Operating heating, ventilation, and air conditioning (HVAC) systems using occupancy sensing systems is described herein. One device includes instructions which, when executed by a processor, cause the processor to receive a mapping between a space of a plurality of spaces of a building, a fixture of a plurality of occupancy sensing system fixtures in the building, and an HVAC device of a plurality of HVAC devices associated with the building, and modify an operation of the HVAC device based on the mapping and responsive to a determination of occupancy in the space by the fixture.