Magazine article American Scientist

Will AC Put a Chill on the Global Energy Supply?

Magazine article American Scientist

Will AC Put a Chill on the Global Energy Supply?

Article excerpt

Several developing nations could soon lead the world in use of air-conditioning.

The United States currently uses more energy for airconditioning than all other countries combined-a sobering statistic from Stan Cox of the Land Institute in Salina, Kansas. That distinction might not remain true for long, however. Several developing countries rank among both the most populous and hottest areas in the world. As personal incomes rise in those countries, their use of air-conditioning will also likely go up, which in turn could lead to an unprecedented increase in energy demand. I have estimated

that in metropolitan Mumbai alone, the large population and hot climate combine to create a potential energy demand for cooling that is about a quarter of the current demand of the entire United States.

According to the U.S. Energy Information Administration, 87 percent of American households are equipped with air-conditioning, and the United States expends about 185 billion kilowatt hours of energy annually on residential cooling. Therefore, it is not surprising that researchers frequently use the United States as a yardstick of high air-conditioning usage. For example, energy consultant George Henderson has recently projected how much energy might be used in the future in various European cities, should the usage of air-conditioning there follow the U.S. pattern. Energy analysts Michael McNeil and Virginie Letschert of the Lawrence Berkeley National Laboratory have projected how much air-conditioning households in developing countries might use if cooling were more affordable to them, again using the United States as a baseline. However, McNeil and Letschert analyzed large regions of the world and considered only a small number of specific countries.

Rapid increases in the ownership of air conditioners are already occurring in many developing countries. According to research by McNeil and Letschert, the percentage of urban Chinese households' with an air conditioner jumped from less than 1 percent in 1990 to 62 percent in 2003. In 2010 alone, 50 million air-conditioning units were sold in China. In another key developing country-India-only 2 percent of households had air-conditioning in 2007. But the situation is changing quickly: McNeil and Letschert estimated that air-conditioning sales there are growing by about 20 percent a year.

As more people around the world adopt air-conditioning, the energy demands in developing countries are certain to increase. At the same time, climate change is expected to make cooling demands even greater than they are today. Morna Isaac and Detlef van Vuuren of the Netherlands Environmental Assessment Agency assessed future residential energy use for cooling in the world in the context of potential climate change. They estimated that by 2100 worldwide energy demand for air-conditioning could increase by 72 percent as a result of climate change alone.

The Cooling Calculation

To gain a greater understanding of potential future air-conditioning needs in each of the countries around the world, I conducted an analysis that takes into account two primary factors: a country's local climate and the size of its population.

The climate is represented through a measure known as cooling degree days, which provides an index of the energy demand required to cool indoor spaces. The cooling-degree-days index is calculated by subtracting 18 from the mean daily outdoor temperature in degrees Celsius and summing up only positive values over a fixed pe- riod, such as an entire year. The selection of 18 degrees as the base outdoor temperature accounts for the additional heat generated by occupants and their activities, resulting in an average indoor temperature of 21 degrees- typical room temperature-when it is 18 degrees outdoors. For an average outdoor temperature higher than 18 degrees, most buildings require cooling to maintain a 21-degree indoor temperature.

My calculations used a pair of underlying variables, the annual cooling degree days for each country (weighted by the geographical distribution of the population) and the country's total population (using figures for 2010). …

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