VAV/Zone Unoccupied Mode Sequences
32
VAV/Zone Controller Package
SEQUENCE OF OPERATIONS
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
On parallel fan powered terminal units, the fan will run when-
ever Space Heating Mode is active. At all other times, 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 if there are no heating stages
active, and no space demand exists.
The check for main fan status setting has no eff ect on the Parallel
Fan box when in the occupied mode. The Parallel Fan will only
be energized when in the Space Heating Mode.
Unoccupied 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 “No Space Demand” on the
Unit Controller display.
Space Cooling Mode
During Unoccupied Mode, the HVAC unit is normally off . Unoc-
cupied Space Cooling Mode is initiated by the temperature in the
space rising to within 0.5ºF of the Unoccupied Cooling Setpoint.
If the HVAC unit is in the Unoccupied Supply Air Heating Mode
because one or more of the VAV/Zone Controllers has a Heating
demand and another VAV/Zone Controller has a Cooling demand,
the damper/airfl ow for the VAV/Zone Controller requiring Cool-
ing will position itself to provide the Heating Minimum 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.
When the HVAC unit is in the Unoccupied Supply Air Cooling
Mode, the damper will be held at the Night Minimum Position
until the Space Temperature begins to rise above the Cooling
Setpoint. As the Space Temperature rises to within 0.5ºF of the
Unoccupied 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 Cooling Setpoint
to 1.5ºF above the Cooling Setpoint.
The damper/airfl ow is never allowed to modulate outside the user-
adjusted minimum and the maximum setpoints. The Maximum
Damper/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 and “Check for Main Status” has been
selected, the series fan relay will activate and run the series box
fan continuously anytime the HVAC unit fan is running. The
damper will be held at the Night Minimum Position until the
Space Temperature begins to rise above the Cooling Setpoint. If
“Check for Main Status” has not been selected, the series fan relay
will activate and run the series box fan when in the Space Cooling
Mode. The damper will be in the fully closed position until the
Space Temperature begins to rise above the Cooling Setpoint.
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
In the Unoccupied Cooling Mode, the parallel fan will be off
whether “Check for Main Status” has been selected or not. If
“Check for Main Status” has been selected, the damper will be
held at the Night Minimum Position until the Space Temperature
begins to rise above the Cooling Setpoint. If “Check for Main
Status” has not been selected, the damper will be held in the fully
closed position until the Space Temperature begins to rise above
the Cooling Setpoint.
