Inside Copenhagen's new deep-bore tunnel

While many in Seattle's green urbanist community were railing against a deep-bore tunnel alternative to replace the Alaskan Way Viaduct, in 2009 Copenhagen, a vaunted international leader in urban sustainability, completed its own 2.5 mile long deep-bore tunnel beneath the heart of the city.

But no need to be alarmed, all you Copenhagen-worshipers, because Copenhagen's tunnel is a horse of a different color: It carries district heating pipes, not cars.

At a diameter of 14 feet, the Copenhagen tunnel is much smaller than Seattle's proposed 54-foot diameter tunnel, so it was a much cheaper and less risky endeavor. Still, the contrast between the functions of the two tunnels says it all about how, when it comes to investments in sustainable infrastructure, Seattle and Copenhagen might as well be on different planets.

Paraphrasing Wikipedia, district heating is a system for distributing heat generated in a centralized location to residential and commercial buildings for space heating and water heating. Centralized plants can be fired with a range of fuels, including oil, natural gas, solar, biomass, and even nuclear. That big new tunnel in Copenhagen was needed to make the connection from the city center to a large, renovated combined heat and power plant fueled primarily by biomass.


A map of the pipelines in Copenhagen's comprehensive district heating system

Copenhagen's system supplies about 30,000 buildings and covers a whopping 98 percent of the city's heating needs. Amazingly, waste incineration generates about 30 percent of the system's total heat. District heating is highly efficient, and consequently Copenhagen's system reduces CO2 emissions by 40 to 50 percent compared to conventional boilers. It all makes us in Seattle look pretty much like kindergartners.

Seattle has a relatively small district heating system run by Seattle Steam Company that supplies about 200 buildings via 18 miles of underground pipe in and around downtown Seattle. In 2009 the company began producing steam from waste wood (i.e. biomass), which reportedly cuts the carbon footprint of the system about in half (even though burning wood emits CO2, it is typically considered to be a carbon-neutral fuel because trees absorb CO2 when they grow).

Expanding Seattle's district heating system would be an effective strategy for cutting building energy use and greenhouse gas emissions. But there are significant barriers, most importantly, the up-front cost of installing the distribution infrastructure and retrofitting existing heating systems. And then there's the issue of who owns and operates the system, and the issue of how to ensure that enough building owners would hook up to the system. Seattle Steam would become even more efficient if it implemented combined heat and power, but that would mean they'd also be producing electricity, which is Seattle City Light's job.

Copenhagen's world-leading district heating system didn't happen by accident. It is the result of a long-term strategy involving an ongoing series of aggressive public policy actions. For example, in 1979 the "Heat Supply Act" allowed the designation of district heating areas in which buildings are required to connect to the system. Today, the use of biomass for energy production in combined heat and power plants is subsidized, while fossil fuels are heavily taxed.

As it turns out, Seattle currently has an unprecedented opportunity to build a brand-new district heating system for Seattle Housing Authority's Yesler Terrace redevelopment. But the Seattle Housing Authority does not have the resources to make that happen alone---they will need proactive, committed participation from a range of government agencies.

One thing they won't need, though, is a deep-bore tunnel. It will be interesting to witness if Seattle's leadership (hello City Council) will be as enthusiastic about investing in infrastructure that truly addresses our future sustainability challenges as they are about an underground highway that will move the city in the opposite direction.