Cooling Concepts

Alternatives to Air Conditioning for a Warm World

Richard Dahl

Disclosures

Environ Health Perspect. 2013;121(1):A19-A25. 

In This Article

Environmental Impacts of Air Conditioners

In addition to placing strains on nations' power grids, air conditioners pose threats to the environment and environmental health, primarily as contributors to global warming. "The amount of electricity that's used for air conditioning is a huge part of an energy load for most countries, and it's going up," says Durwood Zaelke, president of the nonprofit Institute for Governance and Sustainable Development. "You're putting out more climate pollutants as you're burning more coal or gas to run the air conditioners, and you're also putting out the greenhouse gases that serve as the refrigerants in the equipment."

According to Cox, approximately 80% of the impact of air conditioning on climate results from the draw on fossil fuel–fired power plants. The remaining 20% comes from the units' refrigerants, the liquid agents within the coils that are used to cool and dehumidify the air.

Different types of refrigerants have been used in air conditioners over the years. The discovery that chlorofluorocarbons (CFCs) are major contributors to ozone-layer breakdown[9] prompted an international response that led to the creation of the Montreal Protocol on Substances that Deplete the Ozone Layer, which went into effect in 1989 and eventually eliminated production of CFCs in 1996.[10] The CFCs were replaced by hydrochlorofluorocarbons (HCFCs), a transitional fluorocarbon with a reduced impact on ozone depletion to be used only while companies developed better coolants. Today these replacements are, themselves, being phased out[11] and replaced by hydrofluorocarbons (HFCs).

HFCs have no impact on ozone depletion because they lack chlorine. However, they have been found to possess a characteristic that is not covered by the Montreal Protocol: They are super-greenhouse gases with high potential to contribute heavily to global warming.[12] The effort to solve one environmental problem, therefore, is likely exacerbating another.

Stephen O. Andersen, cochairman of the Technology and Economic Assessment Panel (TEAP) of the Montreal Protocol, says the challenge now is coming up with new refrigerants. One of the more promising candidates, he says, is refrigerant-grade propane, which offers the benefits of energy efficiency and minimal climate impact. But propane-powered air conditioners would need to be installed by trained personnel, unlike traditional window units, and with sales of conventional air-conditioning units continuing at a brisk pace and uneven regulation of HFCs worldwide, there's been little motivation to try moving them to the marketplace.

Zaelke says a movement has begun among the Montreal Protocol signatories to address HFCs even though they are not ozone depleters, on the grounds that increased HFC emissions are a result of decisions made under the Protocol. The Federated States of Micronesia, concerned about rising sea levels, last year issued a call seeking a phase-down on the production and use of these chemicals.[13] The United States, Canada, and Mexico similarly have called for a formal amendment to the treaty to phase down HFCs.[14] More than 110 of the Protocol's 197 signatories have shown their support. Clearly, continued movement in that direction would provide a greater stimulus to the search for new refrigerants, as will a measure proposed by the European Commission in November 2012 to reduce HCF emissions in European countries.[15] But when the Montreal Protocol parties met in Geneva in November 2012, a small number of nations blocked progress on the amendments.[16]

Meanwhile, engineers are building more efficient air conditioners that draw less heavily on power supplies. For many years the Japanese government has pursued a number of measures to reduce electrical demand, including an initiative called the Top Runner Program.[17] The program sets efficiency standards for electrical products, including air conditioners, by identifying the most efficient ones being produced and establishing that performance level as the new baseline that other manufacturers must match.

Although energy efficiency provides many benefits that make it worthwhile to pursue, Zaelke and Cox note that improving the operating efficiency of air conditioners may have less impact on reducing global warming than one might anticipate. "There's this rebound effect," Zaelke says. "You improve the efficiency by fifty percent, so people say, 'It only costs me half as much, so I can use more.'"

Cox provides numbers to support this assessment: He says residential air-conditioning units used in the United States between 1993 and 2005 increased in overall efficiency by 28%—which he calls "pretty significant"—but the amount of energy used to cool the average air-conditioned U.S. home went up 37% during those same 12 years.[18]

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