Dynamic Simulation of Liquid Chillers

The impact of refrigeration systems on the environment can be reduced by: a) the use of alternative refrigerants which are less harmful to the environment and b) the optimisation of systems and control strategies to deliver increased levels of energy efficiency_ Mathematical modelling offers the opportunity to test the performance of systems under different operating conditions and with alternative refrigerants. Dynamic models allow comparison of both transient and steady-state behaviour and this is of particular importance for liquid chillers since these systems can operate under transient conditions for long periods. This paper covers the development of a general dynamic model for the simulation of liquid chillers. The reasons for mathematical modelling are discussed and the paper includes brief descriptions of the system component models including a semi-hermetic reciprocating compressor and thermostatic expansion valve as well as a shell-and-tube evaporator and condenser. The integration of the component models into the overall solution for a vapour compression refrigeration system is illustrated. The paper demonstrates the application of the model to predict the steady-state and dynamic performance of water-to-water chillers under a number of different operating conditions_ Predicted results are compared to experimental data from a liquid chiller test rig to demonstrate the accuracy of the modeL