Greenhouse Heating System


The Greenhouse Industry will support most initiatives that may provide a practical and cost efficient alternative to the traditional means of heating greenhouse structures. The most common method of heating a greenhouse in a commercial setting is with the use of fossil fuels such as natural gas, fuel oil, etc. However, any alternative to exact a more efficient controlled interior environment suitable for plant production would likely be well received. It has long been known that burning biomass will generate energy that can reduce dependency on fossil fuel sources.

However, environmental and economical restrictions have impeded these developments within the commercial industry. Only with the most recent technological developments, can energy generation and extraction methodologies for a large commercial enterprise be considered as an economically viable alternative with a very positive environmental impact. Burning biomass, in itself, can be viewed as an inefficient use of energy; the fuel is consumed quickly causing a rapid energy release, much of which can be lost up the exhaust stacks.

In this undertaking, Agrilab has responded to the challenge to research a renewable and environmentally sustainable alternative by extracting the heat of decomposition from biomass over an extended period of time. This passive system will provide some measure of respite to the energy intensive greenhouse industry.

In simplistic terms, it is Agrilab's goal to develop an economical, environmentally friendly heating system, which will promote and sustain plant growth within a greenhouse (or any other structure) by generating, extracting, and distributing the renewable heat energy produced by microbial decomposition of organic biomass within a contained and controlled environment. The heat energy is to be generated in the biological decomposition process, and then transferred and distributed by the use of heat pipes to the interior of the greenhouse structure. The overall objective is to assist greenhouse operations in reducing dependency on natural gas as a primary energy source and to harvest the economic efficiencies of nature's own renewable resources. This same technology could, of course, be transferable to many other heating applications within the rural and agri-business communities, such as farm workshops, livestock facilities, military bases, facilities in the pulp and paper industry, etc.


Canada's greenhouse vegetable industry contributes 17,000 direct and indirect jobs,$3 billion in Canadian economic activity, and $1 billion in leading edge agricultural technology. Within the Leamington and Essex County area, a significant capital investment complete with its regional economic benefits, is highly apparent in the greenhouse industry. In fact, this area represents one of the highest densities in North America with some 1000 acres of greenhouse cover with an estimated property value exceeding $300 million. In the last 5 years, expansion has occurred at an incredible annual rate of 20%. Industry growth and value reflects the importance of its contribution to the domestic food supply and national economies. However, with an expected increase in the annual cost of heating these greenhouse structures reaching 200 - 300% of that of the recent past, alternatives to the traditional natural gas/fuel oil energy source must be found to enhance competitive advantage and ensure economic survival.

The cost of heating has become, most often, the determining factor in establishing the annual cropping programs for many greenhouse operations. This year, many greenhouse structures may not produce a crop because of unfavorable heating economics. As Agrilab continues to succeed in its effort to develop a good working model of a heat extraction/transfer/distribution system using a cost efficient energy source, it may well revolutionize greenhouse production activity on a global basis. The socio-economic benefits are rather obvious!!

In this undertaking, Agrilab constructed a test apparatus to be used on a continuing basis as a container to promote, monitor, and regulate the decomposition of various selected biomass materials. Heat energy generation properties from the biological decomposition process use a variety of organic matrixes while, at the same time, a heat transfer and distribution mechanism was customized to the application requirements complimenting the natural exertion of microbial activity. The optimum goal is to ascertain a readily available biomass material that will slowly decompose while it generates a substantial quantity of usable biothermal energy to be consumed in the elevation of the temperature in a separated confinement area. The operating environment for this decomposition process must be monitored and sometimes regulated to enhance heat generation performance and maximize biomass decomposition service lifetime. Agrilab designs and manufactures a unique heat transfer, retention and distribution system that can extract heat energy from a detached decomposing biomass pile to support an environment that will maintain and promote plant life within a greenhouse (or any other) structure.


In the process of composting, microorganisms break down organic matter and produce carbon dioxide, water, heat, and humus, a relatively stable organic end product.

Organic decomposition is essentially a natural, biological process that compares somewhat to the raising of plants or animals. The rate of composting, like the growth rate of plants or animals can be effected by many factors. Four key factors to establishing and maintaining active organic decomposition are:

a) nutrient balance 
c) temperature
b) moisture content
d) aeration

Nutrient Balance is determined largely by the ratio of carbon to nitrogen in the compost mix (C/N ratio). It is like balancing carbohydrates and protein in a diet. Bacteria, fungi and actinomycetes require carbon and nitrogen for growth. These microbes use 30 parts carbon to 1 part nitrogen. Composting is usually successful when the biomass contains 20 to 40 parts of carbon to 1 part nitrogen. However, as the ratio exceeds 30, the rate of composting decreases. As the ratio decreases below 25, excess nitrogen is converted to ammonia which is wasted into the atmosphere and results in undesirable odors.

