Humidifiers
www.carnes.com
G-13
Humidifiers | Controls
CONDENSATION PROTECTION
A third device may be desirable to provide condensation
protection in the duct system. A high limit humidistat may
be installed ten (10) feet downstream from the steam
distributor pipe. This humidistat is normally set to 90-95%
RH and opens the circuit if the humidity level in the duct
exceeds the set-point. Use of this device is recommend-
ed particularly when the humidifier is used in applications
where cooling air is being humidified or where a VAV
system may throttle back to a point where air flow is
insufficient to absorb the steam being introduced.
Either an on-off or proportional control high limit
humidistat may be used with Carnes humidifiers. If a pro-
portional humidistat is used the output of the humidifier
will automatically be decreased to reduce the possibility
of condensation. Two proportional humidistats may be
used to control Carnes humidifiers if desired, one in the
area to be humidified or return duct and another as a high
limit in the supply duct. The humidifier will automatically
select the lowest signal to control the humidifier output.
CONTROL CONNECTIONS
Two cylinder humidifiers may be wired for simultaneous
or separate operation. Controls should be connected to
the terminals on the electronic circuit board as shown
below using recommended No. 20 AWG wire. Avoid
running control wiring near high voltage primary wires.
Connections shown in Figure H are for typical on-off
controls. For Carnes proportional controls see Figure J.
All controls are shipped with detailed wiring instructions.
EXTERNAL DDC CONTROL SIGNALS
Carnes humidifiers can also accept a 0-10 volt DC
signal to modulate the output of the humidifier. Polarity
must be observed. Input impedance is 20K ohms. If
a 4-20 mA input signal is provided to the humidifier a
470 ohm 1/4 watt resistor must be installed as shown
below (Figure K).
EXTERNAL MONITORING
Terminals, shown in Figure H, are provided for indicating
operation of the humidifier at a remote location. When
the unit is operating, “EXT PWR” terminals are closed.
Terminals are provided to indicate the need for service.
When the output of the humidifier is less than 50% of
set-point, “EXT SRV” terminals are closed. Each set of
terminals are capable of switching 1/2 amp at 24 volts
maximum.
HXHAM control will vary slightly on the connection
identifier, compared to above.
Figure H
MICROPROCESSOR CONTROL
CIRCUIT BOARD
Figure K
0-10 VDC
PROPORTIONAL SIGNAL
(BY OTHERS)
0-10 VDC
PROPORTIONAL
HI-LIMIT HUMIDISTAT
(BY OTHERS)
+ -
+ -
4-20ma
PROPORTIONAL
HI-LIMIT HUMIDISTAT
(BY OTHERS)
470 OHM
RESISTOR
(BY OTHERS)
470 OHM
RESISTOR
(BY OTHERS)
4-20ma
PROPORTIONAL SIGNAL
(BY OTHERS)
+
- +
-
Figure J
PROPORTIONAL HUMIDISTAT
(BY CARNES)
PROPORTIONAL HI-LIMIT
HUMIDISTAT
(BY CARNES)
ON/OFF
HUMIDISTAT
AIR FLOW
SWITCH
ON/OFF
HIGH LIMIT
HUMIDISTAT
EXTERNAL
ON
EXTERNAL
SERVICE
1/2 AMP
@ 24V
MAX
