ABSTRACT

Dynamic Modeling and Gain Scheduling Control of a Chilled Water Cooling System 

Jun Liu

In this thesis, a dynamic model of a chilled water (ChW) cooling system with a stratified ChW tank was developed. The model-based analysis of the energy consumption and the cost under different control strategies were studied. The dynamic model consists of a zone, a cooling coil, a chiller, a stratified ChW tank, and a cooling tower. Nonlinear differential equations were written to describe and evaluate the performance of the entire chiller plant with the ChW tank. 

A PI-based gain scheduling (GS) control was designed and its performance was compared with the constant gain PI control by subjecting to setpoint changes and load disturbances. The simulation results showed that the system with GS control gives good control and has more stable performance.

Five different operation strategies were simulated for comparing the energy consumption and the cost of the ChW cooling system under full load and partial load conditions. The results showed that the operating strategy with optimized chilled water setpoint saved 7.16% energy (21.5% cost) compared to the case with constant setpoint. These savings were more significant (36%) under partial load conditions. 

The gain scheduling control with optimal setpoint has great potential for energy savings as demonstrated by the results presented in the thesis.