AHUs are used to regulate and circulate air as part of the ventilation, heating and air conditioning system. AHUs are often used in medium to large industrial and commercial buildings and are usually installed in the floors, roof or basement. It is common to have lots of smaller AHUs working in different areas of the building.
What is the function of an air handling unit?
The AHU is normally a large metal box that connects to the ductwork that channels conditioned air throughout a building and returns it back to the AHU. Inside this large metal box, there are a number of ventilators with different jobs to do.
AHU’s supply fresh air to the room. The units take air from the outside, filter it and recondition it (cooled by a cooling coil or heated by a heating coil).
How they work?
The easiest way of explaining how AHUs work is to run through the components and their functions:
Usually made of metal and painted to prevent corrosion, the housing contains all the components of the AHU. The coil and fans are insulated in the housing to prevent condensation.
The filters are used to remove contaminants from the air. Different filters are available for different AHUs:
- HEPA filters are often used where businesses have particular concerns for their staff and sensitive equipment as these filters are efficient at removing airborne bacteria and can remove viruses from the air
- Bag filters provide a medium to the high efficiency of filtration
- Panel filters provide a minimum low-efficiency filtration
- Electrostatic filters use highly charged electrodes that ionise the air
- Carbon filters remove smells and gases
The fan within the AHU moves the air to different sections of the building. There are a variety of fans available (forward Curved, Backward Curved, Airfoil and Backward Inclined). The designer will use software to select the right fan, depending on the static pressure and air volume in the AHU.
Over the years technology is improving to make better use of energy and follow the greener agenda. As a result of this the variable air volume (VAV) system is popular as, depending on the need, the volume of the air being discharged can be varied. If the system load and thermal load are low, the speed of the fan will be low and if the loads are high the fan will speed up. Instead of a conventional motor a frequency inverter varies the speed of the fan for better control.