[Bldg-sim] "Opaque" windows

[Sami, Vikram]

True, but when you define your wall assembly you define your external surface reflectance which then factors in the solar absorptance.


Vikram Sami, LEED AP BD+C
Sustainable Design Analyst
1315 Peachtree St. NE, Atlanta, GA 30309
t: 404-443-7462    f: 404.892.5823       e: vikram.sami at perkinswill.com   www.perkinswill.com<http://www.perkinswill.com/>
Perkins+Will.  Ideas + buildings that honor the broader goals of society


From: bldg-sim-bounces at lists.onebuilding.org [mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of Liam O'Brien
Sent: Wednesday, February 29, 2012 7:58 PM
To: energy.wwind at cox.net; bldg-sim at lists.onebuilding.org
Subject: Re: [Bldg-sim] "Opaque" windows

Strictly speaking, every construction (window or wall) has a non-zero SHGC. A portion of absorbed solar radiation will ultimately end up inside a space (via conduction through the surface and later radiation/convection into the space). A highly insulated wall will transmit a negligible amount of energy. The ASHRAE Handbook of Fundamentals (Fenestration chapter) provides a method for calculating the SHGC of window frames.

For your opaque windows, the transmittance may be zero, but the SHGC > 0. The magnitude will depend on the construction of the "window"; with higher U-values leading to a higher SHGC.

Why not use LBNL Window software to calculate it? I ran the following tests with opaque glass and clear glass. Here are the results:
Plain opaque glass: SHGC = 0.31
Opaque outside, air, Clear inside: SHGC = 0.16
Clear outside, air, Opaque inside: SHGC = 0.5


Liam O'Brien
Assistant Professor
Carleton University


________________________________
Date: Wed, 29 Feb 2012 19:11:02 -0500
From: energy.wwind at cox.net<mailto:energy.wwind at cox.net>
To: bldg-sim at lists.onebuilding.org<mailto:bldg-sim at lists.onebuilding.org>
Subject: Re: [Bldg-sim] "Opaque" windows

It depends which surface is black........  S1 (outside) clear >>>  normal reflected / transmitted fractions....etc.


On 2/29/2012 7:00 PM, Alex Krickx wrote:
Hi Robert,

If it's an opaque window, can't it be described as a construction/wall material? Why still define it as a window?

Alex Krickx

Alex Krickx, LEED AP
Building Energy Specialist
Serious Energy, Inc.
1250 Elko Dr, Sunnyvale, CA 94089
(t) 408.541.8124
akrickx at seriousenergy.com<mailto:akrickx at seriousenergy.com>

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-----Original Message-----
From: bldg-sim-bounces at lists.onebuilding.org<mailto:bldg-sim-bounces at lists.onebuilding.org> [mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of RobertWichert
Sent: Wednesday, February 29, 2012 3:59 PM
To: bldg-sim at lists.onebuilding.org<mailto:bldg-sim at lists.onebuilding.org>; EnergyPro at yahoogroups.com<mailto:EnergyPro at yahoogroups.com>; energysoftllc
Subject: [Bldg-sim] "Opaque" windows

Does anybody know a SHGC for "Opaque" windows?  I think they painted
them black.

I don't think "0.00" is appropriate, but I'm willing to listen to reason...




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Robert Wichert P.Eng. LEED AP
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