Sustainable Retail Refrigeration E-Book

• Herausgeber: John Wiley & Sons
• Kategorie: Fachliteratur
• Sprache: Englisch

Seitenzahl: 721

Veröffentlichungsjahr: 2015

Beschreibung

Carbon emissions from the retail segment of the food cold chain are relatively high compared to other parts of the food cold chain. Studies have also shown that food temperature is less well controlled at the retail and consumer end of the cold chain. There is therefore considerable potential to optimize performance of refrigerated display cabinets and the refrigeration systems that are used to operate them to reduce carbon emissions and to improve food temperature control.

Sustainable Retail Refrigeration draws together world experts on retail refrigeration. In a single resource, the authors cover the latest technologies and best current knowledge in the field. With increasing concerns about energy use and global warming gasses, retailers are increasingly being called to account for their actions.

Sustainable Retail Refrigeration is a valuable reference to manufacturers, managers and policy makers, incorporating both a design and an operational perspective.

Leseprobe

Sustainable Retail Refrigeration

Edited by

Judith A. Evans and Alan M. Foster

Department of Urban Engineering, LondonSouth Bank University, London, UK

This edition first published 2015 © 2015 by John Wiley & Sons, Ltd

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Library of Congress Cataloging-in-Publication Data

Sustainable retail refrigeration / edited by Judith Evans and Alan Foster.  pages cm Includes bibliographical references and index.

 ISBN 978-0-470-65940-3 (cloth)1. Refrigeration and refrigerating machinery. 2. Sustainable engineering. I. Evans, Judith A. (Judith Anne), 1962– II. Foster, Alan, 1968– TP492.S88 2015 621.5′6–dc23

    2015018224

A catalogue record for this book is available from the British Library.

Wiley also publishes its books in a variety of electronic formats. Some content that appears in print may not be available in electronic books.

List of Contributors

Mazyar AminEngineering Technology Department, Miami University, Ohio, USA

Jaime AriasDepartment of Energy Technology, Royal Institute of Technology, Stockholm, Sweden

John Austin-DaviesGeorge Barker & Co. (Leeds) Ltd., Bradford, UK

Pradeep Kumar BansalOak Ridge National Laboratory, Oak Ridge, USA

John BonnerCity Facilities Management (UK) Ltd., Glasgow, UK

Tim BrownDepartment of Urban Engineering, London South Bank University, London, UK

Brian ChurchyardASDA WALMART UK, Leeds, UK

Giovanni CortellaDepartment of Electrical, Management and Mechanical Engineering, University of Udine, Udine, Italy

David CowanInstitute of Refrigeration, Surrey, UK

Paola D’AgaroDepartment of Electrical, Management and Mechanical Engineering, University of Udine, Udine, Italy

Judith A. EvansDepartment of Urban Engineering, London South Bank University, London, UK

Ramin FaramarziRefrigeration and Thermal Test Center, Southern California Edison Company, California, USA

Alan M. FosterDepartment of Urban Engineering, London South Bank University, London, UK

Brian FrickeOak Ridge National Laboratory, Oak Ridge, USA

Kristina KamenskyPrismitech LLC, Michigan, USA

Michael KauffeldKarlsruhe University of Applied Sciences, Karlsruhe, Germany

Nasser KehtarnavazDepartment of Electrical Engineering, University of Texas at Dallas, Texas, USA

Onrawee LaguerreIrstea UR Génie des procédés frigorifiques (Refrigeration Process Engineering Research Unit), Antony, France

Ulla LindbergDepartment of Energy and Bioeconomy, SP Technical Research Institute of Sweden, Borås, Sweden

Graeme MaidmentDepartment of Urban Engineering, London South Bank University, London, UK

Homayun K. NavazDepartment of Mechanical Engineering, Kettering University, Michigan, USA

Albert NowakowskiDepartment of Mechanical Engineering, Kettering University, Michigan, USA

Andy PearsonStar Refrigeration Ltd., Glasgow, UK

Svein H. RuudDepartment of Energy and Bioeconomy, SP Technical Research Institute of Sweden, Borås, Sweden

