7. CHILL STORES

7.1 Design and Construction
7.2 Physical Parameters
7.3 Technical Parameters
7.4 Costs

7.1 Design and Construction

Chill stores suitable for holding fresh fish should operate in the range 0-4 �C in order that the fish, which should always be stored in ice, is not frozen or partially frozen. In this range the fish is efficiently cooled by ice melt water and thereby kept moist. Each store should be specifically designed or selected for the operating conditions.

It is not the intention here to describe the detail design of a store but to discuss the operating conditions will effect the design and costs.

In the design of the store the refrigeration engineer will require to know the total weight of product, the turnover of product, the handling methods, the temperature of the fish going into store, ambient temperature, water cooling temperature (if water cooled) and The cost/availability of electricity, water, labour and space. The refrigeration duty will be based upon:

the heat entering through the insulated structure
the heat from the incoming fish
the heat from electrical equipment (including lights)
the heat from men working in the store
the heat from air exchange

Methods of estimating these loads are available in refrigeration manuals.

7.2 Physical Parameters

For a given weight of fish the physical size of the store will depend greatly upon the handling and stowage methods and the requirement for access and withdrawal of stock. For small stores manual loading and unloading is quite feasible and often the cheapest solution but may not be economic for larger stores where large volumes of fish need to be moved quickly. Mechanical handling offers advantages in quicker and cheaper movement of stock and in some cases lower capital and running costs. Fork lift trucks for example enable higher stacking of fish in the chill room and it is therefore possible to design the room to take advantage of this. Consider for example the two following rooms of the same internal volume.

The first store has a total surface area (including floor) of 192 m� and the second only 160 m�. Now the heat gain through the surfaces of the store is proportional to the surface area so the running cost of the first will be higher than that of the second. Additionally, the capital costs of construction will also be higher for the first store as the higher surface area will require extra insulation and floor surfacing. Considering also two stores of the same form but of different sizes as shown below:

The volume per unit surface area in the first case is 0.33 and in the second case 0.66 which illustrates the economy of scale with increasing size. The cost per unit volume, both capital and running, will be lower for larger stores. An important consideration in the sizing of a store is the requirement for access and withdrawal of stock. Consider the stowage of small pelagic species stored in ice at a fish: ice ratio of 3:1 in a box of dimensions 600 x 368 x 214 mm. Each box will contain approximately 25 kg of fish which represents a stowage volume of about 2 m�/t with no allowance for internal clearance, access or handling and evaporator. In practice a minimum of 3 m�/t should be allowed for storage where internal access is not important. This might be the case, for example, where fish is to be unloaded from a fishing vessel one afternoon, held overnight and brought out for sale on the market the following morning. It would not matter that the first fish into the store was the last to be brought out (FILO).

Where access is required for selective withdrawal of stock, possibly of different species or ages, the stowage volume required will depend on the degree of selection required and the methods of handling. Between 4 and 8 m�/t is commonly used and provides sufficient access for most situations. Figure 19 shows the floor plan of a store designed to hold 5 t of boxed fish, handled manually, based on a design figure of 4 m�/t. The plan assumes a box of dimensions 600 x 368 x 214 m loaded with 25 kg of iced fish. The boxes are stacked nine high (1.93 m). The internal dimensions of the store are 3.50 x 2.50 x 2.30 m (high).

Figure 19. Floor plan of a 5-t chill store

Mechanical handling of stock in a chill store is unlikely to reduce the required floor plan area or volume required per t of fish if access is required for selective withdrawal of stock, as the aisles required for access and manoeuvring of a standard fork lift truck will be far In excess of that required for manual handling, and will not be compensated by the extra height of stacking. If selective withdrawal is not necessary then mechanical handling will enable a smaller ground area particularly for larger stores (over 30 t). The width required for a 90� stacking aisle for a standard fork lift (1-1 1/2 t capacity) will vary depending on manufacturer and pallet size, but for a 1 200 x 1 200 mm pallet it is approximately 3.25 m. Special aisle trucks are available, designed for warehouse operation that will turn in a much narrower aisle width but are seldom used in the fish processing industry, Probably because the standard fork lift is better suited to other duties that it may have to perform in addition to work in the chill store. As further examples of storage arrangements, Figures 20, 21 and 22 show the floor stacking plan and elevation of stock within three chill stores. Figure 20 shows a store designed for 25 t of boxed and iced fish to be handled manually. The plan assumes a stack-only box of dimensions 600 x 368 x 214 mm using a fish: ice ratio of 3:1 and holding 25 kg of fish. The boxes are shown stacked to a height of nine boxes. The aisles (1.2 m) between boxes provide access for selective withdrawal from any box column. The internal volume per t of fish stored is 7.0 m�/t.

