Greenhouse, A History
A greenhouse is a house to grow greens in, right? Well, yes – but like many things in this world it’s not quite as simple as that.
According to the White Cottage, an English greenhouse design company, greenhouses were first conceived (in record, at least) by the Roman Empire and “the reign of the Emperor Tiberius (42BC to 37AD) who had cucumbers grown in a ‘Specularium.'” Appropriately bestowed, the word Specularium can be translated to mean “of or belonging to a mirror” (Latin Lexicon). Physically, greenhouses absorb the sun’s energy and radiate it internally. Philosophically, these structures reflect the way that humans interact with the environment.
The first greenhouses were built primarily for the purpose of housing tropical plants in temperate regions. These models suffered from climate control issues and were difficult to seal during winters and through the night. Flash forward to Holland in the late 16th century. Jules Charles, a French botanist, built a glass greenhouse and used it to grow medicinal plants. This model was replicated and refined to grow tropical fruits. One greenhouse in the palace at Versailles was over 500 feet long! It was built for the French royalty and called an “Orangery.” Like the Orangery at Versailles, greenhouses remained a symbol of wealth for some time (White Cottage).
Modern day greenhouses are the product of years of technological and agricultural advances. They can be outfitted with climate control systems, including temperature regulators, insulation technology, fans, heaters, and benchtop warmers for direct delivery of heat to plant roots. Some greenhouses are passive, built intentionally in a particular location to maximize the energy of the sun and use no external heat. There are many exciting new technologies, combining a minimal energy-use approach with passive methods.
The concept behind a greenhouse is logical enough: solar energy permeates the transparent walls of the structure and is absorbed by the objects within. Throughout the day the greenhouse maintains toasty warm and even sizzling hot temperatures. At night, as the outside air cools, the greenhouse (if not well insulated or externally heated) radiates this energy outward and the internal temperature drops. For more detailed general information about greenhouses, please visit HowStuffWorks and read your heart out!
Farmers and gardeners today are tackling the challenges associated with long-term sustainability, fossil fuel costs, and the need to grow food in places with changing climates. Cold winters, harsh summers, excessive rain and drought, and many other meteorological factors are motivating farmers to grow food in controlled, reliable environments. An obstacle in this endeavor is the fact that greenhouses today typically utilize external energy sources, such as heaters and fans, that require electricity and fuel. These energy costs can be discouraging limitations, and also present negative environmental impacts if fossil fuels are used. Although temporarily inhibiting, these challenges provide an open door for innovation to intervene and provide solutions!
Appalachian State University has been pumping out innovative greenhouse research for years. In 2006, research at the University was centered around using solar thermal collectors, water heat storage, a heat exchanger system fueled by biodiesel to heat greenhouses. In 2007, the University released a report for a SARE grant (Sustainable Agriculture Research & Education) on research it had been conducting regarding “affordable bioshelters.”
For the purpose of this project, “affordable bioshelter” is defined as a solar greenhouse that is economically competitive with hoop houses, having a payback period of five to ten years relative to the hoop. More broadly, the purpose of this project is to contribute to a lower fossil fuel input and a more localized agricultural system for the high south and other climates where greenhouses are heated… Currently, wintertime trucking of foods to cold climates consumes vast amounts of fuel. The lack of an affordable local alternative is an impediment to a stronger relationship between local farmers and consumers. (Hoepfl & Strauch, SARE Report, 2007)
This project was also funded by the Environmental Protection Agency (EPA), through its People, Prosperity, Planet (P3) Challenge. Appalachian State University returned to the P3 Competition in 2015, winning an initial $15,000 grant in 2014 and a second $75,000 at the close of the Challenge in 2015 for another research project titled “Biomass Greenhouse-Heating Systems to Extend Growing Seasons for Resource-Limited Farmers.” This most recent project focuses on utilizing three different forms of biomass to heat greenhouses: Heat exchange through a thermal compost pile, the production of biochar, and anaerobic digestion. This research can be found at BioShelter Heating | AppState.
