Thermostatic control of the oil cooler

Oil coolers must be thermostatically controlled, 2 variants are possible:

HS. and CS. compressors are controlled according to the discharge gas temperature.
OS. compressors are controlled according to the oil injection temperature.

Control according to discharge gas temperature (HS., CS. compressors)

The sensor is attached to the discharge gas line.

The control of the oil cooler should correspond to the maximum discharge gas temperature selected in the Bitzer Software (Selecting the oil cooler with the Bitzer Software)!

The default setting in the software is 80°C for HS./OS. compressors and 110°C for CS. compressors. However, these values can be adjusted up to max. 100°C (HS./OS.) resp. 120°C (CS.).

Control of the oil cooler according to discharge gas temperature for HS. and CS. compressors
Type of oil cooler	Setting temperature	Example
air cooled oil cooler: temperature controller of the oil cooler fan	the max. discharge gas temperature chosen during selection (BITZER SOFTWARE)	selection in the Bitzer Software: max. discharge gas temperature 80°C setting temperature for oil cooler: 80°C
water cooled oil cooler: oil mixing valve or flow regulating valve (heat transfer fluid)	5K less than the max. discharge gas temperature chosen during selection (BITZER SOFTWARE)	selection in the Bitzer Software: max. discharge gas temperature 80°C setting temperature for oil cooler: 75°C
oil heater and oil thermostat integrated in the oil separator	70°C

Technical data of the oils (density, viscosity, specific heat capacity) can be taken e.g. from the respective data sheet. For Bitzer oils for CS. compressors, see also

ST-500: Bitzer refrigeration compressor oils for compact screw compressors CS., CSV.

Control according to oil injection temperature (OS. compressors)

With OS. compressors the oil injection temperature must be limited to 50°C resp. 60°C in order not to stress the shaft seal too much thermally. The sensor must be fitted to the oil injection line. Set the following as oil injection temperature:

for mineral oils (MO) of viscosity 68 cSt or poly-alpha-olefin (PAO): max. 60°C
for polyolester oil (POE) and alkylbenzene oil (AB): max. 60°C
for mineral oils (MO) of viscosity 32 or 46 cSt: max. 50°C

The viscosity and further technical data of the oils can be taken e.g. from the respective data sheet. For the oils used by Bitzer for R717 (NH₃) see also

AT-640: Use of ammonia (R717) in Bitzer compressors