The accurate control of temperature and relative humidity during cooling and dehumidifying air conditioning processes may be achieved by compressor and evaporator fan speed variation. Proportional-integral-differential (PID) control methods are shown to be suitable for attaining compressor and evaporator fan speeds such that the sensible and latent components of the refrigeration system capacity equal the sensible and latent components of the system load. The feasibility of the control method has been verified experimentally. A numerical model of an environmental control system, including refrigeration, space, and PID control sub-systems, has been developed. The model is suitable for determining system response to variations of PID coefficient values and to variations of system loads.

KEYWORDS: year 1995, temperature, relative humidity, controls, cooling, dehumidifying, compressors, evaporators, fans, speed, air conditioning, calculating, industrial, variable speed motors, inverters, refrigeration