Carrier 50TCA04-A07 User Manual

Page 45

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 Premier--Link

controller when used as the air source for the 3V control

system.

Table 13 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 13 – 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.

When in the occupied mode and the indoor relative

humidity is greater then the Occupied High Humidity

setpoint, then the H3_EX_RV output point will be

energized. When in the unoccupied mode and indoor

relative humidity is greater then the Unoccupied High

Humidity setpoint, then the H3_EX_RV output point and

supply fan output will be energized. There is a fixed 5%

hysteresis that the indoor relative humidity must drop

below the active setpoint to end the dehumidification

mode and deenergize the H3_EX_RV output. If the

PremierLink controller is in the unoccupied mode, then

the fan relay will deenergize if there is no other mode

requiring to the fan to be on. This function will not

energize mechanical cooling as a result of the indoor

relative humidity exceeding either setpoint.

A high humidity alarm will be generated if the indoor

relative humidity exceeds the high humidity setpoint by

the amount configured in the Control Humidity Hysteresis

in the ALARMS table for 20 minutes. The alarm will

50TC