Handbook of air conditioning and refrigeration / Shan K

12.2 CHAPTER TWELVE
Heat Pump Cycle
A heat pump system consists of heat pumps and piping work; system components include heat
exchangers, heat source, heat sink, and controls to provide effective and energy-efficient heating
and cooling operations. HCFC-22, HFC-134a, and HFC-407C are the most widely used refrigerants
in new heat pumps. According to the data in the EIA’s Commercial Buildings Characteristics, for
the 57 billion ft 2 (5.3 m 2 ) of air conditioned commercial building floor area in the United States in
1992, the use of heat pumps for heating and cooling was about 15 percent (by floor space).
A heat pump cycle comprises the same processes and sequencing order as a refrigeration cycle except
that the refrigeration effect q 1�4 or q rf, and the heat pump effect q 2�3�, both in Btu/lb (J/kg), are
the useful effects, as shown in Fig. 12.1. As defined in Eqs. (9.7) and (9.9), the coefficient of performance
of a refrigeration system COP ref is
COP ref � h 1� � h 4
W
(12.1)
where h 4, h 1� � enthalpy of refrigerant entering and leaving evaporator, respectively, Btu/lb (J/kg)
W in � work input, Btu/lb (J/kg)
The coefficient of performance of the heating effect in a heat pump system COP hp is
COP hp � q 2�3�
W in
and the useful heating effect q 2�3� can be calculated as
� q 1�4
W in
q 2�3� � h 2� � h 3� � h 1� � h 4 � h 2� � h 1�
FIGURE 12.1 Heat pump cycle: (a) schematic diagram; (b) cycle on p-h diagram.
(12.2)
(12.3)