We are planning our smart home in the single-family house

Maybe a dumb question, but is individual room control of the ventilation possible at all with a central ventilation system (Tecalor THZ 5.5 ECO)? According to the user manual, you can only choose between levels 0-3 of the ventilation, but I assume this always applies to the entire house? I would like to be able to control the supply air and/or exhaust air (bathroom) individually. Is something like that possible?

No, not with normal single-family house ventilation systems. Of course, there are larger systems that can be controlled by room or area, but you can't afford those. Moreover, the piping must be done accordingly, i.e., always separate supply and exhaust connections for each room.

By default, you only have supply air in the bedroom and exhaust air in the bathroom—you can imagine that individual control is neither possible nor sensible.

How should one handle it in a case like this, if we want 19 degrees in the bedroom but 22 degrees in the living room? That should be possible, right, or am I misunderstanding?

Difficult. Most interpretations nowadays are 22 degrees in the living area (all rooms) and 24 degrees in the bathroom (or 21/23) -> linear regulation downwards is no problem, this is only about an interpretation of heating load etc. It is then solved so that there is more flow in the bathroom and/or the distances between the heating pipes are closer and thus more heat can be emitted. But 7 different room temperatures spread throughout the house, which maybe or maybe not have different frequencies of adjoining rooms with different temperatures and/or exterior walls. That becomes problematic (yes, 7 is absolutely arbitrarily chosen and exaggerated ;) ) and larger temperature differences are, as already mentioned, also more difficult to achieve. Regarding ventilation, what is additionally still possible within the scope: the ventilation presumably has a bypass function, so that cold outside air can be used at night without heat recovery. But that affects all rooms again and is typically only done in summer. Because as you rightly recognized, ventilation is similar to heating. You can control the ventilation level for the entire system, and each room is supplied with air. There are restrictors to reduce the airflow per room, but these are fixed (set once), so simply put, e.g. airflow in the bedroom is always 20% lower than in the living room. Otherwise, you would have to work with decentralized ventilation to get a real single-room control ((economically) feasible).

I have parametrized KNX (with Dali for lighting) myself, with zero prior experience, currently no fancy stuff but everything works as desired for now. Learning is relatively easy in the ETS. A big advantage is that you can implement everything exactly how you want. Many things are only set once you live in the house and then realize what makes sense. Depending on the equipment, the Home version for 64 actuators is sufficient, which costs under 300 EUR including a voucher from KNX.org if you take a free course. For a normal single-family house with few (!) switches this should be enough. For the underfloor heating we have actuators that are either open or closed.

I programmed KNX (with Dali for lighting) myself, with zero prior experience, currently no fancy stuff but everything works as desired for now. Getting started with ETS is relatively easy. A big advantage is that you can implement everything exactly as you want. Many things are only configured once you live in the house and then realize what makes sense. Depending on the equipment, the Home version for 64 actuators is sufficient, it costs under 300 EUR including a voucher from KNX.org if you take a free course. For a normal single-family house with few (!) push buttons this should be enough. For the underfloor heating we have actuators that are either open or closed.

Good to hear that this is possible. Can you tell a bit about the costs of the wiring? Doesn't the electrician want to at least do a basic programming so that he can at least test the wiring and the components? Or can you also get the individual components yourself and connect them and save some money that way?

That always depends on the specific agreement. I worked with GÜ, who hired an electrician permanently. I agreed with him that he would pull the cables and build the control cabinet. I provided a plan indicating what should go where and where I needed which cable. I procured and parameterized the components myself and handed them to the electrician for installation in the control cabinet. I installed all other components myself. I set up the parameterization so that all basic functions can be tested at handover and then gradually adjusted after moving in.

I would have to check the surcharge for wiring and control cabinet installation; from memory, it was 2-3K€.

But yes, that is not the norm. Usually, there are only fantasy surcharges and no self-procurement.

Wiring can also be tested completely without [KNX actuators]. You can also pre-program components and deliver them fully configured to the construction site.

Installing components is always a bit tricky – flush-mounted actuators, sensors, push-buttons/touch panels can also be installed by yourself, it’s really quite simple. Installing the distribution board is a bit more complicated/delicate – you have to hope that your electrician cooperates, meaning, for example, taking over the installation/wiring according to instructions. Alternatively, there is also the option to have the distribution board including [KNX actuators] planned and delivered ready for installation – then your electrician only needs to feed in the cables and connect them to terminals. Then they don’t need to know anything about [KNX].

Depending on the electrician, you can certainly procure the components yourself. But not all (many?) electricians agree to this (due to warranty, profit margins, etc.).