Which brine-water heat pump Viessmann, Niebe or Stiebel WPE-I 10 H

Meltem Wärmerückgewinnung-II - am I reading correctly on the internet that it is a decentralized system?

Just make sure to have a centralized controlled residential ventilation installed.

Actually, controlled residential ventilation and heating do not need to communicate with each other, unless you are an expert and want to optimize everything. Normally, the controlled residential ventilation calmly runs through its levels throughout the year and doesn't care what the heating is doing.

The Meltem Wärmerückgewinnung II is something between central and decentralized. With 2 devices, we supply a complete floor via flexible ducts in the ceilings, which then supply the supply air rooms (bedroom and living room) or exhaust air rooms (kitchen/bathroom).

Huh, if I read that correctly, the things have an air output of 100 cubic meters during intensive ventilation. For 300 sqm living space and 2.50 ceiling height, 2 devices at the front and back are not enough. I would first do a proper ventilation plan and then choose the device...

The ventilation planning is complete. There are 2 units planned per 100 sqm, so 6 in total.

So what now? 200 or 300 sqm? But even with 200 sqm, at a ceiling height of 2.50, both only achieve the absolute minimum air exchange rate of 0.4 with full pull and barely.

200sqm was not mentioned

6 devices each with a max. air output of 100m³/h for 300sqm