Final Report: The Affordable Bioshelters Project: Testing Innovative Technologies, Working to Make High Performance Solar Greenhouses Cost Competitive

EPA Grant Number: SU833170
Title: The Affordable Bioshelters Project: Testing Innovative Technologies, Working to Make High Performance Solar Greenhouses Cost Competitive
Investigators: Raichle, Brian W. , Black, Henry , Bryant, Andy , Duus, Mike , Fulton, Andrew , Fulton, David , Hackett, Sean , House, Caroline , Martin, Jack , Oswald, Stony Roscoe , Short, Weston , Smith, Joe , Strauch, Yonatan , Taddonio, Brian , Tudiver, Jannah , Zhang, Q. , Zuazmaa, Zola
Institution: Appalachian State University , University of Manitoba
EPA Project Officer: Nolt-Helms, Cynthia
Phase: I
Project Period: September 30, 2006 through May 30, 2007
Project Amount: $9,998
RFA: P3 Awards: A National Student Design Competition for Sustainability Focusing on People, Prosperity and the Planet (2006) RFA Text |  Recipients Lists
Research Category: P3 Challenge Area - Energy , Pollution Prevention/Sustainable Development , P3 Awards , Sustainability


The Need: The steady increase in world population and the problems associated with conventional agricultural practices demand changes in food production methods and capabilities. Greenhouses have the potential to be extremely ecological as they can greatly increase yields per acre and facilitate reduced pesticide use.

Globally there are 2.5 million acres of greenhouse cover, including 30,640 acres in North America1. In Europe, where greenhouses are in wider use they consume 10% of the total energy in agriculture, mostly for heating. Heating and cooling amount to 35% of greenhouse production costs2 due to the extremely poor R-1.25 insulation values (compared to R-19 for a house). In moderate to cold climate zones, it can take up to 2,500 gal of propane to keep a 2000 sq. ft. greenhouse growing all winter, currently costing around $5,000. These wasteful structures produce around 350 tons of CO2 per acre, disproportionately contributing to climate change.

The Challenge: An expected 80% savings of energy can be achieved by passive solar greenhouses, also known as bioshelters, which manage solar energy with high gains, massive heat storage, and heavy insulation3. Unfortunately bioshelters have payback periods that are impractically long. The installation of traditional, double polyethylene greenhouses can cost a mere $10,000, compared to between $40,000-$65,000 for bioshelters per 2,000 sq. ft. Further, productivity is reduced in bioshelters as massive amounts of thermal mass compete with plants for light and space resources, and because tight air seals cause CO2 deficits during the photosynthetic period. The handful of bioshelters in the Eastern U.S. have paybacks on the order of decades.

In order to turn greenhouses into highly ecological systems, breakthrough technologies that give bioshelter performance for lower capital costs are needed. Promising emerging technologies include the Liquid Foam Insulation which provides high insulation levels within a modified traditional low-cost greenhouse, and the Earth Charger which stores heat with out the drawbacks of conventional thermal mass, and with added benefits to plants. These systems need to be investigated, studied, and economically validated before they are ready for market.

The aim of the Affordable Bioshelters project is to test, prove, and bring to the market greenhouse technologies that drastically reduce fossil fuel consumption while paying back their cost within five years.

In order to achieve this aim, during Phase I of the project the student team:

  • Identified liquid foam insulation (LFI), a subsoil heat storage system (EC- for earth charger), and compost exhaust utilization as candidate technologies for insulation, heat storage, supplementary heat/CO2 source (see Figure 1).
  • Built a three unit greenhouse test site with these technologies in order to study them in controlled experiments
  • Conducted experiments comparing the LFI and EC heat storage to a control greenhouse
  • Made adjustments to the LFI system in order to overcome problems
  • Conducted preliminary data analysis and economic evaluations
  • Developed initial designs for an effective LFI greenhouse
  • Developed a design for retrofitting EC with complimentary technologies including compost exhaust utilization

Figure 1.

The team also:

  • Networked with local growers, within the greenhouse industry, and with bioshelter advocates and users
  • Developed capacity in the areas of data acquisition, experimental design, construction, and project management
  • Engaged students through curricular and extra curricular avenues to advance the project

Summary/Accomplishments (Outputs/Outcomes):

The LFI and the earth charger systems were found to have significant beneficial effects as compared to a control greenhouse. The LFI system was able to reduce heat loss and maintain higher temperatures in experiments. The foam cavity was found to have difficulties with sealing and the system was difficult to automate. The foam itself was plagued by freezing and often failed to fill the entire cavity. Solutions to these problems were developed and combined into a proposed prototype design. The EC was found to be an easy to install technology, with virtually no maintenance needs.

Graph 1: Performance of LFI over 1 night
Graph 1.

As shown in Graph 1, during the night of March 18thliquid foam used to insulate the greenhouse envelope showed an average temperature difference from the control of 14°F. Due to concerns with freezing foam, a 20% propylene glycol foam solution was used in the same experiment and prevented freezing, but at a later date. Thermal results were similar. Foam did not require half as many refills with the glycol solution.

Graph 2: EC and thermal mass influence on soil temperature at 2ft depth
Graph 2.

As shown in Graph 2, EC combined with water thermal mass showed that 2’ soil temperature rose to 65°F which was 7.5°F warmer than in the control. Additionally, increased plant growth was observed; greenhouse temperature lows were an average 8°F warmer, and highs 7.5°F cooler. Temperatures at one foot depth reached 70°F.

The EC alone, set to cool the greenhouse when temperatures were above 75°F and warm it below 50°F, showed the following variations from the control that greenhouse air temperature lows were 2-4°F warmer and highs were 0-4°F cooler. Additionally the 2’ soil temperature was elevated by 3.1°F to an average of 50.6°F, and the cover crop grew to 4”-5”, as compared to 1”­2” in the control.

