Dehumidifier 251975 225946949 2008-07-16T03:55:34Z 70.172.210.187 {{Mergefrom | Convectant drying | Talk:Convectant drying |date=April 2008 }} [[Image:Maytag dehumidifier1.jpg|thumb|A typical portable dehumidifier.]] A '''dehumidifier''' is a [[household appliance]] that reduces the level of [[humidity]] in 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, can cause [[condensation]] 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 [[refrigeration|refrigerated]] coil with a small fan. Since the [[saturation vapor pressure]] of water decreases with decreasing temperature, the water in the air [[condensation|condenses]], 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]] temperature. In cold climates, the process is less effective.<ref name="MIT">[http://www.bdt.co.nz/oasis/faq.asp Frequently Asked Questions] (from a reseller website. Retrieved 2007-10-22.)</ref> They are most effective at over 45% relative humidity, higher if the air is cold. <ref name="DESS">[http://www.bry-air.com/applications/moisture_regain_prevention/desiccant-dehumidification-vs-mechanical-refrigeration.html Desiccant Dehumidification vs. Mechanical Refrigeration] (from a manufacturers website. Retrieved 2007-10-22.)</ref> === Dessicantive === A desiccant dehumidifier is a device that employs a [[desiccant|desiccant material]] 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.<ref name="DESS"/> 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. 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 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). === Air conditioners === [[Air conditioner]]s 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. == Water == [[Image:Dehumidifier Partially In Parts.jpg|thumb|right|A dehumidifier partially taken apart.]] === Collection === Most dehumidifiers can be adapted to connect the drip output directly to a drain, though they usually come with a collection receptable. There are usually sensors to detect when the collection device is full. Dehumidifiers are usually marketed by the amount of water per duration they remove from the air. === Potability === Water collected from any dehumidifier is technically [[distilled water]] in that it does contain few of the 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. Dehumidifiers are also not kept to a state of cleanliness required for food-grade standards ([[drinking water]] usually has very high legal requirements). The collected water is therefore not considered safe to drink.<ref name="MIT"/> Also, as the water may sit for a while in the collection bucket, the water may be quite stale, in particular with fungus collected from aerial spores. == 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 dehumidifiers == References == {{Reflist}} == Further reading == {{commonscat|Dehumidifiers}} *Tables with many dehumidifier models. With columns for liters of water removed per day, and liters per [[kilowatt-hour]]: :*[[Energy Star]] Qualified Dehumidifiers [http://www.lipower.org/pdfs/cei/qualified_dehumid.pdf]. :*AHAM Directory of Certified Dehumidifiers [http://207.140.180.12/dirsvc/aham.nsf/vwPDF/DehumFull/$file/DehumFullDir.pdf?OpenElement]. This table has both pints and liters removed per 24 hours. *AHAM Dehumidifier Product Certification Program [http://www.aham.org/industry/ht/d/sp/i/1225/pid/1225]. [[Association of Home Appliance Manufacturers]]. *AHAM searchable Directory of Certified Dehumidifiers [http://207.140.180.12/dirsvc/aham.nsf/fraDehum?OpenFrameset&pgm=Dehumidifiers]. Can search or browse by manufacturer, brand name, daily water removal capability (pints per day), etc.. [[Category:Home appliances]] [[Category:Cooling technology]] [[de:Luftentfeuchter]] [[fr:Déshumidificateur]]