Strategies for cooling data centres and making efficient use of waste heat

In recent years, advances in digitalization across all sectors of society and industry have led to significant growth in data centres in Germany. Between 2010 and 2022, power requirements for data centres and smaller IT facilities increased by 70 percent, from 10.4 billion to 17.9 billion kWh. Cloud services in particular contributed to this growth, with the market increasingly concentrated in a small number of major providers. Germany remains the leading data centre location in Europe, with a three percent share of the global server fleet and energy consumption projected to reach 30 TWh by 2030.

The need to make data centres more efficient is not only driven by the growing demand for digital services such as AI applications and automation, but also by stringent data protection requirements, which require data to be processed at a local level. Despite significant growth in the connected IT load, from 1,362 MW in 2012 to 2,341 MW in 2022, data centre efficiency has increased more than sixfold overall in recent years thanks to technological advances in both hardware and software.

Cooling technologies and their importance

Innovative cooling technologies play a key role in effectively managing rising energy demands while simultaneously minimising the environmental impact. State-of-the-art data centres increasingly rely on advanced cooling methods, such as direct and indirect liquid cooling, which allow heat to be removed more efficiently and directly at the point of generation. These methods are not only more energy efficient, but also improve the power density and reliability of the servers themselves.

Making use of waste heat

Another important aspect of sustainable data centre operations is the utilization of waste heat. Heat recovery technologies allow waste heat to be used to heat office buildings, in urban district heating networks, or even for agricultural applications. These measures not only help to reduce the environmental footprint of data centres, but also help to achieve the climate targets set by the German government, which is planning a gradual transition to carbon-neutral operation.

Outlook

The cooling of data centres and the efficient use of the waste heat from them are key challenges facing the industry. Such challenges are becoming increasingly important in the face of global climate change and the growing demand for digital services. The developments described in the Bitkom study “Rechenzentren in Deutschland: Aktuelle Marktentwicklungen – Update 2023” (Data centres in Germany: Current market developments, Update 2023) show that significant progress is being made despite the challenges. Innovative cooling technologies and the strategic use of waste heat are critical factors when it comes to ensuring the future viability and sustainability of digital infrastructures in Germany and around the world.

Definition and classification of data centres

A data centre consists of the physical infrastructure in which IT services and network solutions operate. Data centre types vary and include corporate, on-premises, hosting, cloud, colocation, university, regional, research, hyperscale, and Edge data centres. Internet Exchange Points (IXPs) also play an important role in the network infrastructure, since they act as the nodes for Internet traffic.

According to the system developed by the Borderstep Institute, structures qualify as data centres if they constitute closed spatial units such as server cabinets, server rooms, sections of a building, or entire buildings in which at least three physical servers are installed. The capacity of a data centre is primarily determined by the number and type of servers installed there.

Germany is currently home to around 3,000 data centres with a connected IT load of more than 40 kW and at least ten server racks. There are also about 47,000 smaller IT facilities. Although Germany is the largest data centre location in Europe, it does not have an active policy for establishing additional data centres. Despite outstanding location factors such as a reliable electricity supply system, excellent connectivity to key Internet nodes, and a high level of legal consistency, high electricity prices and time-consuming approval processes pose significant challenges.

Trends/Developments/Latest

• Energy demand in Germany continues to rise despite increasing efficiency in IT and data centre infrastructure.
• The power of microchips continues to increase: from 400W to 600W and, most recently, 800W.
• Air cooling is reaching its limits; with direct or indirect liquid cooling, heat is released directly into a liquid, often demineralized water, which provides more effective cooling thanks to its greater density. This allows the heat to be extracted directly at the point of origin. Direct liquid cooling allows higher temperatures to be achieved, which increases the power density of servers (>1000 W/microchip) and reduces energy consumption by using free cooling methods, which offer greater potential for waste heat utilization.
• Immersion cooling: This cooling process immerses IT components, including entire servers and storage devices, in a heat-conducting dielectric liquid such as oil (single-phase) or a refrigerant (two-phase). The heat is actively or passively dissipated through the liquid, which is in direct contact with the heat sources, and is transferred to a recooling system via heat transfer media. A prerequisite for immersion cooling is the use of a liquid with low or no electrical conductivity to ensure safe interaction with electronic components.
• Section 4 of the German Energy Efficiency Act (EnEfG), published on 17 November 2023, outlines the requirements for data centres. The objective is to reduce primary and final energy consumption in Germany. The Act applies to data centres with a connected load of 300 kW or more. The specified Power Usage Effectiveness (PUE) must continue to be achieved on an annual average basis; the calculation of the PUE does not include energy used for equipment whose sole purpose is waste heat processing. The following requirements apply starting 1 July 2026:
  • A PUE of ≤1.5 must be achieved effective 1 July 2027.
  • A PUE of ≤1.3 is required effective 1 July 2030.
  • After 1 July 2026, newly commissioned data centres must achieve a PUE of 1.2 and reuse at least 10 percent of their energy.
  • Beginning 1 July 2027, this share will increase to 15 percent, and from 1 July 2028 to 20 percent. Experts consider the target PUE of ≤1.2 to be particularly challenging.
• Opportunities and challenges of heat recovery

The increasing energy demands of data centres make the use of waste heat a key aspect of sustainable operation. The continued use of waste heat, e.g. for swimming pools, laundries, vertical farming, aquaculture, aquaponics, greenhouses, and algae cultivation, as well as in industrial applications, is essential. Although the sector displays a strong willingness to utilize waste heat, the challenges are significant. According to a survey, 70 percent of operators and experts consider the use of waste heat to be an important criterion in the selection of data centre locations, and 67 percent are in favour of data centres making their waste heat available for secondary applications. The Energy Efficiency Act stipulates that at least 20 percent of the waste heat must be sold. However, industry associations such as Bitkom consider this to be too ambitious since this is often impossible to achieve on technical grounds. Effectively exploiting the potential of waste heat requires a comprehensive approach that considers both internal and external use, even if this involves additional costs.

Looking ahead to Chillventa 2024

Since 2015, the Deutscher Kälte- und Klimatechnischer Verein (German Society of Refrigeration and Air Conditioning, DKV)) has organised an annual colloquium on data centre cooling, alternating between the DKV’s own annual conference and the Chillventa CONGRESS. This year, the colloquium will once again be held as part of the Chillventa CONGRESS in Nuremberg on Monday, 7 October 2024, the day before the start of the exhibition.