Is Your Air Conditioning Unit Heating Up Your City?


After a series of scorching days last week, Phoenix, AZ is forecast to see temperatures climbing as high as 110°F by Tuesday — nearly 10 degrees above the average for this time of year. Those sweltering temperatures will mean that air conditioners in homes and businesses throughout the area will be on full blast.

That’s bad news not only for energy consumption, and the capacity of the grid to keep up, but also for Phoenix residents trying to keep cool. A new study in the Phoenix area reveals that all those AC units are measurably raising the temperature of the air outside as they blast hot air out, only increasing the need to cool inside areas even more. That effect helps to set up a vicious, self-perpetuating cycle where the hotter it gets, the more people use their air conditioning, which in turn, makes it even hotter.

According to research conducted at Arizona State University and published in the Journal of Geophysical Research Atmospheres, air conditioners that emit waste heat are raising nighttime temperatures in Phoenix by around 2 °F — a small, but significant amount.

Cities are already global hot spots thanks to the urban heat island effect. According to the EPA, the annual mean air temperature of a city with 1 million people or more can be 1.8–5.4°F warmer than surrounding areas. That’s because dark, paved areas soak up heat, and buildings have displaced vegetation and wetlands — Earth’s natural temperature regulators.

At night, the urban heat island effect is even more extreme, as paved surfaces continue to radiate heat. A city can be as much as 22°F hotter at night than a neighboring rural area.

The effect discovered by the ASU researchers is not limited to Phoenix or Arizona, related research has found similar results in both Tokyo and Madrid.

Extreme heat is already the leading weather-related cause of death in the United States since records began in 1986 and Arizona has the highest rates of heat-related mortality in the country. The latest National Climate Assessment emphasized that heat waves are projected to increase in frequency, duration, and intensity as the climate changes.

In addition to the increased health risks associated with even small increases in temperature, the researchers also calculated that an increase of two degrees for the Phoenix area represents around 1,200 megawatt-hours of extra electricity consumption each day to keep buildings cool. During extreme heat, electricity for air conditioning already consumes about 50 percent of a grid’s total electricity capacity.

The large amounts of heat that the researchers discovered being pumped out into Phoenix also represent a substantial waste of energy. The researchers point out that that heat could be captured and used to heat water, reducing electricity consumption on multiple fronts.

Across the nation, cities are stepping up efforts to keep residents cool through passive design measures. In New York City, for example, former Mayor Micheal Bloomberg set in motion a plan to plant 1 million tress in the city by 2030 and began a campaign to paint city roofs white to help reflect heat away from the urban area. In Australia, researchers are assessing the feasibility of white roads to create a similar cooling effect.