An HVAC zone is a group of spaces or a single space with individual temperature control from a shared HVAC system. So, in order to meet the credit requirements you need to have at least one temperature sensor for each zone with individual control. Note that when pursuing this credit, be sure to also delineate between HVAC zones that contain both perimeter and core spaces, zones that have perimeter areas with different orientations, or zones that have substantially different usage types may require additional temperature sensors.