Data Center Commissioning: Levels, Flushing, Testing and Mechanical Scope

Data center commissioning is the documented process of proving that a facility’s cooling, power and control systems were designed, built and tested to meet the owner’s requirements before IT load goes live, and Paul Industries executes and records the mechanical and piping share of it: installation checks, flushing, pressure testing, startup and functional testing of chilled water, condenser water and liquid cooling systems. We work beside the owner’s commissioning agent and keep crews, records and test equipment ready at every level the cooling systems pass through. This page covers the levels, who does what, how cooling loops are flushed and tested, and what turnover records should contain. Water treatment, loop chemistry and plant piping across the whole building are covered on our data center industry page.

What is data center commissioning?

It is a quality process, running from design into early operation, in which every critical system is inspected, started, tested alone and then tested with every other system under simulated load, with each result recorded and signed. The data center commissioning process follows the framework of ASHRAE Guideline 0, which describes commissioning as verifying and documenting that a facility and its systems are planned, designed, installed, tested, operated and maintained to meet the Owner’s Project Requirements, or OPR. The design engineer answers the OPR with a Basis of Design, and the building is tested against both.

Owners pay for it because of what a late discovery costs. A cooling fault found during integrated testing costs a retest; the same fault found with tenant servers running costs an outage. Commissioning also leaves behind the baseline later maintenance relies on: design flows, pressure drops, setpoints and water chemistry on the day the system was accepted. Redundancy exists on drawings long before it exists in the building, and commissioning is when it is proven by deliberately switching equipment off.

L1 to L5 data center commissioning: what each level proves

Data center commissioning levels split the work into gates, each of which must close before the next opens. The 5 levels of data center commissioning are Level 1 factory testing, Level 2 delivery and installation verification, Level 3 startup, Level 4 functional performance testing and Level 5 integrated systems testing. The scheme is industry practice rather than a code requirement, so the exact boundary between levels comes from the owner’s commissioning specification. Some programs add a Level 0 for planning and design review, in which the agent reviews the OPR and Basis of Design at design milestones, and a Level 6 for closeout and transition to operations, covering the final report, operator training and deferred or seasonal tests. Many owners tag equipment as it passes each gate, commonly red, yellow, green, blue and white in level order, though colors vary between programs. The same numbering appears in specifications written in British English, where they are called data centre commissioning levels, with boundaries that still vary from owner to owner.

Commissioning levels 1-5 at a glance

Level 1: factory witness testing

Level 1 takes place at the manufacturer, before shipment. The owner or agent witnesses performance runs on long-lead equipment: chiller capacity and efficiency, pump curves, coolant distribution unit operation, air handler and fan wall airflow. The mechanical contractor confirms nozzle sizes, orientation, flange ratings and wetted materials against the piping design, because a connection on the wrong side found at the factory is a drawing revision, and on site it is rework.

Level 2: delivery, installation and site acceptance

Level 2 confirms that what arrived matches what was ordered, that it survived shipping, and that it is installed to the drawings and the maker’s instructions. For piping this is where the physical record is built: materials checked against the specification, supports inspected, welds examined, test pressures recorded, and vent, drain and flushing connections confirmed. A system normally cannot start until its Level 2 checklist is closed, so missing paperwork stalls a schedule as surely as missing work.

Data center level 3 commissioning: startup and pre-functional checks

At Level 3, each piece of equipment is energized and started on its own by its vendor or installing contractor, with the agent witnessing. On the cooling side that means pump rotation and alignment checks, chiller startup by the manufacturer’s technician, cooling tower fan and basin checks, CRAH and fan wall startup, control valve stroke tests, and point-to-point verification of every controls input and output. The loops must already be clean, treated and free of air, because a pump started against a dirty or air-bound system damages seals and gives untrustworthy readings.

