This case study investigates the potential energy savings in retro-commissioning an existing building on the University of Virginia’s campus using a reduced-order energy model. The retro-commissioning is focused on HVAC operation, including ventilation reduction and air terminal unit operation. The potential energy savings from the retro-commissioning’s recommended measures are evaluated in a building reduced-order energy model. Prior to the evaluation, the energy model is iteratively calibrated using the building utilities data based on ASHRAE Guideline 14 to ensure accuracy. Based on the reduced-order energy model, the recommended measures result in more than 11% savings in energy cost annually.