Real-Life Apps: Organic Farm Goes Solar
By Kathryn LoConte
Since 2004, Chris Polashenski ’07 Th’07 has bettered the Dartmouth Organic Farm greenhouse one innovation at a time. For an ENGS 190/290 project, Polashenski and Luke Wachter ’06 retrofitted the structure to run on solar power instead of fossil fuels. “This greenhouse is typical of what most farmers have, and it’s a realistic project,” says Polashenski, who is now pursuing his Ph.D. at Thayer School. “A lot of universities have built prismatically shaped solar greenhouses that no farmer could ever possibly afford.”
This idea reflects one of their major criteria: every adjustment must be profitable. “Just the fundamental fact that we’re trying to make a profit is significant. It’s a big step in the right direction,” says Polashenski.
The pair constructed the building so that its ridgeline runs east-west. “It therefore has the most area facing south and gathers the most sunlight over the course of the day,” says Polashenski. “We’re just trying to optimize the process to capture as much heat as possible.”
For additional heating, Polashenski sited 12 734-gallon concentric water tanks along the north wall to capture heat during the day and release it at night through a system of manifolds and piping that runs beneath the soil. “Circulating the warm water from those baths into the root zone of the plants is a way to store heat, but also do more with less,” says Polashenski. “Agricultural studies show that only the roots need to be heated. Most greenhouses heat the air. They’ve got it all wrong.”
The tanks will also work double duty, letting environmental science majors grow local algae and fish as fertilizer for the greenhouse and as a food source. “Originally, the plan was just to use the tanks as thermal storage,” says environmental studies major Tara McNervy ’09. “But they also act as a living laboratory for Dartmouth students to research aquaculture and aquatic ecosystems.”
For the structure Polashenski and Wachter used insulating concrete forms, pouring concrete between two pieces of Styrofoam. “It’s a slick idea,” says Polashenski. “In the old method, people would strip the forms down when the concrete hardened, haul them away, and then add insulation. We eliminate that step by using the insulation as the concrete form in the first place.”
Planned future additions include a vertical reflector to catch sunlight and a retractable night curtain to trap heat. Even without them, however, the greenhouse works, as Polashenksi verified last winter. “It was unbearably warm inside in late February,” he says.
Polashenski is pleased with the progress. “I expect that at some point all of the designs will be done,” he says. “Overall, we’re posing a problem in a way that no one seems to have done before.”
For more photos, visit our Solar Greenhouse Flickr page.
— Kathryn LoConte is assistant editor at Dartmouth Engineer.