Brunel University Professor Savvas Tassou - Grimsby Institute

School of Engineering and Design

Refrigerated Display Cabinets

Progress made and research and development issues

Brunel University Professor Savvas Tassou

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


Brief History 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 Xiang 3. A recent PhD by Dr Abas Hadawey 4. A current PhD project by Ahmad Al-Sahhaf 5. Other investigations funded by DEFRA and EPSRC (Drs Deborah Datta, Richard Watkins and Issa Chaer).



Test facilities and Modelling Tools Receiver

Liquid Line

Filter Drier

Heat Exchanger

TEV

SV4 SV3

Flowmeter

• 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

SV2 SV1

Display Case 2

Display Case 1

Condenser

SV TEV

SOLENOID VALVE THERMOSTATIC Exp. VALVE PRESSURE & TEMPERATURE SENSORS LOW PRESSURE SIDE DEFROST LINE

Compressor Pack

HIGH PRESSURE SIDE



Multi-deck cabinet design issues 45 460

b1 b0 200

60

1430

240

u1

250

u1

250

u1

250

u1

380

u0

Break through

u0

T warm

T cold

510 u1 120 Fan

( ρ 0 b0 u 0 ) Dm = gH 2 ( ρ c − ρ w ) 2

Deflection modulus = 0.14~0.18 www.brunel.ac.uk/about/acad/sed


Multi-deck cabinet design issues 45 460

H = Opening height bo= Air curtain slot width uo = air curtain initial velocity ρc = density of cold air in cabinet ρw= density of space air ρo= density of air at air curtain discharge

b1 b0 200

60

1430

240

u1

250

u1

250

u1

250

u1

380

u0

( ρ 0 b0 u 0 ) Dm = gH 2 ( ρ c − ρ w ) 2

510 u1 120 Fan

Deflection modulus = 0.14~0.18

bo .uo2 Dm = ⎡ To ⎞⎤ 2 ⎛ To g.H ⎢⎜⎜ − ⎟⎟⎥ ⎣⎝ Tc Tw ⎠⎦ www.brunel.ac.uk/about/acad/sed


Multi-deck cabinet design issues Minimum initial air curtain velocities for non-isothermal air curtains. Slot width = 60 mm Height of opening (m) 0.25

Minimum velocity (m/s) 0.4

Minimum air flow rate (m3 /s/m) 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

6.0

Temperature (°C)

5.0 4.0 3.0 2.0 1.0 0.0 0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

Initial velocity (m/s)



Multi-deck cabinet design issues ⎛ To To ⎞ 0.18.g .H ⎜⎜ − ⎟⎟ Tc Tw ⎠ ⎝ = bo 2

uo

2

• 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.



Multi-deck cabinet design issues 6.0 Temperature (°C)

5.0 4.0 3.0

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

2.0 1.0 0.0 0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

Velocity (m/s)

1.6 Cooling load (kW/m)

• 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.

1.4 1.2 1.0 0.8 0.6

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

0.4

Back panel -0.113 m/s

0.2 0.0 0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

Velocity (m/s)



Multi-deck cabinet design issues Air curtain position 45 460

b1 b0

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

60

1430

240

u1

250

u1

250

u1

250

u1

380

u0

510 u1 120 Fan



Multi-deck cabinet design issues Air curtain position

Cooling load (W/m )

1400

278 Cooling load Average product temperature

1380

277.5

1360 277 1340 276.5

1320 1300

0 mm

60 mm

120 mm

276 0

60

120

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

• 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

Without Honeycomb

With Modified Honeycomb

With Normal Honeycomb

0.4 0.2 y-velocity (m/s)

0 -0.2 0

10

20

30

40

-0.4 -0.6 -0.8 -1 -1.2

without honeycomb with normal honeycomb with modified honeycomb

-1.4 Air curtain outlet (mm)

50

60

• 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 www.brunel.ac.uk/about/acad/sed


Multi-deck cabinet design issues Pressure drop and flow distribution

45

410

60

30

225

225

225

Perforated back-panel

225

Lower part of perforated backpanel of the bottom shelf 315

• 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.

Air-on section

Position

Product

Flow distribution (%)

Entrance of back-panel

Air curtain 30.0

Top shelf 13.0

Second shelf 12.0

Third shelf 12.0

Fourth shelf 14.0

Bottom shelf 16.0

Inputs to the CFD model Evaporator section

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



Multi-deck cabinet design issues Flow to bottom shelf Rear flow tunnel

Product

Lower part of perforated back-panel of the bottom shelf

Bottom shelf Evaporator section

4

Rear flow tunnel

Perforated back-panel

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

2 1 0 -1

0

0.01

0.02

0.03

0.04

-2 -3 -4 -5 Entrance of back-panel (m)



Multi-deck cabinet design issues Flow to bottom shelf

Modified honeycomb (A1)

Solid plate (B1)

Case without modifications (C1)

4 3

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

2 1 0 -1

0

0.01

0.02

0.03

0.04

-2 -3 -4

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)

