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Tepid support for reusing waste heat from data centres

Using waste heat from large data centres to heat homes and offices may seem like a no-brainer, but making a business case for getting heat from out-of-town data centres to urban areas at a correct temperature is complicated and costly

Not one of the hyper-scale data centres, where thousands of servers are hosted in the same place, in the US use waste heat in a significant way

The issue:
Growing numbers of data centres all produce large quantities of waste heat that in theory could be used to heat houses and offices

The problem:
With heat tricky and expensive to transport, reusing it is not a priority for data centres, which are typically located away from urban areas

What’s happening:
Countries in Northern Europe are starting to feed waste heat into district heating systems and more projects are planned, but change will take time

Key quote:
Data centres need to become an in-between point for energy use, not an end-point. People then won’t see us as an evil industry that just consumes power.”

Data centres, the beating hearts of the digital age, have a voracious appetite for electricity. They also create vast quantities of waste heat, which is usually vented into the air and squandered. Northern Europe is making steady headway towards using this heat in district heating, but elsewhere little is being achieved beyond niche uses even though almost all electricity consumed by data centres becomes heat and could be captured and reused. The number of data centres globally is growing exponentially as the cloud becomes ever present and computer devices, connected to the internet, become common in everyday objects. Worldwide they consumed around 194 terawatt hours (TWh) of electricity in 2014, about 1% of total demand, says the International Energy Agency. Data centre workload is forecast to triple by 2020, compared to 2016, though related energy demand is expected to grow by only 3% thanks to continued efficiency gains. The big tech industry is, in most cases, tight-lipped about waste heat, perhaps in part because of controversy about their data centres’ appetite for energy. Apple, Google, Facebook, Amazon, Microsoft and eBay all declined to comment on the record, as did two major co-location providers, Digital Realty and Equinix, which rent out space in data centres. An estimated 97% of power consumed by these centres could be captured as waste heat, says a study by academics at Aalto University, Finland. But this is not as easy as it seems. The first problem is that waste heat from data centres is not very hot. Also, the centres are often not close to end users of heat and significant infrastructure is needed to transport heat any distance. This is a particular issue in large countries such as the US, the heartland of the big tech industry. And while district heating is common in northern Europe, it is fairly rare in North America, except in older cities. Not one of the hyper-scale data centres, where thousands of servers are hosted in the same place, in the US use waste heat in a significant way, though they may employ it to fulfil more marginal needs, such as heating their own offices, says Maggie Shillington, analyst with IHS Markit. Waste heat may also be used for dehumidifying a data centre or pre-heating generator sets so they start more quickly if there is a power outage. Such solutions will only soak up a fraction of the available waste heat. A hyper-scale data centre will need around 50 megawatts of power, but only around five kilowatts (kW) will be needed for office heating, states Dale Sartor of the Lawrence Berkeley National Laboratory in California.

Northern Europe

Northern Europe is at the forefront of data centre waste heat use, especially the Netherlands, Denmark and Sweden. But even so, reuse is only just beginning. In Denmark, Sweden, Finland and the Baltic countries, about two-thirds of residential properties rely on district heating to keep warm. In Finland, waste heat from industrial uses made up 3.3% of district heating by 2015. In Sweden in 2014, this figure was 8% and the country’s capital Stockholm has several data centres connected to a district heating system. Around 65% of Danish homes are heated by district heating in which some waste industrial heat plays a role, such as from a concrete factory and an oil refiner. Mikkel Lysgaard of the Danish District Heating Association believes 12-14% of Denmark’s district heating could eventually be provided by data centres. Facebook is planning to send waste heat from its new data centre into the district heating system of Odense, a city in the centre of the country, when it is completed in 2020. Air heated by the servers will pass over water coils to recover the heat and raise the water temperature. A newly constructed heat pump facility, driven by wind power, will help deliver the hot water to the district heating network and then to the local community. The project will produce the equivalent of 100,000 megawatt hours (MWh) of energy a year, enough to warm 6900 homes, says the company.

