---
title: 'Who owns the liquid cooling connection on a data center?'
url: 'https://piper-ai.com/resources/data-center-liquid-cooling-scope-boundaries'
description: 'Liquid cooling adds three loops and three owners. The gap sits between facility water, the CDU and the rack: hoses, valves, flushing, fluid and leak detection.'
contentTypes: [guide]
publishedAt: '2026-09-26T12:00:00.000Z'
updatedAt: '2026-09-27T11:23:35.493Z'
author: 'Ido Gedanken, CEO'
readingTime: 8
---

# Who owns the liquid cooling connection on a data center?

1. Direct-to-chip cooling splits the water into three loops, and ownership changes at each boundary
2. The unclaimed scope sits between the facility piping and the CDU, and between the CDU and the rack manifold
3. The technology cooling loop is a clean-loop trade: materials, filtration and flushing are specification, not courtesy
4. Someone has to own the loop between mechanical completion and IT load, or it corrodes while it waits
5. Level liquid cooling against a loop-by-loop responsibility matrix, not against the mechanical cover price

**On a liquid-cooled data center, the cooling water crosses three loops and at least three owners before it reaches a chip. The scope that goes missing sits at the boundaries between them.** The mechanical contractor runs the facility piping. The cooling distribution unit (CDU) comes from a vendor, often purchased by the owner. The rack and its internal cold plates belong to the owner's IT integrator. The hoses, valves, strainers, fluid, flushing and leak detection that join those pieces are claimed by none of them unless the documents say so.

This guide is for GC estimators and precon managers carrying mechanical packages on AI data centers that use direct-to-chip liquid cooling, whether new builds or retrofits of air-cooled halls. It applies where the owner furnishes the CDUs and racks, which is common, and still applies where the mechanical contractor buys the CDUs, with fewer handoffs. It does not cover immersion cooling, which changes the boundary again, or air-only halls. For how a data center differs from commercial work more broadly, see [data center precon is not commercial precon with more power](https://piper-ai.com/resources/data-center-preconstruction-vs-commercial).

## Why liquid cooling arrived, and what it changed

Air cooling works up to roughly 25 to 30 kW per rack, according to a CIBSE Journal continuing-education module on data center liquid cooling. Current AI racks run far above that. NVIDIA's GB300 NVL72 is specified at about 135 kW per rack in documentation Lenovo publishes, with about 90 percent of its heat going to liquid and the rest still to air. At those densities the water has to go to the chip itself, through cold plates inside the servers.

For precon, that turns part of the mechanical scope into something closer to process piping. The loop that feeds the racks has cleanliness, material and fluid requirements set by the IT equipment. And it connects to equipment the mechanical contractor does not own at both ends.

## The three loops in plain terms

The loop names follow ASHRAE's terminology, as drawn in Schneider Electric's white paper on liquid cooling heat rejection:

- **Condenser water system (CWS):** carries heat from the chillers to cooling towers or dry coolers on the roof or in the yard.
- **Facility water system (FWS):** the building's primary chilled or warm water loop, from the central plant to the CDUs.
- **Technology cooling system (TCS):** the clean secondary loop from the CDU to the row manifolds and into the racks. The CDU is a heat exchanger that keeps the TCS fluid separate from facility water.

The loops carry different fluids, need different cleanliness and are often built by different parties. Most scope gaps sit where one loop hands off to the next.

## Where ownership changes hands

Assignments vary by owner and by contract, so treat this as the questions to answer, not the answers:

| Segment | Commonly owned by | What sits in the boundary |
| --- | --- | --- |
| Heat rejection and CWS | Mechanical subcontractor | Towers or dry coolers, condenser piping, water treatment |
| Central plant and FWS | Mechanical subcontractor | Chillers or dry coolers, pumps, headers to the hall |
| FWS to CDU connection | Often unassigned | Branch piping, isolation and balancing valves, strainers, flexible hoses |
| CDU | Vendor, often owner-furnished | Setting, power and controls connections, startup, filters |
| TCS distribution and row manifolds | Mechanical subcontractor or a specialty vendor | Materials, cleanliness, supports, leak detection, venting and draining |
| Manifold to rack | Often unassigned | Hoses, quick disconnects, fill and first-fill fluid |
| Inside the rack | Owner's IT integrator | Cold plates, server manifolds, rack-level connections |

Two rows say "often unassigned." Those are the two places a careful leveling sheet should start.

## The last five feet

Data Center Dynamics ran an opinion piece calling the connection between the facility loop and the CDU the most common liquid cooling scope gap. The author calls it the "last five feet." The mechanical contractor runs large-bore facility piping to a point near the CDU. The CDU vendor delivers a unit with connection points. The hoses, valves, strainers and fittings between the two are in neither scope.