Richard WatkinsKent School of Architecture, University of Kent, Kent, UK

Abbreviations

μGT

micro gas turbine

ACA

Accelerated Capital Allowance

ACH

air changes per hour

AHU

air handling unit

AMR

active magnetic regenerator

ANN

artificial neural network

ASHRAE

American Society of Heating, Refrigerating and Air Conditioning Engineers

BEMS

building energy management system

BRA

British Refrigeration Association

BTU

British thermal unit

BWS

beer, wines and spirits

CAV

constant air volume

CCGT

combined cycle gas turbine

CCHP

combined cooling, heat and power

CCT

correlated colour temperature

CDEC

calculated daily energy consumption

CE mark

Conformité Européene

CFC

chlorofluorocarbon

CFD

computational fluid dynamics

CHP

combined heat and power

COP

coefficient of performance

CRI

colour rendering index

DAG

discharge air grille

DAT

discharge air temperature

DEC

direct energy consumption

DG

distributed generation

DP

correction factor for influence of indoor relative humidity on defrost in cabinets

DPIV

digital particle image velocimetry

DSM

demand-side management

DX

direct expansion

ECA

Enhanced Capital Allowance

ECM

electrically commutated motor

EEI

Energy Efficiency Index

EER

energy-efficiency ratio

EEV

electronic expansion valve

EFLH

equivalent full load hours

FDA

Food and Drug Administration

F-gas

fluorinated gases

FGB

flash gas bypass

FSIS

Food Safety and Inspection Service

GHG

greenhouse gas

GT

gas turbine

GWP

global warming potential

HACCP

hazard analysis critical control point

HC

hydrocarbon

HCFC

hydroclorfluorocarbon

HER

heat extraction rate

HFC

hydrofluorocarbon

HFO

hydrofluoroolefin

HHV

higher heating value

HNBR

hydrogenated nitrile butadiene

HT

high temperature

HTF

heat transfer fluid

HVAC

heating, ventilation and air conditioning

HVAC&R

heating, ventilation, air conditioning and refrigeration

ICE

internal combustion engine

IOR

Institute of Refrigeration

IPCC

Intergovernmental Panel on Climate Change

KPI

key performance indicator

LCA

lifecycle analysis

LCC

lifecycle cost

LCCP

lifecycle climate performance

LDV

laser Doppler velocimetry

LED

light-emitting diode

LT

low temperature

MAP

modified atmosphere packaging

MCE

magnetocaloric effect

MDEC

maximum daily energy consumption

MEPS

minimum energy performance standard

MOC

method of characteristics

MPE

multi-port extruded

MT

medium temperature

MTP

Market Transformation Programme

NIST

National Institute of Standards and Technology

NS

Navier-Stokes

ODP

ozone depletion potential

OVRDC

open vertical refrigerated display cases

PAFC

phosphoric acid fuel cell

PBP

payback period

PCM

phase change material

PEC

pumping energy consumption

PEM

polymeric electrolyte membrane

PFC

perfluorocarbon

PIV

particle imagery velocimetry

PNS

parabolized Navier-Stokes

PPM

pre-planned maintenance

PV

photovoltaic

RAC

refrigeration and air conditioning

RAG

return air grille

REAL Zero

Refrigerant Emissions And Leakage Zero Project

REC

refrigeration energy consumption

REHVA

Representatives of European Heating and Ventilating Associations

RET

renewable energy technology

RC

resistor capacitor

RH

relative humidity

RTE

ready to eat (food)

