What is the appropriate spacing for floor cooling installation?

Sorry, I got something mixed up again. We were told:

" The 45-liter buffer is installed as a hydraulic separator. It is prescribed by Vaillant (in case of a cooling function). "

Where can I look at the schematics with cooling function?

Ask Vaillant or the heating engineer? Then I would have skipped the cooling function to avoid the separation buffer/hydraulic separator with mixing group.

At Vaillant, I have only received the statement by phone that a buffer is mandatory but no information on how it must be integrated. I will definitely ask the heating engineer before he starts the installation. But he will probably have to follow the general contractor's specifications exactly. However, there also seems to be a difference between a separation buffer and a hydraulic separator, with the separation buffer being energetically better.

In your estimation, how high are roughly the annual losses / additional costs?

The separating buffer separates the heat pump circuit from the heating circuit and acts as the hydraulic separator. Often, the separating buffer is charged with elevated temperature via the heat pump circuit. The heating circuit extracts water at elevated temperature from the separating buffer and mixes it down to the required temperature with the "cold" return flow. How large the efficiency loss is (and the associated higher heating costs) depends on the difference between the required temperature in the heating circuit and the supplied temperature in the heat pump circuit. Keeping the difference as small as possible is not trivial, especially with modulating heat pumps. A buffer connected in series in the return flow has a negligible efficiency loss and does not complicate the heating adjustment. Worse than a separating buffer is only a combined buffer or stratified buffer. Perhaps you can still talk to the heating engineer. Ask Vaillant for a hydraulic diagram without [Trennpuffer-Mischer] and with only a series buffer. If Vaillant provides such a hydraulic diagram as a variant, you might be able to convince the heating engineer. Because although you pay for a mixing group without installing it, you save a lot of time and hassle in setting up the heating system.

The mixing module VR 71 seems to be only a control module for up to 3 mixing circuits. Just Google it.

I am already trying to get an appropriate hydraulic diagram from Vaillant. Unfortunately, this is not so easy as a private customer. Assuming a separation buffer is installed, then I need the VR71 to be able to control the heat pump circuit (mixing circuit 1) and the heating circuit (mixing circuit 2). Have I understood that correctly?