Figure 3: Absorption of moisture in ester oil in comparison to mineral oil in [ppm] by weight at 25°C and 50% relative
humidity. h = hours.
7 Accumulators
An accumulator is normally not required in dedicated heat pump applications.
Durability is ensured by the Copeland Scroll’s inherent ability to handle liquid
refrigerant in flooded start and defrost cycle operation. However, large volumes of
liquid refrigerant which repeatedly flood back to the compressor during normal off
cycles or excessive liquid refrigerant floodback during steady operation can dilute
the oil in any compressor to the point where bearings become inadequately
lubricated and wear may occur. If an accumulator is fitted, and there is no
crankcase heater, it should be piped to allow free liquid drainage during the off
cycle as shown in Figure 4.
Figure 4: Accumulator
8 Crankcase
Heaters
No crankcase heater (CCH) is required when the system charge does not
exceed 7.5 kg. A CCH is to prevent refrigerant migrating into the shell during
standstill periods. It is recommended to fit a CCH if the compressor is located
outside the building, the system charge is above the limits shown. For correct
mounting location of a CCH please see Figure 5.
Fig. 5: Crankcase heater location
9 Screens
The use of screens finer than 30 x 30 mesh (0,6 mm² openings) anywhere in the system is not recommended. Field
experience has shown that finer mesh screens used to protect thermal expansion valves, capillary tubes, or
accumulators could become temporarily or permanently plugged. Such blockage can result in compressor failure.
10 Pump
down
To control refrigerant migration a pump down system could be used. The discharge check valve with refrigeration
scroll compressor is designed for low leak back, and will allow the use of a pump down without the addition of an
external check valve. If the compressor is stationary for prolonged periods, refrigerant could migrate into the
compressor and therefore a crankcase heater must be installed. If constant cold air is drawn over the compressor,
this could make the crankcase heater ineffective, and therefore a pump down system is recommended.
C6.2.16/1004/E 5
