- Crop Production: greenhouses, high tunnels or hoop houses
- Energy: solar energy
There are energy costs and pollution problems with the propane heated hoop houses that dominate the agricultural greenhouse industry. Farmers dependent on greenhouses seek alternatives to the risks of fossil fuel dependence but have few practical alternatives. Solar greenhouses or bioshelters have been repeatedly demonstrated to virtually eliminate heating bills. The ability to produce food locally without fossil fuel input during winter reduces emissions associated with transport and strengthen producer competitiveness. However, the capital cost of bioshelters continues to impede their adoption. There is a need to identify technologies that can provide lower-cost conditioned growing spaces than either the propane-dependent hoop houses or the expensive-to-build solar greenhouses. As fuel costs rise, and farmers face difficult choices, this need will become imperative. The affordable bioshelter project seeks to address the need for lower-cost conditioned grow-spaces by experimentally measuring, and setting within a business context, two emerging technologies, Soap-Foam Insulation (SFI) and Underground Heating and Cooling System (UHCS). These technologies have the potential to make solar greenhouses competitive with hoop houses. An SFI is a moveable foam insulation that can be blown between two layers of glazing as needed. UHCS replaces water-barrel heat storage with an especially effective and economical sub-soil heat storage. The systems have both worked in demonstration projects since 2000, and have been shown to be technically feasible and economical to install. However, while both systems are reported to performance exellently, scientific verification is lacking because neither has been experimentally quantified. Despite their potential, and despite the pressures of rising fuels costs, without an objective performance evaluation and economic analysis these systems represent an unacceptable risk to farmers. By working to make affordable bioshelters a viable option, this project seeks to enable greenhouse farmers to overcome the looming energy crisis and move towards more ecologically and economically sound greenhouse agriculture. Preliminary cost analysis suggests that an affordable bioshelter can be built for approximately $15,000. A state-of-the-art solar greenhouse, demonstrated to require no heating, costs $30,000. The key to this difference is that the latter is a building while SFI allows similar performance with hoop house construction. The standard hoop costs $7,000 to build, and thousands a year to heat, depending on the climate. If it performs as expected, the payback period for an affordable bioshelter over a conventional hoop is projected to be five years using current propane prices, but excluding the 30% federal solar tax credit. A control and two experimental 7' x 14' mini-greenhouses will be built on ASU's Sustainable Development Teaching and Research Farm. They will be constructed of donated bamboo, glazed with polyethylene film, and monitored through a data acquisition system. The study will compare SFI and UHCS performance to theoretical performance calculations and the performance of existing technologies. The findings will be fed into the business analysis and a commercial size SFI/UHCS greenhouse will be designed with a detailed construction estimate. In its final phase the project will focus on outreach.
Project objectives from proposal:
A numbered list of concise project objectives.
1. Design a controlled experiment in which the operation of SFI and UHCS in a greenhouse is validly compared to a control greenhouse.
2. Design a baseline passive solar hoop house for the control
a. design a hoop shape that is a better solar radiation collector than a typical shape hoop house
b. select an optimal amount of bellow grade insulation
3. Build three identical miniature hoop houses out of donated bamboo, simulating the usual metal or PVC pipe construction.
4. Build a basic bubble generation machine, based on plans provided by Homestead Building Solutions Inc. (Elliot, 2005).
5. Design and install an underground piping network for the UHCS with the help of Going Concerns Limited (Cruickshank, 2005).
6. Install and calibrate data acquisition equipment in time for the January-February experimental period.
7. Conduct a series of experiments that will capture the necessary information to establish a meaningful preliminary assessment of SFI and UHCS.
8. Analyze the performance of each system and compare it to theoretically predicted performance, to analyze the performance of the two systems working together.
a. Establish the adaptability of existing theoretical performance calculations for solar greenhouses to apply to an SFI greenhouse.
b. Extrapolate from the data collected for the flow of energy into and out of storage in a UHCS, and graph these patterns of heat flow relative to the changing conditions in the greenhouse.
9. Use the knowledge gained through the experiment and through working with the systems to develop a prototype affordable bioshelter with a reliable construction cost estimate.
10. Conduct an economic analysis comparing SFI and UHCS to a passive solar greenhouse and a hoop house.