Cold stores

In situ insulation of (a) refrigerators (e) chemical plant (b) deep freezers (f) houses (c) cold stores (g) building panels (d) ships 2. Buoyancy goods 3. Chair shells... 

Its closed-cell structure makes cellular glass particularly suitable for refrigeration applications on pipes and cold stores. High load-bearing capacity enables it to be used under rooftop car parks. 

Used mainly in structural applications. Is suitable for refrigeration and cold stores. 

Cold store evaporators having the coil with drip tray under, fans, and possibly the expansion valve. 

Cold store evaporators for use below + 2°C must also have some means of defrosting the coil. If this is to be by electric heat, the elements will be inbuilt. 

Cooling and freezing cannot improve a product, and the hest that can he achieved is to keep it near to the condition in which it entered the cooling process. This means that only the hest produce should he used, and this should he as fresh as possible. (This general principle must, of course, be interpreted in the light of local conditions and needs. In some countries of the world, preservation in cold stores is essential to prevent wastage, regardless of the quality of the crop.)... 

If warm produce is taken into a cold store, moisture will evaporate from its surface and may condense on the cold produce already there. This will be of no consequence with wet products such as fish and leaf vegetables but cannot be permitted with meat or poultry. 

Potatoes are cold stored in bulk or in large boxes of 4 or 1 t capacity (also in sacks in some countries). They are always stored on their own, so special handling methods have evolved. 

Pallets are now mostly standardized at 1.2 X 1.0 m and the total weight will be between 4 and 1 t, depending on the product. Handling in small cold stores can be by hand pallet trucks or hand-steered electric drive trucks. These can transport but not lift one pallet onto another. The usual fork-lift truck is a ride-on vehicle, electric driven, and can lift to form a stack of two, three, four or even five pallets high, according to the length of the telescopic lift and the skill of the driver. 

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 ... 

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. 

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. 

In most cases, the insulation will be the greatest resistance to heat flow and other materials in the construction and surface resistances are ignored in estimating heat gains through cold store walls, ceilings and floors. 

When the evaporator begins to cool a cold store, surplus moisture in the air in the room will condense on the coil and, if cold enough, will freeze. This will continue until the water vapour pressure inside... 

Traditional cold store construction was to build an insulated lining within a masonry shell. The outer skin would be erected in brick and concrete, and rendered as smooth as possible inside with cement plaster, to take the insulation. When the surface was dry, it would have several coats of bitumen applied as a vapour barrier and slabs of insulation material stuck to this with hot bitumen. This was normally carried out in two or more layers so that joints did not pass right through the insulant, but were staggered. The inner skin would be finished with cement plaster, reinforced with wire mesh. The usual insulant was slab cork. 

Care must be taken regarding the method of supporting ceiling panels. Large portal framed steel holdings may provide a cheap outer shell but do have a considerable amount of roof movement. Panels hung from this type of structure can be subjected to movement which cannot be tolerated in cold store construction. A tied portal, however, can be acceptable [38]. The outer shell may also be required to bear the weight of the evaporators and, in the case of stores for carcase meats, the rails and the product itself. 

Figure 15.8 Double sliding cold store doors, power operated (Courtesy of Clark Door Ltd)...

In small cold stores, the coolers will be fixed to the walls, probably blowing the air downwards, or to the ceiling, blowing sideways (see Figure 7.2). 

Automatic stacker cranes were first used in a cold store in the USA in 1962 and there are now many installations throughout the world. The store height can be increased considerably, to 16-20 m, or even higher if the rack frame is used to support the roof of the cold store. The operation of such a store can be by using a crane with the operator inside the store, driving the crane from a heated, insulated cab, or can be fully automatically operated by a computer. One crane can service some 4000 pallet positions at the rate of 50 pallets per hour. 

The value of the produce in a large cold store may be several times the cost of the store itself, and every effort should be made to maintain the refrigeration service at all times, even if plant may be inoperative for inspection, overhaul or repair. The principle of plant security is that there should be sufficient pieces of each item of plant and that they should have enough capacity for conditions to be held as required by the produce, regardless of any one item which might be stopped [29]. 

Other processes (except milk drying) require the finished product to be cooled to a suitable storage temperature, usually 4°C or thereabouts, and kept cool until the point of sale. Conventional-type cold stores can be used for mixed dairy products, since all of them will be packaged and sealed after manufacture. 

During movement of goods between static cold stores and vehicles, every effort must be made to avoid any warming. The principle is to close the vehicle right up to the cold store wall. 

The ideal arrangement is to back the vehicle up to a door with a sealing collar, so that the contents may move directly into the store without exposure to ambient temperatures. If the height differs from that in the store, adjustable platforms are fitted at the door. Where fork-lift trucks have to pass in and out of a cold store, plastic strip curtains are used (see Figure 20.2). 

Figure 20.2 Strip curtain at cold store door...

Conducted heat is that going in through cold store surfaces, tank sides, pipe insulation, etc. It is normally assumed to be constant and the outside temperature an average summer temperature, probably 25-2/°C for the UK, unless some other figure is known. Coldroom surfaces are measured on the outside dimensions and it is usual to calculate on the heat flow through the insulation only, ignoring other construction materials, since their thermal resistance is small. 

Solar radiation may fall on outside walls or roofs, raising the skin temperature, and this must he taken into account. Most cold stores are huilt within an outer envelope which protects them from the elements and from direct sunshine. In cases where the insulation itself is subject to solar radiation, an allowance of 5 K higher outside temperature should he taken. Heat load must he estimated through all surfaces including piping, ducts, fan casings, tank walls, etc., where heat flows inwards towards the cooled system. 

Example 21.9 The cold store in Example 21.3 is now to be located in an ambient of 35°C, and to have the internal load of Example 20.5 and the product load of case 3 of Example 21.6. Include for infiltration and estimate plant capacity. 

Cooling of multi-room cold stores at different temperatures, with brine coils... 

Air filters are not used on cold store coolers, since the air should be a lot cleaner and small amounts of dust will be washed off the fins by condensate or by melted frost. Air-cooled condensers are not fitted with filters, since experience shows that they would never be maintained properly. In dusty areas, condensers should be selected with wide fin spacing, so that they can be cleaned easily. 

Tow-temperature systems and cold stores should be brought down slowly, to allow for shrinkage in the structure. A fall of 5 K per day is reasonable, moving more slowly through the band + 2°C to - 2°C. 

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