Heat by Light

As anyone reading a book on a hot night has discovered, a light bulb puts out a lot of heat. When bunched together in overhead banks, as they are in most modern office buildings, lights can make interior rooms too hot -- even in the dead of winter.

Until recently, builders did little but complain about the problem, spent considerable amounts of money air-conditioning inside rooms at the same time they were heating outside rooms--particularly in glass-walled buildings, whose outside rooms not only lose a great deal of heat in winter but get cooked by the summer sun. Finally, in the early '60s, General Electric engineers lit upon a solution: trap the heat-light through special ducts in the lighting fixtures, pipe it to outside rooms where it is needed most. They found that whole buildings could be heated inexpensively with nothing more than the lamps that light them.

Most dramatic example of the new system to date is a two-year-old high school in Kimberly in northern Wisconsin, where temperatures have been known to drop as low as --31DEG in winter. The school was built with a minimum of outside windows and lots of fluorescent lights, all of which have built-in ducts that trap over 60% of their heat.* The ducts also collect the heat produced by the students' bodies-which is surprisingly high. One average-size incumbent 15-year-old throws off more heat than a 100-watt bulb. Recovered and recirculated by fans, this heat from the lighting and the building's occupants has proved more than enough to keep the building warm even when the outside thermometer reads 18DEG. The excess is transferred to heating coils in two 12,000-gal. water tanks. When the lights go out and the human dynamos go home at night and on weekends, the hot water from the tanks is circulated throughout the building to keep it warm. As a precautionary measure, the engineers also installed emergency electrical heaters, but Kimberly has almost never had to use them.

Heat by light recently got its biggest vote of confidence from two Chicago companies. The First National Bank of Chicago, which is about to start construction on a 60-story structure in the shape of a curved, inverted V, plans to use a similar system to heat the entire building. Last month, the John Hancock Insurance Co. announced that the 34 floors of office space in its planned 100-story, combination office-apartment building (TIME, April 2) will also be heated with light.

* For those who insist on all-glass structures, Pittsburgh Plate Glass is now producing a double-ply glass with a reflective coating that keeps out 70% of the sun's heat and cuts glare by about 80%.

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