ANN ARBOR—Much has been made of the increasing energy demands of the warmest regions of the U.S., but cooling down actually requires less energy than heating up, says a University of Michigan researcher.

“The traditional discussion of climatology and energy demand concentrates on the energy demands for cooling in hot climates,” said Michael Sivak, research professor at the U-M Transportation Research Institute. “However, the focus should be paid to the opposite end of the scale, as well. In the U.S., living in Buffalo, Chicago and Milwaukee is more energy-demanding, and thus less sustainable from this point of view, than living in Las Vegas, Phoenix or Tampa.”

In a new study comparing climate control in Miami (the warmest large metropolitan area in the U.S.) and Minneapolis (the coldest), Sivak found that heating the Twin Cities area is about three-and-a-half times more energy-demanding than cooling Florida’s largest urban area.

His analysis used data on “heating and cooling degree days,” units that relate to the amount of energy needed to heat and cool buildings. One heating (cooling) degree day occurs for each degree the average daily outdoor temperature is below (above) 65 degrees Fahrenheit.

According to Sivak, Minneapolis had annually 4,376 heating degree days and 388 cooling degree days from 1971 to 2000. During that time, Miami had 2,423 cooling degree days and 83 heating degree days.

In addition to considering local climatology, the analysis also included the efficiencies of power-generating plants and heating and cooling appliances.

“To the surprise of many, air conditioners are more energy-efficient than furnaces or boilers,” he said. “It takes less energy to cool down an interior space by one degree than to heat it up by one degree because it takes less energy to transfer heat (air conditioners) than to generate heat (furnaces and boilers).”

Sivak’s study is published in Environmental Research Letters. It can be downloaded at: http://iopscience.iop.org/1748-9326/8/1/014050/article

U-M Sustainability fosters a more sustainable world through collaborations across campus and beyond aimed at educating students, generating new knowledge, and minimizing our environmental footprint. Learn more at sustainability.umich.edu.