4. STORAGE AND EQUIPMENT


4.1. Storage Conditions

4.1.1 Recommended conditions
4.1.2 Densities and stowage rates
4.1.3 Handling
4.1.4 Insulation and refrigeration costs

4.2 Cold Stores

4.2.1 Building
4.2.2 Equipment

4.3 Management

4.3.1 Administrative routines
4.3.2 Equipment routines
4.3.3 Safety


4.1 Storage Conditions

4.1.1 Recommended conditions

Recommendations and codes of practices which relate to the storage of frozen fish products are not always applied, and in many cases they are a compromise or merely state the minimum requirements. Individual countries, or even companies, may have their own standards, therefore, potential customers should be consulted on their requirements before decisions are made on cold storage conditions.

One of the reasons for the differences between one source of information and another is that different criteria are often used to define maximum storage time. In some cases this may be based on a good quality product, whereas in others it may be sufficient that the product is still edible. Maximum storage times must therefore be clarified by also stating the standards applied.

In most recommendations, storage times are given for different temperatures and this may imply that the design temperature of the store need only be sufficient for the storage times contemplated. Cold stores, however, are seldom used for one product only and often the total storage time is made up of stopovers in a series of stores along the marketing distribution chain. Cold stores should therefore be built for the most demanding conditions rather than those immediately contemplated. For instance, it may be realistic to build a store for fatty fish for a total storage time of one year and, thus, ensure good storage conditions for all fish products from one season to another.

Table 42 contains UK recommendations for a temperature of -30C. The Table gives the period within which the product is for all purposes, as good as fresh and the figures should be regarded as the highest obtainable under ideal conditions.

Another set of recommendations, which are now under review, have been issued by the International Institute of Refrigeration in the second edition of their book "Recommendations for the processing and handling of frozen foods", and these are listed in Table 43. In this case, the times are for practical storage life which is defined as the time the product remains suitable for consumption or for the process intended.

A number of codes of practice for fish and fishery products, elaborated by the Codex Alimentarius Commission, Joint FAO/WHO Food Standard Programme, also make recommendations for storage conditions and these are listed elsewhere in this document.

In addition to temperature, humidity is also important, and for the storage of frozen fish products relative humidity in the store should be maintained at as high a level as possible to avoid excessive. dehydration of unwrapped produce. The relative humidity within the store relates to the difference in temperature between the cooler surfaces and the control temperature of the air. Large cooler surface areas require smaller temperature differences to transfer the heat, and this will result in a higher relative humidity. Conversely, a small cooler operating with a large temperature difference will result in a low relative humidity. A compromise has therefore to be made between cost, size of the cooler and storage conditions, and a temperature difference of 5C is a normal design figure. This will give a relative humidity of about 85-90% but in special designs, such as jacketed cold stores, relative humidities of 98% and higher are possible.

Any situation that results in a rise in the store temperature is likely to reduce the relative humidity of the air, therefore, loading warm produce and leaving doors open for long periods should be avoided.

Even when product is frozen down to the intended storage temperature in an adjacent freezer, it is difficult to avoid the product warming up on being transferred to the store. In the cold storage refrigeration load calculations, allowance is made for a product load equivalent to a 10C temperature rise, and this should be the intended limit for all produce.

Table 42 Cold storage lives at -30C.

Item

Storage life in months

White fish, gutted

8

Smoked white fish

7

Herring and mackerel, gutted or ungutted

6

Kippers

4

Shellfish  

raw whole or shelled Nephrops and cooked shucked mussels

8

raw shrimp, raw whole oysters and scallop meats

6

cooked shrimp, cooked whole crab and lobster

6

extracted crab meat

4

Table 43 Practical storage lives of fish products

Product

Storage life in months

-18C

-25C

-30C

Fatty fish
Lean fish
Flatfish
Shrimp

4
8
10
6

8
18
24
12

12
24
>24
12

4.1.2 Densities and stowage rates

Figures for density and stowage rate of frozen fish products are not meaningful, unless the exact conditions are clearly defined. For instance, cartons of fish fingers stored on pallets in master cartons can have a stowage rate of between 2.4 and 3.1 m/t, depending on the weight in the individual carton packages. Clearly, if this difference exists with such a well defined and regular shaped item, there will be little benefit to the designer or cold store operator if only average or typical figures are given or, alternatively, figures are quoted as a range to cover all eventualities. In the following Tables, both detailed and general figures are quoted and these are clearly destinguished so that they are used with the appropriate degree of discretion.

Other than where it is stated, all stowage rates are for pallet loads only and exclude allowances for passageways, etc.

Table 44 Density and stowage rates Fillets IQF -polystyrene trays with stretch wrap

Wt of pack (kg)

Total wt in master carton (kg)

Dimensions of pack (mm)

No of packs in master carton

Dimension of master carton (mm)

Density in master carton (t/m)

No of master cartons per pallet

Total wt per pallet (kg)

Stowage rate with pallet (m/t)

0.284

1.7

188 x 135 x 30

6

305 x 190 x 140

0.21

200

340

5.9

0.227 to 0.298

2.3

220 x 130 x 30

10

270 x 235 x 195

0.19

119

274

7.4

0.255 to 0.369

2.3

270 x 138 x 18

9

400 x 300 x 100

0.19

150

345

5.8

0.255 to 0.369

4.6

270 x 138 x 18

18

400 x 280 x 194

0.21

70

322

6.3

0.173 to 0.355

4.6

215 x 130 x 30

18

260 x 220 x 335

0.24

68

313

6.4

0.184 to 0.340

7.25

264 x 131 x 25

35

400 x 297 x 260

0.23

50

360

5.6

The number of packs in a master carton depends on the catch weight of the pack. The numbers given are the maximum possible

Table 45 Densities and stowage rates - Fish fingers -cartons and bag packs

Wt of pack (kg)

Type of pack

Dimensions of pack (mm)

Density in pack (t/m)

No of packs in master carton

Dimension of master carton (mm)

Density in master carton (t/m)

No of master cartons per pallet

Total wt per pallet (kg)

Stowage rate with pallet (m/t)

0.150

Carton

110 x 100 x 30

0.45

48

375 x 230 x 210

0.40

91

655

3.1

0.255

"

180 x 100 x 30

0.47

48

390 x 210 x 365

0.41

60

734

2.7

0.255

"

182 x 100 x 32

0.44

24

380 x 305 x 130

0.41

110

673

3.0

0.580

"

200 x 100x 55

0.53

10

290 x 215 x 210

0.44

133

771

2.6

2.89

"

280 x 196 x 112

0.47

-

280 x 196 x 112

0.47

286

827

2.4

0.850

Bag pack

115 x 95 x 135

0.58

12

300 x 245 x 300

0.46

85

867

2.3

1.45

"

170 x 100 x 155

0.55

6

355 x 300x 165

0.50

99

861

2.3

Table 46 Density and stowage rates - Fillets IQF -bulk catering packs

Wt of pack (kg)

Type of pack

Dimension of carton (mm)

Density in carton (t/m)

No of cartons per pallet

Total wt per pallet (kg)

Stowage rate with pallet (m/t)

