Heat pumps use the mechanical refrigeration cycle to move heat from one place to another. Just as your fridge moves heat from inside the fridge to the kitchen, so too does your heat pump move heat from relatively cool places to warmer ones. A heat pump is even better than a fridge though: it is reversible, moving heat into the home in winter and out of the home in summer.
In simple terms, the refrigeration cycle works as follows:
- A refrigerant gas at low pressure and temperature absorbs heat through an evaporator in the location where we want to gather heat from (for example from outside in winter, from inside in summer).
- A compressor then squeezes the gas, which raises the pressure and the temperature of the gas. The heat that was absorbed is sent through a condenser to the place where we want to direct the heat (for example, inside in winter and outside in summer).
- The refrigerant is then allowed to expand at the expansion valve which lowers the pressure and temperature and the cycle starts again.
The process is reversible so that heat always travels in the desired direction: toward the inside in winter and toward the outside in summer. Heat pumps are not only used for space heating and cooling, they can also be used to heat water for domestic use or for boilers. Heat pumps of all kinds are very energy efficient because they move several times more heat energy than the systems use to drive the process. The net result is the transfer of heat from one location to another using very little added energy.