Carrier RTU OPEN 11-808-427-01 - Manual (Page 52)

Sequence of Operation
46 RTU Open
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 Continuous Occupied Exhaust is Yes, the Power Exhaust binary output (BO-8) is energized while theRTU
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 Power Exhaust Setpoint value (default = 50%). The output remains
energized until the economizer output falls below the Power Exhaust Setpoint value by a fixed hysteresis of
10%.
Unoccupied Free Cooling
Unocc Free Cool Enable allows rooftop equipment with an economizer damper to utilize outdoor air for free
cooling during unoccupied periods.
The following conditions must be true for unoccupied free cooling to operate:
•
Unocc Free Cool Enable set to Enable
• The system is unoccupied
• The outside air temperature is below the Economizer High OAT Lockout Temp setpoint
• The outside air temperature is less than the space temperature
• Enthalpy (if enabled) is Low
When the RTU Open schedule is unoccupied and the space temperature rises at least 1° above the Occupied
Cooling Setpoint , the supply fan starts. The economizer damper opens as necessary to cool the space. The
RTU Open continues to operate in this mode until the space is satisfied or the outside air conditions are no
longer suitable for free cooling.
Optimal Start
The RTU Open may utilize Optimal Start. Optimal Start adjusts the effective setpoints to achieve the occupied
setpoints by the time scheduled occupancy begins.The Optimal Start recovery period may begin as early as 4
hours prior to occupancy. The algorithm works by moving the unoccupied setpoints toward the occupied
setpoints. The rate at which the setpoints move is based on the outside air temperature, design
temperatures, and capacities.
The following conditions must be true for optimal start to operate:
•
On the Properties page > Equipment tab > Configuration > Setpoints > Optimal Start, the Default Value
must be set greater than 0 and less than or equal to 4 (0.00 disables Optimal Start).
• The system is unoccupied
NOTE If the Open controller does not have a valid outside air temperature, then a constant of 65° F is used.
This value is not adjustable.