19
CONDENSATION PROTECTION
A third device may be desirable to provide condensation
protection in the duct system. A high limit humidistat may be
installed ten 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 setpoint. Use of this
device is recommended 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 proportional 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 humidistat is in the area to be humidified or
return duct and another humidistat is used as a high limit in
the supply duct. The humidifier will automatically select the
lowest signal to control the humidifier output.
CONTROL HUMIDISTAT / TEMPERATURE COMPENSATED
The HXHAT or HXHAMT can be used if your application has a
requirement for an outdoor temperature compensation feature.
Both controls will provide monitoring of RH percentage and
outdoor temperature, along with automatically adjusting the
RH setpoint as outdoor temperatures change. The HXHAT is
a dry contact on-off humidistat, while the HXHAMT provides a
0-10V signal in either a proportional or on-off configuration.
CONTROL CONNECTIONS
The circuit board can provide either a Carnes legacy 18VDC or an
industry standard 24VAC, as a supply for those humidistats which
require it. The supply for both the control humidistat and high limit
humidistat are output on pin1 of J16 and J17 respectively.
18VDC
is set as the supply default
, but the switches on designators SW5
can be flipped to the left to alternatively supply 24VAC as seen in
Photo G
for the H690-0107 circuit board (blue). The humidistat and
high limit can be changed independently. The switch labeled Hu is
switched for humidistat voltage output, and the switch labeled HL is
switched for high limit humidistat voltage output. Switch(es) in the
right position will supply 18VDC and switch(es) in the left position
will supply 24VAC.
Connections shown in
Figure N
are for typical on-off controls.
For Carnes proportional controls see the diagram
Figure O
. 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 P)
.
Two cylinder humidifiers may be wired for simultaneous or separate
and independent operation. Controls should be connected to the
terminals on the circuit board as shown below using No. 20 AWG
wire. Attempting to use two wires in a single control connection will
require a No. 22 AWG wire or less. See wiring diagram for parallel
connections. Avoid running control wiring near high voltage primary
wires due to the possibility of interference and signal distortion.
Figure P
0-10 VDC
PROPORTIONAL SIGNAL
(BY OTHERS)
0-10 VDC
PROPORTIONAL
HIGH LIMIT HUMIDISTAT
(BY OTHERS)
+ -
+ -
4-20ma
PROPORTIONAL
HIGH LIMIT HUMIDISTAT
(BY OTHERS)
470 OHM
RESISTOR
(BY OTHERS)
470 OHM
RESISTOR
(BY OTHERS)
4-20ma
PROPORTIONAL SIGNAL
(BY OTHERS)
+
- +
-
Figure N
ELECTRONIC CONTROL CIRCUIT BOARD
ON/OFF
HUMIDISTAT
AIR FLOW
SWITCH
ON/OFF
HIGH LIMIT
HUMIDISTAT
Figure O
PROPORTIONAL HUMIDISTAT
(BY CARNES)
PROPORTIONAL
HIGH LIMIT HUMIDISTAT
(BY CARNES)
Photo G
