A dehumidifier is a household appliance that reduces the level of humidity in the air. A major appliance is a large machine which accomplishes some routine housekeeping task, which includes purposes such as cooking, food preservation, or cleaning, whether in a household, institutional, commercial or industrial setting. ... Humidity is the concentration of water vapor in the air. ...

Mechanical/refrigerative dehumidifiers

Mechanical/refrigerative dehumidifiers 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, and drips into a collecting bucket. The air is then reheated by the warmer side of the refrigeration coil. It has been suggested that Refrigerator be merged into this article or section. ... The saturation vapor pressure is the vapor pressure of water when air is saturated with water (having the maximum amount of water vapor that air can hold for a given temperature and pressure). ... Water vapor condensing over a cup of hot tea Condensation is the change in matter of a substance to a denser phase, such as a gas (or vapor) to a liquid. ...

Most dehumidifiers can be adapted to connect the drip output directly to a drain. Manufacturers may price dehumidifiers differently solely on the size of the collection bucket. There are usually sensors to detect when the collection bucket is full.

Air conditioners automatically act as dehumidifiers when they chill the air and thus need to handle the accumulated water as well. Newer window units use the condensing coil and fan to evaporate the accumulated water into the outdoor air, while older units simply allow the water to drip outside. Central air conditioning units need to be connected to a drain. Note: in the broadest sense, air conditioning can refer to any form of heating, ventilation, and air-conditioning. ...

Desiccant dehumidifiers

A desiccant dehumidifier is a device that employs a desiccant material to produce a dehumidification effect. Desiccant materials have a high affinity for water vapor. Typically their moisture content is a function of the relative humidity of the surrounding air. Exposed to low relative humidities desiccant materials come to equilibrium at low moisture contents and exposure to high relative humidities results in equilibrium at high moisture contents. 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. Note that the first air stream's water vapor content is reduced while the second air stream's water vapor content is increased. Typically the low relative humidity air stream is air taken from any available source and heated to reduce its relative humidity. Hence desiccant dehumidifiers consume heat energy to produce a dehumidifying effect. A desiccant is a substance that adsorbs moisture from the air. ...

In general a desiccant dehumidifier is comprised of four major components. The component that holds the desiccant of which there are several types, a fan to move the air to be dehumidified (process air) through the desiccant holder, a fan to move the low humidity air for drying the desiccant through the desiccant holder and a heater to heat the air that will be used to dry the desiccant (regeneration air).

Relative effectiveness

Refrigerant dehumidifiers are more efficient when the air is quite humid (over about 45% relative humidity, higher if the air is cold). Sometimes, they are used in tandem, such as when the air is humid, and needs to be made very dry.[1]

Drinking the water

Water collected from any dehumidifier is technically distilled water in that it does not contain minerals and other particulates that are removed in a true distillation process. However, a true distillation process condenses the steam of boiled water, and the boiling process kills any microbes and fungi that may be present in the pre-distilled water. Since the surface coils in a dehumidifier are not kept to food-grade cleanliness, microbes and fungi can (and probably do) exist in the collected water and it is therefore not considered safe to drink. In fact, as the water may sit for a while in the collection bucket, the water may be quite stale. This article or section is not written in the formal tone expected of an encyclopedia article. ... Staling is a chemical and physical process in bread that reduces its palatability. ...

See also

• Atmospheric water generator, a machine that makes pure drinking water from air.
• Humidifier, an appliance that increases the humidity of air.
• Thermoelectric cooling, Peltier dehumidifier.