dMEVs and Heat Loss

[John288]

We are thinking to install three dMEVs in the house. One in the kitchen, one in the toilet upstairs and one in the toilet downstairs.

 

We have recently got a heat pump installed which is working well.

 

Would the dMEVs significantly increase my heat loss and thus my heating bill?

[JohnMo]

1 minute ago, John288 said:

Would the dMEVs significantly increase my heat loss and thus my heating bill?

No, they are providing a low background ventilation and depending on how they are setup will make a real difference.

 

But to perform well they need proper cross flow ventilation. So you need trickle vents in dry rooms and they cannot be closed - better if you install humidity activated ones. 

 

Does your dMEV fans have automatic boost based on humidity if so make sure they are set to in that mode. 

 

To get least heat loss you need to minimise ventilation and only boost when needed based on humidity, not just because someone switches a light on.

 

Are those your only wet rooms in the house?

[Dave Jones]

used the blauberg units on a friends house, very impressed with them.  not cheap though. They can be 'meshed' together to provide cross ventilation if needed. Bathroom have different model than the living area versions to handle the moiusture. the kit is very good and provides for an air tight install.

 

shame they are not MCS certified.

[tetris]

Hi All,

 

I've been reading up on all the ventilation materials on this wonderful forum, and I'm scratching my head about dMEV.

 

I understand the general concept: slow flow of air through the house is good.

But are we, essentially, spending a lot of time & money to draft-proof the house to then just spend more time & money so that drafts happen in higher humidity rooms by installing a dMEV+humidity controlled vents?

 

I also don't get how this is not going to lead to heat loss: we're drawing cold outside air into the house? Esp in winter.

Am I right to think successful dMEV relies on well-balanced heating (ideally, each room on demand, controlled by thermostat)? Only then we get the well-functioning system of:

high humidity -> open vent -> draw in cold air -> add on-demand heating -> dry warm room?

 

Thank you.

[JohnMo]

You are basically making things less drafty to eliminate uncontrolled ventilation, by making things airtight. So on a windy day the heat isn't stripped from the house.

 

Ventilation of any variation is then required to provide a fresh environment and strip away humidity.

 

1 hour ago, tetris said:

Am I right to think successful dMEV relies on well-balanced heating (ideally, each room on demand, controlled by thermostat

All good heating system relies on a balanced heating system, whether you need thermostats is another question and really nothing to do with a ventilation strategy.

 

1 hour ago, tetris said:

also don't get how this is not going to lead to heat loss: we're drawing cold outside air into the house? Esp in winter.

All ventilation leads to heat loss including MVHR, but the amount of heat lost with MVHR is lower in theory.

 

Controlled on demand ventilation doesn't need to loose much more heat than MVHR.  MVHR is generally steady state ventilation it runs a continuous rate almost always. The controlled on demand ventilation only ventilates the areas that need ventilation, not the whole house.  If your out all day it drops back to a minimum setting so reduced heat loss.

 

Not all dMEV fans are equal so but with care

[tetris]

Thank you - OK, that makes sense. When I run the dMEV I don't want the air being drawn from window gaps right next to it of from underneath the floorboards.

 

Further info on types of fans would be greatly appreciated (is there another thread on this forum?).

[JohnMo]

I tried a couple, first was noisy not easily controlled.  The second a Greenwood CV2 - silent at our setting (minimum flow), it boosts based on rising humidity automatically. Really easy to setup.

 

Newer version is CV3.