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Buildings and Cities

Heat Pumps

Robert Simmer, director of Stadtwerke Amstetten, a local utility company in Austria, stands in front of a heat pump designed to capture and recycle energy from the sewer.

The building sector worldwide uses approximately 32 percent of all energy generated; more than one-third of that is for heating and cooling. Maximum efficiency in heating and cooling could cut energy use by 30 to 40 percent.

The means to increase efficiency are at hand, and one technology stands out from the rest: heat pumps. Like a refrigerator, a heat pump has a compressor, condenser, expansion valve, and evaporator, and transfers heat from a cold space to a hot one. In winter, that means pulling heat from outside and sending it into a building. In summer, heat is pulled from inside and sent out. The source or sink of heat can be the ground, air, or water.

While cost can be high and efficiency fluctuates depending on local climate, heat pumps are easy to adopt, well understood, and already in use around the world. They can supply indoor heating, cooling, and hot water—all from one integrated unit. When paired with renewable energy sources and building structures designed for efficiency, heat pumps could eliminate almost all emissions from heating and cooling.


Benjamin Franklin…science of refrigeration: Isaacson, Walter. Benjamin Franklin: An American Life. New York: Simon and Schuster, 2003.

“possibility of freezing a man to death”: Franklin, Benjamin. Letter to John Lining. London, June 17, 1758.

air-conditioning…“epidemic”: “No Sweat.” Economist. January 5, 2013.

understand how this happened: Cooper, Gail. Air Conditioning America: Engineers and the Controlled Environment, 1900-1960. Baltimore: The Johns Hopkins University Press, 1998.

road civilization should never have taken: Cox, Stan. Losing Our Cool: Uncomfortable Truths About Our Air-Conditioned World (and Finding New Ways to Get Through the Summer). New York: The New Press, 2013.

[predicted] increase in AC demand: Henley, John. “World Set to Use More Energy for Cooling Than Heating.” The Guardian. October 26, 2015.

[growth of] air-conditioned homes in Chinese cities: “No Sweat,” Economist.

China will [become] leading consumer of AC: Cox, Stan. “Cooling a Warming Planet: A Global Air Conditioning Surge.” Yale Environment 360. July 10, 2012.

building sector…energy…for heating and cooling: Lucon, O., D. Ürge-Vorsatz, A. Zain Ahmed, H. Akbari, P. Bertoldi, L. F. Cabeza, N. Eyre et al. “Buildings.” In Climate Change 2014: Mitigation of Climate Change. Contribution of Working Group III to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge, UK, and New York: Cambridge University Press, 2015.

unit of electricity consumed…five units of heat energy…transferred: IEA. Transition to Sustainable Buildings Strategies and Opportunities to 2050. Paris: International Energy Agency, 2013.

[potential to] reduce…emissions: IEA HPC. Retrofit Heat Pumps for Buildings. Boras, Sweden: IEA Heat Pump Centre, 2010.

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