Johnson Controls GVA Series, Start-Up & Operation

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Johnson Controls
Start-Up & Operation Guide | 5586996-JSG-A-0120
59
Operation
Indoor CO
2
When DCV is enabled and the indoor CO
2
level is
greater than the DCV setpoint, the DCV position in-
creases as follows:
• When the CO
2
level is greater than the DCV set-
point + 100 ppm, the DCV position increases 1%
per minute up to a maximum value of 50%
• When the CO
2
level is greater than the DCV set-
point + 200 ppm, the DCV position increases 2%
per minute up to a maximum value of 50%
When DCV is enabled and the indoor CO
2
level is less
than the DCV setpoint, the DCV position decreases as
follows:
• When the CO
2
level is less than the DCV setpoint
– 100 ppm, the DCV position decreases 1% per
minute down to the economizer minimum position
setpoint
• When the CO
2
level is less than the DCV setpoint
– 200 ppm, the DCV position decreases 2% per
minute down to the economizer minimum position
setpoint
When the CO
2
level drops to a value below the DCV
setpoint, the DCV position decreases at the same
rates as above.
Comparative CO
2
When differential DCV is enabled and the outside air
quality (OAQ) is equal to/greater than the IAQ by more
than the DCV differential setpoint, the outside air damp-
er is driven closed regardless of economizer suitability.
DCV and Minimum Outside Airflow Control
When both differential DCV and minimum outside airflow
control are enabled at the same time, the unit controller:
• Resets the outside air damper minimum position
setpoint based on an internal algorithm
• When the IAQ sensor PPM is greater than the
IAQ setpoint, the outside airflow setpoint is reset
upwards to 5,000 CFM as the IAQ increases from
the IAQ setpoint to the IAQ se 100 ppm
( Figure 23 )
(5,000 CFM) Fixed
Calculated
Outside Airflow
Setpoint
Outside Airflow
Setpoint
IAQ Setpoint
IAQ Se 100 ppm
Effective IAQ
LD28013
Figure 23: Effective Indoor Air Quality
Continuous Ventilation
This sequence allows the supply fan to run continuous-
ly during the occupied time periods with no demand for
heating or cooling. Continuous ventilation is applicable
to both MZVAV and SZVAV operation.
The fan speed is controlled as follows:
• MZVAV: Supply fan VFD controlled to the active
duct static setpoint
• SZVAV: Supply fan VFD controlled to the SZVAV
minimum fan speed
Continuous ventilation is user enabled/user disabled in
the Views > Details > Supply Fan > Setup menu
Pre-Occupancy Purge
This sequence is only applicable if using the unit con-
roller’s internal schedule
Pre-occupancy purge can be initiated when all of the
below conditions are met:
• The unit must be in an UNOCC mode
• The MAT value must be valid
• The outside air damper is not controlled by a high-
er priority sequence
Pre-occupancy purge is initiated when the time until OCC
mode begins equals the pre-occupancy purge time.
Pre-Occupancy Purge Sequence
• The supply fan VFD is turned ON and controlled
by either MZVAV or SZVAV fan sequences.
• The outside air damper starts to drive open.
• The unit controller turns ON the MZVAV heat com-
mand.