brunel university professor savvas tassou - grimsby · school of engineering and design ...

School of Engineering and Design

www.brunel.ac.uk/about/acad/sed

Refrigerated Display Cabinets

Progress made and research and development issues

Brunel University

Professor Savvas Tassou



1. Work started as a collaboration between Safeway Stores PLC and Brunel University back in 1994. CASE Studentship funded by EPSRC and Safeway– David Stribling

2. Followed by a PhD by Dr Weizhong Xiang3. A recent PhD by Dr Abas Hadawey4. A current PhD project by Ahmad Al-Sahhaf5. Other investigations funded by DEFRA and EPSRC (Drs

Deborah Datta, Richard Watkins and Issa Chaer).

Brief History



• Environmental test chamber to be able to test at EN441 conditions.

• Replication of refrigeration pack and typical supermarket control system in the laboratory for research on modelling and control

• CFD simulation – one of the 1st applications of CFD to display cabinet modelling

Test facilities and Modelling Tools

Condenser

Receiver

Heat Exchanger

Filter Drier

Display Case 1Display Case 2

Liqu

id L

ine

Flow

met

er

Compressor Pack

SV1

SV2

SV3

SV4

TEV

SV SOLENOID VALVE

TEV THERMOSTATIC Exp. VALVE

PRESSURE & TEMPERATURE SENSORS

LOW PRESSURE SIDE

DEFROST LINE

HIGH PRESSURE SIDE



b0

Fan

b1

u0

u1

u1

u1

u1

u1

60

240

250

250

250

380

45460

510

120

200b0

Fan

b1

u0

u1

u1

u1

u1

u1

60

240

250

250

250

380

45460

510

120

200

)()(

2

2000

wcm gH

ubD

ρρρ

−=

u0

TwarmTcold

Break throughu0

TwarmTcold

Break through

Deflection modulus = 0.14~0.18

1430

Multi-deck cabinet design issuesMulti-deck cabinet design issues



b0

Fan

b1

u0

u1

u1

u1

u1

u1

60

240

250

250

250

380

45460

510

120

200b0

Fan

b1

u0

u1

u1

u1

u1

u1

60

240

250

250

250

380

45460

510

120

200

)()(

2

2000

wcm gH

ubD

ρρρ

−=

Deflection modulus = 0.14~0.18

1430


H = Opening heightbo= Air curtain slot widthuo = air curtain initial velocityρc = density of cold air in cabinetρw= density of space airρo= density of air at air curtain discharge

⎥⎦

⎤⎢⎣

⎡⎟⎟⎠

⎞⎜⎜⎝

⎛−

=

w

o

c

o

oom

TT

TTHg

ubD2

2

.

.




Height of opening (m)

Minimum velocity (m/s)

Minimum air flow rate (m3 /s/m)

0.25 0.4 0.023

0.40 0.64 0.038

0.60 0.96 0.057

0.80 1.11 0.089

1.00 1.60 0.096

1.20 1.92 0.115

1.38 2.24 0.134

Minimum initial air curtain velocities for non-isothermal air curtains. Slot width = 60 mm

0.0

1.0

2.0

3.0

4.0

5.0

6.0

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0

Initial velocity (m/s)

Tem

pera

ture

(°C

)




o

w

o

c

o

o bTT

TTHg

u⎟⎟⎠

⎞⎜⎜⎝

⎛−

=

2

2

..18.0

• Experiments and simulation have shown that for multi-deck cabinets H should be the maximum distance between shelves in the cabinet

• Increasing the slot width should reduce the velocity required to provide good sealing

• A loaded cabinet will require a lower air curtain velocity to provide good sealing

• Back panel flow to the shelves will aid the air curtain particularly when the cabinet is not fully loaded.




• Back panel flow to the shelves can help maintain lower product temperature

• High back panel flow reduces the flow requirement from the air curtain

• Increasing the air curtain flow increases the refrigeration load.

0.0

1.0

2.0

3.0

4.0

5.0

6.0

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4Velocity (m/s)

Tem

pera

ture

(°C)

Back panel -0.038 m/sBack panel -0.075 m/sBack panel -0.113 m/s

0.0

0.2

0.4

0.60.8

1.0

1.2

1.4

1.6

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4

Velocity (m/s)

Coo

ling

load

(kW

/m)

Back panel -0.038 m/sBack panel -0.075 m/sBack panel -0.113 m/s



Multi-deck cabinet design issues Air curtain position


• Position of air curtain discharge in relation to edge of shelve can influence performance.

b0

Fan

b1

u 0

u1

u1

u1

u1

u1

60

240

250

250

250

380

45460

510

120

b0

Fan

b1

u1

u1

u1

u1

u1

60

240

250

250

250

380

45460

510

120

1430





0 mm 120 mm 60 mm

1300

1320

1340

1360

1380

1400

0 60 120

Distance of air curtain outlet from front shelf edge (mm)

Coo

ling

load

(W/m

)

276

276.5

277

277.5

278Cooling loadAverage product temperature

• Best performance achieved when b1= slightly above 0 mm• Increasing b1 increases average product temperature and cooling

load



Multi-deck cabinet design issues Honeycomb and air curtain discharge angle

Multi-deck cabinet design issues Honeycomb and air curtain discharge angle

Without Honeycomb

With Normal Honeycomb With Modified Honeycomb

• Reducing turbulence at discharge air grille reduces mixing and ambient air entrainment

• Use of honeycomb will reduce turbulence and can modify discharge velocity distribution.

