Multivariable control of indoor air temperature and humidity in a direct expansion (DX) air conditioning (A/C) system

Research output: Chapter in book / Conference proceedingConference article published in proceeding or bookAcademic researchpeer-review

2 Citations (Scopus)

Abstract

Controlling indoor humidity at an appropriate level is very important since this affects occupants' thermal comfort and indoor air quality (IAQ). The paper presents an investigation on developing a multi-input multi-output (MIMO) control strategy for simultaneously controlling the indoor air temperature and humidity by varying the speeds of both compressor and supply fan in an experimental DX A/C system. The MIMO-based controller was designed based on the linearized dynamic model of the experimental DX A/C system. The Linear Quadratic Gaussian (LQG) technique was used in designing the MIMO-based controller. The controllability tests with respect to both the disturbance rejection capability and the command following capability were carried out to assess the control performance of MIMO controller. The results of disturbance rejection capability test showed that the MIMO control strategy can effectively maintain the indoor air temperature and humidity to their respective settings after an unmeasured heat load disturbance was imposed, by simultaneously varying speeds of both the compressor and the supply fan of the DX A/C system. Furthermore, in the command following capability test for indoor air temperature, the test results showed that the indoor air temperature can be controlled to its new setting while indoor humidity remained unchanged. Similar test results were also observed in the command following capability test for indoor humidity. Therefore, the MIMO controller developed can effectively control indoor air temperature and humidity simultaneously by varying compressor speed and supply fan speed of the DX A/C system. Compared to the previous related studies using conventional on-off control method or single-input single-output (SISO) control strategy which can only effectively control either air temperature or relative humidity, the MIMO controller can simultaneously control the indoor air temperature and humidity with adequate control sensitivity and accuracy. The application of MIMO control strategy developed can be extended to other HVAC systems in the future to improve their operating performance and energy efficiency.
Original languageEnglish
Title of host publicationProceedings of the 1st International Postgraduate Conference on Infrastructure and Environment, IPCIE 2009
Pages62-69
Number of pages8
Publication statusPublished - 1 Dec 2009
Event1st International Postgraduate Conference on Infrastructure and Environment, IPCIE 2009 - Hong Kong, Hong Kong
Duration: 5 Jun 20096 Jun 2009

Conference

Conference1st International Postgraduate Conference on Infrastructure and Environment, IPCIE 2009
CountryHong Kong
CityHong Kong
Period5/06/096/06/09

Keywords

  • Air Conditioning System
  • Direct expansion
  • Multivariable Control
  • Temperature and humidity

ASJC Scopus subject areas

  • Building and Construction
  • Environmental Science(all)

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