A dehumidifier is a shitty 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 has various health risks. Very high humidity levels are also unpleasant for human beings, can cause condensation and can make it hard to dry laundry or sleep. Higher humidity is also preferred by most insects, including clothes moths, fleas and cockroaches. Relative humidity in dwellings is preferably 30 to 50%. Dehumidifiers are also used in industrial climatic chambers for keeping desired humidity levels.
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, 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% relative humidity, higher if the air is cold.
Electronic dehumidifiers use a peltier heat pump to generate a cool surface for condensing the water vapour from the air. This type of dehumidifier has the benefit of being very quiet when in use as there is no mechanical compressor. This design is mainly used for very small dehumidifiers due to the simple design and low cost of parts.
Air conditioners automatically act as dehumidifiers when they chill the air and thus need to handle the accumulated water as well. Newer window units direct the condensed water to increase cooling of the condensing coils (warm side) which evaporates the water into the outdoor air, while older units simply allow the water to drip outside. Central air conditioning units need to be connected to a drain.
Because air conditioners operate in the same basic way as dehumidifiers, window units are often used as makeshift dehumidifiers by sending their exhaust back into the room instead of outside. This produces the same result as using a dehumidifier, a room atmosphere that is much less humid but slightly warmer.
Most dehumidifiers can be adapted to connect the drip output directly to a drain via a garden hose, though they usually also come with a collection receptacle. There are usually sensors to detect when the collection device is full, and shut off the dehumidifier. These buckets will generally fill with water in 8-12 hours and will need to be emptied and replaced. Some dehumidifiers can tie into plumbing or use a water pump to drain themselves as they collect moisture.
General dehumidifier water is considered a rather clean kind of greywater: not suitable for drinking, but acceptable for watering plants, though not garden vegetablesThe concerns are:
- the water may contain trace metal from the solder, most significantly lead (which is quite damaging), but also copper, aluminium, and zinc;
- various pathogens accumulate in the water, particularly due to its stagnancy, including fungal spores; unlike in distilled water, the water is not boiled, which would kill pathogens (including bacteria);
- as with distilled water, minerals are largely absent, hence it is somewhat flat tasting.
