central Air Conditioning

Central air conditioning (or central A/C) is a system in which air is cooled at a central location and distributed to and from rooms by one or more fans and ductwork. The work of the air conditioner compressor is what makes the whole process of air conditioning possible. The compression of the refrigerant gas enables it to discharge heat out of the house, which is how the cool air is created.
The air used in the central air conditioning system is a fresh air, which is necessary for the breathing process and its value varies according to the nature of the individuals in the place to be adapted. For example, the person sitting differs from the sports practitioner and also according to the nature of the place to be adapted, for example the operating rooms are 100% fresh air.
– Return air from the place to be adapted, which is the return air from the place to be adapted after its temperature has risen as a result of thermal loads inside the adapted place where it is taking advantage of its temperature that is less than the temperature of the fresh air to provide the energy needed for the air handling unit.
Chilled water system
The main system components of the central cooling plant are the:
– Chiller
– Air Handling Unit (AHU)
– Cooling Tower
– Pumps
The chiller will usually be located either in the basement or on the roof and this depends on what type of chiller is used. Rooftop chillers are usually “Air-cooled” whereas basement chillers are usually “Water-cooled” but they both perform the same function which is to generate cold water for air conditioning by removing the unwanted heat from the building. The only difference is how the chiller discards the unwanted heat.
Air-cooled chillers
Chillers that used air for cooling the condensing unit, this type does not use a cooling tower.
Water-cooled chillers:
Chillers that used water for cooling the condensing unit, this type use a cooling tower.
Cooling tower:
The cooling tower is usually located up on the roof.
Direct expansion system (dx):
In the direct expansion or DX types of air central conditioning plants, the air used for cooling space is directly chilled by the refrigerant in the cooling coil of the air handling unit. Since the air is cooled directly by the refrigerant the cooling efficiency of the DX plants is higher. However, it is not always feasible to carry the refrigerant piping to the large distances hence, direct expansion or the DX type of central air conditioning system is usually used for cooling the small buildings or the rooms on the single floor.
The direct expansion system in HVAC has been growing rapidly due to its ability to get rid of most ductwork and piping. The popularity of this system is because the installation work has been made easier hence reducing the cost of the overall system.
The DX System works in such a way that the evaporator is located in the space to be refrigerated. When the refrigerant in the evaporator coil expanded, it will cool the space by absorbing the heat from it. The mini-splits, window air conditioners, and packaged units are examples of such systems.
Advantages of Direct Expansion System

Low installation costs.
– Ease to test, adjust, and balance the system.
– Minimum ceiling or wall space needed.
– Low energy consumption.
– Low maintenance costs.
– The individual section can be operated without running the entire system in the building.
– Comfort under varying load conditions.
– Low noise level (NC 35).
– Good relative humidity control.
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