-5 Enterance of back-panel (m)



Energy Saving Potetntial 8%

Infiltration

4% 1%

Radiation

6%

Conduction

6%

Lighting 75% TOTAL = 1885 Watts

Evaporator fans Defrost

Contributions to load of open vertical multi-deck cabinets

ECM motors 67% more efficientTangential fans -Variable speed? More efficient coil More efficient lighting –LEDs – 66% savings Night blinds Savings ~ 20% Air curtain

Energy savings ~ 30%

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


Environmental impact •Materials, energy

•

Open chilled display cabinet

•

Display volume = 500 litres



Environmental impact - Inventory Aluminium

Foam Plastics

Copper Glass 8%

Refrigerant Stainless steel 30%

Mild steel 21%

Chipboard 30%

Stainless steel Chipboard Mild steel Glass Copper Aluminium Foam Plastics Refrigerant

Total mass = 234 kg



Environmental impact, Points

Environmental impact – Life cycle 1600 1400

•8 years, 24 hours a day

1200 1000 800 600 400 200 0 Complete Transport Electricity Transport Chiller EUROPE Human Health

Ecosystem Quality

Landfill

Resources



Environmental impact – Materials

90% of impact



Environmental impact – Materials Environmental impact, Points 0 Nickel Copper Energy US

5

10

15

20

25

30

52% of impact

Steel Heat diesel Energy Asia Glass (white) Aluminium ingots PE (LDPE) Crude oil Remaining processes



Reducing impact – Materials •

Copper and Nickel have similar contributions

•

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

•

Reduces the chiller’s environmental impact from materials by 30%.



Reducing impact – Components & Fabrication

•

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

•

What is needed is clean separation www.brunel.ac.uk/about/acad/sed


Reducing impact – Components & Fabrication GOOD DESIGN FEATURES: •

Minimize number of materials

•

Low use of plastics

•

Use of wood with low embodied energy

•

Flat sheet insulation with minimum bonding

•

Key-hole drop-on fixings or screws, rather than rivets or spot-welding

•

Electrical distribution & components concentrated in one accessible compartment



Simulation of supermarket zone - aisle Symmetrical surface Free boundary Free boundary

H

X Y

1000

L W 1000

X Y



No heating system in zone

2m 2m

Section A 1350mm

Section B

1100mm

Section C 2m Section D

Section A

1600mm

Section C

Section B

1650mm

Section D



No heating system in zone

50% (RH)

72% (RH) 75% (RH )

72% (RH) 75% (RH) 70% (RH)

Moisture content (kg/kg)

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

0.3 m above floor

2.0 m above floor

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

Air temperature (K)

Variation of temperature and moisture content along the aisle centre line (without HVAC system)



Under floor heating system 2m

Section A Section B

2m Section C 2m Section D

Section A

Section B

Section C

Section D

12 m

2.5 m

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

Heating power (W/m2) 0 (No HVAC) 150 200

Cooling load (kW/m) 0.91 0.93 0.96

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

Product temperature (°C) Top shelf 3.1 3.7 3.9

3rd shelf Bottom shelf 2.1 2.5 2.6

3.8 4.7 4.9

Minimum temperature in zone (°C) 7.5 9.0 9.5



Top extract and bottom supply Section A 2m Section B 2m Heat from main refrigeration. rack

Section C 2m

Dehumidifying cooling coil

Section D 12 m

0.1 m 3 /s/m

Evaporator

2.5m 0.1 m3/s/m

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

Bottom supply temperature (°C) No heating system 21 25

Cooling load (kW/m) 0.91 0.82 0.84

Product temperature (°C) Top shelf 3.1 3.3 3.5

3rd shelf Bottom shelf 2.1 2.2 2.4

3.8 4.2 4.4

Minimum temperature in zone (°C) 7.5 10 11



Bottom extract system – no heating in aisle

Section A 2m Section B 2m Section C 2m

Section A

Section D

Section A 12 m

2.5 m

Section C

Section D

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

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



Bottom extract and top supply system Section A 2m Section B 2m Section C

Section A

2m

Section B

Section D

12 m

Section C

Section D

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

2.5m

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



Bottom extract and top supply system

Section A

Section C

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

Section B

Section D

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



Comparison of different systems Latent and total cooling load for different systems

No HVAC

Latent cooling load (kW/m) 0.28

Total cooling load (kW/m) 0.91

Top extract and bottom supply

0.24

0.82

Bottom extract and top supply

0.16

0.84

Zone type

Comparison between bottom extract system, bottom extract and top supply systems and no HVAC system

Zone type Bottom extract Bottom extract and top supply No HVAC system

Temperature Top shelf (ºC) 3.6

Temperature 3rd shelf (ºC) 2.4

Temperature Bottom shelf (ºC) 4.7

Zone minimum air temperature (ºC) 13

3.7

2.4

4.7

17

3.1

2.1

3.8

7.5



Summary • 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 Institute

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