Isn't reducing temps gonna increash RH tho?
cooler air can take less humidity so RH rises with same amount of humidity into the air, but lower temps.
All I know is when I'm growing in the winter and my grow room is 78 F with lights on the RH is around 60% but when the lights go out and the temps drop to about 62 - 58 F the RH drops to around 45-50% at least according to the devices I have measuring temp and humidity. But then again that's measuring the humidity in the air and like you said cooler air takes less humidity or perhaps a better way to phrase it is holds less humidity so you're not going to have the same amount of humidity in the air with lower temps. The humidity there I would figure is condensing into something like a dew and getting absorbed back into the plant and the soil and some is likely being carried out of the room due to air exchange and/or if a dehumidifier is in use. So soil will dry out slower at lower temps so you could say at lower temps there is more moisture in the soil but I'm not talking about what's in the soil. I do use a dehumidifier in my grow room and it does run more at the start of lights out then it does later on, so perhaps that accounts for the changes I see in my humidity meter?
https://en.wikipedia.org/wiki/Humidity
As the temperature of a parcel of air decreases it will eventually reach the saturation point without adding or losing water mass. The amount of water vapor contained within a parcel of air can vary significantly. For example, a parcel of air near saturation may contain 28 g (0.99 oz) of water per cubic metre of air at 30 °C (86 °F), but only 8 g (0.28 oz) of water per cubic metre of air at 8 °C (46 °F).