WattMaster WM-WCC3-TGD-01B - Manual (Page 318)

WCC III Technical Guide 4-8
4. SCUSCR.EXE SCREENS
Modes of Operation
There are 7 possible modes of operation for the HVAC Unit and the
VAVBOX TUC-2R controller. These modes are determined by the
supply air and/or space demand conditions. They are as follows:
Supply Air Neutral Mode - (based on HVAC Unit Supply
Air Temperature)
Space Vent Mode - (based on VAVBOX TUC-2R
Controller Space Temperature)
Supply Air Cooling Mode - (based on HVAC Unit Supply
Air Temperature)
Space Cooling Mode - (based on VAVBOX Controller
Space Temperature)
Supply Air Heating Mode - (based on HVAC Unit Supply
Air Temperature)
Space Heating Mode - (based on VAVBOX Controller
Space Temperature)
Off Mode (Not displayed. See defi nition that follows.)
The process of determining each mode is discussed below, but
the actual operation of each mode is explained in the section that
follows.
Defi nitions of Modes
VAVBOX Control Schemes
On all fan-powered and non-fan-powered terminal units, the supply
air modes are calculated from supply air temperature, and space
demands are calculated from setpoints. If the supply air temperature
rises the deadband amount above the space temperature, the
supply air mode is heating. To cancel the supply air heating mode,
the supply air temperature must fall to within 2ºF of the space
temperature. If the supply air falls the deadband amount below the
space temperature, the supply air mode is cooling. To cancel the
supply air cooling mode, the supply air temperature must rise to
within 2 ºF of the space temperature. If the supply air is between
the heating and cooling deadband amounts, it is considered to be
in neutral mode.
Supply Air Neutral Mode
This mode occurs when the Supply Air Temperature is between the
user-programmed heating and cooling deadband amounts.
Space Vent Mode
This mode occurs when the Space Temperature is between the
user-programmed heating and cooling setpoints.
Supply Air Cooling Mode
This mode occurs when the Supply Air Temperature falls the
deadband amount below the space temperature. To cancel the
supply air cooling mode, the supply air temperature must rise to
within 2°F of the space temperature.
Space Cooling Mode
This mode occurs when the Space Temperature rises above the
user-programmed Space Cooling Setpoint.
Supply Air Heating Mode
This mode occurs when the Supply Air Temperature rises the
deadband amount above the space temperature. To cancel the
supply air heating mode, the supply air temperature must fall to
within 2°F of the space temperature.
Space Heating Mode
This mode occurs when the Space Temperature falls below the
user-programmed Space Heating Setpoint.
Off Mode (Not Displayed)
During unoccupied mode, the mode is considered “OFF” if the
space temperature does not generate a heating mode or cooling
mode based on the unoccupied heating & cooling setpoints.
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 of the VAVBOX TUC-
2R controller. These minimum values 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 VAVBOX 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 VAVBOX damper will go to
the Heating Minimum position.
Vent Minimum
This is the position the VAVBOX damper will move to when the
HVAC unit is in the Supply Air Vent mode.
Nite/Reheat Minimum
This setpoint has two different functions depending on whether the
HVAC unit is in Occupied or Unoccupied mode.
WCC III VAV BOX III Operation Modes