As with the Occupied Mode of operation, two different configurations
are available for the Unoccupied Space Heating mode. If the box is
configured 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 configured 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 configuration, when the HVAC unit is in the Supply Air Heat
-
ing mode, the damper will modulate open proportionally to the space
demand. The proportional window for the space temperature is 0.5 ºF
above to 1.5 ºF below the heating setpoint. This allows the space to take
advantage of the warm supply air in the duct.
If check for main fan 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 fan status is selected, the reheat will
only operate when the HVAC unit fan is operating.
The VAV/Zone Controller can activate auxiliary heating relays if the
Expansion Module has been connected and the correct number of heat-
ing stages (1, 2 or 3) has been configured. During demands for heat, the
first stage will activate whenever the space temperature drops below the
heating setpoint. The second stage will activate if the space temperature
falls 1.0 ºF below the heating setpoint. The third stage will activate if
the space temperature falls 2.0 ºF 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 1.0 ºF of the heating setpoint. The
second stage relay will deactivate when the space temperature rises to
the heating setpoint. The first stage relay will deactivate when the space
temperature rises above the heating setpoint by 1.0 ºF. See
Table 2:
Fan & Reheat Relay Staging
for a complete layout of the various fan
& heat relay staging points.
Modulating (Proportional) Heat
The Non-Modular VAV/Zone Controller Actuator 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 0.5 ºF above the 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 different
from the other heating setpoints. The Auxiliary Heat Relay energizes
at 0.5 ºF below the Auxiliary Heat Setpoint and de-energizes 0.5 ºF
above the Auxiliary Heat Setpoint. The Auxiliary Heat will continue
to function regardless of the HVAC Mode the VCM-X is in, or at any
airflow 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 configured 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 fan 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 posi-
tion 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 fan 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 airflow
from the HVAC unit fan.
Parallel Flow Fan Terminals
If the VAV/Zone Controller has been configured as a Parallel Fan
Powered terminal unit, the Parallel 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. At all other times,
the fan will be off.
If check for main fan status is selected, the damper will remain in the
closed position until 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 Night Minimum position. If check for main fan
status has not been selected, the damper will stay in the closed position
until Space Heating mode is initiated. 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.
Unoccupied Mode Sequences
24
Non-Modular ZCAP Technical
Guide
Sequence of Operations