2.7

Carton

374 x 235 x 100

0.31

195

527

3.8

3.2

"

379 x 238 x 115

0.31

169

541

3.7

3.6

"

379 x 238 x 115

0.35

169

608

3.3

4.1

"

333 x 250 x 150

0.33

140

571

3.5

4.5

"

375 x 284 x 100

0.42

150

675

3.0

6.4

"

410 x 270 x 185

0.31

78

499

4.0

9.1

"

435 x 278 x 250

0.30

54

491

4.1

Table 47 Density and stowage rates - Fish portions

Wt of pack (kg)

Type of pack

Dimensions of pack (mm)

Density in pack (t/m)

No of packs in master carton

Dimension of master carton (mm)

Density in master carton (t/m)

No of master cartons per pallet

Total wt per pallet (kg)

Stowage rate with pallet (m/t)

0.2

carton

140 x 140x 20

0.51

48

430 x 300 x 180

0.41

72

691

2.9

0.6

"

145 x 140 x 40

0.74

12

435 x 295 x 115

0.49

104

749

2.7

0.71

"

190 x 175 x 48

0.44

12

360 x 300 x 200

0.39

70

596

3.4

0.95

"

240 x 137 x 50

0.58

8

282 x 218 x 250

0.49

108

821

2.5

1.1

"

212 x 115 x 70

0.64

12

475 x 225 x 220

0.56

60

792

2.5

2.4

"

333 x 245 x 76

0.39

-

333 x 245 x 76

0.39

252

605

3.3

2.5

"

240 x 180 x 115

0.50

6

500 x 185 x 355

0.46

48

720

2.8

3.2

"

258 x 208 x 80

0.75

6

430 x 280 x 260

0.61

45

864

2.3

Table 48 Density of stowage rates - Fillets blocks

Wt of block (kg)

Dimension of block (mm)

Density (t/m)

No of blocks per pallet

Total wt per pallet (kg)

Stowage rate with pallet (m/t)

5.7

505 x 263 x 38

1.13

176

1003

1.3

6.1

508 x 295 x 41

1.0

168

1025

1.2

6.4

629 x 264 x 38

1.01

160

1024

1.2

7.5

483 x 252 x 58

1.06

128

975

1.4

8.4

484 x 288 x 56

1.08

120

1008

1.2

12

798 x 249 x 60

1.01

84

1008

1.7 a/

25

530 x 525 x 102

0.88

40

1000

1.3

29

802 x 533 x 65

1.04

34

986

1.3

50

1 060 x 530 x 102

0.88

20

1000

1.3

Notes:
(1) Pallet loads kept
(2) No pallet convertors loads stacked on top of each other
(3) 40-mm pallet overlap allowed on each side

a / Dimensions not ideal for maximum utilization of standard pallet

Table 49 Density and stowage rates - Fish cakes

Wt of pack (kg)

Type of pack

Dimensions of pack (mm)

Density in pack (t/m)

No of packs in master carton

Dimension of master carton (mm)

Density in master carton (t/m)

No of master cartons per pallet

Total wt per pallet (kg)

Stowage rate with pallet (m/t)

0.1

Poly sleeve

75 x 150 x 15

0.60

72

480 x 240 x 165

0.38

90

648

3.1

0.5

Poly bag

75 dia x (180+80)

0.63

12

300 x 235 x 180

0.47

128

768

2.6

1.0

Bag pack

137 x 68 x (170 +80)

0.63

8

390 x 310 x 165

0.40

90

720

2.8

3.6

Carton

300 x 230 x 123

0.42

-

300 x 230 x 123

0.42

192

691

2.9

Table 50 Density and stowage rates - Fillets IQF -polybags

Wt of pack (kg)

No. of packs in master carton

Dimension of master carton (mm)

Density in master carton (t/m)

No of master cartons per pallet

Total wt per pallet (kg)

Stowage rate with pallet (m/t)

0.700

12

         

0.800

6

400 x 300 x 135

0.30

110

528

3.8

0.800

12

400 x 300x 210

0.38

63

605

3.3

0.800

12

330 x 292 x 280

0.36

55

528

3.8

0.800

12

395 x 295 x 290

0.28

50

480

4.2

0.800

15

435 x 269 x 271

0.39

54

648

3.1

0.907

10

435 x 278 x 250

0.30

54

490

4.1

Table 51 Density and stowage rates - Fish portions in batter

Description of product

Wt of pack (kg)

Type of pack

Dimension of pack (mm)

Density in pack (t/m)

No of packs in master carton

Dimension of master carton (mm)

Density in master carton (t/m)

No of master cartons per pallet

Total wt per pallet (kg)

Stowage rate with pallet (m/t)

2 oven
cod

0.2

Carton

182 x 117 x 28

0.34

24

350 x 240 x 187

0.31

104

499

4.0

2 crispy
cod

0.2

Carton

174 x 118 x 28

0.35

24

355 x 245 x 183

0.30

104

499

4.0

6 oven
cod

0.6

Carton

185 x 114 x 72

0.4

8

300 x 192 x 235

0.36

120

576

3.5

6 crispy
cod

0.6

Carton

172 x 116 x 61

0.5

8

250 x 185 x 242

0.43

144

691

2.9

Table 52 Density and stowage rates - Fish portions in sauce

Description of product

Wt of pack (kg)

Type of pack

Dimension of pack (mm)

Density in pack (t/m)

No of packs in master carton

Dimension of master carton (mm)

Density in master carton (t/m)

No of master cartons per pallet

Total wt per pallet (kg)

Stowage rate with pallet (m/t)

Cod portion in sauce

0.15

Satchet in carton

130 x90 x 22

0.64

72

400 x 195 x 297

0.47

75

810

2.5

Haddock portion in sauce

0.15

"

125 x 90 x 22

0.61

72

390 x 190 x 300

0.49

75

810

2.5

Cod portion in sauce

0.15

"

126 x 90 x 25

0.53

72

390 x 190 x 300

0.49

75

810

2.5

4 cod portions in sauce

0.6

Satchet in carton

183 x 115 x 45

0.63

12

300 x 195 x 245

0.50

120

864

2.3

Table 53 Density and stowage rates - Nominal values for various frozen products

Product

Density (t/m)

Stowage rate (m/t)

Frozen whole gutted cod in large blocks-weight of fish within dimensions of the block

avg.

.64
(fish very loosely packed in block)

1.6

.88
(very compact block)

1.1

.77

1.3

Frozen whole gutted cod in large blocks, including allowance for supporting structure access, etc

.50

2.0

Frozen fillets in large blocks, including allowance for packaging, structure, access, etc

.64 to .80

1.6 to 1.3

Frozen whole gutted cod, stowed as single fish

.40 to .48

2.5 to 2.1

Frozen whole gutted halibut:  
in wooden boxes

.48 to .56

2.1 to 1.8

stowed loose

.61

1.6

Frozen whole salmon: stowed loose in wooden boxes

.53 to .56

1.9 to 1.8

Frozen shelled shrimps in blocks

.72 to .88

1.4 to 1.1

Frozen shelled shrimp in blocks, including allowance for packing structure, etc

.59 to .72

1.7 to 1.4

Frozen breaded shrimp in consumer packs in master carton

.40 to .48

2.5 to 2.1

4.1.3 Handling

The method of handling and the degree of mechanization used will depend on both the size of the store and the mode of operation.

