Grantee Research Project Results

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

EPA Grant Number: SU833683
Title: The Affordable Bioshelters Project: Testing Innovative Technologies, Working to Make High Performance Solar Greenhouses Cost Competitive
Investigators: Raichle, Brian W. , Strauch, Yonatan , Oswald, Stony Roscoe , Scanlin, Dennis , Martin, Jack , Black, Henry , Bryant, Andy , Duus, Mike , Fulton, Andrew , Fulton, David , Hackett, Sean , House, Caroline , Short, Weston , Smith, Joe , Taddonio, Brian , Tudiver, Jannah , Zuazmaa, Zola , Zhang, Qiang
Institution: Appalachian State University
EPA Project Officer: Page, Angela
Phase: II
Project Period: August 31, 2007 through July 31, 2008 (Extended to July 31, 2012)
Project Amount: $75,000
RFA: P3 Awards: A National Student Design Competition for Sustainability Focusing on People, Prosperity and the Planet - Phase 2 (2007) Recipients Lists
Research Category: Pollution Prevention/Sustainable Development , P3 Awards , P3 Challenge Area - Air Quality , Sustainable and Healthy Communities

Objective:

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 per 2,000 sq. ft, compared to $40,000 - $65,000 per 2,000 sq. ft. for a traditional bioshelter 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 few 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 without 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. 

Summary/Accomplishments (Outputs/Outcomes):

Four independent, but related, research initiatives were undertaken to address these challenges. The initiatives were:

1. long-term thermal performance testing of three greenhouses of nominally identical construction but equipped with various  combinations of thermal mass, subsoil heat storage, and liquid foam insulation
2. design and retrofitting of a subsoil heat storage system in an existing greenhouse
3. characterization of liquid foam surfactant
4. design, fabrication, and construction if a commercial greenhouse that can accommodate liquid foam insulation

Long-term thermal testing: The experimental methodology is shown schematically below. Nighttime low greenhouse temperatures as a function of nightly low ambient temperature are also presented. It can be seen that, relative to a reference greenhouse, a greenhouse with either subsoil heat storage or liquid foam insulation experience milder nighttime lows. For a nightly low temperature around freezing, these greenhouses are around 5°C warmer.  A greenhouse with both technologies experiences even milder nighttime temperatures. For a nightly low temperature around freezing, this greenhouse was around 10°C warmer than the reference greenhouse.

Figf

Figure 1.

Subsoil heat storage retrofit: Subsoil heat storage was determined to be a “DIY” technology, but that growers would benefit from knowing installation best practices. A subsoil heat storage system, which involves burying air ducts below the structure, was retrofitted in an existing greenhouse. Air from the top of the greenhouse is circulated underground during the day, and returned to the greenhouse at night.   While no thermal performance testing was conducted on this greenhouse, valuable lessons were learned about the process of retrofitting.

Liquid foam insulation characterization: It was noticed during the long-term performance testing that liquid foam insulation degrades over time, therefore reducing its insulative value and requiring frequent regeneration. Various surfactant recipes were testing while observing foam texture, bubble size, and duration.

Greenhouse prototype kit: It was determined that liquid foam insulation is not a “DIY” technology. To be adopted, commercially available kits must be brought to market.  A greenhouse structure was designed with a sealed cavity between the glazings capable of accommodating liquid foam insulation. This structure was fabricated by a commercial greenhouse manufacturer and constructed by a general contractor with no greenhouse experience.  This greenhouse is shown below.

 

Figure 2

Conclusions:

Based on long-term thermal testing, both liquid foam insulation and subsoil heat storage individually are effective at moderating nighttime low temperatures. The combination provides even more benefit. Thermal storage and heating power were quantitatively determined, and found to be lower than predicted. This may be due to a lack of insulation below the subsoil and low air flow rates, both of which were know deficiencies. Much of the energy delivered was in the form of latent heat, which does not contribute to temperature moderation and may be undesirable for greenhouse operations (for example, condensation on the glazing will reduce radiative transmission) and growing conditions.

Retrofitting an SHSC proved to be ineffective due to spaced constraints. Specifically, excavating near the walls to install side insulation was difficult, as was removing enough dirt to install insulation below the tubes. However, since greenhouse glazing is typically replaced every few years due to UV degradation of the plastic, a reasonable alternative could be to install the system while the glazing is removed. Any competent greenhouse grower would be capable of undertaking the retrofit, but would benefit from knowledge of best practices.

Liquid foam insulation is quite effective at reducing greenhouse heat loss at night.  However, it is not a candidate for a do-it-yourself project. It is a specialized technology which is relatively complex to design, install, and operate. Adoption can be best promoted by providing growers a predesigned kit they could purchase and self-assemble. Further development is needed before foam insulation generation is market ready.  The prototype greenhouse structure designed here appears to be a success. However, because further development on liquid foam generation was not undertaken, the greenhouse was not tested.

The operation of this LFI system, while suggesting benefits, was never optimized. A foam rinse system was never installed, foam retention time was short, and insulative values were likely not ideal. More development and testing is needed.

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,, Air, Sustainable Industry/Business, Scientific Discipline, RFA, POLLUTION PREVENTION, Technology for Sustainable Environment, Sustainable Environment, climate change, Energy, Air Pollution Effects, Atmosphere, Environmental Engineering, energy conservation, environmental sustainability, bioshelter, green design, sustainable development, solar greenhouse, solar energy, ecological design, environmental monitoring, renewable energy

Progress and Final Reports:

Original Abstract

2008 Progress Report

2009

2010

2011

P3 Phase I:

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