The air in “air balance” comes from having to move the air in a distribution system. In order to do this you need a fan. The fans come packaged in many different ways. Just a few of the devices that these fans are found in are Air handlers, Heat Pumps, Furnaces and Packages Roof Top Units. Then their is duct work that is attached to one of these types of units to complete the air distribution system.
Centrifugal flow and Axial Flow, are basically the two different types of fans that an air balance technician will encounter.
A fan with several different types of blades, curved in different directions is a centrifugal fan. Air will flow radially through the fan. The different types of blades you will find on a centrifugal fan are forward curved, backward curved and radial (flat or straight).
Now Axial flow fans are a little different. They allow the air to flow through the fan instead of radially through. This type of fan is either a propeller like fan, tube axial fan, or a vane axial fan.
In comfort systems, typically in home or business locations, you will see a centrifugal fan being used. These fans can operate very efficiently and at High Pressure. Being able to adjust the air flow easily with a centrifugal fan also makes it more common to use. These types of fans are very simple when it comes to air balancing.
When regarding large industrial air conditioning and ventilation systems, you are normally looking at Axial flow fans. Reasoning behind this is they are used more when a large amount of air is required and noise is a secondary issue. Overall most of the fans have a higher velocity and require guide vanes to run efficiently. A few of them will not require installation of guide vanes.