![Maytag dehumidifier1](https://upload.wikimedia.org/wikipedia/commons/5/50/Maytag_dehumidifier1.jpg)
A dehumidifier is an
air conditioning
Air conditioning, often abbreviated as A/C or AC, is the process of removing heat from an enclosed space to achieve a more comfortable interior environment (sometimes referred to as 'comfort cooling') and in some cases also strictly controlling ...
device which reduces and maintains the level of
humidity
Humidity is the concentration of water vapor present in the air. Water vapor, the gaseous state of water, is generally invisible to the human eye. Humidity indicates the likelihood for precipitation, dew, or fog to be present.
Humidity depe ...
in the air.
[ This is done usually for health or ]thermal comfort
Thermal comfort is the condition of mind that expresses satisfaction with the thermal environment and is assessed by subjective evaluation ( ANSI/ASHRAE Standard 55).ANSI/ASHRAE Standard 55-2017, Thermal Environmental Conditions for Human Occupan ...
reasons, or to eliminate musty odor
An odor (American English) or odour (English in the Commonwealth of Nations, Commonwealth English; American and British English spelling differences#-our, -or, see spelling differences) is caused by one or more volatilized chemical compounds ...
and to prevent the growth of mildew
Mildew is a form of fungus. It is distinguished from its closely related counterpart, mould, largely by its colour: moulds appear in shades of black, blue, red, and green, whereas mildew is white. It appears as a thin, superficial growth consi ...
by extracting water from the air. It can be used for household, commercial, or industrial applications. Large dehumidifiers are used in commercial buildings such as indoor ice rink
An ice rink (or ice skating rink) is a frozen body of water and/or an artificial sheet of ice created using hardened chemicals where people can ice skate or play winter sports. Ice rinks are also used for exhibitions, contests and ice shows. The ...
s and swimming pool
A swimming pool, swimming bath, wading pool, paddling pool, or simply pool, is a structure designed to hold water to enable Human swimming, swimming or other leisure activities. Pools can be built into the ground (in-ground pools) or built ...
s, as well as manufacturing plants or storage warehouses. Typical air conditioning systems combine dehumidification with cooling, by operating cooling coils below the dewpoint and draining away the water that condenses.
Overview
Dehumidifiers extract water from air that passes through the unit. There are two common types of dehumidifiers: condensate dehumidifiers and desiccant dehumidifiers, and there are also other emerging designs.
Condensate dehumidifiers use a refrigeration cycle
Thermodynamic heat pump cycles or refrigeration cycles are the conceptual and mathematical models for heat pump, air conditioning and refrigeration systems. A heat pump is a mechanical system that allows for the transmission of heat from one locat ...
to collect water known as condensate
Condensate may refer to:
* The liquid phase produced by the condensation of steam or any other gas
* The product of a chemical condensation reaction, other than water
* Natural-gas condensate, in the natural gas industry
* ''Condensate'' (album) ...
, which is normally considered to be greywater
Greywater (or grey water, sullage, also spelled gray water in the United States) refers to domestic wastewater generated in households or office buildings from streams without fecal contamination, i.e., all streams except for the wastewater from ...
but may at times be reused for industrial purposes. Some manufacturers offer reverse osmosis filters to turn the condensate into potable water.
Desiccant
A desiccant is a hygroscopic substance that is used to induce or sustain a state of dryness (desiccation) in its vicinity; it is the opposite of a humectant. Commonly encountered pre-packaged desiccants are solids that absorb water. Desiccant ...
dehumidifiers (known also as absorption dehumidifiers) bond moisture with hydrophilic materials such as silica gel
Silica gel is an amorphous and porous form of silicon dioxide (silica), consisting of an irregular tridimensional framework of alternating silicon and oxygen atoms with nanometer-scale voids and pores. The voids may contain water or some other l ...
. Cheap domestic units contain single-use hydrophilic substance cartridges, gel, or powder. Larger commercial units regenerate the sorbent by using hot air to remove moisture and expel humid air outside the room.
An emerging class of membrane dehumidifiers, such as the ionic membrane dehumidifier, dispose of water as a vapor rather than liquid. These newer technologies may aim to address smaller system sizes or reach superior performance.
