A Thermal Comfort based Controller for a Direct Expansion Air Conditioning System

For building HVAC systems, better indoor thermal comfort control and higher energy efficiency could be achieved using a thermal comfort index as the controlled variable instead of air temperature. Although there can be various simplification approaches, indoor air humidity has been commonly assumed constant or left uncontrolled. Neglecting the importance of indoor humidity control would adversely affect the control performance of an air conditioning system. In addition, it is difficult to control local air velocity in the vicinity of a user. Therefore, either a constant local air velocity or an air velocity varying to a preset pattern was assumed in a thermal comfort model. In this paper, a thermal comfort based controller is developed and reported. Controllability tests were carried out which showed that better energy efficiency of the DX A/C system could be achieved when a higher local fan speed was used.