Lawrence Berkeley National Laboratory

Abstract: Vehicle thermal loads and air conditioning ancillary loads are strongly influenced by the absorption of solar energy. The adoption of solar reflective coatings for opaque surfaces of the vehicle shell can decrease the ?soak? temperature of the air in the cabin of a vehicle parked in the sun, potentially reducing the vehicle?s ancillary load and improving its fuel economy by permitting the use of a smaller air conditioner. An experimental comparison of otherwise identical black and silver compact sedans indicated that increasing the solar reflectance (?) of the car?s shell by about 0.5 lowered the soak temperature of breath-level air by about 5?6?C. Thermal analysis predicts that the air conditioning capacity required to cool the cabin air in the silver car to 25?C within 30min is 13percent less than that required in the black car. Assuming that potential reductions in AC capacity and engine ancillary load scale linearly with increase in shell solar reflectance, ADVISOR simulations of the SC03 driving cycle indicate that substituting a typical cool-colored shell (?=0.35) for a black shell (?=0.05) would reduce fuel consumption by 0.12L per 100km (1.1percent), increasing fuel economy by 0.10kmL?1 [0.24mpg] (1.1percent). It would also decrease carbon dioxide (CO2) emissions by 2.7gkm?1 (1.1percent), nitrogen oxide (NOx) emissions by 5.4mgkm?1 (0.44percent), carbon monoxide (CO) emissions by 17mgkm?1 (0.43percent), and hydrocarbon (HC) emissions by 4.1mgkm?1 (0.37percent). Selecting a typical white or silver shell (?=0.60) instead of a black shell would lower fuel consumption by 0.21L per 100km (1.9percent), raising fuel economy by 0.19kmL?1 [0.44mpg] (2.0percent). It would also decrease CO2 emissions by 4.9gkm?1 (1.9percent), NOx emissions by 9.9mgkm?1 (0.80percent), CO emissions by 31mgkm?1 (0.79percent), and HC emissions by 7.4mgkm?1 (0.67percent). Our simulations may underestimate emission reductions because emissions in standardized driving cycles are typically lower than those in real-world driving.