Siemens Building Technologies
Basic Documentation RVL470
CE1P2522E / 30.03.2000
Landis & Staefa Division
Function block "District heat"
41/68
Example of the effect of maximum limitation of the return temperature differential:
100
90
80
70
60
50
40
30
20
10
0
V
P
[%]
DRT
on
DRT
OFF
V
S
t
252
2D
11
DRT
ON
With activated maximum limitation
DRT
OFF
Without maximum limitation
t
Time
V
P
Volumetric flow on the primary side
V
S
Volume saved
12.2.4. Integral action time
With maximum limitation of the return temperature and maximum limitation of the return
temperature differential, the integral action time determines the rate at which the flow
temperature setpoint will be reduced:
•
Short integral action times lead to quick reductions
•
Long integral action times lead to slow reductions
With this setting, the impact of the limitation function can be matched to the type of
plant.
12.2.5. Minimum limitation of stroke (suppression of hydraulic creep)
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
min
function). If the valve is supposed to open below the minimum stroke
position, it will be fully closed and remains closed until the set closing time has elapsed.
The first opening pulse after completion of the closing time will reopen the valve and the
control resumes normal operation.
The stroke assigned to the minimum volumetric flow must be acquired by an auxiliary
switch fitted in the actuator and delivered to the RVL470. When bridging terminals H4–
M, the valve will close and the waiting time starts.
Minimum limitation of the stroke has priority over all limitations.
If minimum stroke limitation is activated, the display shows .
12.2.6. Flow limitation
The RVL470 does not provide flow limitation.
