What is the most common way to cool your home?

In the U.S., most households—around 75%—rely on air conditioning to keep their living spaces comfortable. These cooling systems are a substantial electricity consumer, drawing about 6% of the nation’s power, which translates to homeowners spending roughly $29 billion on energy costs each year. The environmental toll is also notable, with an estimated 117 million metric tons of carbon dioxide emitted annually due to air conditioning use.

Air conditioners work on principles similar to those of a refrigerator, transferring heat from inside a building to the outside air. An air conditioning unit consists of two key parts: the indoor unit, which features an evaporator coil to cool the indoor air, and the outdoor unit, which houses a condenser coil to expel the heat outside.

The system uses a compressor to circulate a refrigerant between these coils. The refrigerant absorbs heat as it vaporizes in the evaporator coil, cooling the indoor air. The refrigerant is then compressed and sent outside to the condenser coil, releasing the absorbed heat into the outdoor air as it condenses into liquid.

Previously, air conditioners commonly employed chlorofluorocarbons (CFCs) as the cooling agent. However, due to their damaging effect on the ozone layer, the U.S. phased out CFC production in 1995. The refrigerants that followed, mainly halogenated chlorofluorocarbons (HCFCs), have also been subject to phase-out processes, with the most recent version, HCFC-22, being banned entirely in 2020.

Today, the shift has been towards using environmentally friendly hydrofluorocarbons (HFCs) and other alternative refrigerants, including ammonia, which do not harm the ozone layer and are expected to grow in usage in the cooling market.