In Paris, architects from Paris Habitat use body heat from a nearby metro station to provide under-floor heating for a public housing project. In Minnesota, the indoor temperature at the Mall of America is consistently maintained at 70 degrees by body heat, light fixtures, and sunlight. In Stockholm, engineers combine body heat from railway travelers to warm an office building close by. "Part of the appeal of heating buildings with body heat is the delicious simplicity of finding a new way to use old technology (just pipes, pumps and water)," says Ackerman, "Hands down, it's my favorite form of renewable energy."
Heating buildings with body heat can be costly in cities like Paris where buildings and Metro stations need to be adapted, but the design works especially well in Sweden where the addition of sustainable elements help save 24 percent on energy bills. "Widening their vision to embrace neighborhoods, engineers from Jernhusen, the state-owned railroad station developer, are hoping to find a way to capture excess body heat on a scale large enough to warm homes and office buildings in a perpetual cycle of mutual generosity," praises Ackerman. "Heat generated by people at home at night would be piped to office buildings first thing in the morning, and then heat shed in the offices during the day would flow to the residences in the late afternoon."
As for the United States, the body-heat design probably won't be coming soon. "Retrofitting city buildings would be costly at a time when our lawmakers are squabbling over every penny," explains Ackerman. "Also, the buildings can't be more tan 100 to 200 feet apart, or the heat is lost in transit. The essential ingredient is a reliable flux of people every day to provide the heat." She concludes, "But it's doable and worth designing into new buildings wherever possible."