Humidifier - AbsoluteAstronomy.com

A humidifier is a household appliance that increases humidity

Humidity

Humidity is a term for the amount of water vapor in the air, and can refer to any one of several measurements of humidity. Formally, humid air is not "moist air" but a mixture of water vapor and other constituents of air, and humidity is defined in terms of the water content of this mixture,...

(moisture) in a single room or in the entire house. 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

HVAC

HVAC refers to technology of indoor or automotive environmental comfort. HVAC system design is a major subdiscipline of mechanical engineering, based on the principles of thermodynamics, fluid mechanics, and heat transfer...

system to provide humidity to the entire house.

Evaporative humidifiers

The most common humidifier, an "evaporative", "cool mist", or "wick humidifier", consists of just a few basic parts: a reservoir, wick and fan.

The wick is a filter

Filter (chemistry)

In chemistry and common usage, a filter is a device that is designed to physically block certain objects or substances while letting others through. Filters are often used to remove solid substances suspended in fluids, for example to remove air pollution, to make water drinkable, and to prepare...

that absorbs water from the reservoir and provides a larger surface area

Surface area

Surface area is the measure of how much exposed area a solid object has, expressed in square units. Mathematical description of the surface area is considerably more involved than the definition of arc length of a curve. For polyhedra the surface area is the sum of the areas of its faces...

for it to evaporate from. The fan is adjacent to the wick and blows air onto the wick to aid in the evaporation of the water. Evaporation from the wick is dependent on relative humidity

Relative humidity

Relative humidity is a term used to describe the amount of water vapor in a mixture of air and water vapor. It is defined as the partial pressure of water vapor in the air-water mixture, given as a percentage of the saturated vapor pressure under those conditions...

. 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 become moldy if they are not dried out completely between fillings, and become filled with mineral deposits over time. They regularly need rinsing or replacement—if this does not happen, air cannot pass through them, and the humidifier stops humidifying the area it is in and the water in the tank remains at the same level.

One type of evaporative humidifier makes use of just a reservoir and wick. Sometimes called a natural humidifier, these are usually non-commercial devices that can be assembled at little or no cost. One version of a natural humidifier uses a stainless steel bowl, partially filled with water, covered by a towel. A weight is used to sink the towel in the center of the bowl. There is no need for a fan as the water spreads through the towel by capillary action and the towel surface area is large enough to provide for rapid evaporation. The stainless steel bowl is much easier to clean than typical humidifier water tanks. This, in combination with daily or every other day replacement of the towel, can eliminate the problem with mold and bacteria.

A humidifier for humidifying a fuel cell composed of an anode side humidifier and a cathode side humidifier each possessing a plurality of hollow fiber membrane modules for migrating moisture between a supply gas, which is supplied to a fuel cell, and an exhaust gas, which is exhausted from the fuel cell to thereby humidify the supply gas, the humidifier comprising: a pair of heads which hold both ends of the hollow fiber membrane modules, a connecting member which connects each of heads, and a device for warming the supply gas composed of conduits through which a cooling medium exhausted from the fuel cell is passed. The device for warming the supply gas is configured so that first warms a humidifier at an outlet side of the supply gas, and then warms a humidifier at an inlet side of the supply gas.

A CPAP device includes a humidifier including humidifier tub having a heat conducting base plate; and a cradle to support the humidifier tub in an operative position. The cradle may also support a flow generator in operative relation to the humidifier tub. The cradle includes a heater plate in communication with the heat conducting base plate of the humidifier tub in use. The cradle further includes a retaining mechanism to retain the humidifier tub in the cradle, the retaining mechanism being structured to force the base plate into engagement with the heater plate. The humidifier and/or flow generator may include various features to manage inadvertent back-spill of water from the humidifier to the flow generator.

A humidifier and a method for producing it can reduce gas leakage through inside the surfaces of humidifying membranes or through interfaces between the humidifying membranes and separators. The humidifier includes water permeable humidifying membranes and gas separators each having one or two channels opened at least one side in a direction of lamination, through which at least one of a dry gas and a wet gas is caused to flow. A humidifying membrane, a gas separator, a humidifying membrane and a gas separator are repeatedly laminated one over another in this order, or a gas separator, a humidifying membrane and a gas separator are repeatedly laminated one over another in this order. Each gas separator has a frame-shaped portion surrounding the one or two channels, and that portion of each humidifying membrane which, when laminated, faces the frame-shaped portion of a corresponding gas separator is filled with a resin.

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 can also be added to the steam vapor to help reduce coughs. Vaporizers may be more healthful than cool mist types of humidifiers because steam is less likely to convey mineral impurities or microorganisms from the standing water in the reservoir. Boiling water requires significantly more energy than other techniques. The heat source in poorly-designed humidifiers can overheat, causing the product to melt, leak, and start fires.

