Building Control (Field Installed)
Zone Controller Retro-fit CV AHU, Application Specific
Air Handler Units CV — Air Manager Sequence of Operation
Note: The following is a sample of a typical sequence of operation that may be adapted for a
particular project with a Constant Volume Air Handler. This is provided as a suggestion on how to
write a sequence of operation for a specific project. The Air Handler Retrofit Controller (ARC)
includes the ability for the operator to select some different sequences. Consult your Carrier
representative if the sample sequence requires alterations.
4.3.6
Air Handler Retrofit Controller (ARC)
4.3.6.1 Sequence of Operation Descriptions — Constant Volume
Sequence of operation for a Constant Air Volume air handler with a supply fan and slaved return
fan, heating and cooling coil, CO2 damper override, economize damper control, and Unoccupied
Free Cooling.
A. General:
The time schedule shall be indexed to the occupied mode based on a global or local time schedule,
timed override command from the EMS operators station (local or remote), or if an occupant has
pushed the override button on the thermostat. After a timed override has expired, the unit shall be
indexed back to its unoccupied mode if the time schedule is still unoccupied, otherwise it shall remain
in the occupied mode.
During the unoccupied cycle, if the unoccupied heat or cool setpoints are exceeded, the unit shall
start with its dampers closed until the unoccupied setpoints are no longer exceeded.
B. Unoccupied Free Cooling (UFC):
The unit shall be indexed to the Unoccupied Free Cooling (UFC) mode whenever the unit is
unoccupied, the space temperature is at least 2°F above the occupied temperature setpoint and the
outside air temperature is at least 8°F below the space temperature. Whenever the outside air
temperature is greater than 60°F (operator adjustable) the algorithm shall lock out UFC.
When the unit is indexed to the UFC mode, the supply and interlock return fan shall start, the
economizer dampers shall open, and the mechanical cooling shall be disabled. UFC shall remain
in effect until the space temperature is below the setpoint or outside air temperature rises above
60°F (operator adjustable).
C. Heating Control:
When the supply fan is on, the heating valve shall be modulated to maintain its occupied and
unoccupied setpoints. The routine shall use the space sensor as the master sensor and the discharge
sensor as the submaster sensor.
When the supply fan is off, the routine shall modulate the heating valve to maintain a minimum
duct temperature and help protect against freezing.
D. Cooling Control:
When the supply fan is on, the cooling coil valve shall be modulated to maintain its occupied and
unoccupied setpoints. The valve shall be closed whenever the space temperature is below the
cooling setpoint. The routine shall use the space sensor as the master sensor and the discharge
sensor as the submaster sensor.
The valve shall be closed whenever the supply fan is off, the system is indexed to UFC, or the unit
is providing heat.
E. Damper Control:
The economizer dampers shall be modulated to maintain a space temperature that is between the
heating and cooling setpoints. The mixed air damper control routine shall automatically determine the
setpoint by reading the setpoint values and determining what value is between the heating and
cooling setpoints.
During the unoccupied cycle, the mixed air dampers shall be closed to outside and exhaust air and
open to return air unless the dampers have been indexed to UFC.
The minimum damper position shall be the greatest of the supplied configured minimum positions as
applicable, from the IAQ routine or this routine, whichever is the greatest.
When the supply fan is off, the mixed air dampers shall be kept closed to outside and exhaust air and
open to return air.
F. Indoor Air Quality (IAQ):
Whenever the supply fan is on, the unit is in the occupied mode and the return CO2 rises above its
adjustable setpoint, a PI loop shall calculate a new minimum damper position necessary to maintain
the CO2 setpoint. As the CO2 level falls below its setpoint the routine shall lower its calculated value
for the minimum damper position.
IAQ shall be suspended whenever the average space temperature or return air humidity are outside
the comfort limits. If the mixed air temperature falls below 48°F, the dampers shall be repositioned to
maintain a minimum mixed air temperature of 48°F.
The maximum damper position shall automatically be limited to a maximum position of 80% (operator
adjustable) whenever the unit is indexed to the IAQ mode.