VRF (Variable Refrigerant Flow) and VRV (Variable Refrigerant Volume) systems are the dominant technology for commercial air conditioning across offices, retail, hospitality, and multi-zone residential applications. Commissioning a VRF/VRV system correctly is significantly more complex than commissioning a residential split — and the consequences of errors are proportionally more serious.
This guide covers the key commissioning steps for VRF/VRV systems, what is different from split system commissioning, and the most common mistakes engineers make on multi-indoor unit installations.
VRF vs Split System Commissioning — Key Differences
| Factor | Split System | VRF/VRV System |
|---|---|---|
| Number of indoor units | 1 | 2–64+ per outdoor unit |
| Pipe network | Simple 2-pipe run | Complex branched distribution |
| Pressure test | Single circuit | Full branched network — all branches |
| Evacuation target | Below 500 microns | Below 250 microns (manufacturer dependent) |
| Refrigerant charge | Factory charge ± pipe run correction | Factory charge + calculated additional charge |
| Additional charge calc | Simple per-metre addition | Complex — liquid line length, diameter, branch configuration |
| Commissioning software | Not required | Required — manufacturer-specific tool |
| F-Gas records | Standard logbook | Full system log — often multiple circuits |
| Commissioning time | 2–4 hours typical | 1–3 days typical for large systems |
Pre-Commissioning Checks
Before any pressure testing or evacuation begins, complete the following checks:
Pipework Inspection
- All pipe joints brazed and visually inspected — no flux residue on external surfaces
- All branch selectors (BS boxes) correctly installed per manufacturer orientation requirements
- Pipe insulation complete on all sections including branch selectors and valve connections
- All service valves confirmed closed (factory position) before pressure test
- Pipe sizing verified against manufacturer's pipe sizing tables for the system configuration
Electrical Checks
- Power supply verified against outdoor unit nameplate requirements
- Inter-unit communication wiring installed and verified (polarity-sensitive on most systems)
- All indoor unit wiring connections verified
- Earth continuity confirmed on all units
Drain Checks
- All condensate drain connections made and fall verified
- Condensate pump operation tested where fitted
- Drain traps installed where required by manufacturer
Documentation Check
- Manufacturer's commissioning manual available on site
- Pipe length and diameter schedule prepared for additional charge calculation
- System configuration drawing available showing all indoor units, branch selectors, and pipe runs
Nitrogen Pressure Testing
VRF/VRV systems must be pressure tested with OFN (oxygen-free nitrogen) before evacuation. The pressure test must cover the entire refrigerant circuit — including all branch selector connections and indoor unit connections.
Test Pressure
Always refer to the manufacturer's commissioning documentation for the specified test pressure. VRF/VRV systems typically operate at higher pressures than residential splits, and test pressures reflect this. Do not apply residential split test pressures to VRF systems.
Typical test pressures for R410A VRF systems are in the range of 40–42 bar. R32-based VRF systems require higher test pressures — always verify against the specific manufacturer's documentation.
Test Procedure
- Connect nitrogen regulator and test gauge to the system service port
- Pressurise to the manufacturer's specified test pressure in stages — do not apply full pressure immediately
- Hold at intermediate pressure (typically 50% of test pressure) for 5 minutes and check for obvious leaks
- Pressurise to full test pressure
- Isolate nitrogen supply and hold for minimum 24 hours on VRF systems (longer than residential splits due to system complexity)
- Record start pressure, ambient temperature, end pressure, and ambient temperature
- Correct for temperature variation — pressure will change with ambient temperature during the test period
Any pressure drop not accounted for by temperature change indicates a leak. Locate and repair before proceeding. See our full guide: Nitrogen Pressure Testing for HVAC Systems.
Evacuation
VRF/VRV systems require deeper evacuation than residential splits due to the larger system volume, longer pipe runs, and greater potential for moisture ingress during installation.
Pump Selection
Use a high-capacity two-stage vacuum pump — minimum 8 CFM for small VRF systems, 12 CFM or larger for systems with extensive pipe networks. Undersized pumps will take excessively long to pull down and may not achieve target micron levels within a practical timeframe.
For R32-based VRF systems, use an A2L-rated vacuum pump. See our comparison: Mastercool vs Javac Vacuum Pumps.
Connection Points
Connect the vacuum pump to both the high and low pressure service ports to ensure the entire circuit is evacuated. On large VRF systems, consider connecting at multiple points to reduce pull-down time and ensure even evacuation across all branches.
Micron Targets
VRF/VRV systems require deeper vacuum than residential splits:
| System type | Target vacuum level |
|---|---|
| Residential split | Below 500 microns |
| VRF/VRV system | Below 250 microns (verify against manufacturer spec) |
| Best practice VRF | 200 microns or below |
Always verify with a digital micron gauge connected directly to the system — not to the pump or manifold. See our full guide: How to Use a Micron Gauge Properly.
Vacuum Decay Test
After reaching target micron level, isolate the pump and perform a vacuum decay test for a minimum of 30 minutes on VRF systems (longer than the 10–15 minutes used for residential splits). A reading that holds stable or rises slowly and plateaus below 1,000 microns is acceptable. A rapid rise indicates a leak or residual moisture.
See our full evacuation guide: How to Evacuate an AC System Correctly.
Additional Refrigerant Charge Calculation
This is the most technically demanding part of VRF/VRV commissioning and the area where errors are most common.
Factory Charge
VRF outdoor units are supplied with a factory refrigerant charge sufficient for a defined pipe length (typically 30–50m of liquid line, depending on manufacturer and model). Any installation with pipe runs beyond this requires additional refrigerant.
