[Bldg-sim] ASHRAE 90.1-2007 Fenestration Areas

[Mehta, Gaurav]

I think you are using the User's Manual for ASHRAE Standard 90.1-2004.

In ASHRAE 90.1-2007, there is no requirement of distributing glazing in horizontal bands.

Please refer Example G-D in 2007 User's manual. (yes, Example G-D and not Figure G-D)

As Jason mentioned, you need to reduce each glazing by 2/3 or 67% (40%/60% = 67%)

Gaurav Mehta, LEED® AP BD+C
Sustainable Building Analyst
Stantec
1932 First Avenue Suite 307
Seattle WA 98101
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Gaurav.Mehta at stantec.com
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From: bldg-sim-bounces at lists.onebuilding.org [mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of Will Mak
Sent: Wednesday, December 22, 2010 8:39 AM
To: bldg-sim at lists.onebuilding.org
Subject: [Bldg-sim] ASHRAE 90.1-2007 Fenestration Areas

Hi all,

I am working on a project that has a large amount of glass. ASHRAE 90.1-2007 states this about baseline modeling for glass:

The fenestration area in the baseline building shall be equal to the fenestration area in the proposed building or 40% of the exterior wall, whichever is less. If it is necessary to reduce window area in the baseline building, then corresponding increases are made in the opaque walls such that the gross exterior wall area is unchanged between the proposed building and the baseline building.

Fenestration area in the baseline building shall be distributed among the thermal blocks and around the building in a uniform manner. In each thermal block, the fenestration area shall be equal to the window wall ratio for the baseline building (the maximum of 40% or the proposed building WWR) multiplied times the exterior wall area for the thermal block. If the thermal block has more than one exterior wall, window area is placed proportionally on each.

The window area is positioned in continuous horizontal bands on each exterior wall, although the configuration of window area on each wall is not significant since neither daylighting or self shading from the building is modeled. See Figure G-D.

While the prescriptive envelope requirements provide an exception for street-level, street-side vertical fenestration (e.g., store display windows), the building performance rating method does not. Window area in the baseline building is always determined as described above.

Based on the wordage above, I must develop the baseline model with either the same glass areas as the proposed building (essentially copying the proposed model and just updating U-values, etc.) or 40% of the exterior wall, whichever is smaller. Since I have roughly 60% of glazing, I will have to redistribute the glass into continuous horizontal bands on each exterior wall, similar to how ASHRAE 90.1-2004. However, as I began to look at the glass % of each exterior wall, I ran into a problem:

Wall

Window SQ FT

Wall SQ FT

Total SQ FT

Window %

North

10727.76

8485.95

19213.71

55.83%

North-East

1812.26

2272.83

4085.09

44.36%

East

2645.52

1846.83

4492.35

58.89%

South-East

1683.46

1222.87

2906.33

57.92%

South

12595.36

3958.92

16554.28

76.09%

South-West

623.46

829.56

1453.02

42.91%

West

3282.3

2924.38

6206.68

52.88%

North

0

104.26

104.26

0.00%

Total

33370.12

21645.6

55015.72

60.66%


There is not enough exterior wall space to redistribute glazing to drop the percentages for each wall to 40%. Do I just reduce each wall to 40% glazing with continuous horizontal bands?

Thanks!

William Mak, LEED Green Associate
Mechanical Design Engineer

EPSTEIN
Architecture
Interiors
Engineering
Construction

600 West Fulton Street
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