Level 4 data center commissioning: functional performance testing

Level 4 tests each system as a whole against its sequence of operations, one system at a time. The chilled water plant is staged up and down, lead and lag pumps are rotated, a running chiller is tripped to confirm the standby picks up, differential pressure control is proven at the most remote branches, and CDUs are switched between redundant pumps and filters. Readings go into a test script the agent signs only when each step meets its acceptance value.

Data center level 5 commissioning: integrated systems testing

Level 5 runs every system together under simulated IT load while the agent stages failures such as loss of utility power, generator start and transfer, UPS response, a chiller or pump trip and a controls fault. Through each scenario the mechanical team keeps the plant and liquid loops ready, operates valves and equipment when the script calls for it, records how temperatures and flows recover, and corrects whatever fails. Heat comes from air-side load banks in the white space or liquid-connected heaters on the technical loop. Planning for IST, data center commissioning teams agree the script, load bank layout, communications and stop criteria well ahead, because an aborted integrated test is expensive to restage.

Commissioning levels: data centers vs commercial buildings

A commercial building commissioned under Guideline 0 usually ends with functional testing of each system and seasonal checks. A data center program goes further at both ends: factory witness testing before equipment ships, and an integrated test that deliberately fails equipment under full simulated load to prove the redundancy the owner paid for. The cooling contractor’s work is the same in kind, only more of it is witnessed and every result is signed.

What is a data center commissioning agent?

The commissioning agent, also called the commissioning authority or CxA, is the party the owner appoints to lead the commissioning process: writing the plan and test scripts, witnessing tests, keeping the issues log and reporting whether the facility meets the owner’s requirements. The agent is normally contracted to the owner rather than the builder, so the person judging the work is not the person paid to finish it. The agent directs and witnesses; contractors and vendors start, operate and adjust their own systems.

Data center mechanical commissioning by system

Mechanical commissioning covers every system that moves heat out of the white space and rejects it outdoors, and each one has its own checks at each level. Data center HVAC commissioning is often understood as air-side work, but in current halls the water side carries more of the risk: CRAH units and fan walls rely on the chilled water plant, and liquid cooled racks rely on a technical cooling loop with a cleanliness tolerance tighter than anything else in the building. The table lists the checks we prepare for and record on each system. Design background for these systems is on our data center cooling systems page.

The plant equipment is covered on our pages for chilled water systems, chillers and heat exchangers. Condenser water has a step of its own: the tower treatment program must be running, with its controller calibrated and biocide feed proven, before handover; see cooling tower water treatment.

What is pipe flushing?

Flushing is the circulation of water through newly installed piping at high velocity, with sensitive equipment bypassed and temporary strainers in the circuit, to carry construction debris out of the system before it goes into service. A new loop holds weld slag, cutting chips, mill scale, thread compound, sand and oil, and control valves, plate heat exchangers and cold plate microchannels will catch all of it. Flushing is normally followed by chemical cleaning to strip oils and mill coatings, a rinse, and treatment. Draining and refilling is not flushing: some owner specifications prohibit it and require continuous fresh-water feed while dirty water is bled off, so solids leave instead of settling back onto pipe walls.

Pipe flushing procedure

A flushing procedure is a written, project-specific method statement setting the circuits, temporary equipment, velocity target, cleaning chemistry and acceptance tests, and it should be approved by the owner and the water treatment provider before any water goes in. On cooling water systems our sequence runs as follows, with the owner’s specification governing wherever it differs.

1. Walk the system and mark everything to be bypassed: chillers, heat exchangers, coils, CDUs, pumps where temporary pumps are used, and every IT connection. Install jumpers and blind flanges.
2. Establish the system volume by metering the fill or by a dilution test, so chemical doses are calculated, not guessed.
3. Install temporary strainers, starting coarse and stepping to finer screens as the water clears.
4. Fill with water of the specified quality through a connection with backflow protection.
5. Circulate circuit by circuit at the target velocity, isolating branches where the temporary pump cannot reach it system-wide.
6. Pull and clean strainers as often as debris requires, logging findings.
7. Dose the cleaner, circulate for the specified period, sample, then rinse by feed and bleed until conductivity, pH and iron return toward makeup values.
8. Add the specified inhibitor or coolant straight away, because a freshly cleaned carbon steel loop left with untreated water starts to flash rust.
9. Remove bypasses, reconnect equipment and record the final chemistry as the commissioning baseline.

