Soda can furnaces

Awesome:

Brown, who teaches mechanical engineering at Metro State, is working with students, as well as a local nonprofit organization, Revision International, to build solar powered furnaces for homes in the neighborhood. With empty soda cans as one of the main parts of the design, the furnaces cost around $30 to make and are expected to save about the same amount in monthly energy costs.

In November, the group installed two of the heaters in homes, with more installations scheduled for later this month. And while it’s possible to “upgrade” the units — spending another $20 for an acrylic cover, $2 for a thermostat or $2.50 for a shower curtain to drape around it — that almost defeats the purpose of providing reliable and inexpensive energy, Brown said.

An initial effort, undertaken with graduate students at the University of Colorado Boulder, yielded a furnace that cost about $60. But Brown thought the price could be lowered. That was the challenge he posed to his students at Metro State, tasking them with making the units faster, cheaper and more efficient and reliable.

“You have to be really creative,” said Richard Anderson, a Metro State senior who’s part of the project team. “Right now, the unit will last for about a winter without any maintenance. If you bumped up the cost to about $100, it would last three or four times longer. But you’re talking about soda cans and computer fans that you can buy six for $10 on eBay and you’re supplying heat to an entire house.”

Anderson said the electricity used by the fans costs about two cents a day. Cool air is drawn into the unit’s base and then heated as it travels up through drilled holes in the 144 aluminum cans, which have been heated by the sun. The air then exits through ventilation holes at the top of the unit. While there has to be a supplemental source for heat at night, the units can reach about 170 degrees during the day. In one of the units installed in November, Anderson said, a room that was about 60 degrees increased to 90 degrees within 20 minutes.

“There was a little boy who was going to be sleeping there. He was going, ‘I’m going to be so warm tonight,'” Anderson said. “That was just so cool — it’s really exceeded my expectations.”