A study of an air-conditioning control system using a variable speed compressor and a variable speed evaporator fan

Relative humidity and temperature are the two essential parameters to be controlled in air-conditioning practice. In this research, a Proportional-Integral-Derivative (PID) control system to simultaneously control space air temperature and space relative humidity was studied. This system employed two PID control loops. One loop controlled evaporator fan motor speed, which varied the evaporator air flow rate, in order to control space relative humidity. The other loop was utilized to control the compressor motor speed, thus varying the compressor volumetric displacement rate, in order to control space air temperature. The experimental results show the system maintained space temperature within ;A numerical air-conditioning system model, which is derived from the Krakow and Lin (1986) heat pump model, was developed in this work. The model employed three-region evaporator model by Oskarsson et al. (1989). The model was utilized to study the air-conditioning system performance characteristics and to create performance maps. The performance maps were utilized to determine the range of sensible and latent system capacities over which the system may be controlled by varying the evaporator air flow rate and compressor volumetric displacement rate.