Pipe flushing velocity

Flushing velocity has to be high enough to lift and carry debris that settles at normal flow, and the common rule of thumb is to flush at or above the system’s design operating velocity, often with a margin. Owner specifications put numbers on it, and they vary: published HVAC standards call for minimums such as 6 ft/s or 8 ft/s, or a final circulation at 10 ft/s, while chemical cleaning is often circulated more slowly, around 3 to 5 ft/s, for a period measured in days rather than hours. Reaching flushing speed in large mains takes properly sized temporary pumps or smaller circuits, so flushing connections and flanged breaks belong on the design drawings, not improvised in the field.

Pipe flushing requirements and acceptance

Flushing requirements should state measurable end points, because “flush until clean” invites an argument at the worst possible time. Typical criteria are strainers that stay free of visible debris over a defined run at the final mesh, conductivity, pH and iron within agreed limits of the makeup water, and, for liquid cooling loops, filter differential pressure or particle data within the CDU and cold plate makers’ limits. For technical loop filtration, see process filtration.

Where makeup or fill water itself needs conditioning to meet a coolant specification, the equipment is covered under industrial water treatment.

Piping: flushing or hydrotest first?

On most closed cooling water systems the pressure test comes first and flushing and chemical cleaning follow, but no ASME piping code fixes the order; the leak-test rules carry no internal cleaning requirement, so the owner’s specification decides. Testing first finds leaks while the loop holds plain water, before cleaning chemicals are in it and before insulation covers the joints, and it confirms the piping can safely take flushing velocities. Some HVAC owner standards assume exactly that, leaving the system full after the test until cleaning starts. Water mains and some process systems are flushed first, to clear debris that could foul test equipment, and some programs flush both before and after. Whichever order is chosen, keep the gap between test and cleaning short and the system full, because wet, untreated carbon steel corrodes while it waits.

Hydrostatic and pneumatic pressure testing

A hydrostatic test fills the piping with water, raises it to a pressure above design, holds it and examines every joint for leaks; a pneumatic test uses air or nitrogen and is reserved for systems that cannot tolerate water, because compressed gas stores far more energy. Chilled water, condenser water and most facility water piping in a data center falls under ASME B31.9, Building Services Piping, which calls for a hydrostatic test of at least 1.5 times design pressure held for at least 10 minutes. B31.9 limits pneumatic testing, with a ceiling of 150 psig, and does not allow it on brittle materials. Piping built to ASME B31.3 is hydrostatically tested at 1.5 times design pressure, adjusted upward where the design temperature reduces the allowable stress, and pneumatically at 1.1 times design pressure. Owner specifications often extend the hold well beyond the code minimum, so read the required duration before scheduling.

Anything not rated for the test pressure, including instruments and every IT connection, is isolated, and relief valves on the technical loop are set below the IT maker’s rated maximum. See hydrostatic testing for method, safety and records.

Liquid cooling commissioning: fill, venting, chemistry and heat load

Commissioning a liquid cooled hall proves that the technical cooling system, the closed loop between the CDU and the cold plates, is clean, filled with the right fluid, free of air, leak tight and able to hold supply temperature as heat load rises. An ASHRAE TC 9.9 bulletin issued in 2026 on technology cooling system coolant integrity and readiness names four risk areas commissioning should cover: coolant composition, air management, passivation of stainless components and system pressure ratings.

