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

Xiangguo Xu, Shiming Deng, Ming Yin Jonathan Chan

Research output: Journal article publicationJournal articleAcademic researchpeer-review

33 Citations (Scopus)


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.
Original languageEnglish
Pages (from-to)578-586
Number of pages9
JournalEnergy Conversion and Management
Issue number4
Publication statusPublished - 1 Apr 2008


  • Air conditioning
  • DX
  • Energy efficiency
  • High-low speed
  • Humidity control

ASJC Scopus subject areas

  • Renewable Energy, Sustainability and the Environment
  • Nuclear Energy and Engineering
  • Fuel Technology
  • Energy Engineering and Power Technology

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