Engineering Inc - September/October 2017 - 24

Sustainable
Cooling From
an Old
Quarry Lake
PROJECT: NASHVILLE
INTERNATIONAL AIRPORT - WATER
SOURCE GEOTHERMAL SYSTEM
FIRM: GARVER
NASHVILLE, TENNESSEE

S

ince early 2016, a new 3,600-ton
capacity geothermal system has been
providing cooling for the entire
terminal building at the Nashville
International Airport, significantly reducing the facility's use of both electricity and
water. The nearly $10.4 million project finished three months ahead of schedule and
under budget.
The idea to use water source geothermal
cooling to replace the cooling towers in the
airport's central utility plant came out of the
Metropolitan Nashville Airport Authority's
(MNAA) participation in the Sustainable
Master Plan Pilot Program launched by the
Federal Aviation Administration in 2010.
As part of that exercise, planners considered
various possible uses for the near-potable
water in a 250-foot-deep lake in an aban24

ENGINEERING INC.

SEPTEMBER / OCTOBER 2017

doned quarry adjacent to
the airport's easternmost
runway. They soon realized
that beyond supplying water
for irrigation, rental car
Ryan Sisemore
washing and construction
use, the lake's thermal profile
made it an ideal source of cooling-below
the 45-foot depth, the water temperature
remains at approximately 50 degrees Fahrenheit throughout the year.
"One of our team members had prior
experience with this type of cooling system
but on a smaller scale," says Ryan Sisemore,
vice president of Garver, which served as
the civil design lead for the design-build
project. "We just took the concept and ran
with it."
At the heart of the system are a dozen
radiator-like lake plate assemblies submerged to a depth of 50 feet in the quarry
lake. Condenser water is pumped through
nearly a mile of 20-inch high-density polyethylene pipe to a manifold at the edge of
the lake. From there, 6-inch pipes feed the
lake plate assemblies where the condenser

GARVER

Pairs of supply
and return lines
connect the
manifold with
the lake plate
assemblies.

water is cooled by 16 degrees
before returning via another
manifold and pipeline to
the central utility plant.
The entire trip takes about
45 minutes, although that
can vary because it is an ondemand system.
MNAA originally anticipated saving
approximately $500,000 per year in electricity costs, but that is turning out to be a
conservative estimate.
"Once you start looking at the reduction
in potable water consumption, that return
grows even higher," Sisemore says. Abandoning cooling towers and using the quarry
lake water for irrigation is saving MNAA 30
million gallons of potable water consumption per year.
These results are especially good in the
long-term perspective. The payback period
initially was expected to be about 10 years
based on energy savings alone. But with a
life expectancy of 50 years, this system will
be functioning long after it has paid for
itself.
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