Carrier 48TCA04---A12 - Manual (Page 72)

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During free cooling operation, a supply air temperature
(SAT) above 50_F will cause the dampers to modulate
between Minimum Position setpoint and 100% open. With
SAT from 50_F to 45_F, the dampers will maintain at the
Minimum Position setting. With SAT below 45_F, the
outside air dampers will be closed. When SAT rises to
48_F, the dampers will re--open to Minimum Position
setting.
Should 100% outside air not be capable of satisfying the
space temperature, space temperature will rise until Y2 is
closed. The economizer control will call for compressor
operation. Dampers will modulate to maintain SAT at 50
to 55_F concurrent with compressor operation. The Low
Ambient Lockout Thermostat will block compressor
operation with economizer operation below 42_F outside
air temperature.
When space temperature demand is satisfied (thermostat
Y1 opens), the dampers will return to Minimum Damper
position if indoor fan is running or fully closed if fan is
off.
If accessory power exhaust is installed, the power exhaust
fan motors will be energized by the economizer control as
the dampers open above the PE--On setpoint and will be
de--energized as the dampers close below the PE--On
setpoint.
Damper movement from full closed to full open (or vice
versa) will take between 1--1/2 and 2--1/2 minutes.
Heating With EconoMi$er IV
During Occupied mode operation, indoor fan operation
will be accompanied by economizer dampers moving to
Minimum Position setpoint for ventilation. If indoor fan is
off, dampers will close. During Unoccupied mode
operation, dampers will remain closed unless a DCV
demand is received.
When the room temperature calls for heat (W1 closes), the
heating controls are energized as described in Heating,
Unit Without Economizer above.
PremierLink Control
THERMOSTAT MODE — If the PremierLink controller
is configured for Thermostat mode (TSTAT), it will
control only to the thermostat inputs on J4. These inputs
can be overridden through CCN communication via the
CV_TSTAT points display table. When in this mode, the
fire safety shutdown (FSD) input cannot be used, so any
fire/life safety shutdown must be physically wired to
disable the 24 vac control circuit to the unit.
Indoor Fan — The indoor fan output will be energized
whenever there is 24 vac present on the G input. The
indoor fan will be turned on without any delay and the
economizer damper will open to its minimum position if
the unit has a damper connected to the controller. This
will also occur if the PremierLink controller has been
configured for electric heat or heat pump operation.
Cooling — For cooling operation, there must be 24 vac
present on G. When G is active, the PremierLink
controller will then determine if outdoor conditions are
suitable for economizer cooling when an economizer
damper is available. A valid OAT, SPT (CCN space
temperature) and SAT (supply air temperature) sensor
MUST be installed for proper economizer operation. It
recommended that an outdoor or differential enthalpy
sensor also be installed. If one is not present, then a
jumper is needed on the ENTH input on J4, which will
indicate that the enthalpy will always be low. Economizer
operation will be based only on outdoor air dry bulb
temperature. The conditions are suitable when: enthalpy is
low, OAT is less than OATL High Lockout for TSTAT,
and OAT is less than OATMAX, the high setpoint for free
cooling. The default for OATL is 65_F. The default for
OATMAX is 75_F.
When all of the above conditions are satisfied and all the
required sensors are installed, the PremierLink controller
will use the economizer for cooling. One of three different
control routines will be used depending on the
temperature of the outside air. The routines use a PID loop
to control the SAT to a supply air setpoint (SASP) based
on the error from setpoint (SASPSAT). The SASP is
determined by the routine.
If an economizer is not available or the conditions are not
met for the following economizer routines below, the
compressors 1 and 2 will be cycled based on Y1 and Y2
inputs respectively.
Any time the compressors are running, the PremierLink
controller will lock out 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.
Routine No. 1: If the OAT ≤ DXLOCK (OAT DX lockout
temperature) and DX Cooling Lockout is enabled when
Y1 input is energized, the economizer will be modulated
to maintain SAT at the Supply Air Setpoint (SASP) =
SATLO1 + 3_F (Supply Air Low Temp lockout for
compressor 1). When Y2 is energized, the economizer
will be modulated to control to a lower SASP = SATLO2
+ 3_F (Supply Air Low Temp lockout for compressor no.
2). Mechanical cooling is locked out and will not be
energized.
Routine No. 2: If DXLOCK (or DX Cooling Lockout is
disabled) < OAT ≤ 68_F when Y1 input is energized, the
economizer will be modulated to maintain SAT at SASP =
SATLO1 + 3_F. If the SAT > SASP + 5_F and the
economizer position > 85% then the economizer will
close the to minimum position for three minutes or until
the SAT > 68_F. The economizer integrator will then be
reset and begin modulating to maintain the SASP after
stage one has been energized for 90 seconds.
48TC