Dehumidification

A dehumidifier is an appliance that reduces the level of humidity in the air, usually for health reasons, as humid air can cause mold and mildew to grow inside homes, which has various health risks. Very high humidity levels are also unpleasant for human beings, cause unsightly condensation and can make it hard to dry laundry or sleep. Dehumidifiers can be used on a day to day basis where this is for comfort or process dehumidification or more recently they have been used for post flood recovery removing the remaining water and moisture from a property once standing water has bee removed.

Mechanical/refrigerative dehumidifiers, the most common type, usually work by drawing moist air over a refrigerated coil with a small fan. Since the saturation vapor pressure of water decreases with decreasing temperature, the water in the air condenses (as it would on a single glazed window), and drips into a collecting bucket where it remains waiting to be emptied or is pumped away. The air is then reheated by the warmer side of the refrigeration coil and expelled by the appliance. They are most effective at over 45% relative humidity, higher if the air is cold.

Desiccant dehumidifier is a device that employs a desiccant material to produce a dehumidification effect. they are more effective for low-temperature and low (relative) humidity levels, they are generally used for these conditions instead of mechanical/refrigerative dehumidifiers - or are used in conjunction with them.

The process involves exposing the desiccant material to a high relative humidity air stream, allowing it to attract and retain some of the water vapor and then exposing the same desiccants to a lower relative humidity air stream which has the effect of drawing the retained moisture from the desiccant. The first air stream is the air that is being dehumidified while the second air stream is used only to regenerate the desiccant material so that it is ready to begin another cycle.