RTOC

Refrigeration, Air Conditioning and Heat Pump Technical Options Committee

RTS

radiant time series

SAR

second assessment report

SCT

saturated condensing temperature

SHR

sensible heat ratio

SNAP

Significant New Alternatives Program

SOFC

solid oxide fuel cell

SST

supermarket simulation tool

STEK

STichting Emissiepreventie Koudetechniek

TDA

total display area

TDEC

total daily energy consumption

TDK

two-dimensional kinetic

TEC

total energy consumption

TEEV

thermistor-type electronic expansion valve

TEV

thermostatic expansion valve

TEWI

total equivalent warming impact

TFC

thermostatic flow control

TP

correction factor for influence of indoor relative humidity in cabinets

TPI

temperature performance indicator

UNEP

United Nations Environment Programme

UNFCCC

United Nations Framework Convention on Climate Change

US EPA

United States Environmental Protection Agency

USDA

United States Department of Agriculture

VSD

variable speed drive

WLHP

water loop heat pump

1Overview of Retail Display in Food Retailing

Alan M. Foster and Judith A. Evans

Department of Urban Engineering, London South Bank University, London, UK

1.1 History

In the first half of the 20th century, retailers operated from small premises, serving only their local community. Few products were displayed as they are today, with many selected by an assistant from behind the counter. Most food was not pre-packaged but was instead measured and wrapped to the customers’ requirements by the shopkeeper. Only fresh foods that could be grown locally were available; these had to be purchased and used on a daily basis. Shopping was a daily process, with meat being bought from the butcher and milk delivered every morning.

After the Second World War there was a greater level of consumer choice, especially with regard to food. Retail trends from the US were becoming popular in Europe, particularly the trend for self-service. Customers wanted to see and choose from an ever-growing range of foods. Helped by the advent of the car, increased road networks and domestic refrigeration, larger stores (supermarkets) developed to serve this thirst for choice. The increasing penetration of domestic refrigerators into the home, in particular, extended the periods between shopping trips. This allowed larger, less regular shopping to be carried out, often weekly or fortnightly. For example, in 1970, over 40% of the UK population did not have a fridge, whereas by 1980 almost all households owned a domestic refrigerator (DECADE, 1997). Combined with changes to the family structure, where more women went out to work and mobility of labour was simpler, householders began to shop less regularly. This resulted in a move from shopping in small outlets to ‘one stop shopping’ in larger supermarkets. Less regular shopping was also driven by the demise of daily deliveries after the Second World War, which led to consumers needing to store food, and an increase in domestic refrigeration sales. For example, until 1980 doorstep milk delivery was common. However, by 2000 doorstep milk delivery had almost disappeared as consumers had refrigerators, and milk that was cheaper than the doorstep delivery could be bought in the supermarket.

After the Second World War there was also a huge expansion in home building. Houses built up until the 1960s commonly had larders to keep food chilled. However, after the Parker Morris report of 1961 there was a greater emphasis placed upon living and circulation space, and larders were often not included in homes. Homes were also better heated from around this time, and so there was less opportunity to store food without some form of refrigeration. Research shows that in 1970 internal household temperatures in the UK had a mean of 12°C, whereas by 2004 the mean had risen to 18°C (Fawcett, 2005).

The advent of chlorofluorocarbons (CFCs) introduced in the 1930s allowed the expansion of refrigeration within retail. This was because CFCs were considered much safer than the previous natural refrigerants (ammonia, carbon dioxide, propane and sulphur dioxide) and therefore more suited to a retail environment. R502, R22 and R12 were the common refrigerants used, until it was found that these refrigerants depleted the ozone layer. These refrigerants were replaced by intermediate HCFC (hydroclorfluorocarbons) and then ozone-friendly hydrofluorocarbon (HFC) refrigerants (e.g. R134a and R404A). These refrigerants are now considered harmful to the environment due to their impact on global warming, called their global warming potential (GWP). These refrigerants can warm the globe thousands of times more than the same quantity of carbon dioxide (the main global warming gas). For this reason much work has recently been carried out on making sure these refrigerants do not escape from the refrigeration system. Some countries (such as Denmark) have placed a high tax on these refrigerants. Chapter 7 (Current and Future Carbon-saving Options for Retail Refrigeration) discusses these refrigerants in more detail.

The post-war period was also a period of great technological growth. Consumers began to own televisions, and the power of advertising grew. Frozen food sales grew in this period partially because of the power of media advertising. As supermarkets displayed more frozen food, the sales of freezers in the home also expanded. Frozen food manufacturers were probably key in this development, and were not just responsible for the greater uptake in frozen foods but also the technological infrastructure surrounding them (Cox et al., 1999). This in turn generated a cycle of improved technology and development of further frozen goods.

