Outside the Lackland commissary. Photo courtesy of CTA Architect Engineers.
LOW-GWP ALTERNATIVES IN COMMERCIAL
REFRIGERATION
Name of the Store:
Lackland Air Force Base Commissary
Location:
San Antonio, Texas, United States
Contact Information:
John Stuit, john.stuit@deca.mil
Type of Facility:
Commissary, Store Area = 117,000 sq ft
Technology Transition:
R-404A direct expansion system to an
ammonia/carbon dioxide cascade system
STORE OVERVIEW
The Defense Commissary Agency (DeCA) currently operates a
117,000-square foot commissary in San Antonio, Texas. The store
is located in the community service area of the Lackland Air Force
Base and is surrounded by other retail stores, banks, schools, and
housing. The previous refrigeration system, which contained more
than 7,000 pounds of R-404A—a greenhouse gas refrigerant blend
with a global warming potential (GWP) of 3,9221—was over 13
years old and was ready for retirement. With help from Hillphoenix
and CTAArchitect Engineers, DeCA replaced the old refrigeration
system with an ammonia (NH3)/carbon dioxide (CO2) cascade
system, which uses a refrigerant with a negligible GWP. The store
remodel, which is being implemented by Summit Construction,
began in January 2014 and is expected to be completed by August
2015, during which time the store has remained open to the public.
The installation of the refrigeration system was completed in
December 2014. As part of the remodel, all cases, piping, controls,
and the HVAC system are also being replaced.
1 Meaning that it is 3,922 times more damaging to the climate system than CO2 on an equal mass basis.
2 Federal mandates (EO13423, EPACT2005, EISA 32007) require that energy consumption be reduced by 30% in new buildings and 20% in remodeled buildings.
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PROJECT BACKGROUND
SYSTEM DESCRIPTION
DeCA chose to adopt a NH3/CO2 cascade system for two main
reasons: (1) to control future capital and operating costs, and (2) to
meet the energy and sustainability goals the U.S. Government has
established for all public buildings.2
Prior to their decision, DeCA reviewed the possible refrigeration
systems that could be used to meet their goals. DeCA wanted
to use a refrigerant with low or no GWP to eliminate climate risk
and address the regulatory uncertainty around climate policies,
which could impose future penalties on the use or emissions of
high-GWP refrigerants or even force a refrigerant conversion.
DeCA also wanted to adopt a system that is more energy efficient
than standard industry rack systems that typically use R-404A
refrigerant, and eliminate safety concerns. They also aimed to
adopt equipment that can be easily serviced and wanted to keep
costs reasonable.
With these criteria in mind, DeCA considered installing either a
transcritical CO2 system or an NH3/CO2 cascade system. Due to
the hot climate of southern Texas, the NH3/CO2 cascade system
was deemed the most suitable choice for the Lackland Air Force
Base commissary.3
The NH3/CO2 cascade system that has been installed at the
Lackland commissary consists of three key pieces: (1)an NH3 direct
expansion system, (2) a CO2 secondary loop system, and (3) a CO2
direct expansion system. The NH3 system, which is contained in an
outdoor enclosure on the roof of the building, relies on a condenser
water loop to connect the NH3 compressors with the evaporative
fluid cooler, and is used to condense vapor CO2 into a liquid. The
liquid CO2, which is stored in a tank adjacent to the NH3 system,
is circulated throughout the store to remove heat from both the
low and medium temperature cases. On the medium temperature
side, the liquid CO2 passes through a coil to remove heat from
the refrigerated space and then returns directly to the liquid CO2
tank prior to being condensed again by the NH3 system (utilizing a
secondary loop design). On the low temperature side, the liquid CO2
first passes through an expansion valve, evaporates into a gas as it
removes heat from the refrigerated space, and then is compressed
prior to returning to the roof.
In total, the system has a low temperature cooling capacity of 304
MBTUs/hr and a medium temperature cooling capacity of 1,233
MBTUs/hr. The system consists of nine ammonia modules, each
NH3 Chiller Modules and
Condenser-Water Pump
Station on Roof
CO2 MT/LT System (Located
next to or below NH3 Chillers)
^ " "
Medium-Temp
Refrigeration Loads
Low-Temp
Refrigeration Loads
Diagram of the NH/CO2 cascade system to be installed at the Lackland commissary. FMI Energy & Store Development Conference presentation,
September 2012, Phoenix, Arizona.
