WattMaster WM-WCC3-TGD-01B - Manual (Page 787)

Operator Interface
VAV/Zone Controller Technical Guide
19
Damper Positions
The actual values for the minimum damper positions that are described in
the following paragraphs can be user confi gured by changing the values
in the setpoint screens for the VAV/Zone Controller. These minimums are
expressed in damper open percentages for pressure dependent terminal
units or in CFM for pressure independent terminal units.
Cooling Minimum
When the HVAC unit is in the Supply Air Cooling mode but the space
does not require cooling, the VAV/Zone damper will go to the Cooling
Minimum position.
Heating Minimum
When the HVAC unit is in the Supply Air Heating mode but the space
does not require Heating, the VAV/Zone damper will go to the Heating
Minimum position.
Vent Minimum
This is the position the VAV/Zone damper will move to when the HVAC
unit is in the Supply Air Neutral mode.
Night/Reheat Minimum
This setpoint has two different functions depending on whether the
HVAC unit is in Occupied or Unoccupied mode.
Occupied Mode
If the VAV/Zone Controller is used on a non-fan-powered terminal unit
that has reheat, the VAV/Zone damper will move to the Night/Reheat
position whenever a Space Heating demand occurs and the HVAC unit
is in Supply Air Cooling or Neutral modes. When the HVAC unit is
in Supply Air Heating mode the VAV/Zone damper will modulate as
required to maintain the Space Heating setpoint.
Unoccupied Mode
When using non-fan powered terminal units, the VAV/Zone damper
will position itself in the Night/Reheat minimum position. In order for
fan powered terminal units to position the damper to the Nite/Reheat
minimum position, the Check for Main Fan Status must be selected and
the HVAC unit fan must be operating.
Occupied Mode Sequences
Occupied Space Vent Mode
This mode only applies to the Occupied Mode of operation. If the
equipment is in the Unoccupied Mode, then a lack of heating or cooling
demand would generate the Off Mode.
If the VAV/Zone Controller is in Supply Air Neutral Mode, the user can
adjust the damper position on pressure dependent terminal units and the
airfl ow on pressure independent terminal units to provide a fi xed amount
of ventilation air into the space when there are no heating or cooling
demands. During this time, the damper does not modulate on pressure
dependent terminal units. On pressure independent terminal units, it
only modulates to the extent required to maintain the vent minimum
airfl ow setting.
If the VAV/Zone Controller detects that the HVAC unit is in Supply
Air Heating mode, indicating that the air handler has activated its heat,
the heating airfl ow minimum will be substituted for the vent minimum
position.
If the VAV/Zone Controller detects that the HVAC unit is in Supply Air
Cooling mode, indicating that the air handler has activated its cooling,
the cooling airfl ow minimum will be substituted for the vent minimum
position.
Occupied Space Cooling Mode
Occupied Space Cooling mode is initiated by the temperature in the
space rising above the Occupied Cooling Setpoint.
If the HVAC unit is in the Supply Air Heating and another VAV/Zone
Controller has a cooling demand, the damper/airfl ow for the VAV/Zone
Controller requiring cooling will position itself to provide the heating
minimum setpoint amount of air into the space. No modulation open
will occur because the space does not want the warm air currently being
supplied by the air handler.
When the HVAC unit is in the Supply Air Cooling mode, the damper is
normally held at the minimum cooling position until the space tempera-
ture begins to rise above the cooling setpoint. As the space temperature
rises to within 0.5ºF of the Occupied Cooling Setpoint, the damper/
airfl ow calculation causes the air valve to open proportionally until the
maximum setpoint is achieved at 1.5ºF above the setpoint. This is a 2ºF
proportional window starting 0.5ºF below the cooling setpoint to 1.5ºF
above the cooling setpoint.
The damper/airfl ow is never allowed to modulate outside the user adjust-
ed minimum setpoint and the maximum setpoint. The maximum damper/
airfl ow setpoint applies to heating and cooling modes of operation only.
All of the modes have their own individual minimum setting.
Sequence of Operations