• Use of honeycomb can slightly reduce air entrainment and cooling load.

• A small positive air curtain discharge angle (5o-10o) can reduce slightly the cooling load

-1.4

-1.2

-1

-0.8

-0.6-0.4

-0.2

0

0.2

0.4

0 10 20 30 40 50 60

Air curtain outlet (mm)

y-ve

loci

ty (m

/s)

without honeycombwith normal honeycombwith modified honeycomb



Multi-deck cabinet design issues Pressure drop and flow distribution

Multi-deck cabinet design issues Pressure drop and flow distribution

• Pressure drop in flow tunnel (rear and top) discharge grille and perforations in the back panel will influence flow distribution and the performance of the cabinet

• Back panel flow to each shelf can be controlled by back panel perforation rate.

410 60 45

30

225

225

225

225

315

Inputs to the CFD model

Air-on section

Lower part of perforated back-panel of the bottom shelf

Perforated back-panel

Entrance of back-panel

Evaporator section

Figure 8.32 Cross section of the cabinet considered in the simulations (Dimensions in mm)

Product Position Air curtain

Top shelf

Second shelf

Third shelf

Fourth shelf

Bottom shelf

Flow distribution (%) 30.0 13.0 12.0 12.0 14.0 16.0



Multi-deck cabinet design issues Flow to bottom shelf


-5

-4

-3

-2

-1

0

1

2

3

4

0 0.01 0.02 0.03 0.04

Entrance of back-panel (m)

Static pressure (Pa)Y-velocity (m/s)

Rear flow tunnel Perforated back-panel

Rear flow tunnel

Evaporator section

Bottom shelf

Product

Lower part of perforated back-panel of the bottom shelf





• Uniform flow distribution in back flow tunnel can be controlled through honeycomb or appropriate flow resistance at inlet to rear flow tunnel

Modified honeycomb (A1)

Solid plate (B1)

Case without modifications (C1)

-5

-4

-3

-2

-1

0

1

2

3

4

0 0.01 0.02 0.03 0.04

Enterance of back-panel (m)

P (pa) (Case A1) V (m/s) (Case A1)

P (pa) (Case B1) V (m/s) (Case B1)

P (pa) (Case C1) V (m/s) (Case C1)



Energy Saving Potetntial

ECM motors 67% more efficient-Tangential fans -Variable speed?More efficient coilMore efficient lighting –LEDs – 66% savings

Energy savings ~ 30%

Air curtain Significant potential

Night blinds Savings ~ 20%

75%

6%

6%

8% 4%1% Infiltration

Radiation

Conduction

Lighting

EvaporatorfansDefrost

TOTAL = 1885 Watts

Contributions to load of open vertical multi-deck cabinets



••Materials, energyMaterials, energy

Environmental impactEnvironmental impact

•• Open chilled display cabinetOpen chilled display cabinet

•• Display volume = 500 litresDisplay volume = 500 litres



Environmental impact Environmental impact -- InventoryInventory

Mild steel21%

Glass8%

Chipboard30%

Stainless steel30%

Foam PlasticsRefrigerant

CopperAluminium Stainless steel

ChipboardMild steelGlassCopperAluminiumFoamPlasticsRefrigerant

Total mass = Total mass = 234 kg234 kg



Environmental impact Environmental impact –– Life cycleLife cycle

0200400600800

1000120014001600

CompleteChiller

Transport ElectricityEUROPE

Transport Landfill

Envi

ronm

enta

l im

pact

, Poi

nts

Human Health Ecosystem Quality Resources

••8 years, 24 hours a day8 years, 24 hours a day



Environmental impact Environmental impact –– MaterialsMaterials

90% of 90% of impactimpact



Environmental impact Environmental impact –– MaterialsMaterials

0 5 10 15 20 25 30

Nickel

Copper

Energy US

Steel

Heat diesel

Energy Asia

Glass (white)

Aluminium ingots

PE (LDPE)

Crude oil

Remaining processes

Environmental impact, Points

52% of 52% of impactimpact



Reducing impact Reducing impact –– MaterialsMaterials•• Copper and Nickel have similar Copper and Nickel have similar

contributionscontributions

•• Nickel (in stainless steel) can be Nickel (in stainless steel) can be avoided by using 430 stainless avoided by using 430 stainless steel instead of 304steel instead of 304

•• Reduces the Reduces the chiller’schiller’senvironmental impact from environmental impact from materials by 30%.materials by 30%.



