e-News
Issue 83  December 2011
Supermarket Refrigeration
 Introduction
 Supermarket Refrigeration Systems
and How They Consume Energy
 Alternative Refrigeration Systems
Efficiency Features and Modeling
 Refrigerated Cases
 Energy Saving Opportunities
n a square foot basis, the food store category, which includes
supermarkets, grocery stores and convenience stores, has the
second highest energy consumption of major building types in
California, with electricity representing over 80% of this. Supermarkets are
open for long hours, and the energy-intensive refrigeration system must
operate continuously in any case.
 Summary of Proposed 2013 Title 24
Supermarket Mandatory Measures
 Related Resources
 Training Highlights
 About e-News
Introduction
O
This newsletter will focus on the refrigeration system as it consumes the
greatest fraction of supermarket electricity use, with lighting and HVAC
each about one-third as large. Also mentioned briefly are applicable
utility incentives, proposed refrigeration requirements in Title 24, and
the analysis of efficiency measures in energy modeling software.
Figure 1: Energy Common Large Supermarket
Refrigeration Diagram
Supermarket Refrigeration Systems and How They
Consume Energy
Numerous components consume energy in a refrigeration
system. To keep product cases cool, fans move air across
an evaporator coil which causes the refrigerant inside it
to boil, absorbing heat from the air circulating in the case.
Heat is introduced to the cases from the warmer store
environment, lights, defrost and anti-sweat heaters, and
the fans themselves. The greater these heat gains, the
greater the amount of work the entire system must do.
In addition, three of four of these heat gains are caused
by components which consume electricity themselves.
This refrigerant is piped to compressor(s) which raise
its pressure and temperature (consuming electricity).
The hot gas from the compressor is piped to an outdoor
condenser coil where a fan (consuming electricity) moves
outdoor air across coil, cooling the refrigerant back to
liquid so it can return to the cases to repeat this cycle. A
typical supermarket will have many cases connected to
a refrigerant “circuit” and each circuit will usually have
multiple compressors. Three to six circuits will serve
each market, each dedicated to different temperature
cases or areas of the store.
Alternative Refrigeration Systems
Source: Supermarket Refrigeration Codes and Standards
Enhancement Initiative (CASE), Pacific Gas and Electric Company,
March 17, 2011 pg. 71
Energy Design Resources
Recently some variations on this design have emerged
in response to concerns about the global warming
contribution of the inevitable leakage of conventional
refrigerants. These involve the use of CO2 or glycol
e-News  December 2011
Refrigerated Cases
“brines” in place of typical refrigerants in some components
of the systems. As these systems are still rare, they are not
detailed here. Recent analyses have shown that energy use
of these variations range is equivalent or somewhat greater
than conventional systems, but have savings in greenhouse
gas emission (due to reduced refrigerant leakage) that more
than offset the GGHG emissions associated with increased
energy use. Many of the applicable EEMs for typical systems
also apply to these variations. (E.g. reducing case heat gain
will reduce energy use in any system.)
The entire refrigeration system must be designed to
remove heat that enters or is generated within the cases,
so this is the first place to look for energy savings. Federal
standards for new supermarket refrigerated cases will
take effect in 2012, and some features which have been
optional will become standard to meet the new standard.
Doors and Open Cases: Many case types never have
doors, some may have doors, and others always have
doors. On average, where the choice exists, choosing
a case with doors will save energy, but care must be
taken to minimize lighting and anti-sweat heater energy
consumption in cases with doors. The thermal gains
through doors can be reduced by utilizing better glazing
and frames. Condensation on the inside of these doors
may increase, but anti-fog films are available to minimize
this. Night curtains will effectively reduce the loads on
open cases during unoccupied periods, if any. Door
gaskets deteriorate with time and should be replaced
when this is apparent.
Utility Incentive Programs in California
New Construction
Incentives for more efficient supermarkets are provided
through the Savings By Design program, and energy
savings must be calculated by modeling the proposed
market against a baseline market. This modeling is
provided by a few specialist firms, using a special
refrigeration version of the eQUEST/DOE-2.2 program.
The baseline supermarket is currently based on recent
historical typical construction.
