Localized Cooling for Human Comfort

Traditional vehicle air conditioning systems condition the entire cabin to a comfortable range of temperature and humidity regardless of the number of passengers in the vehicle. The A/C system is designed to have enough capacity to provide comfort for transient periods when cooling down a soaked car. Similarly for heating, the entire cabin is typically warmed up to achieve comfort. Localized heating and cooling, on the other hand, focuses on keeping the passenger comfortable by forming a micro climate around the passenger. This is more energy efficient since the system only needs to cool the person instead of the entire cabin space and cabin thermal mass. It also provides accelerated comfort for the passenger during the cooling down periods of soaked cars. Additionally, the system adapts to the number of passengers in the car, so as to not purposely condition areas that are not occupied. The present paper reports on a fundamental study of localized cooling to achieve comfort in a vehicle environment. The individual cooling streams are evaluated by human comfort riders for effectiveness and limitations. Based on the local cooling studies, combination local cooling strategies are then created and evaluated by riders. CITATION: Wang, M., Wolfe, E., Ghosh, D., Bozeman, J. et al., "Localized Cooling for Human Comfort," SAE Int. J. Passeng. Cars Mech. Syst. 7(2):2014, doi:10.4271/2014-01-0686. 2014-01-0686 Published 04/01/2014 Copyright © 2014 SAE International doi:10.4271/2014-01-0686 saepcmech.saejournals.org Other cabin thermal load reduction methodologies have also been explored. These include advanced thermal insulation for the cabin, double pane glass windows, solar reflective glazing, solar reflective paint, electro-chromatic films, low mass seats, cabin preconditioning through ventilation, etc. [4, 5, 6]. In general, the existing measures to gain energy efficiency have been directed at either the refrigeration system optimization or thermal load reduction from the cabin as a whole. Progress in technologies such as thermoelectric modules and human thermal comfort modeling now provides a new possibility of load reduction through localized cooling. Basically, local cooling, via a dedicated local nozzle, targets a specific body part with a diffusing stream of air to provide direct comfort for the body part [7]. Use of multiple streams allows efficient coverage of the key, thermally sensitive body parts to ensure thermal comfort of the passenger. Consequently, the general thermal environment in the cabin may be stratified without impacting the comfort of the body due to the isolation effect of the local cooling. The thermal load reduction may be further enhanced with passenger presence sensors to perform zonal cooling management. The combined energy expenditure by the air conditioning system operating at a reduced level and by the local cooling streams is expected to be lower than the traditional method of thermal comfort maintenance in which the entire cabin is cooled regardless of the number of passengers in the car. The present investigation attempts to provide the fundamental understanding of localized cooling in its ability to maintain human thermal comfort by experimentally studying the impact of individual or combined local cooling streams on passenger comfort. The study uses Thermal Comfort rating as well as Thermal Sensation rating to record passenger comfort feedback while subjected to local cooling streams at various flow rates and temperatures in the vehicle environment. Figure 1. Local Cooling Air Supply Figure 2. Air Supply System and Overhead Nozzles Wang et al / SAE Int. J. Passeng. Cars Mech. Syst. / Volume 7, Issue 2 (August 2014)