A model-based control strategy for space humidity of an independent dehumidification system

Air-conditioning system is widely used for cooling/heating buildings to provide a comfortable thermal and humid environment. It is well known that both thermal process and humid process are uncertain, nonlinear and dynamic. In many systems, the temperature and humidity are controlled independently. It is more difficult to achieve a robust and accurate humidity control than the temperature control in real systems. This paper proposes a model-based control strategy for space humidity of an independent dehumidification system, which works by regulating water flow rate of cooling coil. The aim is to improve the robustness and accuracy of the space humidity control. In this control strategy, a supply air moisture content prediction model is developed to predict the system demand supply air moisture content based on the real-time humidity load and the space moisture content. The predictive value is used as the set-point and controlled by adjusting the cold water valve opening. It can guarantee that the dehumidification capacity of the dehumidification system is always satisfied the humidity load demand. Then the robust control of the space humidity is realized. Further, TRNSYS software was used to build a simulation platform of the independent dehumidification system to test the control performance of the proposed control strategy. The test results show that compared with the conventional method that tracks the space humidity by PI control algorithm directly, the proposed control strategy can improve the robustness and accuracy of the space air humidity control significantly.