Anti-Sweat Heaters: In CA, these heaters, which prevent
exterior condensation on doors and cases, should be
needed only occasionally. Controls to make sure these
heaters stay off as long as possible are typically installed
but may not be commissioned or maintained properly.
Some newer case doors are designed with low-conduction
glass and frames, eliminating the need for these heaters,
however the cases themselves will still typically have
ASHs, and the store will still need to control these ASHs.
Retrofits
The utilities have differing programs using different
methods to determine savings or incentives for retrofits
to supermarket systems. All except SDG&E provide
prescriptive incentives for particular retrofits.
PG&E utilizes a program called Energy Smart Grocer
which deploys a subcontracted firm to audit, provide
recommendations and calculate savings for this sector.
Case Lighting: Standard lighting in cases has been
florescent, but both LED lighting and fiber-optic lighting
systems are now available with comparatively less energy
consumption. The fiber-optic lighting appears to reduce
overall energy use to the greatest degree, in part because
more of its heat is left outside the case, where it often
beneficially warms the store, instead of adding to case
heat gains. Any lighting can be switched off by a timeclock.
LED lighting can be controlled by a motion sensor and be
turned off when the area in front of a case is vacant, and
this may be required in non-24 hr stores under the 2013
Title 24.
SCE & SMUD provide both “Custom” (calculated savings)
and “Express” (prescriptive) incentives.
SDG&E utilizes a subcontractor to implement measures
across this segment, and provides them with incentives.
Energy Saving Opportunities
Given the interacting energy consuming components in
supermarkets, many opportunities exist for both energy
waste and savings.
Figure 2 – Luminance Image Comparing the
Same Case Lighted by Different Sources
Store Lighting and HVAC
The ambient store lighting is not covered in this E-Newsletter,
as the applicable EEMs are generally the same as those
used in other large retailers. For restaurant operations
within supermarkets, the EEMs are similar to those for any
restaurant operation.) Special HVAC systems are often used
to dehumidify air for supermarkets, but simulation analysis
has shown limited savings for conventional methods of
providing this extra dehumidification in California.
Energy Design Resources
Source: http://www.sce.com/b-sb/design-services/ttc/
rttc/researchprojects/supermarket/t8-led-fiber-optic.htm
2
e-News  December 2011
Related Resources
Supermarket Refrigeration Codes and
Standards Enhancement Initiative (CASE)
Pacific Gas and Electric Company March 17,
2011
http://www.arb.ca.gov/cc/commref/Supermarket%202013%20NR15%20CASE%20
Report%20draft%2017Mar11.pdf
 Lessons Learned from 15 years of Refrigerated Facility Simulation, Doug Scott, VaCom
Technologies, ASHRAE Annual Conference,
Louisville, Kentucky, June 23, 2009
http://www.vacomtech.com/Downloadfiles/Simulation%20Lessons%20
Learned%20ASHRAE%202009.pdf
 Grocery Store 50% Energy Savings Techni-
cal Support Document Technical Report,
NREL/TP-550-46101, September 2009
http://www.nrel.gov/docs/fy09osti/46101.
pdf
 DOE-2.2R manual
http://doe2.com/download/DOE-22/
DOE22Vol2r-DictionaryRefrigeration.pdf
 Energy Plus manuals
Fans, Coils and Defrost: For cases with similar designs, lower design
power for evaporators will generally minimize energy consumption.
Exact determination of fan power for cases is hindered by lack of
consistent ratings. EC (“Electronically Commutated”) motors are
readily available and are significantly more efficient than older
PSC (“Permanent Split Capacitor”) or shaded-pole motors. These
motors can be retrofit to existing case fans and can be used with
variable speed controls in walk-ins. Floating suction pressure
control can raise the temperature of refrigerant in the coils when
the load is light, saving compressor energy. This requires the use of
electronic expansion controls on the case evaporators, connected
to a computer control system. This has become relatively common
in new stores and may be required in non-24 hr stores under the
2013 Title 24.
Compressors
Centralized supermarket systems are typically served by reciprocating
compressors, with smaller distributed systems often served by scroll
compressors. In all cases, multiple staged compressors typically
serve each circuit. Compressors of similar sizes are typically of similar
design efficiencies for a given temperature range. Part-load efficiency
of various types of unloading may be examined by simulation, but
simulations may not completely capture the systemic effects of
staging.