Apple and Google

Apple’s hyper-scale data centre, the size of 23 football pitches, near Viborg, Denmark, is designed to capture excess heat to help warm homes in the community via district heating. The centre will come online later in 2019, but the waste heat project remains up in the air for financial and technological reasons. Costs associated with the project will come down thanks to changes agreed in June 2018 to the tax on the electricity used to operate the heat pumps, though this will take time to implement, explains Christian Hagelskjær from Energi Viborg. The utility and Apple have also agreed that the US giant will construct a test facility before a final decision is made about using the waste heat. We expect this will be clarified this year,” he says. We want to be sure the technical system works before we invest in a pipeline from the city to the data centre.” Five other large data centres are planned in Denmark and debate about using waste heat is ongoing, says Lysgaard. Apple and Google will build centres near Aabenraa close to the German border and local communities are keen to use the heat. The data centres could heat more than three cities,” says Lysgaard. But they will be some 20 kilometres outside the towns and it would cost DKK 100 million (€13.4 million) to build infrastructure to transport the heat. The Netherlands hosts 98 regional data centres and two hyper-scale campuses. The total residual heat from these centres is an estimated 30,000 terajoules, which in theory could heat a million homes with carbon savings of 600 kilo tonnes a year, says Stijn Grove, managing director of the Dutch Data Centre Association. Sixty-four per cent of the 1400 MW used by Dutch data centres, most of which are near the country’s capital Amsterdam, already reuse some waste heat. But this amounts to just 1-5% of the heat available. To increase this, Google and Microsoft are exploring how waste heat from the North Amsterdam Data Centre Campus could warm greenhouses producing vast amount of fruit, vegetables and flowers. Funnelling waste heat to hothouses would be a sensible solution in the eyes of Otto Van Geet from the National Renewable Energy Laboratory in Colorado, US, who deems waste heat from data centres as low-quality because of its relatively low temperature. He sees it as most useful for supplying under-floor heating or other uses that need lower-temperature, steady heat such as swimming pools or greenhouses. Grove disagrees: It is high quality heat, but at a lower temperature. We can deliver 24/7 and always at a certain level, at 30-35°C.” If you need 60°C tap water for ten minutes, a small heat pump can be used, he adds. Despite his protestations, niche uses of residual heat from data centres are clearly most common.

Barriers:
Two of the biggest barriers for using waste heat are its relatively low temperature and high infrastructure investment costs

Amazon trial

The new headquarters of Amazon in Seattle, US, is buying waste heat from a nearby medium-sized data centre, the 34-storey Westin Building Exchange, which houses the servers of more than 250 telecom and internet companies. Heat is collected from Westin’s servers in PVC pipes and then piped under a busy city street to a central plant in the online retail giant’s Doppler Tower. The waste water arrives at Amazon at about 18.3°C and is run through five heat-reclaiming chillers” to boost its temperature. This concentrates the heat into a smaller volume of water, raising the temperature to about 54°C. Since 2015, the project has heated more than 371,000 square metres of Amazon’s four-block campus with under-floor radiant heating. Because of the upfront investment to build it, the project is not delivering any cost savings, but it will save an estimated 80 million kWh of electricity over 20 years, equivalent to the carbon dioxide emissions of burning more than 29 million kilograms of coal, says Amazon. Adam Meyers, a mechanical engineer with McKinstry, which designed and built the system, estimates that the waste heat saves about 75% of the energy that would otherwise be used for heating the offices and meets Amazon’s heating requirements at about four times the energy efficiency of a comparable heating, ventilation, and air conditioning (HVAC) system. It also reduces Westin’s cooling bill. It remains, though, a modest project. The waste heat used by Amazon accounts for less than half of the heat produced by the electricity-hungry Westin data centre, which is equivalent to 11 MW a day. Of that, 5 MW is piped to Amazon in the winter. The remainder of Westin’s heat is vented into the air. And such a project has to be planned several years in advance in tandem with the building to be heated. It cannot be efficiently added to an existing campus, adds Meyers.

