A new method for the optimal chiller sequencing control

Cooling Load based chiller sequencing Control (CLC) significantly affects the energy performance of multiple-chiller plants. The conventional CLC method has two limitations: first, it cannot guarantee the optimal load distribution; second, it may result in an inappropriate number of operating chillers. Previous research tended to address the two limitations separately. In this paper, we proposed a new CLC method that overcame the two limitations at the same time. The optimization objective is to minimize the total energy consumption of the chiller plant including chillers, cooling towers and pumps. The independent variables are the thresholds for chiller staging and the condenser water set point. We implemented this method in a Model Predictive Control (MPC) framework so that the optimization can be continuously performed according to the predicted cooling load and wet bulb temperature. To compare the performance, we also implemented two existing CLC optimization methods (the optimal load distribution method and the cooling capacity based critical points reset method) in the same MPC framework. Simulation results showed that the proposed CLC method could provide about 5.6% annual energy saving for the studied chiller plant compared to the conventional CLC. The performance of our method is also better than the other two existing CLC optimization methods.