2.1. The heat balance approach
One of the primary purposes of heating, ventilating and air conditioning (HVAC) systems is to make occupants comfortable in terms of thermal comfort. The indicator of human thermal comfort is technically called the thermal comfort index. The most widely used thermal comfort index is the Predicted Mean Vote (PMV) index, which was developed by Fanger [35,36]. Practical applica- tion of the heat balance equation was proposed [6] by formulating a thermal comfort equation which allows the prediction of the thermal sensation of a group of persons in an arbitrary but stationary climate via Predicted Mean Vote (PMV).