Evaluation Method of Thermal Sensation and Comfort for Air Conditioning Performance Reduction

As a method of maintaining thermal sensation and comfort inside a passenger compartment, not only a conventional HVAC system but also a combination of a HVAC system and other devices such as seat heaters, a steering wheel heater, ventilation seats are increasing. This research developed a method to evaluate thermal sensation of a human body when using these various thermal control devices. This method can evaluate the heat balance of the human body by calculating the amount of heat exchange between a human body and the external environment, and it takes into consideration the influence of heat exchange by heat conduction with seats or a steering wheel. The human thermal model is made by dividing a human body into various segments, and it is the model that considers heat transport by blood flow for each segment. As a result of a heat balance of a human body, it is possible to derive the standard environmental temperature which is named the local-body standard new effective temperature (local SET*) for each part of a human body. Local thermal sensation is defined by a model equation that takes into consideration transient changes of a heat balance and an influence of heat storage by a whole body. Therefore, it is possible to evaluate thermal comfort of occupants in a vehicle cabin in transient and non-uniform situation. The authors conducted the experiment using actual vehicles and evaluated how much thermal sensation changes when an air conditioning system is different, using this evaluation method. Energy measurements for maintaining vehicle cabin environment and thermal sensation in the vehicle cabin were simultaneously carried out and the results of thermal sensation evaluation were shown.