Investigation of faults and condition analysis of refrigerant compressors.

We support the industry in its efforts to develop environmentally friendly, energy-efficient and reliable refrigeration systems and heat pumps based on the cold vapour process. In practice, the regulations under the F-Gas Regulation and PEFAS mean increased use of flammable refrigerants (R) in classes A2 and A3. In addition to investigating incidents in refrigeration systems and heat pumps, a key focus of our activities is the condition analysis of refrigerant compressors. We can draw on our many years of experience in analysing different compressor designs (Figure 1) to provide recommendations and guidance on the continued operation of compressors and system behaviour (Figure 2).

The ILK is involved in these consultations and tasks through:

• consultancy services for compressor or system manufacturers, ranging from very small companies with niche refrigeration products to major market leaders with a variety of issues,
• provision of both internal and external test benches with differentiated characteristics for standardised performance tests on compressors or service life tests (see standards),
• Condition analyses of refrigerant compressors from the field, and
• Root cause analysis in the event of damage to systems or compressors.for various applications (heat pumps, tumble dryers, commercial refrigeration applications, mobile refrigeration/air conditioning units), compressor types (primarily reciprocating, scroll and rotary compressors, as well as screw compressors) and power ratings (… > 100 kW).

The services offered include, amongst other things:

1. Condition analysis of refrigerant compressors
2. Identification of the causes of damage to the compressor
3. Recommendations for continued operation following random sampling analysis from the field
4. The definition of LifeTimeTests (LTT) (e.g. 500 h) with varying stress levels within and outside the compressor operating envelope (liquid, continuous operation, frequency, pressure ratio, etc.)
5. The implementation of these various test programmes to determine the service life of the compressor type on a suitable test bench, followed by an analysis of the compressor.

For many years, the ILK has analysed compressors of various designs and has been able to provide guidance on continued compressor operation and system behaviour.

In a condition analysis of the compressor, we examine

• potential damage resulting from field operation or following completion of an LTT500 load cycle test,
• based on macroscopic mechanical wear characteristics, the motor’s electrical properties and the condition of the oil,
• potential causes of damage to the compressor and provideguidance on continued operation following a random sample analysis from the field. Optionally, a technical assessment of the compressor in accordance with VDI Guideline 2225 (objectification of characteristics without directly measurable comparative parameters) can be included: → Running pattern (running marks, grooves, scoring, copper plating) → Wear (edge chipping, dents, deposits, complete fracture, etc.) → Oil analysis following use in the compressor.

In the LifeTimeTest LTT500, we test the long-term thermal/mechanical behaviour and the interaction between the compressor, heat exchanger (A1, A2/L and A3) and oil:

• in accordance with the customer’s specific requirements or
• in accordance with our ILK standard procedure over approx. 500 hours:
  o under defined variable loads within the compressor’s operating map (stress levels 1 … 6)
  o with exceeding of permissible operating parameters (on/off cycles, reduced superheat, oscillation, liquid) and with
  o analysis of the temporal development of the compressor parameters at the reference point (in accordance with DIN EN 13771-1).