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Industry Addresses Key Glazing Issues During ASHRAE 90.1
ASHRAE 90.1 is the primary energy efficiency standard for
commercial and high-rise residential buildings and is used both as an
energy code as well as the basis for above-code programs such as LEED.
The committee responsible for its development met in late June in San
Antonio to focus on issues affecting the glazing industry. This was particularly
important in that they are nearing the deadline for new items to be added
to the 2013 version of the standard. For any potentially controversial
change to make it into the 2013 version, it would have had to be approved
by the committee at this meeting in order to give time for the public
review process, respond to objections, and make any necessary revisions.
The key issues discussed at the meeting that potentially
affect glazing and fenestration are described here. The glazing industry
was well represented on the 90.1 committee. I attended, representing both
the Glass Association of North America (GANA) and the Aluminum Extruders
Council (AEC), and hold a full voting position on the 90.1 committee.
Urmilla Jokhu-Sowell, technical director for GANA, has a non-voting position
on the envelope subcommittee, and Ken Brenden of the American Architectural
Manufacturers Association has been appointed to a similar non-voting position
on the envelope subcommittee.
U-Factor, SHGC and Window Area
In the development of the 2010 version of ASHRAE 90.1, the industry fought
a proposal that would have reduced the amount of allowed glazing area
by 25 percent. Not only would this proposal be harmful to the industry,
but there were serious technical concerns that it would harm building
design by adversely affecting daylighting potential and other non-energy
benefits that come from glazing. In addition to GANA, AEC and the Insulating
Glass Manufacturers Alliance, companies such as AGC Flat Glass, Guardian
Industries and Pilkington North America successfully appealed and stopped
this proposal, keeping the maximum window-to-wall ratio (WWR) in the prescriptive
path at 40 percent. (Larger glazing areas also are allowed in the performance
path, but are compared to this 40 percent WWR baseline.)
Also during the San Antonio meeting there were renewed attempts
to reduce glazing area in a new proposal from Pacific Northwest National
Laboratory (PNNL). PNNL proposed to reduce the WWR from 40 percent down
to 30 percent, and then allow back up to 40 percent WWR if the SHGC is
lowered by 25 percent in the south and U-factor is lowered by 25 percent
in the north. This would result in very aggressive requirements: SHGC
less than 0.19 in the south, and U-factors in the north less than 0.24
for nonmetal windows, 0.29 - 0.32 for metal fixed products, and 0.30 -
0.38 for metal operable products. However, the proposal included no evaluation
of cost effectiveness, and the proposal was not approved.
As a result, the 2013 version will retain the values supported
by the industry for U-factor, SHGC and WWR from the revised version of
“addendum bb” following the previous appeals (see table on page 54). The
committee will continue to work on the next step in prescriptive requirements,
but it will be for the next version of the standard, and any change will
need to consider cost effectiveness.
VT and Daylighting
The other controversial issue was a proposal by PNNL to impose a new minimum
visible light transmittance (VT) requirement on top of the current minimum
VT/SHGC ratio now required as part of addendum “bb.” Similar proposals
were rejected twice on previous subcommittee conference calls for being
overly restrictive on glazing choice and only looking at one aspect of
daylighting, but PNNL brought back yet another version. The original intent
was to look at how to improve daylighting in the standard. Unfortunately,
the subcommittee was reluctant to use the minimum daylight zone and effective
aperture approaches developed by the International Association of Lighting
Designers (IALD) for the green codes. Somehow the discussion turned to
minimum VT, but VT is not the same as daylight design. Proper daylight
design must also include consideration of building type, function of the
space, room and glazing geometry, glare control, shading, balance between
solar gain and light, etc. It’s not always about the highest VT, but about
the right amount of VT. Depending on the application, sometimes you will
want high VT, sometimes medium VT and sometimes low VT. Just look at some
of the newest low-E coatings, which have been purposely designed with
a medium VT—not high VT—to balance daylighting, cooling and glare control.
The choice needs to be left to the designer.
The proposal was decisively voted down 0-9, leaving the
standard with the “bb” requirement of VT/SHGC > 1.1 using whole assembly
values, or center–of–glass LSG > 1.25. This requires solar selective glazing,
but otherwise leaves the specific choice to the designer.
The committee did advance a separate proposal to expand
the spaces requiring automatic daylight controls, and also require that
daylight areas be identified on the floor plan submittals, to encourage
architects to think about daylight and glazing layout earlier in the design
process. This proposal just completed its initial public review on August
The 2010 version of ASHRAE 90.1 already requires the fenestration area
to be larger on the south side of the building than on the west and east
sides. Even with numerous exceptions, this is still very restrictive for
many buildings that have little south-facing wall, such as an elongated
lot along a north-south street. As a result, the committee approved revisions
to go out for public review to add compliance options and increase flexibility.
This includes giving credit for north-facing glazing in addition to south,
and also allowing the designer to address the west side through either
window area, SHGC or exterior shading—not just by reducing window area.
Overall, the revisions should provide more flexibility for designers and
glazing choice, although it could sometimes encourage lower SHGC on all
sides of the building in northern climates, which is not always the most
energy-efficient. The ASHRAE 189.1 committee is also considering something
similar in an effort to better align the two standards.
ASHRAE 90.1 already requires a minimum skylight area and lighting controls
in certain large open spaces greater than 5,000 square feet with tall
ceilings (15 feet), such as big box retail, warehouses, manufacturing
bays, etc. The committee approved a proposal to expand the toplighting
requirement to more spaces by lowering the threshold from 5,000 square
feet down to 2,500 square feet, following a cost effectiveness analysis
by PNNL. While skylights used in these types of spaces often tend to be
plastic domes, this proposal will expand the use of commercial skylights
of all types.
The orientation and toplighting proposals are out for public
review through September 16. Assuming there are no major negative comments,
these proposals will be incorporated into the 2013 version of the standard.
The ASHRAE 90.1 committee will next meet in Chicago October 4-6. n
Dr. Thomas Culp of Birch Point Consulting in La Crosse,
Wis., serves as code consultant for the Glass Association of North America
and is engaged in the energy code process.
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