Reflective pavement can go a long way toward reducing the urban heat
island effect, but the embodied energy and
emissions in some materials may present
unexpected drawbacks, according to new
research from the DOE’s Lawrence Berkeley
National Laboratory.
The research team conducted lifecycle
assessments of conventional and cool pavement materials and simulations of building energy consumption to examine the
environmental impact of each material’s full
lifecycle. Asphalt concrete, the most common material used for pavement, is dark
and has a low albedo (a measure of solar
reflectance). Cement concrete is lighter, and
thus has a higher albedo, but it requires a
high-temperature process that is considerably more energy- and carbon-intensive
than making asphalt from petroleum.
Albedo affects buildings by reflecting more
or less sunlight to them and by changing
the outside air temperature, though a higher
reflectance is generally considered a positive as less heat is absorbed.
The researchers also compared the two
types of concrete to reflective coatings as
well as pavement that includes industrial
waste products like slag and fly ash as a
Are Cool Pavements All They’re Cracked Up to Be?
THE UNEXPECTED CONSEQUENCES OF REFLECTIVE PAVING
Growing in popularity, rainwater harvest- ing systems are helping to reduce stormwater runoff and save energy in commercial
buildings.
Harvesting involves collecting water from
roofs and reusing it for on-site purposes,
eliminating the bulk cost of having to transport the water traditionally.
“You cannot have energy without a lot
of water, and you cannot have water without a lot of energy,” says Jim Harrington
Harvesting Rainwater for Energy Use
HOW SAVING WATER ALSO SAVES ENERGY DOLLARS
RAINWATER HARVESTING not only reduces
potable water consumption, it also cuts
down on energy use.
way to replace some of the energy-intensive
cement in concrete. The energy and emissions associated with each pavement type’s
materials and construction were paired with
a regional climate model and simulated
building energy consumption to determine
the likely impact on buildings. The team
was surprised to find that in most cases, the
extra energy embodied in the cool material
far outweighed the energy savings from
increasing the albedo.
“Over the lifecycle of the pavement,
the pavement material matters substan-
tially more than the pavement reflectance,”
explains Ronnen Levinson, a researcher in
Berkeley Lab’s Heat Island Group. “I was
surprised to find that over 50 years, main-
taining a reflective coating would require
over six times as much energy as a slurry
seal. The slurry seal is only rock and asphalt,
which requires little energy to produce,
while the reflective coating contains energy-
intensive polymer.”
ASPHALT CONCRETE is the most common pavement material, but its dark color absorbs heat
(left). Lighter colors (right) reflect more but often include energy-intensive cement.
of Georgia-based Rainwater Collection
Solutions. “We talk about energy and read
about energy all the time, but we don’t talk
about the fact that probably 60% of the
water that we use in the United States is
used to create energy, for cooling towers and
hydroelectric power. You’re talking about bil-
lions of gallons a day.”
Rainwater catchment is also a practice
that can help property owners achieve LEED
status for their buildings. The Birmingham-
Shuttlesworth International Airport in Alabama
recently received LEED Gold for its terminal
by meeting one of the LEED features in the
design consisting of harvesting that reduces
water consumption and discharge into the
storm water drainage system. B
