A novel hybrid steady-state model based controller for simultaneous indoor air temperature and humidity control

Due to the strong coupling between two control loops, it is always a challenge to develop appropriate control algorithm for simultaneously controlling indoor air temperature and humidity using a direct expansion (DX) air conditioning (A/C) system, making it an engineering application where no expert experience is available. Although the control performance of a steady state model based controller (SSMBC) was normally regarded to be not comparable to that of a dynamic model based controller, the successful development of a SSMBC may provide new insights of the control mechanism. In this paper, a SSMBC was developed based on a previous developed steady state model of a DX A/C system. Its control performance was theoretically analyzed and experimentally tested. It was proven that by utilizing a specific activating method, the SSMBC could achieve much better control performance than that of a traditional On-Off control method. However, the SSMBC could be further improved. Based on the theoretical analysis of the interaction between the changes of system operating states and those of indoor air thermal states, a hybrid SSMBC, which consisted of a SSMBC and a stabilizing controller, was further developed. The accuracy and sensitivity of the novel hybrid SSMBC are experimentally validated.