The energy efficiency
Energy efficiency may refer to:
* Energy efficiency (physics), the ratio between the useful output and input of an energy conversion process
** Electrical efficiency, useful power output per electrical power consumed
** Mechanical efficiency, a ra ...
of dehumidifiers can vary widely.
History
The first dehumidifier was created by American inventor Willis Carrier
Willis Haviland Carrier (November 26, 1876 – October 7, 1950) was an American engineer, best known for inventing modern air conditioning. Carrier invented the first electrical air conditioning unit in 1902. In 1915, he founded Carrier Cor ...
in 1902 to dehumidify a Brooklyn
Brooklyn () is a borough of New York City, coextensive with Kings County, in the U.S. state of New York. Kings County is the most populous county in the State of New York, and the second-most densely populated county in the United States, be ...
printing plant. Carrier cited the discovery as later motivating further discoveries in air conditioning. These “active” dehumidifiers condensed water from air. However, “passive” humidity control, such as increased natural ventilation, has been used since ancient times.
Thermal condensation dehumidification
These methods rely on drawing air across a cold surface. Since the saturation vapor pressure
Vapor pressure (or vapour pressure in English-speaking countries other than the US; see spelling differences) or equilibrium vapor pressure is defined as the pressure exerted by a vapor in thermodynamic equilibrium with its condensed phases ...
of water decreases with decreasing temperature, the water in the air condenses
Condensation is the change of the state of matter from the gas phase into the liquid phase, and is the reverse of vaporization. The word most often refers to the water cycle. It can also be defined as the change in the state of water vapor to ...
on the surface, separating the water from the air.
Refrigeration (electric)
Electric refrigeration dehumidifiers are the most common type of dehumidifiers. They work by drawing moist air over a refrigerated
The term refrigeration refers to the process of removing heat from an enclosed space or substance for the purpose of lowering the temperature.International Dictionary of Refrigeration, http://dictionary.iifiir.org/search.phpASHRAE Terminology, ht ...
evaporator with a fan. There are 3 main types of evaporators. They are coiled tube, fin and tube, and microchannel
Micro Channel architecture, or the Micro Channel bus, is a proprietary 16- or 32-bit parallel computer bus introduced by IBM in 1987 which was used on PS/2 and other computers until the mid-1990s. Its name is commonly abbreviated as "MCA", alth ...
technology.
The cold evaporator coil
An evaporator is a device used to turn the liquid form of a chemical substance, such as water, into a vapor.
Uses
Air conditioning and refrigeration
Some air conditioners and refrigerators use a compressed liquid with a low boiling point, su ...
of the refrigeration device condenses the water, which is removed, and then the air is reheated by the condenser coil. The now dehumidified, re-warmed air is released into the room. This process works most effectively at higher ambient temperatures with a high dew point
The dew point is the temperature to which air must be cooled to become saturated with water vapor, assuming constant air pressure and water content. When cooled below the dew point, moisture capacity is reduced and airborne water vapor will cond ...
temperature. In cold climates, the process is less effective. Highest efficiency is reached above and 45% relative humidity. This relative humidity
Humidity is the concentration of water vapor present in the air. Water vapor, the gaseous state of water, is generally invisible to the human eye. Humidity indicates the likelihood for precipitation, dew, or fog to be present.
Humidity depe ...
value is higher if the temperature of the air is lower.
This type of dehumidifier differs from a standard air conditioner in that both the evaporator and the condenser are placed in the same air path. A standard air conditioner transfers heat energy out of the room because its condenser coil releases heat outside. However, since all components of the dehumidifier are in the ''same'' room, no heat energy is removed. Instead, the electric power
Power most often refers to:
* Power (physics), meaning "rate of doing work"
** Engine power, the power put out by an engine
** Electric power
* Power (social and political), the ability to influence people or events
** Abusive power
Power may a ...
consumed by the dehumidifier remains in the room as heat, so the room is actually ''heated'', just as by an electric heater
Electric heating is a process in which electrical energy is converted directly to heat energy at around 100% efficiency, using rather cheap devices. Common applications include space heating, cooking, water heating and industrial processes. ...
that draws the same amount of power.
