5567611-BIM-B-1218
40
Johnson Controls Ducted Systems
Low ambient minimum position
The low ambient economizer minimum position overrides all
other minimum position functions.
When the control is in the occupied mode, the FAN output is
energized, and the operational OAT is below the low ambient
economizer setpoint, the economizer is positioned to the low
ambient economizer minimum position. When the Operational
OAT is equal to or above the low ambient economizer setpoint,
it exits the low ambient economizer setpoint mode.
Air monitoring station reset
The input for air monitoring station reset is
Fr-Air
.
The fresh air max sensor range must match the range of the air
monitoring station on the unit.
When the fresh air intake value falls below the fresh air intake
setpoint the economizer damper position increases above
minimum position until the fresh air intake value equals the
fresh air intake se/- 40 CFM.
When the fresh air intake value rises above fresh air intake
setpoint the economizer damper position decreases until the
fresh air intake value equals the fresh air intake setpoint or it
reaches minimum position setpoint.
Note:
The low ambient minimum position may force the
damper position below the current setpoint and
disables the air monitoring station reset.
Demand ventilation
The output for demand ventilation is 2 to 10 VDC from the
ECON terminal to the economizer actuator.
The control must be in occupied status with the indoor fan
operating. If the low ambient minimum position is in effect, it
overrides the demand ventilation operation.
If the demand ventilation mode of operation is set to enabled
and the operational indoor CO
2
level is greater than the
demand ventilation se100 ppm, the current operating
minimum position increases as follows.
• With a CO
2
level between the demand ventilation setpoint
+101 ppm and +200 ppm, the operating minimum position
increases 1% per minute.
• With a CO
2
level greater than the demand ventilation
se200 ppm, the operating minimum position
increases 2% per minute.
When the CO
2
levels drop to equivalent values below the
demand ventilation setpoint, the current operating minimum
position decreases at the same rates.
While in a demand ventilation mode, if the supply air
temperature drops below 49°F, the economizer outside air
dampers close until the supply air temperature rises above
49°F but does not go below the current economizer operating
minimum position. The economizer then modulates to control
the supply air temperature at 50°F.
Note:
The exception to this rule occurs when hydronic heat
enable and SAT tempering with hydronic heat enable
(40°F default) are both on. Hydronic heat is used to
control the supply air temperature in this situation and
the hydronic heat tempering setpoint is above 45°F.
If differential AQ enable is on and the OAQ is greater than or
equal to the IAQ by more than the demand ventilation
differential setpoint, the outside air dampers close completely
and override all other minimum position functions.
Free cooling changeover options
Four types of free cooling selection options are available: dry
bulb temperature, single enthalpy, dual enthalpy, and auto.
Auto
The control determines the type of free cooling changeover
based on which sensors are present and reliable. Conditions
include the following items:
• Operational space temperature and operational outdoor
temperature = dry bulb changeover
• Operational space temperature, operational outdoor
temperature, and operational outdoor humidity = single
enthalpy
• Operational space temperature, operational outdoor
temperature, operational outdoor humidity, and
operational space humidity = dual enthalpy
• If the operational outdoor air temperature value is
unreliable, free cooling is not available.
Dual enthalpy
The control determines the type of free cooling changeover
based on which sensors are present and reliable. Conditions
include the following items:
• Operational space temperature and operational outdoor
temperature = dry bulb changeover
• Operational space temperature, operational outdoor
temperature and operational outdoor humidity = single
enthalpy
• Operational space temperature, operational outdoor
temperature, operational outdoor humidity, and
operational space humidity = dual enthalpy
• If the operational outdoor air temperature value is
unreliable, free cooling is not available.
Single enthalpy
The control determines the type of free cooling changeover
based on which sensors are present and reliable. Conditions
include the following items:
• Operational outdoor air temperature = dry bulb
changeover
• Operational outdoor air temperature and outdoor air
humidity = single enthalpy
• If either the operational space temperature or the outdoor
air dry bulb value is unreliable, free cooling is not
available.