Larger stores will inherently require more mechanization since greater quantities of produce have to be moved and stacking heights are higher. Some stores may only be loaded and unloaded in-frequently with a minimum of traffic in and out, therefore, there may not be a requirement for a highly mechanized system to move produce ,quickly. Other stores may be relatively small but with a good deal of traffic and a quick turnover of produce. In these cases, more mechanization may be justified in spite of high costs.

Even when labour is readily available and probably the cheapest method of handling, consideration may have to be given to a degree of mechanization to speed up traffic in and out of the store and thereby avoid long periods when the door is left open. Some simple mechanical aids may also be required to reduce physical effort.

A compromise may also have to be made between strong but more expensive packaging which will allow higher stacking in the store and a palletized or racked system which involves higher capital costs.

Another penalty often incurred with quick handling methods is that more storage space is required for manoeuvring handling equipment, and this means higher cold storage capital and operating costs.

The type of product will influence the method of storing and handling.

Large, regular shaped blocks may be stacked on pallets with one directly on top of the other. If the packages are fragile, supporting structures will be required and, whatever the product, unframed or unsupported pallets should be limited to only two pallets high in the interest of safety. Pallet loads may be placed on the shelves of a fixed racking system, or the pallets may be fitted with a converter which is a sectional steel frame surrounding the load (Figure 41). Mesh sides can be incorporated in the converter frame and non-regular shapes, such as single fish or broken blocks, can then be stored loosely within a regular stacking system.

Loading in pallets also allows full or part loads to be kept separate and identified so that they can be removed with the minimum amount of re-arrangement within the store.

A maximum stack height of six pallets is common in large stores with a roof clearance height of about 10.5 m.

A number of mechanical aids are used for stacking pallets, and when it is considered that a pallet load has a nominal weight of about 1 t, these devices are essential even in the smallest stores.

The minimum requirement would be a hand-operated pallet truck (Figure 42), and for a quick movement of produce this may be mechanized (Figure 43). Better utilization of floor space is achieved with reach trucks (Figure 44). Floor utilization can be improved even further if narrow aisle racking is used with a turret truck (Figure 45), which is, however, more expensive and less versatile. Other mechanical aids are the hand-operated fork-lift stacker (Figure 46), and for reavier duty the fork-lift truck (Figure 47).

Figure 41 Pallet with converter frame Figure 42 Hand-pallet truck

Figure 43 Pedestrian-operated, battery-powered, electric pallet truck

Figure 44 Reach truck

Figure 45 Turret truck

Figure 46 Hand-operated, fork-lift stacker

Figure 47 Fork-lift truck

When small items, such as individual cartons, have to be regularly transported in and out of the cold store, a mobile gravity roller conveyor may be used and operated through a small hatch rather than an open doorway.

Table 54 Handling equipment costs

Item

Capacity

O/A dimensions (m)

Approximate cost (US$)

Pallet

1 t

1.2 x 1.0

12

Pallet convertors

7.5 t

1.68 m high for 1.2 x 1.0 pallet

75

Hand-pallet truck

2 t

0.54 x 1.4 x 0.051 for lowered ht

660

Pedestrian-pallet truck

1.5 t

-

4 200

Fixed racking

16 x 1 t
(4 high)

5.4 x 0.9 x 6.0

750

Roller conveyor

-

0.075 pitch x 0.3 wide x 0.4 high

180/m

Power drive for roller conveyor

0.75 kW

-

600

Manual lift stacker

1 t

1.3 x 1.5 x 1.8

2 250

Counterbalanced - 3-wheeled fork-lift truck

1 t

2.7 x 1.05 x 2.0

13 500

Counterbalanced - 4-wheeled fork-lift truck

2 t

3.0 x 1.05 x 2.2

21 000

Reach truck

2 t

2.2 x 1.05 x 2.2

37 500

Battery charger (8-h charge time)

-

-

1 500

4.1.4 Insulation and refrigeration costs

The thicker the insulation the lower will be the refrigeration requirement; but the thicker insulation costs more, therefore, a compromise has to be made.

Figure 48 shows the effect of thickness insulation on costs and illustrates how a compromise may be reached.

Figure 48 Economic thickness of insulation

Line 'A' is the additional cost of insulation above a given nominal minimum thickness.
Line 'B' is the savings in refrigeration equipment capital costs resulting from the reduced refrigeration requirement.
Line 'C' is derived from 'A'-'B' and, therefore, is the net additional capital cost.
Line 'D' is the savings in refrigeration equipment running costs resulting from using thicker insulation.
Line 'E' is the net annual savings when capital is written off over a five-year period.
Line 'F' is the net annual savings when capital is written off over a 10-year period.

The optimum insulation thickness, as can be seen from Figure 48, depends on the arrangement made for writing off capital costs, but this thickness will also depend on other factors such as power, insulation and borrowing costs which will, in turn, depend on local conditions. Optimum insulation thickness has therefore to be worked out on an individual basis but, in practice, likely savings may not be significant other than in the medium size or larger installations.

Whatever the resulting optimum economic thickness of insulation may be, there is a minimum recommended thickness which does not depend on costs but on the environmental conditions within and out with the cold store. The outer surface of the insulation of a cold store will always be below the temperature of the surrounding ambient air, and if this is below the dew point temperature of the moisture in the air, condensation will occur.

The insulation thickness as given in Table 58 takes this into account as well as the likely economics but, as in the costing case shown in Figure 48, local conditions may have to be applied to determine minimum as well as optimum economic thickness. It is generally the case that the optimum economic thickness is greater than the minimum recommended thickness, but factors such as very high local costs of insulation may change this.

To avoid unnecessary condensation, cold stores Should be sited where they avoid particularly demanding conditions. For instance, they should not be within a building and adjacent to a process such as the cooking of shellfish, unless the water vapour given off is ducted immediately out with the building.

4.2 Cold Stores

4.2.1 Buildings

A good deal of the information in this section has been directly extracted from the second edition of the International Institute of Refrigeration "Guide to Refrigerated Storage", which should be consulted for more detail on both the design and operation of cold stores.

4.2.1.1 Main characteristics:

Almost without exception, modern cold stores are prefabricated panels.

The laminated panels consist of a layer of insulation bound to outer and inner sheets of facing material which are usually made from a coated metal (Figure 50). The facing material gives the panel strength and also protects the insulation from physical damage. The outer sheet also provides a suitable heat reflective surface and, most important, it provides a barrier against vapour in the outside air entering the insulation and accumulating as ice. The inner surface is usually finished with a material or coating which is compatible with the storage of frozen food.

With Some types of insulation, such as polyurethane, a laminated panel allows a thinner layer of insulation to be used. The insulation properties of these cellular type insulations often deteriorate with time due to the diffusion of the gases filling the voids, and the panel construction inhibits this process.

A prefabricated structure results in a very short on-site erection time and this operation can be done by unskilled labour under supervision. This type of construction is therefore appropriate for remote sites where there is no skilled labour for other types of construction.

