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PRODUCT OVERVIEW
Aprilaire Steam Humidifiers create steam by boiling water inside a steam chamber. This is accomplished by the transfer of energy
from electric heating elements to the water inside the chamber. A three-level water probe is used to determine when to turn on
and off a water fill valve in order to bring water into the chamber. Once the chamber is full and there is a call for humidity from
the Automatic Steam Humidifier Control, the heating elements will be energized causing the water to boil. The boiling water
creates steam which, due to the moderate pressurization of the chamber that comes from boiling, is forced through the vapor
hose and steam distribution tube into the duct system. As water is boiled off, the water level in the steam chamber will drop. The
water probe will sense when it reaches a low point and will cause the fill valve to open.
The process of boiling the water in the steam chamber will cause minerals and impurities in the water to drop out. Depending
on the hardness and quality of the water, this can create a substantial build-up within the steam chamber. The unit will drain the
chamber periodically to help clean the steam chamber and reduce the amount of cleaning required during maintenance.
Aprilaire Steam Humidifiers are controlled by an Automatic Steam Humidifier Control mounted in the return duct that will sense
the relative humidity (RH) in the return air. If the return air is below the RH setpoint, the control will send the humidifier a signal
to begin producing steam. Once this happens, the airflow proving switch (included) will check to ensure that the equipment
blower is operating. If the blower is not operating, the humidifier will send the equipment a signal to turn the fan on.
• The Aprilaire Steam Humidifier Model 1150, 12 lb/hr unit, features an Automatic Steam Humidifier Control with on/off control.
The on/off control will send a 10 VDC signal to the humidifier when the measured return air RH is 3% or more below setpoint
to turn the unit on at 100% output.
• The Aprilaire Steam Humidifier Model 1160, 24 lb/hr unit, features an Automatic Steam Humidifier Control with modulating
control. This control sends a signal between 0 and 10 VDC that is proportional to the difference between setpoint RH and
the measured return air RH. The signal for 100% humidifier output is 10 VDC and occurs at a control point that is adjustable.
The signal for 50% output is 5 VDC and occurs at the setpoint. The adjustable RH proportional control band can be set on the
board to 6%, 9%, 12% (default), or 15%. The humidifier uses this varying signal to time-proportion the operation of the heating
elements in the chamber.
The Automatic Steam Humidifier Control features an outdoor temperature sensor and is equipped to provide RH setpoint
compensation based on the actual outdoor temperature. When the weather gets colder outside, there can be problems with
condensation when introducing humidity into the building. The control recognizes this and adjusts the setpoint in the building to
a lower level. The control will still provide humidity to the building, but will not attempt to maintain a humidity level higher than
is appropriate for the current outdoor temperature. For applications that require specific set-point control, regardless of outdoor
temperature, the Control can be set up for manual operation. In Manual Mode, the outdoor temperature sensor is not used and
the RH is controlled to the specific setting on the Control.
MATERIALS PROVIDED MATERIALS NOT PROVIDED
1 Humidifier (Model 1150: 1 heater, 12 lbs/hr; Model 1160: 2 heater, 24 lbs/hr)
1 Distribution Tube (Model 1150: 10” active, 14” overall; Model 1160: 16” active, 20” overall)
1 10 ft. Steam Hose, 1
½” I.D.
1 1 ft. Drain Hose, 1” I.D.
2 Hose Clamps (for Steam Hose), 1
½” I.D.
2 Hose Clamps (for Drain Hose), 1” I.D.
2 Face Plates for Mounting Distribution Tube (1 set)
2 3/8” x 2” Lag Bolts for Mounting Humidifier
1 Automatic Steam Humidifier Control
1 Airflow Proving Switch
1 Installation, Operation, and Maintenance Manual
Electrical Supplies – quick disconnect box,
conduit, and wire (for power to the unit
and wiring to control devices)
Plumbing Supplies – supply and drain
piping, fittings, etc.
High Humidity Limit Switch
Hanging Brackets
(for mounting humidifier from ceiling)
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