MVHR design

[galleon87]

Hi

 

I am in a process of full renovation of a 1930s semi. all walls stripped to brick, external wall insulation, 150mm insulation between joists and 6 m rear extension. I am thinking of installing a MVHR. The question is, is it worth it for an old house? 

If yes, where can I get the design done? Don't mind if it is a paid design.

 

Thanks

[JohnMo]

7 minutes ago, galleon87 said:

The question is, does it worth it for an old house

Really depends on if you did any airtight details to ensure the property is reasonably airtight. If it isn't you are just adding more ventilation in a additional to what would normally occur, so it is likely to increase heat loss.

 

I would look at demand controlled MEV with demand controlled inlets first. Runs to keep humidity levels stable, otherwise it's off or at very low rates. Easier to install cheaper to run.

 

If set on MVHR you should consider a design that is a cascade system and it could also make use of coanda effect supply and extract terminals to minimise duct runs.

[Nickfromwales]

39 minutes ago, JohnMo said:

Really depends on if you did any airtight details to ensure the property is reasonably airtight. If it isn't you are just adding more ventilation in a additional to what would normally occur, so it is likely to increase heat loss.

 

I would look at demand controlled MEV with demand controlled inlets first. Runs to keep humidity levels stable, otherwise it's off or at very low rates. Easier to install cheaper to run.

 

If set on MVHR you should consider a design that is a cascade system and it could also make use of coanda effect supply and extract terminals to minimise duct runs.

+1. 
This needs to have an airtightness test done, and a score recorded, before moving an inch further with this  

[G and J]

1 hour ago, JohnMo said:

coanda effect supply and extract terminals

Just looked these up (it’s incredible the volume of new stuff I’m learning from here!).  
 

Without realising it I’ve stayed in hotel rooms with vents that look like these.  I presume one wouldn’t use them for a new build MVHR as they’d be noisier and/or less effective than normal vents - is that correct?

 

My interest concerns our guest bedroom which does not have an en-suite (I’m not nice enough to our guests lol).  Default case is supply vent in bedroom and gap under door, which will also transmit sound.  But could one of these vents allow a more acoustically sealed door (and stop me hearing the snoring so clearly)?

[Kelvin]

It’s surprising how little sound transfer there is once a door is closed even when there’s a gap under the door. However, being low frequency, snoring can transfer between rooms even if you didn’t have much of a gap. 
 

Some info here

 

https://www.acoustic-supplies.com/soundproof-and-do-not-let-snoring-become-an-issue/#:~:text=Room Soundproofing&text=Although the chances of snoring,bedroom than you previously had.

[JohnMo]

1 hour ago, G and J said:

 

Without realising it I’ve stayed in hotel rooms with vents that look like these.  I presume one wouldn’t use them for a new build MVHR as they’d be noisier and/or less effective than normal vents - is that correct

New build - nearly all my supply terminal are these 

 

https://www.epicair.co.uk/products/supply-air-valve-coanda-effect-8960-90mm

1 hour ago, G and J said:

Default case is supply vent in bedroom and gap under door, which will also transmit sound.

Not really true, but mandatory anyway.

 

1 hour ago, G and J said:

My interest concerns our guest bedroom which does not have an en-suite (I’m not nice enough to our guests lol).

 

You just have a supply in the bedroom, the air travels out of room by undercut, to the nearest extract point h as you balance flow and return it's not an issue.

 

Silent in operation, connected direct to 90mm duct.

 

 

[G and J]

1 hour ago, Kelvin said:

It’s surprising how little sound transfer there is once a door is closed even when there’s a gap under the door. However, being low frequency, snoring can transfer between rooms even if you didn’t have much of a gap. 
 

Some info here

 

https://www.acoustic-supplies.com/soundproof-and-do-not-let-snoring-become-an-issue/#:~:text=Room Soundproofing&text=Although the chances of snoring,bedroom than you previously had.

Crumbs that looks useful - thank you.

[G and J]

1 hour ago, JohnMo said:

New build - nearly all my supply terminal are these 

 

https://www.epicair.co.uk/products/supply-air-valve-coanda-effect-8960-90mm

So these are wall mounted near the ceiling and the benefit is that they spread the fresh air better than a simple ceiling vent?

 

1 hour ago, JohnMo said:

You just have a supply in the bedroom, the air travels out of room by undercut, to the nearest extract point h as you balance flow and return it's not an issue.

That’s what I was trying to say as my base case.  But maybe I’m worrying too much about sound.  I remember being quite pleased with myself at how small the clearances were round all our doors in our current house.  How times change. 

[galleon87]

4 hours ago, JohnMo said:

Really depends on if you did any airtight details to ensure the property is reasonably airtight. If it isn't you are just adding more ventilation in a additional to what would normally occur, so it is likely to increase heat loss.

 

I would look at demand controlled MEV with demand controlled inlets first. Runs to keep humidity levels stable, otherwise it's off or at very low rates. Easier to install cheaper to run.

 

If set on MVHR you should consider a design that is a cascade system and it could also make use of coanda effect supply and extract terminals to minimise duct runs.

 

Thanks for your reply.

 

Considering the house is currently totally stripped, I need to run the ducting soon. Would it be different ducting for MEV and MVHR?

[JohnMo]

2 minutes ago, G and J said:

So these are wall mounted near the ceiling and the benefit is that they spread the fresh air better than a simple ceiling vent?

The air travels all the way across the room, approx 5 to 6m depending on flow rate.

