With this logic group, the solar surplus is used for hot water preparation.

About the function. A percentage value for the dimmer control of the heating element is calculated from the input "current reference/supply".

As soon as the heating element is switched on, the input "Current consumption/supply" is lowered (current consumption of the heating element should not be taken into account), the "Heating element boiler current consumption in kW" is added to the input in order to restore the actual real supply and to calculate the "Heating element setpoint in %" from this.

The comparator at the end of the logic group checks whether the percentage value is less than 0. If it is, it sends a 0 to the output to prevent the dimmer from operating with mains reference.

To the "Value in W (buffer surplus)" input. Since oscillations can occur here, this buffer is provided to have some "air" when larger consumers (e.g. oven) are switched on.
The cyclic transmitter only ensures that the input values are transferred to the maths job at the same time.

To the hardware structure:
The 0-10V dimmer used is from MDT. It controls a thyristor controller.
The thyristor controller passes on the corresponding power to the heating rod with wattage accuracy (0V=>0W, 5V=>1500W, 10V=>3000W).
In this case, the heating rod itself is single-phase. It is also possible to use other heating rods, only a corresponding thyristor controller must be installed.

For this project, the measured values of the PV system are queried via Modbus (with an APPMODULE and the Modbus TCP Smart Home App) and sent to the KNX bus. The consumption of the heating rod is provided via an MDT actuator with current measurement.

O.Stoehr
Contactor GmbH
(232; 2022.11)