Cityplace - Trane

“ Always, the goal has been to
provide the most economical chilled
water service we could. When our
owners and the building managers
were shown the benefits of lower
temperature chilled water, they
wanted us to make the change.”
Operations manager/chief engineer
Mark Webb is discussing the
functional improvements recently
made in the chiller plant for the
Cityplace building, a large office
building in Dallas.
Construction of the Cityplace facility
was completed in 1989. The 43-story
office building encompasses
1.4 million square feet of commercial
space and is owned by 7-11
Incorporated. The building is managed
by Southwest Real Estate Services.
Current major building tenants include
ZixIt Corporation, 7-11 Stores, Fidelity
Investors, Dane Rauscher Wessels, and
Homecomings Financial Network.
Four of the building tenants have
major computer centers, thus highly
reliable cooling systems are a
requirement.
The original building architect was
Cosutta & Associates, and the general
contractor was The Beck Company. The
mechanical contractor for the facility
was TD Mechanical of Dallas.
Cityplace
Dallas,Texas
Showcase Chiller Plant Upgraded To
Provide Lower Temperature Water

The entire changeover
was accomplished
without tenants being
inconvenienced or
suffering any comfort
penalty.
Cityplace’s comfort plant consists of a
centrifugal chiller system in the
basement level, with cooling towers
in a separate architectural enclosure
at street level. The basement
mechanical room is exceptionally
attractive and well arranged. Chilled
water service is provided to air
handlers throughout the building.
Conditioned air is delivered via VAV
and fan powered box networks.
Designed for Chilled Water Storage
An important feature of the design is
ten chilled water storage tanks
totaling 5 million gallons of capacity.
These are also located at the building
© 2002 American Standard Inc. All rights reserved
Chilled water output at 37°F (3°C)
increases plant storage capacity and
improves efficiency.
basement level. According to
Cityplace’s assistant chief engineer
Stephen Spaeth, the chilled water
storage approach allows the facility to
operate from 12:00 p.m. to
8:00 p.m., the electric demand
measurement period, without
operating the chillers or cooling
towers. He notes, “For this building,
removal of the chiller plant from the
demand charge represents a major
reduction in operating costs,
estimated to be about $150,000 per
year. It’s good for the utility and it’s
good for us.” The electric utility
serving the facility is TXU Electric.
The chiller plant consists of six Trane
CenTraVac centrifugal chillers,
Model CVHB, rated at 1500 tons each.
Under the initial design, the chilled
water exiting the chiller at 40°F (4°C)
goes to the storage tanks. The
primary loop water return
temperature as originally designed
was at 54°F (12°C). Chilled water from
the loop travels to a series of plateand-rail
heat exchangers to cool a
secondary chiller water loop.
Secondary loop chiller water is
pumped to groups of eight custom air
handlers that serve five-floor “atrium
groups” within the high-rise building.
Normally, the chilled water
requirement is delivered through the
storage system, except at peak times,
when the chiller can supply the
secondary loop heat exchangers
directly. A total of 84 air handlers
deliver conditioned air for the entire
building. In addition, a smaller
The six Trane CenTraVac chillers were rearranged
in pairs for ultra-low temperature chilled water.

The Trane CenTraVac model CVHB
chillers were equipped with new
UCP2 control panels.
portion of the chilled water is
supplied under contract to a nearby
railroad station and tenant computer
rooms, where it is also used for
comfort cooling.
Targeting Lower Temperature Water
This is the way the system operated
from the time the building was built
until 2000, when it was modified to
take advantage of direct digital
controls and variable speed pumping
technology to deliver lower
temperature chilled water to the
system. Ken Scheepers of the Texas
Trane Service Group in Dallas worked
with Southwest Real Estate Services
to devise a plan to modify the system
to allow it to operate at lower chilled
water temperatures.
According to Alan Ash, sales
manager for Trane Dallas, the method
that was suggested was to re-pipe the
chillers, putting the machines
Chiller plant is monitored and controlled with a
Tracer Summit system.
Heat exchangers operate
at lower temperatures as
a result of the EarthWise
conversion.
together in series in pairs. Ash says,
“The chiller configuration here
allowed us to put together existing
components in a new, better way.
New digital control capabilities make
this possible.”
The six chillers were updated with
Trane UCP2 unit control panels to
provide the close unit control
required for ultra-low temperature
service. Additionally, a chiller plant
management system was installed
using the Trane Tracer Summit
system. This comprehensive chiller
plant management system
communicates with the building
automation system.
In the new configuration, each of the
three pairs of chillers receives water
at 54°F (13°C) and the first chiller
discharges it to the second chiller at
43°F (7°C). The second chiller takes it
down to 35°F (2°C). This lower output
temperature has been made possible
by the more precise digital controls in
the new UCP2 control panels and the
overall chiller plant control from the
Trane Tracer Summit chiller plant
control system. From the second
chiller, primary loop water goes to the
heat exchangers. With the lower
temperature primary loop, the
secondary loop delivers chilled water
to the building at approximately 38°F
(4°C), seven degrees (F) colder than
the original design.
EarthWise Design An Opportunity
According to Ash, this Trane
“EarthWise” design approach has
been widely adopted in recent years
for both new and existing buildings. It
has proven successful in increasing
the capacity of existing chiller plants
and increasing building comfort while
reducing operating costs. Ash notes,
”The EarthWise approach was
especially attractive to the owners of

Chilled water pumps are equipped with variable
speed drives.
Cityplace because the internal heat
load of the building had increased to
the point that there was no longer
adequate storage capacity to carry
the building through the demand
window. With the lower chiller output
temperatures, the effective storage
capacity of the tanks was increased
30 percent.” He points out that there
were additional comfort and control
benefits from lower secondary loop
water temperatures.
Another system change was the
installation of variable speed pump
drives on both the primary loop and
condenser water loops to allow the
system to be optimized for varying
loads and tower water conditions.
Additionally, pressure transducers
were installed at key points on the
system to allow optimization of
pumping rates. The pumping system
redesign further reduced total
comfort system energy requirements
and, with lower chilled water
temperatures, offered better local
temperature control. The system
changes were made to two chillers at
a time beginning in late 1999. The
project was completed before the
summer peak in 2000.
Variable Speed Pumps Enhance
Efficiency
Trane Dallas technical service
specialist Ken Scheepers points out
that under the current configuration,
the system chilled water requirement
peaks at 2.3 million gallons per day
during summer peak periods. Under
winter low load conditions, the
system still requires 1.4 million
gallons per day. Scheepers
emphasizes that the variable speed
primary loop chilled water pumps
and the condenser water pumps
allow the system to operate
CASE-SLX064-EN
April 2002
New
La Crosse
efficiently through the entire seasonal
range of cooling loads. As the system
is currently operated, on most days
the chilled water storage requirement
can be met and the chillers shut
down for the day by 8:00 a.m.
According to Mark Webb, Cityplace
chief engineer, the entire changeover
was accomplished without tenants
being inconvenienced or suffering
any comfort penalty. Since the new
system has become operative, he has
confirmed the expected improvement
in system efficiency and improved
local control with colder chilled water
temperatures. The showcase
mechanical plant at Cityplace
continues to be visited frequently by
building engineers and managers.
The facility is notable not only for its
pristine engineering beauty, but for
the enhanced performance of its
updated energy plant.