Wind Chill Factor

Looking out my window, I see a classic pre-war lower Manhattan office building, twenty-one stories of reproductions of Greek details.  Lots of double-hung windows provide good natural light.  At least one-third of them have a window air conditioner sticking out, and did all winter. Because of the ACs, those windows are never really shut.  I look around in other directions and see several late 20th century residential high-rise buildings.  They are almost all energy abominations, with exposed slab edges efficiently conducting building heat out all winter long, and with large cutouts for PTACs (package terminal air conditioners) under the largest windows. Even though those PTAC openings were designed for their job, a study (There Are Holes In Our Walls) recently completed for Urban Green Council by Steven Winter Associates shows that in real life they leak as much as the window AC units, and that both leak as much as a hole of six square inches. That’s about as big as the hole Rutger Hauer’s character Roy made in the wall he punched through to grab Deckard near the end of Blade Runner.  In post-air-conditioning Los Angeles six square inches may not amount to much; here in New York City SWA found it can add $32-$45 annually to a heating bill, and two to three times that cost if the heat is electric.  That puts the total annual citywide tab at $130 to $180 million.

And then there are carbon emissions.  The back of my envelope tells me that depending on SWA’s low/high estimates, and whether you burn oil or gas, any one of these leaks, on average, contributes as much CO2 to the atmosphere  each year as a trip of 340 to 700 miles in a 25 mpg car.  And they aren’t providing any useful service, they’re just hitting you with a cold draft all winter long, if you sit near that window. So what to do?  Both SWA and our Advisory Committee for the study had lots of suggestions, ranging from leak stopping (send in the polymer foam and duct tape!) to a call for more convenient “split systems,” which connect the two ends of the AC system only by some small tubes and wires, minimizing the wall penetrations. Read the report, then see if you can get your building to set up a “remove and store” program to get the window units into the basement for the winter. Reducing these losses isn’t as glamorous as installing photovoltaic panels, but to let them continue to waste fuel and money is silly. The problem is right in front of us, staring at us like scores of eyes in each of thousands of building envelopes, and if we want to avoid the kind of desperate future we glimpsed in Blade Runner, one step in the right direction will be actions to stop these leaks.

About the authors

Richard Leigh
Richard Leigh is a Visiting Professor of Physics at Pratt Institute, primarily teaching courses in building science. He formerly served as Urban Green's Director of Research, where he managed research projects including the 2016 New York City Auditing and Benchmarking Report for 2013 data and 90 by 50, showing that New York City can reduce its greenhouse gas emissions 90 percent below current levels by 2050.