In addition, if water is condensed in the room, the amount of heat previously needed to evaporate that water also is re-released in the room (the latent heat of vaporization
The enthalpy of vaporization (symbol ), also known as the (latent) heat of vaporization or heat of evaporation, is the amount of energy (enthalpy) that must be added to a liquid substance to transform a quantity of that substance into a gas. T ...
). The dehumidification process is the inverse of adding water to the room with an evaporative cooler
An evaporative cooler (also known as evaporative air conditioner, swamp cooler, swamp box, desert cooler and wet air cooler) is a device that cools air through the evaporation of water. Evaporative cooling differs from other air conditioning s ...
, and instead releases heat. Therefore, an in-room dehumidifier will always warm the room and reduce the relative humidity indirectly, as well as reducing the humidity more directly, by condensing and removing water.
Warm, moist air is drawn into the unit at A in the diagram above. This air passes into a crossflow plate heat exchanger (B) where a substantial proportion of the sensible heat is transferred to a cool supply air stream. This process brings the extracted air close to saturation. The air then passes to the plenum chamber of the extract fan (C) where a portion of it may be rejected to outside. The amount that is rejected can be varied and is
determined either by legislation on fresh air requirements, or by the requirement to maintain a fresh, odour free environment. The balance of the air then passes into the evaporator coil of the heat pump where it is cooled and the moisture is condensed. This process yields substantial amounts of latent energy to the refrigeration circuit. Fresh air is then introduced to replace the amount that was extracted and the mix is discharged by the supply fan (G) to the crossflow plate exchanger (B) where it is heated by the extract air from the pool. This pre-warmed air then passes through the heat pump condenser (F) where it is heated by the latent energy removed during the condensation process as well as the energy input to the compressor. The warm dry air is then discharged to the room.
Conventional air conditioners
A conventional air conditioner
Air conditioning, often abbreviated as A/C or AC, is the process of removing heat from an enclosed space to achieve a more comfortable interior environment (sometimes referred to as 'comfort cooling') and in some cases also strictly controlling ...
is very similar to an electric dehumidifier and inherently acts as a dehumidifier when chilling the air. In an air conditioner, however, the air passes over the cold evaporator coils and then directly into the room. It is not re-heated by passing over the condenser, as in a refrigeration dehumidifier. Instead, the refrigerant is pumped by the compressor to a condenser which is located outside the room to be conditioned, and the heat is then released to the outside air. Conventional air conditioners use additional energy exhausting air outside, and new air can have more moisture than the room needs, such as a pool room that already holds a high amount of moisture in the air.
The water that condenses on the evaporator in an air conditioner is usually routed to remove extracted water from the conditioned space. Newer high-efficiency window units use the condensed water to help cool the condenser coil by evaporating the water into the outdoor air, while older units simply allowed the water to drip outside.
Spray dehumidifiers
When water is chilled below the atmospheric dew point
The dew point is the temperature to which air must be cooled to become saturated with water vapor, assuming constant air pressure and water content. When cooled below the dew point, moisture capacity is reduced and airborne water vapor will cond ...
, atmospheric water will condense onto it faster than water evaporates from it. Spray dehumidifiers mix sprays of chilled water Chilled water is a commodity often used to cool a building's air and equipment, especially in situations where many individual rooms must be controlled separately, such as a hotel. The chilled water can be supplied by a vendor, such as a public util ...
and air to capture atmospheric moisture. They also capture pollutants and contaminants like pollen, for which purpose they are sometimes called "air washers".
Makeshift dehumidifiers
Because window air conditioner units have condensers and expansion units, some of them can be used as makeshift dehumidifiers by sending their heat exhaust back into the same room as the cooled air, instead of the outside environment. If the condensate from the cooling coils is drained away from the room as it drips off the cooling coils, the result will be room air that is drier but slightly warmer.
However, many window air conditioners are designed to dispose of condensate water by re-evaporating it into the exhaust air stream, which cancels out the air humidity decrease caused by the condensation of moisture on the cooling coils. To be effective as a dehumidifier, an air conditioner must be designed or modified so that most or all of the water that condenses is drained away in liquid form, rather than re-evaporated. Even if condensate is drained, a modified air conditioner is still less efficient than a single-purpose appliance with a design optimized for dehumidification. Dehumidifiers are designed to pass air directly over the cooling coils and then the heating coils in a single efficient pass through the device.
