Handbook of air conditioning and refrigeration / Shan K

11.42 CHAPTER ELEVEN
(2048 kPa abs.), and the suction pressure is 91�3 � 88 psia (607 kPa abs.) with a suction temperature
of 45°F (7.2°C). A 10 to 12°F (5.6 to 6.7°C) superheat at the outlet of the DX coil is considered
suitable. Then at an outdoor air temperature of 95°F (35°C), if the discharge/suction pressure
of the operating air-cooled DX system is around 282/73 psig (1944/503 kPag) and the superheat is
between 10 and 12°F (5.6 to 6.7°C), the refrigerant charge is considered all right.
Minimum Performance and Equipment Selection
ASHRAE/IESNA Standard 90.1-1999 mandates the minimum efficiency requirements of aircooled,
water-cooled, and evaporatively cooled packaged units for direct-expansion reciprocating
and scroll refrigeration systems. The requirements are expressed in terms of energy efficiency ratio
(EER) and integrated part-load value (IPLV) as listed in Table 11.6. When multiple rating conditions
or performance requirements are provided, the equipment shall satisfy all stated requirements
unless otherwise exempted. The selected air-cooled packaged unit should meet the minimum performance
guidelines at both design and part-load operation.
11.9 ROTARY REFRIGERATION SYSTEMS
Rotary Compressor
Rotary refrigeration systems using rotary compressors are widely adopted in small refrigeration
systems such as refrigerators, room air conditioners, and room heat pumps having a cooling capacity
from a fraction of a horsepower to about 4 hp (� 0.75 kW to 3.0 kW).
The rolling-piston rotary compressor, shown in Fig. 11.24, is the most widely used rotary compressor
in small refrigeration systems today. A rolling piston is mounted on an eccentric shaft, and a
FIGURE 11.24 A rolling-piston rotary compressor.