An exception to using a prefabricated construction would be when a relatively small store is built within a building against a wall or roof So that there is insufficient room for a self-standing store. The main assurance to be given by the contractor with this type of construction is that an effective and continuous vapour barrier is provided on all the outer faces of the insulation.

Table 58 gives the likely insulation thickness required for a range of operating conditions. These are derived from empirical calculations based on a requirement for 4.6 mm of cork per 1C temperature difference with a corresponding thickness for the other insulations in accordance with their insulation properties.

Cold Stores -evaluation of prefabricated-vs. constructed on the spot:

Prefabricated- advantages

  1. Homogeneous walls
  2. Easily erected store by unskilled labour under supervision
  3. Short erection time
  4. Metal-clad panels provide good vapour barrier
  5. Free standing panels mean little additional building work
  6. Cladding can be treated (galvanized, painted, etc.) to give pleasing internal and external appearance
  7. Store can be increased in size fairly readily if required at a later date
  8. Store can be transferred to another site if required

Prefabricated- disadvantages

  1. Panels have to be factory made
  2. A high standard of quality control is necessary in order to produce uniform panels
  3. Costly equipment (presses, etc.) is required to produce satisfactory panels

Cold Store -constructed on site

Advantages

  1. Semi-skilled local labour should be capable of building store when given adequate guidance
  2. Insulation slabs (e.g., polystyrene) and other building materials are used for other purposes and are likely to be readily available
  3. They can be built to fit exactly into available space

Disadvantages

  1. Longer erection time required than for prefabricated store
  2. Untrained labour could omit necessities such as a vapour barrier because of lack of knowledge
  3. Likely to be more insulation required than in the case of prefabricated panels
  4. More supporting structure required than for prefabricated

Table 55 Cost of cold store prefabricated panels (polyurethane insulation)

Thickness
(mm)

Cost
(US$/m)

75
100
125
150

37.5
39.0
40.5
42.0

Table 56 Cold store costs (prefabricated panel stores)

Size of store
(m)

Cost
(US$/m)

500
1 000
2 000
5 000
10 000

55
40
30
22
18

Notes:
(1) Cost includes refrigeration
(2) Cost for installation on a prepared indoor site within 250-km radius of suppliers premises

Table 57 Insulation properties

 

Desirable values and properties

Polyurethane

Expanded polystyrene

Cork

Density a/ (kg/m3)

Low

30

20

90

Conductivity (kcal/h mC)

Low

0.0198

0.030

0.037

Cross breaking strength (KN /m2 min)

High

206

170

138

Temperature limits C  
High

Large range

+100

+93

+60

Low

<-50

<-50

<-50

Resistance (rot, vermin, fungus etc)

Completely resistant

Completely resistant

Completely resistant

Poor

Resistant (chemical)

Completely resistant

Resistant to chemicals, oils and solvents

Resistant to dilute acids and concentrated alkalis but not to oil, petrol, aliphatic, aromatic, and chlorinated hydrocarbons

Poor

Resistance (fibre)

Completely fireproof

Normally burns but can be made in fire proof form

Burns slowly

Burns

Remarks

No health hazards, odourless and easily worked

Can be supplied in panels, formed in place or sprayed on

Clean and easily worked, resilient

Supplied in board, granulated and bonded forms

Cost (50 mm thick) ($/m2)

Low

18

2.0

4.2

a/ Typical values only. Density and related values can vary widely

Table 58 Recommended minimum thickness for cold store insulation (mm)

Material and conductivity

Ambient Temp.
(C)

Storage Temperature (C)

-10

-18

-20

-25

-30

-50

Cork
0.037 Kcal/hr mC

20

150

175

200

225

250

325

30

200

225

250

250

275

375

40

250

275

275

300

325

425

Polystyrene
0.030 Kcal/hr mC

20

125

150

175

200

225

275

30

175

200

225

225

225

325

40

225

225

225

250

275

350

Polyurethane
0.0198 Kcal/hr mC

20

100

100

125

125

150

175

30

125

125

150

150

150

200

40

150

150

150

175

175

225

Cork thicknesses calculated as 4.6 mm/C difference between ambient and cold store temperatures
Ratio of conductivities -cork, polystyrene, polyurethane 1:0.81:0.53
Thicknesses rounded up to nearest 25 mm

4.2.1.2 Selected stores:

The capacity of a store, quoted in terms of the quantity of produce it can hold, can only be a nominal value which may differ widely from the actual capacity achieved in practice.

Some of the factors which affect store capacity are:

The stores in Table 59 and the layout diagrams are listed under nominal capacity values which, in this case, are close to the capacity achieved by careful matching of the store dimensions to the product storage requirements.

4.2.1.3 Layout:

  1. Store height

The internal height of the cold store should be based on the height of the pallet, the number of pallets to be stacked and an additional height for safety, manoeuvring air distribution, technical installations and the ceiling structure in the case of external insulation.

In the case of stores with false ceilings, approximately o.5-m clearance between the top of the uppermost pallet and the ceiling is adequate. Where the store is provided with internal roof/wall mounted coolers, the clearance should be at least equal to the height of the cooler in order to prevent the pallets obstructing the circulation.

In Europe, two sizes of pallets are widely used, i.e., 1.20 m x 0.80 m and 1.20 m x 1.00 m. Common pallet heights in most European countries are 1.75 m and 1.86 m, but in the United Kingdom it is 1.68 m and in Scandinavian countries 1.25 m.

For forklift truck operated stores using 2.00-m high pallets, stacking heights of 4-5 pallets are the most common. A five-pallet height should be used only for large stores with a slow stock rotation.

For four high-pallet stacking, the most commonly adopted heights for cold rooms are in the range of 7.20 m - 8.00 m, depending on the height of pallet used. If pallets are to be stacked five high, this figure may easily go up to approximately 10 m.

Whatever dimensions of width, length and height be chosen, these dimensions should be checked against existing laws, regulations and insurance requirements which may vary from country to country.

One country may restrict the floor area, another the length of the room (maximum emergency distance), and in yet another the insurance company may not be willing to authorize large volumes in one room unless a high insurance premium is paid.

  1. Store passageways

When designing cold store layouts, an important question is the width of the gangway and, therefore, the use of reach trucks is more common as they do not require gangways wider than 2.60m-2.70 m, as compared to 3.60 m for a counter-balanced truck.

  1. Loading banks and antirooms

As the main purpose of a loading bank is to provide for easy handling of pallets between the cold store and transport trucks, the height of the loading ramp should correspond to the height of the floor of the more popularly used transport vehicles.

This height is normally about 1.40 m for trucks and can be as low as 0.60 m for distribution vans.

As the height of the truck floor varies with its load, it is necessary to use dock levellers between the loading bank and the truck. Depending on whether an open or covered loading dock is chosen, the dock levellers can be hung on the edge of the loading dock or built into a recess in the dock.

The length of a goading bank should enable the simultaneous handling of an adequate number of vehicles.

The width of the loading bank can vary from 4 m to 10 m, depending on traffic intensity and type of equipment used for handling.

The height between the floor and the roof is governed by the height of the forklift trucks operating on the loading dock, the height of the store doors, including the mechanism above the automatic doors, and the height of the vehicles backing on to the loading dock.

