Health Monitoring and Aging Assessment of HVAC Refrigerant Compressors in Railway Systems

An innovative method to evaluate the health of a refrigerant compressor in railway Heating, Ventilation and Air Conditioning (HVAC) systems is described. The performance of the air conditioning unit is highly dependent on the state of health of the compressor. Degradations and faults of this component have a detrimental impact on the operation of the HVAC and may severely affect the comfort of the passengers. A compressor health indicator-based monitoring approach has been developed in the present study. The construction of the health indicator is based on the assessment of the thermodynamic efficiency of the compressor, which is calculated using sensor data collected from the HVAC unit. Unlike other existing efficiency-based methods, the proposed approach also accounts for the ageing process of the compressing system and for the wear associated with usage. The method has been applied first on a real HVAC in a laboratory environment, in order to simulate the effects of performance degradations. Subsequently, a demonstrator unit has been instrumented and installed on a tramway in commercial service to observe the behavior of the health monitoring system in field conditions. The results of the test bench study and the observations from the field confirm that the proposed health indicator-based monitoring method is effective for the implementation of condition-based maintenance strategies of refrigerant compressors in railways.