Heat pump

A heat pump is a device that transfers heat energy from a source of heat to what is called a heat sink. Heat pumps move thermal energy in the opposite direction of spontaneous heat transfer, by absorbing heat from a cold space and releasing it to a warmer one. A heat pump uses external power to accomplish the work of transferring energy from the heat source to the heat sink.The most common design of a heat pump involves four main components – a condenser, an expansion valve, an evaporator and a compressor. The heat transfer medium circulated through these components is called refrigerant.Heat pump coils ready for immersionCoils being immersed in pond A heat pump is a device that transfers heat energy from a source of heat to what is called a heat sink. Heat pumps move thermal energy in the opposite direction of spontaneous heat transfer, by absorbing heat from a cold space and releasing it to a warmer one. A heat pump uses external power to accomplish the work of transferring energy from the heat source to the heat sink.The most common design of a heat pump involves four main components – a condenser, an expansion valve, an evaporator and a compressor. The heat transfer medium circulated through these components is called refrigerant. While air conditioners and freezers are familiar examples of heat pumps, the term 'heat pump' is more general and applies to many heating, ventilating, and air conditioning (HVAC) devices used for space heating or space cooling. Heat pump usually can be used either in heating mode or cooling mode, as required by the user. When a heat pump is used for heating, it employs the same basic refrigeration-type cycle used by an air conditioner or a refrigerator, but in the opposite direction – releasing heat into the conditioned space rather than the surrounding environment. In this use, heat pumps generally draw heat from the cooler external air or from the ground. Heat pumps are also increasingly used to heat domestic hot water, the hot water used for kitchens, bathrooms, clothes washers, etc. In the heating mode, heat pumps are significantly more energy efficient than simple electrical resistance heaters. However, the typical cost of installing a heat pump is higher than that of a resistance heater (see below). When discussing heat pump efficiencies, the following terms are commonly used: coefficient of performance (COP), seasonal coefficient of performance (SCOP) and seasonal performance factor (SPF). The higher the number, the more efficient a heat pump is, the less energy it consumes, and the more cost-effective it is to operate. There are several factors that will affect the efficiency of a heat pump such auxiliary equipment, technology, size and control system, but also temperature and humidity conditions: the efficiency drops when the temperature difference increase or when freezing can occur. Heat energy naturally transfers from warmer places to colder spaces. However, a heat pump can reverse this process, by absorbing heat from a cold space and releasing it to a warmer one. This process requires some amount of external energy, such as electricity. In heating, ventilation and air conditioning (HVAC) systems, the term heat pump usually refers to vapor-compression refrigeration devices optimized for high efficiency in both directions of thermal energy transfer. That is, heat pumps able to provide heating or cooling to the internal space as required.