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Siemens Building Technologies
HVAC Products
27.3
Suppression of hydraulic creep
27.3.1 Mode of operation
To avoid measurement errors in connection with heat metering due to extremely small
flow rates, the flow through the two-port valve in the primary return can be limited to a
minimum (Y
function). This ensures that consumers will not be able to draw heat that
min
cannot be acquired and billed.
If the valve's stroke reaches the minimum limit value, the valve will be fully closed and
then remains closed until the closing time has elapsed.
The first opening pulse delivered by the control after completion of the closing time will
reopen the valve and the control resumes normal operation.
What must always be set is the closing time. This is made on operating line 188, sepa-
rately for each heating circuit; there, the function can also be deactivated by entering --- .
The suppression of hydraulic creep always acts on regulating unit Y1 in the primary re-
turn.
If suppression of hydraulic creep is active, the display shows . It is given priority over all
other limitations and acts on the types of plant with a common flow or with a pre-
controlled flow (plant types 2–x and 3–x), also during d.h.w. heating.
There is no suppression of hydraulic creep in the d.h.w. circuit connected to the primary
side.
27.3.2 Mode of operation
The stroke corresponding to the minimum volumetric flow is acquired by an auxiliary
switch fitted in the actuator and is then delivered to the controller. The auxiliary switch
is connected to terminals B7–M. When the valve reaches the minimum limit value, the
auxiliary switch will close. When B7–M closes, the valve will be shut and the closing
time starts.
If the link is maintained although the controller delivers opening pulses of 20 % of the
running time, or if the flow temperature setpoint exceeds the setpoint by more than
10 K, the function will deactivate itself until the auxiliary switch in the actuator opens
again.
27.4
Raising the reduced room temperature
setpoint
The reduced room temperature setpoint can be raised as a function of the falling out-
side temperature. This ensures that
• the change from the reduced setpoint to the nominal setpoint will not be too great
when outside temperatures are very low
• there will be no extreme peak loads during the heating up phase.
What can be set is a starting point in °C outside temperature (start of compensation,
operating line 189). The reduced room temperature setpoint is raised only at outside
temperatures below that starting point; raising is not required when outside tempera-
tures are higher. The degree of increase is to be set in the form of a slope (operating
line 190); the slope represents the setpoint increase per °C outside temperature drop.
The setting range is 0...10; the effective value is 10 times smaller.
The temperature used is the composite outside temperature.
The function can be deactivated (by entering 0 for the slope) .
Basic documentation RVD240
27 Function block Various functions
CE1P2384en
27.05.2004
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