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In with the cold, out with the heat: Liquid cooling at Nokia’s Tampere Data Center

By Jarkko Kytömäki, Tampere R&D facility

 

There is no data center greener and cooler under the Nokia banner than the Tampere facility, which uses district cooling to achieve those results.

With 13,000 square feet of hardware, supporting 50 kilowatts (kW) per rack that amounts to a total output of up to 4 megawatts (MW), it is a demanding place. It needs a consistent flow of electricity, but more importantly, mechanisms and systems to keep things cool and release the resulting heat to do something productive.

Tampere is in an ideal location for a data center, since the city lies between a number of lakes, the largest of which are Näsijärvi and Pyhäjärvi. Being naturally cold at the bottom means they can also be a great natural resource as a primary liquid cooling solution. By pumping water from the deepest part of the lake through a network of underground pipes, the data center’s air conditioning can keep it sufficiently cool without expending as much electricity to do so.

Tampere, like any big city in Finland, uses a grid line to deliver district heating to residential, commercial and industrial sites. And its district cooling system is the largest such system in Nordic countries, covering most of the population in cities and towns. With the country seeking a carbon-neutral footprint by 2035 and more energy-efficient alternatives, we could use that system to cover heating and cooling needs.

The lakes presented an opportunity for Tampere, which started to consider a district cooling grid line through liquid cooling in 2012. Nokia’s data center located within our 5G R&D facility in the city was among the first to implement it, owing to its considerable energy requirements to cool the infrastructure inside. By Q3 2016, it went on-line and the results have been very encouraging, thanks to a 20 percent improvement in energy efficiency and 90 percent reduction in CO2 emissions.

Data centers use as much as 5 percent of global electricity, and half of that is taken up just by cooling. District cooling on a mass scale would decrease that number dramatically and have a positive effect on carbon emissions and climate change. Even better, the power usage efficiency (PUE) also drops. At Nokia’s Tampere data center, it fell from 1.35 to under 1.1.

District cooling carries a number of other benefits and advantages over time. It’s a closed loop system that doesn’t have many moving parts. And even if the district cooling plant has a malfunction, or it’s pumping in warmer water — like it might in the summer months — the pipeline has a 3 to 5-hour window of cooling while circulating to the site. On-site chillers powered by renewable energy can also step in to cool the water down or help offset any reduction from the liquid cooling system. Built-in redundancies like that ensure the data center isn’t in danger of getting too hot. With lake energy producing 95 percent of the site’s annual cooling energy, every little bit helps to keep things running smoothly.

The efficiency speaks volumes — literally. Water can store a thousand times more energy than air does at the same volume. Thermal conductivity is also up to 22 times lower. It’s not sustainable to run a data center using air-cooled components as the primary source, particularly when a large portion of the center’s power output comes from the cooling system itself. A water stream of 1.5 liters can deliver up to 50 kW of district cooling. It’s a maintenance-free system that perpetually feeds itself.

Location and cost

A data center like this requires a lot of cooling energy, and other structures, like hotels, hospitals and office buildings that are connected to the same system are tiny by comparison. That makes our facility an important customer for the City of Tampere, and the heat we can distribute back to the system an equally valuable asset.

A district cooling grid line is built with the same materials as district heating, which means it’s also out of sight to the naked eye. There are no chillers required in walls or roofs, with maintenance costing a fraction of what it would be to service air conditioning units. It doesn’t hurt that there’s a considerable noise reduction, too.

It also helps the bottom line. The higher the efficiency, the lower actual electricity costs per megawatt hour. So long as data centers can reduce the level of district heating they consume, the more flexible the rate. As part of a broader tax reform, the Finnish government proposed a new energy tax rate for data centers that would see it fall to among the lowest levels allowed in the European Union. It would be set to go into effect in 2021, and once implemented, would make Nokia’s Tampere data center among the most cost-effective in operation.

In with the cold, out with the heat

One thing data centers generate is heat, and that heat should go somewhere useful. A closed-loop system could feed water back to recirculate, but the heat would be wasted if it simply vanished into thin air through an air duct.

In Tampere, waste heat from the data center typically routes back to the city’s grid line for district heating, usually at a modest temperature of 23-24 degrees Celsius. It’s not warm enough to heat up entire buildings on its own, but the heating system pumps can help by raising it to 95-degrees and distribute it out for use at swimming pools and outdoor water facilities for the public.

It’s also not really an option to push the warmer water back into the lakes because we don’t want to warm them up. We like Finnish lakes to be as cold as they are, and the excess heat from the servers is better served elsewhere.

It’s important to remember that a data center can run on 100 percent renewable energy, yet not be 100 percent sustainable. That is the conundrum in wasting excess heat that could otherwise be harnessed to heat buildings as part of the district heating system. The goal is to reduce waste, especially when there are other paths one can take, and the city can pay to collect it. This type of system is self-sustaining in that we would have a method to push the heat out, and still maintain the liquid cooling system necessary to keep the center running at its expected capacity.

Good locations

In real estate, it’s often said that location is everything. Tampere is already well situated next to so many great lakes, but it is also free of any danger from earthquakes and other natural disasters. The electrical grid is robust and inexpensive, with renewable energy available in abundance.

It’s very much a perfect storm to keep the data center stable and functioning effectively. Liquid cooling and heat distribution also make it a key part of the city’s wider infrastructure by not only consuming electricity, but also contributing to its heating needs. It’s a cyclical system that works fluidly with minimized environmental impact and at a reasonable cost.


About the author

Kytomaki

Image source: 2030-lehti / Marjaana Malkamäki

 

Jarkko Kytömäki is a vLab Infrastructure Manager at the Nokia R&D facility in Tampere and ensures that Tampere's green and cool data center is kept running every day of the year. He is interested in all things data center, with a particular interest in storage. His strengths lie in turning business demands into infrastructure reality.