Unoccupied Mode Sequences
Series Flow Fan Terminals
I
f the VAV/Zone Controller has been configured 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 airflow
from the HVAC unit fan.
Parallel Flow Fan Terminals
On parallel fan powered terminal units, the fan will run whenever Space
Heating mode is active. At all other times, the fan will only activate if the
damper/airflow is below a user defined low limit setting. This causes it
to be used as a make-up air source. When the damper/airflow 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 effect 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 the Off Mode.
Off Mode
This mode only applies to the Unoccupied Mode of operation. If the
equipment is in the Unoccupied Mode, then a lack of heating or cooling
demand would generate this mode. The VAV/Zone Controller will put
the damper into the Night Minimum Position if check main fan status
has been selected. If check main fan status has not been selected, the
damper will be in the fully closed position.
Space Cooling Mode
During unoccupied mode, the HVAC unit is normally off. Unoccupied
Space Cooling mode is initiated by the temperature in the space rising
to within 0.5 ºF 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/airflow
for the VAV/Zone Controller requiring cooling 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 tem-
perature rises to within 0.5 ºF of the Unoccupied Cooling Setpoint, the
damper/airflow calculation causes the air valve to open proportionally
until the maximum setpoint is achieved at 1.5 ºF above the setpoint. This
is a 2 ºF proportional window starting 0.5 ºF below the cooling setpoint
to 1.5 ºF above the cooling setpoint.
The damper/airflow is never allowed to modulate outside the user-
adjusted minimum and the maximum setpoints. The maximum damper/
airflow setpoint applies to heating and cooling modes of operation only.
All of the modes have their own individual minimum setting.
Series Flow Fan Terminals
I
f the VAV/Zone Controller has been configured 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 fan 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 airflow
from the HVAC unit fan.
Parallel Flow Fan Terminals
In the Unoccupied Cooling mode, the parallel fan will be off whether
check for main fan status has been selected or not. If check for main fan
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 fan 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.
Space Heating Mode
During unoccupied mode, the HVAC unit is normally off. Unoccupied
Space Heating mode is initiated by the temperature in the space falling
to within 0.5 ºF of the Unoccupied Space Heating Setpoint.
If the HVAC unit is in the Unoccupied Supply Air Cooling mode be-
cause one or more of the VAV/Zone Controllers has a cooling demand
and another VAV/Zone Controller has a heating demand, the damper/
airflow for the VAV/Zone Controller requiring heating will position itself
to provide the Night Minimum Position setpoint amount of air into the
space. No modulation open will occur because the space does not want
the cold air currently being supplied by the air handler.
When the HVAC unit is in the Unoccupied Supply Air Heating mode,
the damper will be held at the Night Minimum Position until the space
temperature begins to fall below the Unoccupied Heating Setpoint. As
the space temperature falls to 0.5 ºF below the Unoccupied Heating
Setpoint, the damper/airflow calculation causes the air valve to open
proportionally until the maximum setpoint is achieved at 1.5 ºF below
the setpoint. This is a 2 ºF proportional window starting 0.5 ºF above
the heating setpoint to 1.5 ºF below the heating setpoint.
23
Non-Modular ZCAP Technical Guide
Sequence of Operations
