

Greater air conditioning demand in city than in suburbs

July 22, 2007|By Tom Skilling

A look at the Cooling Degree Day (CDD) data at O'Hare and Midway airports since 1971 shows indisputably that Midway, which is representative of ChicagoM-9s urban environment, demands more cooling energy than O'Hare, which is representative of the suburbs. When the day's average temperature is above 65(degrees), cooling is needed to maintain ideal indoor comfort. Each degree that the average temperature is above 65(degrees) is counted as one CDD. A simple summation of CDDs gives a good measure of cooling costs. Because of the urban "heat island" effect, Midway has warmer daytime high temperatures (+1.3 degrees) than OM-9Hare. However, a bigger difference occurs at night when the retention of heat by cement/asphalt, buildings and industry, creates nearly a 3-degree average temperature differential (+2.9 degrees). Observations and normal CDD data back to 1971 indicate that Midway has annually demanded 25 percent more cooling than OM-9Hare. Midway averages 1,001 CDDs annually compared to OM-9HareM-9s 830 CDDs.

Sources: Frank Wachowski, National Weather Service

WGN-TV/Paul Dailey


