This process is applied to existing buildings that have never been commissioned to bring the systems to optimum performance. RCx is a systematic process which identifies low-cost no-cost measures to improve the operation of systems and bring the buildings to current usage requirements.

RCx focuses on energy efficiency and is typically limited to energy using systems such as HVAC, controls, hot water and chilled water systems, lightingand related controls. The process is based on optimizing existing systems rather than major replacement of equipment and components. RCx involves tracking, monitoring and trending of the existing systems operation and variable parameters. As such it is important and prerequisite that the existing building has an operational Building Automation System.

RCx involves a detailed audit of energy systems and components including study of utility bills, field investigations and interviews with O&M staff. Building Automation System (BAS) and use of temporary data loggers helps in monitoring and developing diagnostic measures for further evaluation and recommendation. This process helps find and repair operational problems. Finally aRCx Report is presented to the owner, which summarizes the existing system operation, observations andall the findings, recommendations with cost-benefit analysis, and a commissioning plan.