ASU, developers, cities search for ways to get Valley off heat islands
by Mary Jo Pitzl
The Arizona Republic

Rubberized asphalt, applied to Valley freeways to minimize noise, has an unintended benefit: It's cooler at night than other pavement.

Its black, porous skin, although bubbling hot in the sun, cools off better than conventional concrete at night, Arizona State University researchers have found.

"We were all surprised," said Kamil Kaloush, an assistant professor of civil and environmental engineering.

The 2- to 3-degree difference in pavement types may not seem like much, but coupled with other pending projects, it could begin to mitigate the ever-increasing rise in temperatures that has accompanied the Valley's growth.

Still, the Valley lacks any big-scale examples of how to reduce the heat island effect. "This is absolutely not a problem an individual can do anything about," said Phoenix resident Dan Hunting, who has advocated for reducing the heat island through downtown neighborhood groups.

"You can re-landscape your lawn, but you still have a city with hundreds of miles of concrete radiating heat."

Records show that nighttime temperatures in the Valley have climbed steadily over the past half century as development has replaced desert and farmland. The average minimum temperature has risen to 64.9 degrees, an increase of 10.6 degrees since 1948, climatology records show.

It is not uncommon now to have 100-degree temperatures at 10 p.m., whereas a generation ago, Valley residents could open their windows on summer nights without breaking a sweat.

Even 15 years ago, Hunting said, he could do yard work comfortably on summer nights. But those days are past.

However, projects large and small are being undertaken in an attempt to make the Valley cooler:

ASU is researching types of pavement and rating their ability to deflect sunlight and heat. Given that about one-third of the Valley's surface is covered by roads and parking lots, the use of cooler materials could make a difference, said Jay Golden, co-director of ASU's Sustainable Technologies Program.

Arguably the Valley's largest urban heat island, Phoenix Sky Harbor International Airport will use heat-deflecting materials when construction begins on a new terminal building and parking garage. The city signed an agreement earlier this summer to work with ASU to determine what materials would best do the job. The project is years from happening, however.

Architect and developer David Hovey is building a condominium tower at 24th Street and Camelback Road that will include a "living roof." Instead of dark roof shingles, the building's top will feature a garden full of desert plants that is expected to act as a natural insulator, while providing an eye-pleasing amenity for residents.

The patio outside Phoenix Mayor Phil Gordon's 11th-floor office is expected soon to be transformed into a showcase of heat-reflective materials and technologies.

Stumbling on an idea.

But to date, the biggest strides have been inadvertent, such as the rubberized asphalt.

When researchers looked at a nighttime thermal photograph of the Valley recorded by a satellite, the hottest of the hot spots stood out plainly. The slabs of concrete at Sky Harbor, the granite slopes of the mountains that ring the Valley, and the freeway-and-road network all pulsated with the brilliant red color that marked the hottest spots.

But there were puzzling little gaps in the "heat map" of the freeways, recorded last October. Some spots along the Black Canyon Freeway showed up cooler than surrounding roads. Between the Grand Avenue interchange and Metrocenter, the freeway was noticeably "cooler" than stretches north and south of those points.

The reason, Kaloush found, was rubberized asphalt.

That's because air holes constitute 20 percent of rubberized asphalt, Kaloush said. Those pockets of air allow heat to escape, something that dense concrete cannot do.

At nighttime, when the heat island takes its toll, this might make rubberized asphalt a wiser choice, Kaloush said. But it isn't the answer for everything. During the day, the asphalt surface can be 10 to 15 degrees hotter than concrete because its black surface soaks up so much heat.

"If I want to put a parking lot next to a school, I'd probably put in concrete because it's cooler during the day (when the school is occupied)," he said.

But cooler isn't always better, Golden suggested.

Perhaps some buildings might want to increase the heat they absorb during hot summer days, then capture it and redistribute it as energy, he said.

The idea of harnessing the heat is behind an experiment at the park-and-ride lot on Pecos Road in Ahwatukee.

There, city officials put up traditional metal shade canopies over parking spaces; the Salt River Project decided to put photovoltaic panels on top of some of the covers. Then Golden, "on a hunch," came with a thermometer at midday June 15 and took readings.

He found the obvious: The shaded areas, at 94 degrees, were cooler than the 148-degree asphalt parking surface by 54 degrees. But the shaded areas that were topped with the solar panels were cooler still: 87 to 88 degrees.

Golden credits the solar panels with soaking up some of the heat before it can radiate through the canopy. "You're absorbing some of the radiation and, in this case, turning it into electricity," he said.

SRP gets 100 kilowatts from the panels, enough to power 100 homes a year.

What if, Golden theorizes, cities encouraged or required parking lots to have a percentage of solar-cell coverage? It would cost more to build up front, but the cooler effect on both motorists and surrounding areas, coupled with the electricity generation, could more than compensate, he said. Painfully slow progress.

But changing city standards is a slow process. While both Gilbert and Phoenix have added goals to their general plans to mitigate the urban heat-island effect, there are no notable results to date.\

Tom Oteri has been working on changes to Tempe's zoning code as a member of that city's Planning and Zoning Commission.

"What we're trying to do is get a little more shade, get more trees in parking lots, discourage big parking lots," Oteri said.

But, he added, progress is painfully slow.

"We felt a first step was to try and make it not prohibitive to use alternative materials (such as heat-reflecting shingles)," he said. "That's about as good as I could get."

Meanwhile, piecemeal efforts are popping up around the Valley.

The Optima Biltmore Towers condominium project at 24th and Camelback will have one of the area's "living roofs." Although not designed specifically to blunt the urban heat island, architect Hovey said that will be one of the side benefits.

Not only will such roofs allow heat to escape, rather than trapping it, they'll also reduce energy use, whose generation itself causes higher urban temperatures.

"You can imagine the extra air-conditioning load that it takes to cool buildings at night," he said of conventional roofs. And, "it's much nicer to look at a green roof than a black roofing material."

At ASU, Kaloush plans to conclude his study of roadway paving materials later this year. Aside from looking at rubberized asphalt, he's studying the heat-dampening effects of crumb rubber, which is added to concrete.

Golden said individuals can affect their "microclimate" by such actions as using heat-reflecting materials and planting more trees.

"But you still have the regional influences," he said. And it will take a regional effort to tackle them.