 

We're just at the time of year where that changes. In summer it's a lot warmer upstairs, and maybe a central extract upstairs would help when the MVHR is in summer bypass mode.

We are just in design phase for self build with MVHR. The only real passive house we visited was an upside down house on a hill side. Sleeping quarters downstairs were quite a bit cooler that the living spaces (upstairs). As the laws of physics are hard to beat  I am worried that we could end up with sleeping quarters (always upstairs for us) that are considerably warmer than we want...  Our design spec will be 19degC living and 10-12 degC sleeping. I would really like to read a lot more real experience of what its like living with these systems day to day (season to season) with the hope that we can design it right and incorporate some sensible flexibility as it seems that different people feel heat & cold quite differently ..   (ps. 1st post - I'm new to the forum so please be gentle :-)

[Gone West]

6 hours ago, jon3 said:

Our design spec will be 19degC living and 10-12 degC sleeping.

IIRC in the PHPP the default temperature is 20C throughout the house. We actually ran our PH with a temperature of 23C. I think, unless it's a typo, that you will need active cooling for a lot of the year, in order to keep part of the house at 10-12C unless you live a long way north.

[Iceverge]

That's very cold. 

 

You'll be suffering from damp and very high humidity. 18deg is probably better IMO. 

[Jenki]

8 hours ago, jon3 said:

Our design spec will be 19degC living and 10-12 degC sleeping

living in a static on site over last winter, I can assure you 10 to 12 Deg is not, what I'm aiming for in the house. Granted we had much colder some weeks, but even now with summer giving it it's best shot in North Scotland, 10deg in the bedroom is too cold and damp.

 

[Ola]

12 hours ago, jon3 said:

10-12 degC sleeping

That's what we have in the winter time in the unheated bedrooms of the stone cottage we currently live in and... I don't recommend it... It is unpleasantly dump; although I use three duvets and an electric blanket, my poor nose still gets cold when poked out of the covers.

[jack]

On 10/07/2023 at 10:36, jon3 said:

We are just in design phase for self build with MVHR. The only real passive house we visited was an upside down house on a hill side. Sleeping quarters downstairs were quite a bit cooler that the living spaces (upstairs). As the laws of physics are hard to beat  I am worried that we could end up with sleeping quarters (always upstairs for us) that are considerably warmer than we want...  Our design spec will be 19degC living and 10-12 degC sleeping. I would really like to read a lot more real experience of what its like living with these systems day to day (season to season) with the hope that we can design it right and incorporate some sensible flexibility as it seems that different people feel heat & cold quite differently ..   (ps. 1st post - I'm new to the forum so please be gentle :-)

 

For context, our house tends towards being relatively cool in winter given its PassivHaus levels of airtightness and insulation. A lot of this is larger areas of glazing, especially to the north. We certainly seem to use a bit more energy for heating than some with similar sized PassivHaus-type houses.

 

We went away for Christmas and most of January a few years back. The house was empty for a month. I turned off the heating, hot water, and every appliance other than the fridge and freezer. When we got back, the house was around 14 °C.

 

If you add back in incidental heat from people, pets, cooking, hot water generation and storage, showering, appliances, downstairs heating (if you need it to maintain 19 °C), and anything else, there's no way you'll maintain anything like even 12 °C upstairs without active cooling even in winter.

 

Where did you get the 10-12 °C idea? As others have said, that's a worryingly low temperature range in terms of house (and hence occupant) health.

 

More to the point though, 10 °C is bloody cold. My wife complains if it's less than about 18 °C, and even I don't like getting out of bed in the morning if it's much below that sort of temperature.

[jon3]

On 11/07/2023 at 11:05, jack said:

Where did you get the 10-12 °C idea? As others have said, that's a worryingly low temperature range in terms of house (and hence occupant) health.

 

Thanks for your replies. It must be just us - but I'm only talking about 10-12 for the time when we're in bed and under the duvet - heating would kick in 30mins before wake up and then yes set for 19. with bathroom with UFH slightly higher.

I tend generate a lot of heat in bed (no not that!). We have always had heating off just before bedtime and upstairs windows open throughout the year - apart from when its below freezing.  our winter duvet is only 4tog our (summer) duvet is 1tog and has been since the middle of may. 

Hence why i'm a bit worried about the MVHR design. Admittedly 10-12 was a guess. I will make sure we get some actual temperature tracking on our current bedroom asap.

[ProDave]

2 hours ago, jon3 said:

Thanks for your replies. It must be just us - but I'm only talking about 10-12 for the time when we're in bed and under the duvet - heating would kick in 30mins before wake up and then yes set for 19. with bathroom with UFH slightly higher.

In a well insulated air tight house, you simply won't get that level of temperature change in such a short time.  If you have heated the bedroom to 19C to get up, even with no heating in the depths of winter, don't expect it to drop more than a degree or 2 in 24 hours, so no way will you get down to 12C over night.

[Iceverge]

@jon3

 

The house I grew up in was regularly 12deg overnight. Icy noses and fog from your breath, mould on the walls and everyone always had a cold. 

 

The only practical way I can see happening for a modern building is to make an uninsulated "storage space" in the attic, plasterboard it out and use it as a bedroom. Ensure you have a huge amount of ventilation however as it'll quickly get mouldy otherwise. 

 

 

 

 

 

[Conor]

15 hours ago, jon3 said:

Thanks for your replies. It must be just us - but I'm only talking about 10-12 for the time when we're in bed and under the duvet - heating would kick in 30mins before wake up and then yes set for 19. with bathroom with UFH slightly higher.

I tend generate a lot of heat in bed (no not that!). We have always had heating off just before bedtime and upstairs windows open throughout the year - apart from when its below freezing.  our winter duvet is only 4tog our (summer) duvet is 1tog and has been since the middle of may. 

Hence why i'm a bit worried about the MVHR design. Admittedly 10-12 was a guess. I will make sure we get some actual temperature tracking on our current bedroom asap.

You'll never get that. It'll be 18-20c almost all of the time, through every room in the house, regardless of what heating plan you have. Our bedroom is always in that range. We just use a light summer douvet all year round, and sleep on top of it a fair bit. It's different mindset and you kinda have to live it to understand. I wear shorts and t shirt most of the time inside, all year. Only in the office room I'd need to stick a hoodie on for in the winter as it's mostly glass and doesn't have heating, so would be 16c in the morning. And all this for about 1/4 the heating cost of a "normal" house.