An experimental study on the inherent operational characteristics of a direct expansion (DX) air conditioning (A/C) unit

For residential buildings located in the subtropics, direct expansion (DX) air conditioning (A/C) units are commonly used for environmental control. However, the use of standard DX A/C units having constant-speed compressor and relying on on–off cycling often leads to either space overcooling or an uncontrolled indoor humidity level, due to high latent cooling load resulted from hot and humid climates. This paper reports on an experimental study to investigate the inherent operational characteristics of a DX A/C unit at a fixed inlet air state when the speeds of both its compressor and supply fan are varied. The experimental results of the inherent operational characteristics related to both equipment sensible heat ratio (SHR) and operating efficiency are reported. Issues related to the practical applications of the inherent characteristics and their possible constrains are discussed.