Amazon heats its Seattle campus with a neighbour data center's exhaust heat

When Amazon planned a four-block, five-tower, five-million-square-foot campus in downtown Seattle, winter heating was a serious line item. Across 6th Avenue sat the 34-story Westin Building Exchange — a telecom carrier hotel housing hardware for some 250 companies, about 70 percent data center — which had been venting its servers' heat into the Seattle air through cooling towers, at considerable expense. Amazon and the Westin's co-owners struck a deal: Amazon would buy the waste heat, in what Amazon called the first contract between a data center and a heat consumer with different owners.

The machinery is deliberately low-tech: water circulates in PVC pipes through the Westin gathering heat, runs beneath the street (city waivers were needed to cross public rights of way, a historic blocker for such projects), and passes through heat exchangers and five heat-reclaiming chillers that raise it from about 65 to 130 degrees. It then circulates beneath the campus floors as radiant heating, supplying more than three-quarters of the heat the campus needs at about four times the energy efficiency of a comparable HVAC system.

The economics work without subsidies to heat: Amazon avoids gas boiler fuel and maintenance that would have run close to a million dollars a year, plus some 4 million kilowatt-hours of electricity annually, and the source never goes down — the data center runs even off-grid, on backup generators, so in its first two winters Amazon's backup boilers were rarely run. The idea was mostly the brainchild of Jeff Sloan, a McKinstry design engineer, who had to sell it up the chain to McKinstry, Clise, Amazon and the city.

Data centers are heat sources that never sleep — guaranteed running with backup generators — which no boiler-sparing scheme wants to do without.

The trade pays both sides at once: Amazon replaces gas boilers while the Westin sheds most of its cooling bill.

No new technology was required — pipes, exchangers and chillers — so design and city coordination, not invention, carried the project.

Downtown density put the heat buyer a street's width from the heat source, keeping pipe runs short enough to pencil out.

One industry's waste is another's input at street scale: co-locating a heat source and a heat buyer turns two utility bills into one loop.

After two winters the backup boilers had rarely run, and Amazon noted the upfront investment meant the heat was not yet cheaper than a typical system — a bet on electricity prices only rising. The ecodistrict structure left room to extend the loop to more Amazon buildings and, eventually, neighbours.