Orion System VAV/Zone Controller - Manual (Page 15)

VAV/Zone Controller
Technical Guide
15
Dump Zone
If this VAV/Zone controller is to be used as a “Dump Zone” set this
configuration to 1=Yes. The dump zone is a controller without an ac-
tuator that is used to control a duct heater or auxiliary heat. Options
available are:
0 = No
1 = Yes
AHU Heat Call
This setting is located under the “Setpoints” menu on screen #3. This is
used only for the unoccupied mode. For non-fan powered terminal units
this temperature setpoint is used to allow auxiliary heat such as base-
board heaters to be energized in an attempt to satisfy the heating de-
mand prior to initiating the HVAC unit Supply Air Heating mode. For
fan powered terminal units this setpoint can be used to operate the se-
ries or parallel box to satisfy the heating demand by using plenum air
and reheat prior to initiating HVAC Supply Air Heating mode.
During unoccupied mode when the temperature in the space drops be-
low the AHU Heat Call setpoint the VAV/Zone controller sends a signal
to the VAV/CAV controller to initiate the HVAC unit Supply Air Heat-
ing Mode. This setpoint temperature can be set higher or lower than the
Space Heating setpoint.
Scheduling
Occupied/Unoccupied Mode
The VAV/Zone Controller monitors the communications loop for its
Occupied and Unoccupied mode of operation command. Either the VAV/
CAV Controller or a special Optimal Start Scheduling device can trans-
mit the Occupied command to the VAV/Zone Controller. This requires
the VAV/Zone Controllers to all be connected to the system communi-
cation 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 VAV/Zone Controller
and VAV/CAV 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 VAV/Zone Con-
trollers can be configured into groups so that an override generated by
one VAV/Zone Controller can cause several other controllers to follow
along and return to occupied mode for the programmed duration. Other
VAV/Zone 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 VAV/
Zone 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
VAV/Zone 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 VAV/Zone Controller Space Temp.)
•
Supply Air Cooling Mode
(Based on HVAC Unit SAT)
•
Space Cooling Mode
(Based on VAV/Zone Controller Space Temp.)
•
Supply Air Heating Mode
(Based on HVAC Unit SAT)
•
Space Heating Mode
(Based on VAV/Zone 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
VAV & Zone Control Schemes
On all fan-powered and non-fan-powered terminal units, ‘VAV’ or ‘Zon-
ing’, 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 tem-
perature 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 cooling mode, the supply air temperature must rise above
the heating setpoint. If the supply air is between the heating and cooling
setpoints, it is considered 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.