Energy recovery system in use (see drawing)
Bypass valves in position (A): the heat exchanger (HE) is integrated in the water side of the ER
• 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.
2. Depressurize the compressor and drain the oil by opening the drain valve. Also drain the oil from the
heat exchanger by opening the drain valve on the heat exchanger (HE). Close the valve after draining.
Instruction book
2920 7109 23
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