The Power of a Hot Body
As I waited with a throng of Parisians in the Rambuteau Metro station on a blustery day, and my frozen toes finally began to thaw. Alone we may have shivered, ampoule but together we brewed so much body heat that people began unbuttoning their coats. We might have been penguins crowding for warmth in Antarctica’s icy torment of winds. Idly mingling, a human body radiates about 100 watts of excess heat, which can add up fast in confined spaces.
Heat also loomed from the friction of trains on the tracks, and seeped from the deep maze of tunnels, raising the platform temperature to around 70 degrees, almost a geothermal spa. As people clambered on and off trains, and trickled up and down the staircases to Rue Beaubourg, their haste kept the communal den toasty.
Geothermal warmth may abound in volcanic Iceland, but it’s not easy to come by in downtown Paris. So why waste it? Savvy architects from Paris Habitat decided to borrow the surplus energy from so many human bodies and use it to supply radiant under-floor heating for 17 apartments in a nearby public housing project, which happens to share an unused stairwell with the metro station. Otherwise the free heat would be lost by the end of the morning’s rush hour.
Appealing as the design may be, it isn’t quite feasible throughout Paris without retrofitting buildings and Metro stops, which would be costly. But it is proving successful elsewhere. There’s Minnesota’s monument to capitalism, the four-million-square-foot Mall of America, where even on subzero winter days the indoor temperature skirts 70 from combined body heat, light fixtures and sunlight cascading through ceiling windows.
Or consider Stockholm’s busy hub, Central Station, where engineers harness the body heat issuing from 250,000 railway travelers to warm the 13-story Kungsbrohuset office building about 100 yards away. Under the voluminous roof of the station, people donate their 100 watts of surplus natural heat, but many are also bustling around the shops and buying meals, drinks, books, flowers, cosmetics and such, emitting even more energy.
This ultra green, almost chartreuse, body-heat design works especially well in Sweden, a land of soaring fuel costs, legendary hard winters, and ecologically minded citizens. First, the station’s ventilation system captures the commuters’ body heat, which it uses to warm water in underground tanks. From there, the hot water is pumped to Kungsbrohuset’s heating pipes, which ends up saving about 25 percent on energy bills.
Kungsbrohuset’s design has other sustainable elements as well. The windows are angled to let sunlight flood in, but not heat in the summer. Fiber optics relay daylight from the roof to stairwells and other non-window spaces that in conventional buildings would cost money to heat. In summer, the building is cooled by water from a nearby lake.
It’s hard not to admire the Swedes’ resolve. During the 1970s, Sweden suffered from pollution, dead forests, lack of clean water and a nasty oil habit. In the past decade, through the use of wind and solar power, recycling of wastewater throughout eco-suburbs, linking up urban infrastructure in synergistic ways, and imposing stringent building codes, Swedes have cut their oil dependency and drastically reduced their sulfur and CO2 emissions.
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). Hands down, it’s my favorite form of renewable energy.
What could be cozier than keeping friends and strangers warm? Or knowing that by walking briskly or mousing around the shops, you’re stoking a furnace to heat someone’s chilly kitchen?
How about the reciprocity of a whole society, everyone keeping each other warm?
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. 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. Nature is full of life-giving cycles; why not add this human one?
Alas, I don’t see body-heat sharing sweeping the United States anytime soon. Retrofitting city buildings would be costly at a time when our lawmakers are squabbling over every penny. Also, the buildings can’t be more than 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.
But it’s doable and worth designing into new buildings wherever possible.
As a Golden Rule technology of neighbor helping neighbor, it implies a willingness to live in harmony. What could be more selfless than sharing heat from the tiny campfires in your cells? I’ll warm your apartment today, you’ll warm my schoolroom tomorrow. It’s as effective and homely as gathering around a hearth. Sometimes there’s nothing like an old idea revamped.