So, what is a heat pump? A heat pump is part of a home heating and cooling system and is installed outside your home. Like an air conditioner such as central air, it can cool your home, but it’s also capable of providing heat. In cooler months, a heat pump pulls heat from the cold outdoor air and transfers it indoors, and in warmer months, it pulls heat out of indoor air to cool your home. They are powered by electricity and transfer heat using refrigerant to provide comfort all year round. Because they handle both cooling and heating, homeowners may not need to install separate systems to heat their homes. In colder climates, an electric heat strip can be added to the indoor fan coil for additional capabilities. Heat pumps do not burn fossil fuel like furnaces do, making them more environmentally friendly.
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A Heat pump in heating mode operates just like cooling mode, except that the flow of refrigerant is reversed by the aptly named reversing valve. The flow reversal means that the heating source becomes the outside air (even when outdoor temperatures are low) and the heat energy is released inside the home. The outside coil now has the function of an evaporator, and the indoor coil now has the role of the condenser.
The physics of the process are the same. Heat energy is absorbed in the outdoor unit by cool liquid refrigerant, turning it into cold gas. Pressure is then applied to the cold gas, turning it to hot gas. The hot gas is cooled in the indoor unit by passing air, heating the air and condensing the the gas to warm liquid. The warm liquid is relieved of pressure as it enters the outdoor unit, turning it to cool liquid and renewing the cycle.