SEATTLE'S South Lake Union used to be peppered with low-slung, ageing industrial buildings. In the past few years, however, it has begun to change. Amazon moved its headquarters to the neighbourhood in 2010. Microsoft's co-founder Paul Allen has been developing 60 acres (24 hectares) of land he owns there. But perhaps an even bigger transformation is the result of Seattle's embrace not of modern technology but of an old one, albeit with a new twist.

The old technology is so-called district heating, whereby heat is generated at a central plant and distributed to buildings, which no longer need to run their own heating systems. The new twist is that the heat would be scavenged from data centres, which produce lots of it.



District heating was once prevalent in many American cities (and continue to be in many European ones). Since the 1970s, however, many utilities have lost interest in heating networks, which are costly to maintain. But its efficiency and green potential has stoked renewed interest.

Traditional power plants that use coal, gas or nuclear energy typically only convert a third of the energy they produce into electricity. The rest is wasted as heat. A combined district utility can convert 40% of that energy into electricity and 40% to heat buildings, wasting just one-fifth at the generation stage, though another 7% is on average is wasted in distributing the heat around a city.

Christie Baumel, from Seattle's Office of Sustainability and the Environment, also praises its flexibility. If a better, or greener, heat-generating technology comes along it only needs to be installed in the central heating station. All buildings hooked up to the system automatically benefit with no need for costly refurbishment. For instance, some providers still burn coal, but others, like Seattle Steam, a 120-year-old company that heats around 200 buildings in the city centre, have switched to less dirty biomass.



The city is in talks with Seattle Steam, a utility company called Corix and developers in the South Lake Union neighbourhood to build a district-energy system that could harness the wasted heat from two nearby data centres (Westin Building and Fischer Plaza). It could heat new buildings, including, potentially, the towers that Amazon has just begun erecting that will add 3m square feet (280,000 square metres) of office space.



At present, excess heat from the data centres is collected in water and funnelled to cooling towers. This water is not quite hot enough for district heating purposes, but Corix could divert it to a new Seattle Steam facility to be heated further. From there it would be piped to buildings and circulated through radiators.



A number of hurdles remain. One uncertainty is how much the data-centre operators would charge for their hot water—though given that they now spend money on managing it they might even give it away for free. The data-centres have expressed interest in the project but have yet to sort out exactly how it would work, according to Michelle McLarty of Corix. Developers and tenants are also wary of committing themselves.

For instance, installing radiators in buildings currently equipped with electric heating would be expensive. In some cases it might not even be possible (if, say, the walls are too thin to lay pipes). Those with central boilers would be easier to upgrade, although owners may be reluctant to do so if the boilers, installed at considerable expense, have life in them. Then there are the permits and other bureaucratic obstacles that utilities must obtain in order to add water pipes to municipal infrastructure such as underground passageways that run sewer pipes, electric and telecommunications lines.



Short-term costs could, then, ultimately derail the project, as they did in the 1970s. Seattle has commissioned a feasibility study but it too has yet to make a firm commitment. Even Corix, which would foot the bill for the system, is still running the numbers to make sure the business case holds water.