Investigation of Pre-Cooling Effectiveness in Vehicle Cabin Cool-Down

New car developments require that in the initial cabin cool-down it will be necessary to reach a lower average cabin temperature in a shorter time. The aim is to minimize the discomfort of the driver and occupants to just a few minutes during the initial condition of a hot cabin. Today, the target is reached by increasing the evaporator size, the blower capacity, and the compressor power. All of this is done so as to have as much cooling power available in the shortest possible time. After these transient conditions the A/C system generally works at lower heat rejection and the maximum capacity of the system is used in just a few cases. To limit any increase of the A/C system power, some control strategies can be defined and applied to reduce the thermal energy stored in the cabin. This will reduce the transient phase cool-down time, and thus improve fuel economy. A strategy consists of cooling the cabin with outside fresh air before starting the cool-down by use of the A/C system. In this way, the cabin temperature can be reduced by 10-15°C. This paper presents the results of experimental studies on the effects of cabin refreshing by outside air on the cool-down behavior, with the aim to define the real effect of pre-cooling on the cool-down, the most appropriate time of refreshing and the amount of external air flow.