AtlasWater UseMateo Mesenholl, Fiona Wong, Lilo Patt, and Janka Beck

There are numerous ways of how to cool a server. In our research, we focused on the most common five systems, with a special focus on the water usage, looking at systems with no water use and little use. Cooling systems work best when they are conceived in accordance with the existing environment and climate. Therefore, data centre enterprises investigate the soil and existing resources. Favourable locations are near a body of water or in places where they can be connected to the city’s water system. The most commonly used cooling systems are evaporative cooling and mechanical cooling; nevertheless, they are also the systems that need the largest amount of water.

Energie Wasser Luzern (EWL) are the sole supplier of energy and district heating in the City of Lucerne. The company itself is a corporation, with 100 % of the shares hold by the City. EWL owns also a data centre, Rechenzentrum Stollen Luzern. The idea for this data centre was to use synergies between their energy and water production and management and data centre services. Their project came to life in an old civil bunker, owned by the City of Lucerne.

Compared to other data centres, The EWL Rechenzentrum Stollen Luzern is highly secure and energy-efficient. It is a colocation data centre, meaning it rents server spaces to private costumers. Therefore, the data centre needs to be accessible at all times for its customers. To ensure security, biometric scanners have been installed and only a few selected people can enter.

The data centre is located in an old civil bunker, without daylight. To counter this, a unique interior design was developed inspired by sci-fi movies creating a retro-futuristic look.

EWL heats parts of the city with water from the Lake Lucerne. The lake energy network is partly an anergy network and consists of three different loops: The first loop draws in water from the lake at a depth of 30-40 metres and expels the water again into a river. At Inseliquai, the first heat exchangers are situated, building the bridge between the primary loop and the secondary loop. This loop connects the households and companies of the city for heating purposes.

The Rechenzentrum Stollen Luzern, on the other hand, has its own secondary loop, because it needs the water for cooling purposes: cold water arrives at the heat exchangers of the data centre. The cold is transported into the server rooms, which have cold and warm corridors. The cold water inside the server rooms cools the air and therefore transports the heat back to the heat exchangers of the secondary loop. In detail the anergy pipes of the closed loop network run beneath the floor to the coolers between the racks. The cold water is pumped into the air heat exchanger, where it cools the hot outside air down to 18°C and is then blown into the cold corridor of the server racks. During this process the water is warmed up and transports the surplus heat away to the heat exchangers of the secondary loop. The surplus heat of the data centre is then again transferred to the city and used for hot water and heating.

Cooling systems in data centres differ according to the climate zone in which they are located. Evaporative cooling is the most used system and at the same time the most water consuming system. Many data centres rely on drinking water from nearby cities or infrastructures. Special contracts give data centre enterprises precedence when accessing water.

Exact numbers of a data center’s water usage are not published by data centre enterprises for competition reasons. Numbers that highlight the water and energy efficiency on the other hand are more likely to be published, as it serves their marketing strategy.

In Europe, over one hundred data centres agreed to The Climate Neutral Data Center Pact in order to adapt the European net zero targets for 2050 for data centres: a Water Usage Efficiency (WUE) of 0.4 or lower is targeted. The WUE goes hand in hand with the Power Usage Efficiency (PUE). The PUE states how much energy is used only for IT supply.

Most data centres are relatively efficient with a PUE of around 1.2. Since a data centre always needs energy for different uses, such as light, a PUE of 1 is not possible. The problem with the WUE is that it is not standardised where the water meter has to be installed in the data centre and when to measure. In winter, the WUE is normally lower than in summer.

The atNorth data centers are cooling with free air: the outdoor air is taken in, purified, and warmed up to cool the servers. Like many data center enterprises, atNorth gives it surplus heat to the city for heating purposes. Therefore, the acceptance of data centres by the Icelandic population is high, as heating presents itself as a challenge in this climate zone.

Free air cooling is not considered to be energy efficient, but it is the simplest method in a cold climate.

The Dalles data centre is uses mechanical cooling. It is one of the data centres that Google likes to highlight as being sustainable and environmentally friendly. The Columbia River provides the water for the data centre and the nearby city. Since this area has experienced some periods of drought, especially in summer, Google built an aquifer storage and recovery system: a kind of fountain: in winter and during times of rain the dwell collects water and stores it for the summer. In order for the city to benefit from this underground construction as well, the water rights are transferred to the city at no coast.

The Dalles uses around 355.1 Million gallons of water per year, that equals the need for water of 1.3 Million US households per year. Google has the right to be the first to take water from the dwell and to take as much as they need. And if there is not enough water, the city has to provide municipal water: drinking water. Therefore, the population objects new data centre projects by Google in the area.

The Khazna data centre DXB1 in Dubai is built in a desert. Frequent sand storms pollute the air. The subtropical zone is a climate zone which already experiences the climate change strongly and water is scarce. Therefore, DXB1 works with adiabatic cooling where water evaporisation is used to cool the air, to reduce water usage to a minimum.

The Meta Data Center Singapore is one of the newest data centers globally. From the beginning it was planned with the latest technologies and the most ecosystem-friendly approach: the servers are cooled with StatePoint Liquid Cooling, which is a closed loop system. This cooling method is especially designed for a high humidity climate zone.
The data center has to closely monitor the humidity of the outside and inside, facing the challenge of oxidation processes in the server rooms.

There are vast differences in how much water a data centre uses. Some data centres need no water at all. However, free air cooling works best in low-density racks. The best way to tackle the water problem lies in closed loop or adiabatic systems. In order not to waste any energy created, data centres should be connected to the local energy networks to use the waste heat to heat households in cold climates.

Countries located in the polar zone, like Iceland, have welcoming policies for data centre enterprises. Since data centres tend to access any available water supply, strict regulations are needed, as well as collaborations with the nearby communities and governments, to create an environmentally friendly and socially just future for the coming generations.

In Switzerland, there are many unused civil and military bunkers, which offer highly securised and protected spaces for data. Re-using these structures as data centres presents itself as an environmental friendly approach. If these bunkers are located next to bodies of water, they can be integrated into an anergy network, as the example of Rechenzentrum Stollen Luzern has shown, tu reduce the waste of energy and water.