Danfoss VLT Series Design Manual page 31

VLT ® HVAC Drive Design Guide 2. Introduction to the VLT HVAC Drive
Using an adjustable frequency drive to decrease the pump speed is very similar to trimming the
pump impeller, except it does not require any labor and the pump efficiency remains higher. The
balancing contractor simply decreases the speed of the pump until the proper flow rate is achieved
and leaves the speed fixed. The pump will operate at this speed any time the chiller is staged on.
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Because the primary loop doesn't have control valves or other devices that can cause the system
curve to change, and because the variance due to staging pumps and chillers on and off is usually
small, this fixed speed will remain appropriate. In the event the flow rate needs to be increased
later in the systems life, the adjustable frequency drive can simply increase the pump speed in-
stead of requiring a new pump impeller.
Flowmeter Flowmeter
F F
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MG.11.B4.22 - VLT ® is a registered Danfoss trademark.