In heat pumps of the given type the aerothermal environmental energy is taken off the outside air and, owing to transformation and transfer, heats the indoor air.
The example of heat pump application is an ordinary split system (in other words, room air conditioner). As of today, the greater part of models introduced to the market of household equipment are equipped with a heat pump mode. To fulfill this capability a four-way valve is to be a part of air conditioner circuit, aside from main elements of refrigeration unit (compressor, condenser, evaporator, thermal expansion valve). It enables to reverse the refrigerant direction, thus, the condenser “turns into” the evaporator and vice versa. As a result, the indoor air being cooled in conditioner mode and after switching over into heat pump mode is heated.
The operation principle of air-to-air heat pump is shown in figure 2.1.
Designations on the diagram
② – air-cooled condenser (air heater)
③ – thermal expansion valve
④ – air-cooled evaporator and fan assembly
|Medium reference designation||Name||State|
|ⓐ||Outdoor air at the heat pump evaporator inlet||Gas|
|ⓑ||Cooled outdoor air at the heat pump evaporator outlet|
|ⓒ||Indoor air at the heat pump condenser (heater) inlet|
|ⓓ||Preheated indoor air at the heat pump condenser (heater) outlet|
|ⓖ||Refrigerant suction by means of compressor||Gas|
|ⓗ||Refrigerant discharge into condenser||Gas|
|ⓚ||Condensed refrigerant supply to thermal expansion valve||Liquid|
|ⓜ||Refrigerant supply into evaporator||Vapour-liquid mixture|
The operation principle description. The refrigerant boils in the evaporator (pos. 4) taking off the desired low-grade heat from a natural source – in this case from the air. Then the evaporated refrigerant passes to the compressor (pos. 1). The compressor compresses refrigerant vapours, hence, heating them to the temperature in a range of 90-130 °С and discharges them into the condenser (pos. 2). In the condenser air duct the indoor air is heated, cooling and condensing the refrigerant to the liquid state in a freon cavity of the given heat exchanger. The liquid refrigerant is directed to the thermal expansion valve (pos. 3), in which the expansion pressure sharp drop takes place. After TEV the refrigerant comes to the evaporator and the cycle begins to repeat.