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 around the world for decades. Refrigerators and air conditioners are both common examples of this technology.

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 and sent 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.

A heat pump water heater can heat or cool , the heating function is used the most, and commonly used for house heating, domestic hot water or swimming pool water heating. It absorbs heat from air or ground, then transfers the heat to water for pool water heating, room heating by radiator, underfloor coil or water fan coil. 

According to the souce of the heat , there are two types of heat pump water heater, one is air source heat pump and the other is ground source (also called earth energy, geothermal) heat pump. 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 homes at this time. A ground source heat pump which draws heat from the ground (soil, rock) or water (underground water, river, lake), are also becoming more widely used.

Heat pump is a low-carbon energy-saving product, it is high efficiency, energy-saving, safe and reliable, environmentally friendly, intelligent and durable. It can be used all year round the year. The use of heat pump will not be influenced by bad weather such as overcast, rain, snow, and it does not produce any exhaust gas, waste water and waste residue emissions. 

The operation cost of heat pump water heater is only 1/4 of the electric water heater, 1/3 of the oil and gas water heater, and 1/2 of the solar water heater, therefore installing a heat pump is an effective way to reduce our energy costs.