Data centre cooling and mechanical contractors

What the mechanical package actually covers

The package runs from the heat rejection plant in the yard or on the roof to the terminal equipment in the hall: chillers, pumps, buffer vessels and thermal store, headers, valves, pipework and insulation, then CRAH or CRAC units, fan walls, in-row units, rear-door heat exchangers and coolant distribution units. On a liquid job the contractor usually takes the secondary loop up to the rack manifold and stops there, because cold plates, hoses and quick disconnects arrive with the servers. That interface line is where the first argument on any liquid retrofit happens.

What sits outside the package matters as much. Power to the mechanical plant, the motor control centre and the field wiring are usually electrical scope. Structural steel, plinths, roof penetrations and builder's work usually belong to someone else. Acoustic screening is sometimes nobody's until the planning condition is read properly. And a firm that builds new plantrooms is not automatically the firm you want cutting into a loop above live racks, or holding the maintenance contract afterwards. Most contractors offer all three, new build, retrofit and service, and are genuinely good at one or two.

The two jobs, and why they price differently

On a new build you are buying a plantroom, an external plant yard, riser pipework and a hall fit-out delivered in tranches as capacity is sold. Phasing is the part that catches people out. Plant is sized for the finished building but installed in stages, so the first hall runs the system at a fraction of design load, and pump control, chiller staging, minimum flow and coil selection all have to work down there as well as at the top. A scheme that only behaves at full load is a scheme that will be run manually.

The other job, now at least as common, is intervening in a building that already carries IT load. Adding direct-to-chip capacity, replacing end-of-life chillers, changing refrigerant, recoiling air handling units, cleaning and treating a loop that has been neglected for a decade. There is no hot work over live equipment, tie-ins need either valved provision left by the original installer or pipe freezing, work happens out of hours, temporary chillers arrive on hire, and racks get decanted to find floor space for coolant distribution units. Cost and programme there behave nothing like new build.

Chilled water, air, liquid and heat rejection

Chilled water is still the backbone at scale: chillers, primary and secondary pumping, a thermal store sized to hold the hall through a chiller restart after a transfer, and headers valved so any machine or pump can be isolated without dropping a path. Air terminals split between CRAH units fed from that loop and CRAC units carrying their own refrigerant circuit and external condensers, with fan walls and in-row units now normal in large halls. Heat rejection is a site-specific trade: open towers, air-cooled chillers, dry coolers, adiabatic assist, each swapping water against power, area and noise.

Liquid is the live argument. Direct-to-chip arrives as a retrofit problem as often as a new build one, and a coolant distribution unit brings a secondary loop with water quality, filtration, material compatibility and leak containment requirements that ordinary building services pipework has never had to satisfy. Rear-door heat exchangers are a lighter intermediate step. Immersion is a different discipline again, with fluid handling, floor loading and, for some fluorinated fluids, an unresolved regulatory question. Nobody should tell you the industry has converged. Air, rear-door, single-phase direct-to-chip and immersion are all being built, sometimes inside one estate.

How this work is quoted, and what moves the number

This work is tendered against a drawing set, a specification, a plant schedule and a programme. You get a lump sum, usually with a schedule of rates for variations and provisional sums for what is not yet drawn. What that sum actually covers depends on the design responsibility split. A prescriptive specification keeps the design with the consultant and the contractor prices what is drawn. A performance specification, or a contractor-designed portion, moves capacity and efficiency warranties onto the bidder. Those two routes produce different numbers and very different risk, so settle which you are tendering before you compare bids.

What moves the number: long-lead plant, and the awkward fact that chillers, coolant distribution units, plate heat exchangers, large valves and drives are often ordered before the design is frozen, so the order fixes cost and the design then bends around the machine. After that, working over live load, pipework material and jointing method, prefabrication extent, insulation and vapour sealing, commissioning scope, spares and attendance, and who carries flushing and water treatment. Freight and currency on imported plant. Read the exclusions first: builder's work, power to the plant, acoustic treatment and integrated systems testing are the usual gaps.

