It wasn't long ago that commissioning was a new term and needed to be defined. The industry has now evolved to the point of having subcategories of commissioning. I thought a good way to enter 2001 (and the new millennium, according to the purists) is to define the four major types of commissioning so that we're all on the same page.


The term commissioning can have two definitions. The first is to describe the industry as a whole, thus this usage includes all of the other types of commissioning. When talking about specific projects, however, the only "proper" use of the term commissioning is for new construction or large facility renovation projects. This is the type of commissioning we have primarily been concerned with in this column over the past three years.

As a concise refresher, commissioning is defined as:
A systematic process of ensuring by verification and documentation, from the design phase to a minimum of one year after construction, that all building facility systems perform interactively in accordance with the design documentation and intent, and in accordance with the owner's operational needs, including preparation of operation personnel.


Retro-commissioning is performed in existing buildings that have never been commissioned. Retro-commissioning building systems of any age can reduce energy consumption, improve IAQ, and improve temperature and relative humidity control. In addition, it is an opportunity to analyze the air and water system balance within a building and optimize distribution system performance.

Where multiple architectural renovations have taken place over time, retro-commissioning offers an opportunity to re-evaluate the mechanical systems in light of the new building arrangements, including aspects of "small" renovations which are often ignored initially.

Finally, retro-commissioning is a must for systems whose design intent has changed since they were originally constructed. For example, a classroom building may have been converted to a laboratory building. Another common reason for retro-commissioning is that criteria for IAQ, have changed substantially over the past 25-30 years.

One of the distinguishing features of retro-commissioning is the usual absence of the original designers and contractors on the team. Therefore, a building could be new and still be subjected to retro-commissioning, if the owner has chosen to close out the original design and construction contracts prior to embarking on the retro-commissioning process. Refer to the November 1998, "Getting it Right" column for more details on retro-commissioning.


Recommissioning applies only to buildings that have previously been commissioned or retro-commissioned. It involves revisiting the systems at regular intervals and checking/retesting systems using the same checklists and test procedures used during the original process.

This process is critical for verifying that the systems continue to function at their peak efficiency. It also recognizes the importance of documenting inevitable building changes and their effect on the building's systems.

Continuous Commissioning

Continuous commissioning is something of a hybrid of retro-commissioning and recommissioning. Two things distinguish continuous commissioning from retro-commissioning. First, continuous commissioning requires a "baseline" performance measurement prior to making changes to the existing systems. Second, continuous commissioning involves continuously monitoring performance after modifications are made. All of the tasks involved in retro-commissioning are performed at one time in continuous commissioning. However, after completion of the typical retro-commissioning project, the continuously-collected performance data is evaluated either manually or automatically on a regular basis to help identify problems quickly. If a potential problem is identified, recommissioning of the associated systems takes place "as needed" to get performance back to its baseline level. Look for the March 2000 "Getting It Right" column for more on continuous commissioning.


Commissioning (in the broadest use of the term) has proved so beneficial to resolving building system problems that it has expanded beyond being just an "additional service" for a project. In this ever-evolving field, it will be interesting to see how many more "legs" commissioning grows throughout the 21st century.