IBM projects

A small data centre built by IBM in Switzerland has been heating a nearby community swimming pool since 2008. Hot air generated by the data centre in Uitikon, near Zurich, flows through heat exchangers to warm water that is then pumped into the community pool 100 metres away. This means fuel savings of as much as 80% and carbon dioxide reductions of 131,000 kilos a year, says Jörg Schanze, a data centre auditor with IBM. In Munich, Germany, waste heat from IBMs SuperMUC supercomputing centre goes to nearby offices, leading to energy savings equal to €1 million a year when the supercomputer opened in 2012. This still leaves an estimated 4.9 MW of the computer’s energy capacity being vented via the roof, highlights Ingmar Meijer of IBM Research in Zurich. His colleague Bruno Michel says the concept of using SuperMUC’s waste heat is commercially not profitable, but in terms of the carbon footprint it is really interesting”. In London, UK housing and businesses in the Docklands neighbourhood are heated by 9 MW of waste heat from the 19,000-square-metre Telehouse West data centre. It was the first to be built in London after the Greater London Authority introduced strict energy sustainability requirements. The use of waste heat saves up to 1110 tonnes of carbon dioxide emissions a year and energy equivalent to boiling 3000 kettles continuously, says Telehouse.

A high level example

The US government-run National Renewable Energy Laboratory (NREL) in Colorado, in the cold, high Rocky Mountains, has what is billed as the world’s most energy-efficient data centre. It is also an early example of a data centre from which waste heat is recycled.

The 930-square-metre one megawatt data centre, dedicated to renewable energy research, is around a tenth of the size of a typical hyper-scale data centre. For more than five years, residual heat from it has been used in nearby laboratories and offices in NRELs 17,000 square metre Energy Systems Integration Facility (ESIF). The waste heat is even used to warm paving stones outside to melt snow in winter.

To capture the waste heat, water in the data centre’s so-called energy recovery loop” circulates through heat exchangers in the High-Performance Computing (HPC) systems. The water is heated to almost 38°C before passing through another set of heat exchangers, providing heat for offices and laboratories while simultaneously cooling the data centre, says Rob Thompson, a mechanical engineer with SmithGroup in Arizona, which led the design of the project.

In the offices, a combination of underfloor air and active chilled beams”, both low energy convective heating and cooling systems, conditions the space. The office and conference areas are heated entirely by the HPC. The facility’s high-bay laboratories need hotter water (up to 54°C in winter) and extra heat can be added when needed. Excess waste heat in the summer is sent to the heating loop for the NREL campus, saving one month’s use of wood-chip and gas boilers a year.

Water use in the data centre’s cooling towers has also been halved — as more heat is recovered, less water is needed to cool the HPC system. This is important since the climate in Colorado is semi-arid.

The use of waste heat from the data centre reduces the energy needed by ESIFs offices by one-third, estimates Thompson. This results in savings of around $20,000 annually, not a huge amount of money, says Otto VanGeet from NREL. But the impetus for the project was sustainability rather than simply to save money.

Distribution costs

Given the difficulties of building a business case, Rives Taylor from Gensler, an architecture firm, believes the use of waste heat from data centres will remain niche, especially in the US. Waste heat may be free energy, but distribution is not free,” he states, adding that using waste heat is also not a priority for data centre owners, who do not necessarily want to be in the business of power generation. They run data centres and want efficient energy consumption and reliability, and everything else goes to the bottom of a long list.” Changing this would need a sizeable shift in the mind-set of data centre owners. It may even require lawmakers to rule that data centres must be built closer to communities. This debate has started in Denmark with the five planned large data centres, says the Danish district heating association’s Lysgaard. A move by data centres towards water-cooled servers, as Lawrence Berkeley’s Sartor expects, would also make it easier to use waste heat. Data centres are typically cooled by air, which absorbs heat far less efficiently than water. Air-cooled infrastructure is usually less expensive to build and operate, but has a larger footprint. And it is much easier to transport heat via water, which needs only a small pipe and pump versus a big duct and a fan for the transport of hot air, he says. And things are slowly changing elsewhere. France’s new ELAN housing law, passed in 2018, encourages the use of waste heat in national energy efficiency guidelines for new or renovated homes, and in the Netherlands from 2020, waste heat from data centres will be considered green, rather than as industrial waste. This change is creating real interest from the housing industry,” says Grove of the Dutch Data Centre Association. The Dutch regulation was encouraged by the trade group’s decision in 2017 to offer waste heat from data centres free of charge to the Dutch government. It kick-started the conversation,” states Grove. Most [in government] were not aware of the possibility.” He admits there is continuing resistance from the traditional heating industry. We are the new kid on the block. We’re a new industry.” But he remains confident that even the smallest waste heat project can help the big tech industry change its mindset. Data centres need to become an in-between point for energy use, not an end-point, he says. People then won’t see us as an evil industry that just consumes power.”


TEXT Ros Davidson