• Clean before connecting. Secondary piping and row manifolds are flushed with the CDU and IT connections bypassed, then cleaned and passivated wherever stainless has been welded, following ASTM A380 and ASTM A967. One unpassivated component can release free iron into cold plate channels.
• Fill and air removal. The loop is filled from low points with every high point vented, often with a vacuum fill cart. Air separators work best on the warm, low-pressure return near the CDU inlet. Gas leaves solution more readily at higher temperature, so air problems can surface weeks after startup; venting is repeated under heat load, and automatic vents are capped or valved off once the loop is proven air-free.
• Coolant chemistry verification. The fluid, often a propylene glycol blend near 25 percent or treated water to the maker’s specification, is sampled and laboratory tested at first fill, after significant top-ups and on a set schedule. Glycol blends can partly separate during vacuum filling, so the post-fill sample checks concentration, inhibitor level and pH against the design-basis fluid.
• Leak checks. Every joint, quick disconnect and hose is inspected at test pressure and again at operating temperature, and leak detection is proven to alarm.
• CDU startup. The vendor starts the unit; the installer confirms flows, filter pressure drop, pump changeover and supply temperature control.
• Heat load testing. Liquid-connected load banks or heaters on the rack manifolds are stepped up in stages while supply temperature, branch flow and differential pressure are trended.

Loop design and construction are covered under data center liquid cooling.

Data center commissioning plan, schedule and checklists

The commissioning plan is the document the agent writes early in design and updates through construction, setting the scope, team, responsibilities, levels, test procedures, documentation and timing for the program. The mechanical contractor feeds it with method statements: flush and clean procedure, pressure test plan, startup sequence and temporary equipment list.

The data center commissioning schedule sits inside the construction schedule, and its logic is strict. A system cannot start Level 3 until Level 2 is closed, and cannot join IST until everything it depends on has passed Level 4. On phased campuses one hall is often in integrated testing while the next is still being piped, so isolation points and tie-in windows are planned with the agent, not around it. For a cooling system, the usual data center commissioning steps run: design and submittal review, factory test, installation checklist, pressure test, flush and clean, fill and treat, startup, functional test, integrated test, turnover.

A data center commissioning checklist is the level-by-level form that records each check, who performed it, when, and the result. Installing contractors complete the Level 2 and 3 checklists; Level 4 and 5 scripts are written by the agent and executed by the trades. Every failed item is entered in the issues log with an owner and a due date, and it stays open until the fix has been retested.

Data center commissioning documentation and turnover

Commissioning documentation is what remains after the test crews leave, and what an operator reaches for when a pump trips years later. The agent assembles the final commissioning report and, under Guideline 0, a systems manual. Our mechanical share includes completed checklists for each piece of equipment, weld maps and welder records, signed pressure test reports with gauge calibration certificates, the flushing log with bypass lists, velocities, strainer findings and chemistry results, vendor startup reports, executed test scripts, as-built drawings, and the chemistry baseline maintenance will trend against. The structure of a piping turnover set is shown in our piping turnover package guide, and the intervals that follow commissioning are set out under preventive maintenance.

Data center commissioning standards

No single code defines them; a program is assembled from guidelines, piping codes and the owner’s specification. ASHRAE Guideline 0 describes the commissioning process itself, from the OPR through occupancy. ASHRAE Standard 202, derived from Guideline 0, states minimum commissioning requirements in mandatory language that codes and contracts can adopt. ASHRAE Guideline 1.1 applies the process to HVAC and refrigeration systems. Pressure testing follows ASME B31.9 or ASME B31.3, stainless passivation follows ASTM A380 and ASTM A967, and technical cooling loops follow ASHRAE TC 9.9 guidance plus the CDU and IT makers’ fluid and material requirements. Level numbering, tag colors and IST scope come from the owner, not from any of these documents. Our approach to codes, records and inspection is summarized under quality and standards.

Common failures found during data center testing and commissioning

Most mechanical findings trace back to work rushed or skipped at Level 2 or 3, and surface at Level 4 or IST, when they cost the most to fix.

