Economizer - Carrier 48/50PG Series Controls, Start-Up, Operation, Service And Troubleshooting Instructions

Economizer

If an economizer is installed, then Economizer Installed
configuration (Configuration→UNIT→EC.EN) should be set to
YES. The economizer is controlled by the economizer output
signal (Outputs→ECON→EC.CP) on the ECB control. If the
indoor fan is off or the building is unoccupied, the economizer
position is zero. If in Occupied mode and the unit is heating or
cooling and the economizer cannot provide free cooling, the
economizer position is the configured economizer minimum
position (Configuration→ECON→EC.MN) or the position
specified by the IAQ algorithm. If in Unoccupied mode, the
position is 0% open.
The economizer will be allowed to help with cooling if the
outdoor-air temperature (Temperature→AIR.T→OAT) is less than
the configured economizer
(Setpoints→EH.LO) and greater than the configured economizer
low temperature lockout (Setpoints→EL.LO). If an enthalpy
sensor is installed, the outdoor temperature must be below the
economizer high temperature
enthalpy (Inputs→GEN.I→ENTH)
cooling, the economizer position
configured economizer
(Configuration→ECON→EC.MN)
maximum cooling position (Configuration→ECON→EC.MX).
Thermostat Control
If the unit is in cooling, operating under thermostat control, Y1 =
ON, and the economizer is available for cooling, the economizer
will control the supply-air temperature to the low cool set point
(Setpoints→LCSP). When Y2 = ON, the economizer will control
the supply-air temperature
(Setpoints→HCSP).
Space Sensor Control
If the unit is in cooling, operating under space temperature control,
the economizer is available for cooling, and no compressors are
operating, the economizer will control the SAT to either
Setpoints→LCSP or Setpoints→HCSP (See Table 8.) If a
compressor is ON, the economizer will try to position
itself at the economizer maximum
(Configuration→ECON→EC.MX).
If the control senses low suction pressure for any active refrigerant
circuit when the economizer is also providing cooling, the
maximum allowable economizer position will be reduced. Factory
default configurations have been qualified over a large range of
conditions and should only be changed with care. For unit
troubleshooting, factory default maximum economizer limits for
this condition are provided in Table 9.
Table 8 – LCSP and HCSP Transitions for
Space Temperature Mode
CURRENT SAT COOL DEMAND
SET POINT
LCSP
HCSP
LCSP
LEGEND
HCSP --- High Cool Set Point
LCSP --- Low Cool Set Point
SAT --- Supply ---Air Temperature
Table 9 – Maximum Economizer Limits
During Low Suction Pressure
COOLING SIZES
STAGE 03-07
Bottom
50
Middle
—
Top
—
high temperature lockout
lockout and
must be LOW.
can vary between
minimum position
and the economizer
to high cool set
cooling position
NEXT SAT
(∆F) SET POINT
>0.5 HCSP
<0 LCSP
<–0.5 Exit Cooling
SIZES SIZES
SIZE 16
08-14 20---28
50 50 50
— 35 50
25 25 0
Economizer Actuator Communications
The actuator used with 48/50PG and PM units is a Multi- -Function
Technology (MFT) actuator. This allows the ComfortLinkt
system to communicate with the actuator through a feedback
signal. The configuration Economizer Control Type determines the
communication method, either digital or analog, used to
communicate between the ECB and the economizer actuator.
Economizer Control Type is accessible via the Scrolling Marquee
at Configurations→ECON→E.CTL. The power to the unit
must be cycled after E.CTL is changed.
NOTE: If unit is equipped with Adaptive Fan, the control
automatically defaults the economizer control type to 1 (E.CTL =
1) and controls the actuator digitally. This is because the analog
signal from the ECB is used to drive the VFD's speed and therefore
can not be used to control the actuator. The field connection
terminal block TB- -8 no longer represents the commanded or
actual position of the actuator.
E.CTL = 1 or 2 (Digital/Position or Digital/Command)
the
When E.CTL is set to 1, the ECB will communicate with the
For
economizer actuator using the digital protocol, from ECB J7- -1 to
the
actuator pin 5. The commanded position and the actuators actual
position are communicated back and forth between actuator and
ECB. When the ECB and actuator first initiate communication, a
control angle (Operating Modes→ECON→C.ANG) is provided to
the ECB and represents the actuator's range of motion. This control
angle must be
(Configurations→ECON→M.ANG).
During this digital control, the ECB's analog 4 to 20mA output
will represent the actuator's actual position when E.CTL = 1 or
point
commanded position when E.CTL = 2. Because the wiring has a
built- -in 500- -ohm resistor, the 4 to 20mA signal is converted to a 2
to 10- -v signal that is accessible via field connection terminal board
TB- -8 and TB- -9. However, before this signal can be read remotely,
the violet wire that connects the actuator to field connection
terminal board TB- -J10- -8 must be removed or cut.
E.CTL = 3 (Analog Control)
When E.CTL is set to 3, the ECB will NOT communicate with the
economizer actuator using the digital MFT. It will instead control
the actuator directly with the 4 to 20 mA analog signal wired to
TB- -8 and TB- -9 along with the 500- -ohm resistor producing a 2 to
10- -v signal for the actuator. While in this mode, the actuator's
built- -in 2 to 10- -v feedback signal is accessible via TB- -9 and
TB- -10 any time because it is not used by the ECB.
Unoccupied Free Cooling
The unoccupied free cooling algorithm attempts to maintain the
building space temperature half way between the occupied cool
and occupied heat setpoints using only the economizer when the
conditions in the building and the outdoors are suitable. Three
different configurations define this algorithm: Unoccupied Free
Cooling (Configuration→ECON→UEFC),
Preoccupancy Time (Configuration→ECON→FC.TM) and Free
Cool Low Temp Limit (Configuration→ECON→FC.LO).
UEFC = 0 (Disabled)
When UEFC = 0, unoccupied free cooling is disabled. Cooling
will only occur if the space exceeds the unoccupied setpoints.
UEFC = 1 (Unoccupied)
When UEFC is set to 1, unoccupied free cooling can occur
throughout the entire unoccupied period. The space temperature
must be higher then the mid- -point between the occupied cooling
and heating setpoints.
UEFC = 2 (Preoccupancy)
When UEFC is set to 2, unoccupied free cooling can only occur
when the time until the next occupied period is less than the Free
Cool PreOcc Time (FC.TM) in minutes.
23
greater then the minimum
Free
angle
Cooling