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<font face="Helvetica, Arial, sans-serif">As Nick says, a house
still needs airtightness and small AC for dehumidification. In my
experience, more of this is needed than an hourly computer model
like eQuest would suggest. <br>
As Gennaro said, the problem with AC in the north east is more
difficult than can be solved with night ventilation. Night
ventilation (and hence mass) is useful for swing seasons, but will
have limited effect in the heart of summer for many cities,
especially Philly, and to a lesser extent NYC.<br>
NREL weather data at airports, based on the 1960s-1970s
misrepresents the problem of city dwellings. Heat island effect
results in significantly higher night time temperatures and
temperatures for the last decade are several degrees warmer than
NREL/NOAA long term records as well.<br>
The combined effect is that a night that NREL data might say is
68, becomes 75 or 76. 68 is barely adequate to night ventilate
cool: 76 not at all.<br>
Then consider the humidity. At night, since it cools down, the RH
rises. Flooding a house with 68F/80-90%RH air loads the house up
with vapor in all the drywall, wood, furnishings. The next
morning even if the temperature stays low (say 76 or 78) the RH in
the house will be uncomfortably high. If you have more mass (lots
of exposed concrete ceilings for example) the concrete stays cool
enough that you can get condensation on the ceiling. I have seen
this happen in old masonry warehouses .<br>
So some cooling will be helpful/necessay for comfort, not so much
thermal comfort. <br>
<br>
</font>
<div class="moz-signature">Dr John Straube, P.Eng. <br>
<a class="moz-txt-link-abbreviated" href="http://www.BuildingScience.com">www.BuildingScience.com</a></div>
<br>
On 12-06-08 8:02 AM, nick pine wrote:
<blockquote cite="mid:BE79F7059F454898A3F85B5612FD251E@userPC"
type="cite">Drew writes:
<br>
<br>
<blockquote type="cite">occupants ( internal gains) and solar are
the big loads, not the shell
<br>
</blockquote>
<br>
Night ventilation can help a lot, with a massy shell.
<br>
<br>
My simulations using hourly weather data say smart ventilation can
keep a house near Phila comfortable for all but a few days a year,
when a water-filled earth tube can help. Using the earth tube too
often heats up the soil. A house still needs airtightness and a
small AC for dehumidification.
<br>
<br>
Nick <br>
<br>
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