How to choose data center commissioning companies and services

Firms offering this work fall into two groups that owners sometimes blur: independent commissioning agents, who plan and witness the program on the owner’s behalf, and the contractors and vendors who carry out the testing on their own systems. A project needs both, and one firm should not judge and execute the same scope. When evaluating data center commissioning services on the execution side, ask for a written flush and clean procedure with numeric acceptance criteria, pressure test procedures naming the code and medium, sample checklists and a turnover set from a comparable system, crews who can operate equipment on a script’s timing during Level 4 and IST, nights included, and a record of tying into operating plants without interrupting cooling. Scoping of the mechanical trade is covered under data center mechanical contractors.

Paul Industries’ role in data center commissioning

Paul Industries is the mechanical and piping contractor on the commissioning team, working to the agent’s plan and scripts. We install chilled water, condenser water, glycol and technical cooling system piping; set chillers, pumps, heat exchangers and CDU connections; pressure test, flush, clean, passivate, fill and treat the loops; complete the Level 2 and Level 3 checklists for our scope; start up the equipment we install together with its vendors; operate and adjust the cooling systems through Level 4 functional testing and Level 5 IST; correct deficiencies; and hand over the records, so each cooling system can be traced from its first weld to its IST sign-off. For pharmaceutical facilities, where commissioning feeds formal qualification, see validation and commissioning. To scope the mechanical side of a commissioning program, request a quote.

Standards referenced: ASHRAE Guideline 0 · ASHRAE Standard 202 · ASHRAE Guideline 1.1 · ASME B31.9 · ASME B31.3 · ASTM A380 · ASTM A967

Frequently asked questions

Who hires the commissioning agent on a data center project?

Usually the owner, under a contract separate from the builder and the trades. That separation is the point: the agent reports test results and open issues to the owner without a stake in the construction schedule, and contractors take direction on testing from the agent's scripts rather than negotiating their own acceptance.

What is Level 0 commissioning?

It is the label some programs give to commissioning work during planning and design, before equipment is bought. The agent reviews the Owner's Project Requirements and the Basis of Design at design milestones and checks that the drawings show the valves, test ports, vents, drains and flushing connections that later levels will depend on.

Is a commissioning level the same as an Uptime Institute tier?

They measure different things. A Tier rating describes the redundancy and concurrent maintainability built into the design. A level describes how far testing has progressed. A facility designed to a high Tier still has to pass integrated testing to show that its redundancy actually works.

What is the difference between startup and commissioning?

Startup is one step: a vendor or installer brings a single piece of equipment into safe operation to its maker's instructions. Commissioning is the documented process around it, from design review through integrated testing. A chiller can start perfectly and the plant can still fail commissioning if staging or failover does not work.

What is a pre-functional checklist?

A form completed by the installing contractor before a system is tested, confirming that installation is complete and correct: materials, supports, labels, valve positions, pressure test and flushing done, rotation checked, controls points connected. It is the evidence that a system is ready for startup and functional testing.

What is a functional performance test script?

A step-by-step procedure written by the commissioning agent that puts a system through its sequence of operations, with an expected response and an acceptance value for every step. The trades operate the equipment, the agent witnesses, and readings are written into the script as each step passes or fails.

How long does data center commissioning take?

It depends on facility size, how many levels the program includes, whether halls are commissioned in phases and how quickly issues close. Readiness drives the timeline more than test duration does, since each level waits for the one before it. Completing flushing, pressure testing and paperwork early is the most dependable way to protect the window.

Why are load banks used during commissioning?

Because servers are not yet installed, or the owner will not risk them. Air-side load banks heat the room so CRAH units and chillers see real load, and liquid-connected heaters let the technical loop and CDUs be tested at design heat. Load is raised in steps so the response at each stage can be recorded.

Which equipment is bypassed during flushing?

