Key takeaways
- Testing proves the installation is sound; commissioning proves the system performs to design.
- Pipework is flushed and pressure tested, and ductwork leak tested, before insulation and start-up.
- Air and water balancing make each outlet and coil deliver its design flow.
- Handover should include test records, a balancing report, as-built drawings and O&M manuals.
Commissioning is the stage that turns an installed HVAC system into a working one. It is also the stage most often squeezed when a project runs late, which is why so many new systems have rooms that are too hot, too cold, noisy or humid despite having the right equipment. This guide explains the steps of HVAC testing and commissioning and what you should expect to receive at handover.
Testing vs commissioning
Testing checks that the installation is sound and safe: pipes do not leak, ducts are tight, cables are insulated, motors rotate the right way. Commissioning starts the system, adjusts it and demonstrates that it delivers the design performance. Both are needed, and the second cannot be done well if the first has been skipped.
Step 1: Pre-commissioning checks
Before anything is started, the installation is inspected against the approved drawings:
- Equipment installed, levelled, and fitted with vibration isolators as specified
- Belts, pulleys and couplings aligned; guards in place
- Filters fitted, and ductwork and plenums clean inside
- Dampers, fire dampers and access panels installed and accessible
- Electrical supply, cable terminations and insulation resistance checked
- Control wiring, sensors and valves installed and labelled
- Condensate drains trapped and falling correctly
Step 2: Pipework flushing and pressure testing
Chilled water and condenser water piping
New pipework contains welding debris, mill scale and dirt that will block strainers, valves and coils if they are left in. Systems are flushed, often with chemical cleaning, before being filled for operation. Pipework is then hydrostatically pressure tested before insulation is applied, typically at around 1.5 times the working pressure or as the specification requires, and held for a defined period with no pressure drop.
Refrigerant piping for VRF and split systems
Refrigerant piping is pressure tested with dry nitrogen, then evacuated with a vacuum pump to remove air and moisture to the level specified by the equipment manufacturer, before refrigerant is charged. Moisture left in a refrigerant circuit causes long-term damage, so this step should not be shortened.
Step 3: Ductwork leakage testing
Leaky ducts waste fan energy and deliver less air than designed to the rooms at the end of the run. Critical sections, and high-pressure ductwork in particular, are leak tested against the leakage class in the specification, commonly referencing SMACNA methods, before ceilings close.
Step 4: Equipment start-up
Major equipment is started in line with manufacturer procedures, often with the manufacturer’s service engineer present for chillers and VRF systems. Checks include rotation, running currents, vibration, noise, refrigerant pressures and safety cut-outs.
Step 5: Air balancing
Air balancing, part of testing, adjusting and balancing (TAB), makes sure every supply and return outlet delivers its design airflow.
- Set the fan to deliver the total design airflow.
- Measure airflow at each outlet with a flow hood or anemometer.
- Adjust volume dampers, usually working proportionally from the index run furthest from the fan, until each outlet is within tolerance.
- Re-check totals and record final readings and damper positions.
Tolerances are set by the specification; readings within about ±10% of design are commonly accepted for comfort systems, with tighter limits for critical areas such as clean rooms.
Step 6: Water balancing
In chilled water systems, the pipe closest to the pump naturally takes more water than coils at the far end. Balancing valves are adjusted, using flow measurement across each valve, so every AHU and fan coil receives its design flow. Pumps are then set to the resulting duty point, which often reveals energy savings through lower pump speed.
Step 7: Performance verification
- Room temperatures and humidity measured against design conditions
- Chiller or VRF operation checked at the available load
- Fresh air and exhaust quantities confirmed
- Control sequences tested: set points, scheduling, alarms and standby changeover
- Noise levels checked in sensitive rooms
Where the system is handed over in a mild season, a follow-up check at peak summer load is good practice.
Problems commissioning typically finds
| Symptom | Likely cause |
|---|---|
| Rooms at the end of a duct run are warm | Unbalanced airflow, duct leakage or undersized branch |
| Space cold but humid | Oversized equipment, high fresh air load or wrong coil selection |
| Far coils underperform | Unbalanced chilled water flow or blocked strainers |
| Noisy outlets | Excess velocity, dampers nearly closed at the grille |
| Frequent tripping | Incorrect settings, low refrigerant charge or airflow restriction |
Step 8: Documentation and handover
A complete handover pack should include:
- Pressure test and leak test certificates
- Air and water balancing (TAB) report with final readings
- Equipment start-up and commissioning records
- As-built drawings
- Operation and maintenance manuals and warranty documents
- Completed installation quality check lists
- A record of training given to your operating staff
At 1 Worldcrafts, commissioning is carried out by a dedicated team with its own check lists, covering dry runs, air and water balancing, and validation against design parameters. See our engineering process, read about our HVAC services, or contact us about commissioning an existing system that is not performing.
Frequently asked questions
TAB stands for testing, adjusting and balancing. It is the process of measuring airflow and water flow throughout an HVAC system and adjusting dampers and valves so every outlet and coil delivers its design quantity.
It depends on the size and complexity of the system. Small systems may take days, while large buildings with central plant and building management controls can take several weeks. Commissioning time should be included in the project schedule from the start rather than compressed at the end.
Yes. Re-commissioning an existing system, including re-balancing airflow and water flow and checking controls, often solves long-standing comfort complaints and reduces energy use, especially after layout changes.
Expect test certificates, a balancing report, commissioning records, as-built drawings, operation and maintenance manuals, warranties, completed quality check lists and a record of staff training.
Planning a project like this?
Send us your drawings or scope. Our engineers will review the requirement and come back with an itemised proposal.
