Building HVAC (Equipment w/Factory-Installed Controls)
42 Series Fan Coil Controller
Fan Coil - Sequence of Operation
Note: The following is a sample of a typical Sequence of Operation that may be adapted for a
particular project. This is provided as a suggestion on how to write a Sequence of Operation for a
specific project. The Fan Coil includes the ability for the operator to select some different
sequences. Consult your Carrier representative if the sample sequence requires alterations.
4.2.7
Fan Coil Controller (FC) - Product Integrated Control (PIC), Sequence of Operation
4.2.7.1 Sequence of Operation Description
A. Four-Pipe Heating and Cooling
1. Manual Fan Operation:
When the fan speed/mode selector switch is placed in the “AUTO” position and the controller is in
the occupied mode, the controller shall start the fan on “LO” speed and then transition to and from
the other speeds based on the Fan Coil Retrofit Controller (FRC) algorithms. When the fan
speed/mode selector switch is placed in the “OFF” position the FRC shall disable the fan. When
the fan speed/mode switch is indexed to “LO,” “MED,” or “HI,” the FRC shall disable its fan speed
control algorithms and operate the fan at the specified speed.
2. Occupied or Tenant Override Operating Mode:
The fan shall run continuously during the occupied or tenant override modes unless the fan
speed/mode selector switch is indexed to the “OFF,” “LO,” “MED,” or “HI” speed position. If
indexed to “OFF,” the control shall be disabled. If indexed to “LO,” “MED,” or “HI,” the control shall
operate in an occupied mode and the fan shall run continuously at only the specified speed.
3. Temperature Compensated Start:
During the unoccupied mode, the FRC shall calculate an optimum start time based on the
deviation from setpoint, actual occupancy time, present time, and an operator adjustable recovery
rate entered in min./°F.
4. Occupied Heating Mode:
During the heating mode, the fan shall be run at the lowest speed necessary to meet the space
load conditions and minimize fan noise. When the unit is unoccupied and is indexed to the
occupied mode, and the fan speed/mode switch is in the “AUTO” position, the fan shall be started
on low speed. The heating valve shall be modulated open to maintain its heating setpoint. As the
load increases the valve shall fully open. As the load continues to increase the FRC shall increase
the fan speeds. When the load decreases the fan shall be indexed to low speed first before
modulating the valve closed. The valve shall be controlled at all times to limit the discharge
temperature to 140°F.
5. Occupied Cooling Mode:
During the cooling mode the fan shall be run at the lowest speed necessary to meet the space
load conditions and minimize fan noise. When the unit is unoccupied and is indexed to the
occupied mode, and the fan speed/mode switch is in the “AUTO” position, the fan shall be started
on low speed and the valve shall be modulated to maintain its cooling setpoint. If the load
continues to increase, the valve shall be fully open. If the load continues to increase the FRC shall
increase the fan speed. As the load decreases the fan speeds shall be reduced prior to closing the
valve. If the load continues to drop and the fan speed is operating at low speed, the valve shall
modulate closed to maintain its cooling setpoint.
6. Unoccupied Heating Mode (Fan Switch in “AUTO” position):
When the space temperature falls below the unoccupied heating setpoint the fan shall start and
the valve shall modulate open to maintain the unoccupied heating setpoint. If the load continues to
increase the valve shall be fully opened before increasing the fan speeds to maintain the
unoccupied heating setpoint. As the load decreases the fan speed shall be reduced, at which
point the FRC shall begin to modulate the valve closed to maintain the unoccupied heating
setpoint. When the space temperature is above the unoccupied heating setpoint, the fan shall be
de-energized.
7. Unoccupied Cooling Mode (Fan Switch in “AUTO” position):
When the space temperature rises above the unoccupied cooling setpoint the fan shall be started
and the valve shall be modulated to maintain the unoccupied cooling setpoint. If the load
continues to increase the valve shall be fully open before increasing the fan speeds to maintain the
unoccupied cooling setpoint. As the load decreases the fan speeds shall be reduced, at which
point the FRC shall begin to modulate the cooling valve closed to maintain the unoccupied cooling
setpoint. When the space temperature is below the unoccupied cooling setpoint the fan shall be
de-energized.
8. Unoccupied Timed Override:
Timed override shall be used to extend the occupied schedule for zero to four hours. Timed
override shall be initiated by the operator or by an occupant pushing the override button on the
space sensor, if enabled by the operator.
Note: Optional Features and Sequences
9. Remote Occupancy Input:
The remote occupancy input shall be used to control the operating mode of the unit. Whenever a
signal is detected at this input, and the unit is not controlled by the Linkage Thermostat, the unit
shall operate as determined by the occupied and tenant override modes. When the signal is
removed, the unit shall operate as unoccupied unless the FRC has been indexed to its occupied
time schedule by the FRC.
10. Linkage Thermostat Operation:
When the unit is used with the optional Linkage Thermostat, local programming capability for
occupied and unoccupied setpoint and local programming capability for both occupancy and
holiday schedules shall be provided. Also tenant overrides, control of multiple units (up to 8) from a
single thermostat, and a temperature compensated start feature shall also be provided. The
thermostat shall provide an LCD for a digital display of the space temperature, current heating and
cooling setpoints and time. The unit's operating mode and the supply air temperature shall also be
displayed.
The thermostat shall also provide a single common network schedule for any number of units,
broadcast time and holidays. It shall also broadcast the value of a point, common to the entire
system, such as the changeover status on two-pipe applications.
The temperature compensated start feature shall be provided when the Linkage Thermostat is
used. The thermostat and unit(s) shall exchange data through network communications. In this
mode, the unit's occupancy schedule shall be determined by the thermostat. If currently
unoccupied, the unit's control shall determine if the current space temperature is above the
occupied cooling setpoint or below the occupied heating setpoint. If it is, the unit shall calculate the
appropriate biased start time required to achieve the desired setpoints at the scheduled occupancy
time. This value shall then be used by the thermostat to determine the start of the next biased
occupied period. When the biased occupied period is reached, the unit(s) shall control to the
desired occupied heating or occupied cooling setpoint as required.
11. Tenant Override (Linkage Thermostat):
Whenever either setpoint button is depressed on the Linkage Thermostat during an unoccupied
period, the tenant override mode shall be initiated. If the mode is initiated from the Linkage
Thermostat, the duration of the override shall be determined by the value programmed at the
thermostat. The override shall also be cleared at the thermostat if desired.
During the override period, the unit's fan shall operate (if configured for continuous operation
during occupied) and the unit shall operate as described by the occupied modes.