Data centers must process ever-increasing amounts of data. Applications in the fields of artificial intelligence, cloud computing, simulation, and data analysis require powerful processors and graphics processing units. The higher their computing power, the more heat is generated during operation. To ensure that servers operate reliably, this heat must be dissipated in a controlled manner. For a long time, data centers were cooled primarily with air. However, with particularly high-performance servers, traditional air cooling is increasingly reaching its limits. As a result, operators and manufacturers are increasingly turning to liquid cooling. With liquid cooling, heat is absorbed much closer to the heat-generating components. This allows for more efficient and targeted cooling of high-performance servers. A key prerequisite for this is the reliable monitoring of the entire cooling circuit.

Pressure and temperature sensors from i2s help monitor the condition of the coolant, detect changes early on, and regulate cooling performance as needed.

Liquid cooling refers to the process of cooling using a liquid coolant. The coolant is circulated through pipes, manifolds, heat exchangers, and special heat sinks. The liquid absorbs heat from the server components and transports it away from the immediate vicinity of the electronics. The basic principle can be compared to a heating system: A liquid moves through a closed system, absorbing heat at one point and releasing it at another. In a data center, however, this process runs in the opposite direction. The goal is not to introduce heat into a room, but to remove it from the servers and racks as efficiently as possible. Depending on the specific system, treated water, water-glycol mixtures, refrigerants, or electrically non-conductive fluids may be used. The medium used and the design of the cooling circuit determine the requirements for sensors, seals, connections, and materials.

Modern data centers pack a great deal of computing power into a relatively small space. Artificial intelligence and high-performance computing systems, in particular, generate a high thermal load. Amphenol Sensors points out that increasing power density requires more precise sensor monitoring for liquid cooling, immersion cooling, and the control of environmental conditions. Air can absorb and transport only a limited amount of heat. When particularly powerful processors are used, large volumes of air must be moved through the server rooms. This requires high-performance fans and air conditioning systems. In many applications, a liquid can absorb and transport heat in a more targeted manner. The heat is dissipated directly or indirectly from the particularly hot components. As a result, liquid cooling can offer the following advantages, among others:

• more efficient cooling of high-performance servers
• targeted heat dissipation directly at the heat sources
• more uniform temperature control
• reduced load on conventional room air conditioning
• higher potential power density within a server rack
• a better foundation for the use and recovery of waste heat

However, the actual energy savings always depend on the data center’s design, the servers used, the cooling system’s configuration, and the operating conditions.

Liquid cooling is a general term for various cooling methods. In data centers, direct liquid cooling, rear-side heat exchangers, and immersion cooling are primarily used.

Direct-to-Chip Cooling

In direct-to-chip cooling, the coolant is directed directly to components that generate a particularly high amount of heat via so-called cold plates. These components primarily include processors, graphics processing units (GPUs), and accelerators for AI applications. A cold plate is a flat cooling unit with fine channels inside. It rests directly on the component to be cooled. The coolant flows through the channels, absorbs the heat, and transports it out of the server. The fluid does not normally come into direct contact with the electronics; it circulates within a closed-loop system.

Rear Door Heat Exchanger

A rear door heat exchanger is a heat exchanger located at the rear of a server rack. The warm exhaust air from the servers is directed through this heat exchanger. A cooling fluid absorbs the heat before the air is released back into the room. This technology combines air and liquid cooling. The electronics inside the servers continue to be cooled by air. The absorbed heat is then transferred to a liquid circuit at the rear of the rack.

Immersion Cooling

In immersion cooling, suitable electronic components are fully or partially submerged in an electrically non-conductive liquid. The liquid absorbs heat directly from the components. Depending on the method used, the cooling medium remains liquid or vaporizes in particularly hot areas and then condenses again. The technical design therefore differs significantly from conventional water cooling circuits. Amphenol lists cooling distribution units, cold plates, direct-to-chip systems, back-side heat exchangers, immersion cooling, distributors, and pump and valve systems among the key applications of liquid cooling.

What Types of Liquid Cooling Are There? A liquid cooling system must be able to reliably handle different operating conditions. For example, the required cooling capacity changes with server load. As computing power increases, more heat is generated. The cooling system must respond to this and continue to dissipate the heat reliably. Sensors provide the control system with the necessary information. They can be installed at various points in the circuit and continuously record measurement data.

The sensor readings help to

• monitor the temperature of the coolant
• detect pressure changes in the circuit
• control pumps and valves as needed
• identify unusual operating conditions early on
• better plan maintenance measures
• adjust the cooling capacity to actual demand
• protect servers and electronic components from overheating

Sensors do not perform the control functions themselves. However, they form the basis on which control and monitoring systems can make decisions.

The pressure of the coolant is an important operating parameter. It is generated by pumps, flow resistance, and elevation differences within the piping system. Adequate pressure is necessary to ensure that the coolant can flow reliably through pipes, manifolds, heat exchangers, and cold plates.

Causes and Tips for Low Pressure

A drop in pressure can have various causes. Possible causes include reduced pump performance, a valve that is not fully open, or a loss of coolant. A single measurement is not always sufficient to determine the exact cause. However, the change can be an important indicator that triggers further investigation.

