Posted by: "Doug Kalmer" dougkalmer@gmail.com
> It takes energy from the rising hot air to turn the turbine, that
> slows the air down. Anything put into the hole in the roof restricts
> air flow. Insect screening also slows air flow. Oh yeah, mine also
> leaked in heavy rain.
I am in agreement with Doug. Attic venting is about
moving a volume of air, and the volume of air that a vent
will passively move (stack effect) is directly proportional
to the cross-sectional area of the vent. So, anything that
is in the way, will proportionally reduce the air flow. And
as has been poined out, the hottest times, are often times
with the least wind. If you want to maximize hot weather
venting: 1) make sure that your lower vents have as much
area as your upper vents. 2) Maximize the height difference
between upper and lower vents. 3) Make the vents as large
as practical. There are many other factors involved, both
positive and negative, but clerestory vents, belvederes,
cupolas, and oversized gable vents, all can work very well.
But, so can continuous ridge vents. So, pay attention to
the cross-sectional vent area (upper and lower). You are
likely to find that a continuous ridge vent will have more
area than a turbine. If you already have a continuous ridge
vent, a turbine may be redundant. Your effort will be likely
better be directed toward other things, like a lighter color
of roofing, stapling up foil in the attic (under side of the
roof) increasing your attic insulation, or any number of
potentially very effective projects, that you can do very
cost effectively to reduce Summer heat. Think of a sunlit
window like an equal area of hotplate, inside your hot
rooms.....blocking (shading) direct sunlight (Solar
heat) is about the most effective way to reduce
Summer overheating.
Laren Corie-
Natural Solar Building Design Since 1975
www.ThermalAttic.com
Read my Solar house design articles in:
-Energy Self-Sufficiency Newsletter-
www.rebelwolf.com/essn.html
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http://groups.yahoo.com/group/LittleHouses/
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http://groups.yahoo.com/group/WoodGas
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http://groups.yahoo.com/group/RefrigeratorAlternatives
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