Commissioning is often associated with new construction, yet many of the greatest performance improvement opportunities exist in occupied, existing buildings. As facilities age, equipment performance degrades, control strategies are overridden, and system operation gradually drifts from original intent.
Existing Building Commissioning (EBCx) provides a structured, engineering-led approach to understanding how building systems operate today, and how to restore or improve performance based on current facility needs and priorities.
Within EBCx, two commonly used applications are retro-commissioning and re-commissioning. While the terms are sometimes used interchangeably, both apply the commissioning process to existing buildings and follow the same fundamental principles.
What Is Existing Building Commissioning (EBCx)?
Existing Building Commissioning is the application of the commissioning process to buildings that are already in operation. Unlike new building commissioning, which verifies that systems are installed and perform according to the original Owner’s Project Requirements (OPR), EBCx evaluates how systems currently operate relative to present-day functional needs, occupancy patterns, and operational goals.
Best-practice EBCx is a phased, methodical process led by a qualified Commissioning Professional (CxP), acting as the Owner’s advocate. The focus is not simply on identifying deficiencies, but on understanding system interactions, identifying improvement opportunities, and sustaining performance gains over time.
Retro-Commissioning vs. Re-Commissioning
Retro-commissioning and re-commissioning are both forms of Existing Building Commissioning. The distinction is based on a building’s commissioning history, not the rigor of the process.
- Retro-commissioning is typically performed when a building has never been commissioned. Systems may have been installed without formal performance verification, allowing operational issues to accumulate over time.
- Re-commissioning applies to buildings that were commissioned previously but whose performance has drifted due to changes in occupancy, aging systems and equipment, and operating practices.
In practice, retro-commissioning is often used when there is uncertainty about whether a building was originally commissioned, and the terms are frequently used interchangeably.
Why Existing Buildings Underperform Over Time
Many existing buildings experience declining performance even when major equipment remains functional. Common contributors include changes in space use, overridden schedules, sensor drift, control logic modifications, device failures, and evolving operational priorities.
These issues are rarely obvious during routine maintenance and tend to emerge gradually. Existing Building Commissioning addresses these challenges by examining how systems behave under real-world operating conditions, allowing owners to move from reactive troubleshooting to proactive performance improvement.
Why One-Time Commissioning Is Often Not Enough
Traditional retro- or re-commissioning projects often deliver strong short-term results. However, buildings are dynamic systems. Without ongoing visibility into system operation, performance gains can erode as conditions change.
As a result, many organizations now view commissioning not as a one-time corrective effort, but as part of an ongoing performance strategy.
The Role of Monitoring-Based Commissioning (MBCx) and Analytics
Monitoring-Based Commissioning (MBCx) extends the commissioning process by using analytics software and system data to continuously evaluate building performance. Rather than waiting for comfort complaints or rising energy use, MBCx enables early identification of emerging issues and tracks system behavior after improvements are implemented.
Analytics tools analyze equipment responses to changing loads, schedules, and operating conditions, often at five to ten-minute intervals, highlighting faults and non-performing conditions. Advances in data analytics and artificial intelligence further enhance this capability by rapidly evaluating large data sets and prioritizing corrective actions both visually and graphically.
When combined with Existing Building Commissioning, MBCx transforms commissioning into a cost-effective, proactive, data-driven performance management approach that maximizes long-term value.
The Role of the Commissioning Professional (CxP)
The Commissioning Professional (CxP or CxA) leads the commissioning process as an independent technical representative of the Owner. Responsibilities typically include planning and managing commissioning activities, coordinating stakeholders, overseeing testing, managing issue resolution, verifying training and documentation, and delivering the final commissioning report.
Long-Term Value of Existing Building Commissioning
Existing Building Commissioning delivers measurable benefits across energy performance, operational cost reduction, and risk management. Independent research from the Lawrence Berkeley National Laboratory has shown median whole-building energy savings of approximately 16% for existing buildings resulting from commissioning.
Commissioned buildings commonly experience lower energy-related operating costs, improved reliability, and reduced operational risk. When commissioning is paired with monitoring-based approaches, performance improvements are more likely to persist as building conditions evolve.
Choosing the Right Approach
If you operate an existing facility—whether it has been commissioned previously or not—Existing Building Commissioning provides a proven framework for improving performance, reliability, and long-term value.
Contact EEI
Not sure whether existing building commissioning is the right fit for your facility? Contact EEI to discuss how our commissioning professionals can evaluate your building’s performance and recommend the most effective approach.