Experiences with the ring trench collector in the Bavarian region?

Regarding 1. ... you actually only read positive things, that made me a bit suspicious. If the trench collector is so good, why isn't it already standard?

As someone already said, in the south and in Austria it is already quite common. It's just still a bit "special" at the moment. There are not arbitrarily many companies offering it yet, and it originated from the other forum; most people build the trench collector themselves (and even do all the planning with the trench planner, …), which is not everyone's thing. It's not difficult, but you need a bit of trust that it works when going that route, see your post. But why shouldn't it work... it is no different from a surface collector laid in a trench, thus resulting in relatively little installation effort with very good soil utilization.

Regarding 2. ... I am somewhat handy, smaller excavators are fun too... Whether to dig yourself or hire someone to dig, we haven't decided yet.

It was already said, so briefly: big excavator! Don't underestimate the excavation, if you need 1-2 hours with a big excavator for the excavation, you'll be working for days with a mini excavator... also the costs are usually effectively cheaper with a big excavator.

Regarding 3. .... wow, that is also my goal, a as high as possible annual performance factor with low energy consumption

On your property, with the huge area, a high annual performance factor is normally not a problem at all. Do the planning in the other forum, start your own thread, then nothing can go wrong with the planning.

I know the heat pump selection etc. depends on the heating load, but I would still be interested which manufacturer(s) you use, and which? And do you perhaps combine it with a photovoltaic system?

I run a fixed spread Stiebel myself. Works so far without problems, in hindsight I would have chosen a modulating one, but that's often a matter of belief. The manufacturer is almost secondary nowadays; the big manufacturers are all solid and have had experience forever. What's important is that your heating installer knows the device well and above all that the underfloor heating is correctly dimensioned, because a poorly dimensioned underfloor heating leads to excessive cycling of the heat pump, which often means an early death... a well-adjusted heat pump, however, lasts forever.

But with passive cooling there are differences regarding the extra costs. The surcharge should actually not be more than €1,500 all-in (it was even cheaper for me, but it certainly also depends on how the heating installer ticks). Even if my predecessor says you could equip the whole house with split air conditioning for that... no, that definitely isn't the case. In the forum where the trench collector also originated, you will read a lot of positive things about passive cooling, including practical tests with evaluations of the effectiveness. Result: it works well.
Of course, you should not compare it with an air conditioning system. There is no active dehumidification, and the cooling capacity is lower. But it doesn't just cool the room air "simply," it continuously removes heat from the building's large heat storages (screed, walls, concrete ceilings, etc.) and thus keeps it cool.
It is not air conditioning, but a rather ecological variant to keep the house cool in summer, and nearly free of operating costs.

You don't do the BKA (borehole collector) just for cooling either. Even without cooling, BKA makes absolute sense because it improves the efficiency of the entire system. The costs here are super low because you "just have to put pipe in the concrete." That's all, simply the standard heating pipe in the ceiling, done.

Even if my predecessor says you can equip the whole house with split air conditioning for that...

In my post, I did not mean the entire air conditioning of the house. I meant the pipe installation for the future retrofitting of the devices. Of course, overall a split air conditioner is more expensive. Otherwise, as I said, it is a matter of belief. I like both approaches but will first have the pipe installation for split air conditioning laid or will lay it myself (luckily my heating engineer/air conditioning technician is totally relaxed about this). If I only want passive cooling after all, I can privately buy the module for the heat pump and then have not spent more than if I had bought it directly from the heating engineer (after all, about €1,200 difference in our offer). BKA is correct. It is also important for low flow temperatures and more even heat distribution (supposedly feels more comfortable) and costs less than €1,000 and an afternoon of work depending on the house size.

Yes, that is indeed not unimportant... finding a heating engineer who is willing to do everything. I initially had a few discussions with mine, as he had never heard of a trench collector before. In the end, I offered him to gladly use me as a reference if he wanted to offer/implement this solution with other customers. That, together with a clearly defined transition point (input and output distributor), was then acceptable to him.

Passive cooling works, but including BKA in the installation is not cheaper than a split air conditioner. We also wanted to cool passively at first, but have now switched to air conditioning. It gets uncomfortable in summer especially because of the humidity, and passive cooling can't help with that.

If you now move away from BKA and switch to a split air conditioning unit. How does that roughly work? Is it located in the basement next to the controlled residential ventilation and adds cold air to the controlled residential ventilation, or how can one imagine it?

Because implementing a BKA is not exactly associated with high effort and high costs. Equipping a house with an air conditioning system, I imagine, is more expensive. Especially since you then have an outdoor unit standing in the garden again, which you could nicely avoid with the brine-water heat pump.

Controlled residential ventilation and air conditioning will be two separate systems that are not combined. We will "in the traditional way" install a ceiling or wall unit in the rooms to be cooled, which will be activated as needed.

Yes, a split air conditioner is more expensive compared to a BKA. However, we will initially only prepare the installation so that the air conditioning can be installed fairly quickly if needed. After all, a few copper pipes have to be laid under plaster for this. I will probably also include the BKA in the ground floor; after all, it is only 3 pipes, 20x2, each 70m long. This gives us three options: 1) Do not dismantle anything and leave everything as it is – if the temperatures are acceptable for us 2) Retrofit passive cooling on the heat pump and put the BKA into operation (alternatively, use the BKA to further lower the supply temperatures) 3) Retrofit a split air conditioner. However, from my point of view, photovoltaic is mandatory then.

The outdoor unit bothers us less. As the name suggests, it is outside and would be placed on the north side next to the entrance door. This way, it is only visible when entering or leaving the house and does not take up any space in the garden.