Referenced above, a hoop house is an affordable growing structure that allows farmers to work within a more controlled environment without the more expensive costs of operating in a greenhouse. The challenge with hoop houses is that they are not externally heated, so during the winter time their growing power is limited to frost-hardy produce. Many farmers choose hoop houses as an option, and rightfully so, as they are affordable, convenient, and can extend the production season for many farmers.
Water | Thermal Storage
A simple and effective way to extend the season in a greenhouse is to use the thermal storage capacity of water. Large tanks or barrels of water placed into a greenhouse can absorb the heat of the sun during the day, storing this energy until the greenhouse air cools at night. The warm water then slowly cools and warms the greenhouse. The University of Missouri, through Bradford Research farm, constructed a Passive Solar Greenhouse in 2005. Part of the design included water barrels as heat storage. “The rule of thumb is 2.5 gallons/ft2 of glazing for season extension or 5 gallons/ft2 for all season.” So, depending on whether the greenhouse is designed to grow food year long (through the entire winter season) or merely allow for production past the fall frost and before the spring frost, water can be added to achieve those specific goals.
Passive Solar Greenhouses
A passive solar greenhouse is a compilation of multiple technologies that are geared towards one result: a greenhouse that functions all year long (or at least extends the growing season) without utilizing external energy sources. Many of the technologies referenced in this post are utilized in passive solar greenhouses, especially the practice of choosing optimal insulation and using water barrels as thermal storage. Passive solar greenhouses are worthy of special mention, though, because they are built very strategically to maximize the energy input coming from the sun. In northern latitudes this implies that they are built to maximize the amount of sun hitting the south-facing wall in the winter time. Much care is put into constructing these greenhouses to ensure that the materials are well-selected for their insulating properties. Many of these greenhouses include a back-up heating source in the event of extremely cold temperatures or other devastating weather events. In addition to Bradford Research Farm’s greenhouse at the University of Missouri, here is another look at how to design and construct passive solar greenhouses: Rob Avis, 2011.
Climate Battery | Earth Charger | Subterranean Heating & Cooling System
This incredible technology is quite intuitive. Capitalizing on the Earth’s ability to store heat, climate batteries use a small fan to pump warm, daytime air from the greenhouse into a manifold of pipes buried 4 feet deep. This air, by process of convective heat transfer, warms the soil, which acts as a storage bank for the heat. At nighttime, the process is reversed. Air is pumped through the manifold of pipes in the soil, warming on its journey. Then it is circulated through the greenhouse, ideally keeping the plants nice and toasty! Appalachian State University’s SARE research project in 2006 analyzed the efficacy of this technology and found that:
The sub-soil heat storage system known as the Subterrain Heating and Cooling System (SHCS) was shown to improve temperature condition and increase growth for soil plantings compared to a control greenhouse. It provided insufficient heat at night to dramatically elevate temperatures in an uninsulated greenhouse. It increased soil temperature 10F during March.
So although this innovative technology is useful and functional, the greenhouse requires insulation for a climate battery to be relevant and appropriate for meeting a farmer’s winter-time needs. Cere’s Greenhouse Solutions, based out of Colorado, provides consultation and equipment for the installation of a climate battery system.
Liquid Foam Insulation (LFI)
Bubbles! This technology utilizes a liquid foam substance and blower to circulate the LFI between a gap in the glazing (covering) of the greenhouse. As the liquid foam fills the gap, it provides an extra amount of thermal insulation. The foam is useful at night to help maintain the warmer inner temperatures of the greenhouse. During the daytime, the foam is emptied from the gap to allow the sunshine to enter the greenhouse once again. Appalachian State University also researched this technology in its 2006 project and found that although LFI was extremely effective at raising greenhouse temperatures, it was difficult to maintain and control.
A liquid foam insulated greenhouse stayed 14F above the control overnight for low electric costs, but had technical problems. This or another kind of full envelope insulation is needed to make best use of solar heat storage systems.
Biomass Powered Greenhouses
This label incorporates several different technologies with one common theme: biomass. There are many ways to be creative with organic matter and maximize its ability to generate heat.
