WattMaster WM-WCC3-TGD-01B - Manual (Page 788)

VAV/Zone Controller Technical Guide
Operator Interface 20
Sequence of Operations
Series Flow Fan Terminals
If the VAV/Zone Controller has been confi gured as a Series Fan Powered
terminal unit, the series fan relay will activate and run the series box fan
continuously anytime the VAV/Zone Controller is in occupied mode.
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.
Parallel Flow Fan Terminals
During normal cooling or vent mode and adequate air supply, the paral-
lel fan will be off. During the occupied cooling or vent mode, the fan
will only activate if the damper/airfl ow is below a user defi ned low
limit setting. This causes it to be used as a make-up air source. When
the damper/airfl ow rises 15% above the low limit setpoint, the fan will
be deactivated.
The Check for Main Status setting has no effect on the Parallel Fan box
when in the occupied mode.
Occupied Space Heating Mode
Occupied Space Heating mode is initiated by the temperature in the
space falling below the Occupied Heating Setpoint.
If the VAV/Zone Controller is in the Supply Air Cooling mode and an-
other 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 VAV/Zone Controller is in the Occupied Supply Air Heating
mode, the damper will be held at the Heating Minimum position until
the space temperature falls to within 0.5ºF of the Occupied 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 different confi gurations are available for the Occupied 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 VAV/Zone
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 VAV/Zone Controller is in Supply
Air Heating mode. In either confi guration, when the VAV/Zone Control-
ler 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.
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 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 heating setpoint. The third stage will activate if
the space temperature 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 1.0 ºF of the heating setpoint. The
second stage 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:
Relay Staging - Occupied Mode for a complete layout of the various
fan and heat relay staging points.
Modulating (Proportional) Heat
The VAV/Zone 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 1.5ºF below the
Heating Setpoint.
Series Flow Fan Terminals
If the VAV/Zone Controller has been confi gured as a Series Fan Powered
terminal unit, the series fan relay will activate and run the series box fan
continuously anytime the VAV/Zone Controller is in occupied mode.
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.
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/airfl ow is below a user defi ned low limit setting. This causes it
to be used as a make-up air source. When the damper/airfl ow 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.