Circulation pump
Circulation pump| This function block controls the circulation pump of the domestic hot water line. The pump
makes sure that hot water arrives at the tap immediately - and it is at the same time one of
the largest hidden energy consumers in a house: a pump that runs continuously costs more per
year than all the lighting of a single-family home. The block offers three operating modes that can be switched on individually and may overlap. The pump runs as soon as at least one enabled condition applies: Time program - the pump runs during the release period at input ZP, either continuously or in cycles. On demand - a press on a push button or a draw-off detected by the flow switch makes the pump run for a set time. Temperature - if the circulation return gets too cold, the pump runs until the return reaches the setpoint again. The default is the time program with continuous operation only. With that the block behaves like a hand-built solution made of a time switch and a pump. Anything beyond that is switched on deliberately. The recommendation for residential buildings is time program + on demand: a short cycle during the day, off at night - and whoever showers at night presses the button. The temperature mode belongs rather in commercial buildings where pipe lengths matter. Added to this are a minimum running time and a minimum standstill time, a weekly anti-seizing run, the operating hours of the pump and a maintenance message. There is no dedicated control element. For the visualisation a text display at output ST and value displays at LZ and BT are sufficient. The variable for the status text must be of data type string. If input TA is assigned an address, a button element of the visualisation turns into a hot water request button. Note: the controller issues the status text in German plain text, like all blocks of the heating group. |
How it works |
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| Time program. If input ZP carries a value other than 0, the release period applies.
With continuous operation the pump runs for the whole period. With cycle
operation it alternates between on time and pause time within the release period. When
ZP changes to a value other than 0 the cycle always starts with the on time -
otherwise the period would begin with a pause and the first draw-off would find cold water.
When ZP falls away, the cycle ends. On demand. Every press of the push button at input TA and every draw-off detected at input SS is evaluated. If the input is assigned an address, every telegram carrying a value other than 0 counts - a push button sends the same 1 on every press, so the value does not change at all. If the input is fed by a drawn connection instead, the change from 0 to a value other than 0 counts. A request sets the remaining running time to the configured value. It is set anew and never added: a bouncing flow switch produces several triggers in a row during a short draw-off, so the pump must not run longer and longer. If retriggering is switched off, a request is ignored while the previous one is still running. After the running time has elapsed, the lockout time begins. During that time no new request is accepted. This is not a loss of comfort but a necessity: without a lockout time repeated pressing keeps the pump running for hours. Temperature. If the return at input RT falls below setpoint minus switch-on difference, the pump runs. It switches off as soon as the return reaches the setpoint. The setpoint comes from input SO; if that input is not connected or carries 0, the parameter applies. This mode needs a minimum running time. The sensor sits behind the pump and reacts immediately once warm water passes it - without a minimum running time the pump cycles within seconds. Special operation. Input ZS reports a special operation of the hot water system, typically a legionella disinfection. What happens then is decided by the parameter. Running along is the technically correct default: the circulation line has to be heated through as well, because heating only the cylinder leaves the problem in the pipe. The pump is then switched on unconditionally, regardless of all other conditions. Scald protection is not the task of this block. A system that heats to 65 °C needs a mixing valve at the tap. Minimum times. The minimum running time keeps a running pump going even if the condition has already fallen away. The minimum standstill time delays the restart after switching off. The request is not discarded - the pump starts by itself once the time has elapsed, without anything having to trigger again. Both times are 0 by default. Anti-seizing run. On the configured weekday and at the configured full hour the pump runs for the configured duration so that it does not seize up after a long standstill. The run only starts with the pump stopped and is aborted immediately as soon as one of the operating modes calls for the pump anyway. Operating hours and maintenance. Output BT counts the running time of the pump in hours. The value survives a restart of the controller. If a maintenance interval is set, output WA reports maintenance due once that many operating hours have passed since the last acknowledgement. An edge at input QU acknowledges; the current reading becomes the new zero point while the operating hours themselves keep counting. Blocking. If the release at input FR is missing or input SP carries a block, the pump switches off, all times are reset and a running anti-seizing run is aborted. The operating hours are kept. |
Example |
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| Single-family home. Operating modes time program and on demand switched on,
temperature off. Time program set to cycle operation with 3 minutes on and 12 minutes off. A
time switch releases 6:00 to 8:30 and 17:00 to 22:00 via
ZP. Running time on demand 3 minutes, lockout time 10 minutes, a push button in the bathroom
is assigned to TA. Hot water is available during the day without the pump running continuously. Whoever showers at night presses the button and has hot water shortly after. Over the day the pump runs just over 3 hours instead of 16. Commercial building with long pipes. Switch on the temperature mode as well, assign a sensor at the circulation return to RT, setpoint 45 °C, switch-on difference 5 K and minimum running time 2 minutes. The line is then kept warm even while the time window is closed. Interaction with the hot water system. The address with which the cylinder charging block starts its legionella disinfection is additionally assigned to input ZS, and the behaviour is left at running along. The circulation line is then heated through with every disinfection. |
Inputs |
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| ZP |
Time program release |
A value other than 0 opens the release
period, 0 ends it. On the change from 0 to a value other than 0 the cycle starts with the on
time. Only effective if the time program mode is switched on. Optional. Not
connected: there is no time window, so the time program mode never runs. |
| TA |
Request push button |
Starts the running time on demand. If the
input is assigned an address, every telegram carrying a value other than 0 is
evaluated - including a second one with the same value. With a drawn connection the change
from 0 to a value other than 0 is evaluated. Only effective if the on demand mode is switched
on, and only while no lockout time is running. Optional. Not connected: a request is
never made via the push button. |
| SS |
Flow switch |
Like TA, but for a draw-off detected by the
flow switch. Several triggers in quick succession - a bouncing switch - each set the
remaining running time anew, they do not add it up. Optional. Not connected: a request
is never made via a draw-off. |
| RT |
Return temperature |
Measured temperature of the circulation
return in °C. A value below -50 or above 150 counts as a sensor fault; the status text
reports it and the temperature mode stays off. Optional. Not connected: the
temperature mode has no effect even when it is switched on. |
| SO |
Return setpoint |
Setpoint of the return monitoring in °C.