In addition, most air conditioners are controlled by a thermostat
A thermostat is a regulating device component which senses the temperature of a physical system and performs actions so that the system's temperature is maintained near a desired setpoint.
Thermostats are used in any device or system tha ...
which senses temperature, rather than a humidistat
A humidistat or hygrostat is an electronic device analogous to a thermostat but which responds to relative humidity, not temperature. A typical humidistat is usually included with portable humidifiers or dehumidifiers. It can also be included wi ...
that senses humidity and is typically used to control a dehumidifier. A thermostat is not designed for the control of humidity, and controls it poorly if at all.
Ice buildup
Under certain conditions of temperature and humidity, ice
Ice is water frozen into a solid state, typically forming at or below temperatures of 0 degrees Celsius or Depending on the presence of impurities such as particles of soil or bubbles of air, it can appear transparent or a more or less opaq ...
can form on a refrigeration dehumidifier's evaporator coil
An evaporator is a device used to turn the liquid form of a chemical substance, such as water, into a vapor.
Uses
Air conditioning and refrigeration
Some air conditioners and refrigerators use a compressed liquid with a low boiling point, su ...
s. The ice buildup can impede airflow and eventually form a solid block encasing the coils. This buildup prevents the dehumidifier from operating effectively, and can cause water damage if condensed water drips off the accumulated ice and not into the collection tray. In extreme cases, the ice can deform or distort mechanical elements, causing permanent damage.
Better-quality dehumidifiers may have a frost or ice sensor. These will turn off the machine and allow the ice-covered coils to warm and defrost. Once defrosted, the machine usually will automatically restart. Most ice sensors are simple thermal switch
A thermal cutoff is an electrical safety device (either a thermal fuse or thermal switch) that interrupts electric current when heated to a specific temperature. These devices may be for one-time use (a thermal fuse), or may be reset manually or ...
es and do not directly sense the presence or absence of ice buildup. An alternative design senses the impeded airflow and shuts off the cooling coils in a similar manner.
Certain malfunctions of dehumidifiers, such as partial loss of refrigerant, can cause repeated icing of the coils. This condition requires repair or replacement of the equipment.
Thermoelectric dehumidifiers
Thermoelectric dehumidifiers use a Peltier heat pump to cool a surface and condense water vapor from the air. The design is simpler and has the benefit of being quieter compared to a dehumidifier with a mechanical compressor. However, because of its relatively poor Coefficient of Performance
The coefficient of performance or COP (sometimes CP or CoP) of a heat pump, refrigerator or air conditioning system is a ratio of useful heating or cooling provided to work (energy) required. Higher COPs equate to higher efficiency, lower energy ( ...
, this design is mainly used for small dehumidifiers. Ice buildup may be a problem, similar to problems with refrigeration dehumidifiers.
Absorption/desiccant dehumidification
This process uses a special humidity-absorbing material called a desiccant
A desiccant is a hygroscopic substance that is used to induce or sustain a state of dryness (desiccation) in its vicinity; it is the opposite of a humectant. Commonly encountered pre-packaged desiccants are solids that absorb water. Desiccant ...
, which is exposed to the air to be conditioned. The humidity-saturated material is then moved to a different location, where it is "recharged" to drive off the humidity, typically by heating it. The desiccant can be mounted on a belt or other means of transporting it during a cycle of operation.
Dehumidifiers which work according to the absorption principle are especially suited for high humidity levels at low temperatures. They are often used in various sectors in industry so that humidity levels below 35% can be achieved.
Because of the lack of compressor parts, desiccant dehumidifiers are often lighter and quieter than compressor dehumidifiers. Desiccant dehumidifiers can also operate at lower temperatures than compressor dehumidifiers as the unit does not rely on cooled coils for which the moisture condensing efficiency decreases at lower temperatures.
The reason for the limited acceptance of desiccant dehumidification can be attributed to initial installation costs, the fact that operational benefits are not fully understood, lack of technology awareness, and company priorities, which are not focused on benefits of new technology.