The pattern will be familiar to anyone who has leveled [plumbing against site utilities](https://piper-ai.com/resources/plumbing-underground-scope-boundary): two competent bids, each honoring its own drawings, and a connection that belongs to nobody. The cure is also the same. Resolve the boundary in words in the solicitation, item by item. A drawing note is exactly what two bidders will read differently.

## The quick disconnect is the facility and IT line

At the rack end, the Open Compute Project's guidance on liquid cooling connections suggests the quick disconnect as the logical boundary between facility and IT. It also notes that the coolant itself crosses that line, so neither side fully owns it.

That leaves questions a precon team should answer before award:

- Who supplies and installs the hoses and quick disconnects between the row manifold and each rack?
- Who supplies the first fill of TCS fluid, who fills and vents the loop, and who disposes of flush water?
- Who owns the fluid chemistry after turnover, and who is responsible if the fluid does not meet the IT vendor's specification?
- Who reconnects racks that are delivered after the loop is filled?

Each question can have a different answer on the same job. Each needs one answer in writing.

## The TCS is a clean-loop trade

The technology cooling loop feeds equipment with very small internal passages. Its requirements look more like process piping than hydronic heating.

**Materials.** Open Compute Project guidance on modular TCS design notes that carbon steel is generally avoided on the TCS side. Stainless steel is common, and the wetted materials have to be compatible with the fluid and the IT vendor's specification. At least one liquid cooling vendor ships prefabricated, passivated stainless TCS piping joined with grooved couplings, and installs and commissions it with its own team. When that happens, part of the mechanical scope becomes a vendor scope inside the GC's schedule.

**Filtration.** CDUs carry fine filtration. Vertiv, for example, lists 50 and 25 micron filters on its CDU range. The loop has to reach that standard before IT equipment is connected.

**Flushing and cleaning.** Open Compute Project pre-commissioning guidance for TCS row manifolds describes a cycle. Recirculate, measure suspended solids, drain and repeat until the loop passes, then clean chemically, with a copper corrosion inhibitor where copper is present. It also says the construction contractor, IT supplier and fluid supplier should agree on wetted materials. That process takes time, water, chemicals, instruments and disposal, and it has to be in somebody's price.

**Pressure testing.** Ask who supplies the test pump, gauges and test medium, who witnesses, and to what pressure under which document. Do not assume the facility piping test specification covers the TCS.

## Someone has to own the loop while it waits

A liquid cooling loop is often mechanically complete weeks or months before the IT equipment arrives. ChemTreat, writing from water treatment work at more than 200 data centers, describes what happens in that gap. Construction debris such as mill scale and cutting oil survives a rushed flush, and loops left idle between mechanical completion and IT load corrode or foul.

The contract should name who maintains water treatment, circulation and monitoring during that interval, and who re-verifies cleanliness before racks connect. On phased halls the interval repeats for every phase.

## Leak detection, power and the air that remains

**Leak detection.** Vertiv describes typical liquid cooling leak detection as sensing cable along pipe runs and under CDUs, plus point sensors under manifolds and drains. The sensors, wiring and connection to monitoring can sit in mechanical, electrical, controls or the CDU vendor's scope.

**Power and controls to the CDU.** CDUs carry pumps and controls, and on redundant designs they may need power from more than one source. The electrical feeds, the controls integration to the building management system and the alarms are interfaces between three packages.

**Residual air.** Direct-to-chip cooling does not remove the air system. Vertiv says direct-to-chip typically removes about 70 to 75 percent of heat, and current NVIDIA racks run nearer 90 percent. Either way, fan walls or air handlers and containment still have to handle the remainder. Level the air-side scope for the hall as it will actually run, not as an air-cooled hall and not as if liquid removes everything.

## Design churn: the temperature can move

The GB300's documented inlet water limit of 45°C (ASHRAE class W45) allows dry coolers rather than chillers in many climates. ASHRAE's own white paper on liquid cooling warns that future processors may require colder facility water, first W32 and then W27, and advises facilities to plan for it.

For precon, that is a revision risk to price or to qualify. A plant sized for warm water today may be re-scoped before turnover, or between buildings in the same program. Changes like this are why a rack-generation change mid-program reaches the mechanical plant, the electrical loads and the commissioning plan at once.

## What to check in mechanical and vendor proposals

- **"Piping to CDU connections."** Up to the flange, or including valves, strainers and hoses?
- **"TCS by others."** Which others, and does "others" include the manifolds, the hoses or only the rack interior?
- **"Flushing per specification."** Which specification: facility piping or the IT vendor's TCS cleanliness criteria?
- **"Excludes fluid."** Who supplies the first fill and any top-up during commissioning?
- **"Leak detection by controls."** Is the controls contractor carrying the sensors, the wiring, or only the monitoring points?
- **"Water treatment during construction."** Does it continue through the idle period until IT load, and for every phase?