Birds Eye in particular was instrumental in developing display cabinets. Towards the end of the Second World War they were aware that to expand their business they needed to have higher levels of sales than they achieved in their own stores. In 1957 Birds Eye persuaded two manufacturers to design and market ‘open-top’ refrigerated display cabinets for retail use. Birds Eye agreed only to supply to those retailers who installed such cabinets. They later developed a policy of leasing cabinets to their more important retail customers on the proviso that the equipment was used only for stocking Birds Eye products or other foods that were not direct rivals of Birds Eye. At the same time, Birds Eye heavily marketed their products and gave customers inducements to buy.

With the success of Birds Eye, new frozen food companies entered the market and support infrastructure was developed to deliver and stock these items. As the infrastructure grew, so did new frozen food developments, and that in turn led to expansions and improvements in infrastructure. This in the end led to shorter shelf-life meals (e.g. ready prepared meals) that could only be successfully retailed with a highly evolved manufacturing, storage and delivery infrastructure.

Over the years, the design of cabinets has tended to develop incrementally. The basic method of maintaining food at the correct temperature has changed little over the past 30–40 years. However, incremental changes have been made to components (for example to improve their efficiency), temperature control has been improved, energy consumption has been reduced, refrigerants have been changed, and cabinet features have been modified. Energy reduction has increased in importance over the past 10 years, with manufacturers changing to LED lighting, DC fans, and increased use of doors on cabinets. The application of energy labelling for commercial cabinets, which is likely to occur in 2015, means this trend is likely to continue.

1.2 Retail refrigeration and the food cold chain

1.2.1 Temperature

Very little information is available on temperature control throughout the whole cold chain, and generally data are only available for each section of the cold chain. The exception to this is a survey carried out by Derens et al. (2006) which monitored the temperature of yoghurts and meat products throughout the French cold chain. The results clearly show that temperature control becomes progressively worse as the cold chain progresses from production to the consumer (Fig. 1.1). In manufacture, transport, warehouse and distribution, the food was found to be maintained below 6°C for yoghurts and 4°C for meat for at least 86% of the time. In warehouses only 0.5% of food was outside of these temperature levels. Once the food entered the supermarket the number of samples below 4°C or 6°C was reduced to 70%. This was further reduced to 16% during transport to the home and to 34% in the home.

Figure 1.1 Temperatures throughout the French cold chain (from Derens et al., 2006).

Reproduced with permission from EDP Sciences

1.2.2 Emissions

Overall the cold chain is believed to be responsible for approximately 2.4% of global greenhouse gas emissions through direct and indirect effects. The food chain is responsible for greenhouse gas emissions through direct (refrigerant emissions) and indirect (energy consumption) effects. In the developed world, emissions post farm gate are thought to be responsible for approximately half the total food chain emissions (Fig. 1.2) (Garnett, 2011). Overall emissions post farm gate, from each section of the cold chain are reasonably evenly distributed, but vary if just refrigeration processes are examined.

Figure 1.2 Emissions in the food chain (Garnett, 2011).

Reproduced with permission from Elsevier

1.2.2.1 Indirect emissions

There are few data covering refrigeration energy usage or emissions in the whole food cold chain. Data on energy from the UK Market Transformation Programme (MTP, 2006) indicate that within commercial refrigeration, retail display cabinets use most energy (Fig. 1.3). The exception to this is a study on the chicken supply chain that shows that in the case of chicken, catering is a large energy user (MTP, 2005) (Fig. 1.4). Data from Australia (Estrada-Flores and Platt, 2007) indicate that indirect emissions are greatest from retail and domestic refrigeration (Fig. 1.5). It should be noted that both of these datasets exclude significant areas of the food cold chain. In the case of the MTP (2006) data there is no information on industrial refrigeration (food processing and storage or transport) or domestic refrigeration, and in the Australian study, transport and commercial catering refrigeration are excluded.

