Sequence of Operation
RTU Open v5
CARRIER CORPORATION ©2019
Integration Guide
All rights reserved
24
Failed to Fully Open
If the damper command is > 95%, the SAT must equal the OA tempe/- 5°F, otherwise the
Full Open Fail
flag is set. If this condition continues for more than 30 minutes, the Economizer FDD alarm is active. This
indicates that the damper failed to fully open when needed, since the SAT failed to reach the OA tempe/-
5°F.
Stuck Open
If the damper is commanded to < 40% and the SAT is still equal to the OAT +/- 5°F, the
Stuck Open
flag is set. If
this condition continues for more than 30 minutes, then the Economizer FDD alarm is active. This indicates the
damper failed to close when needed, since the SAT failed to increase in temperature.
When the damper is modulating (MUST be above any minimum configured position) and between 25% and 100%,
the FDD logic monitors the current and previous SAT, economizer-commanded position, and the OAT:
Failed to Open
If the FDD logic detects an increase in damper position, for example from 50% to 65%, it expects to also detect a
decrease in SAT. If the SAT failed to decrease, or no change in SAT is detected, the FDD logic generates a
Failed
to Open
alarm after 10 minutes.
Failed to Close
If the FDD logic detects a decrease in damper position, for example from 80% to 65%, it expects to also detect an
increase in SAT. If the SAT failed to increase, or no change in SAT is detected, the FDD logic generates a
Failed to
Close
alarm after 10 minutes.
Power Exhaust
The RTU Open may enable and disable an exhaust fan, based on either the controller’s occupancy or its
economizer damper position. If the
Fan Control
is set to
Two Speed
or
Variable Speed
, the
Power Exhaust
Setpoint
is automatically adjusted based on the fan’s air delivery. The
Calculated PE Setpoint
used for control is
displayed in the
Maintenance
section.
If
Continuous Occupied Exhaust
is
Yes
, the
Power Exhaust
binary output (BO-8) is energized while the RTU Open
is occupied and de-energized when unoccupied.
If
Continuous Occupied Exhaust
is
No
, the
Power Exhaust
binary output (BO-8) is energized when the economizer
damper output exceeds the
Calculated
Power Exhaust (PE) Setpoint
value. The output remains energized until the
economizer output falls below the
Power Exhaust Setpoint
value by a fixed hysteresis of 10%.
Pre-Occupancy Purge
Pre Occupancy Purge
allows the rooftop equipment with an economizer damper to use outdoor air to purge the
space of contaminants just prior to the beginning of the occupied period.
The following conditions must be true for pre-occupancy purge to operate:
Pre-Occupancy Purge
set to
Enable
Economizer Exists
set to
Yes
