Thermoeconomic analysis and diagnosis of a refrigeration plant

Abstract

An application of the so-called Theory of Exergetic Cost to the analysis of a conventional refrigeration plant is presented. In particular, the study of the effects induced on the overall plant by some malfunctions of its components is performed with the help of the thermoeconomic theory. When a component of a thermal plant displays a deterioration (intrinsic malfunction) not only its performance but also those of the remaining units which make up the structure are affected (induced malfunctions), as they work under operating conditions different from the usual ones. In general, this makes it difficult to understand what would be the effect of any intrinsic malfunction in terms of fuel consumption increase for the overall plant, or, in other words, to determine, for any one of the components characterised by a malfunction, how the overall cost of the final product would decrease if that malfunction were eliminated. Nevertheless, this would allow one to decide, for any one of the devices displaying deterioration, whether restoring its original efficiency is profitable or not. Of course, the exposed problem can be easily solved if a simulation programm is available, but this is not always possible, especially for very complex thermal systems. In this case, the Theory of Exergetic Cost can be successfully applied to the analysis and diagnosis of any malfunction of the system, with no need for complex mathematical tools nor computer simulation. As a first example of thermoeconomic analysis for a refrigeration system, the case of a very simple vapor compression plant is here considered. After proposing an appropriate thermoeconomic representation of the plant, in order to evaluate the exergetic costs of the physical flows which interrelate the structure, an example of application is developed. In this example, a perturbation of an assigned, initial state of the system is considered, caused by given malfunctions of its components; then, for each component displaying malfunction, the overall fuel consumption decrease (Impact on Fuel) achievable by restoring its original efficiency is evaluated by means of the previously calculated exergetic costs. The numerical example shows how the thermoeconomic approach can provide satisfactory results when compared to those of a simulation programm.