Closer look: Proposed revisions to ASHRAE 90.1 will have profound effect on industry

Sahely Mukerji
October 27, 2009

Officials at the American Society of Heating, Refrigerating and Air-Conditioning Engineers, Atlanta, are working on a revision to its standard 90.1 to increase building energy efficiency by 30 percent by 2030, including a proposal to reduce the window-to-wall ratio on the prescriptive path to 30 percent from the current 40 percent maximum. Other proposals will limit the light to solar heat gain ratio for the prescriptive path in the standard, and provide designers with a set of tables with new product U-value and solar heat gain coefficient requirements.

ASHRAE standard 90.1 is the basis for many state energy codes and utility rebate programs. It is developed under American National Standards Institute consensus rules in an open and public process where all materially affected industries are able to participate. The standard is published every three years.

“Compliance with the standard can be shown through two primary means, a prescriptive path and a performance path,” explains Leonard Sciarra, senior associate, Gensler, Chicago. A prescriptive path is simple but not very flexible: If the standard says install a glass with a U-factor of 0.45, a product with that U-factor or lower must be installed. A performance path is more complicated but allows a building owner or designer to install a different type of glass, as long as other changes in the building are made to provide total equivalent energy performance.

“From that aspect, there is no impact on the glazing industry in that one would always be able to trade any type of glass against high-performance walls, high-efficiency mechanical systems, etc.,” Sciarra says. “That said, all of this is predicated on an assumed baseline building energy consumption allowance, which as the codes are based on the cost of energy, is going down, which in turn pushes all the building systems, enclosure, lighting and mechanical systems to be more efficient.”

Additionally, a major component to high-performance buildings is good daylighting and designing for daylighting, Sciarra says. “To this end, the glazing industry is extremely important. So, if a designer uses the prescriptive path, the proposal is more restrictive than current codes; if a designer uses the performance path, then there is really no change. However, there is additional language and proposals moving forward that promote daylighting and therefore promote more glass and appropriate glass use.”

The prescriptive standards/codes must become more complex in order to save increasingly more energy in buildings, says Helen Sanders, vice president, operations, Sage Electrochromics Inc., Faribault, Minn. “For example, criteria will need to be developed as a function of not just climate zone, but orientation on the building, and dynamic controls for lighting and facades will need to be included. There is a belief by some within ASHRAE that the prescriptive standards must be kept ‘simple’ to make it easy for code officials to enforce, but this is at odds with what needs to be done in order to achieve greater energy savings. Life must become more complex to capture the needed energy savings.”

Effects of proposed revisions

If the proposed revisions pass, it “will have a profound effect on commercial glazing in the next few years, especially because this change will also be accompanied by an increased focus on energy code enforcement,” says Tom Culp, president, Birch Point Consulting LLC, La Crosse, Wis.

Some of the criteria, for example the light to solar heat gain ratio and amount of glazing area, are being proposed without background supporting data, Sanders says. “The trend to lower glazing area is troubling for the glazing industry as it will result in lower sales,” she says. “If the window area in the envelope goes from 40 percent to 30 percent in this revision, what will happen in the next revision? However, the trend to reducing glazing area will not necessarily result in energy savings--less glass means less natural daylight, which means more artificial lighting use. For example, a building with no windows at all is not the most energy efficient.”

The proposed revisions affect glazing, including complete changes to the U-factor and SHGC requirements, lowered glazing area, and a new proposed requirement for visible light transmittance. “The proposed U-factors are significantly lower, and will push the use of advanced thermal break technology across the country, as well as low-E, argon, and warm-edge spacers,” Culp says. “Basically, you will have to throw everything you have at the window in order to comply. Triple glazing is even being proposed in the far northern areas (zones 7-8). There are still performance options, where you can use higher U-factors if you compensate with improvements in other areas like insulation, equipment, or lighting. However, the added cost for this analysis can be beyond the budget of smaller projects, and there is also less room to trade-off as they also increased the requirements for the other areas.”

The new VT requirement also is controversial, Culp says, and was debated at length at the ASHRAE committee meeting in Atlanta, during GlassBuild America, Sept. 30-Oct. 2. “Although its intention of promoting daylighting is good, the actual proposed requirement of a VT/SHGC ratio was technically flawed,” he says. “The initial proposal--of VT/SHGC > 1.5--was proven to be proprietary in operable windows where only one glass type could simultaneously comply with both the VT and SHGC requirements. Note that this is the whole assembly VT/SHGC number, not just the center-of-glass LSG [light-to-solar gain ratio], and the frame has a significant effect on the number.”

The ASHRAE subcommittee backed off of this number somewhat, but what they proposed next would still have harmed the use of 60 percent of commercial glazing products, according to a survey done by Glass Association of North America’s ASHRAE subcommittee. “Even worse, many newer products purposely designed to balance daylighting and glare would not comply, and the products that would comply were not necessarily the right ones for many applications, potentially increasing energy consumption by causing occupants to close their blinds and turn on the lights in response to visual and thermal discomfort,” Culp says.

The industry came together under GANA’s Energy Committee, and made a presentation of its concerns to the ASHRAE 90.1 committee and envelope subcommittee. After hours of debate, they came to a compromise. The new proposal that will go out for public review will require whole assembly VT/SHGC > 1.1, but also will have other ways to comply, including center-of-glass LSG > 1.25 or a minimum effective aperture of 0.15, Culp says. The effective aperture more accurately accounts for the amount of light entering the space due to both VT and the size of the glass area. “We were also asking that the requirement only apply to spaces where daylighting controls are installed, because without coordinated lighting controls, the energy savings are minimal,” he says. “However, the subcommittee disagreed, and wanted to apply this requirement to all spaces. We will continue to argue this point in the next round of public comments.”

The glass industry needs to more actively participate in the development of these energy standards and codes, Sanders says. “It is great news for the industry that GANA is going to take over the mission of the Glazing Industry Code Committee in the code advocacy arena,” she says. “The industry will also need to work together to provide data that shows that continuing to reduce the amount of glass in buildings is not the path to reducing energy usage in buildings, and how the use of glass with different solar heat gain properties on different elevations can result in greater energy savings.”

The new proposal, which includes both the VT requirement and many revisions to the U-factors, SHGC, and glazing area, was slated to go out for public review in November. The committee will review comments in January and make any further revisions. Its goal is to complete the 2010 version of the standard in June.

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