Large, well-constructed thermal compost piles maintain temperatures of 130 -160 F for several weeks at a time. Pipes can be placed in the center of these piles to circulate water. The compost pile exchanges heat with the water, which is then circulated through the greenhouse. This is most effective when the pipes are run through the beds in the greenhouse, delivering heat directly to the roots of the plant. Any heat exchange system such as this will require a pump and maintenance to ensure that there are no leaks (as temperatures increase, certain materials can perform poorly and potentially disrupt the system).
Anaerobic digestion of organic waste is another potential source of heat, but requires a good amount of maintenance. In anaerobic digestion, organic matter is placed into an environment that lacks oxygen and is innoculated with anaerobic bacteria. These bacteria consume the organic matter and produce a gas which is about 40-50% methane. This gas can be captured and combusted for energy recovery. Additionally the conditions in the anaerobic digester must maintain temperatures above 95 F. This presents another opportunity for a heat exchange system. The anaerobic bacteria require consistent feed and a very specific environment, so utilizing this technology can be a bit more of a challenge. The amount of gas produced correlates directly with the health of the bacterial population.
Gasification of wood is another promising utilization of biomass. This process also produces biochar which is said to be a very beneficial fertilizer and carbon sequestering element in the soil. Rocket mass heaters can be used for this process, and are said to produce less air pollution then typical wood-fueled heaters. To my knowledge, research is currently being conducted to measure the efficacy of these heaters and to confirm the powerful soil-enriching qualities of biochar. Stay posted!
There are also ways to utilize biodiesel as a fuel for a heater, which can either heat water to circulate through the bench tops of the greenhouse or heat the air of the greenhouse (which is less efficient than directly delivering heat to the roots of the plants and the immediate air surrounding the plants).
An article published by Midwest Permaculture in 2013 summarizes 6 methods (some mentioned above) to create a year-round greenhouse. The article describes utilizing water as a heat storage medium, selecting the proper glazing for year-round insulation, LFI technology (soap bubble insulation), thermal mass rocket stoves for heat, wood gasification for heat and electricity (and biochar production), and also how to design structures with earth-friendly materials.
Many people find nature to be a spiritual oasis, opening the mind and heart to peace, calm, creativity and creating a space for connection and refuge. This is especially relevant in today’s Western society, where stress, hypertension, heart disease, and mental illness abound. Relief from stress and anxiety can be hard to come by, especially during cold winter months. Greenhouses provide a solution, not only to the challenge of growing food all year long, but to finding refuge and peace and creating a space for growth (personal and agricultural).
In “The DIY Greenhouse of the Future…,” an article published on The Plaid Zebra, this concept is explored with beautiful imagery.
Francis Gendron recently launched a DIY sustainable greenhouse guide that makes it possible for anyone to construct their own indoor garden-house, built entirely out of recycled and natural materials, and powered entirely by renewable sources.
Grants Available (United States)
Constructing a year-round greenhouse, furnishing it with plants and soil, and maintaining it seems like a daunting and expensive task. Certainly it can be. But, at Bradford Research Farms in Missouri, the passive solar greenhouse constructed in 2005 cost a total of $3,275 to construct. Given that a person can source waste materials (plastic, tires, spent lumber) for relatively cheap costs, and due to the open-source nature of many farm/technology domains, it is possible to construct a passive solar greenhouse made from local materials for a relatively cheap input cost. Additionally, for small farmers, there are grants available through federal and state programs. Visiting the SARE website, the National Resource Conservation Service website, and Grants.gov, and searching for grant/funding opportunities are excellent ways to explore the various funding opportunities that exist. Be creative in searching – for instance, energy-related grants are applicable to greenhouses because renewable energy sources are an excellent way to create sustainable greenhouses! There are also grants available that will aid in providing construction costs for implementing growing structures like hoop houses and greenhouses on-site. The more community-driven and innovative your ideas are, the more likely funding is to occur. Grants are awarded to organizations that spur community development and create lasting change. There are many opportunities out there – good luck!
What are your thoughts? Do you have any critiques, additions or ideas to contribute to this conversation about greenhouse technology? Please post them here!