Supplemental Heating of High Tunnels by Energy-Producing Compost Piles

View the project final report

• 2016 annual report

Commodities

• Vegetables: greens (leafy), greens (lettuces)

Practices

• Crop Production: high tunnels or hoop houses, season extension
• Soil Management: composting

This three-year project has four primary objectives: to heat two 20’ x 50’ high tunnels with a compost heater and hydronic delivery system (in-ground supplemental heat via water pipes); to compare production of crops in high tunnel with and without supplemental heat from a compost heater system; to create valuable humus for enriching fruit and vegetable soils from dismantling the compost heater; and to demonstrate to producers a viable method for expanding the shoulders of the growing season by using in-ground compost heat. Currently, high tunnels provide opportunities for extending growing seasons by passively using solar energy. Some growers further extend the season or protect crops against cold spells within high tunnels by using secondary tunnels or supplementary heat (ambient or in-ground) with heat sources such as gas, electricity, and wood combustion during cold months (Maughan et al. 2014). Each of these heat sources has environmental disvalues, either from the extraction process, delivery process, or exhaust from combustion. Long-term consistent heating of high tunnels (especially above-ground heating) is often not economically viable for producers. We propose using a widely abundant heat source that lacks environmental disvalues and is economically viable: fungal decomposition of woody material. Use of this energy source was pioneered by the Frenchman Jean Pain in the late 1970s and early 1980s in a semi-arid ecosystem, the Provence region of France. He created large mounds of finely ground wood chips, following a precise design of his invention, that generated 140 degrees Fahrenheit for eighteen months; he transported this heat by water in tubes to heat a shed and his home. His success was described in numerous publications in the early 1980s, just prior to his untimely death. Recently, his methods have experienced renewed interest. We propose using a scaled-down version of his mound method principles for heating our high tunnels. Finished compost is widely accepted as a valuable soil amendment. When Jean Pain’s mounds stopped producing sufficient heat, he dismantled them and spread the resulting humus on his vegetable beds, with great increase in productivity. Most organic soil amendments used in Colorado are shipped from afar, with environmental and economic costs to the shipping. We propose using the exhausted compost heating mounds to enrich soils for fruit and vegetable production. The compost heaters are large mounds composed of wood chips, saw dust, shredded bark and limbs, and manure, all of which is soaked with water. The base of each circular mound is twenty feet diameter and the height is eight feet. Coiled within the mounds is hundreds of feet of irrigation tubing filled with water. The anaerobic decomposition of the wood and manure generates heat between 110 and 150 degrees Fahrenheit for six to eighteen months, depending on construction characteristics. The internal tubing is connected, as a closed system, to a horizontal system of irrigation tubing running serpentine just below the soil surface directly through the planted beds in the high tunnels. The water warmed by the heater is pumped through the high tunnel and back to the compost mound for renewed heating of the water (hydronic delivery system). The project will take place on a 3.85-acre vegetable and fruit farm owned by Rod Adams and Amy Yackel, who have operated Sunspot Urban Farm as a successful CSA for the past six years in Fort Collins, Colorado (rated second highest in Colorado, by coloradocsas.info). A guiding principle for all our farming operations is to have a very small carbon footprint; compost heaters are consistent with this principle. We have extensive experience with maintaining high temperatures in various types of compost piles. The 3.85-acre farm, located two miles northwest of Fort Collins, has two adjacent 20’ x 50’ high tunnels. A compost heater will be constructed (outside the tunnel) on the east side of the north high tunnel in the first year of the project (September 2015); a second compost heater will be constructed (outside) in the second year (September 2016) on the east side of the south high tunnel; this construction of the second heater will take place during a hands-on workshop open to producers and the public. In Year 1, we will evaluate the compost heater and delivery system and evaluate the effect of in-ground supplemental heating on soil temperatures and up to two crops (e.g., strawberries and spinach) by comparing one high tunnel with a compost heater system to the adjacent tunnel without such heat. In Year 2 (September 2016) we will have two high tunnels with supplemental heat: north tunnel with a compost heater system that is a year old (built September 2015); the south tunnel with a new compost heater system (built September 2016). In the north tunnel we will evaluate a second year on strawberries extension. In the south tunnel we will evaluate season extension of strawberries, peppers, and tomatoes and winter long successional planting of spinach. For this project, education and outreach will consist of three field days: November 2015, September 2016, and August 2017. The first field day will highlight the working of the compost heater and the hydronic delivery system as a heat source for the high tunnel. The second field day will highlight how to construct a compost heater via a hands-on workshop. The third field day will highlight the use of the finished compost (humus) and will also provide an overview of the compost heater research. Other educational products: summaries of annual and final reports and a how-to guide for building a compost heater. Because sustainable small-scale, organic-principled agriculture in the “off-season” is becoming rapidly popular at local and regional levels, we believe there will be great interest in a project that explores cost-effective and sustainable supplemental heating of high tunnels and on-site generation of soil amendments. Leila Graves, assistant professor in Specialty Crops at Colorado State University, has agreed to be the technical advisor for this project.

List of objectives:

1. To research the viability of providing heat (quality and duration of heat) to high tunnels from compost heaters modeled after Jean Pain’s design (Years 1-3). Proof of concept objective.
2. Record and track temperatures inside compost heater, inside high tunnel — both ambient and soil temperature (multiple locations) and outside high tunnel (Years 1-3).
3. Document duration of compost heat above 110 degrees Fahrenheit that is provided to the high tunnels (Years 1-3) via the hydronic system associated with the composter heaters.
4. Evaluate supplemental compost heat on high tunnel plant growth and production. We will meet this objective with two crops: strawberries and spinach. Evaluate extended fruit yield (weight) and quality from high-tunnel strawberries produced with and without supplemental compost heat (Year 1: Late September 2015-Late November 2015). Evaluate crop yield from late fall planting of high tunnel spinach produced with and without supplemental compost heat (Year 1: Late September 2015-March 2016).
5. Have finished compost chemically evaluated by a soils lab (Year 3).
6. Encourage the adoption of compost-heaters among high tunnel farmers in the region (assuming the composting system works well) by producing a how-to guide (instructions and cost), an informative all day hands-on workshop, two other field days (Years 2 and 3), and brief quarterly email research updates.
7. Quantify the producer adoption potential of this research via surveys/questionnaires during field days (Years 1-3), an electronic online post-survey that targets past participants (Year 3), and emailing 30 randomly selected CSA farms in Colorado (that did not participate in the field days) with composter heater research results to solicit feedback on potential adoption of such a system (Year 3).