Engineering

Solar cooling? Here it comes.

Solar cooling? Here it comes.
So cool: The new rooftop solar collector for the Ripple House. Photo by Charles Barry
by Justin Gerdes |

Santa Clara’s Ripple House, which took third in the 2007 Solar Decathlon, was recently outfitted with a cutting-edge rooftop solar collector. The unit, the first of its kind installed in California, supplies space heating, hot water, and a feature that should ease the burden on the grid on hot summer afternoons: solar thermal air-conditioning.

The device, the Micro-Concentrator (MCT), is the work of Chromasun, a San Jose–based company with strong ties to SCU. The company has hired SCU student interns since 2008, and in 2009, its founder and CEO, Peter Le Lievre, approached the engineering department to show off his solar collector that was then under development. At the time, a team from SCU was constructing a house for the 2009 Solar Decathlon, but Chromasun’s new collector wasn’t yet ready to meet competition requirements.

After the competition, where SCU again took third (see “Bending Light,” Spring 2010), a few SCU Solar Decathlon veterans went to work for Chromasun. One, Tim Sennott ’09, was tasked with overseeing the installation of the MCT, now a full-fledged production model, on the 2007 Ripple House. The upgrade was long overdue, says James Reites, S.J., MST ’71, an associate professor of religious studies who advised both Solar Decathlon teams. While the house’s overall environmental performance was impressive, three years later “the flat thermal panels were deteriorating and the thermal tank was losing too much heat at night,” Reites says.

Not any more. The MCT is similar to the traditional flat panel solar collectors that have heated pools and showers in California for decades. But it uses a new type of concentrated Fresnel reflector panel. (Fresnel lenses are often used in lighthouses and they excel at concentrating light.) As a result, the MCT is able to supply much hotter waterup to 220 degrees Celsius (428 degrees Fahrenheit)hot enough to drive commercial air-conditioning absorption chillers, which are normally gas or steam fired. “We simply replace the natural gas with solar heat. The chillers do the rest,” says Le Lievre. The higher temperatures make the MCT far more efficient than traditional solar water heaters. “They’re actually 140 percent efficient,” says Le Lievre, “able to provide more cold water than the heat we provide them.” That’s because, like many air conditioners, the system also pumps heat from the inside to the outside.

Even before the installation, the house was off grid and produced more energy than it used. The surplus was stored in batteries. The MCT should produce enough energy to completely displace the home’s peak air-conditioning loads. Seniors Ben Frederiksen and Nick Breska, who helped with the installation, are currently developing the computer code for monitoring and control of the house. They are also working with graduate student Sergio Escobar Vargas Ph.D. ’11 and Professor Mark Aschheim to develop a metering system to track carbon savings.

 

Summer 2014

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