Heating actuators are, basically, switching actuators, which, however, are not equipped with mechanical relays, but are equipped with electronic circuits (triac) to control thermoelectric valves (low resistive loads) for closed hot water circuits or cooled water (cooling ceiling). As a result, these devices are silent and completely wear-free. The control difference, which is determined by a KNX room temperature controller, i.e. the difference between set point temperature and actual temperature, is converted into a manipulated variable telegram and sent via KNX bus to the corresponding channel of the heating actuator. The thermoelectric (conventional) actuator is connected to the channel by means of a suitable cable (eg NYM-J 3x1.5), unless the heating actuator is mounted in the immediate vicinity of the actuator. The heating actuator can usually switch directly (1 bit) or process a received 1 byte variable signal internally and control the connected drive. As a result, the KNX bus is considerably relieved because the flow of control telegrams from the room temperature controller to the actuator is omitted and only the calculated control difference is sent to the actuator as a 1-byte manipulated variable telegram. It converts the information into switching signals (on / off) directly to the assigned heating channel. This is referred to as pulse width modulation (PWM). A little example illustrates only the basic function, not the real manufacturer-specific control algorithm: The current temperature (control variable) is 20 degrees Celsius. The desired room temperature is 25 degrees Celsius and represents the set point for the controlled variable (reference variable), the difference between the desired room temperature (set point) and the current temperature (actual value) is the control difference. The control difference is 5 degrees Celsius and is used to determine the manipulated variable over which the room temperature is influenced. Let’s assume the manipulated variable is 20%. This value is sent to the heating actuator in the form of a 1-byte telegram (0-255 = 0-100%). The value 51 is therefore transmitted to the actuator. The time for opening / closing the actuating drive is stored in the parameters of the actuator by means of ETS. This time is stored in the parameters of the respective conventional actuating drive used and must be accepted. For example, the actuating drive requires 2 mns for a complete opening process. In case of, for example, a 20% manipulated variable, the actuator would switch on the 230V AC or 24V DC thermoelectric valve drive for 24 seconds (20% of 2 mns.), turn it off for 96 seconds and then switch on again for another 24 seconds, etc. until another manipulated variable is calculated and sent by the room temperature controller. Depending on the manufacturer of the actuator, several actuating drives per channel can be integrated. The leading manufacturers of EIB, KNX heating actuators at eibabo are ABB, Berker, Busch-Jaeger, EIBMARKT, Elsner, Gira, Hager, Jung, Lingg & Janke, MDT, Merten, Siemens and Theben. Since, contrary to the general opinion, thermoelectric actuators are not wear-free and should be replaced every few years, earlier versions of expensive KNX actuators, i.e. devices that incorporate the KNX actuator and actuating drive, have not sold-well and are disappearing. The ETS parameter 'Rinse' helps to minimize the wear on rarely used valves, e.g. in summer or in bedrooms. This function prevents fast calcifying of the heating valves. The relatively inexpensive thermoelectric actuating drives (valve drives) are directly clicked on or screwed onto the valve upper part (usually directly in the heating circuit distributor) and, thus, connected to the valve spindle. Adapters made of PVC or metal help to compensate for manufacturer-specific differences in distance between drive and valve upper part or thread and receptacle to ensure correct implementation of the manipulated variable.