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DIY dehumidifier design? Answered

This is my first real foray into DIY so help me out here. My original design, which didn't work very well, was to fill some coiled-up tubing with the gel from that blue ice stuff you use to keep lunchboxes cool, then mount that  near the top of a bucket and keep a fan running over it to blow moist air onto the cold tubing and, theoretically, it would condense out. When I left in the morning it was definitely getting lots of condensation, and I even saw a bit dripping off into the bucket, but by the time I got back in the afternoon the whole thing was bone dry. Is there any way to make this freezer-gel-tubing idea work? I think part of the problem was that I used rubber tubing, not thinking about how it acts as an insulator, and I also suspect that keeping a fan on it did as much harm as good what with the whole evaporation thing, but I thought real dehumidifiers used fans too...



I can't answer your question directly as I have no relevant experience. I have however made a dehumidifier that works just great in our clothes drying cupboard, and it didn't cost very much at all. It consists of a peltier device, two scavenged heatsinks, two scavenged PC fans, a scavenged PC PSU and a plastic tray. I have a heatsink bolted to either side of the peltier device. The one on the hot side has a fan bolted directly to it to blow the warm dry air into the room. The one on the cold side blows the damp air across the heatsink. The idea is that water from the damp air condenses on the cold heatsink and drips into the collecting tray, whilst hot and therefore dryer air from the hot side is distributed around the room. The peltier and fans are powered from the 12v of the PC PSU. It works really well; you just have to remember to empty the tray each day!

This is how many commercial dehumidifiers work and the easiest way to do it :)

> Is there any way to make this freezer-gel-tubing idea work?
.  Probably not. As you found out, it doesn't last very long. You need something with a lot more thermal mass or some type of refrigeration unit.
> suspect that keeping a fan on it did as much harm as good
.  The fan on the coil did no harm, but if the fan is blowing into your collection bucket, that will cause the water to re-enter the air much faster.

You have to trap the moisture you collect and either get rid of it or keep it out of the air stream otherwise it just evaporates and rewets the air.

You're underestimating the amount of heat requred to be moved to condense water from the air. The blue gel works for a few minutes, after that its capacity for heat is used up