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Lance,
Sorry for the delay in responding. But I do
have some thoughts on this.
My basic theoretical problem with these passive air
"inlets" is that they are really just fancy holes, even fancy holes with
filtration. Air does need a pathway to move. But it also needs a
driving force. The inlets provide a pathway, but the driving force comes
from somewhere else. The argument goes that with an exhaust fan in the house,
the house will be depressurized by the fan, and make-up air will be drawn
through the inlets. This makes sense. But now we add a few other
common variables: wind, stack effect, and more holes in the building
envelope. The wind blowing around a house can affect the pressure drop
across these inlets so that some go more negative inside to outside thus
bringing in more air than you want at that location. This will be cold air
in the winter in Maine, and it may make people uncomfortable. The wind can
also make the pressure drop go positive on the other side of the house, so the
"inlet" is actually working as an additional exhaust. A similar situation
applies with the stack effect (significant in Maine winters). Above the
neutral pressure plane in the house, air will be trying to leave any opening,
including opening labeled an "inlets"--the air does read. More holes in
the envelope, the unplanned ones, can make predicting what goes on at any inlet
even more nebulous. This is just what me thinking about the physics tells
me anyway.
My thoughts were confirmed by a study by the
Vermont Energy Investment Corporation a few years ago in a field study in
Vermont. A lot of these inlets were in fact acting as exhausts. This
data is from real homes in Vermont. You may be able to able get the report
from them. (http://www.together.net/~veic/
802-658-6060)
Hope this helps.
Mike
----- Original Message -----
Sent: Friday, September 21, 2001 8:12
AM
Subject: [GBlist] Air Inlets
Does anyone have experience with Fresh 80's,
Airlets or any similar passive source of fresh air for residences in northern
climates. I'm thinking particularly of houses which might be minimally heated
and unoccupied for a period of time in the coldest part of the winter during
some years, in which case there is no need for fresh and cold air. (I've had
no complaints so far with the Airlet 100 where houses are continually
occupied).
I'm told by Aldes, on the other hand, that the
Airlet 100 is always open, though it moderates under wind pressure. They do
not recommend it for this climate. The Fresh 80, on the other hand, seems to
rely on the owner to either open it or close it, not a really good long term
solution.
Apparently the Airlet 500 is controlled by humidity and
"almost closes" when under certain conditions, but I'm not clear how well that
would work in Maine, either.
I know about more active systems, including
HRV's, but those are not in play at the moment for this project.
My concerns have to do both with unnecessary
energy use, when the house is not occupied, and with comfort level. If there
are cool drafts, the Fresh 80 will be closed and the Airlet will be "plugged",
the architect's good intentions notwithstanding.
Info on any "real life" results in a
comparable situation will be appreciated.
Thanks,
Lance Fletcher, AIA
14 South Freeport Road
Freeport, ME 04032
207.865.3611
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