Study On Defrosting Performance Of Automobile Air Conditioning Based On Human Thermal Comfort

Automobile air conditioning(AAC) significantly impacts on driving safety and comfort of vehicles. Defrost performance is a critical part of AAC comprehensive performance. It is an important issue in AAC design to clear the frost layer on the windshield quickly and effectively and ensure interior comfort, during the defrosting system operation.In this thesis, based on the AAC system of a light vehicle, a defrosting model is established by considering the impact of occupants. According to the national standard GB 11555-2009, defrosting performance of the AAC system is analyzed by using the computational fluid dynamics(CFD) method under a condition of-18 oC. And an experimental procedure is set to verify the effectiveness of the CFD calculation model. Furthermore, the single factor analysis method is used to study the inlet and structural parameters effect on the defrosting performance. The thermal comfort of driver under defrosting condition is analyzed when the environment is-3 oC. Considering the instability of thermal environment in the vehicle, the equivalent temperature EQT is used to evaluate driver thermal comfort and to study the influence of inlet and structure parameters on thermal comfort. Finally, to optimize the defrosting system of the AAC, based on a group of selected inlet parameters, a procedure of optimal design is performed by combining the approximate model and the genetic algorithm.The study results suggest that the simulation agree with the experiment well, and it can describe the inside flow field of the vehicle with CFD analysis. The intake volume, inlet air temperature, central outlet position and outlet angle of bottom have impact on the defrosting performance. It is beneficial to defrost with the heavy air rate and high temperature. If the central outlet is too far from or close to the windshield?s bottom, it will result in the defrosting dead angle and reduce the defrosting rate for the front windshield. The frost will melt faster around the bottom outlet with outlet angle becoming bigger, but if the angle is too big, it will also lead to the defrosting dead angle and reduce the defrosting rate. It will lead to warming of body temperature with the heavy air rate and high temperature. Different central outlet position will lead to the difference among the equivalent temperature results. The bottom outlet angle affects the thigh and the above parts obviously. By the comprehensive analysis of above-mentioned impact factors, the central outlet position and bottom outlet angle are optimized based on the approximate model and genetic algorithm, which makes the AAC system have good defrosting performance and thermal comfort.