Figure 1.3 Energy used in commercial refrigeration in the UK (MTP, 2006). DEFRA, under the terms of Open Government Licence 3.0

Figure 1.4 Energy used in the UK chicken supply chain (MTP, 2005). DEFRA, under the terms of Open Government Licence 3.0

Figure 1.5 Energy used in the cold chain in Australia (excludes transport). From Estrada-Flores and Platt (2007),

reproduced with permission from S. Estrada-Flores

Retail food stores and supermarkets are energy-intensive commercial buildings and the majority of their energy use is refrigeration. In the US in 2003, 119 trillion BTU (35 billion kWh) was used in refrigeration in commercial buildings used for selling of food: 57% of the total energy use for these buildings (EIA, 2012). Westphalen et al. (1996) estimated that there was the potential to save 53 trillion BTU (16 billion kWh) of refrigeration energy in supermarkets. For this reason, much effort has been expended over the years by retailers and refrigerated equipment manufacturers to reduce energy use.

Chapter 7 describes current and future carbon-saving options for retail refrigeration.

1.2.2.2 Direct emissions

The relative impact of direct emissions from refrigerants compared with the effect of indirect emission from energy usage varies with country. In countries where there is a high level of renewable energy or nuclear energy, the emissions associated with energy generation are low. Therefore the relative effect of refrigerant leakage is high. This can influence policy and actions to reduce emissions country by country.

Information on refrigerant emissions is mainly available from supermarkets where emissions are considered to be greatest. In 2003, UNEP estimated that leakage across all refrigeration systems was 7–10%, whereas Clodic and Palandre (2004) estimated the figure to be closer to 17%. Data covering more than one sector of the food cold chain have been reported by several authors (Heap, 2001; RAC, 2005; MTP, 2008) (Tables 1.1, 1.2 and 1.3). Bivens and Gage (2004) reported leakage figures for different countries (Table 1.4) and systems (Table 1.5). They also demonstrated that there is a large variability in emissions as shown by data from supermarkets in Sweden and the US (Figs 1.6 and 1.7). Rhiemeier et al. (2009) reported consistent leakage rates for retail multi-compressor refrigeration systems of between 5% and 10% in Germany, and 8% for supermarkets in the US. In the Netherlands, where the STEK programme has been in operation since 1992, average emission rates of only 3% are reported, although the reliability of the data is questioned by Anderson (2005).

Table 1.1 Food chain refrigerant emissions estimated by Heap (2001)

Market segment

Global warming emission, Mt CO

2e

% of GW impact related to energy use

Direct HFC emissions

Indirect CO

2

emissions

Total global warming impact

Supermarket refrigeration

9.0

23

32.0

72

Industrial refrigeration

3.4

25

28.4

88

Small commercial distributed

1.8

12

13.8

87

Domestic refrigeration

0.8

30

30.8

97

Transport refrigeration

0.7

6

6.7

90

Other small hermetic

0.3

12

12.3

98

Table 1.2 Food chain refrigerant emissions estimated by RAC (2005)

Source: Reproduced with permission from RAC Magazine, EMAP

Business sector

Estimated leakage rate (% system per year)

Typical charge (kg)

Estimates number of systems

Country

Retail cabinets

<1

<3

4,000,000

UK

Small commercial

<1

3–30

300,000

UK

Supermarket

20–30

30–300

50,000

UK

Industrial

15–20

>300

50,000

UK

Table 1.3 Food chain refrigerant emissions reported by MTP (2008)

Source: DEFRA, under the terms of Open Government Licence 3.0

Sector

Reported leakage (% of charge/year)

Johnson (1998)

March (1999)

Haydock

et al

. (2003)

ETSU (1997)

Domestic

1

 1

0.3–0.7

2.5

Retail Integral cabinet Split/condensing units Centralized supermarket

9–23

 1 10–20 10–25

3–5 8–15 10–20

2.5 15 8

Table 1.4 Emissions by country (from Bivens and Gage, 2004)

Source: Reproduced with permission from D. Bivens

Country

Emissions (% of total/year)

Netherlands

3.2

Germany

5–10

Denmark

10 (20–25 in earlier years)

