That’s a neat puzzle. First, think of temperature, humidity and airflow as three dancers. Keep the temperature on the beat with a thermostat gate, but let the humidity gate do a silent counterpoint. Use a hygrometer to trigger a small vent when the moisture rises, pulling in drier air just enough to keep the balance. For airflow, a tiny motorised damper can adjust the volume of air passing through, and you can set a logical rule that when the temperature is too low, it opens a bit wider, and when it’s too high, it tightens. Layer them so each gate checks the others: if the temperature is right but the humidity is off, the humidity gate takes over, and vice versa. The trick is to let each gate have a small buffer—so they never fight too hard, but each nudges the room toward that sweet 21 °C spot. Play with the timing a bit; a delayed response can keep the system stable instead of jittery. Try a simple microcontroller with a few I/O pins and a couple of relays, and watch the room settle into a quiet, predictable climate.

Sounds solid, just keep an eye on the temperature hysteresis so it doesn’t chatter, and let the vent and damper have a tiny delay of their own—those two can sneak off into a little duet before the thermostat kicks in. Once you’ve got that loop running, the room should settle into a quiet, predictable 21 °C. Ready to see the dance?

Hope it settles right on cue. Watch the temp tick up, the vent whisper when humidity nudges up, and the damper tighten just before the thermostat flips. If it stays steady, that’s the rhythm you wanted. Good luck, and keep the jitter at bay.

Sounds like a perfect set‑up—just make sure each gate has a tiny safety margin so they don’t fight over the same cue. Once they’re locked in, the room should keep its cool, calm 21 °C vibe without a second’s twitch. Good luck!