“126.96.36.199. Vertical Fenestration Area. The total vertical fenestration area shall be less than 30 percent of the gross wall area for buildings smaller than 25,000 ft2 (2500 m2) of gross conditioned floor area and shall be less than 40 percent of the gross wall area for all other buildings. This requirement supersedes the requirement in Section 188.8.131.52.1 of ANSI/ASHRAE/IES Standard 90.1.”
“Modern buildings with low lighting power densities and occupancy sensors cannot save as much energy from windows and daylighting as was previously predicted,” writes ASHRAE in the foreword to the proposal. “Also some simplified daylight simulation tools (split flux method) tend to overestimate how deeply one could daylight from windows. Even though energy consumption increases with increased window area, windows are valued by building occupants for view and marking the passage of time.”
The proposal continues, “Thus this proposal recommends that the prescriptive compliance option allow a moderate amount of windows for the view they provide and other amenities, but limits the WWR to 30 percent in small- and medium-sized buildings for the purpose of reducing energy use.”
The standard previously had a 40-percent WWR for all buildings; this change would only apply to buildings less than 25,000 square feet.
ASHRAE cites a recent Pacific Northwest National Laboratory (PNNL) analysis in its reasoning for the change and claims that the PNNL study “showed that energy consumption of a medium office building increased with increasing WWR.”
“The analysis used radiance to perform daylighting simulations that were ported to EnergyPlus to complete the energy simulation. The analysis considered blinds, window VT, six climate zones, exterior obstructions and interior furniture,” writes the committee.
The study did a comparison in Houston, Phoenix, Baltimore, Chicago, San Francisco and Vancouver, and claims that in each case as WWR rose energy consumption did as well. For example, in Phoenix, the study claims that when the WWR hit 40 percent for a medium office building, energy use rose by almost 20 percent.
The proposal currently is open for a 45-day public comment period that opened Friday and runs through June 17.
Thomas Culp of Birch Point Consulting LLC, code consultant for the Glass Association of North America (GANA), made the following statement in response to the release of the proposal.
“This flawed proposal takes a shallow viewpoint, ignoring why designers put in windows in the first place, and the potential negative human impacts from reducing access to daylight and views,” says Culp. “It is particularly concerning that this is a green standard whose scope specifically includes indoor environmental quality and occupant well-being.”
Culp had warned participants at the recent Building Envelope Contractors (BEC) Conference in Las Vegas that this proposal was on the horizon.
He told attendees that more than three-quarters of all buildings are less than 25,000 square feet, including schools, offices, assisted care facilities, etc. He also warned that if a code change such as this is approved it could ultimately mean fewer windows and shorter/smaller windows.
“Strip windows would become punched openings; curtainwall would become strip windows, etc.” he said.