Generally, when we think about BAS, it is in the context of large commercial buildings, those well over 25,000 sq ft. According to the latest government data though (from the 2012 Commercial Building Energy Consumption Survey), 88% of all commercial buildings are 25,000 sq ft or less. Most of these buildings do not have any sort of BAS, but what they do have are millions of packaged units including rooftops and split systems.
Traditionally, packaged units have fairly basic controls; the manufacturer provides safety and economizer controls as part of the unit and then the contractor furnishes a wall-mounted thermostat that controls the operation of the fan and the stages of heating and cooling. The use of a programmable thermostat allows for the setpoints and fan operation to be scheduled. The controls available for these packaged units are pretty basic, and in operation, often not very effective.