inner diameter and a 38-ft wall height.
Although tank stratification is less efficient
at this lower wall height, the design team
had to weigh the additional cost of a
deeper excavation and taller tank against
tank efficiencies. As the tank is completely
buried, the tank roof was designed to
support up to 4 ft of soil in addition to
a light-duty truck.
Tight Construction Schedule
In May 2004, the design phase ended
and progressed to construction, which
began after commencement ceremonies.
Turner Construction was hired as the
construction manager for the project,
handling the earthwork, tank construction,
piping and associated mechanical work.
Initial site preparation was followed by
excavation, which ultimately removed
more than 30,000 cu yd of soil. Between
150 and 200 trucks left the site each day
during the two-month excavation period.
Trucks were restricted from interfering
with the summer classes, and dust control
required routine street sweeping.
DYK Incorporated served as the tank
contractor. Constructed directly in the
excavated site, the TES tank was subsequently post-tensioned to ensure watertightness. The entire tank construction
process took only five months.
Coordination with all parties during
the construction process was a key concern. The project’s tight construction
schedule could have posed an issue, given
the complexities of constructing on a
university campus operating in an urban
setting. No problems arose, however, and
construction was complete in February
2005, nine months after ground was
Honeywell control system and monitored
remotely by facilities management from
its operations office.
As Drown notes, one of the benefits
of a maintenance-free underground tank
is that “it is out of sight and out of mind.”
The only upgrades to the system the
university may consider would be minor
additions, such as a heat exchanger to
remove the tank from direct contact with
the campus loop. Although this upgrade
is not necessary, it would completely
prevent chilled water in high-elevation
buildings from draining into the lower-elevation tank. In evaluating this option,
however, USC will also take into consideration the loss of system efficiency
through the heat exchanger.
Beyond USC, several other universities
also have incorporated TES systems into
their campuses with no aesthetic impact
by burying the tanks. For example, the
University of California, Riverside installed
one 19,000-ton-hr TES tank in 1993 and
a second 24,000-ton-hr tank in 2002. Both
of these were buried up to the roof line
in an adjoining hillside.
Another method of disguising a TES
tank is to apply ‘architectural enhancements’ once the tank is completed. This
would include applying various external
finishes – perhaps as simple as paint, for
example – to alter tank appearance to
match surrounding buildings. Advances
in finishes give owners limitless options
for changing tank appearance. Other
enhancements include surrounding the
tank with screens or attaching an exterior
insulation and finish system (EIFS) directly
to the tank that mimics brick or stone
buildings found elsewhere on campus.
While all these alternatives cost less than
burying the tank, they do leave the tank
more visible and use valuable land.
As USC and other universities have
demonstrated, it is possible to bring
thermal energy storage to campuses and
other institutions with strict aesthetic
guidelines. Burying the storage tank has
the least impact on campus aesthetics,
while architectural enhancements still
preserve campus aesthetics and provide
cost savings over a fully buried tank.
The possibilities really are endless for
bringing cost-reducing TES technology
to district energy systems.
David Bain has been a business
development engineer with DYK
Incorporated for the past two years.
Prior to joining the company, he
earned a degree in civil/structural
engineering from the University of
Texas at Austin. He also is an active member
on ASHRAE Technical Committee 6.9 Thermal
Storage. He can be reached at firstname.lastname@example.org.
USC’s TES tank has been operating
for more than three years with an excellent performance record and meeting all
of its design requirements. During normal
operation, the tank can provide a maximum cooling capacity of approximately
6,000 tons to the district cooling system
and can sustain this for up to five hours.
Due to limitations on production and
nighttime cooling demands, charging is
accomplished at a rate of 2,000 tons. All
of the charging and discharging parameters are automated by the university’s
Courtesy DYK Incorporated. Photo Warren Aerial Photography.
This 6 million-gal water storage tank serving the city of Ontario, Calif., was designed with architectural
enhancements that allow it to blend in with surrounding buildings. Those enhancements include a burgundy
EIFS truss around the tank and a frosted glass brick and roofing enclosure around instrumentation.