There are times when even commercial refrigerants (not to mention home dehumidifiers) aren't the most efficient choice or simply can't finish the job. This is where desiccants and air exchangers can really save the day.
These dehumidifiers remove water as it passes through a material like silica. The water is chemically attracted, absorbed and held. Heater elements basically bake the moisture off and duct it outside. Dry air making moisture removal difficult isn't an issue since the desiccant doesn't rely on condensation for removal. Thus, desiccants can reduce humidity well below the limits of refrigerant dehumidifiers. Low temperatures also won't obstruct performance - the air exiting is always dryer. Desiccants are particularly good with waterlogged hardwood floors, concrete and tile. They can handle over 400 pints per day and weigh in at over 200 pounds.
The higher-priced desiccant will soak up more moisture than a refrigerant when humidity is low, but it's not as effective when humidity is high. It's often recommended to use a refrigerant unit until it can no longer pull moisture, then switch to a desiccant for the rest.
These machines have very precise requirements. They work well during winter in the northern United States and Canada, when outdoor air is very dry. Indoor and outdoor air are basically traded, with the indoor air warming the outdoor air as they pass each other in an exchange core. Air exchangers are up to three times more efficient at removing water than are large refrigerant units, but only when there are freezing temperatures outside. Low power consumption, which can be under 500 watts, is a bonus, but if outdoor air conditions change, exchangers can easily stop being effective.
A few basic rules
Some guidelines for dealing with water damage: