[Greenbuilding] Passive House Overheating

Gennaro Brooks-Church - Eco Brooklyn info at ecobrooklyn.com
Wed Aug 15 15:35:45 CDT 2012


I have taken the consultant and tradesperson trainings in Passive
House. The key element for a warm winter house and cool summer house
are overhangs that shade in the summer when the sun is at a higher
angle yet don't obstruct the sun in the winter.
The house is built like a thermos so it does not swing with outdoor
temperatures BUT if heat enters it via the windows it has nowhere to
go.

Gennaro Brooks-Church
Director, Eco Brooklyn Inc.
Cell: 1 347 244 3016 USA
www.EcoBrooklyn.com
22 2nd St; Brooklyn, NY 11231


On Wed, Aug 15, 2012 at 11:43 AM, Matt Dirksen <dirksengreen at gmail.com> wrote:
> I've certainly read up on Passivehaus over the years, but this article (and
> other’s I’ve read) make me wonder how one designs these homes to properly
> accommodate for potential of overheating – especially during peak loads?
>
>
>
> I am curious how it was determined that a house is considered "overheating"
> when it surpasses 77 degrees ten percent of the year? Is that during
> daylight hours or a 24 hour period? Because the reality is, if one’s house
> overheats for up to a third of the Summer, I’d expect some serious
> complaints to arise.
>
>
>
> In other words: does PH actually design for the anticipation of a 10+ person
> summer birthday party which happens to land in the middle of a heat/humidity
> wave?
>
>
>
> It would seem to me that a “dumb-ole” back up air conditioner would still be
> required for events like this no matter what. But if that’s the case,
> wouldn’t that count against the 4.75 kbtu/h measurement?
>
>
>
> Obviously I am seeking more enlightenment on this subject, but the “data”
> simply hasn’t eased my skepticism yet.
>
>
>
> Thanks,
>
>
>
> Matt
>
>
> On Wed, Aug 15, 2012 at 10:39 AM, John Straube <john at buildingscience.com>
> wrote:
>>
>> I have mentioned the challenge of high SHGC windows in super insulated
>> homes (eg Passiv Haus) previously
>>
>> A recent article from Maine -you know, that hot humid place in summer :) -
>> is yet another story I have heard on this issue.
>>
>> A really good builder with some experience in PH renovated his own home.
>> The article is at coastalcontractor.net
>>
>> To quote the relevant parts:
>> "“We're very close to the Passive House new construction standard from an
>> annual heating load standpoint," says Corson. “Instead of 4.75 kBTUs/sqft,
>> we've got this house down to about 6 kBTUs/sqft. And the peak load in this
>> house is down to about 10,000 BTUs an hour — which for Maine, is pretty
>> low." Oddly enough for a house in the frozen North, however, it's the summer
>> issues that are now the most vexing. “I need to address shading of the
>> windows, the cooling load, and summer dehumidification," says Corson.
>>
>> “Getting this house so close to Passive House, and living here in the
>> summer, has really given me a sense of the propensity for overheating," says
>> Corson. “The windows I used on this house have a solar heat gain coefficient
>> of .494, the same as the windows we used on the Knox job. For the new house
>> in Montville that we're doing now, we used a .62 solar heat gain unit — much
>> higher. If I had used the .62 solar heat gain window on this house, we would
>> be well below passive house standards for our annual heating demand (though
>> not necessarily for our shell airtightness). But in the summer — we'd be
>> baking in here right now."
>>
>> .....
>>
>> The Passive House standard says a house isn't overheated unless the indoor
>> temperature exceeds 77°F for more than 10% of the year, Corson explains.
>> “Theoretically, on paper, in the PHPP, the house that we're living in now is
>> not overheating," he says. "
>>
>> Short summary: in super insulated homes high SHGC may look good on paper
>> for the solar gain they give in the middle of winter, but hourly spring/fall
>> peaks of gain can cause real discomfort.  Most programs cant reliably
>> predict this.  High SHGC makes sense with really low window areas, but not
>> with the window area people usually want for view and daylight.
>>
>>
>> --
>> Dr John Straube, P.Eng.
>> Building Science Corporation
>> Westford MA Waterloo ON
>>
>> www.BuildingScience.com
>>
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>
>
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