For countries which use shallow lightweight pallets, it could be economic to move two superposed pallets at a time. The height of these two pallets must then be considered when deciding upon the free height of the loading dock roof or canopy.

Cloakrooms, lavatories and offices, together with supervisor's or checker's offices, are sometimes incorporated on the loading bank at one or other end with the checker's office sited to have a good view of the whole length of the loading platform. In addition, personnel warming rooms under visual supervision can be incorporated into the loading bank.

In some instances, battery charging facilities are also incorporated on the platform, the battery chargers being mounted on the rear wall, i.e., the wall that is common to the cold store.

In other instances, it is sometimes desirable to locate the administrative offices of the complete cold store complex above the loading bank and use this as a canopy.

Figure 49 General arrangement for a large store

  1. Stacking plans

In the cold-store layouts shown in Figures 51-61, the products detailed in Table 59 are used in the proportions given in Table 60.

Various combinations of access requirement, method of handling and stacking heights used, and the capacities and storage rates achieved are summarized in Table 61.

In each layout all the produce is palletized, using pallets measuring 1 200 mm x 1 000 mm x 160 mm, to give a pallet height of 1.68 m.

In all stores a substantial area is also left clear immediately inside the doorway to enable loads to be assembled and broken up. This, however, is not a standard requirement for all stores.

  1. Cold store doors

For cold stores with a high traffic turn-round, the power-operated door is best. Such doors can open or close in about 3-5 sec. Doors can be equipped for automatic opening and closing, the pull cord can be positioned sufficiently far away from the door in order to allow the forklift driver to operate the mechanism. A clear door width of 2 m is suitable for normal pallet handling.

The height of the door may vary according to the height of the forklift truck or the merchandise. The door should, however, be kept as low as possible in order to reduce the entrance of warm, humid air while open. Heights of 2.40 m for hand trucks and 3.00-3.30 m for high stacking forklift trucks are normal.

When deciding upon the number of doors, one-way traffic should be considered if the traffic movement is expected to be high.

Table 59 Details of pallet loads used in layouts in Figures 51-61

Product No.

Description

Average
weight/pallet
(kg)

Net storage
volume/pallet
(m)

Storage rate
(m/t)

Storage density
(t/m)

1

Fish fingers

770

2.02

2.6

0.38

2

Fish steaks

730

2.02

2.8

0.36

3

IQF fillets in polytrays

326

2.02

6.2

0.16

4

IQF fillets in bulk catering pack

559

2.02

3.6

0.28

5

IQF fillets in polybags

546

2.02

3.7

0.27

6

Blocks of whole fish

990

1.6

1.6

0.62

Note: For Items 1-5 stowage rates and densities are for pallets fitted with converters

Table 60 Product composition used in the cold-store layouts in Figures 51-61

Product No.

Number of pallets

Store
No. 1

Store
No. 2

Store
No. 3

Store
No. 4

Store
No. 5

Store
No. 6

Store
No. 7

Store
No. 8

Store
No. 9

Store
No. 10

Store
N
o. 11

1

43

43

170

180

188

100

192

175

130

310

400

2

40

40

160

160

160

100

160

160

100

160

400

3

30

30

120

120

120

70

120

120

70

120

280

4

35

35

140

140

140

85

140

140

85

140

340

5

20

20

80

80

80

45

80

80

45

80

200

6

0

0

100

100

100

260

100

100

260

100

1 020

Total pallet load

168

168

770

780

788

660

792

775

690

810

2 640

Table 61 Data on stores with different capacities and storage layouts

Store number

1

2

3

4

5

6

7

8

9

10

11

Nominal capacity (t)

100

100

500

500

500

500

500

500

500

500

2 000

Actual capacity (t)

102.6

102.6

507.7

515.4

521.6

502.3

524.6

511.5

525.4

538.5

2 023.2

Type of handling

Manual

Manual

Manual

Manual

Mechanical

Mechanical

Mechanical

Mechanical

Mechanical

Mechanical

Mechanical

Type of cooling

Internal coolers

Internal coolers

Internal coolers

Internal coolers

External coolers & false ceiling

External coolers & false ceiling

External coolers & false ceiling

External coolers & false ceiling

External coolers & false ceiling

External coolers & false ceiling

External coolers & false ceiling

Total number of
pallets stored

168

168

770

780

788

660

792

775

690

810

2 670

Number high

2

2

2

2

4

4

4

5

5

5

5

Stack height (m)

3.36

3.36

3.36

3.36

6.72
5.12

6.72
5.12

6.72

8.4
6.4

8.4
6.4

8.4

8.4

Rack height (m)

-

-

-

-

7.33

7.33

-

9.2

9.2

-

-

No. of pallets with
convertors

168

168

770

780

416

264

792

405

260

810

2 670

No. of pallets without
convertors

-

-

-

-

100

260

-

100

260

-

-

No. of pallets in racks

-

-

-

-

272

136

-

270

170

-

-

Dimensions of
pallets (mm)

1 200
x
1 000

1 200
x
1 000

1 200
x
1 000

1 200
x
1 000

1 200
x
1 000

1 200
x
1 000

1 200
x
1 000

1 200
x
1 000

1 200
x
1 000

1 200
x
1 000

1 200
x
1 000

Internal dimensions (wall to wall)

 

Width (m)

12.4

9.5

20.5

25.2

14.5

24.0

18.2

14.5

19.3

18.2

28.7

Length (m)

21.1

21.1

52.3

27.5

45.6

23.0

23.6

36.4

23.2

19.7

35.4

Internal dimensions
(kerb to kerb)

 

Width (m)

12.1

9.2

20.2

24.9

14.2

23.7

17.9

14.2

19

17.9

28.4

Length (m)

20.8

20.8

52.0

27.2

45.3

22.7

23.3

36.1

22.9

19.4

35.1

Internal height (m)
(floor to ceiling)

4.73

4.73

4.73

4.73

7.7

7.7

7.17

9.5

9.5

8.85

8.9

Total internal volume (m)

1 237.6

948.1

5 071.3

3 277.9

5 091.2

4 250.4

3 079.7

5 014.1

4 253.7

3 173.1

9 042.2

Internal volume (m)
(kerb to kerb x ht)

1 190.4

905.3

4 968.4

3 203.5

4 953.1

4 142.5

2 990.4

4 869.9

4 133.5

3 073.3

8 871.9

External dimensions(m) (width x length x height)

 

Floor area (m)
(kerb to kerb)

251.7

191.4

1 050.4

677.3

643.3

538

417.1

512.6

435.1

347.3

996.8

Passage widths (m)

2 & 3.9

3 & 4

2; 2.3; 2.7 & 4

2 & 4

2.7; 2.8; 3 & 4

2.7; 3 & 4.3

2.7 & 4

2.7; 3 & 4

2.7 & 4

2.7 & 4

2.7 & 4

Total passage area (m)

141.2

79.2

540.4

151.2

381.5

318.3

151.6

307.3

251.1

130.5

274

Stowage rate (m/t)

2.45

1.87

2.07

1.30

1.23

1.07

0.80

1

0.83

0.64

0.49

Stowage rate (m/t)

