If you’ve had the experience of climbing into a car on a hot, sunny day, you might have wondered whether a light colored car would be less miserable than a dark one. The answer is “yes,” and a recent paper published in Applied Energy reports how much warmer dark cars can be. Going a step further, the paper predicts the extent to which car color may influence fuel consumption and emissions. The press release describes the simple, but effective experiment.
The Heat Island Group of Lawrence Berkeley National Lab’s Environmental Energy Technologies Division borrowed two Honda Civic sedans from the State of California, attached a bunch of temperature measuring instrumentation, parked the cars in a sunny spot of the parking lot and took data.
The only difference between the nearly identical four-door sedans was color: one was silver, the other black. That is, one car had a high solar reflectance (silver) and the other did not (black). Solar reflectance values range from 0 to 1, and the solar reflectance of the silver car was 0.58, while that of the black car was 0.05. As the term implies, surfaces with high solar reflectance stay cooler in the sun.
The cars were subjected to five identical soak-cool cycles comprised of an hour-long soak in the sun without air conditioning followed by a 30 minute cool down with air conditioners running at full blast. Meanwhile, measurements were taken of the cars’ roof, ceiling, dashboard, windshield, seat, door, vent air and cabin air temperatures.
During the soak (warming) phases, researchers found that the roof temperature of the silver car was up to 45°C cooler than the black car’s roof. Also, the cabin air of the silver car was about 10°F cooler.
Next, the researchers developed a thermal model to predict how much air conditioning capacity would be needed meet the industry standard of bringing the cabin temperature to 77°F within 30 minutes. The analysis predicted that the silver car would require 13% less AC capacity than the black car to meet the standard. Thus, light colored cars can be built with smaller air conditioning units, while imparting the same level of comfort to the delicate beings within.
Other benefits could accrue with smaller AC units. Using a simulation tool called ADVISOR, the researchers modeled fuel consumption and emissions for typical driving scenarios including highway, city and a “transient driving cycle” (does that mean suburbs?). The simulation shows that using a smaller AC unit, which a white or silver car would allow, could increase fuel economy by about two percent, while reducing CO2 by about two percent and other emissions by about one percent.
There are about 25 million registered cars in the state of California, so even modest improvements in efficiency and emissions output can multiply out to some pretty big numbers. Now, too, fleet managers can quantify the value of color as they replace their inventories.
To paraphrase the late crooner Nat King Cole, “Straighten up and buy light!”
Coincidentally, DOE’s Office of Energy Efficiency and Renewable Energy just released a Vehicle Cost Calculator and widget to help consumers, fleet managers, and government officials to compare energy-saving vehicles. The widget does not ask for the car’s color, though.