Aprilaire 700M Reference Manual page 22

WHAT YOU NEED TO KNOW ABOUT THE
APRILAIRE STEAM HUMIDIFIER
Capacity
The Aprilaire Model 800 will produce up to 23
gallons per day (gpd) of steam. The unit will
increase capacity as the voltage increases.
The unit requires an electrical draw 11.5 amps ± 10%, use 12.7 amps when sizing circuit and it's recommended the unit
be installed at 240v to achieve maximum capacity. The humidifier control will monitor the humidity levels and not allow
excess humidity into the residence.
Sequence of Operation
The model 800 Aprilaire steam 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 into 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 (backflow prevention) 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 water level in the canister is determined by the unit's control
board. The unit will raise or lower the water level based upon its
conductivity, striving to reach and maintain 11.5 amps.
When the unit drains water it will automatically temper the water by
mixing the water from the canister with incoming water. This eliminates
the need for high temperature drain tubing and pumps. The drain and
fill valves work together to maintain water level in the canister to deliver
the rated steam capacity.
Dispersion Technology
After the water is boiled and steam is produced the technology utilized to disperse the steam into the air stream is
critical to avoid application problems associated with rusting ducts. Aprilaire in partnership with Dri-Steem, both part
of the Research Product Corporation family of companies, offers superior dispersion technology.
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" which 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.
Many resistive residential steam humidifiers simply place the tank that
contains the boiling water directly in the air stream inside the duct of an
HVAC system. When the HVAC blower turns off the tank of water is still hot
potentially leading to condensation on the ducts. The optimal way to disperse
steam into the air stream is to use a properly designed dispersion tube.
The preferred location for the dispersion tube is in the supply duct because higher temperatures will more readily absorb
the moisture. Whether installed in a supply or return, the dispersion tube must be in a straight section of duct to avoid turbulent
airflow and be far enough upstream of any obstructions or bends in the duct to allow the steam to be fully absorbed.
Maximum
Voltage kW
Steam (gpd)
120v 1.4 11.5
208v 2.4 20.5
240v 2.8 23.3
Flow Control
Orifice
Fill
Inlet
Fill Valve
Supply
Water
Current draw
(amps)
11.5
11.5
11.5
Steam
Outlet
Overflow
High Water
Level Sensor
Electrodes
Canister
Drain Valve
Drain Cup
Drain
Tubelet