Greetings, This situation is a real head scratcher. The attachment shows the 2nd floor of a new home which includes a 3 ton heat pump in the hot attic. The system has two zones, one for the bonus room and another for the remaining 2nd floor bedroom areas. Thermostats are Honeywell Vision Pro 8000 WIFI. The bonus room thermostat location is shown in the close up. Also noted is a ceiling fan centered on the windows in the shed dormer.
Here's the head scratching part. Vision Pro tstats read relative humidity. The bonus room thermostat reads 69 degrees F and 64% RH. The homeowner turns on the ceiling fan. Thermostat humidity reading immediately drops to 56%, 54%, 52% and eventually 50%. Turn the ceiling fan off and the RH reading goes right back up to +60%. Bonus room doors always remain open.
My theory is perhaps the inset corner forms a stagnant area and the humidity reading is obviously not representative of the room RH. But I was always under the impression that humidity in open air diffuses to equilibrium fairly easy. Moreover, where did the moisture come from that runs the RH up?