Indoor Fan Operation - Carrier 48LC Series Controls, Start-Up, Operation And Troubleshooting

While using the programmed schedule, occupancy can be
temporarily switched from unoccupied to occupied by pressing the
override button for approximately 3 seconds on the T- -55, T- -56, or
T- -59 space temperature sensor. The length of the override period
when pressing the override button is determined by the Override
Time Limit (TIMED OVR LENGTH). The hours remaining in
override is displayed as Timed Override Hours (TIMED OVR
HOURS). This point can also be changed from the local display or
network to set or change the override period length.
Remote Occupancy Switch (REMOTE OCC SWITCH) can be
forced or configured for operation based on an actual switch. The
physical switch should be configured to either Normally Open or
Normally Closed when the user would like to control the
occupancy with an external switch. This switch is field- -supplied
(24v, single pole, single throw [SPST]). There are two possible
configurations for the remote occupancy switch:
1. (REMOTE OCC TYPE = 0) Normally Open Switch
1. (REMOTE OCC TYPE = 1) Normally Closed Switch
If the switch is configured to No Switch (REMOTE OCC CHAN =
None), the switch input value will be ignored and software will
proceed to level 3 priority. For each type of switch, the appropriate
configuration and states are listed in the table below.
SWITCH
TYPE OF SWITCH
CONFIGURATION
Occupied when Closed
Normal Open (0)
or Unoccupied when
Open
Occupied when Open or
Normal Closed (1)
Unoccupied when
Closed
Level 3 Priority
The following occupancy options are determined by the state of
Occupancy Schedule Number (SCHEDULE NUMBER) and the
Global Schedule Broadcast (BROADCAST SCHEDL?).
1. (SCHEDULE NUMBER = 0) The unit is always
considered occupied and the programmed schedule is
ignored. This is the factory default.
2. (SCHEDULE NUMBER = 1- 64) Follow the local
programmed schedule. Schedules 1 to 64 are local within
the controller. The unit can only store one local schedule
and therefore changing this number only changes the title of
the schedule table.
3. (SCHEDULE NUMBER = 65- 99) Follow the global
programmed schedule. If the unit is configured as a Global
Schedule Broadcaster (BROADCAST SCHEDL? = YES),
the unit will follow the unit s programmed schedule and
broadcast the schedule so that other devices programmed to
follow this schedule number can receive the schedule. If the
unit is not programmed as a Global Schedule Broadcaster
(BROADCAST SCHEDL? = NO), the unit will receive
broadcasted schedules from a unit programmed to broadcast
this schedule number.
Humidity Demand
When the unit is configured for either a Humidistat input
(HUMSTAT CHANNEL) or Space Humidity Sensor (SPRH
SENS CHANNEL) the level 5 demand in Table 8 will include a
determination of dehumidification demand.
Humidistat
When receiving an active
(HUMIDISTAT), dehumidification will be demanded.
Space Relative Humidity
On units with a relative humidity sensor, when the received value
of space relative humidity (SPRH LEVEL) has exceed the
humidity set point (SPRH SET POINT), dehumidification will be
demanded. This demand will remain until the space relative
humidity has fallen below the humidity set point by more than the
STATE OF SWITCH AND
STATE OF OCCUPANCY
Open and Unoccupied
Closed and Occupied
Open and Occupied
Closed and Unoccupied
input from the Humidistat
humidity set point deadband (SPRH DEADBAND). This would
come from the space humidity sensor, or building network.

Indoor Fan Operation

These units use the Staged Air Volume (SAV) method of controlling
the supply fan for a typical constant volume rooftop unit. This control
method employs a variable frequency drive (VFD) to operate the
supply fan at different speeds in order to achieve energy savings
through reduced fan power. This method is specifically not concerned
with controlling static pressure in the supply duct, but rather with
setting different fan speeds for different operating conditions, such as
ventilation mode or part- -load mechanical cooling.
The SAV function is NOT a Variable Air Volume (VAV) function.
The fan adapts its speed to one of eight based on mode and current
state to satisfy a demand. The eight speeds consist of off (0%) and
seven configurable values. The seven configurable fan speeds are:
Maximum Speed (MAXIMUM IDF SPEED), Ventilation (VENT
IDF SPEED), Heating (HEATING IDF SPD), Free Cool (FREE
COOL IDF SPD), Mechanical Low Cooling (LOW COOL IDF
SPD), Mechanical Medium Cooling (MED COOL IDF SPD), and
Mechanical High Cooling (HIGH COOL IDF SPD), The VFD is
powered direct from the distribution block or circuit breaker (CB)
and is always on with power applied unless the CB is tripped.
When the thermostat or space sensor control conditions require the
fan on, the VFD will then ramp to desired speed. Fan speed is
always calculated by evaluating the current applicable conditions.
Each fan speed condition is evaluated independently, and the
highest fan speed is used. For example, if a cooling call occurs
during Ventilation mode, the unit mode will transition to cooling
but the fan speed is set to the higher of the two (VENT IDF
SPEED or LOW COOL IDF SPD). Refer to the speed
configurations below for when the fan will run at them.
Direct Drive Units
Alternately, 48/50LC04- -06 units can have either a direct drive
Electronic Commutated Motor (ECM) fan system or a belt drive
motor powered by a Variable Frequency Drive (VFD). And
IDFTYPE=1 indicates a unit with VFD, while an IDFTYPE=2
indicates a direct drive system. Refer to the unit product data for
Fan Performance tables and physical data. On direct drive units, the
ECM has 5 speed taps to allow a range of fan performance. The
control has 3 output wires to connect to 3 different taps. From the
factory the low and high speed wires are connected to the first and
second speed taps, respectively. The ventilation speed tap is
disconnected. The speed taps increase the speed the higher the tap
number, so the first tap is the lowest speed and tap 5 is the highest
speed. If the low and high speed wires are moved to higher taps,
the ventilation speed wire can be wired into the motor. To activate
the use of the ventilation speed wire, the Number of Speeds
(SETTINGSUNIT CONFIGURATIONSINDOOR FAN
NUMFSPDS) configuration must be set to 3.
The Commanded Fan
FANFANSPEED) represents the controls commanded speed for
the fan at any given time. This commanded speed is determined by
the unit's current HVAC mode and the unit control type. For gas
heating units, the IGC fan request output (InputsGEN.IIGC.F) is
monitored by the control. This can result in additional modification of
fan delays or other operation due to safety functions of the IGC
control. See the Gas Heating operation section for more details. If
configured for IAQ fan operation, the fan may be turned on to satisfy
air quality demands. See the Indoor Air Quality section if using IAQ
(indoor air quality) accessory sensors. The fan can run under
thermostat or space sensor control and will remain on if compressors
or heat relays are ever stuck on. If Shut Down on IDF Failure is
enabled (SHUTDOWN IDF FAIL = Yes), the fan and unit will be
shutdown without delay on fan alarm conditions. Fan off delays are
honored when exiting specific HVAC modes. The Fan- -off Delay
delays are as follows: Cooling (COOL FANOFF DELAY), and
Heating (HEAT FANOFF DELAY).
16
(OUTPUTSINDOOR
Speed