Records, certificates and the regimes that outlive the project

Expect pressure test certificates, flushing and chemical cleaning records with a laboratory water analysis, filtration results measured against a stated cleanliness target rather than a tick, welding procedure specifications with current welder qualifications and non-destructive testing reports on the proportion of joints specified, valve and plant certification, refrigerant charge and leak records, lifting plans, then as-built drawings and an operation and maintenance manual somebody can still use in five years. Pre-commission cleaning of pipework has its own published guidance and its own sign-off, and it belongs before IT load, not alongside it.

Then the statutory layer. Open towers and evaporative equipment bring a legionella risk assessment, a written water safety plan, registration with the local authority in many jurisdictions, and a logged monitoring routine with named responsibility attached. Refrigerant work needs certified operatives and a charge log, and the move to lower global warming potential fluids, some of them flammable, brings plantroom ventilation, gas detection and a different design case. Pressure equipment rules can apply depending on fluid and pressure. Commissioning records are where a client witnessing regime and any certification scheme meet, and where programmes quietly lose weeks.

Where these projects actually go wrong

The electrical interface is the classic scope gap. Who supplies the variable speed drives, who wires actuators and sensors, who terminates in the mechanical switchboard, whose scope is chiller control power, and which pumps sit on uninterruptible supply so water keeps moving through a transfer to standby generation. Thermal ride-through depends on that last answer and on the thermal store, not on goodwill. When the split is left to two contractors to sort out on site, you find the truth during the black building test, at the point in the programme where there is no time left.

Controls are the second. The sequence of operations is the most consequential document in a mechanical package and the one most often unfinished at installation. The contractor's controls subcontractor and the separate building management integrator each assume the other owns chiller sequencing, pump staging, valve strategy, setpoint reset and alarm handling. Points lists arrive incomplete, graphics arrive late, and the plant runs in hand because nobody has signed the sequences off. Part-load behaviour in a half-occupied building is where that hurts most, and it is exactly the condition nobody tests properly.

The third is water. A loop flushed to a certificate but never to a particle count. Oxygen ingress into a system everyone calls closed but which is topped up weekly. Mixed metals, depleted inhibitor, microbiological growth, corrosion under insulation whose vapour seal failed on a chilled line years ago. On a secondary liquid loop the same neglect blocks cold plates, and the consequence lands on IT rather than on a coil. Add the retrofit special: a tie-in with no isolation provision, a leak over live racks, and a crane window that closed while the plant sat in a yard.

How to build a shortlist

Ask for projects of the same shape rather than the same value. A live retrofit under a containment system is different work from a greenfield plantroom, and the reference list should show which one you are buying. Ask who held the design on those jobs and who carried the liability, then get the professional indemnity position in writing: the limit, whether it is project-specific, and whether it responds to any fitness for purpose wording your contract imposes, because most policies do not. Ask about welding capability, prefabrication, and whether spools are built off site.

Then test capacity and continuity. Who would actually be on site, what else that team is committed to in your window, whether commissioning engineers are employed or hired in, and which firm does their controls. On liquid, ask what they have commissioned and handed over rather than what they can quote, because the installed base is young and every reference list is short. The listings here are factual and drawn from public information. They are not a ranking and not an endorsement: use them to assemble a tender list, then run your own diligence on what is on it.

Why location changes the mechanical answer

Climate and water set the answer before anyone opens a drawing. Design wet bulb decides what evaporative heat rejection can achieve and therefore what chilled water temperatures are realistic. A hot, dry site pushes towards air-cooled plant with adiabatic assist, which trades the water argument for more yard, more electrical load and a harder design day. Water is now a permitting question as much as an engineering one, and the discharge consent for tower blowdown, with its dissolved solids and biocide residual, constrains schemes as often as the supply side does.

Rules and people vary just as much. Energy codes, efficiency reporting, heat reuse obligations, refrigerant restrictions, seismic restraint and boundary noise limits differ by jurisdiction and change plant selection, not only paperwork. So does the labour market: whether pipefitters and commissioning engineers are available when your programme needs them, how site agreements work, and what out-of-hours retrofit labour costs. And the plant has to physically arrive. Port capacity, road route, bridge and gradient limits, a crane position and a lift path for a chiller are geography problems that land on the critical path.