A dehumidifier is an air conditioning device which reduces and maintains the level of humidity in the air. This is done usually for health or thermal comfort reasons, or to eliminate musty odor and to prevent the growth of mildew 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 rinks and swimming pools, 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 to collect water known as condensate, which is normally considered to be greywater but may at times be reused for industrial purposes. Some manufacturers offer reverse osmosis filters to turn the condensate into potable water. Desiccant dehumidifiers (known also as absorption dehumidifiers) bond moisture with hydrophilic materials such as silica gel. 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 of dehumidifiers can vary widely. History The first dehumidifier was created by American inventor Willis Carrier in 1902 to dehumidify a Brooklyn 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 of water decreases with decreasing temperature, the water in the air condenses 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 evaporator with a fan. There are 3 main types of evaporators. They are coiled tube, fin and tube, and microchannel technology. The cold evaporator coil