Norway

14

Sweden

3–14

US

5–24

Table 1.5 EU emissions in 2010, business-as-usual scenario (from March 1998) (from Bivens and Gage, 2004)

Source: Reproduced with permission from D. Bivens

Market segment

HFC emissions, Mt CO

2e

% of total emissions

Indirect CO

2

emissions, Mt CO

2e

% of GWP impact related to energy use

Supermarket refrigeration

9.0

32

23

72

Mobile air conditioning

8.9

32

14

61

Industrial refrigeration

3.4

12

25

88

Air conditioning, DX systems

2.6

9

10

79

Small commercial distributed

1.8

6

12

87

Domestic refrigeration

0.8

3

30

97

Transport refrigeration

0.7

3

6

90

Air conditioning, chillers

0.7

1

12

94

Other small hermetic

0.3

1

12

98

Total emissions

28.2

100

144

84

Figure 1.6 Leakage from a Swedish supermarket (from Bivens and Gage, 2004).

Reproduced with permission from D. Bivens

Figure 1.7 Leakage from US supermarkets related to charge size (from Bivens and Gage, 2004).

Reproduced with permission from D. Bivens

Natural refrigerants have much lower global warming potential (GWP) and therefore the ability to reduce direct emissions. Chapter 9 describes the Use of Natural Refrigerants in Supermarkets. The chapter describes five classes of natural refrigerants, ammonia, carbon dioxide, hydrocarbons (HCs), water and air. The only two classes that are currently being deployed in supermarkets to replace HFCs are CO2 and HCs.

High GWP refrigerants have also traditionally been used as foam blowing agents. Data on environmental impact are scarce. Alternative blowing agents such as CO2, water and hydrocarbons (pentane, cyclopentane) are available and are commonly used today.

1.3 Types of store

Refrigeration usually accounts for the major share of the energy used in supermarkets. The proportion of energy used for refrigeration in stores varies according to the type of store and its size.

Retail stores are often characterized into types (Tassou et al., 2010):

Hypermarkets – 5000 m

2

to over 10,000 m

2

sales area

Superstores – 1400 m

2

to 5000 m

2

Supermarkets (mid-range stores) – 280 m

2

to 1400 m

2

Convenience stores including forecourts of less than 280 m

2

Convenience stores are smaller and more local to the community, often in town centres. They may not have much parking and many customers will visit for only enough shopping that they can carry, perhaps even just a carton of milk. They are often open long hours, seven days a week. Supermarkets are often on the edge of town and will be accessed by car. They may be visited weekly. They will be larger than the convenience store and hence sell a wider range of products. Superstores and hypermarkets are larger still and sell many more items than just groceries. They may also contain other shops, restaurants and cafés.

Chapter 8 (Design of Supermarket Refrigeration Systems) describes the different types of refrigeration and HVAC specifically to cater for the food retail section of these different store types.

1.4 Purpose of retail display

The purpose of retail display is to display product to customers such that they will purchase it. Good display will present the product in its most attractive format. For non-food product this is more straightforward as the temperature of the product does not need to be controlled.

With perishable food, its temperature is of prime importance. Fruit and vegetables will generally be displayed below 8°C. Chilled food, such as dairy, cooked meats and ready meals, will be displayed below 5°C, and fresh meat, poultry and fish below 4°C. Frozen food will be below −18°C, but can increase to −15°C during a defrost.

Storing food cold is not difficult or particularly energy intensive, as long as it is kept in a well-insulated box. Duiven and Binard (2002) estimated that cold stores use between 30 and 50 kWh m-2 year-1. The process of displaying cold food in a warm environment creates problems, leading to high energy usage, temperature deviations and increased maintenance. Arteconi et al. (2009) reported approximately 130 MWh/month just for food refrigeration for a 10,000 m2 typical supermarket situated in central-northern Italy. This equates to 156 kWh m-2 year-1. This is three times the energy use of a cold store. Similar energy figures for supermarket stores are given for the US (Energy Star, 2003) and Sweden (Olsson et al., 1998).

1.5 Types of cabinet

There are generally 2 ways to display food.

