Development of a method for calculating steady-state equipment sensible heat ratio of direct expansion air conditioning units

A complete set of calculation method for steady-state equipment sensible heat ratio (SHR) for a direct expansion (DX) cooling coil has been developed and reported. The method was based on the fundamentals of energy conservation and heat and mass transfer taking place in the DX cooling coil, and was experimentally validated using an experimental DX A/C rig. With the method developed, the effect of refrigerant evaporating temperature at fixed inlet air conditions on equipment SHR has been theoretically analyzed. The validated method can be useful in further studying the inherent operating characteristics of a DX air conditioning (A/C) unit and in developing suitable control strategies for achieving higher energy efficiency and better indoor thermal environment.     

Indoor thermal comfort characteristics under the control of a direct expansion air conditioning unit having a variable-speed compressor and a supply air fan

Indoor thermal environment is important as it affects the health and productivity of building occupants. Direct expansion (DX) air conditioning (A/C) units are commonly used for environmental control in small- to medium-scaled buildings. This paper reports on an experimental study to investigate the indoor thermal comfort characteristics under the control of a DX A/C unit having variable-speed compressor and supply fan at a fixed space cooling load but having three different ratios between its sensible part and latent part. The experimental results suggested that under a fixed indoor total cooling load with three different space sensible heat ratios (SHRs) of 0.92, 0.72 and 0.62, varying both speeds of compressor and supply fan in the DX A/C unit would influence indoor thermal comfort. Furthermore, when a DX A/C unit having variable-speed compressor and supply fan is used for indoor thermal comfort control under abnormal indoor load conditions, its ability of indoor thermal comfort control through varying compressor speed and supply fan speed may be duly restricted.