Distributed scroll booster architecture forsustainable supermarket refrigeration
Achieving lower-GWP refrigeration and energy efficiency within a familiar operating footprint

April 2021

Abstract

Depending on their unique operational goals and/orregulatory mandates, food retailers and convenience store

Global, national and regional mandates are driving significant

operators find themselves at widely varying points along thechanges in commercial refrigeration system design tosustainability continuum. Not all supermarket operators areminimize their global warming potential (GWP) and/or total

ready to assume the lifecycle costs and service challenges

equivalent warming impact (TEWI). Conventional large,

that come with a system operating below 150 GWP. Unlike

centralized direct-expansion (DX) refrigeration systems, which

the past several decades when centralized DX systems weretypically utilize large charges of high-GWP hydrofluorocarbon

the prevailing architecture used in supermarkets, there(HFC) refrigerants, are prone to leaks and often suffer fromcurrently is no single system architecture that addresses thedeclining system performance over their lifespan. Whilewide range of sustainability objectives.

natural refrigerants like CO2 (R-744) and propane (R-290)
offer ultra-low-GWP levels, they also introduce operational

Among the leading options for achieving this diversity ofcomplexities that many food retailers may not be prepared tosystem sustainability goals include utilizing lower-GWP

address. Hydrofluoroolefin (HFO) refrigerant blends — such as

refrigerants and deploying lower-charge, distributed

R-513A — offer a simpler alternative while providing excellent

systems. Refrigerant alternatives R-744 and R-290 offer

performance characteristics and much lower GWP than HFCs.

ultra-low-GWP levels, but they also come with significant

When used in emerging distributed booster architectures,operating caveats and design limitations related to highR-513A can present a low-charge, flexible alternative to large

operating pressure (R-744) and flammability (R-290).

centralized systems. This white paper will introduce thedistributed scroll booster architecture, designed for use with
R-513A to deliver significant sustainability improvements andlower lifecycle costs — all within a safe and familiar operating
footprint for supermarket owners/operators and service

Blends of HFO alternatives, such as R-513A, offer very similar
performance characteristics to the low-pressure R-134a —only with a much lower GWP. And since R-513A is classified
as an A1 refrigerant, it requires no special safety mitigation
strategies in system design.

technicians.

Evolving refrigeration system design criteria

To support diverse sustainability requirements and theneed for refrigeration flexibility, distributed refrigeration

For more than 30 years, the evolution of commercial

architectures are becoming a much-preferred alternativerefrigeration system design has been largely driven by

to large centralized DX systems. They support the goals ofenvironmental sustainability initiatives. Recent design

reducing direct and indirect emissions from refrigeration

strategies are typically aimed at lowering the totalsystems by utilizing reduced charges of lower-GWP

equivalent warming impact through two approaches:

refrigerants and system design strategies that maximize

1) reducing direct emissions from refrigerant leaks, andenergy efficiencies.

2) lowering the system’s total energy consumption (i.e.,

Balancing sustainability and serviceabilityits indirect emissions).

Refrigerant choice — a key component of system design — isAt the same time, many supermarkets are guided by theirown aggressive corporate sustainability goals and actively
plan for a transition to lower-GWP systems. But this journey
introduces new challenges as operators try to find their idealbalance among sustainability goals, system costs and longterm serviceability considerations.

2an important consideration for owners/operators. Whenevaluating total lifecycle costs, operators must not only
factor in the initial equipment investment and installation
costs, but also the long-term costs related to maintenanceand system serviceability.

Systems that are designed to use ultra-low-GWP
refrigerants, like R-744 and R-290, present unique system
maintenance and operational challenges. For example,
since R-744 is a high-pressure refrigerant used in complex
system architectures, operators must have access toqualified service technicians to keep the system running
optimally. R-290, which is classified as a highly flammable
A3 refrigerant, requires mitigation strategies as well asbuilding and fire code approval from local authorities having
jurisdiction (AHJ). R-290’s very low charge restrictions also
limit its application potential beyond self-contained cases.

Distributed scroll booster: Elevating performanceand sustainability
A distributed scroll booster architecture is designed for
maximum application flexibility and optimized for use witha low-pressure refrigerant like R-513A. Configurations canscale from small, low-charge systems utilizing condensing
units to larger systems of distributed racks charged withseveral hundred pounds of refrigerant (see Figure 1).
One design feature that makes this booster architecture
unique is its use of a single refrigerant (R-513A) for bothlow- and medium-temperature refrigeration loads. ThisR-513A offers a low-pressure, high-performance and high-approach simplifies system design while maximizing overall

efficiency alternative to these complexities. Designed as aefficiencies.

replacement for R-134a, R-513A is an approved low-pressure
substitute with zero glide that has been used in a wide

Condenser

Scroll Booster RackRed= Discharge gas
Yellow = Liquid
Green = Medium-temp. suction gas

variety of medium-temperature commercial refrigeration
applications. With its A1 classification, it provides thelowest possible GWP (573) among available non-flammable
refrigerant alternatives and presents no risk of ozone
depletion. Compared to R-134a, R-513A provides a 56%
reduction in GWP.

