Demand Control Ventilation

jfh

Hi all,
currently building a 204 sq mt house & looking at ventilation options.
i'm not too worried about heat recovery, more concerned with ventilation, predicted BER of A3.
DCV is working out a lot cheaper than MHRV,

anyone here go with DCV & how do you find it,
appreciate any feedback given,
thanks

Calahonda52

Can you put up the respective lifetime analysis prices for both DCV and MHVR please as well as indicate how far down the road you are build wise.
Thanks

jfh

hmm actually i cannot, the MHRV is working out 1,600 more expensive & ill have to change filters every year.
so from a respective lifetime analysis i'd imagine that MHRV will always be more costly. maybe i'm missing something?

early stages of build, floors down

Calahonda52

Okay, thanks for the answer.
lets look bit more this.
This is not my area of expertise, so am open to correction by the experts here, but I do like to try understand the physics.

In an MHVR setup, you can general say that you will recover 80% plus of the energy used by the fan(s), whereas I believe you save no fan energy on a DCV.
Have you any math for the expected volume of air that the DCV and the MHVR will shift on an annual basis?

Having said all that, in a project that is probably costing you 300k, IMO the non financial reward that MHVR will give you over say a 30 year period at say 50 euro a year plus 50 for a filter, i.e. 100 per annum, is well worth it in my view.

murphaph

With DCV you only have one fan and it spins up and down based on demand (if it gets humid in the bathroom the vent opens, passively, and the drop in vacuum is detected, causing the fan to spin up to extract the humid air faster, before returning to tick over mode).

DCV provides arguably better air quality as it responds to humidity (passively), providing more fresh air to rooms experiencing increased humidity, which is a reliable indicator of occupancy/use.

The primary advantage I see to a centralised heat recovery system is the ability to dehumidify incoming air and in the absence of a basement this isn't really critical I guess. If you do not intend dehumidifying the air like this I wouldn't bother.

I'd say you could argue this one both ways till the cows come home though.

This is obviously marketing blurb but the study it references did take place: https://www.google.de/url?sa=t&source=web&rct=j&url=https://www.aereco.com/wp-content/uploads/2016/04/FLY528GB_v2_display.pdf&ved=0ahUKEwj-1I691fvQAhVEBiwKHQdFDd4QFggaMAA&usg=AFQjCNFE9KmYLQlDaRZEzcM8-mSwHc_gqQ&sig2=3TkuBxVc0MTBLhIOTI_L0g

Calahonda52

Thanks for that, say Hi to Angela!

You have highlighted two important issues here that contribute to the discussion:
1: DCV at higher extract levels, is air quality dependant.
2: DCV will pull in humid air, as will MHVR without the appropriate kit, which can be reread if needed, but humidity is becoming an issue here.

The heat recovery option with MHVR is an attraction but we need differential air volume figure from the OP

murphaph

If I could go back I would install a centralised system with dehumidifier. But only because we have a basement and the summer airing is tricky as warm moist air gets pulled in and cools. I think we might just get away with it though because we have room temps down there of around 20 degrees, but that's because it's a "Brandenburg high cellar", where you have a small flight of steps up to the ground floor and the cellar windows are above ground level. If we'd built completely subterranean it would be a different story I'm sure.

If it turns out that even after the building dries out in a couple of years that humidity remains high in the cellar in Summer, I'll have to automate the DCV to only kick in when the absolute humidity outside is lower than the cellar. This is typically the case at night even in summer.

But if I could go back I'd go for a centralised system, but only because of the cellar, otherwise I'm super happy with DCV.

But yeah, the op needs to give more details of their proposed build.

air

Would you not just put a dehumidifier in the cellar?

murphaph

air wrote: »

Would you not just put a dehumidifier in the cellar?

The cellar and ground floor flow into one another. There is no door separating the floors. A dehumidifier there will dehumidify the whole house and the running costs would be quite high.

I have to see how it all behaves during this summer as the house should be much drier now, but next summer will be the real long term test to see how I handle it (if it needs handling).

tvisdead

I have made the decision for a central mhrv system.
We are spending so much on wall insulation and air tightness membranes that going and piercing the wall for ventillation around the house seemed wrong,
I felt that the centralised system was a better alternative.

One thing to remember is that mechanical ventillation while quiet is not dead silent. Have you gone and been in a residental space with a dcv system running? We did for the mhrv just to make sure expectation met reality

murphaph

I can't hear anything from our DCV system. The fan in the basement utility room has silencers fitted (similar to a car's exhaust) to prevent noise transmission into the ductwork.

bcoll05

Hello.
Just wondering did the original poster go with DCV over MHVR?
If so what's it like?