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Humidistat |
A humidifier is a household appliance that increases humidity (moisture) 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.
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The most common humidifier, an "evaporative" or "wick humidifier", consists of just a few basic parts: a reservoir, wick and fan.
The wick is a filter that absorbs water from the reservoir. Evaporation of water from the wick is dependent on relative humidity. A room with low humidity will have a higher evaporation rate compared to a room with high humidity. Therefore, this type of humidifier is self-regulating: As the humidity of the room increases, the water vapor output naturally decreases. These wicks regularly need cleaning and replacement — if this does not happen, the humidifier stops humidifying the area it is in and the water in the tank remains at the same level.
The fan is adjacent to the wick and blows air onto the wick, thus aiding in the evaporation of the water within
Other types of humidifiers include:
Impeller and ultrasonic humidifiers do not selectively put water in the air, they also add any suspended material in the water to the air such as microorganisms and minerals. The amount of minerals and other materials can be greatly reduced by using distilled water, though no water is absolutely pure. Filters may also reduce the amount of material but the EPA warns, "the ability of these devices to remove minerals may vary widely."1 Depending on the volume, this dust may have negative health effects. Wick humidifiers trap the mineral deposits in the wick.
For buildings with a forced-air furnace, a humidifier may be built right into the furnace. They can also protect wooden objects, antiques and other furnishings which may be sensitive to damage from overly dry air. In colder months, they may provide substantial energy savings, since as humidity increases, occupants feel warm at a lower temperature. These units are typically called bypass humidifiers (because they are connected between the heated and cold air return ducts, using the pressure difference between these ducts to cause some heated air to make a bypass through the humidifier and return to the furnace). The humidifier should usually be disabled during the summer months if air conditioning is used; air conditioners partially function by reducing indoor humidity. There are three basic styles:
For the latter reason especially, drum-style humidifiers should always be turned off at the water supply during summer (air conditioning) months, and should always be used with high quality furnace air filters (MERV ratings as high as possible to ensure small numbers of mold spores reaching the humidifier's pan) when the water supply is turned on.
The use of a humidifier can allow the reproduction of dust mites or the growth of harmful mold, which can be especially harmful for children and the elderly. The relative humidity should be kept between 30% and 50%. 2. Can also cause Hypersensitivity pneumonitis (humidifier lung) 3
Some humidifiers now use Microban technology to reduce mold and bacteria growth within the humidifier.
The EPA provides detailed information of the risks as well as recommended maintenance procedures1. One of the main concerns cited by EPA regarding ultrasonic or impeller humidifiers is a "white dust" that has been reported by some consumers, which usually spreads over furniture, is attracted to static electricity generating devices such as CRT monitors and possibly affects the lungs. Although EPA does not explain the "white dust" generation mechanism, which is undesired and potentially harmful, some manufacturers claim that not only is it beneficial but also that it is intentionally produced. It is claimedwho? that the process is associated to the release of negatively charged ions which attach themselves to allergens and dust particles neutralizing and purifying the air, protecting against molds, mildews, fungi, bacteria, viruses and dust mites.
A controller that measures and controls relative humidity. A humidistat may be used to control either humidifying or dehumidifying equipment by the regulation of electric or pneumatic switches, valves, or dampers.
An electronic humidistat includes a sensing element and a relay amplifier. The sensing element consists of alternate metal conductors on a small flat plate. An increase or decrease of the relative humidity causes a decrease or increase in the electrical resistance between the two sets of conductors and the change in resistance is measured by the relay amplifier.
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