Proposed Building Envelope Criteria for ASHRAE/IESNA Standard 90-1-2010

In the United States, the 1992 Energy Policy Act (EPAct) established ASHRAE/IESNA Standard 90.1 as the baseline for State Energy Codes for commercial buildings. Standard 90.1 is updated every three years. The internal goal for the Standard 90.1 Project Committee for the 2010 version of Standard 90.1 is to achieve a 30% overall additional energy savings beyond that in Standard 90.1-2004.

In response, the Standard 90.1 Project Committee developed addenda to modify Standard 90.1-2004. Some revisions were adopted for Standard 90.1-2007, resulting in slight increases in energy-efficiency for opaque components and more significant improvements for fenestration, largely paralleling the 2006 ICC International Energy Conservation Code (IECC).

For Standard 90.1-2010, the Standard 90.1 Project Committee has proposed significant increases in stringency for insulation and for fenestration. The revised criteria were developed by the Standard 90.1 Project Committee using a combination of calculations and professional judgment.

In addition, new analysis has been done on the insulating systems for metal buildings to better reflect the compression of insulation over purlins and sagging of insulation between purlins. For fenestration, lower U-factors reflect improved glass coatings and better thermal breaks in the frames. In addition, new criteria are specified for visible transmittance (VT) in terms of a minimum ratio of VT/SHGC (solar heat gain coefficient) so as to achieve good daylighting performance while minimizing solar gain.

The criteria for Portland, Oregon are presented as an example.