15
CONTROLS
CONTROL OPTIONS -
Figure M
CONTROL HUMIDISTAT
If an on-off humidistat is used, the humidifier will
generate 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 between 20-100% in the settings menu of the
touchscreen.
If Carnes proportional humidistat is used the humidifier will
automatically vary the steam output rate in the range of
20-100% of the humidifier’s 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.
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 for 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
method 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
methods. 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 is 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
preferred 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
CARNES MODEL
HXHAN
WALL HUMIDISTAT
PROPORTIONAL CONTROL
CARNES MODEL
HXHAM
OR
OR
DUCT HUMIDISTAT
PROPORTIONAL CONTROL
CARNES MODEL
HXHAN
TEMPERATURE COMPENSATED
PROPORTIONAL or
ON-OFF HUMIDISTAT
CARNES MODEL
HXHAMT