Refrigeration systems can undergo many faults that could negatively affect their operation and performance. This paper describes a modeling process to simulate the fault impacts on the operation of a commercial walk-in freezer using semi-empirical models. These models often require less modeling effort than full forward models and could be used in scenarios where detailed information is missing, such as in field-measured systems. An important characteristic of a typical walk-in refrigeration system is the existence of a liquid-line receiver after the condenser, which significantly changes the behavior of the cycle, in comparison to a receiver-less system. Component models described in this paper consist of: a compressor, two heat exchangers, pipelines, receiver, and thermostatic expansion valve. The semi-empirical component models are partially based on physics, and partially based on some empirical coefficients. They are able to predict several dependent variables, including mass flow rates, heat transfer rates, power consumption, and pressures. In this paper, the individual component models are presented and trained with a limited set of faulted and fault-free experimental data. The faults are: heat exchanger fouling, liquid-line restriction, and compressor valve leakage. The results show that models for major components, such as compressor and heat exchangers, give good predictions for some of the most important performance indices. Modeling challenges and future research are outlined.
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