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
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
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 | COOL DEMAND | NEXT SAT |
SET POINT | (∆F) | SET POINT |
LCSP | >0.5 | HCSP |
HCSP | <0 | LCSP |
LCSP | Exit Cooling |
LEGEND
HCSP - High Cool Set Point
LCSP - Low Cool Set Point
SAT -
Table 9 – Maximum Economizer Limits
During Low Suction Pressure
COOLING | SIZES | SIZES | SIZE 16 | SIZES | |
STAGE | 03‐07 | 08‐14 | |||
| |||||
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 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)
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
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