Dehumidifier vs Desicant

Four years ago, in the fall I noticed something I had not seen before; the dreaded black spots, this time on cabin carpeting. Clearly, better humidity control was in order for the cooler season.

A large compressor unit would be a beast on a small boat. Though I have a 30-pint unit at home, the downsides are major:

• A lot of amps on the shore power cord.
• A back injury waiting to happen; the unit is huge and awkward.
• In the way.
• Loud.
•  More capacity than I needed.

 
So I looked around and found the Eva-Dry 2200. The no-compressor  principle is elegant, the only moving part being a small fan. The over simplified explanation is that of a thermocouple, but in reverse. Instead of a temperature difference creating a small electric current, the current is forced in the reverse direction through a whole stack of thermocouples, creating a cold plate. Water condenses on the cold plate and runs into a tank.

The size and weight (just a few pounds) are appropriate; when not in use it's easy to swing it into a cabinet for storage, although for day sailing I just put it in the sink to keep it from falling. They are prone to icing in temperatures below about 45F, but deicing by controlling the run cycle with a light timer is simple; 8 hours on at night and 6 hours off during the day. Even in the depths of the winter, the interior of the boat warms above freezing during the day due to solar heating.

I modified the tank by drilling a hole and tapping in a 1/4 NPT x 3/16" ID hose barb. The hose runs to the sink so that it never fills and to prevent freezing and breaking in the winter.

 So far--four years--the unit has just  purred along, removing 2-8 ounces per day, keeping the relative humidity at 45-65% at temperatures from below freezing to 95F. The boat is always dry, the bedding fresh, and interior corrosion issue non-existent.Just like home.
 

 

 Cold plate frosted

Cold Plate Thawed 

The only real alternative is calcium chloride descant. I did an article about these for Practical Sailor  magazine and still had a few left over. I held a race several years ago, the Eva-Dry in the port cabin and a large absorbant bag on starboard. It wasn't even close. It would take ten 5-pound buckets of CaCl2 to do what this unit will do over 3-4 month winter season.

I also tested a cheaper version from Perfect Home. It lasted about 8 months, just like the reviews said it would.