Scroll Rack

CoolerFreezerFreezerFreezer

For operators and service technicians, R-513A’s low-pressure
characteristics provide a familiar operating envelope andCooler

require no special training, certification or safety mitigation
measures. From a system design perspective, it provides thelowest boiling point of any refrigerant like R-134a, giving itCooler

more flexibility for use in low-temperature operation thanScroll Booster Condensing

other alternatives in a similar pressure range.

Condensing Unit

R-513A: By the numbers• GWP = 573 — per the Fifth Assessment Report (AR5)of the United Nations Intergovernmental Panel on
Climate Change (IPCC)• 56% GWP reduction compared to R-134a

Low-Temp

Medium-Temp• 55% GWP reduction compared to R-448A/R-449A• Ozone depletion potential (ODP) = 0• ASHRAE A1 safety classification• Azeotropic blend with zero glide• Performs well in all ambient conditions

Low-Temp

Medium-Temp

Figure 1: Distributed scroll booster system configurations

3

Overcoming low-temperature challenges
Distributed scroll booster technology is designed toovercome the common challenges of operating a lowtemperature system, which often include: requiring acompressor cooling strategy such as liquid injection;
lowering compressor lifespan due to high compression ratiosand discharge temperatures.

compressors can either be located within a condensing
unit or in a standard rack configuration. Condensers canbe located remotely or integrated into the system andplaced indoors or outdoors. Low-temperature compressors
are placed near the low-temperature evaporators, whichhelps to reduce refrigerant charge, piping and associatedcosts (see Figure 2). For example, in supermarket reach-in
freezers, this could be directly on top of or beside the case orInstead, the distributed scroll booster’s straightforward

remotely near the load.

architecture leverages the advantages of R-513A’s low-This system design strategy provides a performance boostpressure, high-efficiency and key system components

by discharging the low-temperature compressor directly into

to provide:

the nearest medium-temperature compressor’s suction line.

• Lower discharge temperatures and compression ratios:

The lower discharge temperatures of the low-temperature

1.9:1 at -10 °F saturated suction temperature (SST) andscroll compressor minimize the suction gas temperature

20 °F saturated discharge temperature (SDT)of the medium-temperature unit and allow the medium-• Reduced compressor strain and related maintenanceissues• Increased overall system efficiency and lifespan• Reduced stress on pipes and fittings, which lowers thepotential for leaks

temperature compressors to operate within their design
limits without the need for additional cooling.
The net result of boosting low-temperature compressors
directly into the medium-temperature compressors
is an overall system efficiency gain while keeping themechanical load on the low-temperature compressors very

Mechanics of a distributed scroll booster systemlow. Compared to conventional systems, where the lowtemperature scrolls are subject to the most demanding

The core of the system is comprised of one or morehigh-compression ratios and high-discharge temperatures,

medium-temperature compressors coupled with one or

the distributed scroll booster system operates at consistently

more low-temperature compressors. Medium-temperature

low and predictable values.

Condenser

Distributed Scroll Booster SystemRed= Discharge gas
Yellow = Liquid
Green = Medium-temp. suction gas

Scroll Rack

CoolerFreezerFreezerFreezer

CoolerCooler4

Figure 2: Low-temperature compressors arelocated near low-temperature evaporators.

Distributed scroll booster:
Performance analyses

Proof of concept: Gem City Market

Thermodynamic analyses of a distributed scroll boosterserviceability made the distributed scroll booster an ideal

system in Los Angeles demonstrate its performancechoice for a new small-format supermarket built in a foodcharacteristics compared to other supermarket systemdesert in Dayton, Ohio. The project involved collaborationarchitectures. Using a centralized DX as the baseline foramong the affected Dayton community, city officials andcomparison, Figures 3 and 4 evaluate the annual energy,

commercial refrigeration industry leaders, who donatedpeak load and lifecycle climate performance (LCCP) of

their respective expertise and resources to the project.

The combination of high performance, sustainability andthese systems. The loads used for analyses were 100,000• Chemours — Opteon™ XP10 (R-513A) refrigerant

Btu/hr (29.3 kW) for the medium-temperature and33,000 Btu/hr (9.67 kW) for the low-temperature. SST for• Hussmann — medium-temperature Protocol™ systems,

the low-temperature is -25 °F (-31.7 °C) and 20 °F (-6.7refrigeration units and display cases with CoreLink,°C) for the medium-temperature.

micro-channel condensers, unit coolers and extensive
commercial refrigeration expertise

Annual Energy and Peak Power Consumption

8.3%-10.3%

120,000

25.0

Copeland scroll booster low-temperature modules,

4.6%
-7.5%

-4.1%

-16.9%

Lumity™ site supervisor facility management control,

20.0

9.0%

-11.5%-8.4%

100,000• Emerson — Copeland™ scroll compression technology,
25.6%= Peak

4.2%

140,000

Annual Energy (kWh)= MT Annual

15.0

-19%

80,00010.0

60,00040,000Peak Power (kW)= LT Annual

160,000

5.0

20,000--(R-404A)
Centralized(R-407A)
Distributed(R-407A)
Secondary,Glycol MT,
CO2 LT

R-134a/CO2Cascade(R-513A)
CO2Distributed
Transcritical
Scroll Booster Booster Parallel

CO2
Transcritical
Booster

Figure 3: Comparison of annual energy and peak power consumption

XM case controls, electronic expansion valves (EEVs) andexpertise in distributed scroll booster architecture
The collaboration with Gem City Market stakeholders took
place within The Helix Innovation Center, an Emerson facility
located on the University of Dayton campus. The teamdesigned a custom configuration of the distributed scroll
booster system according to the store’s unique footprint,
floor plan and refrigeration requirements.

Annual CO2 EmmissionThe inherent advantages of the refrigeration system= LT Direct-45.2%

CO2 Transcritical Booster= LT Indirect= MT Direct

CO2 Transcritical Booster - Parallel= MT Indirect-51.7%aligned well with the market’s financial, operational andenvironmental sustainability goals of:-57.0%

R-513A Distributed Scroll Booster
R-134a/CO2 Cascade• Low-GWP refrigeration-41.1%

R-407A Secondary, Glycol MT, CO2 LT• Long-term energy savings-43.6%

R-407A Distributed• Low operating costs-36.6%

R-404A Centralized-50,000-20,000

100,000

150,000

40,000 60,000

200,000250,000

300,000 350,000

400,000• Familiar servicing footprint

80,000 100,000 120,000 140,000 160,000 180,000

The store opened in spring 2021.
Figure 4: Lifecycle climate performance5Conclusion: Wide industry potential
and benefits
The unique combination of a low-pressure, low-GWP
refrigerant and a simple, distributed architecture based onfamiliar operating principles fills an urgent need within thelarger food retail market. For operators who seek to meettheir sustainability goals without introducing unnecessary
serviceability complexities, a distributed scroll booster
system is an ideal choice.
While its design flexibility lends itself to store formats ofvarying sizes, its benefits check many key boxes on the list ofmodern supermarket refrigeration priorities:• Lower-GWP, A1 refrigerant (R-513A)• Reduced refrigerant charge• Lower leak rates due to lower-pressure system• Lower utility costs• System familiarity with technicians and end users• Low total cost of ownership (from lower annual energy
consumption and LCCP)• Secure remote facility monitoring capabilities
In the future, as even lower-GWP refrigerants (such as A2Ls)
are approved for use by applicable codes and standards, thedistributed scroll booster system can be adapted for use withultra-low alternative refrigerants (less than 150 GWP).
For more information about the distributed scroll booster
architecture, please contact this paper’s authors.

6Authors
Andre Patenaude

to Emerson’s food retail and chiller markets. Prior to that,

Director of Solutions Integration

he had managed Emerson’s global CO2 development.

EmersonAndre has more than 35 years of industry experience in sales,andre.patenaude@emerson.com

marketing, training and business development of HVACR
system architectures and applications with compression

Andre Patenaude is responsible for supporting system-and component technologies. He is a certified Mechanicalrelated innovation and leveraging Emerson’s global cold

Engineering Technologist C.E.T. (since 1984), and is achain to drive adoption of integrated solutions in North

member of AHRI, ASHRAE and RSES.

America. He most recently led marketing efforts pertaining

Dr. Charles Allgood

Prior to joining DuPont, he worked as a research chemist forTechnology Leader — Refrigerants

the National Institute of Standards and Technology. He has

Chemours
charles.c.allgood-1@chemours.com
Dr. Charles Allgood is the technology leader — refrigerants
with Chemours in Wilmington, Del. He currently leads

held a variety of research, technical service and market
development assignments during his 25+ years in therefrigerants industry.
Dr. Allgood earned a Ph.D. in chemistry from the Universityof Delaware.

the company’s technical support, training and applications
development for the Opteon™ and Freon™ refrigerants andis a frequent speaker at many HVACR industry events.

Andres Lacassie

Exchange Locker, microDS, Freedom Line and Self-ContainedVice President, Core and Distributed
Cases Product Linemerchandisers. In his role, Andres has accelerated theHussmann Corporation

North America. He also currently serves on the planning

leadership position for refrigerated merchandisers acrosscommittee for the annual FMI E+SD conference, which isandres.lacassie@hussmann.com

focused on innovations and technologies that propel theAs the vice president of the core and distributed cases productfood retail industry forward.

line at Hussmann, Andres Lacassie is responsible for theAndres earned a bachelor’s degree in communication fromdevelopment and delivery of the company’s largest productthe University of New Orleans and an MBA in international

portfolio, including Insight Multideck, Reach-In, Smartmarketing from the University of Dallas.

7About Emerson
Emerson (NYSE: EMR), headquartered in St.
Louis, Missouri (USA), is a global technology
and engineering company providing innovative
solutions for customers in industrial,commercial and residential markets. Our
Emerson Automation Solutions businessis a leader in helping process and discrete
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production processes through our best-inclass technologies and industry expertise. Our
Emerson Commercial & Residential Solutions
business develops technologies and services
that improve human comfort, safeguard food,protect the environment, enable sustainable
food waste disposal, and support efficientconstruction and maintenance of buildings andmunicipal infrastructure. For more information,
visit Emerson.com.

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