Moisture Content of compost should ideally be 60 % after organic components have been well mixed. As moisture content exceeds 60 %, the structural strength of the compost deteriorates, oxygen movement is inhibited and the process tends to become anaerobic. Low C/N ratio materials putrefy when anaerobic. High ratio materials ferment. Both processes produce undesirable odors. As moisture content decreases below 50 %, the rate of decomposition decreases rapidly. A mixture of organic wastes that contains 60 % moisture feels damp to the touch but is not soggy.

Temperature increase which occurs during composting is a result of the breakdown of organic materials by bacteria, actinomycetes, fungi and protozoa. The temperature range can be from freezing to 180 F . Starting from ambient temperature, compost can reach 150 F in less than 2 days. Applying heat to compost from external sources serves no purpose; heat is generated from within the compost medium.

Aeration is a key element in composting. Proper aeration is needed to control the environment required for biological processes to thrive with optimum efficiency. A number of controllable factors are involved. Carbon dioxide is a product of the biochemical reactions that are part of composting. This gas must be removed from the compost micro-environment to avoid toxic concentrations that inhibit the process.

Under normal circumstances, the basic principles of composting are quite simple and adhering to them will result in an efficient and successful outcome. Composting has become an excellent way to manage certain wastes responsibly, prevent the wasting of a natural resources, and produce a value-added, inexpensive soil amendment product. Composting also generates another valuable resource that may be recaptured and re-used:

However, harnessing this energy source for commercial use such as greenhouse heating, presents new challenges to Agrilab. This form of energy is unlike any standard within the heat transfer industry. To heat a greenhouse structure from this energy source, it must be viewed in three separate components:

a) heat energy generation,
b) heat transfer, and 
c) heat distribution/use

Agrilab has an abundance of experience in heat transfer and, although challenging, this goal is achievable. Heat distribution and use within a greenhouse facility is well documented with much information and data available. However, modifications should be pursued to enhance heat retention and use within these structures to maximize the heat re-capture benefits.

The most critical and difficult challenge of this project comes in the heat energy generation phase. It has been proven that temperatures, in the best enhanced aerobic composting situations, can reach up to 180 F by intensive aeration (oxygen replenishment) on a continual basis; this methodology is commonplace in the production of compost as a growing media used in mushroom operations. These temperatures are a requirement for the safe destruction of any contained pathogens within the organic composting components. However, this particular method of composting may not be practical for the purpose pursued in this application because of the constant need to mechanically aerate by turning and fluffing the piles or windrows. This form of composting is very rapid, causing the components to be 'consumed' very quickly.

The underlying challenge for Agrilab in each case, is to establish composting systems that will function within the designed confinement criteria, presenting a consistent temperature range of 140 - 160 F, sustainable for a practical time frame of up to 20 weeks, while mitigating the negative effects of the generated by-products. Compost component selection, means of aeration, moisture content maintenance, and by-product management are all of great importance to the development of a satisfactory biomass heat generation system, which can present a suitable and affordable alternative to traditional heat energy sources, while demonstrating a positive effect on the environment. Further, engineering designs of the heat transfer and distribution systems are to be customized to the structural applications and parameters as per client needs. This technology is essentially transferable, enabling Agrilab to provide this service to a vast array of structural heating applications.

Note: The system described above has been submitted for patent protection and has currently been designated as 'patent pending' by the U.S. Patent Office.

In this undertaking, energy generation is the first and perhaps the most technically unpredictable variable to be studied. A number of biomass materials and mixtures were tested for biological properties with the primary focus on heat generation capacity and process longevity. The organic materials tested for greenhouse biomass energy generation consist largely of greenhouse waste materials and matrixes from crop production such as waste tomato leaves and vines. Energy generation, process longevity, response to various levels of biological culture catalysts were determined over a wide range of products in the formation of 'biomass recipes'. The goal is to customize a blend with available and compatible materials for specific applications. This testing was undertaken in a controlled environment to maximize biomass performance and mitigate the effects of any undesirable byproducts of decomposition such as odor, methane, ammonia, carbon dioxide, etc.

The normal duration of the heating process for biomass decomposition occurs within a 42 day time period, establishing a high temperature range of 130 - 150 degrees F. With very specific parameter definition of the biomass micro-environment within this test apparatus, Agrilab has extended the heating period for its 'recipe' biomass beyond 150 days at temperatures above 130 degrees F, while simultaneously extracting heat energy from the biomass: an extraordinary achievement!

The heat transfer testing consisted of the modification and customization of a series of heat pipes that remove the heat energy created in the natural decomposition of the biomass materials. Apparatus 'A' contains 2 separated chambers equal in size; one containing the biomass, the other empty to be heated by heat pipes from energy contributed by the biomass decomposition. The biomass/heat pipes system was challenged in extreme conditions by the addition of dry ice into the heated chamber; the response was observed and computer monitored to provide for the development of the most efficient energy transfer system. The passive and self-regulating nature of the heat pipe repeatedly demonstrated extraordinary compatibility with heat energy generation from the biomass decomposition process.

