Carrier RTU OPEN 11-808-427-01 - Manual (Page 50)

Sequence of Operation
44 RTU Open
Supply fan
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
• SAT alarm
• SPT alarms
The RTU Open does not include smoke-control functions such as smoke-purge, zone-pressurization, or smoke-
ventilation. Each of these modes require a field-designed circuit to operate the following, as required by local
fire codes:
•
RTU supply fan
• RTU economizer
• RTU power exhaust
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 two stages of cooling with an additional output for a reversing valve (heat pump applications).
The following conditions must be true for the cooling algorithm to operate:
•
Outdoor Air Temperature is greater than the Cooling Lockout Temperature setpoint
• The indoor fan has been on for at least 30 seconds
• The unit has a valid Supply Air Temperature input
• The unit has a valid Space Temperature input
• Heat mode is not active and the time guard between modes has expired
• Economizer is active and open > 85% with SAT > (Minimum Cooling SAT + 5°F) and SPT > Effective
Cooling Setpoint + 0.5°F, or the Economizer is unavailable