Performance maps for an air-cooled air conditioning system as a preliminary instrument for the diagnosis of evaporator fouling

Abstract

During the past few decades, there has been increased interest in the development of automated approaches for detecting and diagnosing faults in air conditioning systems. One diagnostic approach involves the use of exergy analysis. As a first step towards understanding the application of exergy analysis to diagnostics, this work is focused on the thermodynamic and exergy analysis of a direct expansion air conditioning system used in small commercial building applications. The analysis was carried out by means of experimental activities on a 17.5 kW rooftop unit installed at the Herrick Laboratories, Purdue University, Indiana (USA). The system under investigation was equipped with a variable-speed compressor and variable-speed fans, thus allowing the unit to meet different loads without cycling on-off. A detailed mapping of the performance of this system was carried out by considering the effect of the outdoor temperature and the cooling load. In addition, the effect of evaporator fouling was considered. Results showed that poor exergy performance are achieved, regardless the outdoor temperature and the cooling capacity tested. This fact is easily explained by considering the exergy destruction occurring in the evaporator. When testing evaporator fouling, exergy results showed that this fault contributed to increase mainly the consumption of the mechanical exergy of the air, thus allowing for an easy detection of this fault.