Written by Brian Thompson '16, guest blogger and intern on the Clean Energy Greenhouse project
In 2012, the Clean Energy Fund sponsored a project exploring how capturing the heat produced by decomposing compost can be used to heat greenhouses. The ability to capture heat using compost, which is readily available on farms, has huge potential for many farmers interested in extending their growing seasons, or even growing through the winter. With modest investments, farmers can use commonly abundant materials like cow manure, stall linings, wood chips, and other materials that are compostable, to produce useful heat to grow for an extended season.
This project was initiated by Tad Cooke and Erick Crockenburg, UMV sophomores at the time. The pair presented to the Clean Energy Fund in the spring of 2012 with what they called a ‘clean-energy greenhouse’. This type of system, once built, would rely on free materials as ‘fuel’ and much of the carbon dioxide emitted by decomposition would be captured in the soil or plants. Tad and Erick helped adapt the concept to a research-scale design and adapt to existing greenhouse infrastructure at UVM.
This research project is sited at the UVM Horticultural farm. It consists of a large bunker for the compost pile, connected to two biofilters in an adjacent greenhouse through underground plumbing. An electric fan sucks hot air from the compost pile through the pipes and delivers it into the soil in the biofilters, which act as raised beds. The “negative air system” also pulls fresh air into the center of the pile, eliminating the need to aerate it by turning the material. The pile is almost entirely comprised of manure from dairy cows from the nearby UVM dairy farm.
Construction of the necessary infrastructure took place during the summer of 2013. This past fall, I had the opportunity to assist as one of the interns on the project. The beds were planted with tomato seedlings, and the system was left to run. The system was self-reliant, and so most of our efforts were for the health of the tomatoes rather than the compost energy system itself. We tied the tomatoes straight up using plastic clips, and pruned suckers to encourage strong central growth and lateral fruiting. In fact, even in mid-October, the plants were producing young tomatoes. Unfortunately, a sudden, hard frost killed the plants on October 28th but it is fairly remarkable that they were able to fruit so far into the fall.
We were able to collect valuable temperature data, since embedded in the compost pile are four temperature sensors that log the temperature every minute and collected it via a wireless internet router. There are also nineteen more sensors at multiple locations in the pipes and in the beds in the greenhouse. This vast quantity of data allows us to create a benchmark to better understand what is happening throughout the system, particularly over multiple experimental trials of compost.
As the project continues, the data it provides will be a valuable resource in the study of optimal pile configurations and compositions, as well as BTU comparisons to other ways of heating greenhouses through the winter, like propane, fuel oil, and wood. The infrastructure in place for this project will continue to be a tool in exploring compost heating at UVM into the future.
Stayed tuned for a full report analyzing data from the first compost pile trial run, which will be published on the CEF website later this semester.