PRINCIPLES & SEQUENCE OF OPERATION
The Aprilaire® Steam Humidifier delivers humidity in the
form of steam to the conditioned space via the HVAC
system duct or the Fan Pack. 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.
To control the Steam Humidifier as part of the HVAC
system, the Model 62 Automatic Digital Humidifier Control
(ADHC) is installed to detect the RH level in the duct.
When the ADHC detects RH below the set point, and the
humidifier and HVAC system blower are operating, the
humidifier energizes the electrodes to provide steam.
Steam is delivered into the duct work via the steam hose
and through the dispersion tube. The dispersion tube
is fitted with “Tubelets™.” 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. The blower activation function on the ADHC allows the control to turn on the HVAC system blower to maintain the
proper RH level even when the furnace or air handler is in stand-by mode. See ADHC installation manual.
Humidity can be distributed directly into the living space via the Fan Pack. When the Model 65 Manual Digital Humidistat detects RH below the set
point, the humidifier energizes the electrodes to provide steam via the steam manifold at the bottom of the Fan Pack. Steam is dispersed by the fan
located behind the grille above the steam manifold. The fan will operate for two minutes after the call for humidity ends, to disperse any residual steam.
To provide precise control to the Modulating Steam
Humidifier, the Automatic Digital Modulating Control
(ADMC) should be installed in the living space. The ADMC
will vary the Modulating Steam Humidifier output based
on the difference between set point and actual RH. The
ADMC sends a proportional signal to the Modulating
Steam Humidifier providing precise control of living space
humidity. See FIGURE 2 for Steam Humidifier output vs
RH demand. The ADMC can be used in place of the ADHC
and Manual Digital Humidistat to provide On/Off control to
the Steam Humidifier not equipped with the modulating
feature. See the ADMC installation and operating manual
for details.
STEAM HOSE
DISPERSION
TUBE
IN DUCT
STEAM
OUTLET
DRAIN
SUPPLY
DRAIN CUP
DRAIN VALVE
CANISTER
ELECTRODES
HIGH WATER LEVEL SENSOR
OVERFLOW
FILL
-2% -5% -10%
20%
100%
HUMIDIFIER OFF
PROPORTIONAL BAND
RH DIFFERENCE FROM SETPOINT (%)
HUMIDIFIER OUTPUT (%)
2% PROPORTIONAL BAND SETTING
5% PROPORTIONAL BAND SETTING (DEFAULT)
10% PROPORTIONAL BAND SETTING
90-1522
90-2008
FIGURE 1 – FILL AND DRAIN SYSTEM AND CANISTER
FIGURE 2 – HUMIDIFIER OUTPUT FOR ADMC SIGNAL
4 English
