The Aprilaire
®
Steam Humidifier delivers humidity in the
form of steam to the conditioned space via the HVAC
system duct or 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 opening called “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 .
PRInCIPleS & SeqUenCe of oPeRaTIon
fIGURe 1 – fill and Drain System and Canister
Steam Hose
Dispersion Tube
in Duct
Tubelets
Steam
Outlet
Drain
Supply
Water
Drain Cup
Drain Valve
Canister
Electrodes
High Water Level Sensor
Inlet
Fill Valve
Overflow
Fill
90-1522
-2%
-5%
-10%
20%
100%
HUMIDIFIER OFF
PROPORTIONAL BAND
RH DIFFERENCE FROM SETPOINT (%)
HUMIDIFIER OUTPUT (%)
2% PROPORTIONAL BAND SETTING
5% PROPORTIONAL BAND SETTING (DEF
AUL
T)
10% PROPORTIONAL BAND SETTING
fIGURe 2 – Humidifier output for aDMC Signal
90-2008
4
