Module 1. Moisture content and its determination.
Module 2. EMC
Module 3. Drying Theory and Mechanism of drying
Module 4. Air pressure within the grain bed, Shred...
Module 6. Study of different types of dryers- perf...
Module 5. Different methods of drying including pu...
Module 7. Study of drying and dehydration of agric...
Module 8. Types and causes of spoilage in storage.
Module 9. Storage of perishable products, function...
Module 10. Calculation of refrigeration load.
Module 11. Conditions for modified atmospheric sto...
Module 12. Storage of grains: destructive agents, ...
Module 13. Storage of cereal grains and their prod...
Module 14. Storage condition for various fruits an...
Module 15. Economics aspect of storage
Lesson.27 Types of Cooling Load
The total amount of heat required to be removed from the space in order to bring it at the desired temperature by the air conditioning and refrigeration equipment is known as cooling load. The purpose of load estimation is to determine the size of the equipment. Cooling loas on refrigeration equipment is the summation of heat given up by different sources.
27.1 COMMON SOURCES OF HEAT
Heat that leaks into the refrigerated space from the outside by conduction through the insulated walls.
Heat that enters the space by direct radiation through glass or other transparent material
Heat that is brought into the space by warm outside air entering the space through open doors or through cracks around window and doors.
Heat given off by a warm product
Heat given off by a people occupying the refrigerated space
Heat given off by any heat-producing equipment located inside the space eg. Motors, lights, electronic equipment, material handling equipments etc.
27.2 TOTAL COOLING LOAD
The total cooling load is divided into four separate loads;
The wall gain load
The air change load,
The product load,
The miscellaneous or supplementary load.
27.2.1 Wall gain load
Wall gain load or wall leakage load is a measure of heat flow rate by conduction through the walls of refrigerated space from the outside to the inside. There is no perfect insulation i.e. there is always a certain amount of heat passing from the outside to the inside. The heat gain through walls, floor & ceiling vary with
- The types of insulation
- Thickness of insulation
- Construction material
- Outside wall area
- Temperature difference between refrigerated space and ambient air
27.2.2 Air change load
When the door of a refrigerated space is opened, warm outside air enters the space to replace the more dense cold air that is lost from the refrigerated space through the open door. The heat which must be removed from this warm outside air to reduce its temperature and moisture content to the space design conditions, becomes a part of the total cooling load. This is called the air change load.
Air change load, Qa = m (ho-hi) ………… (27.1)
Where, m= mass of air entering, kg /h
ho = Enthalpy of outside air, kJ/kg dry air
hi = Enthalpy of inside air, kJ/kg dry air
Fruits and vegetables respire even at low temperature storage Heat produced due to respiration of the fruits and vegetables, is required to be considered for cold storages. It can be calculated as
Qr = mp (kg/h) x Respirate rate (kJ/kg) ……….. (27.2)
Where, Qr = Respiration load
mp = mass
27.2.3 The product load
Product load is the heat that must be removed from the refrigerated product in order to reduce the temperature of the product to the desired level. The term product means any material whose temperature is to be reduced. When, the product is to be frozen, in this the latent heat removed is also a part of the product load.
27.2.4 Miscellaneous load
This load takes into account all miscellaneous sources of heat. Chief among them are people working in or otherwise occupying the refrigerated space, along with lights or other electrical equipment operating inside the space.