[BLDG-SIM] "Cool Roofing"

[Kirchhoff, Eric]

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 at semprasolutions.com
 
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-----
From: Wade McLaughlin [mailto:wmclaughlin at dmiinc.com]
Sent: Monday, October 07, 2002 10:55 AM
To: BLDG-SIM at GARD.COM
Subject: [BLDG-SIM] "Cool Roofing"
 
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 McLaughlin
DMI
450 Lexington St.
Newton, MA  02466
p 617-527-1525 x103
f  617-527-6606
 
 
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