Variable water flow system (VWF)
Variable water flow is a hydronic control function package
that permits control of the water flow rate.
COOLING
The VWF not only ensures control at full load, a specific
Carrier algorithm linked to an electronic frequency converter
also continuously modulates the flow rate to minimise pump
consumption at full load as well as part load.
The hydronic module includes pressure transducers that
permit intelligent measurement of the water flow rate and
real-time display on the Touch Pilot Junior interface. All
adjust-ments can be made directly on the interface, speeding
up start-up and maintenance.
As VWF acts directly on the pump, the system no longer
requires the control valve at the unit outlet. However, for
applications with two-way valves a bypass system must be
kept to guarantee the minimum flow rate.
Operating logic
■■ Full-load set point
The flow rate control at full load uses the Touch Pilot Junior
interface, reducing the pump speed. This first control saves
energy that would normally be dissipated in the control valve.
For example, if the pressure supplied by the pump is reduced
by 20% the power consumption of the pump is reduced by
the same ratio, compared to a traditional installation.
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■■ Operating mode at part load
Touch Pilot Junior includes two part-load operating modes:
-- Constant outlet pressure control
-- Constant delta T control.
1 – Constant unit outlet pressure control
The control continuously acts on the pump speed to ensure a
constant outlet pressure.
This solution is suitable for installations with two-way valves.
When these close, the water speed will accelerate in the
system branches that are still open. For a fixed-speed pump
this results in an unnecessary increase of the pressure at the
pump outlet.
The outlet pressure control mode ensures that each circuit
branch always has a uniform supply, without unnecessary
energy waste.
In industrial processes such as plastic injection moulding,
this solution ensures that each terminal unit has the correct
pressure supply.
2 – Constant delta T control
The VWF algorithm maintains a constant delta T no matter
what the unit load, reducing the flow rate to the minimum.
This solution can be used for systems with two-way or threeway valves and achieves higher energy savings than the
“Constant unit outlet pressure control” mode. It is suitable for
the majority of comfort applications.
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