# eQuest 90.1 Window U Values

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I'm to the point in an Energy Model where I'm changing my 'Proposed
Model' to my 'Baseline Model' and I'm having issues changing the window
data. For the ASHRAE 90.1 region, the Assembly U value needs to be set
to 0.57 and the Assembly SHGC needs to be set to 0.39...where do I input
these numbers?? The only window data values eQuest is letting me change
is Glass Conductance, VLT and Emissivity...

Josh Greenfield, PE, LEED AP

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Joined: 2011-02-17
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Under DOE2 Help, Dictionary/Glass-Type..

GLASS-CONDUCTANCE

The conductance of the glazing, excluding the outside air film
coefficient. The conductance given in glass manufacturers' data sheets
usually includes the outside air film resistance for a wind speed of 7.5
mph (summer) or 15 mph (winter). Table 10 can be used to obtain the corresponding value of GLASS-CONDUCTANCE. For
example, if U(7.5 mph) = 0.64 Btu/ft2-hr-F, then GLASS-CONDUCTANCE =
0.79 (by interpolation). For U-values of different glazing types, see
manufacturers' data sheets or the ASHRAE 1989 Handbook of Fundamentals,
p. 27.16-17.

Table 10
Correspondence between Glass manufacturers U-value and GLASS-CONDUCTANCE
(excluding outside air film) [all values are in Btu/ft2-hr-F (W/m2-K)]

U-Value
(including outside air film)

GLASS CONDUCTANCE

(7.5 mph wind speed)

(15 mph wind speed)

0.1 (0.57)

0.10 (0.57)

0.10 (0.57)

0.2 (1.14)

0.21 (1.19)

0.21 (1.19)

0.3 (1.70)

0.33 (1.87)

0.32 (1.82)

0.4 (2.27)

0.45 (2.56)

0.43 (2.44)

0.5 (2.84)

0.59 (3.35)

0.55 (3.12)

0.6 (3.41)

0.73 (4.14)

0.68 (3.86)

0.7 (3.97)

0.89 (5.05)

0.81 (4.60)

0.8 (4.54)

1.05 (5.96)

0.95 (5.39)

0.9 (5.11)

1.23 (6.98)

1.09 (6.19)

1.0 (5.68)

1.43(8.12)

1.24 (7.04)

1.1 (6.25)

1.64 (9.31)

1.40 (7.95)

1.2 (6.81)

1.87 (10.62)

1.57 (8.91)

1.3 (7.38)

2.13 (12.09)

1.74 (9.88)

Josh:

Convert your GLASS-CONDUCTANCE to come up with the appropriate U-Value.

See the attached for an ASHRAE window I did.

Why didn't you start with the ASHRAE run as Base, rather than the
Proposed model first?

John R. Aulbach, PE, CEM

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Joined: 2011-09-30
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I'm curious - with the simplified glass model does eQUEST calculate the variable reflectance as a factor of the incident angle? (It was my impression that it did this only with the detailed option).

Vikram Sami, LEED AP

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Joined: 2011-09-30
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Josh,

Those are the numbers Equest uses. You need to adjust (de-rate) your
proposed assembly numbers ("NFRC 100: Procedure for Determining Fenestration
Product U-Factors" is a good source). You can back the glass conductance
(and shading coefficient?) out using this procedure.

Good luck.

-Jon

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Joined: 2011-09-30
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Will the glass-conductance conversion method give the "assembly"
U-value? I thought assembly U-value included the frame. Also, what
would you do to get the assembly SHGC?

Why not just pick an existing glass type code after finding one that
most closely matches the desired assembly U-value and assembly SHGC? I
can usually find one that is close to, if not exactly the same as, the
required values. The best match I see from the DOE glass library for
U=0.57 and SHGC=0.39 is GTC 6840 - Double Pilkington Arctic
Blu/Air1/Clr6.

Select "Create another Glass Type Code" by right clicking on an existing
pick 6840. Then change the properties of the affected glass types to
reflect the change in glass type code (above the glass type codes as
listed in the component tree).

William Bishop, EIT, LEED(r) AP

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Joined: 2011-09-30
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Since the glazing needs to be modeled as an assembly, you also have to
verify the correct frame conductance is being used. This value is found in
the detailed edits under the window details.

Frame Conductance= 1 / [(1/u-value) - 0.197]

So, by example, if the ASHRAE 90.1 fenestration assembly u-value = 0.57, the
frame conductance should = 1/ [(1/0.57) - 0.197] = 0.642

When this is used in conjunction with the correct glass conductance (as
previously described), the output file will give the proper u-value averages
on the LV-D report.

Amanda Bogner, PE LEED AP

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Joined: 2011-09-30
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(I'm not an Equest user, so, my question is strictly coming from?a glazing and window assembly composite U-value standpoint).??
I don't see how there can be a single formula?to characterize the frame conductance.? Wouldn't the conductance of the frame be a function of the frame materials and construction....i.e. if it is insulated, thermally broken, wood, metal, pvc.....etc?

----- Original Message ----

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Joined: 2011-10-01
Reputation: 3

When the assembly u-value of the glazing system (window + frame) is
determined, the frame properties you described are taken into account. The
equation below is just to convert all of this to something that eQuest will
use...

In the baseline case, ASHRAE 90.1 stipulates what the assembly value needs
to be. For the actual design, an assembly value will need to be determined
using real frame data and center of glass u-values. Check out LBNL's Window

Amanda

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Joined: 2011-09-30
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Can also interpolate to find the U-value for varying wind speeds? The wind
speed number is found in the weather file hourly reports?

Kevin Kyte, LEED AP

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Joined: 2011-09-30
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