[Bldg-sim] "Horses mouth" question.

[Bishop, Bill]

John,
 
Nay. I believe you should be leaving the emissivity alone (or changing
it only slightly). By decreasing the emissivity, you make it more
difficult for the roof to get rid of heat that is absorbed. White/cool
roofs have higher reflectance. You want to change the absorptance (= 1 -
reflectance) of the roof, which is entered in the roof construction in
eQUEST. See my previous email, attached, for more info.
 
Regards,
Bill
 
William Bishop, PE, BEMP, LEED(r) AP | Pathfinder Engineers & Architects
LLP
Mechanical Engineer
 
134 South Fitzhugh Street
Rochester, NY 14608
T: (585) 325-6004 Ext. 114
F: (585) 325-6005
wbishop at pathfinder-ea.com
www.pathfinder-ea.com
P   Sustainability - the forest AND the trees. P
 
________________________________

From: bldg-sim-bounces at lists.onebuilding.org
[mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of John
Aulbach
Sent: Monday, October 11, 2010 3:01 PM
To: bldg-sim at lists.onebuilding.org
Subject: [Bldg-sim] "Horses mouth" question.
 
All:

Question on Cool Roof and the way to simulate them in eQuest.
 
My boss came to me with a cool roof and asked me to do a quick eQuest on
it. I did a 25,000 sf single story office in Los Angeles, saw the roof
outside emissivity was 0.9.  I changed it to 0.5 and the electric usage
went UP. I change it again to 0.12 and the electric usage went up AGAIN.
The HVAC is a standard single zone pacakge unit with furnace heat.
 
Am I seeing reality or what am I missing?
 
Thanks.
 
 
John R. Aulbach, PE, CEM
Senior Energy Engineer
________________________________

Partner Energy
1990 E. Grand Avenue, El Segundo, CA 90245
W: 888-826-1216, X254| D: 310-765-7295 | F: 310-817-2745
www.ptrenergy.com <http://www.ptrenergy.com/>  | jaulbach at ptrenergy.com
<mailto:%7C%20jaulbach at ptrenergy.com> 
 
 
 
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From: "Bishop, Bill" <wbishop at pathfinder-ea.com>
Subject: Re: [Bldg-sim] Why should roofs have high emissivity?
Date: Wed, 2 Dec 2009 08:38:00 -0400
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