Additional Charge Calculation
Additional charge is calculated based on:
- Liquid line length — the primary factor. Measure the total liquid line length from the outdoor unit to each indoor unit, accounting for the branched pipe network
- Liquid line diameter — larger diameter pipe requires more refrigerant per metre
- Branch selector configuration — some manufacturers include branch selector internal volume in the calculation
Each manufacturer provides a specific additional charge calculation method in their commissioning documentation. Do not use one manufacturer's calculation for another manufacturer's system. Daikin, Mitsubishi Electric, Samsung, LG, Hitachi, and Toshiba all use different calculation methods and pipe volume tables.
Charging Procedure
- Calculate total additional charge required from manufacturer's documentation
- Open outdoor unit service valves
- Power on the system and run the manufacturer's commissioning mode (required on most VRF systems before or during charging)
- Add refrigerant in liquid phase via the liquid service port using calibrated refrigerant charging scales
- Add refrigerant in small increments — do not add the full calculated charge in one step
- Monitor system operating parameters throughout charging
- Record total refrigerant added
Never charge by pressure alone on a VRF system. Always charge by weight to the manufacturer's calculated value.
Manufacturer Commissioning Software
Most major VRF/VRV manufacturers require or strongly recommend the use of their proprietary commissioning software or tool during commissioning. This typically:
- Runs an automatic refrigerant distribution check across all indoor units
- Verifies communication between all units
- Checks operating parameters against expected values
- Generates a commissioning report for handover
- May be required to validate the manufacturer's warranty
Commissioning without the manufacturer's tool may invalidate the system warranty. Check the specific requirements for the system being commissioned before starting work.
Post-Commissioning Checks
After charging and running the manufacturer's commissioning routine:
- Verify all indoor units are operating in both cooling and heating modes
- Check suction and discharge pressures against manufacturer's expected values for the ambient conditions
- Verify superheat and subcooling are within manufacturer's specified ranges
- Check all indoor unit airflows and temperature differentials
- Perform a post-charge leak check on all joints and connections using electronic leak detection equipment
- Verify condensate drainage from all indoor units
F-Gas Handover Requirements
VRF/VRV systems typically contain sufficient refrigerant to trigger F-Gas record keeping obligations. Calculate the system tCO2e and advise the operator of their obligations:
- Total refrigerant charge (factory charge + additional charge added) must be recorded
- If the system contains 5 tCO2e or more, the operator must maintain a system logbook and arrange annual leak checks
- Provide the operator with a completed commissioning record including refrigerant type, total charge weight, and next leak check date
See our full F-Gas compliance guide: F-Gas Compliance Checklist for AC Engineers.
Common VRF/VRV Commissioning Mistakes
- Insufficient evacuation — using residential split micron targets (500 microns) on VRF systems. Target 250 microns or below.
- Undersized vacuum pump — using a 5 CFM pump on a large VRF system significantly extends pull-down time and may not achieve target vacuum.
- Incorrect additional charge calculation — using the wrong manufacturer's table, measuring gas line instead of liquid line, or ignoring pipe diameter.
- Charging without commissioning mode active — most VRF systems require a specific operating mode during charging. Check manufacturer documentation.
- Not correcting pressure test for temperature — ambient temperature changes during a 24-hour test will affect pressure readings. Always record and correct for temperature.
- Skipping manufacturer commissioning software — may invalidate warranty and miss refrigerant distribution faults.
- Not recording total charge for F-Gas — factory charge plus additional charge must both be recorded in the system logbook.
See our full guide: Common HVAC Commissioning Mistakes.
Frequently Asked Questions
What micron level should I target for a VRF system?
Below 250 microns as a minimum for VRF/VRV systems. Best practice targets 200 microns or below. Always verify against the specific manufacturer's commissioning documentation.
How do I calculate additional refrigerant charge for a VRF system?
Use the manufacturer's specific additional charge calculation table from their commissioning documentation. Calculate based on liquid line length and diameter. Do not use one manufacturer's calculation for another manufacturer's system.
Do I need commissioning software for VRF systems?
Most major manufacturers require or strongly recommend their proprietary commissioning tool. Commissioning without it may invalidate the system warranty. Check the specific requirements for the system being commissioned.
What size vacuum pump do I need for a VRF system?
Minimum 8 CFM for small VRF systems. 12 CFM or larger for systems with extensive pipe networks. Undersized pumps will take excessively long to pull down and may not achieve target micron levels.
How long should I hold the nitrogen pressure test on a VRF system?
Minimum 24 hours for VRF systems. Longer for large or complex systems. Always correct the final pressure reading for ambient temperature change during the test period.
Related HVAC Commissioning Guides
- How to Evacuate an AC System Correctly — full evacuation procedure including micron targets and decay testing
- Nitrogen Pressure Testing for HVAC Systems — OFN test pressures and standing test procedure
- How to Use a Micron Gauge Properly — correct placement, target levels, and decay test interpretation
- R32 vs R410A — What Engineers Need to Know — refrigerant comparison including A2L tooling requirements
- F-Gas Compliance Checklist for AC Engineers — leak check schedules, record keeping, and 2024 regulation updates
- Common HVAC Commissioning Mistakes — evacuation, pressure testing, and charging errors to avoid
VRF/VRV Commissioning Equipment
- Vacuum Pumps — high-capacity two-stage pumps for VRF system evacuation
- Diagnostic & Testing Tools — digital micron gauges and refrigerant charging scales
- Nitrogen Equipment — OFN regulators and pressure testing gauge sets
- Leak Detection Equipment — electronic detectors for post-charge leak checks
- Gauges & Manifolds — manifold gauge sets for system pressure monitoring
- Mastercool Tools — high-CFM vacuum pumps and digital commissioning equipment
All equipment available for same-day dispatch across the UK.