Feb. 13, 2007 — The use of air conditioners to cool big city buildings is making it hotter outdoors, say Japanese researchers.
A study comparing the summer temperatures in downtown Tokyo on weekends versus weekdays shows air conditioners dump enough heat into the streets to raise the temperature at least 2 to 4 degrees F (1 to 2 degrees C).
In turn, the heat blasting from the rear-ends of air conditioners is contributing to the "heat island" effect that makes cities hotter and their weather sometimes more severe.
"In the office areas of Chiyoda and Chuo Wards in the Tokyo metropolitan area in Japan, the waste heat resulting from the air conditioning operation is more than one-half of the sensible heat from the surface during the summer," reported Yukitaka Ohashi of the Okayama University of Science in Okayama, Japan.
Ohashi and colleagues have published their results in the latest issue of the Journal Applied Meteorology and Climatology.
"In office areas in the big cities of Asian countries, this 'waste' heat from air conditioners into the urban atmosphere is significant, especially during summer," Ohashi explained.
Air conditioners remove not only ambient heat from buildings, but they expel heat from their use of electricity. In other words, coolers don't just move heat from the inside to the outdoors. They also add new heat just by being machines that consume power.
In fact, Tokyo sucks up about 1.6 gigawatts of electricity for every 2 degrees of warming on a hot summer day, the researchers reported. That's equivalent to the output of one-and-a-half nuclear power plants.
The researchers reproduced real temperatures in Tokyo using two computer models coupled together. One model simulated building energy use and waste heat, and the other, air temperature in an urban environment.
