Air conditioners make cities hotter

An Arizona State University (ASU) research team has found that the excess heat released from air conditioners running during the night raises outside temperatures. This worsens the urban heat island effect and increases cooling demands.

Air conditioners have long had a bad reputation when it comes to the environment, and for good reason, too. They consume a large amount of electricity and many also contain hydrofluorocarbons that are harmful to the ozone layer.

Researchers from ASU have now discovered yet another reason to avoid air conditioning systems: By simulating a 10-day period of extreme heat days in Phoenix, they discovered that the waste heat emitted by air conditioner (AC) systems at night increases mean air temperature by more than 1 degree Celsius in some urban locations. They also discovered that the effect of AC systems is stronger during the night, meaning that a smaller quantity of excess heat released during the night can increase the air temperature more compared to a greater quantity released during the daytime when the hot sun is beating down.

The findings are significant because summertime extreme-heat days in certain parts of the world are projected to become more frequent and intense as a result of climate change at the same time that urban populations are skyrocketing. Unless a mitigation strategy is implemented that uses waste heat from AC systems for other purposes, such as for water heaters in homes, or reduces AC electricity consumption by using better building technologies, the urban heat island effect will continue to increase and present significant challenges for the energy sector and electric grid.

 

Photo credit: Jan Tik/Creative Commons

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