Dehumidifier
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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, cause unsightly condensation and can make it hard to dry laundry or sleep.
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[edit] Process
[edit] Mechanical/refrigerative
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, and drips into a collecting bucket. The air is then reheated by the warmer side of the refrigeration coil. This process works best with a strong temperature gradient - since the refrigeration coil usually works at a set temperature, this means that this kind of dehumidifier works best at high ambient temperatures, and may be strongly reduced in effectiveness in colder climates.[1] They are most effective at over 45% relative humidity, higher if the air is cold. [2]
[edit] Dessicantive
A desiccant dehumidifier is a device that employs a 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.[2]
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).
[edit] 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.
[edit] Water
[edit] 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.
[edit] 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.[1] 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.
[edit] Consumer Considerations
When selecting dehumidifiers, consumers are influenced by several factors. These factors include: moisture removal rate, the quantity of water removed by a dehumidifier in a given amount of time; the size of the area that needs to be dehumidified; temperature range of where the dehumidifier will be used; the quality of the humidistat; energy usage; noise level; and ease of use.[3]
[edit] 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
[edit] References
- ^ a b Frequently Asked Questions (from a reseller website. Retrieved 2007-10-22.)
- ^ a b Desiccant Dehumidification vs. Mechanical Refrigeration (from a manufacturers website. Retrieved 2007-10-22.)
- ^ Dehumidifier Buying Guide (from a retailers website. Retrieved 2008-6-1.)
