Against Hydrophobicity: Why Energy Efficiency is a Question of Cooling

Digitalization in economy and society is increasing the demand for computing power rapidly. Dr. Jens Struckmeier discusses chances of a green perspective for the efficient computing and storage.

(Cloud&Heat Technologies) – In recent years, the number of enterprises using cloud computing has steadily increased. More and more devices and sensors are connected to the internet, their control, measurement and tuning processes are digitally coordinated. According to an estimate of Gartner, today there are about 4.9 billion connected devices[1]. Cisco experts are predicting 50 billion connected devices by 2020[2]. Thus, the number will quadruple within the next few years! Consumers will especially use these networked devices in the “smart home” segment. For example, an empty refrigerator could automatically create a new shopping list or request the re-ordering of popular food directly in the store. Networked devices also play an increasingly important role in industry and business in order to better plan production and manufacturing processes, as well as to make them more cost- and time-efficient. The increasing digitalization of the economy and society leads to a very high demand for computing and storage capacities. The current requirements for data protection and security demand further computing power. New technologies such as Industry 4.0, Machine Learning or Augmented Reality do not only mark the next stage of technologized life, but represent a growing need for a reliable and efficient IT infrastructure.

So far, so good: The developments of the digitalization seem to inspire the whole IT industry in the next decades. The rapid progress of technology and its promise of a more efficient and comfortable world are more tangible than ever before. But not everything that glitters is gold in the end: The key challenge of directional innovations is the question of their energy efficiency, since IoT, SmartHome & Co. do not only have a demand for new computing capacities, but also a new demand for energy.

Electricity costs as the driver of energy efficiency

According to the U.S. Department of Energy, the power consumption for operating and cooling data centers reached 70 billion kWh in the USA in 2016[3]. In 2020, the energy demand is expected to increase up to 73 billion kWh. In order to reduce high operating costs, as well as CO2 emissions, one of the greatest future challenges is the improvement of energy efficiency in data centers.

The fact is that data center operators, who are already dealing with the measurement and optimization of energy consumption, are saving energy costs. In particular, the cost- and energy-efficient cooling of the servers is in the focus of the operators in order to reduce their immense high operating costs. Saving energy means not only saving money, but also making a significant contribution to climate protection. For this purpose, cooling methods become more mature and adaptive. In the future, IT hardware will withstand ever higher temperatures and produce even less heat.

The question of the appropriate cooling system

Status quo in the air conditioning of data centers is cooling by mechanically cold air. The entire room is cooled, but more than half of the cold air does not reach the heat hotspots, like the CPU. In doing so, huge sums of money are literally blown into the air. One of the alternatives to air cooling is to use methods with water or other liquids. But as soon as the data center industry is confronted with “water,” it frightens them immediately. Water and IT equipment – they do not fit together. Nevertheless, there are a few operators already who rely on the alternative cooling medium. The data centers of Green Mountain in Scandinavia use water from a nearby fjord to cool their data centers. Cologix and Equinx from Toronto use the water to air-condition their servers from the Lake Ontario. In both cases, however, the water is only indirectly involved in the cooling process: by means of a heat exchanger, the air in the data center is correspondingly cooled down by the liquid cooling medium and is then used for free cooling of the hardware – air cooling 2.0.

From the thermodynamic and efficiency point of view, however, it is advisable to bring the heat sinks as close as possible to the IT equipment to be cooled and not to air-condition the entire room. The direct cooling of the heat hotspots would be optimal, for example by means of hot water cooling. Hot water with flow temperatures of up to 40 degrees Celsius offers energetic and economic savings potential, because of the physical advantages of water compared to the air: water can absorb 3,330 times as much heat as air and has a 20 times higher conductivity. The closer the cooling medium reaches the heat source, the more efficiently the potential can be used. By means of an intelligent design, concentrated cooling of the sensitive components such as the CPU is achieved. Because of the higher cooling performance, power densities of 45 kW per rack are possible with a simultaneous reduction in energy consumption compared to a conventional cooling system. A water-cooled system can also provide additional energy savings if the dissipated heat provides additional benefits. Due to the relatively high temperatures in the server racks, water output temperatures of up to 60° C are possible. Water at this temperature level can be used, for example, for hot water or heating systems of buildings.

Additional savings through intelligent waste heat utilization possible

The search for new synergy effects by increasing the energy efficiency by means of waste heat utilization is currently becoming more and more important. According to a recent survey by the Borderstep Institute[4], 50 percent of respondents see medium to very high saving potentials due to the reuse of server heat from their data centers. IBM, for example, is heating a nearby swimming pool in Switzerland, the data center at Notre Dame University in Indiana is a greenhouse, while Apple and AWS provide warmth to residential homes near their data centers in Scandinavia.

The reuse of waste heat is, however, usually based on two essential problems. On the one hand, only very low output temperatures of less than 60 degrees Celsius are usually reached. However, in order to reuse the cooling water, for example for heating buildings or for hot water preparation, at least 60 degrees Celsius are necessary. Hence, heat pumps plays an important role to compensate for the difference. On the other hand, the transport of heat represents a not negligible challenge. As the previous examples show, the data center waste heat is only used in applications close to the location. Overcoming longer distances would lead to high heat losses and thus to low temperatures for the heat consumers.


Due to the rapidly growing demand for computing capacity and thus the steadily increasing energy consumption in data centers, innovative green concepts are needed that reduce overall power consumption in the industry. One possibility to drastically reduce the enormous energy consumption is the consistent use of cutting-edge cooling systems, such as hot water cooling, and the intelligent reuse of data center heat. The industry needs to overcome its hydrophobicity and become more receptive to water cooling in order to achieve long-term significant savings. In addition to the green cooling techniques, the waste heat from data centers can also be used to generate adsorption chillers, that is, for cooling with heat. Combining both systems, homes can be heated in winter and air-conditioned in summer. This allows a year-long utilization of the data center waste heat and a further important step towards the fulfillment of the targets for the reduction of energy consumption.


Dr. Jens Struckmeier is a founder and CTO of Cloud&Heat Technologies GmbH, a startup company founded in 2011 focusing on environmental friendly and cost effective cloud computing. From 2004-2009 he successfully managed the company nAmbition GmbH a nano-biology startup company focused on fully temperature controlled automated force spectroscopy instrument and software development.

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