Residential Humidifiers for Central Air Systems : Residential humidifiers designed for central air systems depend on airflow in the heating system for evaporation and distribution.
Pan Humidifiers :
A Pan Steam Humidifier uses a heating element inside a water tank. The tank is mounted at the bottom of the air duct. The air flowing over the water surface will cause some evaporative cooling which results in drop of air dry-bulb temperature.
Basic pan. A shallow pan is installed within the furnace plenum. Household water is supplied to the pan through a control device.
Electrically heated pan. Similar to the basic unit, this type adds an electric heater to increase water temperature and evaporation rate.
Pan with wicking plates. Similar to the basic unit, this type includes fitted water-absorbent plates
Wetted Element Humidifiers :
Air circulates over or through an open textured, wetted medium. The evaporating surface may be a fixed pad wetted by either sprays or water flowing by gravity, or a paddle wheel,drum, or belt rotating through a water reservoir
Fan type. A small fan or blower draws air from the furnace plenum,through the wetted pad, and back to the plenum.
Bypass type. These units do not have their own fan, but rather are mounted on the supply or return plenum of the furnace with an air connection to the return plenum
Duct-mounted type. These units are designed for installation within the furnace plenum or ductwork with a drum element rotated by either the air movement in the duct or a small electric motor.
Atomizing Humidifiers :
The ability of the air to absorb moisture depends on the temperature,flow rate, and moisture content of the air moving through the system. Small particles of water are formed and introduced into the airstream in one of the following ways:
A spinning disk or cone throws a water stream centrifugally to the rim of the disk and onto deflector plates or a comb, where it is turned into a fine fog (Figure 3E).
Spray nozzles rely on water pressure to produce a fine spray.
Spray nozzles use compressed air to create a fine mist.
Ultrasonic vibrations are used as the atomizing force.