At the beginning of Phase I, compost exhaust utilization was judged too problematic due to cause air contamination. An improved design integrating compost exhaust into the earth charger was developed that keeps exhaust from mixing with greenhouse air.


The preliminary results from the experiments and studies performed during Phase I suggest that the LFI and the EC can be effective technologies for raising greenhouse air and soil temperatures at affordable costs. These technologies should be further refined, studied, and combined into complementary design packages with demonstrated payback periods.

Specific conclusions The Earth Charger (EC) system

  1. The EC is able to elevate greenhouse soil temperatures by at least 2-5°F by absorbing between 20-30% of solar income into subsoil during the day and releasing 5-10% of solar income back into the greenhouse at night.
  2. The EC is easy to install, cost effective, and simple to operate. Preliminary payback analysis shows savings in energy costs will payback in 2-4 years.
  3. The EC in combination with water thermal mass can elevate the sub-soil temperatures up to 65°F in the spring and fall.

The Liquid Foam Insulation (LFI)

  1. Experiments show that the LFI can be an effective nighttime insulation providing average higher greenhouse air temperatures of up to 14°F.
  2. The LFI can be used to increase solar gain and daytime light intensity by up to 38% by insulating the north cavities during the day.
  3. The payback period of the prototype design is expected to be less than 5.5 years if it reduces annual heating bills by 50%.

Proposed Phase II Objectives and Strategies:

The objective of Phase II is to develop effective, affordable, immediately deployable bioshelter designs using proven technologies. The results will be shared and implementation encouraged by methods ranging from a website to an international workshop. In Phase II three distinct complimentary prongs of research will be undertaken. These prongs are bioshelter test site modifications, liquid foam insulation research & development, and a retrofit study.

  1. Bioshelter test site modifications: The existing greenhouses will be enhanced with the addition of an improved foam system and sensors that will enable experiments which test various configurations of the liquid foam insulation and earth charger. Winter ‘07-‘08 experiments will promote better understanding of their combined capabilities.
  2. Liquid Foam Insulation (LFI) Research & Development: Improvements in the cavity design, foam surfactant mixture, and foam generating devices will allow the LFI to greatly surpass previous results. Improvements will be made through rigorous lab testing and gradual scaling of a prototype wall system which will be developed with our research partners at other institutions.
  3. Retrofit study: The retrofit study proposed at Lily Patch Farms will involve the installation of an earth charger, argon insulation, and composting exhaust utilization system. An identical, adjacent greenhouse will be used as a control. Fuel consumption and crop yields will be compared. The argon-filled bag insulating system consists of gas tight bags filled with argon and attached to the south side interior of a greenhouse providing improvements in insulating values from R-1.25 to R-5. It was developed by a proposed Phase II partner Dr. Zhang of the University of Manitoba. The earth charger will be supplemented with an additional layer of tubing supplying heat from an outdoor compost pile. The compost pile will be monitored and feeding cycles adjusted in order to match heat generation to meet demand.
  4. Dissemination of results will be accomplished through a detailed website, campus presentations, local farmers’ networks, and through an international workshop. The workshop, planned for Spring 2008, will provide an opportunity for researchers to present their studies allowing further understanding of various bioshelter components and how they interact together. Invited participants will include many current partners, researchers/experts, advocates and potential early adopters so that barriers to implementation are identified and tackled.

    This project benefits people. Successful bioshelter designs will economically extend the greenhouse growing season; benefiting farmers and increasing the local food production. Designs can be utilized by traditional greenhouse growers, organic grower groups, the backyard gardener, and those living in cold weather, developing areas of the world. The research will benefit prosperity by saving energy. Energy savings will drastically lower costs and payback initial investment in less than five years. The planet will benefit from a reduction in energy use produced from these improved greenhouses will have a lower embodied energy, reducing emissions. The Affordable Bioshelter will aim to gain the most out of local renewable resources while minimizing the use of nonrenewable ones.


  1. Cook, Roberta and Calvin, Linda. (2005). Greenhouse Tomatoes Change the Dynamics of the North American Fresh Tomato Industry. Economic Research Report No. (ERR2) 86 pp, April 2005 USDA.
  2. Pan Q, Huang ZD, Ma CW. Study on the energy conservation of huabei-type multispan plastic greenhouse and its practice. Transactions of the CSAE. 1999;15(2):155–159. (in Chinese).5.
  3. Mazaria (1979) The Passive Solar Energy Book. Rodale Press. Emmuas, PA.

Supplemental Keywords:

global climate, clean technologies, innovative technologies, manufacturing, conservation, agriculture, cleaner production/pollution prevention, renewable fuels, life-cycle analysis, Energy, Biosystems Engineering, Sustainable Development, Technology, Technology for Sustainable Environment, North Carolina (NC), energy conservation, energy efficiency, environmentally benign alternative, renewable energy, renewable fuel production, greenhouses, protected cultivation,, RFA, Scientific Discipline, Air, Sustainable Industry/Business, POLLUTION PREVENTION, Sustainable Environment, Energy, climate change, Air Pollution Effects, Technology for Sustainable Environment, Environmental Engineering, Atmosphere, energy conservation, bioshelter, environmental monitoring, sustainable development, green design, ecological design, environmental sustainability, solar greenhouse, energy efficiency, solar energy

Relevant Websites:

Phase 2 Abstract

P3 Phase II:

The Affordable Bioshelters Project: Testing Innovative Technologies, Working to Make High Performance Solar Greenhouses Cost Competitive  | 2008 Progress Report