30
VAV/Zone Controller Package
SEQUENCE OF OPERATIONS
VAV/Zone Occupied Mode Sequences
When the HVAC unit is in the Supply Air Cooling Mode, the
damper is normally held at the Minimum Cooling Position until
the Space Temperature begins to rise above the Occupied Cool-
ing Setpoint. As the Space Temperature rises to within 0.5ºF of
the Occupied Cooling Setpoint, the Damper/Airfl ow calculation
causes the air valve to open proportionally until the Maximum
Setpoint is achieved at 1.5ºF above the setpoint. This is a 2ºF
Proportional Window starting 0.5ºF below the Occupied Cooling
Setpoint to 1.5ºF above the Occupied Cooling Setpoint.
The Damper Position/Airfl ow is never allowed to modulate out-
side the user-adjustable Minimum and Maximum setpoints. The
Maximum Damper Position/Airfl ow Setpoint applies to Heating
and Cooling modes of operation only. All of the modes have their
own individual minimum setting.
Series Flow Fan Terminals
If the VAV/Zone Controller has been confi gured as a Series Fan
Powered terminal unit, the series fan relay will activate and run
the series box fan continuously anytime the HVAC unit fan is
running.
In all cases, before the series box fan can be activated, the air
damper is driven fully closed and held that way for 30 seconds to
make sure the series box fan hasn’t inadvertently started to spin
backwards. Once the series box fan starts, it waits an additional
10 seconds to allow the fan to spin up before it starts to open the
damper and introduce airfl ow from the HVAC unit fan.
Parallel Flow Fan Terminals
During normal cooling or vent mode and adequate air supply, the
parallel fan will be off . During the Occupied Cooling Mode, the
fan will only activate if the damper/airfl ow is below a user-defi ned
low limit setting. This causes it to be used as a supplemental air
source. When the damper/airfl ow rises 15% above the low limit
setpoint, the fan will be deactivated.
NOTE:
A VAV/Zone Controller Expansion Module is
required for each VAV/Zone Controller used when you
are using a Fan Terminal even if you do not have any heat
requirements. All Single Duct Terminal Units with multiple
heat stages or modulating heat also require a VAV/Zone
Controller Expansion Module.
Night Minimum
This is the position that the damper moves to during the Unoc-
cupied mode. When using non-fan powered terminal units, the
VAV/Zone damper will position itself in the Night Minimum
position. In order for fan powered terminal units to position the
damper to the Night Minimum position, the check for main fan
status must be selected, and the HVAC unit fan must be operating.
Box Heating Minimum
This is the position that the damper moves to when Reheat is
initiated. If the VAV/Zone Controller is used on a terminal unit
that has reheat, the VAV/Zone damper will move to the Reheat
position whenever a Space Heating demand occurs and the HVAC
unit is in Supply Air Cooling or Vent Mode. When the HVAC
unit is in Supply Air Heating Mode, the VAV/Zone damper will
modulate as required to maintain the Space Heating Setpoint.
Occupied Mode Sequences
Space Vent Mode
This mode only applies to the Occupied Mode of operation. If
the equipment is in the Unoccupied Mode, then a lack of heating
or cooling demand would generate the Off Mode.
If the HVAC unit is in Supply Air Vent Mode, you can adjust
the damper position on pressure dependent terminal units and
the airfl ow on pressure independent terminal units to provide a
fi xed amount of ventilation air into the space when there are no
heating or cooling demands. During this time, the damper does
not modulate on pressure dependent terminal units. On pressure
independent terminal units, it only modulates to the extent re-
quired to maintain the Vent Minimum Airfl ow setting.
If the VAV/Zone Controller detects that the HVAC unit is in Sup-
ply Air Heating Mode, indicating that the air handler has activated
its heat, the Heating Airfl ow Minimum will be substituted for
the Vent Minimum.
If the VAV/Zone Controller detects that the HVAC unit is in Sup-
ply Air Cooling Mode, indicating that the air handler has activated
its cooling, the Cooling Airfl ow Minimum will be substituted for
the Vent Minimum.
Space Cooling Mode
Occupied Space Cooling mode is initiated by the temperature in
the space rising to within 0.5ºF of the Occupied Cooling Setpoint.
If the HVAC unit is in the Supply Air Heating Mode and another
VAV/Zone Controller has a cooling demand, the Damper Posi-
tion/Airfl ow for the VAV/Zone Controller requiring cooling will
position itself to provide the Heating Minimum Damper Position/
Airfl ow Setpoint amount of air into the space. No modulation
open will occur because the space does not want the warm air
currently being supplied by the air handler.
