Innovative thermoeconomic diagnosis of multiple faults in air conditioning units: Methodological improvements and increased reliability of results

• An improved thermoeconomic diagnosis of refrigeration systems is proposed.
• Condenser and expansion valve are both modelled as dissipative units.
• Filtering the effects of refrigerant undercharge improves the performance of diagnosis.
• Appropriate distribution ratios must be accurately fixed to increase diagnostic performance.
• The method was tested for several multiple faults scenarios, resulting sufficiently reliable.

Thermoeconomic faults diagnosis of air conditioning units is a pioneeristic approach to detect single or multiple faults and quantify their impact in terms of additional energy consumption. The poor reliability of conventional thermoeconomic approaches has been limiting the interest for practical applications of this technique. In this paper an improved thermoeconomic diagnosis is proposed and applied to a reference 120 kWc air-cooled air conditioning system; a simulator is used to evaluate thermodynamic data under normal and faulty conditions. Four faults are individually or simultaneously imposed: fouling at condenser and evaporator, refrigerant undercharge and compressor valve leakage. For setting up the diagnostic tool only a few numerical or experimental tests are required; the results testify the procedure to be sufficiently reliable both when heavy or light faults are considered. Also, the performance of the diagnostic procedure slightly improves when the effects of “system level” faults like refrigerant undercharge are preliminarily filtered.