Existing-Building Commissioning (EBCx)

Dec. 1, 2009
Existing-building commissioning (EBCx) combines elements of new-building commissioning, the energy audit, and the building “tune-up.”

Accounting for about 40 percent of energy consumption in the United States and contributing more carbon dioxide to the atmosphere than entire nations, existing buildings are becoming the proverbial elephant in the room of energy security. Few had the benefit of commissioning when built and even fewer have undergone existing-building commissioning (EBCx), or, as it was more commonly (and less accurately) known, retrocommissioning.

Although it has been around since the early 1990s, EBCx is little understood. It combines elements of new-building commissioning, the energy audit, and the building “tune-up” (Table 1).

EBCx differs from new-building commissioning considerably in that there is no design phase. And it differs from the energy audit in that it includes more tasks and lasts for a longer period of time. In definition and practice, EBCx is similar to Continuous Commissioning, an “ongoing process to resolve operating problems, improve comfort, and optimize energy use.”1

“While most commissioning processes focus on bringing building operation to the original design intent, Continuous Commissioning focuses on optimizing heating-, ventilation-, and air-conditioning-system operation and control for the existing building conditions,” Energy Systems Laboratory, a division of the Texas Engineering Experiment Station, which trademarked the term “Continuous Commissioning,” and a member of the Texas A&M University System, explains.2

In short, EBCx is “a systematic process for investigating, analyzing, and optimizing the performance of building systems through the identification and implementation of low/no-cost and capital-intensive facility-improvement measures and ensuring their continued performance,” the Building Commissioning Association says. “The goal of EBCx is to make building systems perform interactively to meet the current facility requirements and provide the tools to support the continuous improvement of system performance over time.”3

What's more, according to Portland Energy Conservation Inc. and Oak Ridge National Laboratory, “Not only does retrocommissioning identify problems that occurred at construction, just as traditional commissioning does, but it also identifies and solves problems that have developed during the building's life.”4


Many clients are asking for EBCx, but describing it as a list of services amounting to an energy audit.

The primary purpose of an energy audit is to identify energy-saving opportunities to reduce yearly operating costs. The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) defines three levels of energy audits:

  • Level I, which involve a visual inspection of a building's mechanical and electrical systems and interviews with building operating personnel.

  • Level II, which include a more detailed building survey and in-field measurements.

  • Level III, which provide dynamic energy models of existing systems and proposed capital improvements.

Building owners and operators have become so used to the idea of the energy audit over the last 30 years that EBCx is being forced into a similar mold to get contracts signed. This is unfortunate for clients because the EBCx process goes beyond the traditional energy audit.

With EBCx, additional information is gathered up front, before the audit portion of a job begins. This comes through the process of developing a current-facilities-requirements (CFR) document. These requirements usually are neither the original design intent of the building nor the original design intent of the various building systems. The development of the CFR leads to the “investigation” portion of the EBCx process, which is similar to an energy audit, but develops into a long-term strategic plan for a facility. This plan anticipates planned equipment obsolescence, as well as shifting corporate goals.

The first sign that a client is requesting an energy audit in EBCx clothing is that the deliverables do not include the CFR. This indicates the client is seeking short-term cost savings, rather than long-term strategic operational improvements. The EBCx process not only identifies ways to spend less; it provides a foundation for ensuring a building's goals are met in the future.

The first sign that a client is requesting an energy audit in EBCx clothing is that the deliverables do not include the CFR. This indicates the client is seeking short-term cost savings, rather than long-term strategic operational improvements. The EBCx process not only identifies ways to spend less; it provides a foundation for ensuring a building's goals are met in the future.


An energy audit can be improved considerably with the addition of a building, or maintenance, “tune-up.”

“A maintenance tune-up is a systematic process … which includes a conditions assessment and the implementation of maintenance measures that have not been completed during the regular preventive-maintenance schedule,” the California Commissioning Collaborative (CCC) explains.5 “This is often done prior to putting an ongoing preventive-maintenance program in place or as the initial step in providing an ongoing maintenance-service contract. Tune-ups tend to focus on maintenance of components and equipment and address their physical condition.”

