A Study on Cabin Heat Load Reduction Using Solar Reflective Glasses in Automotive Application

<div class="section abstract"><div class="htmlview paragraph">Over the past few decades, there has been a notable increase in stakeholder’s attention on Earth's climate. The automotive industry, being a major contributor to this phenomenon, has been endeavoring to mitigate its impact through various measures. These efforts include reducing emissions in existing internal combustion engine (ICE) vehicles and promoting electric vehicles (EVs) as a feasible alternative for consumers. Despite these initiatives, there remains a persistent challenge in improving the fuel economy and driving range of vehicles.</div><div class="htmlview paragraph">India, located along the Tropic of Cancer, experiences both tropical and subtropical climates. As a result, a substantial portion of the total heat absorbed is from solar radiation. The higher heat load necessitates extensive use of air conditioning (AC) systems, which significantly contributes to the overall power consumption of vehicles. Various measures are being implemented to mitigate this heat load and enhance the efficiency of AC operations. This study aims to investigate the properties of different types of photochromatic glass and their effects on cabin heat load. Various proposals involving solar-coated glass, including absorptive and reflective types as well as combinations of these types are examined. Digital simulations are conducted to identify the most suitable alternatives for glass and their combinations.</div><div class="htmlview paragraph">In this study, a combination of the Lattice-Boltzmann (LBM) based Power FLOW solver and the Finite Element based solver is utilized to simulate long transient soak and cool down processes. Furthermore, human thermal physiology is incorporated into the model to account for subjective evaluations of the in-cabin thermal environment. The Berkeley Comfort Model library, available in software, is employed for this purpose. This model addresses vasodilation and vasoconstriction effects based on external ambient conditions, as well as the influence of clothing and passenger metabolic rate. Digital simulations indicate that solar-coated reflecting-type glasses exhibit promising results.</div><div class="htmlview paragraph">The mentioned glass is installed in vehicles, and various trials are conducted under different conditions, including highway cycles, city cycles, and range trials, in both moderate and severe ambient conditions. Temperatures inside the cabin, at the grill level, and at most of touch points including glass surface are recorded for trials. The rate of rise of temperature during soaking reduced by ~15-18 % at cabin level and by ~32-35 % on touchpoints. In the vehicle-level test results, it is observed that touch point temperatures decrease by ~11-12°C, and air conditioning power consumption reduced by ~9-13%.</div></div>