What could be more environmentally friendly than a chiller that uses water vapor as a refrigerant? Well, such devices are around, but they are costly — compressor fans are hand assembled from titanium hubs and cost about $50,000. And such chillers are only efficient for applications that need more than 300 kW of cooling capacity. They are also large, measuring 8 m long and 2 m in diameter. Part of the technical problem is that with water vapor, the cooling cycle takes place entirely under subatmospheric vacuum pressures. So it takes relatively high pressure ratios — about twice as high as when using classic refrigerants.
A recent design competition sponsored by the Barr Foundation and Inno- Centive Inc. (innocentive.com) sought out chiller designs for smaller applications. The team of John Barrie, an industrial designer, and Norbert Muller, a professor at Michigan State University submitted the winning entry.
Key to the new chiller is a woven carbon-fiber compressor wheel that is easy to manufacture. Fibers in the wheel are aligned to withstand high forces and the wheel houses a bearing and motor, so all electric circuits operate in an ambient atmosphere. Computer models suggest chillers built on this design would be 30% more efficient to operate and less expensive to manufacture. The device also scales, so it can cool refrigerators, cars, or commercial buildings. Its target applications will need 3 to 300 kW (or 1 to 100 ton) of cooling.
