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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 high temperature lockout (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 lockout
and the enthalpy (Inputs→GEN.I→ENTH) must be LOW. If a return
air temperature (RAT) sensor is installed and Diff Dry Bulb Control
(Configurations→ ECON → DF.DB = Enable) is enabled, the
outdoor air temperature must be lower than the return air temperature
in addition to the the lockouts and enthaply. For
cooling, the economizer position can vary between the configured
economizer minimum position (Configuration→ECON→EC.MN)
and the economizer 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 to high cool set point (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 cooling position
(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
SET POINT
COOL DEMAND
(∆F)
NEXT SAT
SET POINT
LCSP
>0.5 HCSP
HCSP
<0 LCSP
LCSP
<–0.5 Exit Cooling
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
STAGE
SIZES
03‐07
SIZES
08‐14
SIZE 16
SIZES
20-28
Bottom
50 50 50 50
Middle
— — 35 50
Top
— 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 ComfortLink
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)
When E.CTL is set to 1, the ECB will communicate with the
economizer actuator using the digital protocol, from ECB J7−1 to
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 greater then the minimum angle
(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
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), Free Cooling
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.
48/50PG and PM