To move the air in a distribution system you need a fan. This is where the air in “air balance” comes from. These fans are package many different ways. Air handlers, Heat Pumps, Furnaces and Packages Roof Top Units are just a few of the devices that these fans are found in. The duct work is attached to one of these types of units to complete the air distribution system.
There are basically two different types of fans that an air balance technician will encounter; Centrifugal flow and Axial Flow.
A centrifugal fan’s air will flow radially through the fan. This fan will have several different types of blades; forward curved, backward curved and radial (flat or straight).
An Axial flow fans air flows through the fan. The fan is either a propeller like fan tube axial fan or a vane axial fan.
You mostly see a centrifugal fan in most comfort systems. They can operate very efficiently and at High Pressure. The air flow in most of the centrifugal fans can be easily adjusted. Airs balancing these types of fans are very simple.
Axial flow fans are use more when a large amount of air is required and noise is a secondary issue. They are mainly used in large industrial air conditioning and ventilation systems.
Most of these fans have a higher velocity and require guide vanes to operate efficiently. There are some that will not require the guide vanes to be installed.