Dynamic simulation and analysis of a water chiller refrigeration system

In this paper, a lumped-parameter dynamic model of a water chiller refrigeration system based on mass and energy balance principles is developed. First the component models for an evaporator, compressor, condenser and a thermostatic expansion valve (TEV) were derived. These models were integrated to develop an overall model of a water chiller system. A control-oriented approach to model development was taken and the effect of control inputs such as compressor operational frequency and TEV opening fraction on the output performance of the system was investigated. The transient response characteristics show that the thermal system responses are much slower than pressure and mass flow rate responses revealing a two time-scale property of the system. Steady state performance of the system is also analyzed and graphical relationships between refrigerant mass flow rate, suction vapor superheat temperature, operation frequency and thermostatic expansion valve opening fraction are presented.