 

A normal door needs about 8 to 10mm, some of ours area little smaller, but doesn't seem to affect anything.

[galleon87]

3 hours ago, Nickfromwales said:

+1. 
This needs to have an airtightness test done, and a score recorded, before moving an inch further with this  

Can I run the ducting now, and then do airtightness test to decide MEV or MVHR?

[JohnMo]

2 minutes ago, galleon87 said:

Would it be different ducting for MEV and MVHR?

MVHR is supply and extract so every room needs an air supply. But by using a cascade system some of this air doesn't need to be directly ducted to the room.

 

This is my house and what it would look like in a cascade system, I did do this in the end for various reasons.

In the above there are only two units and two supply terminals and three extracts and one through wall fan unit. It uses the principles of what goes must come out, and fans to force air wherexit wouldn't otherwise travel. Those units where Fresh-R, but any normal MVHR unit can do the same thing with a little thought.

 

MEV would only extract from wet rooms, and use cross flow ventilation to sweep the house. Supply points would be either trickle vents on windows or through wall ducting.

 

[JohnMo]

14 minutes ago, galleon87 said:

Can I run the ducting now, and then do airtightness test to decide MEV or MVHR?

You could, but unless you have considered and worked on airtightness, it not likely that airtight.

 

Another alternative is dMEV, same as MEV (nearly) but no ducts, just a silent fan in each wet room and the same inlets.

[Sparrowhawk]

4 hours ago, galleon87 said:

I am in a process of full renovation of a 1930s semi. all walls stripped to brick, external wall insulation, 150mm insulation between joists and 6 m rear extension. I am thinking of installing a MVHR. The question is, is it worth it for an old house? 

If yes, where can I get the design done? Don't mind if it is a paid design.

 

Hi @galleon87 I say it's worth doing, even if your airtightness isn't as good as it could be. It means you can get rid of the bathroom/kitchen extract vents (a big source of air leakage which is excluded from the airtightness test figures), gives you enough ventilation on still days and - most importantly for some - filtered air.

 

Plus you get the chance to improve airtightness in the future (new doors, windows etc) but running ducting in a finished house is seriously hard (I'm doing it now in a 1920s detatched house). If you can work out routes, fit the ducts now, it'll only be a few hundred pounds of plastic tube and you can decide later.

 

If you haven't considered some airtightness measures yet, like a VCL over the insulation between joists and taped to the walls, or over upstairs ceilings, you're at the right stage to improve the airtightness of your renovation.

 

I'd recommend reading pages 4-8 of https://www.passivhaustrust.org.uk/UserFiles/File/research papers/MVHR/2020.04.27-The Case for MVHR-v7 new cover.pdf and also https://www.passivhaustrust.org.uk/UserFiles/File/Technical Papers/Thermal bypass risks v1.0 222909.pdf for ways insulation can lose effectiveness that you might not have yet considered.

[galleon87]

25 minutes ago, Sparrowhawk said:

 

Hi @galleon87 I say it's worth doing, even if your airtightness isn't as good as it could be. It means you can get rid of the bathroom/kitchen extract vents (a big source of air leakage which is excluded from the airtightness test figures), gives you enough ventilation on still days and - most importantly for some - filtered air.

 

Plus you get the chance to improve airtightness in the future (new doors, windows etc) but running ducting in a finished house is seriously hard (I'm doing it now in a 1920s detatched house). If you can work out routes, fit the ducts now, it'll only be a few hundred pounds of plastic tube and you can decide later.

 

If you haven't considered some airtightness measures yet, like a VCL over the insulation between joists and taped to the walls, or over upstairs ceilings, you're at the right stage to improve the airtightness of your renovation.

 

I'd recommend reading pages 4-8 of https://www.passivhaustrust.org.uk/UserFiles/File/research papers/MVHR/2020.04.27-The Case for MVHR-v7 new cover.pdf and also https://www.passivhaustrust.org.uk/UserFiles/File/Technical Papers/Thermal bypass risks v1.0 222909.pdf for ways insulation can lose effectiveness that you might not have yet considered.

Thanks again. 

 

I am replacing all windows and doors now plus the external wall insulation and floor insulation. Can you advice where i can get the design done i.e what kind of ducting to run, manifolds, silencers etc. where to locate the vents?

 

 

[Sparrowhawk]

1 hour ago, galleon87 said:

Thanks again. 

 

I am replacing all windows and doors now plus the external wall insulation and floor insulation. Can you advice where i can get the design done i.e what kind of ducting to run, manifolds, silencers etc. where to locate the vents?

 

 

I'll message you directly with a list and indicative costs.

[Mike]

7 hours ago, Sparrowhawk said:

Hi @galleon87 I say it's worth doing, even if your airtightness isn't as good as it could be. It means you can get rid of the bathroom/kitchen extract vents (a big source of air leakage which is excluded from the airtightness test figures), gives you enough ventilation on still days and - most importantly for some - filtered air.

 

Plus you get the chance to improve airtightness in the future (new doors, windows etc) but running ducting in a finished house is seriously hard (I'm doing it now in a 1920s detatched house). If you can work out routes, fit the ducts now, it'll only be a few hundred pounds of plastic tube and you can decide later.

+1. And you can also avoid the need for trickle vents in the windows.

 

12 hours ago, galleon87 said:

all walls stripped to brick

In that case it's the perfect time to make the building airtight. There are plenty of threads about that on here.