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<font face="Helvetica, Arial, sans-serif">I have mentioned the
challenge of high SHGC windows in super insulated homes (eg Passiv
Haus) </font>previously<br>
<br>
A recent article from Maine -you know, that hot humid place in
summer :) - is yet another story I have heard on this issue.<br>
<br>
A really good builder with some experience in PH renovated his own
home. The article is at coastalcontractor.net<br>
<br>
To quote the relevant parts:<br>
"“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.<br>
<br>
“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."<br>
<br>
.....<br>
<br>
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. "<br>
<br>
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.<br>
<br>
<br>
<div class="moz-signature">-- <br>
Dr John Straube, P.Eng.<br>
Building Science Corporation<br>
Westford MA Waterloo ON<br>
<br>
<a class="moz-txt-link-abbreviated" href="http://www.BuildingScience.com">www.BuildingScience.com</a></div>
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