What Color is Your Parking Lot: New Research Combats Heat Island Effect

The art and science of sustainable coatings is on display at the Lawrence Berkeley National Laboratory in California, where researchers have taken over part of a parking lot to test a series of differently colored treatments intended to cool down paved surfaces that are exposed to sunlight.

Uncovered parking lots account for a large part of the surface area in typical cities, making them a major contributor to increased urban temperatures called the "heat island" effect. The extra heat packs a triple whammy by contributing to smog formation and adding to the public health impacts of excessive outdoor temperature, increasing the energy needed to cool interior spaces, and putting an extra strain on the grid by exacerbating peak energy loads.

Parking lots and solar power

As reported by Julie Chao at the Berkeley Lab, up to half of the surface area of a typical city can consist of paved surfaces. Of that, about 40 percent consists of un-roofed parking lots made mostly of asphalt and other dark materials.

That is exactly the problem, as explained by Berkeley  Heat Island Group researcher Haley Gilbert:

“Because dark pavements absorb almost all of the sun’s energy, the pavement surface heats up, which in turn also warms the local air and aggravates urban heat islands.”

On the other hand, vast stretches of unshaded surfaces are perfect for solar carports, as many property owners are beginning to discover. They are becoming increasingly popular at commercial establishments as well as government facilities and sports venues, the Washington Redskins' new solar parking lot being just one recent example.

A solar array can help alleviate the heat island effect while also generating renewable energy. However, they also represent a significant investment that is not within reach of many property owners, and they may not necessarily be the best solution for heat island issues in some cases.

Cooler roofs, cooler parking lots

The Berkeley tests were inspired by the "cool roof" trend, which basically involves applying a light-colored coating to rooftops in order to help cool the air within the building as well as mitigating the heat island effect outdoors.

According to Chao, asphalt pavement reflects only five to 20 percent of the sun's energy, depending on its age (asphalt lightens as it ages). In comparison, "cool pavement" could reflect from 30 to 50 percent.

Developing new kinds of paving material is one approach, but for now the Heat Island Group is focusing on the development of alternatives to conventional sealants. Typically, sealants are applied to reduce damage from weathering, but they can exacerbate the heat effect by restoring a darker color to older asphalt.

Though it may seem that white would be the alternative sealing color of choice, the research team is examining coatings that range into yellow, blue and green territory. That's because the coating's ability to reflect invisible light from the infrared end of the spectrum can be a critical factor.

The tests are being conducted in a real parking lot under real-life conditions, so the lab will be able to measure the effect of wear and tear on the coatings, loss of efficiency due to the accumulation of dirt and dust, and the ability of rainwater to restore efficiency.

The idea is to come up with an alternative sealant that "sells itself," by providing the benefits of conventional sealants with the added attraction of the cooling effect, at roughly the same cost.

For most properties, the cooling effect would not involve a direct bottom line benefit but it could certainly go to help raise the sustainability profile of the property owner.

In addition, some properties could realize a direct and significant savings on their electricity bills, since the brighter surfaces would reduce the amount of energy needed to light open-air parking lots at night.

As of now, the lab is testing six coatings, which were donated by its partner Emerald Cities Cool Pavement and the company StreetBond, and the Heat Island Group is in the process of soliciting additional participants.