Why it Pays to ASHRAE
By Brian Redlein
Continuing on the theme of Energy Code filings here at Manhattan New Buildings, your humble filing rep has been increasingly enlightened on why ASHRAE can be a superior compliance path than NYCECC, and while to some of you this may be Old News, many of us are just getting to grips with the differences.
ASHRAE is the American Society of Heating Refrigerating and Air Conditioning Engineers and they’ve been setting standards for ventilation and heat since they were founded 1894. They also set the standards on air conditioning and refrigeration since they merged with the American Society of Refrigerating Engineers in 1959. Their building standard 90 has been the bedrock for commercial building energy consumption standards since 1975, which makes the International Energy Conservation Code (IECC), put out by the International Code Council (ICC), look like a late-comer to the party.
Standard 90-1975 became the 90.1 we all know and love in 2004 and even though 90.1 and IECC are separate standards IECC, and therefore NYCECC, does reference the ASHRAE standards from time to time. That said, there are key differences between the two with perhaps the single most critical being how each defines walls.
IECC breaks out its wall areas strictly as above-grade and below-grade and the Window-to-Wall Ratio (WWR) that I’ve been harping about for months is strictly measured against the above-grade wall areas in the IECC universe. ASHRAE however lets you include the below-grade wall area (up to 10’ deep) in the total wall area, and in the ASHRAE universe WWR is measured against the total wall area, not just the above grade area. In English, this means the more wall area you can include in your analysis, the more glass you can add to your façade while staying below the 30-40% threshold. This isn’t a slight-of-hand on ASHRAE’s part but rather a more holistic approach to envelope design.
One thing to keep in mind however, is that ASHRAE 90.1 contains provisions limiting the amount of fenestration on the east and west facades of a building and again this reflects the cleverer nature of ASHRAE energy analysis. The east and west facades of a building get the most direct exposure to the sun’s rays as the sun stays low on the horizon in the morning and evening hours pumping large quantities of light, and therefore heat, into the building. Therefore it makes good sense to limit the amount of clear glass on those exposures at least from an energy standpoint. Architects looking to maximize Manhattan river views may want to keep this in mind, less they start failing their energy compliance COMchecks for no other obvious reason than too much glass on the west and east facades.
There’s a myriad of other differences between IECC and ASHRAE that I could go on for days about, but they’re probably best left for after the turkey and feasting of the Thanksgiving holidays. Have a good November everyone!