Central Air Handling Unit Function

Central Air Handling Units. They are a very important machine. It is a very essential equipment in any building, be it in Industrial, Commercial, or in future, Residential.

This equipment is one of the huge energy consumption for every building. Approximate 40% of the total electrical bills.

The function of a Central Air Handling Unit is to draw in air from fresh air ducting and building air, and mix it. After mixing the air in the CAHU room, some of the air will go through a smoke detector device, and together with the rest of the air, they go through filtration.

Filtration varies with the function of a building. In term of filtration, it have a class standards, with class 1 being the highest, and class 1’000’000 being the lowest. Filtration is important in CAHU, because it will affect the life span of the cooling coil, which the air is going through after filtration. Without filtration, cooling coils will get dusty, and loses its suction.

Cooling coil is the device, which helps to extract heat out of the air. In this cooling coil, buffer medium such a saltwater or in most cases, chilled water passes through the long coil. With the assistant of the fins attached to the coil, they are able to slow down the air flow, which may run as much as 25’000cubic meter per hour, depending of the size. Other than slowing down the air, the cooling coil fins also allows the chillwater to be more efficient, because the fins expand the contact area of the chill medium, thereby, making the most use of the heat exchange, before the chill water returns to the chiller.

After going through the Cooling coil, the air will goes through some sensors, such as manometer, thermometer, air differential meter, and then gets vacuumed into the blower.

In the blower, there are numerous vanes, rotated by 3 phase alternative current electric motor. It is then expel to diverter vane, where the air is distributed, and vanes. At the end point, they will go to the outlet diffuser and goes to extract the heat from the building.

The most essential thing to monitor in the CAHU is the filters. The first picture shows the condition of the filters 24 days ago. The second picture shows the same filters after 24 days. The condition of the filters have shown 2 things. They are the condition of the cooling coil, and the efficiency of the filters. It also tells the technician the condition of the rotor vane.

In certain environment, where products is not to exposed to moisture, heating coil is added after the cooling coil, And some even put in an air dryer after the cooling coil.

CAHU are really convenient to service technician, because they have cut down the number of fan coil unit in the building, and reduces the accident risk of the technician. This is because most fan coil unit are mounted on top of the shops or tenant, and to repair or cleaning requires the permission of the tenants. In CAHU, as long as the room is not in the tenant side, technician can go in any time to check on the CAHU, and even do adjustment. They also simplified the layout of the chill water piping, electrical distribution and drainage piping. The only set-point is that when the CAHU breakdown, an emergency team have to get a standby power supply and electrical motor, and rush to start up the CAHU. This is why, in our building, we have at least two electrical motor, and 2 sets of electrical equipment as a standing by.

CAHU in event of fire, is also useful, because when the smoke detector is activated, it will stopped running, and closes up all the inlet vane, so that the fire will not go into the room, and stops the risk of fire. It also stops the fire from being distributed to another room. In Fan coil unit, however, this is not possible. If the ducting goes to another room, the smoke will be blown to another room, and blacken the entire room.