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If you
model energy savings for roofing products, be sure to account for smog. Yes I’m in Los Angeles. But ASHRAE does also note that energy
savings is negligible in industrial areas due to smoke and smog. I believe the real point here is that
unless the direct irradiation level is high then there isn’t much chance of savings. The diffuse irradiation will have the
same affect on a wall as it does a roof--White paint or rock anyone (as opposed
to snowcap type products)? Your
point about New England’s latitude would fit in here about the diffuse radiation
part. Additionally, I do recall that
there was a researcher at LBL who was educating people about albedo (smooth vs.
fluffy) as a surface property that needs to also be addressed; this is in
addition to abosorptance, reflectance, and emisstivity. I do not
believe very highly in the accuracy of the energy performance estimates for the
high performance roofing products.
All you need is a hazy month in June, and you’ve got more savings then
the prior year. Wash the roof, for
that matter, and the results will change. My point
is, don’t expect much from your model, and expect less in real life. Eric Kirchhoff, PE Project Engineer Sempra Energy Solutions Phone: (213)
244-4228 Fax: (213)
244-4244 ekirchhoff@xxxxxxxxxxxxxxxxxxx Sempra Energy Solutions is not the same
company as the utility SDG&E or SoCalGas, and Sempra Energy Solutions is
not regulated by the California Public Utilities Commission. -----Original
Message----- Has
anyone had any success modeling cool roofing options (i.e. reflective or light
colored surfaces) in PowerDOE? So far, I have seen negligible results
from the adjustment of roof construction absorptance values (emissivity is also
known to play a role, but there is no input for this in PowerDOE). I have
seen data showing cooling energy savings from 0.06 to 0.54 kWh/sqft/yr,
depending on building type. I am getting only a very small fraction
of this. Data collected in the study was from facilities in the
southern and western US, and I work primarily on buildings in the Northeast. My
questions: How
well can I expect PowerDOE to simulate this? Is there a better
way to simulate cool roofing? Is the sun simply too low in the sky in New
England to yield substantial savings? Your
thoughts are appreciated. Wade
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