Danfoss VLT HVAC Drive FC 102 Design Manual page 38

Product Features
compensating for the changing resistance in the primary piping loop as chillers and their pumps are staged on
and off.
•
The operator can use local speed determination by decreasing the output frequency until the design flow rate is
achieved. Using a drive to decrease the pump speed is similar to trimming the pump impeller, but more efficient.
The balancing contractor simply decreases the speed of the pump until the proper flow rate is achieved and leaves
the speed fixed. The pump operates at this speed any time the chiller is staged on. Because the primary loop lacks
control valves or other devices that can change the system curve, and the variance due to staging pumps and
chillers on and off is small, this fixed speed remains appropriate. If the flow rate must be increased later in the life
of the system, the drive can simply increase the pump speed instead of requiring a new pump impeller.
5 5
Frequency
converter
Illustration 5.20 Drives Used with Primary Pumps in a Primary/Secondary Pump System
For more information, consult the Danfoss supplier for the Primary Pumps: Improving Primary Pumping in Pri/Sec System
application note.
36
VLT
Flowmeter
F
Danfoss A/S © 11/2017 All rights reserved.
®
HVAC Drive FC 102
Flowmeter
Frequency
converter
F
MG16C302