ASHRAE Drops Proposal to Reduce Window-to-Wall Ratio

The ASHRAE working group voted 18-1-1 yesterday in favor of withdrawing the proposed ASHRAE 189.1 addendum to reduce the allowable prescriptive window area. Today the full committee confirmed the vote to withdraw the proposal.

Tom Culp with Birth Point Consulting and a Glass Association of North America (GANA) code consultant explained that the workgroup heard two presentations yesterday. One was from Jon McHugh, the proposal’s key proponent, and another that he presented on behalf of GANA, the Aluminum Extrusion Council (AEC) and the Glazing Industry Code Committee (GICC).

“I am very appreciative of how the entire industry came together including manufacturers, suppliers, fabricators, installers, and designers,” says Culp. “Altogether we had the support of 126 individual companies and 13 associations representing probably well over 2500 companies big and small, which is tremendous. This was a big win for us all.”

 

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One Response to ASHRAE Drops Proposal to Reduce Window-to-Wall Ratio

  1. Jon McHugh says:

    In the article above, I am described as the “key proponent” of the WWR proposal. I was asked to lead the task group on this proposal given my long history with daylighting and my participation in daylighting and productivity research studies. I developed code change proposals to require daylighting in Title 24 and to bring back daylighting to ASHRAE 90.1. Some of my research on daylighting can be found at the webpage: http://www.mchughenergy.com/publications/
    The statement below describes my reasons for abstaining on the vote for this proposal. It is my sincere hope that the readers of this publication take up the challenge listed at the end of the abstention statement.

    “Thirty five years ago Std 90.1-1989 allowed more window area if perimeter daylighting controls were installed and the VT was greater than the shading coefficient. This is equivalent to the light to solar heat gain (LSG) ratio being greater than 1.15. Thirty five years later high performance windows, regularly exceed LSG ratios of 1.5. The California 2013-Title 24 minimum efficiency standard requires that windows have a minimum VT of 0.42 for fixed windows with a maximum SHGC of 0.25 for a LSG ratio of 1.7. In comparison both Std 189.1 and ASHRAE 90.1 limit the LSG ratio to 1.1; in regards to LSG, these standards fall short of what were considered high performance windows 35 years ago. Currently Std 189.1 does not require high performance windows.
    The PNNL study fairly conclusively showed that decreasing WWR to 30% would save energy. It also showed that the increased energy consumption associated with maintaining a 40% WWR could be offset by increasing window VT. Most of the commenters were concerned about dropping WWR as it could reduce the amenity and productivity of these buildings. I appreciate these concerns and I agree that the prescriptive standards should focus on improving window performance (similar to what was proposed for the exception to the WWR requirement) rather than reducing window area. If this high performance Green standard caught up with the Title 24 minimum standard in regards to window VT, we could cost-effectively reduce energy consumption and INCREASE daylight availability while maintaining the current level of views. Some members of the window industry inform me that there are other mechanisms to yield similar levels of savings. Thus I challenge this committee and the manufacturers of high performance windows to propose a suitable replacement to this WWR proposal so the 189.1 standard is providing guidance on high performance envelope design.”

    Jon McHugh

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