How Central Air System's Works ?

The Central Air Condition system is  suitable for air-conditioning large spaces such as theaters, cinemas restaurants, exhibition halls, or big factory spaces where no sub-division exists. The central systems, are generally employed for the loads above 25 TR and 2500 m3/min of conditioned air. The unitary systems can be more economically employed for low capacity (below 25 TR) units. 

In central system, the equipment such as fans, coils, filters and their encasement are designed for assembly in the field. A central system serves different rooms, requires individual control of each room. A central air conditioner has a primary appliance such as an air handler or furnace ,the condenser, compressor, dampers, heating, cooling and humidifying coils and fan located in an out-of-the-way place such as a basement or attic. The conditioned air is carried to the different rooms by means of supply ducts and returned back to the control plant through return ducts.—often the same system utilized by a forced-air furnace during the heating season. One or more thermostats in the house turn the cooling system off and on as room temperatures rise and fall.

Part of the supply air to the rooms may be exhausted outdoors. Outdoor air enters from an intake which should be situated on that side of the building least exposed to solar heat. It should not be close to the ground or to dust collected roof. The air after passing through damper passes through filters. The filters may be of a mechanical cleaned type, replaceable-cell type or may be electrostatic. 

The cleaned air then passes to the conditioning equipment in the following order : 

  • Tempering (or preheater) coil, 
  • humidifier (Air washer), 
  • heating coil and finally fan. 

Advantages of central system : 

1. Low investment cost as compared to total cost of separate unit. 
2. Space occupied is unimportant as competed to a room unit conditioner which must be placed in the room.
3. Bette accessibility for maintenance. 
4. The running cost is less per unit of refrigeration. 
5. Noise and vibration troubles are less to the people in air-conditioned places as the air-conditioning plant is far away from the air-conditioned places. 
6. The exhaust air can be returned and partly reused with obvious saving in heating and refrigeration. 
7 . The conditioned air is carried to the different rooms by means of supply ducts and returned back to the control plant through return ducts.

Disadvantages of central system : 

The disadvantage of the central system is that it results in large size ducts which are costly and occupy large space.

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