All Topics  
Dehumidifier

 

 
   Email Print
   Bookmark   Link
 

 

Dehumidifier
 
 
  Topics Dehumidifier Topic Home

A dehumidifier is a household appliance that reduces the level of humidity
Humidity

Humidity is the amount of water vapor in the air. In daily language the term "humidity" is normally taken to mean relative humidity. Relative humidity is defined as the ratio of the partial pressure of water vapor in a Air parcel of air to the saturated vapor pressure of water vapor at a prescribed temperature....
 in the air, usually for health reasons, as humid air can cause mold
Mold

Molds include all species of microscopic fungi that grow in the form of Multicellular organism filaments, called hyphae. In contrast, microscopic fungi that grow as single cells are called yeasts....
 and mildew
Mildew

Mildew refers to certain kinds of mold or fungus. In Old English, it meant honeydew , and later came to mean mildew in the modern senses.*The term mildew is often used generically to refer to mold growth, usually with a flat growth habit....
 to grow inside homes, which has various health risks. Relative humidity is preferably 30 to 50%. Very high humidity levels are also unpleasant for human beings, can cause condensation
Condensation

Condensation is the change of the physical state of aggregation of matter from gaseous phase into liquid phase. When the transition happens from the gaseous phase into the solid phase directly, bypassing the liquid phase the change is called Deposition , which is the opposite of sublimation....
 and can make it hard to dry laundry or sleep.

Mechanical/refrigerative
Mechanical/refrigerative dehumidifiers, the most common type, usually work by drawing moist air over a refrigerated
Refrigeration

Refrigeration is the process of removing heat from an enclosed space, or from a substance, and moving it to a place where it is unobjectionable....
 coil with a small fan.






Discussion
Ask a question about 'Dehumidifier'
Start a new discussion about 'Dehumidifier'
Answer questions from other users
Full Discussion Forum



Encyclopedia


A dehumidifier is a household appliance that reduces the level of humidity
Humidity

Humidity is the amount of water vapor in the air. In daily language the term "humidity" is normally taken to mean relative humidity. Relative humidity is defined as the ratio of the partial pressure of water vapor in a Air parcel of air to the saturated vapor pressure of water vapor at a prescribed temperature....
 in the air, usually for health reasons, as humid air can cause mold
Mold

Molds include all species of microscopic fungi that grow in the form of Multicellular organism filaments, called hyphae. In contrast, microscopic fungi that grow as single cells are called yeasts....
 and mildew
Mildew

Mildew refers to certain kinds of mold or fungus. In Old English, it meant honeydew , and later came to mean mildew in the modern senses.*The term mildew is often used generically to refer to mold growth, usually with a flat growth habit....
 to grow inside homes, which has various health risks. Relative humidity is preferably 30 to 50%. Very high humidity levels are also unpleasant for human beings, can cause condensation
Condensation

Condensation is the change of the physical state of aggregation of matter from gaseous phase into liquid phase. When the transition happens from the gaseous phase into the solid phase directly, bypassing the liquid phase the change is called Deposition , which is the opposite of sublimation....
 and can make it hard to dry laundry or sleep.

Processes


Mechanical/refrigerative


Mechanical/refrigerative dehumidifiers, the most common type, usually work by drawing moist air over a refrigerated
Refrigeration

Refrigeration is the process of removing heat from an enclosed space, or from a substance, and moving it to a place where it is unobjectionable....
 coil with a small fan. Since the saturation vapor pressure of water decreases with decreasing temperature, the water in the air condenses
Condensation

Condensation is the change of the physical state of aggregation of matter from gaseous phase into liquid phase. When the transition happens from the gaseous phase into the solid phase directly, bypassing the liquid phase the change is called Deposition , which is the opposite of sublimation....
, and drips into a collecting bucket. The air is then reheated by the warmer side of the refrigeration coil. This process works most effectively with higher ambient temperatures with a high dew point
Dew point

The dew point is the temperature to which a given parcel of air must be cooled, at constant barometric pressure, for water vapor to Condensation into water....
 temperature. In cold climates, the process is less effective. They are most effective at over 45% relative humidity, higher if the air is cold.

Desiccative


A desiccant dehumidifier is a device that employs a desiccant material
Desiccant

A desiccant is a hygroscopic substance that induces or sustains a state of dryness in its local vicinity in a moderately-well sealed container.Commonly encountered pre-packaged desiccants are solids, and work through absorption or adsorption of water, or a combination of the two....
 to produce a dehumidification effect. As 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 tandem with them.

