Design Considerations

Until now we have discussed that cold storage is required to store the food/dairy products at low temperature so as to preserve these for a set period of time. Thecooling coil of refrigeration system installed inside the cold storage extract the heat of the product and lower down their temperature. After lowering down the temperature to a set range, this temperature should be maintained so as to preserve the products. To maintain that temperature it is necessary to extract all that heat energy which enters the cold storage by some means. Thus to know the capacity of refrigeration plant required, we must know the amount of heat to be extracted in a given period of time i.e. the cooling load on refrigeration plant. There are various types of cooling loads that are taken into consideration in a cold storage.

All these are explained as follows:

i. Heat of Products

This is the main part of heat, which is required to be extracted and is known as major cooling load. When the products are stored in a cold storage, these are initially at higher temperature. To lower down their temperature, their heat is required to be extracted. It is divided in three groups:

(a) Chilling load above freezing

Thus in case of chilling only, first type of load is considered. In case of freezing,first and second type of load are added and taken into consideration. In case of deep freezing, all three types of loads are taken into consideration.

ii. Heat Conducted in through Walls, Roof and Floor of Cold Storage
A cold storage is generally situated at such a place in a dairy, which is not exposed to direct sun. All the walls, roof, floor are insulated i.e. insulating material is fixed around which prevent the heat flow from surroundings. But, in spite of that there may be some cooling loss to the surroundings, however, it may be negligible,depending on the difference in temperature inside and outside of cold storage and type of material of wall and insulation. This continuous heat flow through walls,roofs etc. is added in the cooling load of refrigeration plant.

iii. Heat Gain from Product Handling Labourers

The products are stored and arranged in cold storage by labourers. They also loose some heat in cold store due to its low temperature. This heat also puts some cooling load on refrigeration system.

iv. Heat Gain from Lighting and Power equipment

There may be a variety of appliances like fan or blower motor, any safety device,lights etc., which continuously loose heat in cold storage and put some cooling load on the refrigeration plant.

v. Heat Gain due to Infiltered Air
While loading or unloading the product in cold storage, the door is opened. During this period, the cold air of cold storage escapes out and hot air from surrounding come in, putting extra cooling load on the system, which depends on the time for which door is kept opened.

vi. Heat Gain through Ducts

After evaporation in the evaporating coil, the refrigerant gas, which is at lower temperature, flows to compressor through pipes. These pipes are exposed to higher temperature of surrounding and some heat gain to refrigerant gas takes place.However, it can be generally reduced by properly insulating the suction line of compressors outside the cold store.

All the above-mentioned heat gains are required to be removed by refrigeration plant of cold storage. Thus all these contribute to the cooling load which is considered before designing or finding out the capacity of refrigeration plant required.

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