The Zennio web site https://www.zennio.com/products/clima/klic-di has lots of useful details about the KLIC-DI device and this explains many of the details of how the KLIC-DI works with an air-conditioning unit. However, as a novice with KNX and air-conditioning control I wanted to try and highlight aspects of this functionality. What I write here may not be relevant to every KLIC-DI and Daikin install.
Via the KLIC-DI it's possible to turn the air-conditioner on and off, set the fan speed, set the mode (e.g. heating or cooling) and the temperature. However, what does setting the temperature mean. Clearly an air-conditioner will have a temperature that it is trying to achieve. In the language of the KLIC-DI this is referred to as the 'Setpoint' group object. It's possible to both read and write (set) this group object on the KLIC-DI via the KNX bus. It's the responsibility of the KLIC-DI to communicate (send and receive) these details from and to the air-conditioner itself via the two wire connector between the KLIC-DI and the air-conditioning unit. The air-conditioner also needs to be able to know what temperature has actually been achieved to know whether to heat or cool further. So to do this it can monitor the return air. Based on the setpoint and the return air temperature the air-conditioner knows what to do. Most of the complexity associated the temperature with a ducted system rests with providing a different value as to what temperature has been the achieved. On ducted systems this is referred to as 'reference temperature' group object.
On a wall mounted split system an air-conditioner likely has some probe on it's air input to measure the temperature of the intake. With a zoned system this is potentially more complex. For example in my house there are 9 zones but only one return. So it's possible that the return air temperature could be significantly different from the temperate required or that is current in a particular zone.
Ducted air-conditioners do measure the temperature at the unit itself (I assume this is on it's intake as the KLIC-DI manual mentions: "The indoor unit uses its own return temperature"). This temperature value is reported to the KLIC-DI and available as a KNX object and referred to as the 'Internal Temperature'. To quote from the user manual: "commercial A/C units include several sensors for measuring the temperature at different internal points. KLIC-DI monitors the value of one of these internal measures, called Internal Temperature..."
However, although a ducted air-conditioner monitors the temperature a further temperature value can be communicated to the air-conditioner through a group object. This is referred to as the 'Reference Temperature'. Again - quoting from the user manual: "The Reference Temperature is the actual ambient temperature of the room under climate control. It is necessary that KLIC-DI provides the machine with this value, which implies that it should be sent first to KLIC-DI through the corresponding communication object (generally from an external sensor)."
The KLIC-DI manual also mentions about the Reference Temperature that: "The Reference Temperature communication object has a default value of 25ºC and is only available when the control type of KLIC-DI is master."
Setting the reference temperature via the KLIC-DI may be as simple as doing nothing (as the manual suggest it defaults to 25ºC), but if it was technically possible to do nothing it probably would not be a great idea because it would suggest that if the setpoint was set above or below this the air-conditioner would work to cool or heat the room but with no feedback it was achieving the required setting as the air-conditioner would be told it was still at 25ºC . One would also assume that if the setpoint was also set to 25ºC, the air-conditioner would neither heat nor cool as it would all appear to be at the required temperature. A better alternative (as suggested in the manual) would be to read the temperature from one of the temperature sensors from one of the zones and send that to the KLIC-DI as the group object value. A still better alternative would be to use some more complex calculation based on temperature readings from several or all the zones to determine some form of average (or other calculation). Having only the vaguest of understandings as to how this might be achieved I will not describe how this might best be achieved - other than to say that it's possible.
So in summary, there are 3 or 4 group object values associated with Temperature. 3 if KLIC-DI is a slave and 4 if it is a master. Two of the objects are read objects being the:
Setpoint Temperature status
Internal Temperature of the air-conditioning unit itself (which I would understand to be a measurement of the return air)
The other two group objects can be written to and are:
for setting the Setpoint Temperature
setting the Reference Temperature (only available when the KLIC-DI is a master)