Condensers
http://apps1.eere.energy.gov/buildings/energyplus/pdfs/engineeringreference.pdf
Condensers are available which cool refrigerant with either outside
air alone or outside air and the evaporation of water. For recent new
http://apps1.eere.energy.gov/buildings/ensupermarkets in CA the market is about evenly split between the two.
ergyplus/pdfs/inputoutputreference.pdf
Under some utility programs, incentives are available for replacement
 Supermarket Controls and
of air-cooled condensers with evaporative condensers in dry climates.
Commissioning:Uncovering Hidden OpporParticularly during hot, dry weather, evaporative condensers decrease
tunities, Diane Levin and Lawrence Paulsen,
compressor power demand by decreasing the temperature and
Portland Energy Conservation, Inc., 2006
pressure which the compressor must achieve. They should reduce
ACEEE Summer Study on Energy Efficiency in
annual energy consumption, but may not perform as well as expected
Buildings
at part loads. Condenser fan energy use is reduced by lower specific
http:// www.peci.org/documents/Supermarfan power (rejected heat/fan power) and by variable speed fans,
ket_Diane_2006.pdf
and the proposed 2013 Title 24 will regulate both. Two less common
condenser types are water-loop, where refrigerant condensers are
attached to water loop cooled by central fluid cooler(s) and hybrid,
where a condenser which can switch between evaporative cooling and air cooling.
A tradeoff is always made between the energy use of the condenser and the compressor, because the condenser fans
must run harder to produce the cooler refrigerant condensing temperatures and pressures that allow compressors to run
more efficiently. Because the compressors use more energy than the condenser, the most efficient systems use controls
which adjust the pressure the condenser is trying to achieve in response to outside drybulb or wetbulb temperature,
particularly when the fans are operated by VSDs.
Heat recovery is the use of additional refrigerant heat exchangers to reject heat to coils in the store’s heating system or
domestic hot water system. These typically save considerable heating energy, more than offsetting the small compressor
power penalty which will occur while in this heating mode.
System and Piping
While most of the EEMs discussed above relate to individual components, the overall design of the store and systems
will contribute to the energy consumption. The maximum achievable efficiency decreases with the temperature of
the lowest temperature case on a system. So in general energy consumption will be minimized by maximizing the
number of circuits as long as this is done so that the temperatures on each circuit are similar. Greater pressure drops
Energy Design Resources
3
e-News  December 2011
Summary of Proposed 2013 Title
24 Supermarket Mandatory Measures as of September 12, 2011.
(Claim CASE Item 27)
Floating head pressure –
require controls to float refrigeration
system SCT to 70°F during low-ambient
temperature conditions, with ambientfollowing control logic and variable speed
condenser fans
Condenser specific efficiency –
require a maximum fan power per unit of
capacity on air-cooled and evaporativecooled refrigerant condensers
Floating suction pressure –
require controls to reset refrigeration
system target suction temperature based
on refrigerated display case or walk-in temperature, rather than operating at a fixed
suction temperature setpoint
through components will increase compressor energy consumption.
Some piping designs may decrease efficiency of condenser operation.
Systems are now being installed which distribute smaller compressor/
condenser units around a store roof, closer to the case groups served,
reducing piping runs and refrigerant inventory.
Liquid-to-suction heat exchangers (LSHXs) cool the hot refrigerant
before it enters a case through heat exchange with cool refrigerant
leaving the case. Simple LSHXs are common, but high-performance
LSHXs significantly improve the efficiency of low temperature circuits,
and some medium temperature circuits.
Mechanical subcooling (use of medium-temperature circuits to reduce
the load on low-temperature circuits) is a common cost-effective feature
in new stores and may be required by the 2013 T24.
Some components in refrigeration systems can be de-activated on a
call for load shedding, qualifying for further incentives. Defrost can be
deferred, and some case lighting can be switched off.
Retrofits
Energy cost savings can justify the replacement of some components
of the refrigeration system. These are typically either case components
or controls. Published results from a program in San Diego reported
savings averaging 309,000 kWh per market. The distribution of those
savings is shown in the following chart.