Although a tune-up can be of tremendous benefit to a building, it lacks strategic planning. No attention is paid to altering the operation of the building. A preventive-maintenance contractor is to maintain the building in the “as-found” condition. To take the next step and qualify as EBCx, a tune-up must consider the bigger picture of a building's mission into the future.

“Retrocommissioning includes tune-up procedures, but it also … look(s) at operational issues, using a systems approach,” the CCC says.5 “It focuses more on operation than on maintenance, addressing why a piece of equipment is operating, not just how it is operating. Retrocommissioning looks at the operation of the entire system, in addition to the individual components. It looks at the root causes of operational problems, and, thus, its benefits are much more likely to persist. The focus on training and documentation also improves persistence.”

An important part of EBCx is the immediate repair/correction of minor operation-and-maintenance (O&M) problems as instrumented data are gathered. While, for example, an ASHRAE Level II audit might include analysis of a boiler-blowdown heat-recovery improvement based on assumed heat losses when a steam-condensate meter is broken, EBCx would include repair of the meter, with further analysis based on actual heat loss. That translates into O&M savings as well as energy savings. Often, such a repair pays for itself before the EBCx process is finished.


The lack of persistence of energy savings always has been the Achilles' heel of the audit process, even when combined with a tune-up. After fast-payback energy-conservation items are installed, immediate O&M issues attended to, and long-term energy-saving items analyzed and placed into the client's capital-expenditure plan, everyone walks away with a sense of achievement. But when controls, shafts, and linkages go out of adjustment, lose programming, or just plain fail, the overworked O&M staff has to abandon good energy practices to avoid getting fired because of occupant complaints. It is not enough merely to improve a facility; the O&M staff has to be trained and left with documentation to diagnose and fix breakdowns quickly and keep the building in “continuous-commissioning” order.

Just as a building's original design usually does not reflect its current mission, original design documents often do not include what needs to be done to maintain a building. The placement of small, inconspicuous labels on ceiling tiles in conjunction with simple one-line diagrams, for example, allows O&M workers to track a complaint to a box and replace an actuator before lunch on his or her first day on the job.

Another aspect of the EBCx process not included in the audit or the tune-up is the use of trend logging, real-time energy analysis, and/or automated fault diagnosis for fast correction of energy-wasting failures. During the last phases of the EBCx process, after immediate corrections have been made and fast-payback energy-conservation measures implemented, a commissioning authority should implement data-acquisition trend logs that allow a picture of building operation at a glance.


In addition to offering the fast payback of the energy audit and the quick fixes of the building tune-up, EBCx allows building equipment to look after itself and provide savings for years to come.


  1. Harrell, S. (2008, November). Continuous commissioning. HPAC Engineering, pp. 20, 22, 23, 25.

  2. Continuous commissioning. (n.d.). Retrieved from http://esl.eslwin.tamu.edu/continuous-commissioning-.html

  3. BCA. (2008). Best practices in commissioning existing buildings. Retrieved from http://www.bcxa.org/downloads/bca-ebcx-best-practices.pdf

  4. Haasl, T., & Sharp, T. (1999). A practical guide for commissioning existing buildings. Retrieved from http://eber.ed.ornl.gov/commercialproducts/RetroCommissioningGuide-w-cover.pdf

  5. CCC. (2006). California commissioning guide: Existing buildings. Retrieved from http://www.documents.dgs.ca.gov/green/commissionguideexisting.pdf

A commissioning project manager for AKF Group LLC and a longtime member of HPAC Engineering's Editorial Advisory Board, Ron Wilkinson, PE, LEED AP, is the author of the first commissioning training program for the Leadership in Energy and Environmental Design for New Construction and Major Renovations Green Building Rating System; the chair of the commissioning advisory committee of The American Institute of Architects (AIA) Committee on the Environment; the recording secretary for American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) Guideline Project Committee 0.2/1.2, The Commissioning Process for Existing Building Systems and Assemblies/The Commissioning Process for Existing HVAC&R Systems; and a member of the Building Commissioning Association. An ASHRAE Distinguished Lecturer and an AIA Continuing Education Lecturer, he has spoken on commissioning practices internationally.