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

Nick Caton ncaton at smithboucher.com
Mon Nov 11 12:55:46 PST 2013


For 90.1/LEED documentation purposes, this is all spelled out in Table G3.1 under the envelope piece, and that passage includes the cited SRI thresholds at which you can model an improved reflectance.

~Nick

[cid:489575314 at 22072009-0ABB]

NICK CATON, P.E.
SENIOR ENGINEER

Smith & Boucher Engineers
25501 west valley parkway, suite 200
olathe, ks 66061
direct 913.344.0036
fax 913.345.0617
www.smithboucher.com

From: equest-users-bounces at lists.onebuilding.org [mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of David Griffin
Sent: Monday, November 11, 2013 10:36 AM
To: 'Aaron Powers'; jeff at rbgb.com; equest-users at lists.onebuilding.org
Subject: Re: [Equest-users] Roof reflectivity, emissivity and absorptance in equest

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<mailto:dgriffin at etcgrp.com>
www.etcgrp.com<http://www.etcgrp.com>

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Energy Engineering for a Sustainable Future
1997 South 1100 East, Salt Lake City, UT 84106-4471
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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<mailto:jeff at rbgb.com>; equest-users at lists.onebuilding.org<mailto: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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