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

The heat pump can only respond based on the supply or return temperature and the outdoor temperature; it has no way of knowing the actual temperature inside the rooms or whether valves are open or closed.

This means that as soon as the temperature drops in just one room, causing the supply temperature to fall below the required value, the heat pump will start running.

The less heating water circulating, the faster the supply temperature reaches the target value, causing the heat pump to switch off.

However, because the small amount of water also cools down faster, the heat pump must start again sooner.

The result is many starts per day.

Since modern heating systems control the circulation pumps independently from the heat source, a larger volume of water means the heat pump can run longer at low output and also have longer periods when it does not need to heat.

In a properly tuned system, this results in a single-digit number of starts per day.

That is why it is better to use modulating heating systems with as low a minimum output as possible.

By switching off, thermostats also prevent heat that is too high in one room from being absorbed and then released into other rooms.

Most systems today are controlled by outdoor temperature with supply temperature regulation.

The heat pump begins to heat when the supply temperature drops below the set value (allowing for a certain tolerance of a few degrees).

If thermostats in some rooms shut off the flow, the volume flow and mass decrease.

If the flow falls below the minimum required, it can happen that the heat pump cannot release its heat quickly enough and reports an error.

In air-to-water heat pumps, this can cause the defrost cycle to fail.

To prevent this, buffer tanks are often installed, which, however, reduce efficiency.

Daniel-Sp schrieb:

Well, without a hydraulic balancing valve, no heat would be delivered to the underfloor heating, and the high return temperature would cause the heat pump to shut down, preventing the costly and pointless reheating of the buffer tank.

...exactly...

Alessandro schrieb:

But the pump would still run continuously and consume electricity. Pumps, no matter how efficient, consume a relatively high amount of power and are among the components with the highest wear in the system.

...and how much electricity does your hydraulic balancing valve use?

untergasse43 schrieb:

Is it possible to apply this ERR / heat pump discussion to modern gas boilers with solar support as well?

Yes, a condensing boiler also prefers to run for a long time at a low temperature.

Alessandro schrieb:


The self-regulating effect is actually enhanced by an ERR, which again supports the use of thermostats.

Here is an example of what a thermostat can be good for:

The heat pump is programmed so that no hot water is supplied to the underfloor heating until the outdoor temperature reaches 18°C (64°F).

However, since it was warm for several weeks beforehand, causing the building structure to heat up and continue releasing heat that keeps the rooms at 22°C (72°F), the thermostats close the valves.

The self-regulating effect is prevented because shutting off the rooms stops circulation in the system.

The self-regulating effect means the underfloor heating releases heat proportionally to the surrounding temperature.

Room/screed 15°C (59°F), underfloor heating 25°C (77°F) = High heat output due to large temperature difference.

Room/screed 22°C (72°F), underfloor heating 25°C (77°F) = Low heat output due to small temperature difference.

Room/screed 28°C (82°F), underfloor heating 25°C (77°F) = The heating water starts to absorb and remove heat from the room/screed.

If you turned off the ERR and only ran the pump, the heat pump wouldn’t have to heat because the supply temperature would not drop below the target temperature due to the warmed-up screed.

I consider 18°C (64°F) as the heating limit far too high for a new building; it should be around 10°C (50°F).

In my 1996 older building, the heating limit is only 13°C (55°F).

untergasse43 schrieb:

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

Yes, absolutely, because the same thermodynamic laws and processes apply. This is true as long as the heating systems are the same (low-temperature underfloor heating).

Alessandro schrieb:

The self-regulating effect is actually enhanced by an ERR, which also supports the use of thermostats.

It’s actually the other way around, because the ERR works against the self-regulating effect. The way thermostats operate in each room tries to regulate everything down to zero heat output.

Alessandro schrieb:

Since it was warm for weeks beforehand, causing the masonry to heat up and this heat release still maintains the rooms at 22°C (72°F), the thermostats close the valves.
Therefore, there is no heating demand, and the heat pump only heats the storage tank.

Because no heat is being released into the rooms—just as you described, the masonry has warmed up—an ERR in this case is as unnecessary as a third wheel. With or without an ERR, no energy is delivered to the rooms, so the ERR can safely be omitted here.

Everything you say sounds logical.
I was just skeptical because I assumed that a continuous heat distribution to all rooms, even though only one room requires it, would cause unnecessary pump operation and longer room heating times – in other words, energy waste.

So, you mean I should set all thermostats to the maximum temperature permanently and adjust the target temperature for each room directly on the heat pump?