11.6

8.8

9.8

6.2

9.5

8.2

5.7

9.5

7.9

5.7

4.4

Investment costs (US$)

62 000

49 000

132 000

99 000

188 000

177 000

150 000

186 000

177 000

153 000

264 000

 

Figure 50 Typical cold-store panels

Figure 51 Store layout -1.
100-t store with manual operation.
Access to each pallet.
Pallets stacked- 2 high

Figure 52 Store layout -2.
100-t store with manual operation.
Access to 5 different products.
Pallets stacked- 2 high

Figure 53 Store layout -3.
500-t store with manual operation.
Access to all pallets except for frozen blocks (product 6).
Pallets stacked - 2 high

Figure 54 Store layout -4.
500-t store with manual operation.
Access to 6 different products.
Pallets stacked -2 high

Figure 55 Store layout -5.
500-t store operated with mechanical assistance.
Access to all pallets except for frozen blocks (product 6).
Pallets stacked - 4 high

Figure 56 Store layout -6.
500-t store operated with mechanical assistance.
Access to all pallets except for frozen blocks (product 6).
Pallets stacked - 4 high

Figure 57 Store layout -7.
500-t store operated with mechanical assistance.
Access to 6 different products.
Pallets stacked -4 high

Figure 58 Store layout -8.
500-t store operated with mechanical assistance.
Access to all pallets except for frozen blocks(product 6).
Pallets stacked - 5 high

Figure 59 Store layout -9.
500-t store operated with mechanical assistance.
Access to. all pallets except for frozen blocks(product 6).
Pallets stacked - 5 high

Figure 60 Store layout -10.
500-t store operated with mechanical assistance.
Access to 6 different products.
Pallets stacked - 5 high

Figure 61 Store layout -11.
2 000-t store operated with mechanical assistance.
Access to 6 different products.
Pallets stacked - 5 high

4.2.2 Equipment

4.2.2.1 General:

The value of produce in a cold store can be considerable, therefore, some back-up is required in case of major failure in the refrigeration plant. For instance, two smaller condensing units can be used instead of one large unit and one of these, operating on its own, may be used to hold the cold store at a reasonable temperature while the other is repaired. In larger stores, two units may be necessary to meet the refrigeration capacity required, and in this case it would not be unreasonable to have a third unit and operate any two of the three on a rotational basis, with the third unit as a standby.

Another method is to connect the cold-store refrigeration system to that of the associated freezing plant, and in an emergency, the freezer plant can be used to operate the cold store. This crossover, however, needs the attention of a skilled operator since mixing the refrigerant charges from two separate systems may not always be a simple operation.

Another system operated to ensure back-up for the cold-store operation is to have a common plant shared between the store and the freezer. This will make the operation of a multi-unit system cheaper, but this combined operation is not recommended except under special circumstances. Intermittent operation of a freezer, on the same refrigeration system as the cold store, will result in temperature fluctuations in the store, particularly with a batch-freezer operation. Freezers also require a much larger refrigeration capacity than the associated store, therefore, when the freezer is not in operation, the cold store may be operated uneconomically, with a condensing unit which is now grossly oversized.

Sharing of refrigeration equipment between the cold store and freezer is therefore only appropriate in larger systems where a number of condensing units are used and capacity can be readily matched to the demand which will vary depending on the services in operation.

4.2.2.2 Evaporators:

Evaporators used for cold stores and air blast freezers are interchangeable, therefore, reference should be made to Section 3.1.2.4 and Tables 18, 19 and 20. Different criteria, however, apply to the choice of evaporator for a cold store, particularly with regard to the type of fan and defrost arrangement.

In cold stores, propeller fans can be used if the store is small; air is discharged into an open space and the cooler arrangement ensures that the maximum air-throw requirement is within the limited capability of this fan design. In larger stores, where the air throw requirement is greater or when ducting or a false roof is used for uniform distribution, aerofoil fans will be required.

All coolers can be made with the fan upstream (blow through) or downstream (draw through) of the cooler. Positioning of the fan is important and the criteria applying to cold stores is different from those applying to freezers.

In an air blast freezer, an upstream position is recommended for a number of reasons: the cooler acts as a diffuser between the fan and the produce, and this will ensure a more uniform air distribution. Heat from the fan is quickly transferred to the cooler, whereas with the fan down stream this heat will reduce the relative humidity of the air and increase the weight lost by the product during freezing. Finally, in a freezer, the air-throw capability of the fan is not important since it is a closed circuit and the pressure-drop rather than the air-throw governs the air velocity achieved over the surface of the product.

In a cold store, the air-throw requirement may be more important than other considerations, therefore, the fan may be required to be positioned downstream. However, the need should be avoided whenever possible by using a suitable cold-store layout and cooler arrangement. High humidity is also desirable in a cold store, but if all produce is suitably wrapped, this may not be critical.

Cold storage space can also be saved by siting the cooler as close as possible to the wall, therefore, the fan would require to be positioned on the inside, downstream of the cooler, to allow access for repair and maintenance.

Cold stores must have an arrangement for a quick, systematic defrost, unless the coolers are plain-pipe wall grids which, generally, only require defrosting about once or twice/year.

In extreme cases, finned tube unit coolers may require defrosting a number of times/day, and this is usually done at regular intervals with a time-clock initiating a fully automatic defrost sequence. However, even in these cases, there may be times when the store is little used, at weekends for instance, and defrosting is therefore unnecessary. A manual switch should therefore be used to by-pass the clock switch during these periods.

No firm recommendation can be made about defrosting frequency other than to say that this should not be more or less often than necessary, since both extremes have detrimental consequences.

Defrosting of a cold store should not involve methods which result in the spillage of liquid within the store since this will be accumulated as ice on the floor or the produce. One possible exception to this is in large stores where a false roof or ducting is used and the cooler units are located out with the store in an insulated space, usually at roof level, above the loading bay.

4.2.2.3 Cold-store refrigeration requirement:

  1. Sample calculation

A good deal of experience is required to make a correct calculation of a cold-store refrigeration requirement and this should therefore only be done by a qualified person. The following calculation is not complete, but it serves two purposes: it allows the reader to make a similar calculation for his own store and thereby obtain an approximate refrigeration requirement. It also helps the reader to appreciate the number of factors that have to be taken into account in calculating the heat load and, also, gives him some idea of their relative importance.

One important heat load not shown in the calculation is the heat gain due to solar radiation.

This factor depends on conditions which are related to both the location of the store and its method of construction. In some cases, solar heat load may not be significant, but in other instances precautions, such as an outer cladding, may be necessary to reduce its effect. Table 65 gives allowances to be made for sun radiation when calculating cold-store refrigeration requirements.