Open (no barrier between the customer and the product) – these have been the common method of displaying chilled food for many years. This method is also used for both vertical and horizontal display of chilled and frozen foods.

Closed cabinets (door or lid between customer and product) – this is the common method to display frozen food in vertical cabinets, but it becoming more common for display of chilled food.

1.5.1 Open-fronted vertical display

The advantage of open-fronted vertical cabinets, and the reason why they are the preference for high-value product in supermarkets, is that there is no barrier between the customer and the product. Customers can browse and handle the products without opening the doors. Customers can be drawn to products that they were not considering buying (impulse buying), which may not be the case if the food is behind a door.

The disadvantage is that open-fronted cabinets use considerably more energy than closed cabinets. They also entrain more moisture, requiring more defrosting. The barrier between the cold product and the food is maintained by an air curtain. This air curtain is not perfect and allows warm air to infiltrate into the cabinet. Approximately 70% of the refrigeration load on these types of cabinets comes from entrainment through the air curtain. Chapter 7 describes the design of an open curtain in detail. With this entrainment comes moisture. When moist air passes over a cold evaporator coil, the moisture in the air will condense and freeze onto the evaporator. This will require regular defrosting. If the cabinet is not defrosted regularly enough, the air curtain velocity drops, reducing the effectiveness of the air curtain, causing more entrainment. This can lead to a cabinet that performs very badly (poor temperature control). The air curtain is also very sensitive to outside influences. This can be from draughts from store doors opening, nearby ventilation outlets, or even customer movements. A disrupted air curtain can increase energy consumption and temperature deviations.

Chapter 4 (Airflow Optimization in Retail Cabinets and the Use of CFD Modelling to Design Cabinets) shows how important optimal airflow is to these types of cabinets. It is time-consuming and costly to optimize a cabinet’s airflow by trial and error in a test room. Computational fluid dynamics (CFD) offers a more efficient way of optimizing the airflow, although this should be carried out in parallel with experimental verification. Chapter 4 demonstrates the use of CFD along with experimental flow visualization and measurement techniques to study the airflow pattern of these cabinets. Flow visualization techniques, mainly particle image velocimetry (PIV) and laser Doppler velocimetry (LDV), are used to achieve a better understanding of the flow pattern and characteristics, as well as CFD code validation.

1.5.2 Closed display

Due to concerns about energy consumption, chilled closed vertical cabinets are becoming more popular. Fricke and Becker (2010) compared two stores where they received either a new set of open-fronted or closed cabinets. They found that the energy consumption of the open-fronted cases was 30% more than the closed cabinets, and there was no change in sales. It is important that the doors are well maintained and that their seals are effective. Heaters are often required to prevent condensation on the glass surface, but can be minimized by anti-sweat heater controls.

Chapter 7 describes these cabinets in more detail. It explains that closed cabinets have a lower refrigeration duty (around 50%) due to less ambient air entrainment and reduction of radiation.

1.5.3 Food display

Chilled food can be displayed either wrapped or unwrapped. Produce tends to be unwrapped, whereas processed food and meat tends to be wrapped. An exception to this is meats, fish and cheese in the delicatessen area where the food is generally displayed unwrapped.

Wrapped food is much easier to display from a food safety and quality point of view because the wrapping stops the food from drying, keeps it clean, and if the food is packaged in modified atmosphere packaging (MAP) the shelf life can also be increased. Unwrapped food is often considered better from a marketing point of view, as it is more appealing to the customer.

Chapter 5 (Display of Unwrapped Foods) discusses cabinets for unwrapped product in detail.

