33
VAV/Zone Controller Package
SEQUENCE OF OPERATIONS
VAV/Zone Unoccupied Mode Sequences
Space Heating Mode
During Unoccupied Mode, the HVAC unit is normally off . Un-
occupied Space Heating Mode is initiated by the temperature
in the space falling to within 0.5ºF of the Unoccupied Space
Heating Setpoint.
If the HVAC unit is in the Unoccupied Supply Air Cooling Mode
because one or more of the VAV/Zone Controllers has a cooling
demand and another VAV/Zone Controller has a heating demand,
the damper/airfl ow for the VAV/Zone Controller requiring heat-
ing 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 0.5ºF below
the Unoccupied Heating Setpoint, the damper/airfl ow calculation
causes the air valve to open proportionally until the maximum
setpoint is achieved at 1.5ºF below the setpoint. This is a 2ºF
proportional window starting 0.5ºF above the Heating Setpoint
to 1.5ºF below the Heating Setpoint.
As with the Occupied Mode of operation, two diff erent confi gura-
tions are available for the Unoccupied Space Heating Mode. If
the box is confi gured to allow reheat during Supply Air Heating
Mode, the reheat relays can be activated even when the HVAC
unit is in the Supply Air Heating Mode. If the box is confi gured
not to allow reheat when the HVAC unit is in Supply Air Heating
Mode, the box heat relays will be de-energized when the HVAC
unit is in Supply Air Heating Mode. In either confi guration, when
the HVAC unit is in the Supply Air Heating Mode, the damper
will modulate open proportionally to the space demand. The
proportional window for the space temperature is 0.5ºF above to
1.5ºF below the Heating Setpoint. This allows the space to take
advantage of the warm supply air in the duct.
If “Check for Main Status” is not selected and the VAV/Zone
terminal unit has auxiliary heat (baseboard heat etc.) that does
not require the HVAC unit fan to operate, reheat can be used
without the HVAC unit fan operating. If “Check for Main Status”
is selected, the reheat will only operate when the HVAC unit fan
is operating.
The VAV/Zone Controller can activate auxiliary heating relays.
Multiple heat stages or modulating heat can activate if the Ex-
pansion Module has been connected and the correct number of
additional heating stages (2 or 3) has been confi gured. During
demands for Heat, the fi rst stage will activate whenever the Space
Temperature drops below the Heating Setpoint. The second stage
will activate if the Space Temperature falls 1.0ºF below the Heat-
ing Setpoint. The third stage will activate if the Space Tempera-
ture falls 2.0ºF below the Heating Setpoint. There is a two-minute
delay between staging. This prevents stages from activating at
the same time. Once a heating stage has been activated, it must
remain on for at least one minute. Once it has been deactivated,
it must remain off for at least two minutes. The third stage relay
will deactivate when the Space Temperature rises to within 1.0ºF
of the Heating Setpoint. The second stage relay will deactivate
when the Space Temperature rises to the Heating Setpoint. The
fi rst stage relay will deactivate when the Space Temperature rises
above the Heating Setpoint by 1.0ºF. See
Table 3, page 31
for
a complete layout of the various fan & heat relay staging points.
Modulating ( Proportional) Heat
The VAV/Zone Controller Package also provides an analog output
for control of a Modulating Hot Water Valve or SCR Electric
Heater. It provides a 0-10 VDC signal to control the heating
device. When the Space Temperature drops to 0.5ºF above the
Unoccupied Heating Setpoint, the output starts at 0 VDC and
ramps up to 10 VDC at 1.5 below the Heating Setpoint.
Auxiliary Heat
The Auxiliary Heat option allows for a separate setpoint that is
diff erent from the other heating setpoints. The Auxiliary Heat
Relay energizes at 0.5ºF below the Auxiliary Heat Setpoint and
de-energizes 0.5ºF above the Auxiliary Heat Setpoint. The night
off sets would apply to these values. The Auxiliary Heat will
continue to function regardless of the HVAC Mode the Unit
Controller is in, or at any airfl ow condition. This is typically used
to control baseboard heat or an external duct heater.
Series Flow Fan Terminals
If the VAV/Zone Controller has been confi gured as a Series Fan
Powered terminal unit, the series fan will run continuously when
the VAV/Zone Controller is in the Space Heating Mode, no matter
whether check for main fan status has been selected or not. If
the HVAC unit is in Supply Air Heating Mode, the damper will
modulate to maintain the Space Heating Setpoint.
Any series fan terminal unit that has “Check for Main Status”
selected will also operate its series box fan anytime the HVAC
unit controller is broadcasting that the HVAC unit fan is operating,
regardless of whether it is calling for heat or not. The damper will
be held at the closed position until the main fan status broadcast
is received. Once the broadcast is received, the damper will then
move to its Reheat Minimum position. If “Check for Main Status”
has not been selected, the series box fan will only activate and
run when it is in Space Heating Mode. When in Space Heating
Mode, the damper will move to its Reheat Minimum position.
When in Supply Air Heating Mode, the damper will modulate
to maintain the Unoccupied Heating 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.
