Economizer - Carrier RTU Open v5 Integration Manual

Economizer

The RTU Open provides an analog economizer output for rooftop units with economizer dampers. Economizer
dampers may be used to provide indoor air quality control and free cooling when outside air conditions are
suitable.
The following conditions must be true for economizer operation:

The Outdoor Air Temperature is less than the Space Temperature and less than the Economizer High OAT
Lockout Temp setpoint

The indoor fan is on

The unit has a valid Supply Air Temperature input

The unit has a valid Space Temperature input
If the RTU Open is configured for VFD or 2-speed fan, the economizer minimum position is adjusted to provide a
constant amount of outdoor air. If the fan is on high speed or is configured for single-speed fan, the economizer
minimum position will be set to the Vent Dmpr Pos / DCV Min Pos setpoint. If it is configured for VFD or 2-speed
fan, and the fan is on low speed, the economizer minimum position will be set to the Low Fan Econ Min Pos.
If all preceding conditions are true, the economizer PID loop modulates the damper between the minimum
position and 100% open.
The economizer will modulate to maintain the configured Minimum Cooling SAT limit when the unit is in an
economizer only mode and will modulate closed only when the SAT drops below the Minimum Cooling SAT limit -
5 °F (-2.8 °C) when mechanical cooling is also operating.
SAV Economizer Mode - When the economizer mode becomes active, the fan runs at the configured minimum
airflow (IDF Min Speed Voltage / Min VFD Output). The economizer algorithm will first modulate the economizer to
lower the SAT until reaching the configured Minimum Cooling SAT limit, while maintaining the minimum fan
airflow. If this alone is insufficient to maintain the space temperature, the RTU Open increases the fan speed to
provide more OA for cooling. As necessary, the fan speed may increase up to the configured maximum VFD speed
(IDF Max Speed Voltage / Max VFD Output) to provide the required cooling.
Economizer Fault Detection & Diagnostics (FDD)
The RTU Open provides FDD (Fault Detection and Diagnostics) for economizer operation in compliance with
California Title 24. The FDD logic detects 4 economizer faults:

fails to close

fails to open

stuck fully open

fails to fully open
Each condition causes an Economizer Operation alarm and displays the specific fault condition.
The following must be true to enable the FDD logic:

RTU Open must be in Economizer mode

30 minutes must elapse since the last time heating or cooling was active

OAT must be < (OAT economizer lockout - 15°F)
RTU Open v5
Integration Guide
23
Sequence of Operation
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