How complicated are heat pumps in practical operation?

Just on the topic of efficiency - and these are existing buildings with correspondingly high supply temperatures. I think that's not bad at all.

First of all, I would say that it is absolutely no problem to get your house or apartment comfortably warm with it!

I find this statement and the excerpt from the Fraunhofer study very reassuring for all homeowners who want to base their systems on this state of the art.

In the end, the question will also be what you mean by "economical"

I wrote it that way on purpose to mean by "economical" that the system delivers what the calculation promises. After all, the calculations are an important part of the decision for a heating system. It seems that a "poor" setting costs efficiency and lifespan. I find it interesting to what extent the calculated consumption values later match the actual consumption values without any user intervention. To borrow the parallel brought up by to cars: it is also the case that the great consumption values of a downsizing engine are not worth much if the driving behavior in practice is somewhat brisker.

I think the same could have been said about gas or oil heating systems 30 years ago. Only hardly anyone cared then.

That’s true. The information and interest situation was different back then. I no longer drive Bavarian V8 station wagons, although sound, agility, and power still appeal to me very much. Times change.

1. How much knowledge and skill does a home builder actually need to acquire in order to really achieve the economic efficiency they expect from their decision?

The decision to choose a heat pump is made because one does not want to build a passive house. All other heating technologies disqualify themselves after reading the climate report or trying to conclude a gas supply contract. Once you understand that, you can read up – the principle is quite simple: An external company produces a room-by-room heating load calculation for all rooms including the bathroom at ~22°C with a max. 30°C flow temperature. The underfloor heating installer needs this anyway if he doesn’t want to lay pipes blindly. The selected heat pump should then have been on the market for no longer than two or three years AND should not be sized larger than the maximum heating load according to NAT from the above document. No allowances for anything whatsoever. One gets exempted from the individual room controllers with the above document and refuses their installation. One refuses the installation of a heating buffer. The heating engineer performs the hydraulic balancing. You can fine-tune it later if you want with the help of the internet. No witchcraft.

2. How likely is misuse by inexperienced users who just want to have a comfortably warm house?

According to the above instructions = 0.

3. Which habits must a person unlearn when living for the first time in a house with a heat pump in order to achieve the expected economic efficiency?

“Turning” any knobs. Without the mentioned controllers, it becomes so complicated that this simply won’t happen anymore. Every room has the same temperature (+-2°). That’s how it is and how it stays.

You can free yourself from the individual room controllers with the above document and refuse their installation.
You refuse the installation of a heating buffer.

Regarding individual controllers, I have often read the recommendation simply to open them fully. If that is so obvious, why are they apparently installed as standard?

The "turning" of any knobs.

I understand that people do not turn knobs that are not there. Leaving them out saves discussions with family members.

The threads about heat pump consumption and flow temperature settings are full of technical terms, values, and settings.

I think it's really great that you are therefore opening another thread about heat pumps :)

I have very often read the recommendation to simply open individual regulators fully. If that is so clear, why are they apparently installed that way as standard?

In an emergency, you can follow the recommendation - but by that point, thousands of euros have already been thrown away. So it's rather stupid. It's standard because it has become mandatory for some energy-saving regulation classifications. Lobbyism would be assumed as the main reason. Maybe a bit of backwardness as well. It wasn't quite so stupid not to heat in the past.