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

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) and the exhaust air rooms (kitchen/bathroom).

In a single/two-family house, several MELTEM devices would not necessarily be my first choice, but maybe a user experience report is interesting for you: I have been operating 4 Meltem devices of generation I for several years in a multi-family house, one device per residential unit - with supply/exhaust air via ventilation ducts in the apartments. The only weak point: a motor-driven rotating plastic flap built into the device closes the supply and exhaust air channel when switched off. This plastic part can get stuck - it happened to me 2-3 times and is annoying.

Otherwise, the devices reliably do their job and can also be integrated into KNX via RS485 (and at least back then somewhat patchy documentation). In the apartments, I use an MDT KNX push button next to an iPad for control to regulate the fan speed in the bathroom. The devices are invisibly hidden behind drywall.