Cabin Heat Transfer and Air Conditioning Capacity

This paper describes a first order differential equation that relates the cabin heat transfer coefficient, discharge panel temperature and discharge volumetric air flow to the average interior temperature. The solution to this equation leads to an overall understanding of automotive air conditioning designs and tests. Use of this solution in transient form can provide a relationship between interior temperature changes vs. time during a typical cool down or idle test. Use of this solution in steady state form provides the same under highway speed test conditions. Most importantly, this solution provides a means to determine experimentally the overall heat transfer coefficient of any vehicle body style with different type of insulation materials. It is otherwise quite impossible to accomplish due to the complicated automotive body designs. Once the overall heat transfer coefficient is thus determined, it becomes a link between the demand from the air side and the supply from the refrigerant-side. The use of this methodology is four folds. First, the capacity of refrigerant-side (sizing of components) can be determined based on the demand from the air side (functional objectives). Secondly, the actual A/C performance of an existing system can be evaluated from the components that are already in use by employing this method in reverse. Unless the performance of certain components is increased, repetitive testing does not improve system outcome. It bears some very significant economic considerations. Thirdly, this method also leads the establishment of unified validation procedures and requirements to various components. Lastly, an integrated approach can be developed to enhance computer simulation in both velocity and thermal fields.