Overview Storage charge request



This function block reports the heat demand of a storage - cylinder or buffer - to a generator (e.g. heat pump or boiler) and switches the charging pump. It works with two sensors and two setpoints, which are present as inputs and can therefore be adjusted from the visualization.

The block corresponds to scheme 2 of the HMI-Master and is executed every second.
  • Charging on: storage top (TO) ≤ setpoint on - hysteresis.
  • Charging off: storage top ≥ setpoint on + hysteresis and storage bottom (TU) ≥ setpoint off + hysteresis. The storage is therefore charged all the way through. In between, the state stays as it is. Without a bottom sensor, the top sensor applies.
  • Maximum charging time: Once it has expired, charging ends and a pause of the same duration follows. This way a generator that supplies several storages cannot be permanently occupied by one of them. If the storage is full during the pause, the pause is cancelled.
  • Charging pump: runs only during charging. If a flow sensor (VL) is linked, it only starts once the flow is warmer than the storage bottom by the pump switch-on difference, and switches off again at half that difference - the storage is not cooled down with cold water.
  • Lock SP: no request, pump off, times reset.
Typical uses: cylinder charging via a heat pump (AN to the generator's request), buffer request for heating operation, or domestic hot water preparation from the buffer (output PU only, VL = buffer top).

System diagram

Generator Storage VL PU TO TU AN AT Request ON: TO ≤ SE - hysteresis OFF: TO ≥ SE + hysteresis and TU ≥ SA + hysteresis PU: only during charging and VL > TU + switch-on difference Input (sensor) Output

Inputs

TO Storage temperature top Must be linked. If the sensor is missing or outside -50 to 150 °C, charging does not take place (fault in the status text).
TU Storage temperature bottom Optional. Condition for ending charging. Not linked or outside -50 to 150 °C: the top sensor applies.
SE Setpoint on (top) Optional. Switch-on threshold at the top sensor. Not linked or 0: parameter Setpoint on applies.
SA Setpoint off (bottom) Optional. The bottom sensor must reach this temperature for charging to end. Not linked or 0: parameter Setpoint off applies.
VL Flow temperature generator Optional. Releases the charging pump only once the flow is warmer than the storage bottom by the pump switch-on difference. Not linked: the pump runs during the whole charge.
SP Lock Optional. Not equal to 0 locks: no request, pump off, times reset. 0 releases. Not linked: never locked.

Outputs
AN Heat request 1 during charging.
AT Request temperature Setpoint off + request boost during charging, otherwise 0. If the output is connected to a heat request, leave the boost there at 0, otherwise it counts twice.
PU Charging pump On/off.
RZ Remaining time charge/pause Seconds until the end of the maximum charging time or the pause. 0 without limit.
ST Status text State as plain text. For a text address (14 byte).

Parameters
Setpoint on / Setpoint off Fallback values as long as SE or SA are not linked. Default 55 °C or 45 °C.
Hysteresis Switching gap around both setpoints. Default 0 K.
Maximum charging time In minutes, then a pause of the same duration. 0 = unlimited.
Request boost Addition to setpoint off for output AT. Default 0 K.
Pump switch-on difference Flow versus storage bottom, above which the charging pump runs; switches off at half that difference. Default 5 K.

See also general parameters of all function blocks.