What is retro-commissioning (RCx) and how does its focus differ from new construction Cx?

• A. RCx disregards existing systems.
• B. RCx is identical to new construction Cx.
• C. RCx optimizes existing building systems for current use; often limited documents, emphasis on performance improvements.
• D. RCx is only about architectural aesthetics.

Answer: (C)

Retro-commissioning focuses on how a building actually operates today, with the goal of making the existing systems work better for current occupancy and usage. It starts from the current performance, often with incomplete or old documentation, and seeks practical, often low-cost improvements that boost energy efficiency, comfort, and reliability. The process typically involves establishing a baseline of how the building runs, identifying operational faults or mismatches, tuning controls and sequences, calibrating sensors, and verifying that the changes deliver measurable performance gains. It also includes training building staff and creating an ongoing commissioning plan to maintain improvements.

This differs from commissioning for new construction, which is about verifying that new systems are installed and operate according to the design intent and owner requirements before occupancy, using the complete design documents and commissioning tests.

So the best description is that retro-commissioning optimizes existing building systems for current use, often with limited documentation, with a focus on performance improvements.