Multi Louver Damper as the name implies consists of multiple louvers placed along the cross section of duct rotating simultaneously about their own axis which cause the louvers to align themselves along the direction of flow or block the flow. They serve as a better option as compared to butterfly dampers.
AIGV’s (Adjustable inlet guide vanes) will allow more efficient operation than an inlet butterfly damper at reduced head requirements for a constant speed driven single stage centrifugal fan.
Butterfly damper is a disk-shaped valve turning on an axis along its diameter, serving especially as a damper in a pipe or as a choke or throttle in a duct. The butterfly damper does not decrease the power consumption when throttled, in contrast to IGV.