What Is a Heat Pump and How Does It Work?
A heat pump is an electrical device that extracts heat from one place
and transfers it to another. The heat pump is not a new technology; it
has been used in Canada and around the world for decades. Refrigerators
and air conditioners are both common examples of this technology.
Figure 1: Basic Heat Pump Cycle
Heat pumps transfer heat by circulating a substance called a refrigerant
through a cycle of evaporation and condensation (see Figure
1). A compressor pumps the refrigerant between two heat exchanger
coils. In one coil, the refrigerant is evaporated at low pressure and
absorbs heat from its surroundings. The refrigerant is then compressed
en route to the other coil, where it condenses at high pressure. At this
point, it releases the heat it absorbed earlier in the cycle.
Refrigerators and air conditioners are both examples of heat pumps operating
only in the cooling mode. A refrigerator is essentially an insulated box
with a heat pump system connected to it. The evaporator coil is located
inside the box, usually in the freezer compartment. Heat is absorbed from
this location and transferred outside, usually behind or underneath the
unit where the condenser coil is located. Similarly, an air conditioner
transfers heat from inside a house to the outdoors.
The heat pump cycle is fully reversible, and heat pumps can provide year-round
climate control for your home – heating in winter and cooling and
dehumidifying in summer. Since the ground and air outside always contain
some heat, a heat pump can supply heat to a house even on cold winter
days. In fact, air at –18°C contains about 85 percent of the
heat it contained at 21°C.
An air-source heat pump absorbs heat from the outdoor air in winter and
rejects heat into outdoor air in summer. It is the most common type of
heat pump found in Canadian homes at this time. However, ground-source
(also called earth-energy, geothermal, geoexchange) heat pumps, which
draw heat from the ground or ground water, are becoming more widely used,
particularly in British Columbia, the Prairies and Central Canada.
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