Critical analysis of conventional thermoeconomic approaches to the diagnosis of multiple faults in air conditioning units: Capabilities, drawbacks and improvement directions. A case study for an air-cooled system with 120 kW capacity

Faults diagnosis in air conditioning systems is a crucial activity, since malfunctions may induce heavy degradation of performance. Among the available techniques, thermoeconomic diagnosis has played a marginal role due to the difficulties encountered when applying the methodology to refrigeration plants. In this paper a critical analysis on capabilities and limits of thermoeconomic diagnosis is proposed. The reference plant is a 120 kWc air-cooled air conditioning system; a simulator is used to evaluate thermodynamic data under normal and faulty conditions, setting up “virtual experiments” to simulate each fault. Five malfunctions are imposed, either individually or simultaneously: fouling at condenser and evaporator, refrigerant undercharge, compressor valve leakage and extra-superheating along suction line. From a qualitative viewpoint, the examined approach resulted efficient in identifying some faults, although false fault signals eventually emerged. Methodological improvements were suggested, to make thermoeconomic diagnosis capable of quantifying the additional energy consumption provoked by any specific fault.

► The reliability of thermoeconomic diagnosis of an air conditioning unit is discussed.
► Single- and multi-faults operating conditions are determined by a plant simulator.
► The diagnosis technique often provides under- and over-estimation of fuel impacts.
► The limits of the procedure are mainly related with modeling the TXV.
► Improvements needed to make the methodology reliable are discussed.