Desiccant materials have a high affinity for water vapor. An example of dessicant material is silica gel
Silica gel

Silica gel is a granularity, vitreous, highly porosity form of silica made synthetically from sodium silicate. Despite its name, silica gel is a solid....
. 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.

In general a desiccant dehumidifier comprises 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 heater to heat the air that will be used to dry the desiccant (regeneration air);
  • a fan to move the low humidity air for drying the desiccant through the desiccant holder.


Air conditioners


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.

Convectant drying


Slowly and continuously exhausting the coolest, most humid air at the floor also dehumidifies the indoor air.

Water


Collection


Most dehumidifiers can be adapted to connect the drip output directly to a drain via a garden hose, though they usually also come with a collection receptacle. There are usually sensors to detect when the collection device is full, and shut off the dehumidifier. These buckets will generally fill with water in 8-12 hours and will need to be emptied and replaced. Some dehumidifiers can tie into plumbing or use a water pump to drain themselves as they collect moisture.

Potability


General dehumidifier water is considered a rather clean kind of greywater
Greywater

Greywater, also known as sullage, is non-industrial wastewater generated from domestic processes such as dish washing, laundry and bathing....
: not suitable for drinking, but acceptable for watering plants, though not garden vegetables. The concerns are:
  • the water may contain trace metal from the solder, most significantly lead (which is quite damaging), but also copper, aluminium, and zinc;
  • various pathogens accumulate in the water, particularly due to its stagnancy, including fungal spores; unlike in distilled water, the water is not boiled, which would kill pathogens (including bacteria);
  • as with distilled water, minerals are largely absent, hence it is somewhat flat tasting.
The trace metal poses a danger if used on edible plants, as they can accumulate; however, the water is otherwise usable for irrigation.

One can make food-grade dehumidifiers (avoiding toxic metal and keeping the collection tank clean), which are called atmospheric water generator
Atmospheric water generator

An Atmospheric water generator , is a device that extracts water from humidity ambient air. An AWG operates in a manner very similar to that of a refrigerated dehumidifier: air is passed over a cooled coil, causing water to condense....
s.

See also

  • Atmospheric water generator
    Atmospheric water generator

    An Atmospheric water generator , is a device that extracts water from humidity ambient air. An AWG operates in a manner very similar to that of a refrigerated dehumidifier: air is passed over a cooled coil, causing water to condense....
    , a machine that makes pure drinking water from air
  • Food dehydrator
    Food dehydrator

    A food dehydrator is an appliance that uses warm air to Drying of foods. This is usually done to preserve foods that do not normally store well....
    , device for decreasing humidity of food
  • Humidifier
    Humidifier

    A humidifier is a household appliance that increases humidity in a single room or in the entire home. There are point-of-use humidifiers, which are commonly used to humidify a single room, and whole-house or furnace humidifiers, which connect to a home's HVAC system to provide humidity to the entire house....
    , an appliance that increases the humidity of air
  • Thermoelectric cooling
    Thermoelectric cooling

    Thermoelectric cooling uses the Peltier effect to create a heat flux between the junction of two different types of materials. A Peltier cooler, heater, or thermoelectric heat pump is a solid-state active heat pump which transfers heat from one side of the device to the other side against the temperature gradient , with consumption of electri...
    , Peltier dehumidifiers


Further reading

  • Tables with many dehumidifier models. With columns for liters of water removed per day, and liters per kilowatt-hour:
  • Energy Star
    Energy Star

    Energy Star is an international standard for Energy conservation consumer products. It was first created as a United States government program in 1992, but Australia, Canada, Japan, New Zealand, Taiwan and the European Union have also adopted the program....
     Qualified Dehumidifiers .
  • AHAM Directory of Certified Dehumidifiers . This table has both pints and liters removed per 24 hours.


  • AHAM Dehumidifier Product Certification Program . Association of Home Appliance Manufacturers
    Association of Home Appliance Manufacturers

    The Association of Home Appliance Manufacturers or AHAM represents the manufacturers of household appliances and products/services associated with household appliances sold in the United States....
    .
  • AHAM searchable Directory of Certified Dehumidifiers . Can search or browse by manufacturer, brand name, daily water removal capability (pints per day), etc..