[Bldg-sim] Queary

Larry Degelman ldegelman at suddenlink.net
Wed Jan 13 06:11:49 PST 2010

Hello Sambhav,

In regard to exterior surface solar reflectance, ASHRAE 90.1 focuses only on 
roofs and not walls.  In the 90.1-2007 version, Table has U-Factor 
requirements for high albedo roofs (formerly referred to as "cool roofs".) 
This single table is a replacement for the roof U-Factor requirements found 
in Tables 5.5-1 through 5.5-3 (i.e., climate zones 1 through 3.)  The 
definition of "high albedo" is found earlier in Section as roofs 
with a minimum Solar Reflective Index (SRI) of 0.82.  Typically, this is a 
roof of high emissivity as well as high reflectance.  The 90.1 User's Manual 
shows values that achieve an SRI of 0.82 in Table 5-D, ranging from an 
(e=0.75, refl=0.7) to (e=0.1, refl=0.81) combinations.


Larry O. Degelman, P.E.
Professor Emeritus of Architecture
Texas A&M University

From: "sambhav tiwari" <tiwari.sambhav at gmail.com>
Sent: Tuesday, January 12, 2010 11:31 PM
To: <bldg-sim at lists.onebuilding.org>
Subject: [Bldg-sim] Queary

> Hi,
>        I had a query  whether  ASHRAE 90.1 mentions what value has to
> be taken for wall and roof absorptance as it mentions for U value . As
> absorptance value has great impact on heat gains and further on energy
> consumption.
> Can we have a better wall absorptance in proposed case from base case
> so to improve energy performance
> Any response will be highly appreciable.
> Thanks
> Sambhav Tiwari.
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