Specifications

13
CONTROLS
CONTROL OPTIONS - Figure K
CONTROL HUMIDISTAT
If an on-off humidistat is used, the humidifier will gener-
ate steam at the max output rate and cycle on or off as
necessary to satisfy the conditioned area requirements.
All humidifiers are preset at the factory for the maximum
rating of the unit. The maximum output may be easily reset
to a lower limit in the range of 25-100% using the True
Touchscreen options.
If Carnes proportional humidistat is used the humidifier will
automatically vary the steam output rate in the range of
20-100% of the humidifiers maximum output (set by the
user) in response to the 0-10V signal from the humidistat.
However, the output of the humidifier will not drop below
20% of the preset nominal output of the humidifier set at
the factory. Proportional control provides less cycling of the
humidifier.
Either a wall humidistat or duct mounted humidistat in
the return air may be used. The wall mounted humidistat
is the most common as it allows the setting to be easily
changed to accommodate changing requirements or to
lower the level of relative humidity in the space to prevent
condensation on windows during extremely cold weather.
In applications where it may be desirable to prevent the
occupants of a space from changing the setting, a duct
mounted humidistat in the return may be used. This is
normally mounted in the equipment room or in the duct
where it is accessible only to maintenance personnel.
AIR FLOW DETECTION
The humidifier control circuit should include some meth-
od to determine air flow. If the steam distributor pipe is
located in a duct where there is no air flow and the control
humidistat is calling for humidity, steam would be
discharged into the duct where it would immediately
condense. Air flow may be detected by several meth-
ods. The humidistat circuit may be interlocked by using
a fan relay if the fan is direct driven. A fan relay is not
recommended if a belt driven fan is used as a broken belt
would stop air flow even though the fan relay was closed.
Among the alternatives are the use of a pressure
differential switch that determines air flow by sensing a
pressure differential caused by air movement in the duct.
A paddle type switch is also available to determine air
flow. The pressure differential switch is normally the pre-
ferred device as it is less susceptible to erratic operation
caused by improper positioning in the duct system. Paddle
switches require careful positioning in the duct to insure
sufficient air flow to activate the switch.
CONTROL HUMIDISTAT AIR FLOW DETECTION CONDENSATION
PROTECTION
WALL HUMIDISTAT
PROPORTIONAL CONTROL
CARNES MODEL HXHCG
OR
WALL HUMIDISTAT
ON-OFF CONTROL
CARNES MODEL HXHAA
OR
DUCT HUMIDISTAT
PROPORTIONAL CONTROL
CARNES MODEL HXHCH
OR
PRESSURE
DIFFERENTIAL
SWITCH
CARNES MODEL HXAAE
OR
DUCT HUMIDISTAT
ON-OFF CONTROL
CARNES MODEL HXHAB
AIR
FLOW
SWITCH
CARNES MODEL HXAAF
OR
DUCT PROPORTIONAL
HIGH LIMIT
HUMIDISTAT
CARNES MODEL HXHCH
DUCT ON-OFF
HIGH LIMIT
HUMIDISTAT
CARNES MODEL HXHAD
OR
OR
DUCT PROPORTIONAL
HIGH LIMIT
HUMIDISTAT (NEW)
CARNES MODEL HXHAN
WALL HUMIDISTAT (NEW)
PROPORTIONAL CONTROL
CARNES MODEL HXHAM
OR
OR
DUCT HUMIDISTAT (NEW)
PROPORTIONAL CONTROL
CARNES MODEL HXHAN
TEMPERATURE COMPENSATED
(NEW) PROPORTIONAL or
ON-OFF HUMIDISTAT
CARNES MODEL HXHAMT