Impeller Humidifier (Cool Mist Humidifier) — A rotating disc flings water at a diffuser, which breaks the water into fine droplets that float into the air.
Ultrasonic Humidifier — A metal diaphragm vibrating at an ultrasonic frequency
Ultrasonic sensor
Ultrasonic sensors work on a principle similar to radar or sonar which evaluate attributes of a target by interpreting the echoes from radio or sound waves respectively. Ultrasonic sensors generate high frequency sound waves and evaluate the echo which is received back by the sensor...

creates water droplets that silently exit the humidifier in the form of a cool fog. Ultrasonic humidifiers use a piezo-electric transducer to create a high frequency mechanical oscillation in a body of water. The water tries to follow the high frequency oscillation but cannot because of its comparative weight and mass inertia. Thus, a momentary vacuum is created on the negative oscillation, causing the water to cavitate into vapor. The transducer follows this with a positive oscillation that creates high pressure compression waves on the water’s surface, releasing tiny vapor molecules of water into the air. This is an extremely fine mist, about one micrometre in diameter, that is quickly absorbed into the air flow. Unlike the humidifiers that boil water, these water droplets contain any impurities that are in the reservoir, including minerals from hard water
Hard water
Hard water is water that has high mineral content . Hard water has high concentrations of Ca2+ and Mg2+ ions. Hard water is generally not harmful to one's health but can pose serious problems in industrial settings, where water hardness is monitored to avoid costly breakdowns in boilers, cooling...

(which then forms a difficult to remove white dust on nearby objects and furniture), and pathogens growing in the stagnant tank. Ultrasonic Humidifiers should be cleaned regularly to avoid bacterial contamination which may be projected into the air.

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." Depending on the volume, this dust may have negative health effects. Wick humidifiers trap the mineral deposits in the wick; vaporizer types tend to collect minerals on or around the heating element and require regular cleaning with vinegar

Vinegar

Vinegar is a liquid substance consisting mainly of acetic acid and water, the acetic acid being produced through the fermentation of ethanol by acetic acid bacteria. Commercial vinegar is produced either by fast or slow fermentation processes. Slow methods generally are used with traditional...

or citric acid

Citric acid

Citric acid is a weak organic acid. It is a natural preservative/conservative and is also used to add an acidic, or sour, taste to foods and soft drinks...

to control buildup.

Forced-Air Humidifiers (whole-house)

For buildings with a forced-air furnace

Furnace

A furnace is a device used for heating. The name derives from Latin fornax, oven.In American English and Canadian English, the term furnace on its own is generally used to describe household heating systems based on a central furnace , and sometimes as a synonym for kiln, a device used in the...

, a humidifier may be installed 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. Bypass humidifiers 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. Common styles:

Drum style (bypass): A pipe brings water directly to a reservoir (a pan) attached to the furnace. The water level in the pan is controlled by a float valve
Valve
A valve is a device that regulates, directs or controls the flow of a fluid by opening, closing, or partially obstructing various passageways. Valves are technically pipe fittings, but are usually discussed as a separate category...

, similar to a small toilet
Toilet
A toilet is a sanitation fixture used primarily for the disposal of human excrement, often found in a small room referred to as a toilet/bathroom/lavatory...

tank float. The wick is typically a foam pad mounted on a drum and attached to a small motor; hot air enters the drum at one end and is forced to leave through the sides of the drum. When the hygrostat calls for humidity, the motor is turned on causing the drum to rotate slowly through the pan of water and preventing the foam pad from drying out.

Advantages include:

Low cost
Inexpensive maintenance (drum-style pads are cheap and readily available)

Disadvantages include:

Requirement for frequent (approximately monthly) inspections of cleanliness and pad condition
Water evaporation even when humidification is not required (due to the pan of water which remains exposed to a high velocity
Velocity
In physics, velocity is speed in a given direction. Speed describes only how fast an object is moving, whereas velocity gives both the speed and direction of the object's motion. To have a constant velocity, an object must have a constant speed and motion in a constant direction. Constant ...

air stream)
Mold
Mold
Molds are fungi that grow in the form of multicellular filaments called hyphae. Molds are not considered to be microbes but microscopic fungi that grow as single cells called yeasts...

growth in the pan full of water (this problem is exacerbated by 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 should always be turned off at the water supply during summer (air conditioning) months, and should always be used with high quality furnace air filter

Air filter

A particulate air filter is a device composed of fibrous materials which removes solid particulates such as dust, pollen, mold, and bacteria from the air. A chemical air filter consists of an absorbent or catalyst for the removal of airborne molecular contaminants such as volatile organic compounds...

s (MERV

Merv

Merv , formerly Achaemenid Satrapy of Margiana, and later Alexandria and Antiochia in Margiana , was a major oasis-city in Central Asia, on the historical Silk Road, located near today's Mary in Turkmenistan. Several cities have existed on this site, which is significant for the interchange of...

ratings as high as possible to ensure small numbers of mold spores reaching the humidifier's pan) when the water supply is turned on.

Disc Wheel Style (bypass): Very similar in design to the drum style humidifiers, this type of furnace humidifier replaces the foam drum with a number of plastic discs with small grooves on both sides. This allows for a very large evaporative surface area, without requiring a great deal of space. Unlike the drum style humidifiers, the disc wheel does not need replacing.

