Commissioning Procedures for HVAC Engineers

Commissioning (Cx) verifies HVAC systems meet design intent and owner’s project requirements through systematic functional performance testing. Proper commissioning reduces energy consumption by 10-20% and minimizes occupant complaints.

Commissioning Process

graph TD
    A[Pre-Design Phase] --> B[Design Phase]
    B --> C[Construction Phase]
    C --> D[Acceptance Phase]
    D --> E[Post-Acceptance Phase]
    
    A --> A1[OPR Development]
    B --> B1[Basis of Design]
    B --> B2[Design Review]
    C --> C1[Submittal Review]
    C --> C2[Installation Verification]
    D --> D1[Functional Testing]
    D --> D2[TAB Verification]
    D --> D3[Systems Manual]
    E --> E1[Training]
    E --> E2[Seasonal Testing]
    E --> E3[10-Month Review]

Commissioning phases:

Pre-design: Develop Owner’s Project Requirements (OPR)
Design: Create Basis of Design (BOD), review submittals
Construction: Verify installation, review submittals
Acceptance: Functional performance testing
Post-acceptance: Training, seasonal testing, warranty review

Owner’s Project Requirements (OPR)

Documents owner’s expectations:

Indoor environmental quality (temperature, humidity, IAQ)
Energy performance targets
Maintenance requirements
Special requirements (cleanrooms, labs, etc.)
Budget and schedule constraints

Example OPR requirements:

“Maintain operating room at 68-73°F, 20-60% RH, +0.01 "w.g. pressure”
“Achieve LEED Gold certification with 30% energy cost savings”
“Design system for 24/7 operation with N+1 redundancy”

Basis of Design (BOD)

Engineer’s documentation of how OPR will be met:

System descriptions
Design parameters and assumptions
Equipment specifications
Control sequences
Maintenance requirements

Links OPR to design decisions

Functional Performance Testing

Verifies equipment operates per design intent under actual and simulated conditions

Test Categories

1. Pre-functional checklists:

Verify installation completeness
Check nameplate data vs. submittals
Confirm startup procedures completed
Document deficiencies

2. Functional performance tests:

Test control sequences
Verify safeties and interlocks
Simulate failure modes
Measure performance at design conditions

Example: AHU Functional Test

Test sequence:

Economizer test:
- Simulate OA temp < RA temp → OA damper opens to 100%
- Simulate OA temp > RA temp → OA damper returns to minimum
Heating sequence:
- Lower space temp setpoint → verify heating valve opens
- Verify discharge air temp maintains setpoint
- Check freeze protection (DA temp < 40°F → alarm)
Cooling sequence:
- Raise space temp setpoint → verify cooling valve opens
- Verify discharge air temp maintains setpoint
- Check high-limit safety (DA temp < 50°F → cooling lockout)
Ventilation:
- Verify minimum OA damper position (per ASHRAE 62.1)
- Measure actual OA flow with pitot traverse
- Check CO₂-based DCV if applicable
Alarms and safeties:
- Simulate dirty filter (increase DP) → verify alarm
- Simulate fan failure → verify alarm and backup fan start
- Simulate freeze condition → verify shutdown

Worked Example 1: VAV Box Functional Test

Test: Verify VAV terminal unit responds correctly to thermostat

Given:

Design airflow: 1,200 CFM max, 360 CFM min (30%)
Space setpoint: 72°F
Reheat coil valve

Test Procedure:

Step 1: Verify minimum airflow

Set space temp to 65°F (call for heat)
Measure airflow with flow hood
Expected: 360 CFM ±10%
Result: 355 CFM → PASS

Step 2: Verify maximum cooling airflow

Set space temp to 80°F (call for cooling)
Expected: Airflow increases to 1,200 CFM before reheat
Result: 1,180 CFM → PASS

Step 3: Verify reheat operation

Maintain space at 80°F, increase setpoint to 72°F
Expected: Airflow reduces to minimum, reheat valve opens
Measure discharge air temp increase
Result: Airflow 360 CFM, DA temp 95°F → PASS

Step 4: Verify deadband

Set space temp = setpoint (72°F)
Expected: Airflow at minimum, no heating or cooling
Result: 360 CFM, reheat closed → PASS

Conclusion: VAV terminal operates per sequence

TAB Verification

Commissioning agent verifies TAB contractor work:

Review TAB plan: Methodology, instruments, tolerances
Witness testing: Observe 10-20% of measurements
Review reports: Check calculations, balance tolerances
Spot-check: Re-measure 5-10% of points independently

Acceptance criteria:

Airflow: ±10% of design
Hydronic flow: ±10% of design
Temperature: ±2°F of setpoint
Pressure: ±0.02 "w.g. of setpoint

Controls Verification

Verify BAS trends and sequences:

Trend setup:
- Sample rate: 15-minute intervals minimum
- Duration: 48-72 hours (capture occupied/unoccupied cycles)
- Points: Supply/return temps, damper positions, valve positions, fan status
Trend analysis:
- Check control stability (hunting, oscillation)
- Verify setpoints match design
- Confirm reset schedules active
- Identify simultaneous heating/cooling

Common issues found:

PID tuning too aggressive (oscillation)
Economizer not enabled
Night setback not programmed
Outdoor air damper stuck

Seasonal Testing

Some systems require testing outside of construction season:

Heating: Test in winter (or simulate low OA temp)
Cooling: Test in summer (or simulate high OA temp)
Free cooling: Test economizer at shoulder season conditions

Deferred testing: Schedule within first year of operation

Issues Log and Deficiency Tracking

Maintain master issues log:

Issue #	System	Description	Priority	Responsible	Status	Resolution
CX-001	AHU-1	Economizer damper stuck at minimum	High	Contractor	Closed	Actuator replaced 5/12
CX-002	VAV-205	Airflow 20% below design	Medium	TAB	Open	Damper adjustment scheduled

Priority levels:

Critical: Life safety, code violation
High: Significant energy waste, comfort impact
Medium: Minor performance issue
Low: Documentation, cosmetic

Systems Manual

Deliverable to owner:

Design narrative: System descriptions, design basis
Equipment documentation: O&M manuals, shop drawings, warranties
Control sequences: Detailed written sequences with points list
As-built drawings: Red-lined to reflect actual installation
TAB reports: Final airflow and water flow measurements
Functional test reports: Results of all Cx tests
Training documentation: Training session materials, video recordings

Training

Provide to facilities staff:

Systems overview: How each system operates
Operator interface training: BAS navigation, override procedures
Preventive maintenance: Filter changes, belt inspections, seasonal tasks
Troubleshooting: Common problems and solutions

Training sessions:

Minimum 4 hours for complex systems
Hands-on demonstrations
Provide training manual
Record sessions for future staff

Practical Applications

New construction: Full commissioning per ASHRAE Guideline 0
Existing buildings: Retro-commissioning (RCx) identifies 5-15% energy savings
LEED: Enhanced commissioning (EAc3) requires additional testing
Code compliance: Some jurisdictions require commissioning (California Title 24)

Related Technical Guides:

References:

ASHRAE Guideline 0: The Commissioning Process
ASHRAE Guideline 1.1: HVAC&R Technical Requirements for the Commissioning Process
ASHRAE Standard 202: Commissioning Process for Buildings and Systems
NEBB Procedural Standards for Building Systems Commissioning