[BLDG-SIM] EQuest question: glass conductance

Vikram Sami VSami at lasarchitect.com
Thu Apr 5 14:05:17 PDT 2007


Ery,
I'm pretty sure eQUEST takes the layers into account when it does this.
I think the 1.47 is the U-value for a standard pane of glass, which
doesn't really change all that much between window assemblies. What
changes is the effective COG U-Value for the whole assembly depending on
the gas used in the air gap, the layers and the coating (also the tilt -
a horizontal IGU has a much higher U-value than a vertical one.

A simple way to test whether the layers are being taken into account is
to try glass assemblies with different U-values but similar optical
properties and see what difference it makes.


Vikram Sami, LEED AP
Direct Phone 404-253-1466 | Direct Fax 404-253-1366

LORD, AECK & SARGENT ARCHITECTURE
Responsive Design * Technological Expertise * Exceptional Service
www.lordaecksargent.com


-----Original Message-----
From: BLDG-SIM at gard.com [mailto:BLDG-SIM at gard.com] On Behalf Of Ery
Djunaedy
Sent: Thursday, April 05, 2007 2:21 PM
To: BLDG-SIM at gard.com
Subject: [BLDG-SIM] EQuest question: glass conductance

All,

I want to know how EQuest calculates the conduction through the
multi-pane window that is defined through the glass library,
specifically which value is actually used as the conductance.

In the component tree "Glass Type" (spreadsheet view), we have the
"Glass Conductance" value specified (1.47 is the default value,
regardless how many panes the window have). This value exists even if
the glass specification is read from the library. If we click on the
detailed properties of the glass, the library will be read and we can
see the conductance of every layer the window has.

My question is, which value is used when EQuest calculates the
conduction from the window? Is it the "Glass Conductance" value (which
is 1.47 by default) or from the value from the library (which will be
different depending on how many layers the window has)?

I noticed that when I imported a new glazing from Window5, the new
window type will be given the default "Glass conductance" value of 1.47.
I do not change this value because I assume EQuest will take the
conductance values of every layer from the library. Should I change this
manually? (If yes, this will reduce the benefit of having a
library)

Another question:
If we right click on the Glass Conductance cell, and view the default
value, there is a status bar message which says "amount of heat that
glass conducts (includes outside air film but not inside air film)".
If we choose the DOE2 help, however, Glass Conductance is "The
conductance of the glazing, excluding the outside air film coefficient."

So which one is used by EQuest: including or excluding?

Regards,

Ery

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