Specification
Capacity 20 m x 10 m x 5 m= 1 000 m
Insulation thickness (.2 m polystyrene or equivalent)
Total store surface area (771.5 m)
Maximum ambient temperature (+30C)
Store temperature (-18C)

Table 62 Evaporator-fan data

Evaporator capacity
(kcal/h)

No. of
fans

Type
of fan

Dia.
(mm)

RPM

Fan motor output
(kW)

Air throw (M)

Blow through

Draw through

3 024

1

Propeller

457

1 450

0.3

7.6

9.1

6 048

2

"

457

1 450

0.3

8.5

9.1

9 072

2

"

610

960

0.45

9.8

12.2

12 096

2

"

610

960

0.45

9.8

12.2

16 128

2

"

762

900

0.67

12.2

13.7

18 144

3

"

610

960

0.45

12.2

12.2

21 168

3

"

762

900

0.67

13.7

13.7

24 696

3

"

762

900

0.67

14.6

13.7

28 224

3

"

800

920

1.3

15.8

15.2

32 760

3

"

800

920

1.3

16.8

15.2

Notes:
(1) Capacities quoted are at 5.5C TD
(2) Draw through aerofoil fans would give 1.7-3 times draw through values given for propeller fans

Table 63 Ceiling mounted high-capacity evaporators (dimensions and costs)

Evaporator capacity
(kcal/h)

Length
(mm)

Width
(mm)

Height
(mm)

Approximate
Cost ($
)

3 024

1 245

953

782

1 400

6 048

2 007

953

782

2 080

9 072

2 311

1 029

934

2 765

12 096

2 921

1 092

934

3 450

16 128

3 226

978

1 086

4 300

18 144

3 531

1 029

1 086

4 720

21 168

4 140

978

1 086

5 355

24 696

4 140

978

1 239

6 060

28 224

4 674

1 080

1 239

6 765

32 760

4 674

1 080

1 391

7 675

Table 64 Power requirement for electrical defrosts

Evaporator capacity
(kcal/h)

Electrical Load (kW)

Total load
(kW)

Coil

Drain pan

Fan casing

024

2.2

1.1

0.3

3.6

048

4.2

2.1

0.7

7.0

072

6.3

2.5

0.9

9.7

096

8.2

3.3

0.9

12.4

128

9.3

3.7

0.9

13.9

144

10.2

4.1

1.3

15.6

168

12.2

4.9

1.3

18.4

696

14.7

4.9

1.3

20.9

224

16.7

5.6

1.6

23.9

760

19.5

5.6

1.6

26.7

Load calculation

  1. Insulation heat leak through walls, roof and floor
Conductivity of polystyrene 0.03 kcal/h m C
Temperature difference between +30C and -18C = 48C
Thickness of cork = 0.2 m
Surface area of store = 771.5 m
Heat leak
  1. Air changes Air changes
Average of 2.7 air changes in 24 h
Store volume = 1 000 m
Heat gain = (30C and 60% RH air) 29.5 kcal/m
Air change heat gain
  1. Lights (left on during working day)
1 000 w = 860 kcal/h
  1. Men working

1 man working at -18C gives off 328 kcal/h
2 men working is equivalent to 656 kcal/h

  1. Product load
5.5 kcal/kg for fish loaded at an average temperature of -11C
Fish loaded per day = 35 000 kg
Product load
  1. Fan load
4 x 0.67 kW = 3 357 kcal/h
  1. Defrost heat
1 defrost of 13.9 kW for 40 min
Recovery in 6 h = 1 328 kcal/h
Total calculated refrigeration load (sum of Items 1-7) = 23 095 kcal/h
Total refrigeration requirement with allowances = 23 095 x 24/18= 30 793 kcal/h

Note:
It is normal practice to design a new cold store on the basis of 18 h running/24 h under full load conditions. This allows for deterioration in the fabric of the store and the refrigeration machinery over the normally expected 20 years of operational life.

  1. Individual load calculations

Comprehensive Tables are available to simplify many of the load calculations. The method and values sometimes vary between one source and another, but the differences are unlikely to greatly influence the figure for the total load requirement. Some of the tables, most likely to be widely used, are reproduced in Tables 66-69.

Table 65 Cold store heat gain allowance for sun effect

Typical surface types

East/West Wall

North/South Wall

Flat roof

C

C

C

Dark coloured surface

5

3

11

Medium coloured surface

4

3

9

Light coloured surface

3

2

5

Notes:
(1) The above allowances are added to the normal temperature difference for heat leakage calculations to compensate for sun effect
(2) The table is relevant to a location about 300 north or south of the Equator, therefore, adjustments will be required for other locations where the incidence of the sun rays may be substantially different. For example, on the Equator, the values may be increased by about 20%

Table 66 Average number of air changes/24 h for storage rooms due to door opening and infiltration

Room
volume (m)

Air change
per 24 h

Room
volume (m)

Air change
per 24 h

Room
volume (m)

Air change
per 24 h

Room
volume (m)

Air change
per 24 h

2.5

70

20

22

100

9

600

3.2

3.0

63

25

19.5

150

7

600

2.8

4.0

53

30

17.5

200

6

1 000

2.4

5.0

47

40

15.0

250

5.3

1 500

1.95

7.5

38

50

13.0

300

4.8

2 000

1.65

10.0

32

60

12.0

400

4.1

2 500

1.45

15.0

26

80

10.0

500

3.6

3 000

1.3

Correction factors: for heavy usage multiply the above values by 2 for long-term storage multiply the above values by 0.6

Table 67 Heat removed in cooling air to storage room conditions (kcal/m)

Cold Store Temp (C)

Outside air condition

+20C & 60% RH

+30C & 60% RH

+40C & 60% RH

-18

20.5

29.5

43.0

-25

23.5

33.0

46.5

-30

26.0

35.5

49.5

-50

36.5

47.5

62.5

Table 68 Heat equivalent of occupancy

Cold Store Temp. (C)

Heat Equivalent per Person (kcal/h)

-18

328

-25

365

-30

391

-50

494

Table 69 Heat equivalent for electric motors

Motor size

Heat equivalent under conditions of:

1

2

3

Load inside refrigerator box
and motor outside kcal/h/W

Motor inside refrigerator box and
load outside kcal/h/W

Motor and load inside
refrigerator box kcal/h/W

90 W - 375 W

0.86

0.58

1.44

375 W - 2.2 kW

0.86

0.39

1.25

2.2 kW- 15 kW

0.86

0.14

1.0

Notes:
(1) The heat equivalent of electric motors is made up of two components:
column 1- the useful horsepower output of the motor, and
column 2- the frictional and electrical losses of the motor.
column 3 is the sum of these two components.

(2) Use values in column 1 if the driving motor is outside the refrigerator and the load is inside the box: for example, if a pump motor outside the box is circulating brine or chilled water within the box.

(3) Use values in column 2 if the driving motor is inside the refrigerator box and the load is outside the box: for example, if a motor within the box is driving a pump or fan outside the box or in another space.

(4) Use values in column 3 if the driving motor and its load are in the refrigerator box: for example, if a motor is driving the fan of a forced-circulation unit cooler.

  1. Compressor and condenser requirements

Compressor and condenser requirements will depend on the size of the store, the storage temperature and local ambient conditions. There are, however, other factors which will also influence the capacity requirement, and all the possible variations are too numerous to be dealt with individually.

The figures quoted therefore are only correct for the conditions stated, and if they are to be used in a more general sense they should be used as a guide only.

Variations of the refrigeration load requirement for sizing the compressor for a 1 000 m cold store are given in Figure 62.

