Overview Boiler charging


This function block realizes a boiler charging. The block compares the two boiler sensors with the setpoint and reports the demand to the heat generator – as a bit, as a temperature or as a percentage.

Charging starts as soon as Boiler top falls below the setpoint minus Hysteresis on. It only ends when Boiler bottom exceeds the setpoint plus Hysteresis off and at the same time Boiler top has reached at least the setpoint – the cylinder is therefore always charged completely. In between, the demand remains.

The setpoint is Setpoint hot water. While a Legionella heat-up is running, Setpoint Legionella applies instead; the Legionella heat-up acts independently of Enable hot water and is therefore completed even if the hot-water enable is withdrawn in the meantime. With a setpoint of 0 no charging takes place.

System diagram

Heat generator Cylinder Hot water Cold water T1 T2 Demand AB AP AT ST Setpoints / enables FW FL SW SL Input (sensor) Output

Inputs

FW
 Enable hot water
 Optional. Enable hot water preparation. Non-zero enables, 0 blocks. Not linked: the block is always enabled. While the block is blocked all outputs go to 0, but a running Legionella heat-up is completed.
FL
 Enable Legionella
 Enable Legionella heat-up. With a positive edge at the input the Legionella heat-up is started. The Legionella setpoint is used here; once this temperature is reached, 0 is sent to the connected variable and the setpoint for hot water is used again. The variable at the input can, for example, be set to 1 by a timer; once the  Legionella heat-up is finished, the variable is set back to 0 by the block.  The change from 0 to non-zero is evaluated. Optional – not linked: no Legionella heat-up is ever started.
T1
 Boiler top*
 Actual temperature boiler top. This sensor starts the charging. Not linked: the block calculates with 0 °C and demands permanently. This sensor must be linked.
T2
 Boiler bottom*
 Actual temperature boiler bottom. This sensor ends the charging. Not linked: the block calculates with 0 °C, the switch-off condition is never met and the demand remains. This sensor must be linked.
SW
 Setpoint hot water*
 Setpoint temperature hot water. With 0 no charging takes place. Not linked: 55 °C is used. This setpoint should be linked.
SL
 Setpoint Legionella
 Setpoint temperature Legionella. Optional – not linked: heat-up is done to 80 °C.

Outputs
AB
 Demand bit
 Output is set to 1 when the boiler is heated up. This output can be used for a pump or heat-generator enable.
AP
 Demand percent
 Current setpoint temperature in percent. This is set with the parameter Factor percent output.
AT
 Demand temperature
 Current setpoint temperature in degrees.
ST
 Status
 Status bit-coded. Bit 0 = Legionella heat-up active.

Parameters
Hysteresis on
 Hysteresis for hot water preparation on. If the temperature boiler top falls below setpoint minus hysteresis, hot water preparation is started.
Hysteresis off
 Hysteresis for hot water preparation off. If the temperature boiler bottom exceeds setpoint  plus hysteresis and boiler top is greater than setpoint, hot water preparation is ended.
Offset setpoint temperature
 This parameter is added to the output Demand temperature. It can be used for a setpoint boost.
Factor percent output
 This parameter sets the percent output. This is the temperature at 100 percent. With a value of 80, at setpoint temperature 80, 100 percent is output; at 40 degrees, 50 percent etc. In the calculation the parameter Offset setpoint temperature is also added.



See also common parameters of all function blocks.