Carrier 48TCA04---A12 User Manual

Page 74

If 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

When Temperature Compensated Start is active

When Free Cool is active

When Pre--Occupancy Purge is active

Whenever there is a demand for cooling or heating in the

unoccupied mode

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)

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

Whenever 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:

indoor fan has been ON for at least 30 seconds

heat mode is not active and the time guard between

modes equals zero.

mode is occupied or the Temperature Compensated Start

or Cool mode is active

SPT reading is available and > (OCSP + STO)

If mode is unoccupied and the SPT > (UCSP +

Unoccupied Cooling Deadband). The indoor fan will be

turned on by the staging algorithm.

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

a demand 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

STAGES

(ECONOMIZER*)

Compressor 1

Off

Compressor 2

Off

* 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.

48TC