The corresponding condenser load requirements for the 1 000 m store are given in Figure 63. It should be noted that the values for the condenser requirement are greater since this equipment has to reject both the refrigeration and compressor heat.

  1. Cooler requirements

The capacity figures given for coolers in manufacturers catalogues refer to the specified operating conditions only.

They are usually quoted for a temperature difference of 5.5C (10F), between refrigerant and air, and this condition will normally apply to most cold storage operation. If, however, a higher relative humidity is desirable to reduce evaporative weight loss from stored produce, a reduced temperature difference can be used with a directly proportional increase in cooler size.

Other factors affect the cooler capacity and some typical correction curves are shown in Figure 64.

Cooler capacity will vary with the operating conditions and typical values for a 1 000-m store at different ambient and cold storage air temperatures will be similar to the compressor capacities shown in Figure 62.

 

Figure 62 Refrigeration requirement for a 1 000 m

Figure 63 Condenser requirement for a 1 000 m cold Store

Key:
— – — – Pump circulation - ammonia
— — — Pump circulation - R22
----------- Dry expansion - ammonia
———— Dry expansion - R22

Figure 64 Evaporator/cooler, capacity correction curve

  1. Power requirements

When calculating power requirements, consideration has given to the mode of operation as well as the power requirements of the various components.

The 1 000-m cold store used in the example shown in Table 70 would have two cooler units to ensure uniform cooling. However, each cooler may have an independent condensing unit or they may share a unit rated for the full refrigeration requirement. The cooler units may have electrical defrosting or alternatively, since there are two coolers, a hot gas defrost may be used.

Other variables may apply, which also affect the total power requirement of the store, therefore, detailed knowledge of the equipment and operation will be necessary to calculate accurate figures. The figures quoted in Table 70 apply to a store operating under the stated conditions only, and they represent the rated consumption figures for the equipment listed.

Table 70 Power requirements for a 1 000-m cold store (in kW)

Cold store temperature (C)

-18

-18

-18

-25

-25

-25

-30

-30

-30

-50

-50

-50

Ambient temperature(C)

20

30

40

20

30

40

20

30

40

20

30

40

Compressor

22.3

25.9

32.3

26.1

30.6

37.3

31.5

35.9

41.1

51.5

56.6

70.5

Defrost/cooler

13.9

13.9

17.6

13.9

13.9

17.6

17.6

17.6

17.6

17.6

21.3

19.7

Cooler fans

1.4

1.4

1.4

1.4

1.4

1.4

1.4

1.4

1.4

1.4

1.4

1.4

Condenser fans

0.6

0.6

1.7

1.7

1.7

1.7

1.7

1.7

1.7

0.8

0.8

2.2

Under-floor and door heating

2.8

2.8

2.8

2.8

2.8

2.8

2.8

2.8

2.8

2.8

2.8

2.8

Pump

0.4

0.4

0.4

0.4

0.4

0.4

0.4

0.4

0.4

0.4

0.4

0.4

Mechanical handling equip.

1.5

1.5

1.5

1.5

1.5

1.5

1.5

1.5

1.5

1.5

1.5

1.5

Total

42.9

46.5

57.7

47.8

52.3

62.7

56.9

61.3

66.5

76.0

84.8

98.5

Notes:
(1) Two coolers operating with one condensing unit
(2) Cooler defrosts in sequence
(3) Total power calculated for condensing unit, plus one cooler defrost

The relationship between installed power and power consumption at full rated conditions will depend on a number of factors, and there are no widely used or accepted rules on this relationship. Electrical motor selection often depends on the range normally stocked by the suppliers, but installed power will also depend on more tangible factors such as starting loads. The peak load will, therefore, depend on the starting sequence of the equipment and this can often be arranged to reduce excessive peak loads and thereby avoid additional installation costs and also maximum demand of electrical tariff penalties.

4.3 Management

Many different routines are needed to organize, plan and control the operation of a cold store in relation to the goods being moved in and out, the refrigeration plant, handling equipment, vehicles and personnel. This is an important aspect of cold store management, particularly when the store is used for a variety of products belonging to different owners.

Goods should be readily identified and stored so that they can be retrieved in the right quantities with the minimum of effort. Temperature and other conditions relating to the quality of the goods should also be systematically recorded at the time of reception and delivery so that any defects found later can be traced to the correct source rather than this being always attributed to the cold store operation.

Systematic recording of information relating to all machinery need only occupy a short time, but it can be useful for tracing and even anticipating defects which may be time-consuming and expensive to rectify, if they are allowed to develop, and little or no information is available.

Safety standards have to be high in a cold-store operation since even minor accidents can be serious if they happen within the 10w temperature environment of the store. The capital invested in the building and, even more so, in the stored goods can also be high, therefore, strict fire precautions, for instance, should prevail and normal routines should ensure that this is always the case.

Some of the routines are listed, but for more details on management and safety aspects of cold storage, the IIR book mentioned in Section 4.2 should be consulted.

4.3.1 Administrative routines

inloading/outloading sheets: owner of the goods; date and time of delivery; customer name/number; car or waggon number, temperature of the goods. For different articles: information about article (name and number, handling code, quantities: pallet/cartons/weight, appearance of goods and packages, temperature);

picking lists: which articles (name, number) shall be picked, in which order they shall be picked and which order they shall be picked and where they can be found;

control;

differences;

weight lists; ..

Waybills.

FIFO (First-In, First-Out);
location; .
stock-taking.

4.3.2 Equipment routines

Two routines are important: systematic recording of information and planned inspection and maintenance.

Depending on the type of refrigeration plant installed, some or all of the following information , should be recorded either continuously or at regular intervals (at least daily). A permanent record of the information gathered should be kept and should be examined at least weekly by a competent engineer.

General

Cold store temperature (C)
Ambient temperature (C)
Defrost duration (min)
Store usage (heavy/medium/light)

Compressor

Compressor (No.)
Suction gauge pressure (N/M)
Intermediate gauge pressure (N/M)
Discharge gauge pressure (N/M)
Suction line temperature (C)
Intermediate line temperature (C)
Discharge line temperature (C)
Compressor duty (%)
Motor load (A)
Motor running time (h)

Intercooler

Line temperature in (C)
Line temperature out (C)

Liquid pump

Pump gauge pressure (N/M)
Liquid line temperature (C)

Condenser (water cooled)

Water temperature in (C)
Water temperature out (C)

Any drastic change in operating conditions should be noted and reported immediately to the appropriate person.

Handling equipment and vehicles should have a planned inspection and maintenance routine. This can be daily, weekly or monthly. or based on operational hours or distance covered and advice on the frequency of these operations are usually contained in manufacturers instructions.

Good maintenance. however. has three elements which ensure that it is done:

Inspection
Recording
Checking (records and work)

4.3.3 Safety

Again, full details of the many aspects of safety are given in more detail in the IIR "Guide to Refrigerated Storage". therefore, only a list is given below as a reminder of some of the various elements that have to be taken into account when formulating safety routines.

Fire Moving vehicles
Gas leaks Stability of stacked produce
Flooding Machinery guards
Power failure Instruction and training
Protective clothing Notices
Personnel locked in the store Reporting and checking