Supply Fan - Carrier RTU Open v5 Integration Manual

Supply fan

The RTU Open supply fan may be configured for 1 of 3 Fan Control modes:

Single - The fan operates at one speed only and provides on/off operation

Two Speed - The fan operates at 1 of 2 speeds depending on the mode of operation and load conditions.
During fan only or single stage cooling, the fan operates at low speed. During heating, second stage cooling,
dehumidification, or if maximum economizer operation is required, the fan operates at high speed.

Variable Speed - The fan operates at a variable speed to maintain the desired supply air conditions when
heating or cooling are operating. Variable speed fan control provides Staged Air Volume (SAV) operation by
maximizing energy savings and minimizing fan horsepower consumption. Fan speed is NOT controlled to
maintain duct static pressure.
The RTU Open supply fan may be configured for 1 of 3 Fan Modes:

Auto - The fan cycles on/off in conjunction with heating or cooling

Continuous - The fan runs continuously during occupancy and intermittently during unoccupied periods with
heating or cooling

Always On - The fan runs continuously regardless of occupancy or calls for heating and cooling
Occupancy can be determined by Linkage, BACnet schedules, BAS schedules, or in response to a remote
occupancy switch.
A Fan Off Delay allows the supply fan to continue operating after heating or cooling stops.
If the following alarms are active, the fan turns off immediately, regardless of the occupancy state or demand:

Fire Shutdown

Safety chain

Supply Air Temp Sensor alarm

Space Temp Sensor alarm
The RTU Open does not include smoke-control functions such as smoke-purge, zone-pressurization, or smoke-
ventilation.
The RTU Open may be configured to accept a Supply Fan Status input to provide proof the supply fan is operating.
When enabled, a loss or lack of fan status will stop heating and cooling operation.
A Supply Fan Alarm Service Timer function is available to track the number of supply fan run hours and generate
an alarm when the accumulated runtime exceeds the set threshold.
Vent / Fan Only mode – When the space temperature is between the heating and cooling setpoints, the fan
operates at the minimum VFD speed (IDF Min Speed Voltage / Min VFD Output) configured under normal
operating conditions.
NOTE SAT must be above the SA Vent / Temper Setpoint if SA Tempering is disabled or SAT must be above the
SA Vent / Temper Setpoint -7.5°F (-21.9°C) if SA Tempering is Enabled and OAT is below the Minimum Cooling
SAT.
Fan Only Override w/Variable Speed fan control — The RTU Open monitors the SAT in fan only mode to ensure the
SAT remains above an acceptable minimum value. Fan Override typically occurs when the outdoor air is cold in
winter and the economizer increasingly opens at lower fan speeds to maintain a constant amount of outdoor air. If
SA Tempering is disabled, then when the SAT drops below the SA Vent / Temper Setpoint, the fan speed
increases up to the maximum configured speed (while at the same time, the economizer position will
correspondingly decrease from the Low Fan Econ Min Pos toward the Vent Dmpr Pos / DCV Min Pos. The Vent
Dmpr Pos / DCV Min Pos is used when the fan is at the configured maximum fan speed. The Low Fan Econ Min
Pos is used when the fan is at the lowest speed and depends on which value, minimum vfd speed or heating
speed, is set lower.
RTU Open v5
Integration Guide
21
Sequence of Operation
CARRIER CORPORATION ©2019
All rights reserved