ᐅ Air-to-Water Heat Pump: Current Consumption and Data

Alessandro schrieb:

I need your collective intelligence,
....
Is a temperature difference of 2–3°C (3.6–5.4°F) in the underfloor heating desirable or simply too low?
Do you have any idea?
Does it make sense to increase the pressure in the secondary pump and throttle all heating circuits to have a flow with a 5°C (9°F) difference?

You should balance the flow rates between the circuits and have equal flow in both loops. Only in this way can you prevent turbulence in the buffer tank, which reduces efficiency and thus requires a higher heating curve. However, I don’t know your buffer tank and cannot say if turbulence-free flow is even possible. Some buffer tanks have guide plates installed at the inlet; if you have such a model, achieving turbulence-free flow will be difficult. In that case, the temperature difference becomes a secondary concern. The mixing valve must, of course, not mix.
During the heating cycle, depending on the heat pump’s output, I have a temperature difference between 2 and 4.5°C (3.6–8.1°F), and it still heats adequately.

Yes, I understand that.
However, if the temperature difference in the underfloor heating is smaller than that of the heat pump, and the flow rate of the secondary pump is fixed while the heat pump is modulating, the flow rate of the heat pump will always be lower than that through the underfloor heating.
Ideally, it should be the other way around: the heat pump flow rate should be slightly higher (100-200 liters per minute) than the flow rate in the underfloor heating.

If the secondary pump runs at level 1 with constant pressure, I get heat pump supply temperature equal to underfloor heating supply temperature without losses, and an exact 5°C (9°F) temperature difference in the underfloor heating!
However, this only results in 900 liters per minute, 1.8 meters, and about 12 watts.

Could it be that the buffer tank eventually reaches an average temperature once all the water is fully mixed?

Or should I set the temperature spread of the heat pump to 3K (5.4°F) as well?

Doesn't the heat pump regulate the temperature difference on its own?

I’m not a professional and haven’t fully understood your setup yet. How large is the buffer tank? Is it solely a heating buffer, with domestic hot water handled separately? What temperature do you heat the buffer tank to?

Alessandro schrieb:

Yes, I understand that.
However, if the temperature difference (delta T) in the underfloor heating system is smaller than that of the heat pump, and the flow rate of the secondary pump is fixed while that of the heat pump is modulating, the flow rate of the heat pump will always be lower than that through the underfloor heating.
Ideally, it should be the other way around: the flow rate of the heat pump slightly higher (100-200 liters/min) than that in the underfloor heating.

If the secondary pump runs at constant pressure on level 1, I get the heat pump supply temperature equal to the underfloor heating supply temperature without losses, and an exact temperature difference of 5°C (9°F) in the underfloor heating!
However, it only delivers 900 liters/min, 1.8 meters (5.9 feet) head, and about 12 watts.

I already mentioned this in another thread. With a modulating heat pump, this mixer/buffer setup is really problematic due to the modulating flow rate in the primary circuit and the fixed flow rate in the secondary circuit.