A dynamic dehumidifier model for simulations and control of liquid desiccant hybrid air conditioning systems

Abstract

Liquid desiccant (LD) dehumidification has attracted increasing attentions and its applications in air conditioning are emerging in recent years. The dynamic characteristics of the dehumidifier are essential to design and tune controllers for LD hybrid air conditioning systems. Existing research on liquid desiccant dehumidifier focuses on steady state condition. There is a lack of a computationally efficient yet accurate dynamic dehumidifier model for the purpose of control and dynamic simulations. This study develops a simplified one-dimensional dynamic model of a counter flow packed-type dehumidifier. The approach to quantifying the thermal mass of packing material and desiccant solution held in dehumidifier is developed for the first time and implemented in the dynamic model. Validation results show that the dynamic model is in better agreement with experiment than the static model. Root-Mean-Square Errors (RMSEs) between the simulation results of dynamic model and the experimental results are about 0.2 g/kg for the outlet air humidity ratio and 0.2 °C for the outlet air temperature. In addition, sensitivity analysis is conducted to investigate the effects of the thermal mass on the dehumidifier dynamics. The dynamic model and the results are valuable to design and tune controllers and dynamic simulations of the LD hybrid air conditioning systems.