Carrier 50TCA04-A07 - Manual (Page 43)

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outdoor--air dampers closed to maintain the proper
supply--air temperature.
HEATING, UNITS WITH ECONOMI$ER IV — When
the room temperature calls for heat, the heating controls
are energized as described in the Heating, Units Without
Economizer section.
ECONOMIZER IN OCCUPIED MODE — The
economizer logic will be energized when the unit IFC is
energized. The economizer damper will open to the
minimum position setting and remain open until the IFC is
de--energized.
ECONOMIZER IN UNOCCUPIED MODE — The
economizer damper will remain closed during Unoccupied
Mode periods.
Operating Sequence, 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 Premier--Link 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.
When Y2 is energized, the economizer will be modulated
to control to a lower supply air setpoint SASP= SATLO2
+ 3_F If the SAT > SASP + 5_F it will close the
economizer to minimum position for 3 minutes, reset the
integrator for the economizer, then start modulating the
economizer to maintain the SASP after the stage two has
been on for 90 seconds. This provides protection for the
compressor against flooded starts and allow refrigerant
flow to stabilize before modulating the economizer again.
By using return air across the evaporator coil just after the
compressor has started allows for increased refrigerant
flow rates providing better oil return of any oil washed out
during compressor start--up.
Routine No. 3: If the OAT > 68_F and the enthalpy is low
and the OAT <SPT then the economizer will open to
100% and compressors 1 and 2 will be cycled based on
Y1 and Y2 inputs respectively. If any of these conditions
are not met the economizer will go to minimum position.
If there is no call for heating or cooling, the economizer,
if available, will maintain the SASP at 70_F.
Heating — For gas or electric heat, HS1 and HS2 outputs
will follow W1 and W2 inputs respectively. The fan will
also be turned on if it is configured for electric heat.
50TC