Refrigeration Dehumidifiers
A refrigeration dehumidifier removes moisture from the air by passing it over a cooling coil. The cool surfaces of the coil cause the moisture in the air to condense. This moisture then collects on the coils and eventually runs into a collection tray or pan located below the unit, or through a hose into a nearby drain. Portable electrically operated refrigeration dehumidifiers are the type of units most commonly found in residences.
The amount of moisture removed from the air by a refrigeration dehumidifier will depend on the volume of air and its relative humidity. The initial amount of moisture removed will be relatively large in comparison to the amount removed at later stages in the operation of the dehumidifier. This reduction in the amount of moisture removal is not an indication that the dehumidifier is not operating properly. This is a normal operating characteristic. As the relative humidity approaches the desired level, the amount of mois- ture being removed from the air will be considerably less.
Dehumidifying coils depend on the dew point of the air entering and leaving the coil for removal of moisture from the air. To accomplish moisture removal, the dew point of the air entering the coil must be higher than the dew point of the air leaving the coil.
Automatic Controls
A refrigeration dehumidifier consists of a motor-driven compressor, a condenser or cooling coil, and a receiver. A refrigerant circulates through the cooling coil of the unit, the refrigerant flow being con- trolled by a capillary tube circuit.
The room air is drawn over the cooling coil by means of a motor-operated fan or blower. When the moisture-laden air comes in contact with the cool surfaces of the cooling coil, it condenses and runs off the coil into a collection tray or pan, or through a hose into a drain.
Dehumidifier operation is controlled by a humidistat, which starts and stops the unit to maintain a selected humidity level. The humidistat accomplishes this function by switching the compressor and unit fan on and off in response to changes in the moisture con- tent of the air.
Humidistat control settings will generally range from dry to extra dry to continuous to off. During the initial period of opera- tion (usually 3 to 4 weeks), the humidistat should be set at extra dry. If the moisture content of the air has been noticeably reduced, the humidistat setting can be moved to dry. Minor adjustments may be required from time to time.
Never purchase a dehumidifier that does not have a humidistat. Without a humidistat, a dehumidifier will run long after the humid- ity of the air has dropped to a satisfactory level. Operating such a dehumidifier can prove to be very costly and wasteful of energy.
Dehumidifiers that empty the condensate into a container are equipped with an integral cutoff (float) switch to turn the unit off when the condensate container is full. This action avoids overflow conditions. Most of these dehumidifiers will also have a signal light that indicates when the condensate container needs emptying.
Installation Suggestions
A dehumidifier is most effective in an enclosed area where good air
circulation is found. For maximum effectiveness, the unit should be located as close to the center of room, space, or structure as possible.
Operating and Maintenance Suggestions
A dehumidifier generally will not operate very satisfactorily at temperatures below 60°F. The reason for this is obvious. When the ambient temperature is below 60°F, the cooling coil must operate at below-freezing temperatures in order to cause the moisture in the air to condense. Unfortunately, operating at these temperatures also causes ice to form on the coils, and this ice formation may eventually
damage the dehumidifier. The ice is removed by running the dehumidifier through a defrost cycle. When a defrost sensor in the dehumidifier detects frost on the coils, it turns off the compressor but allows the fan to continue running. The fan draws the warmer surrounding air across the coils and melts the frost. After the frost has melted, the compressor restarts and the appliance resumes reducing the moisture in the indoor air.
Note
The dehumidifier cannot remove moisture from the air while it is in the defrost cycle.
Fungus will sometimes collect on the cooling coil. This accumulation of fungus can be removed by loosening it with a soft brush and washing away the residue with water.
The principal components of a refrigeration dehumidifier are hermetically sealed at the factory. These components are permanently lubricated and should not require any further servicing. On the other hand, both the condensate collector and the dehumidifier filter can be inspected and cleaned.
As an alternative to manually emptying the condensate container, a unit located in the basement can be connected by a hose to a floor drain, or it can be positioned directly over the drain. In any event, the dehumidifier should be equipped with a cutoff (float) switch to turn off the unit when the condensate container is full.