Blog / 04.09.2017

The Next Step in Data Center Energy Efficiency Thinking

Ville Toivanen, Strategic Development Manager, Real Estate, Telia Finland

The most widely used metric of data center energy efficiency, the PUE value, has been the dominant method for comparing the efficiency, and thereby the environmental impact, of data centers for over a decade. Short for Power Usage Efficiency, the PUE is used today in the internal workings of the industry. As an overall stick to measure eco-friendliness, or even as a metric for financial management, however, it has its flaws.


Defined as the ratio between the total energy consumed by a data center and the fraction of the energy that goes to the servers that do the actual work in the facility, the PUE turned into a more or less abused marketing tool soon after its inception. Being proud of a PUE value as close to the theoretical minimum of one as possible is often justified, but the PUE is not a metric for true environmental impact. It merely describes the efficiency of getting rid of the waste heat generated by the computing done in a facility. And that, alone, is not nearly enough in a world wrestling with climate change and a chronic shortage of natural resources.


The questionable mental state of the global data center business is already apparent in the term “waste heat”. A surprisingly ecological way to work in the modern world is to redefine things in a positive way, and it is a bit silly to see heat as “waste” instead of as a “resource” in a world that uses a huge fraction of its energy to heat buildings and water.


Instead of engaging in a futile competition on the efficiency of wasting useful energy, data center operators should collectively challenge themselves to find uses for leftover heat. This heat should be seen as something valuable instead of as an irritant or a physical by-product toxic to IT equipment.


Naturally, issues of scale do cause problems. A heat load of a few hundred kilowatts can be turned into a source of heating for a greenhouse or an indoor pool, but things get more complicated when the stream of energy reaches half a dozen megawatts. A single user, no matter how large, can rarely use anything close to ten megawatts of heat. For this reason, a method for distributing this valuable asset to a wider user base must be found.



An easy and suitable solution can be found in the Nordic countries.

An easy and suitable solution can be found in the Nordic countries. Sweden, Denmark, and Finland all have well-developed district heating infrastructures, and reusing dozens of megawatts of thermal energy is simply a matter of relatively basic engineering. The Helsinki metropolitan area alone requires roughly 250 megawatts of heat even during the summer, and much more during the Finnish winters.

Every megawatt recovered from cooling, primed with heat pumps, and injected into district heating directly reduces the carbon dioxide emissions of a city. Even better, if those megawatts originate in electricity generated from renewable sources, the CO2 balance can actually be strongly negative.

The Finnish climate is not just a convenient environmental element useful in free cooling. It’s actually much more; it offers a way to use an already renewable energy not just once but twice. This can be done in a way that successfully competes with free cooling even in financial terms. In this manner, a bothersome by-product of a data center’s metabolism can be turned into a useful product that not only gives the operations a verifiable green stamp but also makes sense financially.


We can recycle glass, metal, paper, and even concrete and bricks of demolished buildings. We can use domestic waste as valuable fuel, and turn old wooden houses into chipped wood for energy production. So why should a steady and very dependable megawatt-scale source of energy be wasted? We can do better than that. Come to Helsinki, give me a call, and I’ll show you how.


Ville Toivanen works as a Strategic Development Manager in Telia Finland’s Real Estate team. Telia Helsinki Data Center provides sustainably based data center services for all companies. The Data Center is expected to be completed in spring 2018, but the services are already on sale. As an engineer and a technology-oriented global scale tree-hugger, Ville considers heat recovery as an important way for the digital industry to contribute its fair share to the fight against the looming climate change.


Image: Telia