[Equest-users] Roof reflectivity, emissivity and absorptance in equest

David Griffin dgriffin at etcgrp.com
Mon Nov 11 08:34:03 PST 2013


Jeff,

Keep in mind, ASHRAE 90.1 baseline roof reflectance value is 30%. If the project design calls for a highly reflective roof (i.e. reflectance, emittance, and SRI) then a 45% reflectance is modeled in eQUEST rather than the specified reflectance per the design documents.

Thanks,

David W. Griffin II
Energy Analyst
ETC Group, LLC
801-278-1927 x 128
Cell 480-736-2945
dgriffin at etcgrp.com
www.etcgrp.com

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Energy Engineering for a Sustainable Future
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From: Aaron Powers [mailto:caaronpowers at gmail.com]
Sent: Friday, November 08, 2013 7:11 PM
To: jeff at rbgb.com; equest-users at lists.onebuilding.org
Subject: [Equest-users] Roof reflectivity, emissivity and absorptance in equest

Jeff,

For an opaque surface, you can just convert reflectance to absorptance by: absorptance = 1 - reflectance.  This is the absorptance in the solar spectrum.  The emittance (in IR spectrum) is a little more hidden.  In detailed mode, if you select an exterior roof and look under the "Daylighting - Shading - Other" you'll see the Outside Emissivity input.  It sounds like you know where to input the absorptance, but just in case, it is under the roof construction in detailed mode.  SRI is a calculated value used to compare roof materials and so is not useful for energy modeling software.

Aaron

Hi All,

ASHRAE refers to roof properties in terms of reflectance, emittance, and SRI (Appendix G Table G3.1 5c). However, eQuest uses absorptance. I am unable to find in the eQuest input areas (wizard and detailed) where there is a means to input values other than absorptance. Is there a conversion factor, or a place to input reflectance, and emittance or SRI that I am unable to find?

Many thanks for your comments.

Best regards -

Jeff Ross-Bain, PE, LEED AP BD+C, BEMP
Principal
404-220-8940<tel:404-220-8940> Office
404-220-8955<tel:404-220-8955> Direct
www.rbgb.com<http://www.rbgb.com/>

Build Green. Save Time
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