Membrane dehumidification
Several approaches can remove water vapor by flowing air past a membrane that allows vapor to enter. Dehumidification with membranes can allow for water vapor removal without condensation; this avoids the energy required with the enthalpy of vaporization, offering high efficiency for well-designed systems. Such dehumidification can be done passively with a reject air stream; see Energy recovery ventilation
Energy recovery ventilation (ERV) is the energy recovery process in residential and commercial HVAC systems that exchanges the energy contained in normally exhausted air of a building or conditioned space, using it to treat (precondition) the inc ...
. Active systems can use pressure gradients or electrocatalytic approaches.
Selective membrane dehumidification
Selective membranes use materials that block other ambient gases besides water vapor. Water vapor will then diffuse through these membranes under a concentration difference. Such a difference in concentration (partial pressure) can be caused by vacuum pumping, or simply passing by an airstream with a lower concentration of water. The most efficient configurations save energy by using two membranes that isolate a vacuum pump from ambient air. This dramatically reduces the pressure across the vacuum pump, saving energy. While such systems are often termed "Isothermal Membrane Dehumidification," recent research has show that these systems can be made more efficient by combining them with heat exchange. Such integration can improve performance by improving the vapor compression cycle's COP (by operating between closer temperatures), and enhancing air mixing near the membrane.
Selective membranes can be made by immobilizing a liquid that that can absorb water (or another solute) within a membranes, dubbed "supported liquid membranes". Typically, there are two layer types; a highly porous membrane that contains the absorbing liquid, and a trapping layer that prevents the liquid from escaping. This liquid absorbing layer allows them to behave like selective membranes, without having a solid selective materials or very small pores. The liquids within which absorbs water well (hygroscopic
Hygroscopy is the phenomenon of attracting and holding water molecules via either absorption or adsorption from the surrounding environment, which is usually at normal or room temperature. If water molecules become suspended among the substance ...
) may include glycol
A diol is a chemical compound containing two hydroxyl groups ( groups). An Aliphatic compound, aliphatic diol is also called a glycol. This pairing of functional groups is pervasive, and many subcategories have been identified.
The most common ...
mixtures or ionic liquids.
Ionic membrane dehumidification
An ionic membrane can be used to move humidity into or out of a sealed enclosure, using chemical reactions rather than condensation or selective materials. These systems use electrodes and proton-conducting membranes to remove water vapor by electrolysis
In chemistry and manufacturing, electrolysis is a technique that uses direct electric current (DC) to drive an otherwise non-spontaneous chemical reaction. Electrolysis is commercially important as a stage in the separation of elements from n ...
. At the anode, H2O is split into protons, O2, and electrons, where the protons travel through a material and react with ambient oxygen on the other side to create water again.
Perhaps the first materials for such electrolysis-based dehumidification were solid polymer electrolyte (SPE) membranes. This approach provides a low power, steady-state dehumidifier for enclosed areas where long-term maintenance is difficult. This electrolytic process delivers dehumidifying capacities ranging from 0.2 grams/day from a 0.2 m³ (7 cu ft) space to 58 grams/day from an 8m³ (280 cu ft). SPE systems generally do not have high dehydration capacities, but because the water vapor is removed through electrolysis, the process is maintenance-free. The process also uses very little electrical energy to operate, requiring no moving parts, making the ionic membranes silent in operation and very reliable over long periods of time. SPE dehumidifiers are typically used to protect sensitive electrical components, medical equipment, museum specimens, or scientific apparatus from humid environments.
The SPE consists of a proton-conductive solid polymer electrolyte and porous electrodes with a catalytic layer composed of noble metal particles. When a voltage is applied to the porous electrode attached to the membrane, the moisture on the anode
An anode is an electrode of a polarized electrical device through which conventional current enters the device. This contrasts with a cathode, an electrode of the device through which conventional current leaves the device. A common mnemonic is ...
side (dehumidifying side) dissociates into hydrogen ions (H+) and oxygen. The hydrogen ions migrate through membrane to be discharged on the cathode (moisture discharging) side where they react with oxygen in the air, resulting in water molecules (vapor), being discharged. Oxygen is released from the dehumidifying side, and if a large amount of water has been introduced to an airtight enclosure then oxygen can build up inside the enclosure.
