Chilled Water Storage Facility for Citizens Energy Group of Indianapolis.

1. 8 Engauge - February 2018
PERL Project Spotlight: Thermal Energy
Storage at Citizens’ Chilled Water Facility
More than 60 commercial and industrial
customers in Downtown Indianapolis depend
on Citizens Energy Group for cost-effective
and reliable delivery of chilled water. The
benefits of utilizing chilled water from
Citizens are numerous, but with our focus
on continuous improvement, it’s important
to explore ways in which we can provide an
even greater value to our customers.
To address that subject, as part of a
Partnership for Excellence in Research
and Learning (PERL) capstone project,
IUPUI mechanical engineering technology
students Jeff Tucker, Kossi Ahialegbedzi and
William Betts set out to develop a feasibility
study for a thermal energy storage (TES)
system for Citizens’ chilled water plant with
the goal of determining the potential for
reducing energy costs.
Under the guidance of IUPUI Professor
Jerry Piskorowski and Citizens Chilled
Water Facilities Manager Todd Fuller, the
three students researched TES systems,
ultimately settling on ice storage for the
purposes of this project.
TES systems operate on the premise
of using energy during off-peak hours
to reduce energy consumption during
peak hours. Taking into account Citizens’
needs, Tucker, Ahialegbedzi and Betts
explored two types of systems: ice
building and ice harvesting.
The students stated in their
presentation, “Ice building systems are
static and are generally more compact and
less costly than dynamic systems. They also
use modular ice storage tanks and, as an
added benefit, are fairly easy to install.”
With ice building systems, glycol is
cooled during off-peak hours by a chiller,
which produces ice in a storage tank.
During peak
hours, the ice
is allowed to
melt, chilling the
water returning
to the plant. This
process results
in a reduction
of the energy
load required to
cool the water
and a decrease
in energy costs
to the supplier
(in this case,
Citizens).
Ice harvesting,
on the other
hand, is a dynamic
system in which ice-making machines dump
ice into storage containers. “An advantage of
ice harvesting is that the equipment comes
pre-assembled and installs as a single unit,”
reported the team. “However, there are also
some downsides: The system is open to
the atmosphere, which necessitates water
treatment, and it is likely more costly due to
its stainless steel construction.”
The students then investigated
equipment; chillers for the ice building
system and tube ice machines for the ice
harvesting system. They also took into
consideration efficiency, demand charge,
tons of refrigeration and volume of ice
needed, and they compared chiller load data.
After completing their research and
comparing the data, the students came
up with three possible options: convert
the existing chiller; convert the existing
chiller and add a new chiller; or install
an ice harvesting
system. However,
before making their
recommendation,
there was one more
task to complete.
“To arrive at our
recommendation,”
the students
said, “we had to
conduct a number
of calculations
for each option,
including annual
savings, total cost
and payback, which
is the time it would
take to recover the
initial investment in
energy savings.”
Here were the results:
Convert the existing chiller
Annual savings: $150,866
Total cost: $2 million
Payback: 13.2 years
Convert the existing chiller and add a
new chiller
Annual savings: $224,561
Total cost: $4.9 million
Payback: 21.7 years
Install an ice harvesting system
Annual savings: $150,289
Total cost: $5.2 million
Payback: 34.6 years
In the end, based upon their
research and Citizens’ goals, the
students made the recommendation to
convert the existing chiller.
Chilled Water Facilities Manager
Todd Fuller said, “Bob Purdue,
Director of Thermal Operations, and I
were very impressed with how quickly
the students were able to advance
from not being familiar with our
industry to providing a detailed study
that we will be able to reference going
forward. Although the payback doesn’t
currently justify moving forward, as
electricity prices continue to rise,
thermal energy storage may be a
viable option at some point. The work
these students performed provided
valuable information for Citizens, and
I’m sure the experience they gained
will serve them well as they pursue a
career in engineering.”