Carrier 48TC*D08 User Manual

Page 80

If the OAT is between DXLOCK and 68_F (DXLOCK <

OAT < 68_F) and additional cooling is required, the

economizer will close the to minimum position for three

minutes, the economizer integrator will then be reset to 0

and begin modulating to maintain the SASP after the stage

has been energized for about 90 seconds. This will allow

the economizer to calculate a new ECONSR that takes

into account the cooling effect that has just been turned on

and not return to the value require before the cooling was

added. This will prevent the economizer from causing

premature off cycles of compressors while maintaining the

low SAT temperature setpoint for the number of stages

active. In addition to preventing compressor short cycling,

by using return air across the evaporator coil just after the

compressor has started allows for increased refrigerant

flow rates providing for better oil return of any oil washed

out during compressor start--up.

If the OAT > 68_F and OAT < SPT and the number of DX

stages requested is > 0 by the staging algorithm, then

ECONSR is set to its minimum value 48_F and the

damper will go to 100% open.

If the Auxiliary Relay is configured for exhaust fan

(AUXOUT = 1) in the CONFIG configuration table and

Continuous Power Exhaust (MODPE) is Enable in the

SERVICE configuration table, then the AUXO output

(HS3) will be energized whenever the PremierLink

controller is in the occupied mode. If the MODPE is

disabled then AUXO output will be energized based on

the Power Exhaust Setpoint (PES) in the SETPOINT

table.

Heating — The heat stages are controlled by the Heating

Control Loop, which is used to calculate the desired SAT

needed to satisfy the space. It will compare the SPT to the

Occupied Heat Setpoint (OHSP) + the T56 slider offset

(STO) when occupied and the Unoccupied Heat Setpoint

(UHSP -- Unoccupied Heating Deadband) if unoccupied to

calculate a Staged Heat Submaster Reference (SHSR).

The heat staging algorithm compares the SHSR to the

actual SAT to calculate the required number of heating

stages to satisfy the load. This loop runs every 40 seconds.

The following conditions must be met in order for this

algorithm to run:

Indoor fan has been ON for at least 30 seconds.

Cool mode is not active and the time guard between

modes equals zero.

Mode is occupied or the Temperature Compensated Start

or Heat mode is active.

SPT reading is available and < (OHSP + STO).

If it is unoccupied and the SPT < (UHSP -- Unoccupied

Heating Deadband). The indoor fan will be turn on by the

staging algorithm.

When all of the above conditions are met, the SHSR is

calculated and up to 3 stages of heat will turned on and off

to satisfy to maintain the SAT = SHSR. If any of the

above conditions are not met, the SHSR is set to its

minimum value of 35_F.

The Staged Heat Submaster Reference (SHSR) is

calculated as follows:

SHSR = Heating PID function on (error) where error =

(OHSP + STO) -- Space Temperature

The Maximum SHSR is determined by the SATHI

configuration. If the supply--air temperature exceeds the

SATHI configuration value, then the heat stages will turn

off. Heat staging will resume after a delay to allow the

supply--air temperature to drop below the SATHI value.

The maximum number of stages available is dependent on

the type of heat and the number of stages programmed in

the CONFIG and SERVICE configuration tables. Staging

will occur as follows for gas electric units, Carrier heat

pumps with a defrost board, or cooling units with electric

heat:

For Heating PID STAGES = 2

HEAT STAGES = 1 (50% capacity) -- energize HS1.
HEAT STAGES = 2 (100% capacity) -- energize HS2.

For Heating PID STAGES = 3 and AUXOUT = HS3

HEAT STAGES = 1 (33% capacity if) -- energize HS1
HEAT STAGES = 2 (66% capacity) -- energize HS2
HEAT STAGES = 3 (100% capacity) -- energize HS3

Staging will occur as follows For heat pump units with

AUXOUT configured as reversing valve:

For Heating PID STAGES = 2 and AUXOUT = Reversing

Valve Heat (the H3_EX_RV output will stay energized

until there is a cool demand) HEAT STAGES = 1 (50%

capacity) shall energize CMP1, CMP2, RVS.

HEAT STAGES = 2 (100% capacity) shall energize HS1

and HS2.

Heating PID STAGES = 3 and AUXOUT = Reversing

Valve Heat (the H3_EX_RV output will stay energized

until there is a cool demand)

HEAT STAGES = 1 (33% capacity if) shall energize

CMP1, CMP2, RVS

HEAT STAGES = 2 (66% capacity) shall energize HS1

HEAT STAGES = 3 (100% capacity) shall energize HS2

If AUXOUT is configured for Reversing Valve Cool, then

the H3_EX_RV contact will be deenergized when there is

a demand for heating. The heat stages will be cycled to

temper the SAT so that it will be between the SPT and the

SPT + 10_F (SPT < SAT < (SPT + 10_F)) if:

the number of heat stages calculated is zero

the OAT < 55_F

an IAQ sensor is installed

the IAQ Minimum Damper Position > minimum damper

position

and the SAT < SPT --10_F.

48TC