Condensate
Not all dehumidifiers collect condensate; for example, many desiccant types discharge an airflow from the heated desiccant which contains water-saturated air. This can either be recondensed and collected as condensate, or expelled outside. Also, some air conditioner types spray any collected condensate onto the exterior condenser coils to cool it by evaporation, improving overall efficiency.
Disposal
Products using condensation technology have traditionally used a cold surface where humidity in warm air is condensed. Today, warm condensation technology, based on the concept of over-saturated steam inside a closed environment, makes it possible to dehumidify air at sub-zero temperatures. This is a very energy-efficient technology and equally efficient in all temperatures.
Most portable dehumidifiers are equipped with a condensate collection receptacle, typically with a float sensor that detects when the collection vessel is full, to shut off the dehumidifier and prevent an overflow of collected water. In a warm humid environment, these buckets will generally fill with water in 8–12 hours, and may need to be manually emptied and replaced several times per day to ensure continued operation.
Many portable dehumidifiers can also be adapted to connect the condensate drip output directly to a drain via a hose. Some dehumidifier models can tie into plumbing drains or use a built-in water pump to empty themselves as they collect moisture. Alternatively, a separate condensate pump A condensate pump is a specific type of pump used to pump the condensate (water) produced in an HVAC (heating or cooling), refrigeration, condensing boiler furnace, or steam system.
Applications
Condensate pumps may be used to pump the condensate ...
may be used to move collected water to a disposal location, when gravity drainage is not possible.
Central air conditioning
Air conditioning, often abbreviated as A/C or AC, is the process of removing heat from an enclosed space to achieve a more comfortable interior environment (sometimes referred to as 'comfort cooling') and in some cases also strictly controlling ...
units typically need to be connected to a drain, because frequent manual emptying of multiple containers of condensate water extracted by such systems is impractical. If the condensate water is directed into the sewer system, it should be suitably trapped to prevent septic odors and sewer gases from entering the building. The condensate should not be directed into a septic system
Onsite sewage facilities (OSSF), also called septic systems, are wastewater systems designed to treat and dispose of effluent on the same property that produces the wastewater, in areas not served by public sewage infrastructure.
A septic tank a ...
of a house, because it does not need special treatment as effluent
Effluent is wastewater from sewers or industrial outfalls that flows directly into surface waters either untreated or after being treated at a facility. The term has slightly different meanings in certain contexts, and may contain various pollut ...
. When the height of the air handler
An air handler, or air handling unit (often abbreviated to AHU), is a device used to regulate and circulate air as part of a heating, ventilating, and air-conditioning (HVAC) system. An air handler is usually a large metal box containing a blowe ...
(containing the evaporator) is above the level of the surface drains used for rainwater, the condensate drain lines can often be routed into them. Air handlers located below grade level, e.g. the basement of a house, may need to use a condensate pump to lift the water to a surface drain.
Potability
Generally, dehumidifier water is considered a rather clean kind of greywater
Greywater (or grey water, sullage, also spelled gray water in the United States) refers to domestic wastewater generated in households or office buildings from streams without fecal contamination, i.e., all streams except for the wastewater from ...
: not suitable for drinking, but acceptable for watering plants, though not garden vegetables. The health concerns are:
*The water contains trace metals from the heat exchanger, such as copper
Copper is a chemical element with the symbol Cu (from la, cuprum) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkis ...
and aluminum
Aluminium (aluminum in American and Canadian English) is a chemical element with the symbol Al and atomic number 13. Aluminium has a density lower than those of other common metals, at approximately one third that of steel. It has ...
