[Greenbuilding] Passive House Overheating (Corwyn)

Paul Hadfield paul.hadfield at firelight.co.uk
Thu Aug 16 16:13:41 CDT 2012


Hi

John Straube wrote:
So they invented "enthalpy control"
        which only ventilates when the air outside has less energy in
        it, eg some combination of temperature and humidity.  Dont
        ventilate when it is 65F and raining, do ventilate when it is
        70F and 40%RH.

I'm just wondering if the 'Passivent' passive ventilation system I recently
installed in my 1950s very-far-from-passivehouse (single-glazed) in the UK east
midlands http://www.passivent.com/passive_stack_ventilation.html   is an
entry level version of v. v. simple enthalpy control, for our near
zero-cooling climate. Maybe y'all are familiar, but as far as I can gather
it works on rubber bands. When it is humid in the wet room where the
extract vent (with the rubber bands) is located, the rubber bands contract
and open the vent. If at the same time it is more humid in that room than
it is outdoors, lighter humid air rises up the stack, all else
(temperature) being equal inside and out, and so it draws air in through
vents from the uninsulated crawl space in the dry rooms. But if the
relative humidity is high outdoors, then all else (temperature) being
equal, no stack effect occurs despite the opening of the vent.

Meanwhile during the heating season, the rubber bands only open the vent
when the RH in the wet room is high, so keeps the stack effect just for
those times, minimising heat loss as warm air.

Our building regulations here in the UK seem keen on this type of passive
ventilation, but it isn't widely used yet in domestic buildings as far as I
can gather, and I guess perhaps it wouldn't be right for a very
well-insulated house where you'd no doubt want MVHR. I haven't recognized
any mention of passive ventilation on this list, but perhaps it is too
basic, and wasteful of heat, for you erudite and energy-minimising guys and
gals. Anyway, I'd be interested in any comments.

We've been pleased with it so far. I say we are a non-cooling climate, but
perhaps it's just that our warm beer has a special hidden cooling effect,
and that helps us through this time of year.

Brgds, or for any Zulu speakers, salani kahle

paul dot hadfield at firelight.co.uk
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