Desiccants are hygroscopic substances used as drying agents. They attract water-vapor molecules from the air using an absorptive or absorptive process. They’re often open dehumidification systems used for the cold storage of food products to ensure appropriate relative humidity levels. Desiccant wheel and liquid desiccant dehumidification systems are among the most common used for cold food storage because they’re more efficient, produce less heat and prevent the formation of frost. The best system for cold storage depends on the type of food stored, the location of the storage unit and its size.
Liquid Desiccant Dehumidification Systems
Liquid desiccant systems are a newer technology that use liquid water-lithium chloride as a sorbent and cooling material. In general, they remove more moisture from the air than desiccant wheel dehumidification systems.
Liquid desiccant systems have two chambers—a conditioning chamber and regeneration chamber. In the conditioning chamber, the concentrated liquid desiccant absorbs moisture from the incoming air and dehumidifies. The diluted lithium chloride flows to a heat exchanger. In the regeneration chamber, moisture from the desiccant transfers to the exhaust air, humidifying it. The desiccant or exhaust air is then heated to remove the moisture, re-concentrating the diluted liquid desiccant. The desiccant then flows back to the conditioning chamber for reuse.
Dry Desiccant Dehumidification Systems
Desiccant wheel dehumidification uses adsorbents in which a desiccant doesn’t change phase as it collects moisture. Common types of dry desiccants include zeolites, silica gel and activated alumina. When the desiccant absorbs moisture, it changes chemically or physically.
In dry desiccant dehumidification systems, the desiccant is on a rotating wheel. As the wheel slowly turns, it rotates through two streams of air. “Process” air goes through one section of a desiccant-coated wheel, which absorbs moisture and makes the air drier than when it first entered.
As it rotates, the wheel exposes the desiccant to a “regenerating” air stream that dries and expels, or desorbs, the moisture that it collected from the process air. The moisture transfer occurs because vapor pressure differences at the desiccant’s surface. The desiccant traps moisture when the surface’s vapor pressure is lower than the vapor pressure of the passing air. The desiccant releases the moisture when the surface’s vapor pressure rises. The direction of the moisture transfer is the result of the difference between the process air stream’s relative humidity and the regeneration air stream’s relative humidity.
Dry desiccant humidification systems are good for mixed air systems and cold storage areas that require warmer air or supply-air dew points to be below 50°F. Desiccant wheel dehumidification is also good for dedicated outdoor food storage units, so the air within them is less humid.
The Best Desiccant Dehumidification System
The best system depends on your needs, the type of cold storage unit and its location. If you simply need a desiccant dehumidification system, one that uses a desiccant wheel may be appropriate for your needs.
A liquid desiccant system is better if you need tighter controls over the environmental conditions within a cold storage unit. Such systems are generally more energy efficient, provide humidity control, improve indoor air quality, are more compact and are simpler to maintain.
Polygon offers desiccant dehumidification solutions that aid with document recovery, water damage restoration and creating the ideal climate for organizations in the food processing, manufacturing, storage and retail industries. Talk to a Polygon specialist to learn more about the custom desiccant technologies available for your precise needs.
