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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 meet the load conditions and SAT safety
requirements to provide maximum energy savings by minimizing fan horsepower consumption. Fan speed is
NOT controlled by 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.
Cooling
The RTU Open's application and configuration determines the specific cooling sequence. The RTU Open can
control up to 2 stages of cooling with an additional output for a reversing valve (heat pump applications). The
number of stages is configurable or is defined by unit type.
The following conditions must be true for the cooling algorithm to operate:
•
Outdoor Air Temperature, if valid, is greater than the Cooling Lockout Temperature setpoint
•
The indoor fan is on
•
The unit has a valid Supply Air Temperature input
•
The unit has a valid Space Temperature input
RTU Open v3
Installation and Start-up Guide
45
Sequence of Operation
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