Only effective with a value other than 0 - 0 counts as not yet received. This allows
the setpoint to be adjusted from the visualisation. Optional. Not connected or 0: the
parameter return setpoint applies. |
| ZS |
Circulation special operation |
A value other than 0 reports a special
operation of the hot water system, typically a legionella disinfection. With the setting
running along the pump is then switched on unconditionally, with the setting off it is
switched off unconditionally - both override all other conditions. Optional.
Not connected: there is never a special operation. |
| FR |
Release |
A value other than 0 releases the block, 0
blocks it. When blocked the pump switches off and all times are reset. Optional. Not
connected: the block counts as released. |
| SP |
Block |
A value other than 0 blocks the block, 0
releases it. Acts like a missing release. Optional. Not connected: never blocked. |
| QU |
Maintenance acknowledgement |
The change from 0 to a value other than 0 is
evaluated. The current operating hours reading becomes the new zero point of the maintenance
message; the counter at output BT keeps running unchanged. Optional. Not connected:
the maintenance message can only be reset by changing the maintenance interval. |
Outputs |
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| PU |
Circulation pump |
1 while the pump is to run, otherwise 0. |
| LZ |
Remaining running time |
Remaining running time of the request in
seconds. If no request is running, this shows the remaining time of the current cycle section
in cycle operation, otherwise 0. |
| ST |
Status text |
Plain text for a text display, for example
"laeuft (Zeitprogramm)" (running, time program), "laeuft (Anforderung, noch 3:20)" (running
on demand, 3:20 left) or "aus (Takt, Pause noch 8:30)" (off, cycle pause, 8:30 left). The
variable must be of data type string. |
| BT |
Operating hours |
Running time of the pump in hours. Updated
every minute and survives a restart of the controller. |
| WA |
Maintenance due |
1 as soon as as many operating hours have
passed since the last acknowledgement as configured in the maintenance interval, otherwise 0.
Always 0 without a configured interval. |
Parameters |
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| Time program |
Switches on the time program mode. Default
on. |
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| On demand |
Switches on the on demand mode. Default
off. |
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| Temperature |
Switches on the temperature mode. Default
off. |
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| Type of time program |
Continuous: the pump runs for the whole
release period. Cycle operation: it alternates within the release period. Default
continuous. |
|
| Cycle on time |
Running time per cycle. The release period
always begins with this running time. Default 180 s. |
|
| Cycle pause time |
Standstill time between two cycles. Default
720 s. |
|
| Running time on demand |
The pump runs this long after a request via
TA or SS. Default 180 s. |
|
| Retriggering allowed |
Yes: a new request sets the running time
anew. No: it is ignored while the previous one is still running. The running time is never
added up. Default yes. |
|
| Lockout time after request |
No new request is accepted for this long
after the end. 0 switches the lockout off - repeated pressing then keeps the pump running
indefinitely. Default 600 s. |
|
| Return setpoint |
From this temperature on the circulation
line counts as warm. Only applies if input SO is not connected or carries 0. Default 45
°C. |
|
| Switch-on difference |
The return may fall this far below the
setpoint before the pump starts. It switches off when the setpoint is reached. Default 5
K. |
|
| Minimum running time |
The pump runs at least this long, even if
the condition has already fallen away. Essential for the temperature mode: the sensor sits
behind the pump and reacts immediately, without a minimum running time the pump cycles.
Default 0 s. |
|
| Minimum standstill time |
The pump stays stopped at least this long
after switching off. The request is not lost - the pump starts by itself once the time has
elapsed. Default 0 s. |
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| Behaviour on special operation |
Running along: input ZS switches the pump on
unconditionally, so the circulation line is heated through as well. Off: input ZS switches
the pump off. Default running along. |
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| Anti-seizing run |
Moves the pump once a week so that it does
not seize up after a long standstill. Only runs with the pump stopped. Default on. |
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| Anti-seizing run weekday |
Weekday of the anti-seizing run. Default
Sunday. |
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| Anti-seizing run time of day |
Full hour at which the anti-seizing run
starts. Default 10. |
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| Anti-seizing run duration |
Running time of the pump during the
anti-seizing run. Default 60 s. |
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| Maintenance interval |
After this many operating hours output WA
reports maintenance due. 0 switches the message off. Default 0 h. |
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