Wednesday, January 9, 2008

Air-distribution System :

The evaporator fan used in the room unit is of the centrifugal or propeller type and is surrounded by acoustical insulating material that reduces operating noise. The evaporator fan pulls in fresh outside air through louvers and a ventilation damper. Room air enters at the room end of the air-conditioner through return louvers in the cabinet. The fresh air and room air mix and are drawn through the evaporator cooling coil. The cooled air is then supplied to the room through the discharge grills in the front of the cabinet. A one-ton unit circulates air at 40 m3/min in the room. If 25% fresh air and 75% recirculated room air are used then one ton unit results in 1.3 air changes per hour for a room of 40 m3 volume.

Air should be filtered as soon as possible after it enters the air-conditioner. In the window unit, the air filter is located on the air entering side of the cooling coil. Either permanent or replaceable filters are used. The permanent filter is a metallic mat or plastic foam type. It is coated with odourless mineral oil that helps in catching dust particles. It may be cleaned as needed by washing in soap flakes. Replaceable filters are made of spun glass or similar materials and are also coated with oil or other suitable adhesive. They may be easily removed from the unit and replaced by a new filter.

The fresh air intake to the room conditioner is regulated by a dampered door inside the cabinet. Most units operate with from 0 to 25% fresh air, depending upon the damper-control knob adjustment within the ventilate position. On hot days, the proportion of fresh air intake should be decreased, because the more fresh hot air, the greater the cooling load on the unit.

To exhaust room air, the fan control is set to EXHAUST position. The condenser blower starts operating when this is done. The exhaust damper musrt also be open to permit room air through to the outside and therefore the damper control is also set to its exhaust position. With these controls are in this setting, the room air-conditioner acts as an exhaust fan. In this way, smoke and odours are removed from the room by the condenser fan which draws air through the damper and exhausts it through the louvers in the rear of the unit.

The air system on the outside includes in the condenser fan and dissipates the heat taken from the cooled area to the outside atmosphere. The air system within the cooled area circulates room air over the cooling unit. These two air systems are so arranged that the cooling coils are located on the room side of the window and condensing units on the outside of the window. It is important that no intermingling of hot condenser air and cooled room air takes place. A partition inside the air conditioner separates the room air from the condenser air. The rubber seals and panels at the window prevent exchanges of inside and outside air. Tight installation at the window is of utmost important.

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