WattMaster WM-WCC3-TGD-01B - Manual (Page 322)

WCC III Technical Guide 4-12
4. SCUSCR.EXE SCREENS
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.
NOTE: If check for main fan status is selected, the series fan
will activate any time the HVAC unit fan is operating.
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 mainfan status has been selected, the damper will be
held at the Nite/Reheat minimum until the space temperature
begins to rise to 0.5 ºF below the unoccupied 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 to 0.5 ºF below the unoccupied 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 below the Unoccupied Space Heating Setpoint.
If the VAVBOX TUC-2R controller is in the Unoccupied Supply
Air Cooling mode because one or more of the VAVBOX TUC-2R
controllers has a cooling demand and another VAVBOX controller
has a heating demand, the damper/airfl ow for the VAVBOX
controller requiring heating will position itself to provide the Night/
Reheat 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 VAVBOX TUC-2R controller is in the Unoccupied
Supply Air Heating mode, the damper will be held at the Night/
Reheat minimum position until the space temperature begins to fall
below the Unoccupied heating setpoint. As the space temperature
falls to 0.5 ºF above the unoccupied Heating Setpoint, the damper/
airfl ow 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.
As with the Occupied Mode of operation, two different
confi gurations are available for the Unoccupied Space Heating
mode. If the box is confi gured to allow reheat during HVAC Heat
mode, the reheat relays can be activated even when the VAVBOX
TUC-2R controller is in the Supply Air Heating mode. If the
box is confi gured not to allow reheat when the HVAC unit is in
Heat mode, the box heat relays will be de-energized when the
VAVBOX TUC-2R controller is in Supply Air Heating mode. In
either confi guration, when the VAVBOX TUC-2R controller 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 0.5 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 VAVBOX
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 VAVBOX TUC-2R controller can activate auxiliary heating
relays if the relay Expansion Board has been connected and the
correct number of heating stages (1,2, 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 1.0 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 fi rst stage relay
will deactivate when the space temperature rises above the heating
setpoint by 1.0 ºF.
See Table 4-3: Relay Staging - Unoccupied Mode for a complete
layout of the various fan & heat relay staging points.
Modulating (Proportional) Heat
The VAVBOX TUC-2R controller expansion board 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 ºF below the Heating Setpoint.
WCC III VAV BOX III Operation Modes