Hydraulic balancing air-water heat pump + efficiency circulation pump

Congratulations that you were lucky enough to find someone like that. In our area, they usually say, "If you buy the stuff online, then you also have to find someone online to install the stuff for you," or "I will install the stuff for you but without any warranty; if you want it installed with a warranty, I have to charge double."

I believe you. You also have to start planning early enough. The installation of the racks and modules took place in the last week of October. But the modules were already installed in August. The order for the installation was placed at the beginning of September, just as the shell construction was starting. If you want a good price, then it doesn't work with a contractor who has long lead times and consultants/salespeople. They all want to be fed. Some courage and willingness to rethink when difficulties arise is required.

To come back to hydraulics and optimization again

Just a claim, without much physical depth or going into detail.

"The return temperature cannot be below room temperature."

True or false?

Why the claim?

For there to be heat transfer, there must be a temperature gradient (also called delta-T, spread, or temperature difference); otherwise, no heat transfer takes place. U-values, floor coverings, and their properties are initially left aside.

If I want to maintain or reach a room temperature of 21°C, that would mean my return temperature must be at least 21°C.

If the modulating heat pump is running at its lowest modulation limit and at the same time operates with a spread of at least 2-3K (or °C), that would mean my flow temperature to maintain those 21°C must be approximately 24°C at minimum?

So I would have basically defined a minimum flow temperature or a base point of the heating curve?

Or complete nonsense because U-value, outside temperature, and type of floor coverings also play an additional role?