Mechanical cooling is not necessary here – saving energy

In the small-scale Appenzellerland, many things can become big – not relatively, but absolutely. The St. Gallisch-Appenzellische Kraftwerke (SAK) is currently constructing a data centre, and the shell structure is now complete. Its defining features: maximum security, high capacity, and the highest possible ecological sustainability.

A total of 3,670 m³ of concrete and 320 tonnes of reinforcement enclose the data centre. Across two floors, 150 server racks will be installed on 450 m² each. From 2018, customers will store their data here. The building will be “redundantly accessible down to each individual rack,” according to electricity supplier and data service provider SAK, which is expanding into a new line of business with the data centre. According to the regional newspaper, this will create in eastern Switzerland a “data vault of the highest Tier IV security level, with almost 100 percent availability.”

SAK selected the Gais location with care: situated at 919 metres above sea level, the site’s climate is ideal for a data centre. Free cooling using drawn-in outside air and adiabatic cooling are sufficient to keep the server rooms permanently cool. Mechanical cooling is not required.

The ServeCool air-conditioning units – developed by Hoval specifically for data centres – therefore operate in Gais without a chiller for additional cooling and thus without compressors. For adiabatic cooling, water is sprayed into the outside air within the units to cool it down. This process uses moisture, which absorbs heat from the air and thereby lowers its temperature. In Gais, rainwater is collected for adiabatic cooling.

At the heart of the ServeCool air-conditioning units are cross-flow plate heat exchangers. Hoval developed these together with Hoval Enventus specifically for the ServeCool line. With a side length of 1.20 metres, they are among the largest individual plates produced by Hoval Enventus. This design enables an above-average heat recovery rate.

The total surface area of the highly efficient plate heat exchangers in Gais amounts to 1,200 m². As the outside air and recirculated air flow separately through the heat exchanger, neither dust nor moisture can enter the highly sensitive data centre.

Naturally, the eight ServeCool air-conditioning units per floor, with their cross-flow plate heat exchangers, take up considerable space. However, no water pipes are needed to dissipate heat. Thanks to their efficiency, these systems make a major contribution to achieving a PUE value of 1.15 – well below the average of 1.5 for data centres.

The PUE, or Power Usage Effectiveness value, is calculated by dividing total power consumption by the energy consumption of the server racks.

And what happens to the waste heat from the Gais Data Centre? Here, SAK’s pioneering spirit comes into play once again – where technology meets nature: right next to the data centre is the Gais mountain cheese dairy, which will use part of the waste heat to pasteurise milk.

Christoph Baumgärtner, responsible at SAK for the construction and operation of the Gais Data Centre, expects a heat output of around 1.5 million kWh. “However, this means we are only using around 10% of the waste heat produced,” he adds, noting that waste heat is also intended to be used for heating the building.

Incidentally, the striking black cube in Gais owes its colour to the photovoltaic panels that cover the roof and all four exterior walls. Solar energy can help cover peak loads, while hydropower remains SAK’s core business. The Gais Data Centre takes sustainability very literally.

Two scientists have reached a remarkable conclusion: in a joint study, the Irish researcher Peter Corcoran and the Swedish scientist Anders S. G. Andrae state that the global energy consumption of data centres is comparable to that of global air traffic.

Christian Richter, who is responsible for adiabatic cooling of data centres at Hoval, adds an equally striking figure: