Volume 47, Issue 9 - September 2012


Raising Awareness
Industry Addresses Key Glazing Issues During ASHRAE 90.1 Meeting

by Thomas Culp

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 12.

Fenestration Orientation
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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