ᐅ What installation spacing should be used for radiant floor cooling?

Sorry, I mixed things up again.
We were told:

"The 45-liter (12-gallon) buffer tank is installed as a hydraulic separator.
This is required by Vaillant (when a cooling function is used)."

Where can I find the diagrams showing the cooling function?

Ask Vaillant or the heating installer?
In that case, I would have skipped the cooling function to avoid the separation buffer/hydraulic separator with mixing group.

With Vaillant, I have only received a statement over the phone that a buffer tank is mandatory, but no information on how it must be integrated.
I will definitely ask the heating engineer before he starts the installation. However, he will probably have to follow the general contractor’s specifications precisely.
There also seems to be a difference between a separation buffer and a hydraulic separator, with the separation buffer being more energy-efficient.

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

The separation buffer separates the heat pump circuit from the heating circuit and functions as the hydraulic separator. Often, the separation buffer is charged via the heat pump circuit with increased temperature. The heating circuit draws water at the higher temperature from the separation buffer and mixes it with the "cold" return flow to the required temperature. The efficiency loss (and consequently higher heating costs) depends on the difference between the required temperature in the heating circuit and the temperature provided by the heat pump circuit. Keeping this temperature difference as small as possible is especially challenging with modulating heat pumps. In contrast, a buffer connected in series on the return flow causes negligible efficiency loss and does not complicate the heating system’s settings. Worse than a separation buffer is only a combination buffer or stratified buffer.

Perhaps you can discuss this further with the heating installer. Ask Vaillant for a hydraulic diagram without a separation buffer mixer and only with a series buffer. If Vaillant offers such a hydraulic diagram as an option, you might be able to convince your installer. Although you would pay for a mixing group without installing it, you would save a lot of time and effort when setting up the heating system.

The VR 71 mixing module appears to be just a control module for up to three mixing circuits. Try searching for it on Google.

I am trying to get a corresponding hydraulic diagram from Vaillant. Unfortunately, this is not so easy as a private customer.

Assuming a separation buffer is installed, I would 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 this correctly?