Figure 21 shows a store designed for 25 t of fish handled by fork lift truck. The plan assumes a pallet size of 1 200 x
1 200 m with 24 boxes per pallet (6 boxes per layer x 4 layers). The pallets are shown stacked three high. The layout allows access to any pallet stack. The floor plan area is less than that required for manual handling but the volume . required per t of fish is greater at 8.0 m�/t.

Figure 22 shows a store designed for 100 t of iced fish held in 1 200 x 1 200 x 750 mm (high) box pallets handled by fork lift truck. The pallets are stacked four high and it is assumed that they each hold 450 kg of iced fish. Access is available to any box pallet stack. The internal volume required per t of fish stored is 9 m�/t.

In each of the foregoing examples the capacity is greatly increased if selective with drawal is not required.

The examples assume the storage of small pelagic species in a stack only box at a fish: ice ratio of 3: 1. Different fish species, box sizes and designs and fish: ice ratios will effect the space requirement for storage. For larger species such as cod, the volume should be increased by as much as 16 percent depending on size of fish. If a stack-nest type of box is used the volume should be increased by as much as 18 percent depending on size and design. At a 2:1 fish: ice ratio it should be Increased by 20 percent, and at 4:1 decreased by 12 percent.

Figure 20. 25- t chill store manual operation

Figure 21. 25-t cold store-fork lift operation

Figure 22. 100-t chill store-fork lift operation

7.3 Technical Parameters

As previously stated, it is not the intention here to describe the detail calculation of technical parameters such as optimum insulation thickness, refrigeration duty, etc., and selection of equipment which is the province of the refrigeration engineer and must be determined for each case in point. However, it is often necessary for purposes of feasibility study or planning to have some estimation of the consumption of electrical and water services and the size and connexion of installed electrical machinery. To this end the following three cases serve as examples which by interpolation might, for the purposes stated, be used in the planning of chill stores.

Three sizes of store are considered: 5 t, 25 t and 100 t (assuming a design factor of 4 m�/t) under increasingly adverse (higher) conditions of ambience, water temperature and product temperature. In each case a daily product loading of half the capacity of store is assumed. The 5-t store operates under an ambient air temperature of 20 �C with mains water supply (for cooling) at 15 �C and with incoming fish at a temperature of 5 �C. The 25-t store is assumed to operate under an ambient air temperature of 30 �C with mains water supply at 25 �C and with incoming fish at a temperature of 10 �C. The 100-t store is assumed to operate at an ambient air temperature of 40 �C with mains water supply at 30 �C and with incoming fish at a temperature of
20 �C. The refrigeration duty is respectively: 2 654 kcal/h, 11 335 kcal/h and 75 113 kcal/h. Note that the difference in power consumption between air cooled and water cooled in Cases I and II is small, but in Case III it is significant (103.5 cf. 79 kW). The installed power rating of the compressor for Cases 1 and II is the same, but for Case III is only 55 kW for water cooled compared with 90 kW for air cooled. For Case III it is assumed that the motor is star delta connected, whereas for Cases I and II the motors might be connected direct on line. There is a slight difference in the compressor running times: Case I - 18 h; Case II - 19 h; and, Case III - 20 h.

7.4 Costs

The capital costs of the three chill stores considered in Section 7.3 and specified in Table 18 are shown in Table 19. The total capital cost is given for stores with air- and water-cooled condensers, and broken down into component costs of the store and fittings (insulation, surface finishes, doors and floor), refrigeration equipment (air and water cooled) and erection (including electrical wiring).

Analysis of the costings illustrates the economy of scale mentioned in Section 7.2 with the cost per unit volume of store dropping from US$ 600/m� for Case I, the 5-t store, to less than US$ 300/m� for Case III, the 100-t store (which operates under higher ambient conditions).

For the smaller stores the difference in capital costs between the air and water-cooled plants is not significant and might well depend on the manufacturer's product range as to which works out the cheaper. In Case III (100 t) the water-cooled plant works out to be nearly US$ 6 000 cheaper (5 percent less than air cooled), but again could be influenced by the manufacturer's product range or actual site conditions. The question of choice between an air-cooled or water-cooled condenser would normally be made on running costs depending on the relative costs (or possibly availability) of electricity and water. Note the difference in power consumption given in Table 18 between air-cooled and water-cooled plants and the water consumption in the case of the water-cooled condenser.

Table 18 Wet fish chill rooms - specification and utilities consumptions

Table 19 Chill store costs (US$)