Dipping a toe into MVHR

[Bitpipe]

Remember to allow space for wrapping them in insulation - 20mm or so all round.

 

I got a bit caught out by this and had to tweak my install.

 

In winter, these steel ducts will get cold (cold fresh air coming in, cold stale air going out) and you''ll get a lot of condensation on them where they pass through your nice warm house. 

 

You also need to allow for 75mm pipe bends where they meet the manifold.

 

My BPC required them to meet the manifold dead on and then sweep away - the radius is limited and you probably don't want it too tight anyway as it may restrict airflow.

 

 

[Moonshine]

27 minutes ago, Bitpipe said:

Remember to allow space for wrapping them in insulation - 20mm or so all round.

 

I got a bit caught out by this and had to tweak my install.

 

In winter, these steel ducts will get cold (cold fresh air coming in, cold stale air going out) and you''ll get a lot of condensation on them where they pass through your nice warm house. 

 

You also need to allow for 75mm pipe bends where they meet the manifold.

 

My BPC required them to meet the manifold dead on and then sweep away - the radius is limited and you probably don't want it too tight anyway as it may restrict airflow.

 

 

 

Good points, which ducts need to be wrapped in 20mm? the 150mm atmosphere side ones?

 

Bends are going to be tight, and may need to put rigid 90 degree bends for the ducts from the floor manifold going down the riser.

 

Something else i haven't factored is silencers on the room side ducts (supply and return), between the mvhr and manifolds. These are typically 600mm long, with a further 150mm allowance.

 

With the current layout these won't fit and a re-design is needed to fit them in the space.

Edited February 27, 2020 by Moonshine

[joe90]

I had to wrap both external 150mm pipes as condensation was forming on the “air in” pipe within my warm loft (I just did it in loft insulation off cuts wrapped with duct tape at intervals).

[MJNewton]

1 hour ago, joe90 said:

I had to wrap both external 150mm pipes as condensation was forming on the “air in” pipe within my warm loft (I just did it in loft insulation off cuts wrapped with duct tape at intervals).

 

Doesn't the insulation layer need to be vapour tight? If not, surely the moist air passes through the insulation and condenses on the pipe, which would actually be even colder than without the insulation in place hence increase the condensation further. Or am I jumping to the wrong conclusions when you say 'loft insulation'? 

[Jeremy Harris]

7 minutes ago, MJNewton said:

 

Doesn't the insulation layer need to be vapour tight? If not, surely the moist air passes through the insulation and condenses on the pipe, which would actually be even colder than without the insulation in place hence increase the condensation further. Or am I jumping to the wrong conclusions when you say 'loft insulation'? 

 

 

Yes, it does.  Failure to make it vapour tight can lead to it getting waterlogged and very soggy over time.  I used closed cell neoprene insulation around our intake and exhaust^[1] ducts.  PITA to fit and tape up, but I can be reasonably confident that it won't end up as a soggy mess.

 

^[1] The reason for doing the exhaust duct is only because the Genvex MVHR we have can exhaust air at about -5° C if it's ever run in heating mode.

[JFDIY]

Another option is ubbink insulated foam ducts, I used it and it's nice to work with and easy to remove and clean for servicing.

[joe90]

1 hour ago, Jeremy Harris said:

Failure to make it vapour tight can lead to it getting waterlogged and very soggy over time

I have checked mine and it’s dry!!!, perhaps I am lucky but I will keep an eye on it ?

[Moonshine]

The silencer is not typically required on the return air, and looking at the noise data for the MVHR return is 9 dB quieter than the supply side, so i have just put a silencer on the supply, with a 10 port manifold for supply (may only need 8) and a 6 port manifold for the return.

 

So a couple of tweaks of getting a silencer on the supply side, as below.

 

 

Its a mess and too cramped in, with the silencer tight over the ground floor riser, and the silencer going through a 100mm internal wall, also there is a ridiculous long extract so have tweaked it to be (a more space efficient design may be achievable with different manifolds, but its enough for now); 

 

 

This gives frees up loft space / maintenance, gives 275mm clearance over the riser, and 1m between atmosphere pipes on the facade.

 

In addition, all ducts are 150mm, and for the MVHR model quoted they are 125mm so some clearance tolerances allowed for.