Direct and Indirect Cooling Systems
Direct cooling systems, heat transfer directly volatile refrigerant. Indirect systems include intermediate liquid for transportation of cooled fluid between refrigeration equipment and process.
Any surface of heat transfer in which volatile liquid expands and evaporates to produce a cooling effect is called direct expansion evaporator. Liquid absorbing die thermal energy is called direct expansion of the refrigerant. Direct expansion system uses direct expansion of the refrigerant in the evaporator Ana, evaporators, heat transfer surfaces in direct contact with the controlled variable. In the controlled variable to die in air, water, or other materials, equipment designed for cooling. Controlled variables in the space cooling process, the office building is air delivered zone at the reference temperature (55F, 12.8C).
In many structures, it is not economical to circulate a direct expansion of the refrigerant for all zones or processes in commercial, institutional and industrial buildings. Long direct expansion of the refrigerant lines rarely in practice, as they are expensive to install and to increase the refrigerant charge significantly.
Long refrigerant lines, particularly in the long risers, create problems with the oil return, the reason for the excessive refrigerant pressure drops that reduce the capacity and effectiveness of the system. In addition, the leak is more likely to occur in long lines due to the increase exposed pipe and the number of seams. Repair of these systems after the leak is more time consuming and expensive. In these applications, indirect refrigeration system works.
Indirect refrigeration systems operating in any installation, when the space of a product or cooling is located at a considerable distance from condensation equipment. Water, brine or another suitable liquid cooled direct expansion of the refrigerant is pumped spaces or food in the refrigerator. In these applications, the chilled fluid is called a secondary refrigerant. Secondary refrigerants apply directly to the product or a receptacle for refrigerated or indirectly for multiple locations using air cooling heat exchange coils. A secondary refrigerant absorbs heat energy from the air, water or product before returning to the chiller barrel, where it is cooled up to circulating back to the remote sites.
Indirect refrigeration is also required in many industrial processes, cooling where it is impractical to maintain vapor-tight seal around die, or the tank or product being cooled. It is also used when the leakage of refrigerant and oil pipelines will cause unacceptable pollution or damage of the product...