Integrated Window Blinds in Dual Pane Windows

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Ok. . . I have a situation where I'm modeling a facility relative to ASHRAE
90.1 baseline. The customer is using dual pane, low-e windows, with integrated
venetian blinds between the two panes of glass. One pane is low-e and the other
is clear. Air gap between the two (not Argon or anything like that).

I use the LBNL Windows tool, with blinds set at 45 deg, and the blinds increase
the window assembly U value and SHGC significantly.

So for performance relative to 90.1, would it be acceptable to simply utilize
the U & SHGC from with Windows tool? Are there any restrictions on the angle of
the blinds, or whether the angle should be different for winter vs summer?

I'd appreciate any guidance on how to best model this scenario.

Thank you,
Pete Baumstark
San Jose, CA

Peter Baumstark's picture
Joined: 2012-07-14
Reputation: 0


I think this is a very unwise way to model complex fenestration, because you'll be using
the Simple Window Model in DOE-2, which assumes that the angular
variation of SHGC and temperature variation of U-factor are the same as for single-pane
clear glass. I haven't followed the development of LBNL's Window (not Windows :-))
program for the past five years, but the program used to produce a text "WINDOW 4" file
that can be read into DOE-2 or eQUEST. If this is still possible, I would recommend
using that method. There are still the questions of venetian blind shading that is not
dependent only on the angle of incidence, but also the azimuth relative to the blinds
(there must be a technical term for this, but I don't know that off the cuff), and if you
want to change the angle of the venetian blinds depending on season. I can think of ways
of dealing with these issues, but it would require writing a USER FUNCTION, which I don't
think has been implemented in DOE-2.2.


Joe Huang

Joe Huang's picture
Joined: 2011-09-30
Reputation: 406


Are you doing an Appendix G model? If so, I thought I'd remind you that, per Table G3.1, "manual fenestration shading devices such as blinds or shades shall not be modeled." If the integrated blinds are automatically controlled then they can be modeled.

I'm curious about the U-value changing (presumably improving - decreasing). Why would blinds change the U-value?


[Senior Energy Engineer 28Jun2012]

Bill Bishop's picture
Joined: 2012-02-25
Reputation: 7

Window6 can model complex glazing like Venetian blinds between the glass panes.

>> Christopher Jones, P.Eng.

Chris Jones's picture
Joined: 2011-09-30
Reputation: 0

I can really apply this in my Window Blinds. What is the right U-value of mine?

Lilly Jerrems's picture
Joined: 2013-03-14
Reputation: 0