Handbook of air conditioning and refrigeration / Shan K

Energy Use Index
In Eq. (9.71), m˙ r represents the mass flow rate of refrigerant, lb/min (kg/min). For reciprocating
compressors, can be calculated as
m˙ r
REFRIGERANTS, REFRIGERATION CYCLES, AND REFRIGERATION SYSTEMS 9.55
where piston displacement, cfm (or m3 /min, to be covered in Chap. 11)
�suc � density of suction vapor, lb/ft3 (kg/m 3 m˙ r � V˙ p�v�suc V˙ p �
V˙ p
)
(9.72)
Although the actual compression processes for most compressors are irreversible polytropic
processes, for simplicity, an isentropic analysis is often used. In other words, � isen is a widely used
efficiency index for refrigeration compressors, and actual power input to the compressor P com is
usually calculated by Eq. (9.71).
According to ASHRAE/IESNA Standard 90.1-1999, the following are the current energy use indices
for refrigeration compressors, packaged units, heat pumps, and chillers:
● Energy efficiency ratio (EER) is defined as the ratio of the net cooling capacity of a refrigeration
compressor, a packaged unit, or other device, in Btu/h, to the electric power input to that device,
in W, under designated operating conditions.
● SEER indicates the seasonal energy efficiency ratio. This is the total cooling capacity of a device
during its normal annual usage period, in Btu, divided by the total electric energy input during the
same period, in watt-hours.
● IPLV indicates the integrated part-load value. This is a single index of merit that is based on partload
EER or COP. It expresses part-load efficiency for refrigeration compressors, packaged units,
and heat pumps based on the weighted operation at various load capacities.
● HSPF indicates the heating season performance factor. This is the total heating output of a heat
pump during its normal annual usage period for heating, in Btu, divided by the total electric energy
input to the equipment during the same period, in watt-hours.
● kW/ton indicates the electric power consumption of a refrigerating compressor per ton of refrigeration
output. It is a clear and widely used energy index.
From Eq. (9.71) and because m˙ r � Qrc /qrf, the kW/ton for a hermetic refrigeration compressor
can be calculated as
� (9.73)
where Win � work input to compressor (including single-, two-, or three-stage) per lb of refrigerant
flowing through condenser, Btu/lb (kJ/kg)
qrf � refrigeration effect per lb of refrigerant flowing through condenser, Btu/lb (kJ/kg)
�isen � isentropic efficiency of compressor
�mo � motor efficiency
3.516
kW / ton �
COPref 3.516 Win qrf�isen�mo From Eq. (9.73), primary factors that affect the energy use of the kW/ton index for a refrigeration
compressor are as follows:
● Difference between the condensing and evaporating temperature T con � T ev
● Isentropic efficiency � isen or compressor efficiency � com
● Refrigeration effect of the specific refrigerant