[Bldg-sim] Glass center-of-glass to assembly U-Value?

Rosenberg, Michael I michael.rosenberg at pnl.gov
Mon Sep 22 09:56:58 PDT 2008


Table C3.5 from ASHRAE 90.1, 2004 gives baseline Visible Light
Transmission factors which are multiplied by the Solar Heat Gain
Coefficient to determine VLT for the base case when using the envelope
trade-off option for compliance. 
 
Mike

__________________________ 

Michael Rosenberg 
Senior Commercial Buildings Energy Analyst 
ENERGY & ENVIRONMENT DIRECTORATE 

Pacific Northwest National Laboratory 
2032 Todd Street 
Eugene, OR 97405 
(541) 844-1960 
michael.rosenberg at pnl.gov 
www.pnl.gov 

 

________________________________

From: bldg-sim-bounces at lists.onebuilding.org
[mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of karen mozes
Sent: Monday, September 22, 2008 9:47 AM
To: Josh Greenfield
Cc: equest-users at lists.onebuilding.org; bldg-sim at lists.onebuilding.org
Subject: Re: [Bldg-sim] Glass center-of-glass to assembly U-Value?


Hi,
Chapter 31 (Fenestration) of Ashrae handbook fundamentals has average
overall U-values for different frame types (weighted average for a frane
of 2.5" I believe, which also includes the glassedge effect). Accurate
U-values need to be calculated using NFRC standards, using approved
software (in the US this is LBNL Windows and Therm). 
 
I am not aware of a visible light transmittance requirement, but the
lower the transmittance, the less daylighting benefits you will get, as
you know, so there are no energy benefits for having a low Vt. Glass
manufacturers work hard to keep light transmittances high and SHGC low.
 
Hope this helps
Kind regards,
Karen
(Arup Facades)


On Mon, Sep 22, 2008 at 12:06 PM, Josh Greenfield
<JGreenfield at primerachicago.com> wrote:


	Does anyone have any rules of thumb on a quick/easy
approximation for taking a Center-of-Glass U-value and converting it to
an Assembly U-value based on industry standard assembly constructions?
I know this depends on a lot of variables, like frame material and
conductance, and the size of the overall glass assembly, etc., but I'm
just looking for a quick estimate on performance reduction for
comparisons to other window types for a particular building.

	 

	Also, is there an ASHRAE 90.1-2004 Baseline glass Visible Light
Transmittance (VLT)?

	 

	Josh Greenfield, PE, LEED AP
	Senior Associate
	Primera Engineers, Ltd.
	100 S. Wacker Drive, Suite 700
	Chicago, IL 60606
	312.606.0910 Main
	312.242.6392 Direct
	312.606.0415 Fax
	jgreenfield at primerachicago.com
	http://www.primerachicago.com <http://www.primerachicago.com/> 

	Be Green...please consider the environment before printing this
email.


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-- 
Karen Elisabeth Mozes

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