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The system should be evacuated down to 0.3 mbar or lower. If there is uncertainty, as to the moisture content in the
system, an oil sample should be taken and tested for moisture. Sight glass/moisture indicators currently available can
be used with the HFC refrigerants and lubricants; however, the moisture indicator will just show the moisture contents
of the refrigerant. The actual moisture level of POE would be higher than the sight glass specifies. This is a result of
the high hygroscopicity of the POE oil. Oil samples would have to be taken from the system and analyzed to
determine the actual moisture content of the lubricant.
Figure 9. Absorption of moisture in ester oil in comparison to mineral oil in [ppm] by weight at 25°C and 50% relative
humidity. h = hours.
10 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 10.
Recommended tests are described in section 22 to 24.
Figure 10. Accumulator
11 Crankcase Heaters
No crankcase heater (CCH) is required when the system charge does not
exceed 4.5 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 11.
Figure 11. Crankcase heater
C6.2.17/1004/E
10
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