13.2 Building Commissioning: Existing Building Commissioning (EBCx) & Retro-Commissioning (RCx)

Building Commissioning and EBCx/RCx

Building commissioning is a quality assurance process ensuring that a building's systems are designed, installed, and operated to meet the Owner's Project Requirements (OPR). While new construction commissioning (Cx) focuses on verifying initial installation, Existing Building Commissioning (EBCx) focuses on resolving operational issues, optimizing energy performance, and improving occupant comfort in operational facilities.

EBCx vs. RCx vs. ReCx

The terminology surrounding existing buildings can be nuanced:

• Retro-Commissioning (RCx): The commissioning process applied to an existing building that was never previously commissioned. This often uncovers hidden design flaws or construction errors that have been wasting energy since the building opened.
• Re-Commissioning (ReCx): The commissioning process applied to an existing building that was previously commissioned. The goal is to return the building to its original commissioned performance level or adjust it to meet new operational requirements.
• Existing Building Commissioning (EBCx): An umbrella term encompassing both RCx and ReCx. EBCx is characterized by a focus on low-cost/no-cost operational improvements, primarily through Building Automation System (BAS) sequence optimization, sensor calibration, and minor mechanical repairs, rather than major capital upgrades.

The Five Phases of EBCx

A rigorous EBCx process follows a structured methodology to ensure that energy savings are realized and maintained. The process is generally divided into five phases:

1. Planning Phase

The foundation of a successful EBCx project is established during planning. Key activities include:

• Developing the Current Facility Requirements (CFR), updating the original OPR to reflect how the building is used today.
• Assembling the commissioning team (CxA, facility staff, controls contractors).
• Benchmarking current energy use (e.g., using ENERGY STAR Portfolio Manager).
• Creating the initial EBCx Plan, detailing the scope, schedule, and systems to be investigated.

2. Investigation Phase

During this phase, the Commissioning Authority (CxA) identifies specific energy conservation measures (ECMs) and operational improvements.

• Site Walkthroughs & Documentation Review: Inspecting equipment condition and reviewing BAS trends, sequences of operation, and as-built drawings.
• Functional Performance Testing (FPT): Discussed in detail below.
• Master List of Findings: The CxA compiles a list of identified issues, calculates estimated energy savings, estimates implementation costs, and calculates simple payback periods. The owner selects which measures to proceed with based on ROI and budget.

3. Implementation Phase

The selected measures are put into action. This may involve:

• Reprogramming BAS control sequences (e.g., implementing static pressure reset or supply air temperature reset).
• Repairing or replacing faulty sensors, stuck dampers, and leaking valves.
• Re-testing systems to verify that the implemented repairs and sequence changes perform exactly as intended.

4. Hand-off / Turnover Phase

The focus shifts to knowledge transfer to ensure the facility staff can operate the optimized systems.

• Updating the Systems Manual with new sequences and setpoints.
• Providing targeted training to O&M personnel on the newly implemented strategies.
• Delivering the Final EBCx Report summarizing the project, the measures implemented, and the verified savings.

5. Persistence Phase

Commissioning is not a "fix and forget" endeavor. Buildings naturally degrade over time, and human intervention (like hard-coding overrides) can erase energy savings. The persistence phase ensures savings endure by:

• Setting up automated alarms to track deviations from commissioned baselines.
• Implementing Continuous Commissioning (CCx) or Monitoring-Based Commissioning (MBCx) platforms.
• Scheduling periodic re-testing or reviewing BAS trend data quarterly.

Functional Performance Testing (FPT)

Functional Performance Testing (FPT) is the core diagnostic tool used during the Investigation and Implementation phases. It involves dynamic testing of systems through all modes of operation (e.g., full load, part load, unoccupied, emergency) to verify they respond correctly to changing conditions.

FPT Procedures

Unlike passive trend analysis, FPT is an active process. The CxA manipulates the system to observe its response:

• Setpoint Manipulation: Temporarily changing a zone temperature setpoint to force a VAV box into maximum cooling or heating mode to verify damper actuation, reheat valve operation, and airflow readings.
• Sensor Override: overriding an outdoor air temperature sensor reading in the BAS to trigger an economizer sequence, ensuring dampers modulate correctly without waiting for the actual weather to change.
• Failure Modes: Tripping a pump to verify that the lead/lag sequence correctly starts the standby pump and triggers the appropriate alarms.

Through FPT, the CxA frequently discovers issues such as simultaneous heating and cooling, economizers stuck fully open or closed, and variable frequency drives (VFDs) running at constant 100% speed regardless of demand. Resolving these control discrepancies often yields the highest return on investment in an EBCx project.