Pool temperature control over KNX with Pool’nX (hysteresis)

Pool’nXAdministratorInstaller

Can’nX Cloud, Pool’nX window: Temperature Control

Temperature Control turns Pool’nX into an on/off controller on the KNX bus: it compares the water temperature sent by a KNX sensor with a setpoint, then writes on or off to a command address, for example the address of a heat pump actuator. Control uses only KNX telegrams; it works whatever the type of pool.

Intended for the installer who controls pool heating from KNX.

Before you start

A KNX sensor writes the water temperature to a group address, in DPT 9.001.
A KNX actuator receives the heating on/off command, in DPT 1.001.
In ETS, plan the addresses for the setpoint and the status feedback, in DPT 9.001 for the setpoint and 1.001 for the control feedback.

Fill in the control settings

In the Pool’nX window, next to Temperature Control, click the button with the thermometer icon.
Fill in the group addresses using the table below, in X/Y/Z format.
In Hysteresis, enter the difference in °C, for example 1 (example).
Turn on Enabled.
Click Save. Success! confirms the save.

Field	DPT	Role of Pool’nX
Setpoint	9.001	Receives the setpoint written by the visualization or a KNX button.
Setpoint feedback	9.001	Writes the setpoint at each new value, on save and in response to a read.
Current Temperature	9.001	Receives the temperature written by the sensor.
Control	1.001	Writes 1 to switch on, 0 to switch off.
Control feedback	1.001	Answers read requests with the control state.

The DPTs are set by Pool’nX: the window only offers the addresses.

Understand the control logic

At each telegram received on Setpoint or Current Temperature, Pool’nX compares the two values:

temperature below the setpoint minus the hysteresis: 1 is written to Control;
temperature above the setpoint plus the hysteresis: 0 is written to Control;
in between: nothing is written, the command keeps its state.

Pool’nX keeps only the integer part of the temperature and the setpoint: 29.8 °C counts as 29 °C. Example: with a setpoint of 28 °C and a hysteresis of 1 °C, heating starts below 27 °C and stops from 30 °C.

Control is only recalculated when a telegram is received: set the sensor to send its measurement regularly.

Check the result

In the ETS group monitor, write a setpoint to the Setpoint address: the same value is written to Setpoint feedback.
Watch the sensor telegrams, then the write of 1 or 0 to Control when the temperature leaves the range.
Check that heating switches on or off.

Troubleshooting

Symptom	Cause and action
Nothing written to Control	Enabled turned off, settings not saved or temperature within the range. Check the Setpoint and Current Temperature addresses.
Inconsistent values	The sensor or the visualization does not send in DPT 9.001.
No answer to reads of the status feedback	Enabled turned off or feedback address not filled in.