Variable Shading Coefficient

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I have a 230,000 square feet, 400 room office building currently modeled
in Trane Trace. Fifty percent of the building?s exterior envelope is
windows. The solar heat gain coefficient (SHGC) for the windows is
currently modeled as a constant. The goal is to use this model for LEED
V3.0, EA Credit 1 - Optimize Energy Usage.

The actual windows installed in the building are sunlight responsive
thermochromic (SRT). With SRT windows their SHGC changes as the intensity
of incident solar radiation changes. The SHGC is at minimum when the
sun?s intensity is greatest. When the window?s temperature is 77 ? F the
SHGC is 0.29 at 149 ? F the SHGC is 0.18. More information about this
product is available at
It is my understanding that eQUEST V3.55 can model variable tint windows
based on total incident solar radiation, transmitted solar radiation or
outdoor temperature. Since the building is already modeled in Trace
totally changing to eQUEST is considered impractical.
I would like to know your experience and/or thoughts on how this building
can be modeled with the SRT windows, preferably in Trace or possibly some
combination of Trace and eQUEST. The model needs to be accurate,
acceptable to the LEED reviewer, and consume as little of my time as
Thank you in advance for your assistance.

Phil Grossman, PE, LEED?AP, HFDP

Phil_Grossman at's picture
Joined: 2011-10-01
Reputation: 0


The short answer is TRACE is not setup (directly) to model SRT?s. Creating a custom internal shading library member and a custom internal shading schedule that utilizes the reset and lockout table is a possibility. The reset and lockout table would allow you to modify the load based on hourly OADB, but not directly based on glazing temperature.

Scott Hintz

KSC-ISC-4013's picture
Joined: 2011-10-01
Reputation: 0