User Manual

White paper | Saving Energy using PICVs | June 2017
© Siemens Switzerland Ltd, 2017 5
Full-Stroke Further Increases Control Accuracy
Even finer control accuracy is provided by Siemens PICVs, in
which pre-setting is obtained by limiting the free control
path area. Since the full travel of the flow control valve is
available to manage the opening, the volumetric flow can
be defined using a much larger number of steps (Figure 6).
The temperature can be reached in smaller increments, thus
reducing even further the temperature fluctuations and
discomfort.
Preventing the Setpoint Shift Leads to Energy Savings
As a consequence, users do not experience any discomfort
at the original setpoint and will not shift energy demand up
to compensate for the peaks of temperature variations.
When carried over the entire building for an entire season,
this adds up to substantial energy savings.
Enabling Optimal Distribution Strategies
Conventional Systems Require Constant Pressure
Modern energy transportation systems, such as variable-
speed controlled pumps, adapt the delivery head of a pump
and the volume flow to the demand load. There are a
variety of control strategies on the market today. Control
can be done in connection with differential pressure,
effective volume flow through a flow sensor, differential
temperature, outside temperature, or supply temperature.
As explained above, a conventional hydronic system is
‘‘statically balanced.’’ The hydraulic resistance of the MBVs is
dimensioned so that the system is perfectly balanced for a
nominal operating condition. Typically, since such a system
might still be sensitive to pressure differences, the pump
control strategy is designed to ensure a constant differential
pressure in the system (Figure 7).
Pumps Have to Battle against Unnecessary Resistance
Any reduction of the pressure difference could lead to the
starvation of some terminal units. Even when fully opened,
they do not get the necessary flow required. As a
consequence, the energy exchange is insufficient and the
temperature setpoint cannot be ensured anymore.
To ensure the necessary flow, pumps have to operate
against the hydraulic resistance that has been introduced
into the system to ensure a nominal operating condition,
even if the actual operating conditions are much different.
Figure 7: Pump control strategy ensuring that differential
pressure is constantly maintained at the desired value.
Figure 6: PICVs with pre-setting obtained by limiting the
flow control valve’s travel (stroke limitation) have reduced
control accuracy (purple). Siemens PICVs with pre-setting
obtained by limiting the free control path area still have
the full stroke available and provide a much more
granular control of the flow and temperature (green).
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