Test & measurement T


THE DATA CENTRE INDUSTRY HAS SOLVED COOLING… NOW COMES THE HARD PART


he data centre industry has made its decision on liquid cooling. Facilities running high-density AI workloads led the way. The major hardware vendors have designed their latest AI processor hardware around it. Direct-to-chip cooling, where liquid is routed through cold plates directly onto the processors, is now the reference architecture for any new AI-optimised facility. The question is no longer whether liquid cooling will become standard. It already has. The real question now is: ‘What do accurate, reliable measurements look like in this new scenario?’


Liquid cooling is not a new idea. IBM pioneered water-cooled mainframe computers in the 1960s, and the technology has been standard in supercomputers and high-performance computing clusters ever since. For the mainstream data centre industry, however, it remained a niche concern: interesting in principle, unnecessary in practice. Air worked well enough, and the economics of switching did not justify the complexity. That calculation changed, and fast. The trigger was artificial intelligence. As AI moved from research to large-scale commercial deployment, it introduced workloads that generate heat at a scale air cooling cannot handle.


A conventional server rack draws between 5 and 10 kilowatts. An AI rack today can draw ten to twenty, even thirty times that. At those densities, air cooling simply reaches its physical limits: the heat capacity of air is relatively low, and moving enough air to extract the heat would require so much fan energy that it becomes economically absurd. Even then, the hottest parts of the chip would not be reached in time. Liquid, with a heat capacity roughly 3,500 times greater than air by volume, is the only viable path forward. Liquid cooling solves the thermal problem. But how to operate these systems reliably over time is a question the industry is still working out, and the measurement infrastructure that makes reliable operation possible is where much of that work remains.


THE THERMAL TRAJECTORY HAS ONLY ONE DIRECTION


To understand where the measurement challenge is headed, it helps to understand the rate at which the underlying hardware is changing. According to AFCOM’s 2025 State of the Data Center Report, average rack density has already risen from 7 kW in 2021 to 16 kW today, and 79 per cent of industry respondents expect the climb to continue. At the leading edge, NVIDIA’s 2027 Kyber rack platform is projected to reach 600 kW, with NVIDIA CEO Jensen Huang indicating


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that future racks could eventually require a full megawatt. That would make a single enclosure as power-hungry as an entire small data centre was a decade ago.


The gap between average and leading- edge deployments is widening with each new generation of AI hardware, and the leading edge sets the infrastructure requirements that everyone else must eventually meet.


Air cooling reaches its practical limit at roughly 20 to 30 kW per rack. At higher densities, fan energy alone makes air-only cooling economically unworkable. Liquid, with its vastly superior thermal conductivity, is not a preference at these densities; it is a physical requirement.


FROM ONE DOMAIN TO TWO Running a liquid-cooled facility is not a straightforward extension of running an air-cooled one. It is a categorically different operational environment, demanding new expertise across power, structural and mechanical engineering, fluid dynamics, chemistry and instrumentation. Across all these disciplines, measurement is the layer that makes the others controllable. In a traditional air-cooled facility, the management of controlled environments is well understood. Parameters such as temperature, relative humidity and differential pressure have decades of industry practice behind them. They are standardised in guidelines such as those published by ASHRAE, the American Society of Heating, Refrigerating and Air-Conditioning Engineers, and served by mature sensor technology. Operators know what they are measuring, why, how that feeds into controls and what the numbers mean.


Liquid cooling extends that domain significantly. Pipes carrying cold water have always been part of data centre infrastructure, delivering chilled water to air handlers and fan wall units. But the scope and criticality of liquid measurement expand dramatically when cooling is brought all the way to the chips through coolant distribution units (CDUs) and cold plates. The parameters that now require dedicated instrumentation include liquid temperature, pressure, flow rate and level, as well as leak detection and coolant health indicators such as pH, turbidity, conductivity and refractive index. Each carries its own failure modes, all requiring careful monitoring to ensure effective cooling loop performance and maintain the required coolant quality near hardware that may be worth tens of millions of euros per square metre of floor space.


Liquid cooling takes over where air runs out of power, but air-side management remains essential


By Anu Kätkä, head of Data Centers and Critical Environments, Industrial Measurements, Vaisala


for everything else. Direct-to-chip cooling removes heat from the hottest components, but the residual heat from the rest is removed by air cooling. As the hardware being protected becomes more expensive per square metre, the cost of any failure grows with it, whether from overheating, condensation or a coolant leak on the liquid side, or from inadequate airflow on the air side. The stakes around every rack are higher, and so is the value of ensuring that the controlled environments are exactly as they should be at all times. In liquid-cooled environments, the reliability and dependability requirements for measurement are even more critical than before.


MEASUREMENTS IN A LIQUID-COOLED ENVIRONMENT


Alongside the liquid-side parameters, ambient conditions in the data hall and in the critical parts of the cooling system must be actively managed. Dew point is where the risk concentrates. Liquid cooling’s efficiency depends on delivering cold liquid to the cold plates, but colder piping inside an air-conditioned space creates a condensation risk. When the pipe surface temperature drops below the ambient dew point, water forms. This is not a maintenance inconvenience, but a potential failure event with consequences that far exceed any maintenance budget.


The standard practice is to maintain coolant supply temperatures at least 2 °C above the measured ambient dew point. The coolant distribution unit is responsible for holding that margin, but only if it knows what the dew point actually is, continuously.


The measurement challenge across all these parameters is not exotic. It draws on well-established sensor physics. But applying it correctly – knowing where to measure, how frequently and how sensor data feeds into control decisions – requires a thorough understanding of both the technology and the environment in which it operates.


October 2026 Instrumentation Monthly


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