Small and medium sized commercial buildings, such as retail stores, restaurants and factories, often utilize multiple roof top units (RTUs) to providecooling and heating for open spaces. A conventional control approach for these buildings relies on local feedback control, where each unit is cycled on andoff using its own thermostat. Because thermostats operate independently with no knowledge of the building's behavior, conventional control approachestypically result in high energy use and electrical peak demand because of lack of coordination among the units. Recently, a model-based control algorithm(MPC) for coordinating multiple RTUs that serve open building spaces was developed. The control solution is not site-specific and provides reduced energyconsumption and peak demand with low sensor requirements. In this paper, we provide recent results of long-term performance evaluation of the RTUCoordinator at a small commercial building field site.