Carrier 48TC*D08 User Manual

Page 84

The Holiday schedule is created to override the Daily

schedule and identify a specific day and month of the year

to start and stop the unit and change control to the

unoccupied heating and cooling setpoints. Follow the

same steps to turn on one of the twelve Holiday schedules

and start and stop times. Next, select one out of the twelve

months and one out of the thirty--one days of that month.

The RTU--MP will now ignore the Daily schedule for the

specific day and time you selected and follow the Holiday

Schedule for this period.
The Override schedules primary purpose is to provide a

temporary change in the occupied heating and cooling

setpoints and force the unit to control to the unoccupied

heating and cooling setpoints. This would occur on a set

day in a particular month and last during the start and stop

time configured. The Override schedule is enabled by

following the same steps to create the Holiday schedule.
NOTE: Push button override is only available when

running a local or BACnet Schedule.
BACnet Schedule
For use with a Building Automation System that supports

native BACnet scheduling is scheduling the unit. With the

Occupancy Source set to BACnet schedule the BAS will

control the unit through network communication and it’s

own scheduling function.
BAS On/Off
The Building Automation System is scheduling the unit

via an On/Off command to the BAS ON/OFF software

point. The Building Automation System can be speaking

BACnet, Modbus, or N2 and is writing to the BAS On/Off

point in the open protocol point map.
NOTE:

If the BAS supports NATIVE BACnet

scheduling, then set the Occupancy Source to BACnet
schedule. If the BAS is BACnet but does NOT support
NATIVE BACnet scheduling, then set the Occupancy
Source to BAS On/Off.
DI On/Off
A hard--wired input on the RTU--MP will command the

unit to start/stop. Inputs 3, 5, 8, and 9 on plug J5 can be

hard--wired to command the unit to start/stop.
NOTE: Scheduling can either be controlled via the unit
or the BAS, but NOT both.
Indoor Fan
The indoor fan will be turned on whenever any one of the

following conditions is true:

It is in the occupied mode. This will be determined by its

own internal occupancy schedule.

Whenever there is a demand for cooling or heating in the

unoccupied mode.

Whenever the remote occupancy switch is closed during

DI On/Off schedule type or if occupancy is forced

occupied by the BAS during BAS On/Off schedule type.

When transitioning from unoccupied to occupied, there

will be a configured time delay of 5 to 600 seconds before

starting the fan. The fan will continue to run as long as

compressors, heating stages, or the dehumidification

relays are on when transitioning from occupied to

unoccupied with the exception of Shutdown mode. If Fire

Shutdown, safety chain, SAT alarm or SPT alarm are

active; the fan will be shutdown immediately regardless of

the occupancy state or demand.
The RTU--MP has an optional Supply Fan Status input to

provide proof of airflow. If this is enabled, the point will

look for a contact closure whenever the Supply Fan Relay

is on. If it is not enabled then it will always be the same

state as the Supply Fan Relay. The cooling, economizer,

heating, dehumidification, CO

and power exhaust

routines will use this input point for fan status.
Cooling
The compressor outputs are controlled by the Cooling

Control PID Loop and Cooling Stages Capacity algorithm.

They will be used to calculate the desired number of

stages needed to satisfy the space by comparing the Space

Temperature (SPT) to the Occupied Cool Setpoint plus the

T56 slider offset when occupied and the Unoccupied Cool

Setpoint (UCSP) plus the T56 slider offset, if unoccupied.

The economizer, if available, will be used for cooling in

addition to the compressors. The following conditions

must be true in order for this algorithm to run:

Indoor Fan has been ON for at least 30 seconds.

Heat mode is not active and the time guard between

modes equals zero.

If occupied and the SPT >(occupied cool setpoint plus

the T56 slider offset).

Space Temperature reading is available.

If it is unoccupied and the SPT > (unoccupied cool

setpoint plus the T56 slider offset). The indoor fan will be

turned on by the staging algorithm.

If economizer is available and active and economizer

open > 85% and SAT > (SAT low limit + 5_F) and SPT >

effective setpoint + 0.5_F.

Economizer is available, but not active

Economizer is not available

OAT > DX Lockout temperature.

If all of the above conditions are met, the compressors

will be energized as required, otherwise they will be

de--energized.
There is a fixed 3--minute minimum on time and a

5--minute off time for each compressor output and a

3--minute minimum time delay between staging up or

down.
Any time the compressors are running the RTU--MP will

stage down the compressors if the SAT becomes less than

the cooling low supply air setpoint.
After a compressor is staged off, it may be started again

after a normal time--guard period and the supply air

temperature has increased above the low supply air

setpoint.

48TC