Masonry vent (as opposed to window trickle vent) for the 'in' side of dMEV

[Redbeard]

dMEV usually functions with a window trickle vent as the 'inlet' part. Some of these are baffled which helps to reduce excessive ('unwanted') ventilation. Due to the window design a window vent is not possible. There simply is not enough 'meat' on the frame. I am trying to source a baffled wall vent to use as the 'in' part of a dMEV installation (probably a Greenwood CV2) but am really reluctant to use a bog-standard air-brick which is not baffled at all. Does anyone have any ideas as to what I might use? Thanks.

[gravelld]

Doesn't it depend on the dwelling's current overall air permeability? If leakage is high enough from throughout the property it might not require an extra vent.

[JohnMo]

29 minutes ago, Redbeard said:

Does anyone have any ideas as to what I might use

You need something like these, others are available, but this was the first I found, they are humidity controlled and silenced. So they will open and close based on humidity and not transfer noise from outside.

 

https://www.bpdstore.co.uk/glidevale-fresh-99hdb-humidity-sensitive-acoustic-wall-ventilator/p/232

 

 

[Redbeard]

56 minutes ago, gravelld said:

Doesn't it depend on the dwelling's current overall air permeability? If leakage is high enough from throughout the property it might not require an extra vent

Agreed, to some extent, but the aim is to eliminate unintentional ventilation and replace it with intentional, even if there's a bit of overlap as the 'unintentional' is being designed out.

 

47 minutes ago, JohnMo said:

You need something like these, others are available, but this was the first I found, they are humidity controlled and silenced. So they will open and close based on humidity and not transfer noise from outside.

Thanks @JohnMo. I had looked at those, but since they 'will open and close based on humidity...' and the 'air in' will be in one room with the fan 'out' in a wetter room  it may depend on how good the inlet units are at their job. In a less-than-ideal situation the humidity could reduce in the 'inlet' room, making the inlet vent close. However the dMEV fan is running permanently (albeit at only 1-2W) and pulling against a closed inlet. As @gravelld suggests, at the 'start of things' the dMEV fan will just pull in air via 'unintentional' routes, but when these are all closed...? I suspect the Glidevale unit may be fine, but any comments on my 'scenario' gratefully received.

[JohnMo]

50 minutes ago, Redbeard said:

comments on my 'scenario' gratefully received.

The way the humidity control ventilation will work 

 

dMEV units are running at minimum speed for room they are installed. The Greenwood CV2 will automatically boost on rising humidity. The inlet vents in different rooms will have a minimum open position (from install manual - "At low levels of relative humidity, the extract never fully closes, providing a low level of background ventilation to ensure continuous ventilation"), so all rooms will have a background ventilation rate. So the ventilation in will wash the room with a small rate at all times. Door under cuts allow air to freely be drawn from the inlet valves. No inlet valves in wet rooms ensures good cross ventilation.

 

When your say in the lounge generating humidity by breathing, drinking tea etc, the ventilation inlet in that room will start opening. More air wash will occur in that area as the ventilation inlet opens, lowering the system resistance compared to other vents in a more closed position. At bedtime your lounge humidity drops and the inlet closes and the bedroom one starts to open etc. No one home all vents are in the minimum position. Take a shower fan in bathroom goes into boost and just pulls harder on the vents in the minimum open position.

 

The inlet vents just provide a variable inlet resistance to give preferential flow in areas of higher humidity.

Edited Saturday at 20:48 by JohnMo
Added quote from install manual

[nod]

We were told by building control and our Architects No MVRH You need trickle vents on a new build Extensions refurbed No need 

Nothing in between

 

Its crazy that the air testers tape all these up 

[JohnMo]

31 minutes ago, nod said:

You need trickle vents on a new build Extensions refurbed No need 

Nothing in between

But that isn't fully correct and is piss poor advise. The correct wording background ventilators. Which can be through wall or through top of window provided they meet the minimum open volume.

 

Read here, similar rules apply in Scotland.

 

https://www.gov.uk/guidance/approved-document-f-volume-1-dwellings-frequently-asked-questions

Edited Sunday at 07:49 by JohnMo
Expanding explanation

[nod]

10 minutes ago, JohnMo said:

But that isn't fully correct and is piss poor advise. The correct wording background ventilators. Which can be through wall or through top of window provided they meet the minimum open volume.

 

Read here, similar rules apply in Scotland.

 

https://www.gov.uk/guidance/approved-document-f-volume-1-dwellings-frequently-asked-questions

What do you do when they won’t budge On both our builds We didn’t want MVRH due to the obvious reasons 

What would you have done If BC are telling you they won’t sign you off with TVs It’s ok saying it’s bad advice 

It’s wasn’t really advice We pressed them both times and was met with the same answer 

[JohnMo]

You point at building regs, tell them you comply, tell them to put in writing what parts of building regs you don't comply with.  Trickle vents doesn't even get mentioned in building regs part F, it just mentions background ventilators.

 

You have to have inlet vents, but they do not have to be in the window. They have to meet minimum mm² requirements.