Grantee Research Project Results
Final Report: Biomass Greenhouse-Heating Systems to Extend Growing Seasons for Resource-Limited Farmers
EPA Grant Number: SU835695Title: Biomass Greenhouse-Heating Systems to Extend Growing Seasons for Resource-Limited Farmers
Investigators: Yu, Ok-Youn , Domermuth, David , Houser, James , Ferrell, Jeremy , Oh, Sang-Hwa
Institution: Appalachian State University
EPA Project Officer: Page, Angela
Phase: I
Project Period: August 15, 2014 through August 14, 2015
Project Amount: $14,806
RFA: P3 Awards: A National Student Design Competition for Sustainability Focusing on People, Prosperity and the Planet (2014) RFA Text | Recipients Lists
Research Category: Pollution Prevention/Sustainable Development , P3 Challenge Area - Air Quality , P3 Awards , Sustainable and Healthy Communities
Objective:
The purpose of the Appalachian State University Nexus Project is to develop greenhouse heating technologies that provide affordable means to improve the food-growing capacities and standard of living for farmer communities in rural Appalachia while eliminating the use of fossil fuels. The student-led initiative seeks to engage both university students and the greater community in educational opportunities that will ultimately promote greater environmental awareness and economic self-sufficiency throughout the region. The Department of Technology and Environmental Design at Appalachian State University (ASU) in Boone, NC has built a 20 feet by 30 feet greenhouse, a bio-volatilization (BV) system, and an anaerobic digestion (AD) system using previous grants including EPA P3 funding. This ready-to-test site called “Nexus” is located at the Watauga County Landfill, in Boone, NC. BV and AD systems already existing at Nexus have been integrated into the research as sources of biomass energy. In addition, a compost heating and a solar thermal systems have been built with funds from the Phase I grant. Therefore, our biomass greenhouse heating system involves AD, BV, compost, and solar energy sources, utilizing all of the feedstocks typically available on a small farm. AD and compost generate energy from readily digestible materials and the BV system handles relatively indigestible biomass, such as wood scrap. In summary, our primary objectives in Phase I are the following:
1. Integrate heating technologies into greenhouse heating system
- Construct heat storage tank and connect heating technologies,
- Construct an automated manifold system that has inputs for every heat source, and
- Research greenhouse heat distribution system.
2. Incorporate heating sources into the Nexus greenhouse
- Design, construct, and test compost heating system,
- Design, construct, and test solar thermal system,
- Integrate existing BV system into Nexus, and
- Integrate existing AD system into Nexus.
3. Outreach and Education
Summary/Accomplishments (Outputs/Outcomes):
Objective 1: Integrate Heating Technologies Into Greenhouse Heating System
Heat collection and storage system: A 1,500 gallon, 23 feet by 3 feet by 3 feet, insulated solar thermal storage tank was built along the north wall of the greenhouse to store heat from various heating sources. During the 3 days of trials with the BV and the solar thermal heat exchange systems, approximately 88,200 BTUs were delivered to the tank during the 5 hours of solar thermal and BV system operation. The tank can lose a few thousand BTUs per hour through radiative heat loss, but that heat is lost into the greenhouse space so helps to passively heat the greenhouse. The large amount of thermal mass helps to moderate temperatures in the greenhouse. During the month of December when the tank was full of water, plants in the greenhouse did not freeze even when nighttime temperatures were well below freezing.
Automated manifold system: A manifold with multiple inputs and outputs was set up on the thermal storage tank. Eventually, this system will be able to deliver BTU to the thermal storage tank from multiple heat sources as well as deliver BTU to numerous heat distribution systems within the greenhouse. An Arduino module was programmed to control the flow of water from the tank to various heat exchange systems based on temperature differentials. The programmed system worked correctly during trial runs of the BV and solar thermal systems.
Greenhouse heat distribution system: Specific methods of delivering heat to the greenhouse from the storage system were investigated. Our research team attended a workshop sponsored by Clemson University entitled “Alternative Greenhouse Heating Systems to Reduce Energy Costs” and toured the EnergyXchange near Burnsville, NC that uses biomass energy to heat its greenhouse complexes. We examined and assessed many different methods for delivering heat to the greenhouse, from tubes carrying hot water to maintain soil temperature (i.e., learned about root-zone radiant tubing, which has been shown to lower energy use by 50% while maintaining plant growth) to forced-air hot water systems. In addition, we developed and are testing computerized heat transfer models that will allow us to compare theoretical heat deliveries of all systems with observed heat deliveries monitored for the BV, solar thermal, and compost systems.
