5121835-TIM-J-1118
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Johnson Controls Ducted Systems
If the supply air temperature cannot be maintained within 5°F of
the economizer setpoint, the first stage compressor (C1) will be
turned on. Second stage compressor (C2) will be added as
needed to keep the supply air temperature within the 5°F of the
economizer setpoint.
Sensor
In free cooling, with a demand from the zone/return sensor for
the first stage of cooling, the dampers modulate to control the
supply air temperature to the Economizer se/- 1°F.
If the economizer output is at 100%
and
the SAT is greater than
the Economizer se 1°F, the control starts a 12-minute
timer to energize a compressor output.
If at any time the economizer output drops below 100% the
timer stops and resets when the economizer output returns to
100%.
Once a compressor output is turned ON, the economizer
dampers continue to modulate to control the supply air
temperature to the Economizer setpoint.
At no time will a compressor output be turned ON if the
economizer output is less than 100%, even if the differential
between zone (or return) temperature and the current cooling
setpoint is great enough to demand more than one stage of
cooling.
If the economizer output goes to minimum position
and
the SAT
is less than Economizer setpoint -1°F, the control starts a 12-
minute timer to de-energize a compressor output.
If at any time the economizer output goes above the minimum
position the timer stops and resets when the economizer output
returns to minimum position.
If the demand for cooling from the space/return is satisfied, the
economizer output will modulate to minimum position and the
compressor outputs will be de-energized as long as their
minimum run timers have expired.
Power exhaust
Setpoints
• Economizer enable ON
• Power exhaust enable ON
• Modulating power exhaust OFF
• Exhaust VFD installed OFF
• Building pressure sensor enabled OFF
• Econo damper position for exh fan ON Percent
• Econo damper position for exh fan OFF Percent
Inputs
No inputs are present for non-modulating power exhaust.
Outputs
• 2-10 VDC from ECON on the economizer expansion
module
• 24 VAC from EX-FAN to energize the exhaust fan on the
economizer expansion module
Operation
Operation details include:
a. Compares the economizer output to the economizer
damper position for exhaust fan on and off
b. Energizes the exhaust fan when the economizer output
is above the economizer damper position for exhaust fan
on
c. De-energizes the exhaust fan when the economizer
output is below the economizer damper position for
exhaust fan off
