Passive cooling: How do you stack vent?

[joth]

as in: how do you stack vent?

 

I get the general idea, but wondering how people in highly insulated / passive houses use stack venting in practice?

 

Remember to open a window overnight? Electrically opening window somewhere low down? Don't bother -- the air circulates well enough? some other forced air input? something else?

 

Our scenario is unexceptionally shaped 2 story house plus some vaulted loft area (over the main hallway) planning an EnerPHit retrofit.  We're having to make window selections now before tendering etc. as PHPP modeling is blocked on it - at least plausible placeholders. 

We have 2 skylights planned in the vaulted loft over the hallway. These will have to be electronically opening. So that lets the air out,  but where is the corresponding inflow of air going to come from? I'm keen to automate this (inside temp over 25 degrees,  outside is cooler than inside, no rain -> vent). Presumably I could put the MVHR onto boost mode (maybe cutting that off at 10pm - 6am).  

Our ideal is to have a small downstairs window that can also electronically open. Sourcing such a thing is tricky, I'm getting a quote from Schüco for AWS90.si with electrical opening, but already anticipating I won't like what comes back...

Also, the idea of leaving downstairs windows open overnight concerns me. I did consider doing something with the attached garage (maybe put the petWalk through to it, and program to leave open for venting!) but realized that even though the garage is on the northwest side of the house, the garage will likely be too warm, and too restricted airflow to be useful. I found this, but poor U and terrible airtightness makes it a non-starter.

 

Do others in similar situation find stack venting works well enough even without downstairs window open? Or... some other way of forcing in a larger volume of air.

 

I'm fully expecting consensus to be we just suck it up and commit to doing it manually ? but still interested what others do in practice?

 

 

Edited May 2, 2019 by joth

[Ferdinand]

 

Auto opening on the Passive Cat Flap.

 

They usually come with remote as well as RFiD control, so it should not be that difficult.

 

Simples.

 

(This is a suggestion not what I do, since my former cat is pushing up bamboo. I open windows manually or turn up the PIV setting, which can shift a lot of air.)

 

Ferdinand

Edited May 2, 2019 by Ferdinand

[Jeremy Harris]

Just let the MVHR do it's thing.  Seems to work very well, and keeps the air in the house cool and fresh in summer.

[jack]

We use floor cooling downstairs during really hot periods, so for us stack cooling is all about bedrooms.

 

We have a large centrally located electric skylight. Opening windows in the bedrooms does result in some air movement via the stack effect, but it feels to me that cross-ventilation is much more effective unless there's no air movement at all. It very much helps to open the windows as soon as the temperature outside drops below the internal temperature.

 

Insects are the main issue with this strategy, and if I were doing this all again, I'd include retractable insect screens on the bedroom windows.

[joth]

Really useful, thanks.

@JSHarris you also have active cooling in the downstairs slab, so more chance for the MVHR to "keep up". We are more seriously considering ASHP now (just weeks after I declared it out totally of the question) so the cost of doing that might be offset by the cooling improvements it adds meaning we can save on overly complex automatically opening windows (with 8kW of PV, daytime  active cooling can be considered much less of an decadence now too).

 

@jack this is a fantastic point. It's of little consolation to know the rest of the house is cooling down superbly overnight, if the bedrooms are not part of that stack design and stay relatively stuffy and hot. We're getting quotes on Gaulhofer windows, looks like they have an external insect screen option, I'll investigate adding that to the bedroom. Perfect timing!

 

@Ferdinand definitely ... automating the petWalk is not a problem, technically. The concern (that the executive calmly pointed out to me) is it allowing foreign feline visitors into the house. I'm not sure the motor moves the door fast enough to slam it shut if a motion sensor detects an uninvited guest approaching (and if it was fast enough closing, there's a risk of it becoming a bit of a  kitty catapult)