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How do Dehumidifiers work?

A dehumidifier is typically a household appliance that reduces the level of humidity in the air, usually for health reasons. Humid air can cause mold and mildew to grow inside homes, which pose various health risks. Very humid climates or air make some people extremely uncomfortable, causing excessive sweating that can't evaporate in the already-moisture-saturated air. It can also cause condensation that can disrupt sleeping, or prevent laundry from drying thoroughly enough to prevent mustiness.

The first step to dehumidifying air is through the fan. The fan on a dehumidifier draws warm air from the room in. The constant pulling of warm air into the dehumidifier allows for the moisture in the room to be collected efficiently. The warm air then passes over the cold coil.

The cold coil is essentially the same concept as an air conditioner to cool the air. The ability for air to hold moisture is lost when the air is cooled. When the warm air touches the cold coils, the water in the air condenses and forms on the coils. The water then falls into a collection bucket. This is the same concept when you leave a glass of ice water outside on a hot humid day. The cold glass collects the moisture from the warm air onto the glass surface.

Finally, the cooled air runs across the hot coils, bringing the air back to room temperature. This is the differentiating aspect between an air conditioner and dehumidifier. A dehumidifier is not meant to change the temperature of the air in the room, only to remove the moisture.

Mechanical/refrigerative - dehumidifiers, the most common type, usually work by drawing moist air over a refrigerated coil with a small fan. Since the saturation vapor pressure of water decreases with decreasing temperature, the water in the air condenses on the evaporator coils, and drips into a collecting bucket. The air is then reheated by the warmer side of the refrigeration coil. This process works most effectively with higher ambient temperatures with a high dew point temperature. In cold climates, the process is less effective. They are most effective at over 45 percent relative humidity, higher if the air is cold.

Absoption/desiccant - This basic dehumidification process uses a special humidity-absorbing material called a 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 is usually mounted on a belt or other means of transporting it during a cycle of operation.

Electronic - dehumidifiers use a Peltier heat pump to generate a cool surface for condensing the water vapor from the air. The design is simpler as there are no moving parts, and has the benefit of being very quiet compared to a dehumidifier with a mechanical compressor. However, because of its relatively poor Coefficient of Performance (energy efficiency), this design is mainly used for small dehumidifiers.

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