“The industry needs to overcome its hydrophobia and become more receptive to water cooling in order to achieve long-term significant savings.”
Posted on November 10, 2017
By: Dr. Jens Struckmeier
In the first part of this two part series, I outlined why computing power has steadily increased over the years and which challenge it inherently brought for today and in the future. In Part 2, I address why the question of the appropriate cooling system and how additional savings through intelligent waste heat utilization is possible as well as why there are still reservations to water cooling to reduce energy requirements.
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 thin 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 degrees Celsius are possible. Water at this temperature level can be used, for example, for hot water or heating systems of buildings.
Save More Through Intelligent Waste Heat Utilization
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, 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 play 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.
The industry needs to overcome its hydrophobia 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.