Frequency
converter
Water
Inlet
Water
Outlet
BASIN
Flow or pressure sensor
Condenser
Water pump
Throttling
valve
Supply
CHILLER
130BB452.10
Illustration 5.19 Drive Used with a Condenser Pump
For more information, consult the Danfoss supplier for the Condenser Pumps: Improving Condenser Water Pumping Systems
application note.
5.3.4.5 Primary Pumps
Primary pumps in a primary/secondary pumping system can maintain a constant ow through devices that encounter
operation or control diculties when exposed to variable ow. The primary/secondary pumping technique decouples the
primary production loop from the secondary distribution loop. Decoupling allows devices such as chillers to obtain constant
design ow and operate properly while allowing the rest of the system to vary in ow. As the evaporator ow rate
decreases in a chiller, the water begins to become overchilled. As the water becomes overchilled, the chiller attempts to
decrease its cooling capacity. If the ow rate drops far enough, or too quickly, the chiller cannot shed its load suciently
and the low evaporator temperature safety trips the chiller, requiring a manual reset. This situation is common in large
installations, especially when 2 or more chillers in parallel are installed if primary/secondary pumping is not used.
VLT
®
solution
A drive can be added to the primary system, to replace the throttling valve and/or trimming of the impellers, leading to
reduced operating expenses. Two control methods are common:
•
A ow meter installed at the discharge of each chiller can control the pump directly because the desired ow rate
is known and constant. Using the PID controller, the drive always maintains the appropriate ow rate, even
Product Features Design Guide
MG16C302 Danfoss A/S © 11/2017 All rights reserved. 35
5 5
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