CARNES HBGH Installation, Operation And Maintenance Manual page 14

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 set-point. 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 humid-
istats 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 HUMIDISTAT / TEMPERATURE COMPENSATED
If your application has a requirement for an outdoor temperature
compensation feature, the HXHAT, or HXHAMT would satisfy.
Both controls will provide monitoring of RH percentage and
outdoor temperature, along with automatically adjusting the RH
set-point as outdoor temperature changes. The HXHAT is a dry
contact on-off humidistat, where as 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 jumpers on designators W5
and W7 can be moved to the left two pins to alternatively supply
24VAC as seen in Photo G (location of designators shown only, no
pins or jumper).
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.
Photo G
Figure L
J10
TERMINAL
1/2 AMP
@ 24V
MAX
EXTERNAL
ON
EXTERNAL
SERVICE
ON/OFF
HUMIDISTAT
ELECTRONIC CONTROL CIRCUIT BOARD
Connections shown in Figure L are for typical on-off controls.
For Carnes proportional controls see the diagram Figure M. All
controls are shipped with detailed wiring instructions.
Figure M
PROPORTIONAL HUMIDISTAT
(BY CARNES)
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 N).
Figure N
0-10 VDC
PROPORTIONAL SIGNAL
(BY OTHERS)
470 OHM
RESISTOR
(BY OTHERS)
PROPORTIONAL SIGNAL
14
ON/OFF AIR FLOW
HIGH LIMIT SWITCH
HUMIDISTAT
PROPORTIONAL HI-LIMIT
HUMIDISTAT
(BY CARNES)
+ -
+ -
0-10 VDC
PROPORTIONAL
HI-LIMIT HUMIDISTAT
(BY OTHERS)
470 OHM
RESISTOR
-
- +
+
(BY OTHERS)
4-20ma
4-20ma
PROPORTIONAL
HI-LIMIT HUMIDISTAT
(BY OTHERS)
(BY OTHERS)