What Is Building Commissioning?
Building commissioning (Cx) is the systematic process of verifying that a building's systems are designed, installed, and performing to meet the Owner's Project Requirements (OPR). The term comes from the ship-building industry — a ship is "commissioned" when its crew verifies all systems before it leaves port. A building is commissioned before occupancy, with similar intent: ensure everything works as designed before the owner takes possession.
Commissioning is not inspection (which verifies code compliance) and is not TAB (which sets airflow and waterflow). It is a broader quality assurance process that covers system design intent, installation quality, controls sequences, interoperability between systems, and occupant comfort. Commissioning is required for LEED certification and increasingly required by energy codes (ASHRAE 90.1 Appendix G, California Title 24, IECC).
The Commissioning Team
- Owner — defines the Owner's Project Requirements (OPR), a written statement of performance goals, energy targets, indoor environmental quality requirements, and operating preferences
- Commissioning Authority (CxA) — independent third party that leads the commissioning process, develops the commissioning plan, reviews submittals, witnesses functional tests, and issues the final commissioning report
- Design team — engineer of record develops the Basis of Design (BOD) document explaining how the design meets the OPR; reviews CxA comments and issues clarifications
- General contractor and subcontractors — install systems and complete pre-functional checklists (PFCs) confirming installation is complete and ready for functional testing
- TAB contractor — measures and adjusts air and water system flows to match design values; submits TAB report as a commissioning deliverable
- Controls contractor — programs building automation system (BAS) controllers, loads sequences of operation, and assists with functional performance testing
The Commissioning Process
Phase 1: Pre-Design
The CxA is engaged during pre-design (or at least during design development). The owner documents the OPR — what the building needs to do, how it needs to feel, what energy targets it must hit, and how systems should be operated. The design team documents the BOD — how the design achieves those goals. The CxA reviews both for gaps.
Phase 2: Design Review
The CxA reviews design documents at each submittal stage (schematic design, design development, construction documents) from a commissioning perspective:
- Are controls sequences written and complete?
- Are monitoring points (temperature sensors, flow meters, energy meters) specified at locations needed for verification?
- Are all systems testable as designed — is there a way to command each mode of operation?
- Are owner training and O&M manual requirements specified?
The CxA issues a design review comment log. The engineer of record responds with clarifications or revisions.
Phase 3: Construction — Pre-Functional Checklists (PFCs)
Before functional testing can begin, each system must pass a Pre-Functional Checklist. The CxA develops PFCs for each commissioned system — typically a multi-page checklist that the installing contractor completes and signs off. PFCs for an air handling unit might include:
- Supply and return fans installed, belts tensioned, rotation verified
- All dampers (OA, RA, EA, fire dampers) installed and operable
- Coils connected to piping, pressure tested, and insulated
- All sensors (temperature, humidity, pressure, CO₂) installed and connected to BAS
- Controls wiring complete, controller on-line, points addressed
- TAB complete for supply and return air quantities
- Motor starter and VFD installed, protected, labeled
The CxA spot-checks PFC completion before scheduling functional performance tests.
Phase 4: Functional Performance Testing (FPT)
Functional performance testing is the core commissioning activity. The CxA (or an agent) witnesses each test, with the controls contractor and mechanical contractor present. Tests exercise each mode of operation specified in the sequence of operations. Example FPT for a VAV AHU:
| Test | Procedure | Expected Result |
|---|---|---|
| Occupied mode startup | Command to occupied mode via BAS | AHU starts, OA damper opens to minimum, supply air setpoint 55°F |
| Economizer enabled | Set OAT below 65°F in BAS simulator | OA damper modulates to 100% or mixed air setpoint |
| Low supply air temp limit | Command supply air setpoint to 45°F | Heating coil activates, alarm generated if SAT below 42°F |
| High static pressure limit | Close all VAV boxes via BAS, observe SP rise | VFD reduces speed when SP exceeds setpoint |
| Fire alarm override | Simulate fire alarm from FACP test panel | AHU shuts down, smoke dampers close, BAS logs event |
| Occupied to unoccupied | Command to unoccupied via BAS | AHU sets back per schedule, OA damper closes |
Failed tests generate deficiency reports. The subcontractor corrects the issue and the test is repeated until the system passes.
Phase 5: Electrical Commissioning
Electrical commissioning is sometimes treated separately from mechanical Cx but should be integrated. Key activities:
- Switchgear and distribution — overcurrent protective device (OCPD) settings verified against the arc flash study; breaker ratings match one-line diagram
- Emergency power — generator load test under full building load, ATS transfer time verified (≤10 seconds for life safety per NEC 700), battery backup runtime tested
- Lighting controls — occupancy sensors, daylight sensors, and dimming sequences tested zone by zone; ASHRAE 90.1 Section 9 shutoff compliance verified
- Power monitoring — energy meters verified for accuracy; submetering points for LEED energy credits confirmed active
- UPS systems — battery runtime and bypass tested under load
Phase 6: Integrated Systems Testing
After individual systems pass FPTs, integrated systems testing verifies that systems work correctly together. Example integrated tests:
- Fire alarm system activates → HVAC shuts down, smoke dampers close, stairwell pressurization fans start, doors unlock, elevator recalls to lobby
- After-hours occupancy sensor detects occupancy → BAS starts HVAC zone, access control logs entry, lighting turns on
- Generator starts under power outage simulation → all emergency loads transfer, BAS receives power status, UPS bridges critical loads during transition
Phase 7: Documentation and Training
Commissioning deliverables include:
- Final commissioning report (all PFCs, FPT results, deficiency logs, resolution records)
- Updated O&M manuals with commissioning test results embedded
- Owner training sessions for facility management staff
- Seasonal testing schedule (for systems that cannot be fully tested in one season — economizers, heating coils, freeze stats)
Seasonal Commissioning
Some functional tests cannot be performed during construction because they require specific weather conditions. A heating coil cannot be tested in summer; an economizer cannot be fully verified without cold, dry outdoor air. Seasonal commissioning (or deferred commissioning) schedules return visits to complete season-dependent tests during the first full year of occupancy. ASHRAE 202 and LEED Enhanced Commissioning require seasonal testing documentation.
Retro-Commissioning (RCx)
Retro-commissioning applies the commissioning process to existing buildings that were never commissioned or whose systems have drifted from original design intent. RCx typically finds 5–15% energy savings opportunities in systems that are running inefficiently — oversized pumps, mistuned control loops, failed sensors, and override commands that were never reset. It is one of the highest-ROI energy strategies for existing commercial buildings.