• Compressor start-up
When the compressor is started up from cold, the oil temperature will be low. Bypass valve (BV1)
shuts off the oil supply to the oil cooling system to prevent the compressor oil from being cooled.
The oil flows from the oil separator vessel (AR) through the oil filter(s) (OF) back to compressor
element (E).
All energy input is used to rapidly warm up the compressor oil. No energy is recovered.
• Maximum energy recovery
As soon as the oil temperature reaches the set point (opening temperature) of bypass valve
(BV1), the valve starts closing off the bypass over the oil cooling system, gradually allowing the
oil to flow through the heat exchanger (HE). As the oil temperature rises to approx. 75 ˚C (167
˚F) , all the oil passes through the cooling system. The exchange of heat between the
compressor oil and the heat recovery water is maximum. The oil from the heat exchanger outlet
flows via oil filter (OF), compressor element (E) and separator (AR) back to the inlet of heat
exchanger (HE).
Bypass valve (BV2) bypasses the main oil cooler (Co) as long as the oil temperature remains
below its set point.
Operation principle at different loads:
• Low consumption of recovered energy
The temperature of the oil leaving heat exchanger (HE) rises. When the temperature rises
above its set point, oil cooler bypass valve (BV2) will gradually allow the oil to be cooled in
the oil cooler (Co).
• Recovery water flow too high/temperature too low
In this case, bypass valve (BV1) will open the bypass line allowing oil from heat exchanger
(HE) to be mixed with oil from separator (AR). Energy is transferred from the compressor oil
to the water, but at a relatively low temperature level.
Energy recovery system not in use
Bypass valves in position (B): the heat exchanger (HE) is bypassed in the water side of the ER.
The oil circuit is the same as without installation of the energy recovery system.
No energy is recovered.
This situation should be considered as exceptional, e.g. in case of maintenance of the energy
recovery system or when no energy is required for a long period.
Stopping the unit for a long period
In case of an open water system and/or if freezing temperatures can be expected, isolate the
compressor water system and blow it through with compressed air.
5.1.4 Maintenance
Compressor oil
For references used consult section Energy recovery unit.
Oil change:
1. Run the unit until warm. Stop the unit, switch off the isolating switch and close the air outlet
valve of the compressor.
Instruction book
70 2920 7110 05
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