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Although green energy developers have created a buzz around district energy systems, people have used the systems for centuries.

You’ll find them on college and hospital campuses, where steam and chilled water circulates through pipes. They can run on several energy sources, from combustion to geothermal wells to heat recovery form sewer pipes.

Producing electricity can be horribly inefficient, said John Sorenson, executive director of energy-system nonprofit N2e. A coal-fired power plant might convert only 30 percent of the energy produced into electricity.

The rest is given off as heat. And that heat is often wasted.

“We’re awash in energy,” Sorenson said. “Just not good methods to distribute and store it.”

District energy systems solve some of those problems, circulating chilled water or steam where they’re needed in buildings.

While gaining in popularity, district energy systems are often hard to create, Sorenson said. Although building owners who connect to a system can save money, both from lower utility costs and from not having to provide their own boilers and chillers, systems cost money to build.

“It comes down to a chicken and egg,” he said. Building owners would want to tap into a district energy system, but they have to build where there’s a system planned.

“How do you build a system where there’s no demand because the buildings aren’t built yet?”