Figure 3 – Distribution of Savings from Retrofit Program*
Mechanical subcooling –
require liquid refrigerant to be subcooled
to 50°F or less for low-temperature loads
Display case lighting control – require
automatic controls to turn off display case
lights during non-business
Refrigeration heat recovery –
require equipment and controls to utilize
rejected heat from refrigeration system(s)
for space heating, with a limited increase
in refrigerant charge
Title 24 Part 11 (Reach) Code Measures
CO2 secondary or cascade cooling –
require that refrigerated display cases and
walk-in coolers and freezers utilize carbon
dioxide (CO2) for cooling to reduce HFC
refrigerant charge
* (ECMs = Electronically Commutated Motors; ASHC
= Anti-Sweat Heater Control; FHPC = Floating Head
Pressure Control; FSPC = Floating Suction Pressure
Control)
Source: PECI (Supermarket Controls and Commissioning:
Uncovering Hidden Opportunities Diane Levin and Lawrence
Paulsen, Portland Energy Conservation, Inc. 2006 ACEEE Summer
Study on Energy Efficiency in Buildings
Annual Energy Simulation of Supermarket Systems
In CA, supermarkets have been modeled using the DOE-2.2R program
to determine incentives under the Savings By Design program.
Because of the complexity of refrigeration systems, this modeling is
performed by a few select consultants. The DOE-2.2R program has
also been used to analyze measures for inclusion into Title 24.
The DOE-2.2R program requires numerous specific inputs for
refrigeration components. For instance, the representation of a fixture
© 2004–2011 Energy Design Resources. All Rights Reserved.
Energy Design Resources
4
e-News  December 2011
About e-News
D
on’t miss future issues—to sign up
for a free email subscription, please
visit www.energydesignresources.
com. Send letters to the editor, suggestions
on topics for future issues, or other comments
to [email protected].
Follow EDR on Twitter: http://twitter.com/
edrcalifornia.
e-News is published by Energy Design Resources (www.energydesignresources.com),
an online resource center for information on
energy efficiency design practices in California.
Savings By Design
(www.savingsbydesign.com) offers design assistance and incentives to design teams and
building owners in California to encourage
high-performance nonresidential building
design and construction.
or case includes 130 input values, though not all would be needed
for any given case. Some of these inputs are not clearly evident from
manufacturers’ literature. The program also makes assumptions
about operation of controls that may not be always be achieved in
actual operation.) All programs share these issues.
Other Programs
The EnergyPlus program has been updated to include detailed
models of refrigeration system components, libraries of American
components, secondary loops and new refrigerants. The EnergyPlus
representation of components generally requires fewer inputs than
the DOE-2.2R; for instance a case is represented by a maximum of 35
inputs. This program is being used at NREL to model prototype markets
to develop Advanced Energy Design Guidelines for supermarkets and
to model energy efficiency measures for specific supermarket design
projects.
CyberMart is a Swedish program with simplified inputs and libraries
of European components.
Energy Design Resources and Savings By Design are funded by California utility customers
and administered by Pacific Gas and Electric
Company, Sacramento Municipal Utility
District, San Diego Gas and Electric, Southern
California Edison and Southern California Gas
Company, under the auspices of the California
Public Utilities Commission.
Training Highlights
California utilities offer outstanding educational opportunities that
focus on the design, construction and operation of energy-efficient
buildings. Listed here are a few of the many upcoming classes and
events; for complete schedules, visit each utility’s website.
distinguishing older, inefficient equipment from newer efficient
systems. In-class exercises and a mock-audit at the end of the
last day will allow the attendees to apply what they have learned.
Though geared to the non-experts, attendees should have a
fundamental understanding of building components and energy
concepts.
Energy Auditing Techniques for Small & Medium Commercial
Facilities
January 9-11
(Monday, Tuesday, Wednesday, 8:30 am to 4:30 pm)
San Francisco — PEC
The intention of this three-day workshop is to develop the energy
auditing skills of individuals associated with small-and mediumsized (under 500 kW) commercial facilities. We will provide
an overview of building technologies with an emphasis on
http://www.pge.com/mybusiness/edusafety/training/pec/classes/
© 2004–2011 Energy Design Resources. All Rights Reserved.
Energy Design Resources
5
e-News  December 2011