Objective 2: Incorporate Heating Sources Into the Nexus Greenhouse
Compost heat delivery system: A final design was determined for the compost system based on the compost-based bioenergy systems developed by French inventor Jean Pain. The system is alarge static pile of green wood chips with aeration pipes running underneath it. Halfway up the pile, heat exchange tubing was installed. The pile is surrounded by straw bales for insulation. Construction of the pile was completed at the end of December 2014. By February the pile reached and maintained an internal temperature of 120oF during the coldest months of the year in Boone. Moisture measurements of the pile indicate that it is maintaining sufficient moisture to foster aerobic bacterial growth. It is anticipated that the pile may reach temperatures of 140oF. A closed-looped heat exchange system has been designed and tested, and is being installed to utilize the heat of the compost pile to maintain operating temperatures in the AD system. In addition, the compost will also be able to contribute heat to the thermal storage tank in the greenhouse.
Solar thermal system: A solar thermal system was installed on the roof of the greenhouse. The system has demonstrated that it can deliver 42,000 BTUs on an average solar insolation day. Empirical data collected during three trials that combined heat delivery from the BV and solar thermal systems to the heat storage tank found that the combined systems could deliver up to 28,000 BTU per hour.
Bio-volatilization (BV) system: Heat exchangers were incorporated into the BV system to deliver energy to the thermal storage tank inside the greenhouse. Three trials for the system were run and it was determined that the BV system could deliver between 10,000 and 15,000 BTUs per hour to heat storage. In addition, the system producers biochar that is used as a soil amendment in the greenhouse, bio-oil that can be used as fuel, and syngas that can be stored and used to fire a boiler or run a generator. We used the produced syngas to run a small generator in trial applications. We discovered that the gas will need additional filtration to be an acceptable fuel for generators, but should be fine to use within a boiler with minimal filtration.
Anaerobic digestion (AD) system: The insulated AD system was monitored for temperature maintenance during the winter with additions of heated influent slurry. It was determined that heated influent was capable of raising the temperature of the system, but that the system could not maintain sufficient operating temperatures in average Boone winter temperatures. Heat exchangers have been added to the system, and a closed-looped heat exchange system with the compost has been designed and tested, though not fully implemented. Glycerin from our biodiesel production facility is being used to create a freeze-resistant heat transfer fluid for the system. It is anticipated that heat from the compost system will be enough to maintain adequate digester temperatures, however, provisions will also be made to attach the system to the thermal heat storage system in the greenhouse. Some minimal methane production was observed.
Objective 3: Outreach and Education
The Nexus facility was incorporated into the curriculum of the undergraduate and graduate Biofuels Technology classes of the Department of Technology and Environmental Design, for both demonstration and hands-on research. In addition, several other ASU classes and representatives from energy or agriculture related fields with whom we are developing working relationships like the North Carolina Department of Agriculture and Consumer Services and the local Farmers Incubator Group (FIG) have toured the site. Other outreach efforts included open-houses and presentations. In addition, a website was created (http://ok.tec.appstate.edu/biomass/) to disseminate information about Nexus to a very wide audience. A presentation on the research is currently scheduled for the Association for the Advancement of Sustainability in Higher Education (AASHE) 2015 conference. Further presentations and journal articles will be pursued.
Conclusions:
In spite of a number of setbacks that are inherent to working toward an off-grid, self-sufficient greenhouse facility, the project has had a successful initiation. We completed our major objectives–constructing and monitoring a compost heating system–as well as researching, constructing, testing and monitoring heat storage and delivery systems. We have positively tested the heating and heat transfer apparatus, and the heat storage tank, in a trial that delivered 88,200 BTUs in 5 hours. Heat transfer computer models predict that 26,000 BTUs per hour will be necessary to maintain a 60oF temperature in our greenhouse in Boone through winter. Results from our tests indicate a capability of producing 16,899 +/- 6,337 BTUs per hour from the BV and solar thermal systems alone. With the addition of compost heating and biogas energy (i.e., 35,000 BTUs per hour estimated from the computer model), results indicate a strong potential for complete greenhouse heating using biomass energy available to any farm. Incorporation of the Nexus into curricula and other outreach activities has been very successful. The Nexus is an excellent vehicle for research, teaching and outreach concerning issues of non-fossil fuel based agricultural production, and promotion of local economies.
References:
Supplemental Keywords:
Biomass energy, greenhouse heating, limited-resource farming, biogas compression, pyrolysis, synthesis gas, biogas, compost heating, thermal mass, greenhouseRelevant Websites:
NEXUS: Biomass Greenhouse-Heating Systems to Extend Growing Seasons for Resource-Limited Farmers Exit
P3 Phase II:
Biomass Greenhouse-heating systems to extend growing seasons for resource-limited farmers | 2016 Progress Report | 2017 Progress Report | 2018 Progress Report | Final ReportThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.