1.5.4 Refrigeration systems

Display cabinets can either be locally (integral) or centrally refrigerated (remote). Large supermarkets have predominantly used central refrigeration systems as this can be more efficient (figures on the increased efficiency are scarce but are probably in the region of 20%) than providing a separate refrigeration system for each cabinet. Control and monitoring systems can also be centralized. The main disadvantage of a centralized system is the long pipe runs carrying refrigerant. Therefore leakage rates for centralized systems have traditionally been high. Typical leakage rates of 15–20% of the charge per year (A.D. Little Inc., 2002) were not uncommon a few years ago. However, as the problem of leakage has received greater exposure, supermarkets have made improvements and leakage rates have fallen. As the refrigerants have generally high GWP, this has a large impact on the environment, as well as the cost of the refrigerant. Velders et al. (2009) estimate global HFC emissions in 2050 equivalent to 9–19% (CO2-eq. basis) of projected global CO2 emissions. Centralized systems also allow the waste heat to be dealt with, rather than allowing it to heat the store. Chapter 11, Maintenance and Long-term Operation of Supermarkets and Minimizing Refrigerant Leakage, has information on leakage rates and methods to reduce them.

Integral systems tend to be used in small stores, where there are not many cabinets. They are also common as additional cabinets in large stores, for example in the restaurant area or end of aisles, where impulse buys are located. This is because they can be placed anywhere as long as there is a source of electrical power, as opposed to centralized cabinets which require refrigerant to be piped to the cabinet.

The safety implications of a centralized plant running a hydrocarbon (HC) refrigerant are too great. HC refrigerants are classed as A3 (EN 378-1:2008) which means lower toxicity (A) and higher flammability (3). EN 378-1:2008 states the maximum charge allowable for different space designations. For a supermarket with a direct expansion refrigeration system using A3 refrigerant, maximum charge is restricted to 1.5 kg (this can be lower for small spaces), whether a remote or integral system.

With integral systems, any leak is likely to be restricted to one cabinet with a limited refrigerant charge, and therefore safety is greatly increased. Large integral cabinets may use a split system such that each system contains less than the maximum allowable charge (1.5 kg). HC refrigerants have benefits with regards to increased efficiency (COP) and low GWP in case of leakage. They are also generally factory-assembled and tested, so leaks are identified in the factory where repairs can be made. Spatz and Yana Motta (2004) showed comparable or slightly better efficiency of propane (R290) (<5%) than a medium temperature R22 system. However, the biggest benefit is the greatly reduced GWP of R290, which is 3, compared with GWP for R404A, which is 3700 (100 year) (UNEP, 2010).

Secondary systems allow a remote refrigeration system, but instead of long pipes runs of high GWP refrigerants with their potential for leakage, the cooling from the central refrigeration system is transferred to the cabinets via a more benign heat transfer fluid (e.g. brine or most recently CO2).

1.6 Cabinet performance

It is important to know how refrigerated equipment performs. For refrigerated cabinets, the purchaser should be interested in the temperature performance in a worst-case scenario (e.g. summer ambient) and the energy consumption of the cabinet. This information can be used to prove that temperature legislation covering the product is being enforced. There are different international standards, energy performance thresholds and legislation applicable in different countries. Chapter 3, Retail Display Testing Standards and Legislation, discusses these standards and legislation in detail.

Performance of cabinets varies considerably. Even similar cabinets may perform differently due to often quite subtle differences in construction. Work carried out by Evans and Swain (2010) demonstrated that the positions of minimum and maximum temperature can vary considerably. In the study, 319 cabinets were tested according to the EN441 or EN23953 test standards. Positions of maximum and minimum temperature within different cabinet types varied, but generally maximum temperatures were in open or exposed (to ambient) areas of the cabinet and minimum temperatures in the least exposed areas. Temperature range (minimum to maximum) in the cabinets examined was significantly greater in frozen than chilled cabinets. The range in temperature in freezers varied from a mean of 15.2 K in well freezers to 19.5 K in chest freezers. Reducing this range would have significant effects on reducing energy consumption. Chilled cabinets with glass doors had the lowest mean temperature range (5.1°C).

Evans and Swain (2010) also demonstrated that energy use, average temperature and temperature range varied between and within cabinet types. Table 1.6 shows energy consumed as total energy consumption (TEC) divided by the total display area of the cabinet (TDA). TDA is a standard methodology used to present the area of a cabinet that is visible to a consumer. Temperature control was also found to vary between cabinet types, with some cabinet formats having overall lower temperatures and less variation between the minimum and maximum temperatures in the cabinet.

Table 1.6