Volume 28, Issue 2 - March/April 2014

Staying Energized
A Look at Glazing in the New ASHRAE Standards
by Thomas D. Culp, PhD.

SHRAE 90.1 is the predominant energy efficiency standard for commercial buildings, and mid- and high-rise residential buildings over three stories. States are required by federal legislation to consider its adoption, and ASHRAE 90.1 is also referenced as a full compliance option within the International Energy Conservation Code (IECC). ASHRAE 189.1 is a companion standard for high-performance green buildings, using 90.1 as a basis, but then also overlaying other “green” concepts such as site selection, water use, material choice, daylighting, and indoor environmental quality.

ASHRAE published the new 2013 version of ASHRAE 90.1 last October, and they are now finalizing the 2014 version of ASHRAE 189.1 to be published later this fall. Overall, ASHRAE 90.1-2013 is estimated to be approximately 7 to 8 percent more stringent than the 2010 version, and approximately 38 percent more stringent than the 2004 version. A number of changes affect fenestration, glazing and daylighting.

The stringency of the prescriptive window requirements has been increased in 90.1-2013. Overall, U-factors were lowered by approximately 10 percent compared to 2010. Solar heat gain coefficient (SHGC) requirements stayed the same, already set at appropriate levels for each zone. The new values do not require triple glazing to comply, but will require low-E glass everywhere (either for U-factor in the north or SHGC in the south), thermally-broken frames in all zones but the far south, and higher performance frames and argon gas filling in the north.

There is also a new minimum requirement for the visible transmission (VT)/SHGC ratio in spaces where automatic daylighting controls are required. The value was set to require solar selective glazing (whole product VT/SHGC = 1.1 or center-of-glass LSG = 1.25), but to leave the final choice on VT to the designer based on the daylight design, function of the space, glare control, and other factors.

While it is still being finalized, it appears ASHRAE 189.1-2014 will simply set the U-factor and SHGC requirements as 10 percent lower than ASHRAE 90.1, but the SHGC is only reduced on east and west facades, and no lower than 0.25.

There is significantly increased focus on daylighting in the new standards. One small, but important, change is a new requirement that the daylight zones be identified on submitted floor plans. This, hopefully, will encourage architects and daylight designers to work together earlier in the design process to optimize daylighting before the envelope configuration is locked in place. It will also help with determining which spaces will require automatic daylighting controls.

Additionally, following a cost effectiveness study, the toplighting requirements in 90.1 have been expanded to require a minimum amount of skylights and lighting controls in spaces more than 2,500 square feet with ceiling heights over 15 feet, reduced from the prior threshold of 10,000 square feet. Finally, the lighting control requirements were significantly rewritten to require automatic daylighting controls in many more spaces (where the combined general lighting power is greater than 150 W in the primary zone or 300 W in the primary and secondary zones), and to require better multistep or continuously dimming controls with a full-off state to maximize energy savings.

“Recent proposals to reduce the prescriptive window area limit were soundly rejected once it was determined that reduced window area could actually harm indoor environmental quality and occupant well-being.”

Both 90.1-2010 and 189.1-2011 included orientation requirements to encourage designers to reduce energy and peak load by orienting their buildings with the long sides of the building facing south/north when possible. However, if a building does not comply based on its initial design, position, and/or shading, then either the window area and location must be adjusted (e.g. place more windows on the south, and reduce windows on the east/west), or the performance path must be used to demonstrate compliance. Many designers considered this section too onerous when considering real life practicalities, so the language for 90.1-2013 and 189.1-2014 has been modified to provide more flexibility including new options to use window SHGC and/or exterior shading on the east and west to help comply.

No Reductions in Window Area
One very important item that was not changed is the prescriptive window area limit. The window-to-wall ratio (WWR) limit in the prescriptive path remains the same in both ASHRAE 90.1 and 189.1 at 40 percent WWR. Higher window areas are allowed when equivalent performance is shown in the envelope trade-off option or performance path.

In fact, recent proposals to reduce the prescriptive window area limit were soundly rejected. They were rejected once it was determined that reduced window area could actually harm indoor environmental quality and occupant well-being, and be counter to high performance building design.

A number of research studies have shown that improved access and quality of daylighting and views will benefit occupant productivity, health, and well-being (see the information below). The studies make it clear that design of high-performance spaces must take a balanced approach to consider all factors including energy efficiency, productive use of the space, and occupant health and well-being. One aspect should not be traded off for another, and high-performance glazing products help all these factors to be optimized.

Once the Department of Energy makes an official determination later this year that ASHRAE 90.1-2013 saves more energy than the previous version, all states are required to consider its adoption for use. States will also start considering adoption of the 2015 IECC, which includes ASHRAE 90.1-2013, once it is published this spring. As with all building codes, adoption will vary widely across the country. Some proactive states could adopt it in January 2015, if not sooner. Other states will not make any changes at all. Regardless, architects can already look to the new version and start to use it in making design decisions.

ASHRAE 189.1-2014 will be published this fall, and it is also very likely to be included as a full compliance option in the 2015 International Green Construction Code (IgCC). As a green standard, ASHRAE 189.1 and/or the IgCC will generally be used as a voluntary stretch standard, as an alternative to LEED.

However, they could be considered for required use in certain state and federal buildings, and the Department of Defense will look at incorporating parts or all of these standards into its Unified Facilities Criteria requirements.


Let the Sun Shine In: Daylighting Benefits

20% increase in office worker cognitive test rates

21% increase in student test scores

6% increased retail sales

22% reduced development of surgical post-op delirium

Reduced depression, improved sleep

Increased real estate value, rental rates15% decreased absenteeism in office workers; Decreased office worker turnover; 39 additional work hours per year in office worker productivity; 9 to 16% improved performance on visual memory tests

Reduced length of hospital stay by 2.6 days

22% less pain medication in post-spinal surgery patients

Dr. Thomas Culp of Wisconsin-based Birch Point Consulting is GANA’s code consultant and is engaged in the energy code process.

Architects' Guide to Glass & Metal
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