WattMaster VAVBOX - Manual (Page 14)

Technical Guide
VAVBOX Controller 14
Sequence Of Operations
During unoccupied mode when the temperature in the space drops be-
low the AHU Heat Call setpoint the VAVBOX controller sends a signal
to the WMVAV controller to initiate the HVAC unit Supply Air Heating
Mode. This setpoint temperature can be set higher or lower than the
Space Heating setpoint.
Scheduling
Occupied/Unoccupied Mode
The VAVBOX Controller monitors the communications loop for its
Occupied and Unoccupied mode of operation command. Either the
WMVAV Controller or a special Optimal Start Scheduling device can
transmit the Occupied command to the VAVBOX Controller. This re-
quires the VAVBOX Controllers to all be connected to the system com-
munication loop through their RS-485 connector and to be properly
addressed for the command to be received.
Push-button Override Operation
During unoccupied hours, the user can force the VAVBOX Controller
and WMVAV Controller back to occupied operation by pressing the
override button for a period of time less than 3 seconds. This initiates
the override or resets the override timer back to zero during unoccupied
hours of operation.
During Override operations, the user can cancel the override by press-
ing the override button for a period of time between 3 seconds and 10
seconds. This restores the normal unoccupied operation.
On larger installations with several terminal units, the VAVBOX Con-
trollers can be configured into groups so that an override generated by
one VAVBOX Controller can cause several other controllers to follow
along and return to occupied mode for the programmed duration. Other
VAVBOX Controllers not in the same group will simply maintain an
unoccupied damper or airflow setting as set by the user.
Push-button overrides are broadcast continuously by the initiating
VAVBOX Controller until the controller itself times out or the override
is cancelled by the user. This broadcast forces the air handler to start its
main fan and provide cooling or heating, if so configured. It will remain
on until the override broadcast has not been detected for at least 2 con-
secutive minutes.
Modes Of Operation
General
There are 7 possible modes of operation for the HVAC Unit and the
VAVBOX controller. These modes are determined by the supply air
and/or space demand conditions. They are:
•
Supply Air Vent Mode
(Based on HVAC Unit SAT)
•
Space Vent Mode
(Based on VAVBOX Controller Space Temp.)
•
Supply Air Cooling Mode
(Based on HVAC Unit SAT)
•
Space Cooling Mode
(Based on VAVBOX Controller Space Temp.)
•
Supply Air Heating Mode
(Based on HVAC Unit SAT)
•
Space Heating Mode
(Based on VAVBOX Controller Space Temp.)
•
Off Mode (Not displayed. See definition below)
The process of determining each mode is discussed below, but the ac-
tual operation of each mode is explained in the section that follows.
Definitions Of Modes
VAVBOX Control Schemes
On all fan-powered and non-fan-powered terminal units, supply air
modes and space demands are calculated the same. If the supply air
rises 1 ºF above the cooling setpoint, the supply air mode is heating. To
cancel the supply air heating mode, the supply air temperature must fall
below the cooling setpoint. If the supply air falls 1 ºF below the heating
setpoint, the supply air mode is cooling. To cancel the supply air cool-
ing mode, the supply air temperature must rise above the heating setpoint.
If the supply air is between the heating and cooling setpoints, it is con-
sidered vent mode.
Supply Air Vent Mode
This mode occurs when the Supply Air Temperature is between the
heating and cooling setpoints.
Space Vent Mode
This mode occurs when the Space Temperature is between 0.5 °F be-
low the Cooling Setpoint and 0.5 °F above the Heating Setpoint.
Supply Air Cooling Mode
This mode occurs when the Supply Air Temperature falls to 1.0 °F
below the Space Heating Setpoint.
Space Cooling Mode
This mode occurs when the Space Temperature rises to 0.5 °F below
the Space Cooling Setpoint.
Supply Air Heating Mode
This mode occurs when the Supply Air Temperature rises to 1.0 °F
above the Space Cooling Setpoint.
Space Heating Mode
This mode occurs when the Space Temperature falls to 0.5 °F above
the Space Heating Setpoint.
Off Mode
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.