The purpose of a cold store is to provide an insulated and refrigerated enclosure suitable for the handling and storage of perishable goods, at some predetermined temperature.
The shape and size of the cold store will depend on:
1. The quantity and variety of goods to be stored 2. The size and shape of the packaging
3. Proposed methods of handling 4. Storage times
Since the handling methods require power-driven fork-lift trucks, nearly all cold stores are now erected as single-storey buildings with the insulation in the form of factory-made panels. The main loading bay will probably be at tailboard height, so that products can be taken directly in and out of insulated vehicles.
Example 15.1 What will be the internal dimensions of a cold room to store 900 t of boxed frozen meat if the box size is 700 × 450 × 150 mm and the net weight 30 kg?
Number of boxes in store = 900 000
30 = 30 000 boxes
These can be stacked on pallets 1200 × 1000 mm, the height per pallet being 1400 mm, say a box height of 1250 mm, allowing for the base of the pallet. Boxes would be loaded flat, three per layer and eight layers high, making 24 boxes per pallet:
Number of pallets = 30 000
24 = 1250 pallets
These pallets can be stacked three high without auxiliary support, and this will be the cheapest and most flexible arrangement, leaving
the floor clear for any other type of produce if there is less than a full load in the store:
Floor space required, pallets = 1250 3 = 420
The net area will be 420 × 1.2 m2, plus a space of some 75 mm between pallets to allow clearance in handling, giving an occupied floor area of about 575 m2.
Since it is a one-product store, it seems unlikely that any one pallet must be accessible, so stacking the pallets in rows three deep should be acceptable.
One or two sketch layouts can be tried based on these figures, unless the shape of the store is already decided by the available site.
One such layout is shown in Figure 15.1. It will hold a maximum of 1278 pallets and requires a floor area 34.5 m long by 27 m wide, a gross floor area of 932 m2. The stacks will be 4.05 m high. To this must be added a clearance for lifting and the depth of the evaporators.
If the latter are 1.1 m, the store internal height will be 5.25 m. The volume is 4890 m3 and the storage density is 5.4 m3/t or 184 kg/m3.
27 34.5 m
Door 22
Door
Door
22
27
27 m
Emergency door
Figure 15.1 Schematic layout of 900-t pallet store
Example 15.2 What would be the volume of this store if the pallets were arranged on racks?
The solution to this would require constructional details of the proposed racking system and each pallet will now require an area of about 1.400 × 1.075 m. Height clearance must be allowed for each tier – a total of 1.600 m each pallet high. Also, it is not possible for a fork-lift truck to reach three pallets deep into a stack, so the arrangement would now be two deep along the sides and four-deep
islands. However, with racking, the pallets could be stacked four high and possibly five.
A provisional arrangement would possibly be with 30 pallets along the walls and two islands 24 pallets long. The internal dimensions will now be approximately as follows:
Length, 30 × 1.400 = 42 m Width, 12 × 1.075 + (3 × 3) = 22 m
Floor area = 924 m2 Height, (4 × 1.600) + 1.2 = 7.6 m
Volume = 7022 m3 Density, 900 000/7022 = 130 kg/m3
A store of the same capacity, designed to give immediate access to any one pallet, would have a floor area of 1260 m2 and a volume of 9600 m3, giving a storage density of 94 kg/m3.
Cold stores intended only for carcase meat will have the product hung from an overhead rail system (see Figure 15.2). The meat is hung on hooks on roller carriers – possibly one side of beef on a single hook or smaller carcases and cuts on multiple-hook carriers.
750 900
Figure 15.2 Schematic plan of rail layout
Rails for beef sides will be spaced 900–1200 mm apart, and the length for a side is 450 mm of rail. The height to the top of the rail may be up to 3.35 m, but may be less. The average side weight in the UK is 140 kg, with a variation of 80–225 kg throughout the world;
the local trend should be taken as a guide. Space is required for the service rails and junctions at the door end, possibly 1 m being taken up by this. Rails should be well clear of walls so that air can circulate and the meat cannot touch the wall.
Example 15.3 What will be the floor area of a railed coldroom to take 500 head of beef in sides?
Number of sides = 500 × 2 = 1000
Rail length required = 1000 × 0.450 m = 450 m
A possible arrangement would be 15 rails, each 30 m long.
Width, say 1 m spacing, 15 × 1 = 15 m Extra wall clearance on each long side = 0.5 m
Overall = 15.5 m Length, 30 m + clearance for service rails = 32 m
Giving a floor area of 32 × 15.5 = 496 m2
A room as large as this may require an access door at each end, with rail points and an exit rail, adding another 1 m to the length.
This would be decided by the amount of traffic in and out and the direction, if part of a factory production line.
Small stores for miscellaneous products must allow for random stacking of a variety of different packages. The storage density may be between 100 and 450 kg/m3 when the store is fully loaded, allowing for access passages. A closer estimate could be made if probable loadings and package shapes were known [29, 33].
More than one chamber may be required, based on the separation of products by type and by storage temperature. These will be sized on the probable individual contents. Where a low-temperature room is required as well as some at higher temperatures, it should be placed between them, to reduce heat gains.
Old stores, especially those occupying valuable land in city centres, were built several stories high. Access was by lifts and most of the handling was by hand or with hand pallet trucks. Such stores are occasionally built today, but the general use of mechanical handling has led to the single-storey building close by a main road but away from a city centre.
The majority of transport of frozen foods is by 12-m-long articulated
trailers. Access, turning, docking and parking space is needed for such vehicles and the loading dock should be at the tailboard height, with adjustable ramps to allow for small differences in this. The loading platform usually runs across the full side or end of the store with doors opening onto it. The absolute minimum width is 3 m and many docks are as wide as 12 m. The check-in office will be on the dock and may have a weighbridge or rail scale for carcases. The refrigeration machine room should have separate access.