A new control algorithm for direct expansion air conditioning systems for improved indoor humidity control and energy efficiency

This paper presents an experimental study to develop a new control algorithm to replace the traditional on–off control algorithm widely used by direct expansion (DX) air conditioning (A/C) systems, which are widely used in small to medium sized buildings. The new control algorithm, which enables both the compressor and the supply air fan in a DX A/C system to operate at high speeds when the indoor air dry bulb temperature setting is not satisfied and at low speeds otherwise, is termed the H–L control. Extensive experiments have been conducted with an experimental DX A/C system at simulated different climates under both H–L and on–off control. The results suggest that the use of H–L control would result in better control performance in terms of an improved indoor humidity level and a higher energy efficiency of the DX A/C system when compared to the use of the traditional on–off control. The H–L control is also simpler, and its associated hardware cost is much lower than that of the control algorithms based on variable speed technology.