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Humidifier
A humidifier is a household appliance that increases humidity(moisture) in a single room or in the entire home. There arepoint-of-use humidifiers, which are commonly used to humidify asingle room, and whole-house or furnace humidifiers, which connectto a home's HVAC system to provide humidity to the entire house.
Evaporative humidifiers
The most common humidifier, an "evaporative" or "wick humidifierfilter", consists of just a few basic parts: a reservoir, wick andfan.
Reservoir
Reservoirs are common to most humidifiers and come in differentshapes and sizes. The reservoir is a containing tank of waterfilled prior to operation, and provides the water for the moistureoutput. Other types have a continuous feed from a water line.
Wick
The wick is a filter that absorbs water from the reservoir.Evaporation of water from the wick is dependent on relativehumidity. A room with low humidity will have a higher evaporationrate compared to a room with high humidity. Therefore, this type ofhumidifier is self-regulating: As the humidity of the roomincreases, the water vapor output naturally decreases. These wicksregularly need cleaning and replacement — if this does not happen,the humidifier stops humidifying the area it is in and the water inthe tank remains at the same level.
Fan
The fan is adjacent to the wick and blows air onto the wick, thusaiding in the evaporation of the water within the wick.
[edit] Other types of humidifiers
Other types of humidifiers include:
Vaporizer (Steam Humidifier) (Warm Mist Humidifier) — Boils water,releasing steam and moisture into the air. A medicated inhalant canalso be added to the steam vapor to help reduce coughs. Vaporizersare more healthful[1] than cool mist types of humidifiers becausesteam is sterile and free from minerals. Vaporizers use moreelectricity to boil the water.
Impeller Humidifier (Cool Mist Humidifier) — A rotating disc flingswater at a diffuser, which breaks the water into fine droplets thatfloat into the air.
Ultrasonic Humidifier — A metal diaphragm vibrating at anultrasonic frequency creates water droplets that exit thehumidifier in the form of a cool fog silently. UltrasonicHumidifiers should be cleaned regularly to avoid bacterialcontamination which may be projected into the air.
Impeller and ultrasonic humidifiers do not selectively put water inthe air, they also add any suspended material in the water to theair such as microorganisms and minerals. The amount of minerals andother materials can be greatly reduced by using distilled water,though no water is absolutely pure. Filters may also reduce theamount of material but the EPA warns, "the ability of these devicesto remove minerals may vary widely."[2] Depending on the volume,this dust may have negative health effects. wick humidifier filterstrap the mineral deposits in the wick.
Forced-Air Humidifiers
For buildings with a forced-air furnace, a humidifier may be builtright into the furnace. They can also protect wooden objects,antiques and other furnishings which may be sensitive to damagefrom overly dry air. In colder months, they may provide substantialenergy savings, since as humidity increases, occupants feel warm ata lower temperature. These units are typically called bypasshumidifiers (because they are connected between the heated and coldair return ducts, using the pressure difference between these ductsto cause some heated air to make a bypass through the humidifierand return to the furnace). The humidifier should usually bedisabled during the summer months if air conditioning is used; airconditioners partially function by reducing indoor humidity. Thereare three basic styles:
Drum style: A pipe brings water directly to a reservoir (a pan)attached to the furnace. The water level in the pan is controlledby a float valve, similar to a small toilet tank float. The wick istypically a foam pad mounted on a drum and attached to a smallmotor; hot air enters the drum at one end and is forced to leavethrough the sides of the drum. When the hygrostat calls forhumidity, the motor is turned on causing the drum to rotate slowlythrough the pan of water and preventing the foam pad from dryingout.
Advantages include:
Low cost
Inexpensive maintenance (drum-style pads are cheap and readilyavailable)[citation needed]
Disadvantages include:
Requirement for frequent (approximately monthly) inspections ofcleanliness and pad condition
Water evaporation even when humidification is not required (due tothe pan of water which remains exposed to a high velocity airstream)
Mold growth in the pan full of water (this problem is exacerbatedby the large quantity of air, inevitably carrying mold spores,passing through the humidifier whether in use or not).
For the latter reason especially, drum-style humidifiers shouldalways be turned off at the water supply during summer (airconditioning) months, and should always be used with high qualityfurnace air filters (MERV ratings as high as possible to ensuresmall numbers of mold spores reaching the humidifier's pan) whenthe water supply is turned on.
Disc Wheel Style: Very similar in design to the drum stylehumidifiers, this type of furnace humidifier replaces the foam drumwith a number of plastic discs with small grooves on both sides.This allows for a very large evaporative surface area, withoutrequiring a great deal of space. Unlike the drum style humidifiers,the disc wheel does not need replacing.[1]
Advantages include:
Very low maintenance (basin of humidifier should be cleaned outperiodically, unless automatic flushing device is installed)
No regular replacement of parts necessary
Higher output due to large evaporative surface area
Can be installed in hard water situations
Maintains efficiency throughout lifespan
Disadvantages include:
Higher price
Water evaporation even when humidification is not required (due tothe pan of water which remains exposed to a high velocity airstream)
Flow-Through Style (also known as "biscuit style" or many other,similar variant names): A pipe brings water directly to anelectrically-controlled valve at the top of the humidifier. Airpasses through an aluminum "biscuit" (often called a pad; using theterm "biscuit" to emphasize the solid rather than foamy form) whichis similar to a piece of extremely coarse steel wool. The biscuithas a coating of a matte ceramic, resulting in an extremely largesurface area within a small space. When the hygrostat calls forhumidity, the valve is opened and causes a spray of water onto thebiscuit. Hot air is passed through the biscuit, causing the waterto evaporate from the pad and be carried into the building.
Advantages include:
Reduced maintenance (new biscuit only when clogged with dust ormineral deposits, typically once per year)
Lack of a pan of potentially stagnant water to serve as a breedingground for mold as with a drum-style humidifier
No incidental humidification caused by a constantly-replenished panof water in a high velocity air stream
Reduced requirement for expensive air filters
Uses no electricity
Disadvantages include:
A somewhat higher purchase price
Manufacturer and model-specific replacement biscuits versus therelatively generic drum-style pads
A portion of the water supplied to the unit is not evaporated. Thiscan generate a considerable amount of waste water, and does requireconnection to a drain.
Disadvantages and risks
The use of a humidifier can allow the reproduction of dust mites orthe growth of harmful mold, which can be especially harmful forchildren and the elderly. The relative humidity should be keptbetween 30% and 50%. [3]. Can also cause Hypersensitivitypneumonitis (humidifier lung) [4]
Some humidifiers now use Microban technology to reduce mold andbacteria growth within the humidifier.
The EPA provides detailed information of the risks as well asrecommended maintenance procedures.[5]
Some humidifiers have no silent operation.
Humidistat
A controller that measures and controls relative humidity. Ahumidistat may be used to control either humidifying ordehumidifying equipment by the regulation of electric or pneumaticswitches, valves, or dampers.
An electronic humidistat includes a sensing element and a relayamplifier. The sensing element consists of alternate metalconductors on a small flat plate. An increase or decrease of therelative humidity causes a decrease or increase in the electricalresistance between the two sets of conductors and the change inresistance is measured by the relay amplifier.
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