Our centrifugal fans with free running impellers are designed for installation into appliances such as air handling units (AHUs).
An air handling unit is a factory-made case assembly consisting of a fan or fans and other necessary equipment to perform one or more of the functions of circulating, cleaning, heating, cooling, humidifying, dehumidifying and mixing air. The air handler is normally constructed around a framing system with metal infill panels to suit the configuration of the components.
The AHU is used to control the following:
- Temperature
- Humidity
- Air Cleanliness
There are commonly two types of air handling unit: Draw-Through or Blow-Through.
In the Draw-Through type, the fan pulls the air through a plenham box, filters and cooling coil before discharging it from the fan outlet to the space to be conditioned or to the ducting network. The design can be vertical or horizontal. In this case, the section before the fan has negative pressure.
In the Blow-Through type, the fan blows the air through a plenham box, filters and cooling coil before discharging it to the space being conditioned or the ducting system. In this case, the section after the fan has positive pressure.
AHU Fan Selection
In air handling units, centrifugal fans are used to circulate air to various parts of the building. Fan selection will depend on the air volume (measured in m³/h) and the static pressure (measured in Pascals Pa) required of the system. Usually the designer of the system will use a specialised software to do this selection.
In order to reduce the effect of vibration on the panel, the motor and the fan are usually installed with anti vibration mounts, except when the drive assembly is external to the fan casing.
The use of variable air volume (VAV) systems is becoming more popular as within these systems the volume of the air being discharged can be varied depending on the load condition. If the load is high, the fan speed will be higher and if the load is lower, the speed of the fan will be lower. The speed of the fan is varied using a frequency inverter instead of a conventional motor. A whole range of fan speed, from super low to super high, can now be utilised with a frequency converter based on the load conditions required. A greater focus on the development in EC technology has enabled better use of energy and is in line with the move to more energy efficient products (ERP).
Requirement of AHU Systems
Ventilation system requirements are not always the same. In many applications all that is required is a straightforward exchange of air, whereas in other applications the requirements can vary according to the temperature, humidity and purity of the air. Noise is also a significant factor to consider when choosing AHU fan components.
Moduflow Fans can supply components for efficient air movement within air handling units, including backward-curved impellers, EC motorised impellers within their centrifugal fans and belt driven options, where required.