Advantages include:

Very low maintenance (basin of humidifier should be cleaned out periodically, 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 to the pan of water which remains exposed to a high velocity air stream)

Bypass Flow-Through Style (bypass - also known as "biscuit style" or many other, similar variant names): A pipe brings water directly to an electrically-controlled valve at the top of the humidifier. Air passes through an aluminum "biscuit" (often called a pad; using the term "biscuit" to emphasize the solid rather than foamy form) which is similar to a piece of extremely coarse steel wool
Steel wool
Steel wool, also known as wire wool, is a bundle of strands of very fine soft steel filaments, used in finishing and repairing work to polish wood or metal objects, and for cleaning household cookware....

. The biscuit has a coating of a matte
Matte
Matte may refer to:In film:* Matte , filmmaking and video production technology* Matte painting, a process of creating sets used in film and video* Matte box, a camera accessory for controlling lens glare...

ceramic, resulting in an extremely large surface area within a small space. When the hygrostat calls for humidity, the valve is opened and causes a spray of water onto the biscuit. Hot air is passed through the biscuit, causing the water to evaporate from the pad and be carried into the building.

Advantages include:

Reduced maintenance (new biscuit only when clogged with dust or mineral deposits, typically once per year)
Lack of a pan of potentially stagnant water to serve as a breeding ground for mold as with a drum-style humidifier
No incidental humidification caused by a constantly-replenished pan of water in a high velocity air stream
Reduced requirement for expensive air filters
Uses little electricity

Disadvantages include:

A somewhat higher purchase price
Manufacturer and model-specific replacement biscuits versus the relatively generic drum-style pads
A portion of the water supplied to the unit is not evaporated. This can generate a considerable amount of waste water, and does require connection to a drain.

Spray Mist Type: A pipe, usually a small plastic tube, brings water directly to an electrically-controlled valve in the humidifier. Water mist is sprayed directly into the supply air, and the mist is carried into the premises by the air flow.

Advantages include:

Low cost.
Simpler than bypass types to install - single cut hole for installation, no additional ducting.
Uses little electricity.
Small, compact unit - fits where other types cannot. (Approx 6 inches square.)
Because it does not require bypass ducting it does not undermine the pressure separation (and therefore, blower efficiency) of the return and supply ducts.
Does not require use of moisture pads (on-going expense).
Highly efficient usage of water. Does not generate waste water and does not require separate connection to a drain.
Requires little maintenance. Periodic cleaning of nozzle may be required in hard water environments.
Lack of a pan of potentially stagnant water to serve as a breeding ground for mold as with a drum-style humidifier.

Disadvantages include:

Spray nozzle can become clogged in hard water situations, necessitating the use of water filter, periodic cleaning of nozzle, or nozzle replacement.

Additional types: 'Non-Bypass Flow-Through' (fan augmented), 'Steam', 'Impeller or Centrifugal Atomizer' and 'Under Duct'.

Disadvantages and risks

Unnecessary or overuse of a humidifier can raise the relative humidity to high levels, promoting the growth of dust mites and mold. A relative humidity of 30% to 50% is recommended for most homes. Can also cause Hypersensitivity pneumonitis

Hypersensitivity pneumonitis

Hypersensitivity pneumonitis is an inflammation of the alveoli within the lung caused by hypersensitivity to inhaled organic dusts. Sufferers are commonly exposed to the dust by their occupation or hobbies.-Pathophysiology:Hypersensitivity pneumonitis involves inhalation of an antigen...

(humidifier lung).

The EPA provides detailed information of the risks as well as recommended maintenance procedures. If the tap water contains a lot of minerals, also known as hard water, then the ultrasonic or impeller humidifiers will produce a "white dust" (calcium is the most common mineral in tap water), which usually spreads over furniture, and is attracted to static electricity

Static electricity

Static electricity refers to the build-up of electric charge on the surface of objects. The static charges remain on an object until they either bleed off to ground or are quickly neutralized by a discharge. Static electricity can be contrasted with current electricity, which can be delivered...

generating devices such as CRT

Cathode ray tube

The cathode ray tube is a vacuum tube containing an electron gun and a fluorescent screen used to view images. It has a means to accelerate and deflect the electron beam onto the fluorescent screen to create the images. The image may represent electrical waveforms , pictures , radar targets and...

monitors. The white dust can usually be prevented by using distilled water and a demineralization cartridge in ultrasonic humidifiers.

Deeming the design to be unsafe, the Supreme Court of Minnesota held the manufacturer of a humidifier strictly liable

Strict liability

In law, strict liability is a standard for liability which may exist in either a criminal or civil context. A rule specifying strict liability makes a person legally responsible for the damage and loss caused by his or her acts and omissions regardless of culpability...

in products liability in the 1960s when a three-year-old knocked it over, severely burning herself.

Evaporative humidifiers

Other types of humidifiers

Forced-Air Humidifiers (whole-house)

Disadvantages and risks

See also