3 According to DeCA analysis, transcritical CO2 systems are the preferred option for use in cooler climates.
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containing nine pounds of refrigerant, for a total of 81 pounds of
NH3 as well as roughly 1,800 pounds of CO2. To increase energy
efficiency, LED lighting is used in all refrigerated cases and cold
storage rooms. Additionally, display cases with glass doors are used
for the majority of products (except produce and fresh meat).
PERFORMANCE AND COSTS
Compared to the existing R-404A rack system, it is expected that
compressor energy use of the new system will be reduced by
8%, resulting in a system-wide energy reduction of roughly 3%.
Additionally, due to the avoided leakage of more than 600 pounds
of refrigerant each year4—equivalent to roughly 1,100 metric tons
of CO2—refrigerant costs are expected to be over 90% lower.
Maintenance costs are also expected to be almost 40% lower.
While upfront costs of the NH3/CO2 cascade system were
roughly 15% higher than a standard system—an incremental
cost of roughly $334,000—operational savings from energy use,
refrigerant use, and maintenance costs will greatly offset these
costs, likely resulting in only a small overall cost increase over the
estimated 20-year lifetime of the system. Once the technology
reaches large scale commercialization, it is expected that the life
cycle cost of future systems will be equal to or less than a typical
R-404A rack system.
CHALLENGES AND
LESSONS LEARNED
The greatest challenge DeCA faced in implementing the NH3/
CO2 cascade system at the Lackland commissary was public
acceptance of using NH3 in a building near sensitive areas, such
as day care facilities and schools. To address this concern, the
National Renewable Energy Lab (NREL) and the Environment
Protection Agency (EPA)—with technical assistance from CTA
Architects Engineers and Hillphoenix—conducted an ammonia
plume study, which analyzed the potential effects of ammonia
being released from the system into the community. Results of
the study showed that the system poses minimal threat to human
health, with impacts mainly limited to short-lived unpleasant odors.
The risk of public health impacts can be mitigated through the use
of a continuous leak monitoring system. In addition to conducting
the study, DeCA also conducted public outreach to community
leaders to effectively communicate the results of the study and
alleviate concerns. While DeCA is confident that concerns over the
use of NH3 will fully dissipate, a key lesson learned is the need to
actively engage the community from the start in order to proceed
with an ammonia system.
Other key lessons learned include the need to prepare
maintenance teams and maintain spare parts on hand. For
instance, because the NH3/CO2 cascade system is designed
differently than conventional systems, DeCA's personnel must
be trained on how to service and maintain them. To address
this important issue, Hillphoenix will conduct training sessions
over the course of several days to educate DeCA maintenance
teams on how to handle the system. These training sessions are
incorporated into the Hillphoenix service contract. In addition,
DeCA recommends having spare system components on hand
(e.g., ammonia compressor) to allow for timely repairs, since parts
delivery may take several days until the technology is more widely
in use. As more NH3/CO2 cascade systems are adopted across the
United States and more technicians are trained on how to service
these systems, personnel training and component availability will
pose less of a challenge for users.
Moving forward, DeCA anticipates adopting NH3/CO2 cascade
systems as the standard technology at other commissaries
located in warm climates. NH3/CO2 cascade systems will also
be considered for installation in other types of facilities such as
DeCA's cold storage and central distribution center at Sagami
General Depot in Japan. In addition, transcritical CO2 systems will
be considered for use at commissaries in cooler climates, such as
at the facility at the U.S. Air Force Base in Spangdahlem, Germany
and in the commissary in Newport, Rhode Island.5 Worldwide,
there are approximately 250 U.S. commissaries.
^
SNAP
SIGNIFICANT NEW ALTERNATIVES POLICY
EPA 430F14023 -www.epa.gov • June 2015
4 Based on the average leak rate of the existing R-404A system during 2012 and 2013.
5 Construction began at the Spangdahlem commissary in February 2014. The new commissary, which will use a transcritical CO2 refrigeration system, is expected to be
complete by the spring of 2016.
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