5567611-BIM-B-1218
Johnson Controls Ducted Systems
43
VAV unit sensor option A
The operating VAV SAT setpoint is determined by the reset
function not by the number of compressors operating.
When free cooling available and the SAT is above the operating
VAV SAT setpoint, the dampers modulate to control the
operating, upper or lower, SAT se/-0.5°F.
If the economizer output is at 100% for 5 consecutive minutes
and the operating space temperature is 0.6°F or greater than
the operating cooling setpoint, the control starts to energize
compressors. See for additional information.
As soon as the staged percent command begins to increase,
the economizer remains at 100%. If the SAT drops to less than
the operating VAV SAT se1.8F, the staged percent
command holds the current value.
If the SAT drops to less than the operating VAV SAT setpoint -
1.8°F, the staged percent command begins to decrease.
If the staged percent command remains at 0% for 5 consecutive
minutes, the economizer modulates to control to the upper SAT
se/-0.5°F.
VAV unit sensor option B
When free cooling available and the SAT is greater than the
operating VAV SAT setpoint, the dampers modulate to control
the operating VAV SAT se/-0.5°F.
If the economizer position remains at 100% for 10 consecutive
minutes and the SAT is greater than the operating VAV SAT
se5°F, the first compressor output energizes. If the
economizer position remains at 100% for another 5 minutes
and the SAT is greater than the operating VAV SAT setpoint
+5°F, the second compressor output energizes. If the
economizer position remains at 100%, the process repeats
every 5 minutes until all the compressors energize.
If the economizer position drops below 100% and does not
reach the minimum position then returns to 100%, remains at
100% for 5 minutes, and the SAT is greater than the operating
VAV SAT se5°F, the next available compressor
energizes. If the economizer position remains at 100%, the
process repeats every 5 minutes until all the compressors
energize.
Any time the economizer remains at the minimum position for 5
consecutive minutes or the SAT is lower than the operating
VAV SAT setpoint -5°F, the last energized compressor turns
off. If it remains at the minimum position or the SAT remains
lower than the operating VAV SAT setpoint -5°F, the
compressors de-energize every 5 minutes until all the
compressors are off.
If all compressor outputs de-engerize, the economizer
modulates to control to operating VAV SAT Se/-0.5°F.
When the cooling demand ends the compressors de-energize
immediately and the dampers return to operating minimum
position.
Economizer loading
The economizer loading function only works when only one
compressor is operating.
If the SAT is less than the SAT low limit setpoint and the
operating OAT is greater than 60°F, the economizer output
increases to control the SAT to the operating SAT se/-
0.5°F.
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 the following items:
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
