Mathematical modelling of supermarket refrigeration systems for design, energy prediction and control

This paper describes a mathematical model developed to simulate the performance of supermarket refrigeration systems. Such a model can be used for the comparison of different systems and control strategies in terms of their energy and total equivalent warming impact. The model is based on a large number of component models which have been linked together within the TRNSYS environment. Major component models include the compressor, air-cooled condenser, thermostatic expansion valve, display cabinet and control. The overall system model has been validated against monitored data obtained from both a laboratory-based system and a full-scale system in a supermarket in Scotland. The value of the model is illustrated by determining and comparing the effectiveness of head pressure and variable-speed control against fixed head pressure and constant speed control. It is shown that even at summer ambient conditions the system can be operated without problems at much lower head pressures than is done in practice under fixed-pressure control strategies. The use of variable-speed control on one of the compressors can also provide better control of the suction pressure and a substantial (up to 23 per cent) energy savings compared to on-off control.