, or zinc
Zinc is a chemical element with the symbol Zn and atomic number 30. Zinc is a slightly brittle metal at room temperature and has a shiny-greyish appearance when oxidation is removed. It is the first element in group 12 (IIB) of the periodi ...
from galvanized steel supporting the frame and drain pan. Condensate would only be exposed to tin-lead solder
Solder (; NA: ) is a fusible metal alloy used to create a permanent bond between metal workpieces. Solder is melted in order to wet the parts of the joint, where it adheres to and connects the pieces after cooling. Metals or alloys suitable ...
in copper drain pipe, but the lead
Lead is a chemical element with the symbol Pb (from the Latin ) and atomic number 82. It is a heavy metal that is denser than most common materials. Lead is soft and malleable, and also has a relatively low melting point. When freshly cu ...
content is particularly dangerous. Trace metals may pose a danger if used on edible plants, as they can bioaccumulate
Bioaccumulation is the gradual accumulation of substances, such as pesticides or other chemicals, in an organism. Bioaccumulation occurs when an organism absorbs a substance at a rate faster than that at which the substance is lost or eliminated ...
. However, the water is considered usable for irrigation
Irrigation (also referred to as watering) is the practice of applying controlled amounts of water to land to help grow Crop, crops, Landscape plant, landscape plants, and Lawn, lawns. Irrigation has been a key aspect of agriculture for over 5,00 ...
of ornamental plants and lawns.
*Various pathogen
In biology, a pathogen ( el, πάθος, "suffering", "passion" and , "producer of") in the oldest and broadest sense, is any organism or agent that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a germ ...
s, including fungal spores, may accumulate in the water, particularly due to its stagnancy. Unlike in distilled water
Distilled water is water that has been boiled into vapor and condensed back into liquid in a separate container. Impurities in the original water that do not boil below or near the boiling point of water remain in the original container. Thus, di ...
production, the water is not boiled, which would kill pathogens (including bacteria).
*As with distilled water, beneficial minerals are largely absent.
Food-grade dehumidifiers, also called atmospheric water generator
An atmospheric water generator (AWG), is a device that extracts water from humid ambient air, producing potable water. Water vapor in the air can be extracted by multiple techniques, including condensation - cooling the air below its dew point, ex ...
s, are specifically designed to avoid toxic metal contamination and to keep all water contact surfaces clean. The devices are primarily intended to produce pure water, and the dehumidifying effect is viewed as secondary to their operation.
Maintenance
If condensate water is handled automatically, most dehumidifiers require very little maintenance. Because of the volume of airflow through the appliance, dust buildup needs to be removed so it does not impede airflow; many designs feature removable and washable air filters. Condensate collection trays and containers may need occasional cleaning to remove debris buildup and prevent clogging of drainage passages, which can cause water leakage and overflow; if large amounts of certain particulates or dust are collected, then this may need to be performed frequently to avoid microbial growth.
Applications
Relative humidity in dwellings should preferably range from 30% to 50%.
Homes and offices
Dehumidification within buildings can control:
*excessive body perspiration buildup that cannot evaporate in moisture-saturated air
*condensation dripping from cold-water pipes
*warping and sticking of furniture and doors
*mold
A mold () or mould () is one of the structures certain fungus, fungi can form. The dust-like, colored appearance of molds is due to the formation of Spore#Fungi, spores containing Secondary metabolite#Fungal secondary metabolites, fungal seco ...
and mildew
Mildew is a form of fungus. It is distinguished from its closely related counterpart, mould, largely by its colour: moulds appear in shades of black, blue, red, and green, whereas mildew is white. It appears as a thin, superficial growth consi ...
, which can cause fabrics, books, and furnishings to develop mustiness
* clothes moths, flea
Flea, the common name for the order Siphonaptera, includes 2,500 species of small flightless insects that live as external parasites of mammals and birds. Fleas live by ingesting the blood of their hosts. Adult fleas grow to about long, a ...
s, cockroach
Cockroaches (or roaches) are a paraphyletic group of insects belonging to Blattodea, containing all members of the group except termites. About 30 cockroach species out of 4,600 are associated with human habitats. Some species are well-known as ...
es, woodlice
A woodlouse (plural woodlice) is an isopod crustacean from the polyphyleticThe current consensus is that Oniscidea is actually triphyletic suborder Oniscidea within the order Isopoda. They get their name from often being found in old wood. ...
, millipede
Millipedes are a group of arthropods that are characterised by having two pairs of jointed legs on most body segments; they are known scientifically as the class Diplopoda, the name derived from this feature. Each double-legged segment is a resu ...
s, and dust mites
House dust mites (HDM, or simply dust mites) are various species of acariform mites belonging to the family Pyroglyphidae that are found in association with dust in dwellings. They are known for causing allergies.
