Of the reporting cities, Seattle recorded the highest number of airside economizer hours, followed by Minneapolis, Denver, Detroit, and Chicago. Seattle is a good example of a city where airside economizers make a lot of sense but waterside systems may not. Approximately 62% of the year in Seattle was below 55 degrees dry bulb on average. But only 25% of the year was below 40 degrees wet bulb (only about 7% for operation during typical business hours).
Minneapolis recorded the highest number of waterside economizer hours at 4,443, 11% higher than in 2001. Detroit also saw a jump of 16% compared to 2001 — or an additional 561 hours of waterside economizer cooling. These differences are significant when evaluating utility costs. For example, for a constant 750-ton waterside economizer load in Detroit, the cooling costs were $42,000 lower in 2002 (at 1.0 kW/ton and $0.10/kWh) compared to 2001, simply because of the difference in available waterside hours.