Chillers, plate heat exchangers, coils, CDUs and every IT connection are bypassed or isolated while debris is being moved, because their passages are the first place it lodges. They come back into the circuit only after the piping meets its cleanliness criteria, with strainers protecting them during early operation.

What is the difference between flushing and chemical cleaning?

Flushing removes loose solids by velocity. Chemical cleaning removes what velocity cannot: oils, cutting fluids, mill coatings and light rust films, using a detergent or alkaline cleaner circulated for a set period. Stainless systems that have been welded may also need passivation. Most specifications call for all three in sequence, followed by treatment.

When is a pneumatic test used instead of a hydrostatic test?

Only where water cannot be tolerated in the system, for example piping that cannot be fully drained or dried before a non-water fluid goes in. Compressed gas stores far more energy than water, so pneumatic tests run at lower pressures, need an exclusion zone and a written safety plan, and are restricted by the piping codes.

What minimum hold time do ASME B31.9 and B31.3 set for a leak test?

The codes set a minimum of 10 minutes at test pressure under ASME B31.9 and ASME B31.3 before joints are examined. Owner specifications commonly require longer, sometimes several hours with no water added and the pressure recorded on a calibrated gauge or chart. The longer hold is contractual rather than code, so read it before pricing the test.

How is trapped air found and removed from a liquid cooling loop?

Look for unsteady flow readings, pump noise and temperature swings at particular racks. Vertical dead legs, inverted U-bends and hoses without vents hold air indefinitely, so high-point venting has to be designed in, not added later. Venting is repeated as the loop warms under test load, because more dissolved gas comes out at higher temperature.

What is an issues log in commissioning?

The running list, kept by the commissioning agent, of every deficiency found from design review onward, each with a description, a responsible party, a due date and a status. An item closes only after the fix has been verified, and the final log becomes part of the commissioning report.

What records should a chilled water plant have at the end of commissioning?

Equipment startup reports, executed functional test scripts showing staging and failover results, balancing data, pressure test reports, the flushing and cleaning log, the treatment program and starting chemistry, controls trend data from testing, and the closed issues list. Together they form the reference for every later troubleshooting call.

How does Paul Industries work with the commissioning agent?

We build our method statements into the agent's plan, give notice of every witness point for pressure tests and flushing, complete the mechanical checklists before each level opens, and staff Level 4 and IST with the crews who built the loops. Issues assigned to our scope are corrected and retested quickly, so the log closes and the schedule holds.

What does the cooling team do during a utility failure test?

It watches the plant ride through the event. Crews stationed at the chillers, pumps and CDUs record how long flow and supply temperature take to recover after power transfers, confirm that standby equipment restarts in the right order, and operate valves or reset equipment only when the script calls for it.

Can an existing data center be recommissioned after adding liquid cooling?

Yes. New technical loops, CDUs and facility water tie-ins go through the same levels at a smaller scale, and the existing chilled water plant is retested where added load or new connections change how it operates. New piping is tested and cleaned before it is connected, so debris and air never reach the running system.

How does data center commissioning differ from pharmaceutical commissioning and qualification?

Data center commissioning proves performance and resilience against the owner's requirements. In a pharmaceutical plant, commissioning feeds formal installation, operational and performance qualification under GMP expectations, where the records themselves are subject to regulatory inspection. The flushing, testing and record discipline overlaps; the regulatory framework does not.

Who supplies temporary pumps and strainers for flushing?

Normally the mechanical contractor, as part of the flushing scope, because permanent pumps should not push construction debris through their own seals and impellers. Where an owner allows permanent pumps to be used, specifications typically require temporary fine-mesh strainer inserts and replacement of seals or screens after flushing.

Related: Data Centers · Data Center Cooling Systems · Hydrostatic Testing · Validation & Commissioning (IQ/OQ/PQ) · Chilled Water Systems · Pharmaceutical Commissioning And Qualification · Request a quote · Server Immersion Cooling: Tanks, Piping and Facility Water for Data Centers