[Equest-users] Modeling Windows: Center of Glass vs Assembly

[Kelsey VanTassel]

There are several ways to enter window properties in eQUEST. If you are in wizard mode, you can choose from the library (but this will not work for LEED compliance models in eQUEST 3.64). The other two choices in Wizard mode are "NFRC U-factor/SHGC" and "U-value/Shading Coefficient". NFRC U-factor/SHGC automatically sets your window frame width to 0 because the value you enter (NFRC rated U-factor provided by the manufacturer or installer) should be for the entire assembly. This is the way to do it for LEED compliance models.

For the "U-value/Shading Coefficient" method, you should enter the center-of-glass U-value including air films. Often, the glass manufacturer lists two U-values, summer and winter. You should enter the average value. You must also enter a frame width and choose a frame type. Both "NFRC U-factor/SHGC" and "U-value/Frame Conductance" map to the simplified input in detail mode.

Do not confuse GLASS-CONDUCTANCE with U-value or U-factor. GLASS-CONDUCTANCE is the thermal conductance of the glass without the external air films. eQUEST calculates this automatically if you have entered your window properties in Wizard mode. If you want to enter window properties in detail mode, you will need to look up the appropriate GLASS-CONDUCTANCE value from the table in the DOE2 help file (attached).

Kelsey Van Tassel
Mechanical Engineer | kvantassel at sustaineng.com<mailto:kvantassel at sustaineng.com>
608.836.4488 ext. 20 | Fax: 608.836.4477

Sustainable Engineering Group
901 Deming Way, Suite 201
Madison, WI 53717
www.sustaineng.com<http://www.sustaineng.com/>


From: equest-users-bounces at lists.onebuilding.org [mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of STEVE SAMENSKI
Sent: Thursday, September 16, 2010 6:48 PM
To: Carol Gardner; equest-users at lists.onebuilding.org
Subject: Re: [Equest-users] Modeling Windows: Center of Glass vs Assembly

Thanks, Carol.  I have two problems with Window 5:

 *   It can't seem to handle complicated multi-pane geometries (though perhaps there's a way to finesse that), and
 *   It makes as much sense to me as your average Lady Gaga music video

After I work my way through the Fenestration chapter I plan to wade into Window 5.

Steve Samenski, PE, LEED AP, BEMP
Vice President - Sustainable Technologies
The Spinnaker Group, Inc.
http://equest-diary.livejournal.com/
www.thespinnakergroupinc.com <http://www.thespinnakergroupinc.com>  <http://www.thespinnakergroupinc.com>
Become the solution... Join the USGBC!

On 9/16/10 7:20 PM, "Carol Gardner" <cmg750 at gmail.com> wrote:
Happy reading. I'm not sure exactly how eQUEST handles all of this but I would assume, oooh, dangerous, that if you put in your glass type carefully and take care to specify the width and type of frame you have, all of which are in the Wizards, you should be good. You could test the output by comparing it to a Win5 calculation of your COG U value and frame, or just import the Win5 data into the model.

Carol

On Thu, Sep 16, 2010 at 2:38 PM, STEVE SAMENSKI <steve at thespinnakergroupinc.com> wrote:
Does anyone know definitively if eQuest calculates window assembly U-values based on user input?

As many have pointed out, the USGBC is now being careful about the distinction between center-of-glass U values and assembly U values.  I've been entering center-of-glass U-values and precise window geometry, counting on eQuest to do the heavy lifting for me.  Report LV-D says "U-VALUE INCLUDES OUTSIDE AIR FILM; WINDOW INCLUDES FRAME, IF DEFINED".  However, combing through several posts to this forum, some say eQuest doesn't really calculate an assembly's U-value, because it ignores the edge-of-glass effects due to the frame.  (Not to be confused with the thermal conductance of the frame itself, which I'm sure eQuest uses in its calcs.)  I'm hoping that one of the programmers can answer this, or maybe someone who got the story from a programmer.

I plan to read the ASHRAE Fundamentals Chapter on Fenestration this weekend.  Wish me luck.

Steve Samenski, PE, LEED AP, BEMP
Vice President - Sustainable Technologies
The Spinnaker Group, Inc.
http://equest-diary.livejournal.com/
www.thespinnakergroupinc.com <http://www.thespinnakergroupinc.com>  <http://www.thespinnakergroupinc.com>
Become the solution... Join the USGBC!


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Steve Samenski, PE, LEED AP, BEMP
Vice President - Sustainable Technologies
The Spinnaker Group, Inc.
786-385-3510
www.thespinnakergroupinc.com <http://www.thespinnakergroupinc.com>
Become the solution... Join the USGBC!
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