Page 49 - Advanced Course

KNX ADVANCED COURSE

2.1 Individual Room Control
The individual room control system can be implemented relatively simply by the electrical
installer as only a small amount of specialist knowledge of the heating industry is required.
It is possible to distinguish between 2 types of individual room control:

2-step control
continuous control (3-step control)

In our examples, we are starting with hot water convector heating.

2.1.1 Principle of Individual Room Control
The control system consists of a room thermostat and a valve drive. The valve drive
influences the heating valve of the heater or phase. The heating system must only have a
direct heating circuit. There should also be an option for displaying the temperature.

A room thermostat measures the current temperature (current room temperature) and
compares it with the predefined setpoint. The control value is calculated (e.g. as a
percentage or ON/OFF commands) from the differential of the current and setpoint
temperature using the set control algorithm. The control value indicates the heating or
cooling capacity that should be supplied to the system.

Figure 21: Control system

2.1.2 Types of Control

2.1.2.1 Two-step Control

This is the simplest type of control. A control value is not calculated. The controller
switches on or off. The room temperature oscillates around the setpoint temperature
(hysteresis value).
Example: Setpoint 30 °C, hysteresis 1 Heating switches on at 29 °C and switches off
at 31 °C.
The continually fluctuating room temperature is a disadvantage of this extremely simple
control system. This leads to an overshooting of the temperature because the valve drive
requires approx. 3 minutes until it is fully closed. The heater also continues to supply heat
to the room even once the water has stopped flowing.

Home and Building Management Systems KNX Association
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