ᐅ Central room temperature controller for the fan coil unit (FCU) of the underfloor heating system

It is always a matter of settings.
And when everything is perfectly coordinated, a room thermostat can also be useful—even though it is essentially just a temperature limiter.
What I meant to say is that you should not imagine the heat pump pushing against closed valves with overheated components while the full volume flow passes through the open valves. It automatically monitors the demand based on the requirements and adjusts itself accordingly. This allows for some energy savings.

@Alessandro

If your heat pump is providing too high supply temperatures, then the heating curve is set incorrectly.

You should read up on hydraulic balancing and the self-regulating effect.

An ERR (Electronic Radiator Regulator) might make sense in rarely used rooms with potentially varying usage patterns (like hobby rooms or similar).

If the balancing is done properly and the underfloor heating system is designed correctly (this is a prerequisite; otherwise, it becomes difficult), then the ERR does not need to regulate anything.

Through the balancing, I adjust the flow rates for each room according to its specific requirements (room-by-room heat load calculation). The heating system only provides one supply temperature, not a different one for each room. In contrast, an ERR opens or closes the valve.

Can this ERR/heat pump discussion also be applied to modern gas heating systems with solar support?

The self-regulating effect is, however, amplified by an ERR, which is another argument in favor of thermostats.

Here is an example of how a thermostat can be useful:
For us, the outdoor temperature has been consistently 15–16°C (59–61°F) for a week, sometimes even colder at night. The heat pump is set so that domestic hot water for the underfloor heating is only provided when the outdoor temperature exceeds 18°C (64°F).
Since it was warmer for weeks before, the masonry had heated up and this residual heat still keeps the rooms at 22°C (72°F), so the thermostats close the valves.
As a result, there is no heating demand, and the heat pump only heats the storage tank.
Of course, the energy needed to heat the domestic hot water for the underfloor heating would be relatively low due to the heating curve, but the pump would still run continuously and consume electricity. Pumps, as efficient as they are, consume a comparatively high amount of electricity during operation and are one of the components with the highest wear in the system.

Alessandro schrieb:

It’s always a matter of settings.
And when everything is perfectly coordinated, then the room thermostat can also be useful.

And if that’s the case... you don’t need the ERR.

To give another example:

You have 10 rooms. Two of them currently require a supply temperature of 30°C (86°F). These are bathrooms, so they have relatively small volume. All the others need less. But the heat pump cannot differentiate, so you set it to a supply temperature of 30°C (86°F). What happens? The ERR closes in 8 rooms and remains open in two. The heat pump sends out 30°C (86°F) at a minimum flow rate. It wants/has to release the energy, but can’t because the ERR has closed 8 rooms. So what happens?
It depends on the system design.
Either you have a heating buffer in between that stores the energy from the heat pump. This is not ideal because energy is lost until it is needed again.
Another or additional way is the bypass valve, so the supply water is redirected back into the return line and circulates in a loop.

This is a simplified example but it should illustrate why the ERR usually does not contribute to energy savings.

Well, without ERR no heat would be transferred to the underfloor heating, and the high return temperature would cause the heat pump to shut off, avoiding the expensive and pointless reheating of the storage tank.
You might also consider lowering the heating limit; 18°C (64°F) is quite high for a new build, in my opinion.