Heat pump is a device used to transfer heat from source to sink with the use of small energy. In simple words, Heat pump absorbs heat from cold zone and transfers to the hot zone.
Common type of heat pumps is based on refrigeration system which absorbs heat at evaporator and recovered at condenser. While operating heat pump condensers of refrigeration system are used to recover heat as shown below:-
Typically for HVAC application heat pumps are 3-4 times efficient than direct heating, apart from generating heat chilling effect can be simultaneously generated from the evaporator end of refrigeration system. COP of refrigeration system decided how much extra heat that supplied can be generated from heat pump. Suppose a refrigeration system is designed to operate at 4.5 COPR, COP of heat pump shall be
COPHP =COP R+ 1
Therefore, heat recovery in refrigeration type heat pump shall be Refrigerating effect + work done. Both vapour compression refrigeration system VCR and vapour absorption machine (VAM) type refrigeration system can be used as heat pump based on operating temperature range.
As we know Vapor compression system is having higher COPR, heat generation at condenser end is higher than vapour absorption system, Hence VCR system is widely used for heat pump application.
All major manufacturer of refrigeration system also offers heat pump. In heat pump operational control PLC is based on condenser pressure or outlet temperature of media. Also as the heat pump system are used to generate heat at higher temperature, refrigerant is operated at higher pressure therefore extra safety care is taken for the design of heat exchanger, piping and controls.
Application of heat pump:-
- Heat pump can be used to generate hot water efficiently upto 70 DegC.
- Used to preheat air after dehumidification in HVAC system.
- For comfort conditioning in winter season.
- For various heating application in process industry.
Limitation of heat pump:-
- Operating temperature is major limitation of heat pump as heat pumps are generally efficient below 70 deg C.
- Initial cost is high in comparison to direct heating.