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Object, BACnet

A piece of information in a BACnet system, described by its properties. An object might represent information about a physical input or output, or it may represent a logical grouping of points that perform some function, such as a zone setpoint. Every object has an identifier that allows the BACnet system to identify it. An object is similar to a data point however it contains additional information other than present value and is monitored and controlled though its properties.


Occupancy Sensor

See Motion Sensor


Occupant Override Switch

Or simply override switch - A control option that allows building occupants to override the Building Automation System lighting or HVAC schedule for a limited period of time.


Occupant Setpoint Adjustment

A control option that allows building occupants to adjust - within limits set by the Building Automation System - the heating, cooling or lighitng setpoints of selected zones. Typically the user interface for this function is built into the zone sensor.


Optimal Start-Up

A control strategy that automatically starts an HVAC system at the latest possible time yet ensures comfort conditions by the time the building becomes occupied.

In a typical implementation, a controller measures the temperature of the zone and the outside air. Then, using design heating or cooling capacity at the design outside air temperature, the system computes how long a unit must run at maximum capacity to bring the zone temperature to its occupied setpoint.

The optimal start algorithm often includes a self-learning feature to adjust for variations from design capacity.

A distributed system must use Run on Request with Optimal Start.



Acronym for Open Systems Interconnection whichis a standard description for how messages should be transmitted between any two points in a telecommunication network. Its purpose is to guide product implementers so that their products will consistently work with other products.


Example of use: ISO/OSI


Override Switch

A control option that allows building occupants to override the programmed HVAC schedule for a limited period of time.


Outlet Box

Also Junction Box or J Box. Enclosure that protects spliced wires and supports surface fixtures.