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PRINCIPLES OF OPERATION
The Steam Humidifier delivers humidity in the form of
steam to the conditioned space via the HVAC system
duct . The humidifier generates steam by energizing two
electrodes that extend into a canister of water . Current
flowing between the electrodes causes the water to boil,
creating steam . Water is introduced to the humidifier
through a fill valve to a fill cup located in the top of the
cabinet . The fill cup serves as an overflow reservoir and
provides an air gap between the humidifier and water
source . The steam canister is filled from the bottom . The
canister is seated in a drain cup assembly which includes
a drain valve . The drain and fill valves work together to
maintain water level in the canister to deliver the rated
steam capacity based on the electrical conductivity of
the water and to temper drain water . See Figure 1 for
representation of fill and drain system and canister .
Steam is delivered into the airstream through a dispersion
tube mounted in the HVAC system ductwork . Openings
in the dispersion tube are fitted with "Tubelets
extend into the center of the tube . The design of the
dispersion tube and tubelets distribute steam over a wide
area in the duct and direct any condensed moisture back
into the steam hose .
WATER QUALITY
Minerals that are naturally found in water cause the water to be electrically conductive . Water conductivity is measured in micro Siemens per
centimeter (uS/cm) . Mineral content, also described as "water hardness" is usually measured in grains per gallon . Because of the variety of
minerals that are found in water, there is no direct correlation between water hardness and conductivity, but generally the higher the mineral
content, the higher the conductivity .
The Steam Humidifier is designed to operate on water with conductivity between 125 and 1,250 uS/cm . This correlates loosely with water with
hardness between 3 and 36 grains/gallon . Water that is considered "hard" and also softened water work well in the humidifier . The humidifier
will make steam when plumbed to low-conductivity water but it takes longer to reach nominal capacity .
With low conductivity water, it may take the humidifier one week or more of operation to reach rated capacity, especially if it is
wired to operate on 120 volts. When operating on 208/240 volts, the humidifier usually will reach nominal capacity within a few
hours, even with lower conductivity water.
As water in the canister boils and turns into steam, minerals are left behind . Minerals remaining in solution increase the conductivity of the
water . Minerals also deposit onto the submerged portions of the electrodes rendering those areas ineffective . As this occurs, the level of water
in the canister rises to expose uncoated electrode surface .
There are benefits and trade-offs to consider when the application allows a choice between hard and softened water:
Hard water: The benefit of hard water is less frequent draining and filling than with soft water, which results in better energy and water
efficiency and more consistent steam output . However, canister replacement could be more frequent with hard water, because mineral deposits
coat the electrodes . The harder the water, the more frequent the need for a new canister .
Softened water: The benefit of softened water is longer canister life (depending on water chemistry) than with hard water, because softened
water does not coat the electrodes nearly as much as hard water . However, softened water ions stay in solution to much higher concentrations
than hard water ions . This requires more frequent draining and filling, which results in lower energy efficiency, higher water consumption and
less consistent steam output .
FIGURE 1 – Fill and Drain System and Canister
Overflow
Inlet
Fill Valve
" which
™
Supply
Water
Steam Hose
Steam
Outlet
High Water Level Sensor
Electrodes
Canister
Fill
Drain Valve
Drain Cup
Drain
Tubelets
Dispersion Tube
in Duct
90-1522
3
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