I have a small (5ft x 5ft x 5ft) "cold room" vault accessed from my basement. It's outside the envelope of the house (under 6" of dirt above too) except for the door from the basement. It's where the well pump and pressure tank is for my house. There is no vent or airflow in the room. Even though, years ago, I excavated down and exposed the concrete walls to apply tar and heavy plastic to waterproof, it still gets humid in there. 60+% RH is not uncommon according to hygrometer I have in there. But it also gets cold (40+/- in winter), which is why I do not want to vent it into my finished basement.
I tried using my dehumidifier in there, but it frosts up pretty quickly and doesn't seem effective. Not to mention, I don't want to hear the thing growl if I can help it. I was thinking of buying a chemical dehumidifier like "Damp Rid", or making my own from calcium chloride (which is what Damp Rid uses). But I also read that calcium chloride is very corrosive and possible that any dust it creates can make rust an issue in that enclosed room.
Any experience with this product, or similar situations, is greatly appreciated.
Thank you. Theodore