dehumidification

Dehumidification:  To remove moisture from the air or a gas.

There are many types of dehumidifiers all with their positives and negatives.  It is important to consider these positives and negatives to properly apply a dehumidifier to a space or process. 

The primary types of dehumidification are as follows:

A.  Compression

B.  Mechanical/Refrigeration

C.  Adsorption Based Desiccants

D.  Absorption Based Desiccants

To better understand the process of dehumidification it is important to understand the various types of dehumidification systems on the market today.  All of the basic dehumidification types identified above are available but this does not mean that all types are created equal for each particular application.

Compression
As air is compressed, the dew point or temperature at which water will condense is raised. Therefore, to get dry air we need to find a way to cool the compressed air. But costs can be prohibitive because equipment, space, and auxiliary equipment are necessary for the process. However, if compressed air is already used in the primary operation and only very small amounts of dry air are needed for humidity control, compression may be a feasible route to dry air.  The primary limiting factor with dry air via compression is simply the volume of air required.

Mechanical/Refrigeration
Mechanical/Refrigeration based dehumidifiers use either a chilled water/glycol loop or a vapor compression system coupled with an evaporator coil at dew point to condense the water vapor as the air passes through the evaporator.  The common systems available on the market today often operate reliably down to approximately 45°F dew point.  Below this point the typical mechanical/refrigeration system will begin to have frosting/freezing issues as desired dew point falls below 45°F.  Therefore, a mechanical/refrigeration system applied to lower dew point applications will require a defrost cycle during which dehumidification is not taking place.
Desiccants - Adsorption Type
Adsorption based dehumidifiers utilize an adsorbent desiccant material such as silica gel or activated alumina to reduce moisture content in the air without a chemical or physical change to the material.  Typical systems include a fluted or corrugated media configured in a rotating mass.  These systems require reactivation via a heat source to expel moisture via a separate airstream commonly referred to as the reactivation air stream.  Typical applications for these units include dew points below 45°F and some manufacturers, including Bry-Air, produce systems that can maintain dew points of -80°F.  The common concern with this type of dehumidifier is that reactivation energy transferred coupled with the heat of conversion during the adsorption process increases the air temperature of the process airstream.  However, this can be combated with cost effective energy recovery and energy management solutions.
Desiccants - Absorption Type
Absorption based dehumidifiers utilize an absorbent desiccant material such as calcium chloride to absorb moisture via a chemical change in the material structure.  Typical systems utilize storage tanks to hold the liquid based absorption material often diluted with water which is pumped through a spray bar over a media pad.  As the moisture laden air comes in contact with the absorption material the chemical change in structure takes place bonding the moisture molecules with the absorbent.  The absorption based dehumidifier also requires reactivation to change the material structure causing the absorbed water molecules to be exhausted from the reactivation air tunnel.  It is often seen as a benefit that these systems, when using a liquid absorption system, offer some evaporative cooling effects while dehumidifying the air.  Potential pitfalls of this system include desiccant carryover and system corrosion (including ductwork), additional maintenance, accurate system control, among other things.  It should be noted that there are dry bed/rotor systems available as well, which also utilize the absorption media.  However, even in dry form these types of systems often have pitfalls, so caution should be taken in the application of this technology.

Some of the best systems available today offer a combination of system technologies such as refrigeration coupled with adsorption, as often used by Bry-Air.  Contact Bry-Air today to discuss these systems and how they may be applied to your specific moisture control challenge.