Thermoeconomic Diagnosis of Air conditioning Systems: an Innovative Approach for Improved Reliability of the Technique

Thermoeconomic diagnosis is an exergy-based fault detection and diagnosis technique which has been recently extended to air conditioning systems. One of the main features of this technique is to provide quantitative information of the impact of each fault on the increased energy consumption of a system. This information is then used for programming cost-effective maintenance strategies. Only few papers have focused on it and a lot of work is needed for further improvements. In this work, the approach was developed by means of experimental activities carried out on a 17.5 kW packaged rooftop air conditioning unit (RTU). The RTU was tested in psychrometric chambers under a wide range of operating conditions and fault levels. Two faults that are commonly found in rooftop systems were investigated: (i) evaporator fouling and (ii) condenser fouling. Also, scenarios involving the presence of multiple faults were investigated. Experimental data were used to refine and improve the innovative thermoeconomic model proposed by some of the authors, in order to improve the technique performance. To this aim, a sensitivity analysis of some thermoeconomic parameters with a boundary conditions set was carried out. Results showed a great sensitivity with the temperature of the outdoor environment and some correlations were derived and then included within the thermoeconomic model. Also, an exergy modelling of the compressor behavior was carried out in order to filter the extra irreversibility generated in this component by faults occurring in the condenser and in the evaporator. After filtering the extra irreversibility on the compressor, results showed an improvement of the technique performance.