Causes and Tips for High Pressure

Unusually high pressure can occur, among other things, when flow paths are blocked, valves are not functioning correctly, or the coolant expands due to changed operating conditions. Since components, connections, and seals are designed only for specific pressure ranges, the system pressure should be reliably monitored.

Pressure Measurement Upstream and Downstream of Components

When pressure sensors are installed at various points in the system, pressure differences can be detected. A noticeable drop in pressure across a filter, heat exchanger, or section of piping may indicate increasing flow resistance. In this way, pressure measurements can serve not only for direct monitoring but also provide information for maintenance and condition monitoring.

i2s – Intelligente Sensorsysteme Dresden GmbH develops and manufactures sensors for measuring pressure and temperature, as well as combined sensor solutions. For applications in the field of liquid cooling, i2s sensor solutions can help monitor key conditions of the cooling medium. Possible measurement points include:

• Cooling distribution units
• Pumps and pump assemblies
• Valves and control loops
• Supply and return lines
• Heat exchangers
• Distributors and manifolds
• Supply and return lines of individual server racks
• Cold-plate circuits
• Refrigeration and air conditioning systems

The appropriate sensor design depends, among other factors, on the cooling medium used, the pressure range, the temperature range, the installation situation, the required output signal, and the accuracy requirements.

Pressure sensors monitor the operating pressure of the coolant and can be installed at various points in the fluid circuit. The materials in contact with the medium are particularly important for reliable pressure measurement. They must be suitable for the fluid being used and the intended operating conditions. i2s uses robust sensing elements in various sensor solutions and offers pressure sensors for liquid media as well as for applications with increased requirements for media compatibility and durability. Depending on the application, pressure sensors can support the following tasks, among others:

• Monitoring system pressure
• Controlling pump operation
• Detecting abnormal pressure fluctuations
• Monitoring individual cooling loops
• Measuring pressure losses
• Protecting pipes and components
• Providing measurement data for a higher-level control system

Liquid cooling systems differ significantly from one another. A cooling circuit for a single server rack has different requirements than a central cooling system for a large data center. The cooling medium used, the pipe dimensions, the connection types, and the communication interfaces can also vary. Therefore, the same standard sensor is not suitable for every system. Thanks to a modular design, mechanical and electronic properties can be adapted, or sensors can be newly developed to meet specific requirements.

Sensors in liquid cooling systems must provide reliable measurement data over a long period of time. They are in constant contact with the cooling medium and may be exposed to fluctuating temperatures, pressures, and flow rates.

Media Compatibility

All components that come into contact with the fluid must be suitable for the cooling medium being used. These include, for example, the sensing element, the sensor housing, the seal, and the process connection. Media compatibility should not be assessed solely based on a fluid’s general designation. Concentration, additives, temperature, pressure, and the intended service life can also play a role.

Leak Tightness

Since the fluid is used in close proximity to sensitive electronics, reliable connections are particularly important. The sensor and process connection must be designed so that they can be safely integrated into the cooling circuit.

Measurement Accuracy

The required accuracy depends on the sensor’s application. A sensor for general operational monitoring may have different requirements than a measuring point used directly to control cooling capacity. Accuracy at room temperature is not the only important factor; the sensor should provide reliable readings within its specified operating range.

Response Time

Response time is particularly important in temperature measurements. A fast response helps detect changes in the cooling medium in a timely manner. The actual response time depends not only on the sensor element. The installation orientation, the housing, the flow velocity, and contact with the medium also influence the measurement.

Long-Term Stability

Data centers are designed for continuous operation as much as possible. Sensors should therefore provide stable measurements even over extended periods. Good long-term stability can help reduce maintenance efforts and reliably detect changes in the system.

Electrical Interfaces

Measurement values must be transmitted to control systems, monitoring systems, or a building management system. Depending on the system design, analog or digital output signals may be required. The interface should be taken into account as early as the sensor design phase. The same applies to supply voltage, connector type, cabling, and electromagnetic requirements.

A liquid-cooling system operates most efficiently when its output is adjusted to actual demand. A pump operating continuously at maximum capacity may consume more energy than necessary. Conversely, insufficient cooling capacity can lead to high temperatures. Pressure and temperature readings provide the basis for demand-based control. Depending on the system design, the pump speed, valve position, or cooling capacity can be adjusted to the current conditions. In addition, continuously recorded measurement data enables long-term analysis. If measurement values are stored and evaluated, changes can be detected early on. For example, a slowly increasing pressure drop or a growing temperature difference may indicate a change in the cooling circuit. In this way, sensors support not only immediate operation but also maintenance, fault analysis, and system optimization.

As computing power increases, reliable liquid cooling continues to grow in importance. Pressure and temperature are among the key parameters in this context. They provide important information about the condition of the coolant and the entire cooling circuit. i2s develops and manufactures pressure sensors, temperature sensors, and combined sensor solutions. Thanks to customizable mechanical and electronic designs, sensors can be tailored to the varying requirements of cooling systems. From temperature monitoring in the supply and return lines to pressure measurement at pumps and manifolds, to the combined measurement of both parameters: Properly designed sensors provide the data foundation for the reliable, safe, and energy-efficient operation of modern liquid cooling systems.