RACA Journal June 2019 | Page 58

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CALCULATION OF LOW PRESSURE SWITCH SETTING
5 CUT- IN
= 236.5 kPa
BT = 3˚C (Automatic Defrost Required)
TD = 9K
ET = 6˚C = 132.9 kPa
COP = Cut out Pressure
CIP = Cut in Pressure
PD = Pressure Drop (21 kPa) (General rule)
MSP = Minimum Suction Pressure (14 kPa)
Cut out Pressure:
COP = ET - MSP - PD
COP = 132.9 - 14 - 21 kPa
COP = 97.9 kPa
Cut in Pressure
1
AVERAGE SUCTION PRESSURE
(Compressor runnning ½ way into
cycle)
4 PRESSURE DROP IN COIL
3 MINIMUM SUCTION PRESSURE
2 CUT OUT POINT
= 132,9 kPa
CIP = BT +1˚C
CIP = 3˚C + 1˚C
CIP = 4˚C (Convert to kPa)
CIP = 236,5 kPa
= 21 kPa
=14 kPa
= 97,9 kPa
Calculation of low-pressure switch settings in practice
56
RACA Journal I June 2019
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