VAV/Zone Occupied Mode Sequences
31
VAV/Zone Controller Package
SEQUENCE OF OPERATIONS
Space Heating Mode
Occupied Space Heating mode is initiated by the temperature in
the space falling to within 0.5ºF of the Occupied Heating Setpoint.
If the HVAC unit is in the Supply Air Cooling Mode and another
VAV/Zone Controller has a heating demand, the damper/airfl ow
for the VAV/Zone Controller requiring heating will position itself
to provide the Cooling Minimum 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 Occupied Supply Air Heating
Mode, the damper will be held at the Heating Minimum posi-
tion until the space temperature falls to within 0.5ºF of the Oc-
cupied Heating Setpoint. As the Space Temperature falls below
the 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.
Two diff erent confi gurations are available for the Occupied 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 to 1.5ºF below the Heating Setpoint. This allows
the space to take advantage of the warm supply air in the duct.
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
for a complete
layout of the various Fan & Heat relay staging points.
Modulating ( Proportional) Heat
The VAV/Zone Controller Package with the Zone Controller
Expansion Module 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 Heating Setpoint the output
starts at 0 VDC and ramps up to 10 VDC at 1.5 below the Heat-
ing 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
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.
See
Table 3
for a complete layout of the various fan and
heat relay staging points.
Fan & Reheat Relay Staging
Relays Stage
On At
Series
Fan
Parallel
Fan
Heat
Stage
1
Heat
Stage
2
Heat
Stage
3
Aux.
Heat
0.5ºF Above Box
Heat Setpoint
ON With
HVAC Fan
*See
Note 1
X
At Box Heat
Setpoint
X
1.0ºF Below Box
Heat Setpoint
X
2.0ºF Below Box
Heat Setpoint
X
0.5ºF Below
Aux. Heat
Setpoint
X
Relays Stage
Off At
Series
Fan
Parallel
Fan
Heat
Stage
1
Heat
Stage
2
Heat
Stage
3
Aux.
Heat
1.0ºF Above Box
Heat Setpoint
OFF With
HVAC Fan
See Note 1
X
See
Note 2
1.0ºF Above Box
Heat Setpoint
X
At Box Heat
Setpoint
X
1.0ºF Below Box
Heat Setpoint
X
0.5ºF Above
Aux. Heat
Setpoint
X
NOTES:
:
1.) If check for main fan status is selected when confi guring the controller, the
series fan will energize anytime the HVAC unit’s fan is operating, even in the
unoccupied mode.
2.) The parallel fan will continue to run for 2 minutes following the relay stag-
ing off .
Table 3: Fan & Reheat Relay Staging
