Smarter fan strategy for climate devices, including heat distribution support

[zimivanende]

Description

I would like to propose smarter fan handling for climate devices.

At the moment, setpoint control and learning are already very useful. But for air-to-air devices, fan speed is also a major control lever and should be part of the control strategy, not just left static or permanently on Auto.

A closely related reference is Versatile Thermostat’s over_climate documentation, which explicitly describes an Auto-Fan mode. In VTherm, when the temperature difference is significant, the thermostat can force a stronger ventilation level to distribute heat faster, and then fall back to a more normal mode once the gap becomes small again. It also chooses the fallback mode from the equipment’s supported modes such as Mute, Quiet, Auto, or Low. 

Reference links
• Versatile Thermostat, over_climate

Why this matters
Fan speed changes real-world behavior a lot:
• it affects how quickly heat or cooling spreads in the room
• it affects overshoot and comfort near target
• it affects noise
• it affects how useful the unit is when it is helping redistribute already-produced heat

This is also interesting in mixed systems. For example, when radiator heating is already warming the room or nearby rooms, an AC indoor unit in fan mode could sometimes help redistribute that heat more evenly instead of passively doing nothing.

So this is not only about “fan harder when delta is big”. It could also become a smart circulation tool.

Suggested implementation ideas
• Add an optional fan strategy layer for compatible climate devices.
• Support delta-based fan escalation.
• Support a quieter fallback mode when delta becomes small.
• Optionally allow a “circulation assist” mode where fan-only can be used to redistribute already-available heat, even when the AC is not actively heating or cooling.
• Optionally expose settings such as:
• max fan when far from target
• preferred quiet mode near target
• allow fan-only circulation, yes/no
• minimum delta before active fan escalation
• different settings for heating vs cooling

Use case

1.	Large delta to target

Increase fan speed to distribute heat or cooling faster.
2. Near target
Reduce fan speed to avoid overshoot and reduce noise.
3. Radiator heat spreading
If another source is already heating the room or connected zone, allow optional fan-only circulation to improve comfort and reduce stratification.
4. Per-mode behavior
Heating and cooling may deserve different fan logic.

Why I think this fits well
This would improve both comfort and responsiveness, while staying aligned with predictive control. The MPC can decide what is needed, but fan strategy can improve how the room gets there.

Alternatives considered

No response