The underlying method is the same as any [HVAC interface hunt](https://piper-ai.com/resources/hvac-scope-gaps-and-double-ups-bid-leveling). The boundaries are simply newer, and fewer people have seen them fail.

## Where Piper fits

A liquid cooling scope is defined across documents that rarely sit together:

- the mechanical drawings and specifications;
- the owner's IT and cooling standards;
- the CDU vendor's data;
- the rack integrator's requirements;
- the commissioning plan;
- the wording of each proposal.

When the rack generation or the supply temperature changes, the effect reaches all of them at once.

Piper is the AI operating system for preconstruction. It builds an understanding of the project from those documents and the company's own scope standards. It uses that understanding to show, segment by segment, what each mechanical and vendor proposal includes, excludes or never addresses, with the sheet or clause behind each finding. When a revision changes the cooling design, the same understanding shows which loops, packages and commissioning steps it touches. The team still decides who owns each boundary and what to carry.

### What is a CDU in a data center?

A coolant distribution unit. It is a heat exchanger with pumps, filters and controls that transfers heat from the clean technology cooling loop serving the racks to the facility water system, while keeping the two fluids separate.

### What is the difference between the FWS and the TCS?

The facility water system (FWS) is the building's primary loop from the central plant to the CDUs. The technology cooling system (TCS) is the clean secondary loop from the CDU to the racks, with tighter requirements for materials, filtration and fluid quality because it feeds the servers' cold plates.

### Who is responsible for liquid cooling hoses and quick disconnects?

Whoever the documents name, and they are often unassigned. The hoses and fittings between facility piping and the CDU, and between the row manifold and each rack, fall between the mechanical contractor, the CDU vendor and the IT integrator. Assign them item by item in the solicitation.

### Why do liquid cooling loops need flushing and cleaning?

The technology cooling loop feeds cold plates with very small internal passages, so construction debris, mill scale and oils can block or damage them. Published pre-commissioning guidance calls for repeated flushing until suspended solids meet criteria, followed by chemical cleaning and corrosion protection.

## Sources

- CIBSE Journal, [CPD module on data centre liquid cooling](https://www.cibsejournal.com/cpd/modules/2025-09-lcdca/) (air cooling density limits and secondary fluids).
- Lenovo Press, [Lenovo NVIDIA GB300 NVL72 rack-scale AI](https://lenovopress.lenovo.com/lp2357-lenovo-nvidia-gb300-nvl72-rack-scale-ai) (rack power, heat split between liquid and air, inlet water temperature).
- Schneider Electric, [White Paper 133, liquid cooling heat rejection architectures](https://www.ashb.com/wp-content/uploads/2024/10/IS-2024-173.pdf) (CWS, FWS and TCS loops, CDU types).
- Data Center Dynamics, [The last five feet failure](https://www.datacenterdynamics.com/en/opinions/the-last-five-feet-failure-solving-the-1-scope-gap-in-liquid-cooling/) (opinion; the facility-to-CDU scope gap).
- Open Compute Project, [liquid cooling connection guidance](https://www.opencompute.org/documents/ocp-acs-connection-guidance-acf-wp-05032022-pdf), [modular TCS design](https://www.opencompute.org/documents/ocp-modular-tcs-rev-1-final-2025-pdf) and [TCS row manifold pre-commissioning guidelines](https://www.opencompute.org/documents/ocp-document-submission-guidelines-for-pre-commission-preparation-of-technology-cooling-system-tcs-row-manifolds-revq-pdf-1).
- Vertiv, [CoolChip CDU](https://www.vertiv.com/en-us/products-catalog/thermal-management/high-density-solutions/vertiv-coolchip-cdu/), [leak detection systems](https://www.vertiv.com/en-us/about/news-and-events/articles/product-class-articles/leak-detection-systems/) and [liquid cooling options](https://www.vertiv.com/en-emea/solutions/learn-about/liquid-cooling-options-for-data-centers/).
- ChemTreat via WaterTech, [Lessons from treating water at 200 data centers](https://www.watertechonline.com/water-reuse/article/55404413/lessons-from-the-field-what-treating-water-at-200-data-centers-taught-us-about-cooling-system-readiness) (flushing, idle loops and water readiness).
- ASHRAE, [Emergence and expansion of liquid cooling in mainstream data centers](https://www.ashrae.org/file%20library/technical%20resources/bookstore/emergence-and-expansion-of-liquid-cooling-in-mainstream-data-centers_wp.pdf) (water temperature classes and future requirements).