Efficient cooling systems for stable, high-performance processes

Whether working from home or streaming digital content via the Internet, the global COVID-19 pandemic, and the resulting need to limit contact with other people to an absolute minimum, have led to a considerable increase in the private and work-related use of digital applications. The result is a strong degree of utilisation of the entire data network. Technological innovations, such as cloud computing, big data or AI, will continue to fuel the demand for computing power in the future. Data centres and server rooms must be continuously cooled to keep them working. Ingo Gdanitz, Business Development Manager of technotrans SE and an expert in this field, explains the challenges and potentials of server cooling solutions.

"Every server must be cooled. As a result, the need for cooling and the associated energy consumption is also steadily on the rise, as data centre capacity continues to be in strong demand," explains Gdanitz. technotrans, a technology supplier from Sassenberg in Germany, is specialised in developing and providing cross-industry cooling and temperature control solutions. They expect the demand to remain at a very high level, even after the coronavirus crisis. The selection of an efficient cooling system that is perfectly adapted to very specific requirements is the most important factor according to Gdanitz.

Server cooling units are available in a wide range of a sizes and performance categories, depending on the thermal load of the application. Medium-sized technology and research institutions, for example, use relatively small data centres. However, even these data centres produce a thermal load of up to 100 kW. The thermal load can easily be in the range of several megawatts with large colocation centres.

What is important when it comes to the cooling of servers?
In this context, Gdanitz particularly emphasises the energy efficiency of the cooling systems: "Nearly half of the energy that is required by a data centre is used for cooling. However, optimisation measures can significantly improve the energy efficiency of the cooling systems." Another important aspect is the reliability of the technology. For users with highly sensitive data requiring 100% availability, a failure of the cooling system would be fatal and must be avoided at all cost. In addition, a monitoring concept – especially for so-called colocation server centres where servers or their infrastructure are available on a rental basis – is of utmost importance. This is due to the fact that the operators are often under the obligation to document the ambient conditions in the server room, e.g. air temperature or humidity. If a data centre is planned with several stages of expansion, the expandability of the systems is another essential factor for ensuring a later upgrade of the cooling power.

"We know from several years of experience that there is quite a number of factors that need to be taken into consideration and weighted accordingly when planning the cooling technology," says Gdanitz. In this context, several customer-specific circumstances must be taken into account:

• Thermal load: The heat that is emitted by the servers mainly depends on the computing power. The greater the computing power is, the higher the resulting thermal load will be. The cooling system needs to withdraw the heat from the data centre.

• Climatic conditions: The temperature outside of the server locations often determines the type of cooling technology that will be used. While free cooling solutions, offering several energy-related advantages, are perfectly suitable for cool to temperate climates due to their lower air temperatures, the situation is clearly more difficult in the warmer regions of Southern Europe.
• Investment budget: A cooling system should be designed to provide the users with an economical and cost-efficient solution.
• User model: Depending on the specific user requirements, server cooling systems need to fulfil a range of requirements, e.g. in terms of their availability or expandability. In view of numerous different models, this factor is particularly important to achieve a precise, needs-based configuration of the cooling system.

In-row heat exchangers for a modular setup
"Server cooling systems often use in-row cooling technology to supply the server room with cold air," says Gdanitz. In-row heat exchangers do not require any extensive modifications by the customer and are positioned directly between the server racks. They absorb the waste heat of the servers, transfer it to the cooling water and supply the servers with cool air. An example of this concept is the in-row heat exchanger for optimised cooling made by the technotrans group. Thanks to the modular design the individual fans of a cooling unit can be added, removed or replaced even during operation.

Reliable cooling concepts based on the active production of chilled water
Solutions based on the active production of chilled water are particularly suitable for cooling entire rooms. Chillers are refrigeration units that can actively cool the server rooms with the aid of a fluid circuit. "We make use of the good thermodynamic characteristics of water-based fluids as the heat transfer medium, in order to be able to withdraw even a large amount of heat economically from the building," explains Gdanitz.

The chillers made by the technotrans group are atmospherically sealed systems and several modular units of these chillers can be used in parallel. "As a result, the system for refrigeration can be expanded and the solution has a high level of availability due to the redundant setup," says Gdanitz. He recommends splitting the total cooling requirement over several smaller units, for example by installing four units each covering 30% of the total cooling capacity. Should one unit fail, 90% of the maximum cooling capacity is still available.

High level of energy efficiency with a free cooling concept
Free cooling with chillers is a highly effective method for reducing the operating costs of a refrigeration system. It is intended for the outside area of server centres where the warm water emits its heat into the ambient air. technotrans uses an indirect free cooling concept to achieve this effect. "Since the heat is removed by way of a water-based fluid cooling system, the free cooling concept can be integrated into the customers' cooling water system even during a later phase," says Gdanitz. The free cooling concept uses the low outside air temperature to cool the central cooling circuit. This feature can be used at an outside air temperature slightly below the desired server room temperature. When the outside temperature falls further, the system takes over more of the workload from the compressor system until the compressors can be deactivated altogether.

Based on a combination of active and free cooling, substantial energy savings can be realised and the so-called power usage effectiveness (PUE) of data centres can be considerably increased. The PUE value is the ratio of the total amount of energy used by a data centre to the energy used for operating the IT infrastructure. It is a measure of the efficiency of a data centre over a specific period of time. "Compared to conventional compressor cooling systems, the total energy demand for cooling the servers can be reduced by up to 50%," explains Gdanitz.

Depending on the temperature difference between the outside temperature and the reliable temperature in the server area, there are several different cooling methods that can be applied. Ideally, the outside temperature is sufficiently low for cooling the server area by way of the free cooling system alone. During warmer periods, an active fluid cooling concept, with additional refrigeration produced by compressors, can be used to ensure reliable cooling.

Sustainable cooling of server rooms
"Sustainability is an important aspect for most users. Together with our partners, we want to shape the technology used throughout the industry, which is why we strongly focus on increasing the energy efficiency of our systems," says Gdanitz. In this context, the cooling systems must excel in three areas: design, components and control system. Whenever feasible from a climatic point of view, technotrans uses free cooling concepts to increase the sustainability of the concept. In addition, the speed of all of the active components is adaptable in order to be able to control the refrigeration and to avoid energy waste.

In doing so, the specialists for fluid technology applications follow a holistic approach. technotrans supplies all of the necessary components and handles the entire project planning, installation and commissioning of the systems. The company offers a comprehensive portfolio of proven server cooling systems for a wide range of performance categories and industry standards.