LG AR-DR12-05A Installation And Operation Manual page 38

OPTIONAL COMPONENT OPERATION
• Two configurable analog outputs for transmitting outdoor and/or exhaust airflow rate, outdoor air temperature, or a proportional-integral-de-
rivative (PID) control signal based on an outdoor airflow set point.
• A configurable digital output that operates based on an airflow set point or range.
Operation
Outdoor and/or exhaust airflow monitoring is accomplished using two thermal dispersion sensors that accurately measure airflow velocity
down to zero feet per minute (fpm). The airflow controller takes the average measurement for two sensor configurations, and determines
the outdoor airflow rate based on the effective intake area. Field calibration of the outdoor airflow monitoring device determines the effective
intake area of the unit.
For additional information on how to navigate through the airflow controller menus, refer to technical manuals from GreenTrol® Automation
Inc. at www.greentrol.com.
For the airflow monitoring device to perform as intended, field calibration is required. Calibration of the airflow monitoring device requires an
independent measurement of airflow and should be performed when the system undergoes test and balance.
VFD Compressor
If the VFD compressor option is included, the compressor VFD is mounted in the end of the condensing section. Condensing section internal
components are accessible via the access panel on the side of the condenser coil.
Envelope Control
The unit controller tracks the operating point of the VFD compressor within the operating envelope at all times. If the operating point is out of
the envelope, the controller will take action to bring it back in. If unsuccessful, the controller will shut down the compressor. DO NOT operate
the compressor VFD in hand mode because the envelope control safeties will not be in place. Refer to the controls IOM for more information
on envelope control.
Electronic Expansion Valve
An electronic expansion valve is provided on the VFD compressor circuit to ensure tight superheat control throughout the compressor modu-
lation band. The EXV acts as a liquid line solenoid valve when the compressor is off to prevent refrigerant migration.
Crankcase Heat
The VFD compressor will be heated by the compressor stator. To ensure optimal performance and reliability, do not disable stator heat. All
other compressors will be provided with a crankcase heater.
Oil Return Management
The compressor VFD has an oil return purge cycle such that if the compressor has been operating below a set RPM for a set period of time,
the VFD will accelerate the compressor to ensure sufficient lubrication.
DO NOT disable the oil return management function.
DO NOT operate the compressor VFD in hand mode because the oil return management will not be operational.
Frost Control
Extremely cold outdoor air temperatures can cause moisture condensation and frosting on the energy recovery wheel. Frost control is an
optional feature that will prevent/control wheel frosting. Three options are available:
1. Timed exhaust frost control
2. Electric preheat frost control
3. Modulating wheel frost control
All of these options are provided with a thermodisc mounted in the outdoor air intake compartment and a pressure sensor to monitor pres-
sure drop across the energy wheel.
An outdoor air temperature of below 5°F and an increase in pressure drop would indicate that frost is occurring. Both the pressure sensor
and the outdoor air thermodisc must trigger in order to initiate frost control. The two sensors together ensure that frost control is only initiated
during a real frost condition.
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