TYPES OF HUMIDIFIERS
The plenum-mount humidifier is mounted in the supply plenum or the return air plenum. The furnace fan forces air through the media where it picks up moisture. The air and moisture are then distributed throughout the conditioned space . The under-duct humidifier is mounted on the underside of the supply duct so that the media is extending into the air flow where moisture is picked up in the air stream.
Atomizing humidifiers discharge tiny water droplets (mist) into the air, which evaporate very rapidly into the duct air stream or directly into the conditioned space. These humidifiers can be spray-nozzle or centrifugal types, but they should not be used with hard water because it contains minerals (lime, iron etc) that leave the water vapor as dust and will be distributed throughout the house or building. Eight to ten grains of water hardness is the maximum recommended for atomizing humidifiers.
The spray nozzle type sprays water through a metered bore of a nozzle into the duct air stream where it is distributed to the occupied space. Another type sprays the water onto an evaporative media where it is absorbed by the air stream as a vapor. They can be mounted in the plenum, under the duct or on the side of the duct.
The self-contained humidifiers may use the evaporative, atomizing or infrared processes. These units may include an electric heating device to heat the water or the water may be distributed over an evaporative media. A fan must be incorporated in the unit to distribute the moisture throughout the room or area.
Humidifiers are available in several designs with various kinds of media. A type using disc screens are mounted on a rotating shaft, causing the slanted discs to pick up moisture from the reservoir. The moisture is then evaporated into the moving air stream. The discs are separated to prevent electrolysis, which causes
the minerals in the water to form on the media. The wobble from the discs mounted at an angle washes the minerals off and into the reservoir. The minerals then can be drained from the bottom of the reservoir.