Biology
Species
The current ...
, which thrive in damp conditions (basements, crawl spaces, kitchens, bedrooms, bathrooms, spas or indoor pool areas, warehouses, workshops)
Construction
Dehumidifiers are also used in construction areas and renovations of indoor space to remove excess humidity or mildew.
Industrial processes
Dehumidifiers are used in industrial climatic chambers, to reduce relative humidity and the dew point in many industrial applications from waste and fresh water treatment plants to indoor grow rooms where the control of moisture is essential.
Some industries include:
*Printing
Printing is a process for mass reproducing text and images using a master form or template. The earliest non-paper products involving printing include cylinder seals and objects such as the Cyrus Cylinder and the Cylinders of Nabonidus. The ea ...
*Grinding and machining
Machining is a process in which a material (often metal) is cut to a desired final shape and size by a controlled material-removal process. The processes that have this common theme are collectively called subtractive manufacturing, which utilizes ...
*Food packaging
Food packaging is a packaging system specifically designed for food and represents one of the most important aspects among the processes involved in the food industry, as it provides protection from chemical, biological and physical alterations ...
and processing
*Lithium-ion battery
A lithium-ion or Li-ion battery is a type of rechargeable battery which uses the reversible reduction of lithium ions to store energy. It is the predominant battery type used in portable consumer electronics and electric vehicles. It also se ...
production
*Equipment room
* Cold storage room
*Museum and Archive room
Market size
According to a 2015 estimate, the projected annual global total addressable market
Total addressable market (TAM), also called total available market, is a term that is typically used to reference the revenue opportunity available for a product or service. TAM helps prioritize business opportunities by serving as a quick metr ...
of dehumidifiers was about $3.5 billion by 2022. This includes various types and applications, encompassing different applications such as household and industrial and different technologies such as ventilating and desiccant.
See also
*Air ionizer
An air ioniser (or negative ion generator or Chizhevsky's chandelier) is a device that uses high voltage to ionise (electrically charge) air molecules. Negative ions, or anions, are particles with one or more extra electrons, conferring a net ne ...
, a different device for conditioning air
*Atmospheric water generator
An atmospheric water generator (AWG), is a device that extracts water from humid ambient air, producing potable water. Water vapor in the air can be extracted by multiple techniques, including condensation - cooling the air below its dew point, ex ...
, a machine that extracts pure drinking water from air
*Food dehydrator Tomato slices ready to be dried in a convection-type food dehydrator. In this model, multiple trays can be stacked on top of each other and warm air flows around the food.
A food dehydrator is a device that removes moisture from food to aid in its ...
, device for decreasing moisture in food, to prevent spoilage
*Humidifier
A humidifier is a device, primarily an electrical appliance, that increases humidity (moisture) in a single room or an entire building. In the home, point-of-use humidifiers are commonly used to humidify a single room, while whole-house or furnac ...
, an appliance that increases the humidity of air
*Thermoelectric cooling
Thermoelectric cooling uses the Peltier effect to create a heat flux at the junction of two different types of materials. A Peltier cooler, heater, or thermoelectric heat pump is a solid-state active heat pump which transfers heat from one side o ...
*Cromer cycle
The Cromer cycle is a thermodynamic cycle that uses a desiccant to interact with higher relative humidity air leaving a cold surface. When a system is taken through a series of different states and finally returned to its initial state, a thermodyn ...
, a cycle that combines a desiccant with air conditioner as dehumidifier
References
Further reading
Energy Star Qualified Dehumidifiers
table listing removal rates and efficiencies. Long Island Power Authority, January 2011.
AHAM Dehumidifier Product Certification Program
Association of Home Appliance Manufacturers
The Association of Home Appliance Manufacturers or AHAM represents the manufacturers of household appliances and products/services associated with household appliances sold in the United States. AHAM also develops and maintains technical standards ...
.
{{Home appliances
Heating, ventilation, and air conditioning
20th-century inventions
American inventions
Cooling technology
Home appliances