Two-layer control of multi-chiller systems

In HVAC plants of medium-high cooling capacity, multiple chiller systems are often employed. The performance of the system is evaluated in terms of user comfort, energy use, and financial costs. In this paper a two-layer control structure is proposed for control and optimization of a multiple chiller system. Set points and operating modes for cooling plant equipment can be set by the supervisor to maximize overall operating efficiency. At any given time, cooling needs can be met with various combinations of modes of operation and set points. In the proposed control architecture, a cooling load estimation algorithm is employed, and the selection of the optimal set of operation modes and set point values is performed by means of a PSO algorithm. The performance of the two-layer control is evaluated by resorting to a dynamic simulation environment developed in Matlab/Simulink™, where the plant dynamics are accurately described. It is shown that the proposed technique gives superior performance with respect to standard approaches.