We are developing a software tool that measures room air change rates in commercial building HVAC systems and thus enables minimizing those airflow levels, while still meeting ventilation and thermal comfort needs. Optimization of airflow can achieve significant sustainability savings by reducing energy for conditioning and transporting building air, since most buildings were designed when energy costs were low, so comfort and fresh air requirements were easily met with conservatively high air change rates. Our novel approach utilizes the Building Automation System (BAS) to conduct experiments that determine room-by-room airflow rates and thus easily identifies opportunities for resetting minimum airflow rates for each room. This unique approach is based on a proprietary algorithm that combines experimental system identification and modeling methods, and determines actual air change rates from the room temperature responses to BAS driven air flow perturbations. Our technology achieves building-wide optimization through aggregation of room-by-room results, achieving significant energy savings at low cost without the need for new HVAC hardware or labor intensive testing. This talk will focus mainly on the technology research and development, including proof of concept through testing in Boston University campus buildings. Potential energy savings and the challenges to commercializing this technology will also be covered.