[Equest-users] Glass Library Question

Fri Sep 8 08:37:39 PDT 2017

Sounds like we could benefit from an updated DOE-2 window library based on Bruce’s observations.
As to the meaning of “e3=.4”, per Table 7 in the DOE-2 help entry for “WINDOW Library”:

Low-E:

A low emissivity metallic coating is applied in order to increase thermal IR reflectance.  The coated surface is indicated by en = v, where n = 1 is the outside of the outer pane, n = 2 is the inside of the outer pane, etc., and v is the emissivity (see, for example, G-T-C = 2635, where e2 = 0.1 indicates a coating with an emissivity of 0.1 on surface #2).

So, “e3=.4” describes an assembly with a low-e coating of emissivity 0.4 on the inside surface of the inner pane.
Syracuse Glass has a good list of considerations for low-e coatings and whether to have them on the #2 or #3 surface. Generally, coat the #3 surface if heat loss is the primary consideration, and the #2 surface to limit solar heat gains.
http://www.syracuseglass.com/E-DOCS/Insulating%20Glass/EDOCS/LOW-E%20Coating%20Orientation.pdf

Regards,
~Bill

William Bishop, PE, BEMP, BEAP, CEM, LEED AP | Pathfinder Engineers & Architects LLP
Senior Energy Engineer

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From: Equest-users [mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Bruce Easterbrook via Equest-users
Sent: Friday, September 08, 2017 11:19 AM
To: Paul Diglio <paul.diglio at sbcglobal.net>; Equest-users <equest-users at lists.onebuilding.org>
Subject: Re: [Equest-users] Glass Library Question

Hi Paul,
http://doe2.com/download/DOE-22/DOE22Vol4-Libraries_47.pdf, go further down to page 27 or page 33 on the pdf numbering.  The last paragraph explains that the coatings on the different glass surfaces have complicated the library.  I assume the e?.? is the new attempt to keep track of the different coatings and also which glass surface they are on.
You are in the emissivity table.  The table above is the reflective glazing and below is electrochromic glazing.  With a thermopane there are 4 glass surfaces and the new windows can have all 3 of these types of coatings and more in a single unit.
I suspect you can find the actual meanings here: https://windows.lbl.gov/software/window/6/W63_faq.html or https://windows.lbl.gov/
Glass has got very complex in the last few years and those charts represent products sold in mid 2006.  Our new code asks for much better performance than these glass types are capable of.  The best of these represented a window ER of 18 to 20.  Our code wanted 25.  Some of the new windows are getting up to an ER of 30 for a thermopane.  That huge bump is almost all due to coatings and their arrangement.
Bruce Easterbrook P.Eng.
Abode Engineering
On 9/8/2017 8:59 AM, Paul Diglio via Equest-users wrote:
In the DOE-2 glass library I am looking at the double low-e (e3=.4) clear product, glass type code 2600.

Does anyone know what the e3=.4 means?  There are other products, such as type 2630 with e2=.1 with a much different assembly u-value.

Thank you,

Paul Diglio
87 Fairmont Avenue
New Haven, CT 06513

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