Reducing impact Reducing impact –– Components & Components & FabricationFabrication

•• At End of life, cabinets At End of life, cabinets are shredded into 2cm are shredded into 2cm size piecessize pieces

•• What is needed is What is needed is clean separationclean separation



•• Minimize number of materialsMinimize number of materials

•• Low use of plasticsLow use of plastics

•• Use of wood with low embodied energyUse of wood with low embodied energy

•• Flat sheet insulation with minimum bondingFlat sheet insulation with minimum bonding

•• KeyKey--hole drophole drop--on fixings or screws, rather than on fixings or screws, rather than rivets or spotrivets or spot--weldingwelding

•• Electrical distribution & components Electrical distribution & components concentrated in one accessible compartmentconcentrated in one accessible compartment

Reducing impact Reducing impact –– Components & Components & FabricationFabrication

GOOD DESIGN FEATURES:GOOD DESIGN FEATURES:



Simulation of supermarket zone - aisleSimulation of supermarket zone - aisle

Free boundary

X

L

X

Y

Y

1000

1000

W

Free boundary

Symmetrical surface

H



No heating system in zoneNo heating system in zone

Section A

Section B

Section C

Section D

2m

2m

2m

Section A Section B

Section C Section D

1100mm1350mm

1600mm 1650mm



No heating system in zoneNo heating system in zone

Temperature coded velocity vectors (K) on two horizontal planes (without HVAC system)

Moisture content (kg/kg)

Air temperature (K)

70% (RH)

50% (RH)

72% (RH) 72% (RH)75% (RH ) 75% (RH)

0.3 m above floor 2.0 m above floorVariation of temperature and moisture content along the aisle centre line (without HVAC system)

Temperature coded velocity vectors (K) on two horizontal planes (without HVAC system)



Under floor heating systemUnder floor heating system

2.5 m

Section A

Section B

Section C

Section D 12 m

2m

2m

2m

Temperature contours (K) on a horizontal plane 0.3 m above floor level

Section A Section B

Section C Section D

Temperature contours (K) at different sections (floor heating system)

Product temperature (°C) Heating power (W/m2)

Cooling load

(kW/m) Top shelf 3rd shelf Bottom shelf

Minimum temperature in

zone (°C) 0 (No HVAC) 0.91 3.1 2.1 3.8 7.5

150 0.93 3.7 2.5 4.7 9.0 200 0.96 3.9 2.6 4.9 9.5



Top extract and bottom supplyTop extract and bottom supply

0.1 m 3/s/m

Heat from main refrigeration. rack

Dehumidifying cooling coil

Evaporator

0.1 m3/s/m

0.1 m 3/s/m

Heat from main refrigeration. rack

Dehumidifying cooling coil

Evaporator

12 m

2.5m

Section A

Section B

Section C

Section D

2m

2m

2m

Product temperature (°C) Bottom supply temperature (°C)

Cooling load

(kW/m) Top shelf 3rd shelf Bottom shelf

Minimum temperature in

zone (°C) No heating system 0.91 3.1 2.1 3.8 7.5

21 0.82 3.3 2.2 4.2 10 25 0.84 3.5 2.4 4.4 11

Temperature contours (K) on a plane 0.3 m above floor level (top suction and bottom supply system)



Bottom extract system – no heating in aisleBottom extract system – no heating in aisle

Section A Section A

Section C Section D

12 m

2.5 m

Section A

Section B

Section C

Section D

2m

2m

2m

Temperature contours (K) at different sections (bottom extract system

Temperature contours (K) on a horizontal plane 0.3 m above floor level (bottom extractsystem)



Bottom extract and top supply system Bottom extract and top supply system

Section A Section B

Section C Section D

2m

2m

2m

Section A

Section B

Section C

Section D

2.5m

12 m

Temperature contours (K) on a horizontal plane 0.3 m above floor level (bottom extractand top supply system)

Temperature contours (K) at different sections (bottom extract and top supply system)



Bottom extract and top supply system Bottom extract and top supply system

Section A Section B

Section C Section D

Moisture content (kg/kg) at Sections A, B, C, and D (bottom extract and top supply system)

Temperature coded velocity vectors (K) at Section D (bottom extract and top supply system)



Comparison of different systemsComparison of different systems

Zone type Latent cooling load (kW/m)

Total cooling load (kW/m)

No HVAC 0.28 0.91

Top extract and bottom supply 0.24 0.82

Bottom extract and top supply 0.16 0.84

Zone type Temperature

Top shelf (ºC)

Temperature 3rd shelf

(ºC)

TemperatureBottom shelf

(ºC)

Zone minimum air temperature

(ºC) Bottom extract 3.6 2.4 4.7 13 Bottom extract and top supply 3.7 2.4 4.7 17

No HVAC system 3.1 2.1 3.8 7.5

Latent and total cooling load for different systems

Comparison between bottom extract system, bottom extract and topsupply systems and no HVAC system



SummarySummary

• Progress has been made but further work needs to be done to gain an in-depth understanding of the factors influencing the performance of air curtains in display cabinets.

• Becoming more important with the use of higher opening heights.• Evaluation of performance of ECM fans and LED lighting in field

trials.• Control integration and system optimisation in real time.• Compact and efficient evaporator/cooling coil designs to minimise

material use and frosting/defrosting losses.• Impact of merchandising approaches on cabinet design, sales and

energy use

brunel university professor savvas tassou - grimsby · school of engineering and design ...

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