Carrier 48TCA04---A12 appendix Available Cooling Stages

48TC

SIf the PremierLink controller is in the occupied mode and ASHRAE 90.1 Supply Fan is configured for Yes when Linkage is active and the Linkage Coordinator device is sending an occupied mode flag

S When Temperature Compensated Start is active S When Free Cool is active

SWhen Pre-Occupancy Purge is active

SWhenever there is a demand for cooling or heating in the unoccupied mode

S Whenever the Remote Contact input is configured for Remote Contact (RC_DC=1 in SERVICE table) and it is closed or the point is forced Closed via communications in the STATUS01 points display table (remote contact closed = occupied, remote contact open = unoccupied)

S Whenever the H3_EX_RV point is configured for Dehumidification (AUXOUT=5 in CONFIG table) and it is in the unoccupied mode and the indoor RH exceeds the unoccupied humidity setpoint

SWhenever the Supply Fan Relay point is forced On in the STATUS01 points display table

The fan will also continue to run as long as compressors are on when transitioning from occupied to unoccupied with the exception of Fire Shutdown mode. If the Fire Shutdown input point is closed or forced in the STATUS01 points display table, the fan will be shutdown immediately regardless of the occupancy state or demand.

The PremierLink controller 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 the input is not enabled, then it will always be the same state as the Supply Fan Relay. The cooling, economizer and heating routines will use this input point for fan status.

Cooling — The compressors are controlled by the Cooling Control Loop that is used to calculate the desired SAT needed to satisfy the space. It will compare the SPT to the Occupied Cool Setpoint (OCSP) + the T56 slider offset (STO) when occupied and the Unoccupied Cool Setpoint (UCSP + Unoccupied Cooling Deadband) if unoccupied to calculate a Cooling Submaster Reference (CCSR) that is then used by the staging algorithm (Cooling submaster loop) to calculate the required number of cooling stages. The economizer, if available, will be used as the first stage of cooling in addition to the compressors. This loop runs every minute. The following conditions must be met in order for this algorithm to run:

S indoor fan has been ON for at least 30 seconds

S heat mode is not active and the time guard between modes equals zero.

S mode is occupied or the Temperature Compensated Start or Cool mode is active

S SPT reading is available and > (OCSP + STO)

S If mode is unoccupied and the SPT > (UCSP + Unoccupied Cooling Deadband). The indoor fan will be turned on by the staging algorithm.

S OAT > DXLOCK or OAT DX Lockout is disabled

If all of the above conditions are met, the CCSR will be calculated, otherwise it is set to its maximum value and DX stages is set to 0. If only the last condition is not true and an economizer is available, it will be used to cool the space.

The submaster loop uses the CCSR compared to the actual SAT to determine the required number of capacity stages to satisfy the load. There is a programmable minimum internal time delay of 3 to 5 minutes on and 2 to 5 minutes off for the compressors to prevent short cycling. There is also a 3-minute time delay before bringing on the second stage compressor. If the PremierLink controller is configured for Heat Pump and AUXOUT is configured for Reversing Valve Cool, the H3_EX_RV output will energize 2 seconds after the first compressor is energized and stay energized until there is a demand for heat. If AUXOUT is configured for Reversing Valve Heat, then the H3_EX_RV contact will be deenergized when there is

ademand for cooling. An internal 5 to 10-minute user-programmable time guard between modes prevents rapid cycling between modes when used in a single zone application. The Time Guard is lowered to 3 minutes when Linkage is active to allow the 3Vt linkage coordinator to have better control of the PremierLink controller when used as the air source for the 3V control system.

Table 29 indicates the number of stages available. The staging algorithm looks at the number of stages available based the number of cool stages configured in the SERVICE configuration table. The algorithm will skip the economizer if it is not available and turn on a compressor.

Table 29 – Available Cooling Stages

NUMBER OF	0	1	2	3
STAGES		(ECONOMIZER*)
Compressor 1	Off	Off	On	On
Compressor 2	Off	Off	Off	On

* If conditions are suitable for economizer operation.

Any time the compressors are running, the PremierLink controller will lockout the compressors if the SAT becomes too low. These user configurable settings are found in the SERVICE configuration table:

Compressor 1 Lockout at SAT < SATLO1 (50 to 65_F) (default is 55_F)

Compressor 2 Lockout at SAT < SATLO2 (45 to 55_F) (default is 50_F)

After a compressor is locked out, it may be started again after a normal time-guard period and the supply air temperature has increased at least 8_F above the lockout setpoint.

Dehumidification — The PremierLink controller will provide occupied and unoccupied dehumidification control when AUXOUT = 5 in the CONFIG table and is installed on HVAC units that are equipped with additional controls and accessories to accomplish this function. This function also requires a space relative humidity sensor be installed on the OAQ/IRH input.

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