A very specific design of heat distribution system was employed in the greenhouse apparatus to distribute the heat throughout the entire greenhouse facility. The heat was extracted from the decomposing biomass (located in the pit adjacent to greenhouse) by means of heat pipes inserted into the sub-floor area where the heat is permitted to rise by convection to warm the internal atmosphere of the structure. The entire system functions without the use of any external energy source whatsoever!

In Energy Generation experimentation, Agrilab's 'recipe' biomass has surpassed, by a wide margin, the normal decomposition heating time period of 42 days before the biomass enters the cool down phase. By controlling the air and moisture conditions within the biomass environment, Agrilab has extended the duration of energy generation to almost 4 times the expected time period, while consistently yielding temperatures in excess of 130 degree F. Agrilab has established 'recipe' biomass mixtures that will decompose rapidly at very high (+160 F) temperatures, or slowly to provide a predictably consistent moderate to high (130 -140 F) temperature for up to 5 months.

In Heat Transfer experimentation, Agrilab has successfully modified and customized its heat pipe technology to suit the application of biomass heat extraction. The gentle, passive and self regulating nature of the heat pipe demonstrated an extraordinary compatibility with the energy generating biomass. When the biomass was challenged through the heat pipes (with extreme cold of dry ice), the biological reaction remained a constant because of the gentle nature of heat extraction by the heat pipe.

In the Heat Distribution study, it was determined that the heat pipes surrendered the biothermal energy extracted from the biomass into the greenhouse interior through the concrete block matrix, gently by convection. To retrofit into existing greenhouse water or steam distribution system, an array of heat pipes can be assembled to preheat the water supply.

Economic Impact:
Traditional heating sources in the energy intensive greenhouse industry have always represented a high percentage of the operating costs of vegetable production. In the recent past, the unit energy costs of fossil fuels have risen significantly, thereby rapidly eroding grower profitability. At the same time, millions of kilowatts of heat energy from organic waste decomposition can be recaptured and used as a valuable resource. It is projected that Agrilab's technique of biomass heat generation combined with heat pipe transfer technology functioning in a commercial greenhouse operation could, in some instances, reduce dependency on fossil fuel supplies by up to 70%.

For a typical commercial 10 acre greenhouse farm in Essex County, experiencing annual heating costs of $500,000, the projected return on investment for an Agrilab heating system, in an average weather growing season, is 2-3 growing seasons.

Environmental Impact:
The decomposition of organic materials is a process that exists in nature and occurs every day in the forest floors, farmers fields, and even in your garden. The materials projected for use in greenhouse structural heating through biomass decomposition, will undergo the same natural process wherever they may land.

However in Agrilab's process, the regulated decomposition occurs over a longer period of time, in a controlled environment and with the usual byproducts passing through biofilters to minimize the effects of nuisance odors, ammonia and methane. Because of the aerobic activity, if methane production occurs at all, the volume is minimal. Reducing dependency on fossil fuels diminishes the volume of harmful exhausts gases from fuel oil or natural gas boilers.

The Agrilab system can, in effect, reduce the overall waste stream by composting, reduce the volume of organic wastes entering landfills, and reduce the volume of gases produced by burning fossil fuels, which are believed to contribute to global warming.

A greenhouse waste product can become its own economical fuel source !!
Application Potential:

The possible applications of using energy from biomass decomposition are all but endless. From severe cold climates to a much more temperate region, this system will provide economic and environmental relief from traditional reliance on the world's diminishing fossil fuel supplies to any heating application conceived. Greenhouse structures, livestock barns, farm workshops, and even rural residential dwellings could be considered as logical applications for biomass heating. In Eastern Europe, many fodder rich but energy starved countries may be able to alter living standards by using this type of energy for greenhouse food production and shelter heating. Shelters in cold climates can provide areas for winter overnight truck parking, permitting engine shutdown, thus reducing atmospheric emissions. The forestry industry which produces a huge quantity of biofuel could heat many of its facilities with its own waste products without burning it. Manufacturing facilities, food processors, even in semi-urban areas can effectively take advantage of biomass heating.

Application options present almost limitless potential!!

Biomass is often referred to as an alternative energy source. Most often this material is burned in a controlled environment in what appears to be an efficient manner.

However, estimates have been made that up to 80% more heat energy is captured from the same volume of organic material when extracted as biomass decomposition, than is recovered when a rapid burn occurs.

Composting is an established method employed in the waste management field with the ultimate goal to reduce volumes of organic waste entering landfills while producing humus, a soil enhancement product. Few have successfully attempted to manage organic decomposition with the expressed purpose of energy generation and extraction. Agrilab has established some significant benchmarks in temperature generation, active residency time, and environmental controls in its efforts to date. Thousands of tonnes of quality biomass decompose in piles, on farm fields and in the forest each year; this biomass can be used as an economical alternative fuel source by capturing the heat of decomposition.

Agrilab has successfully extracted this heat energy from the biomass by employing heat pipe technology to heat a small greenhouse structure, its pilot project.

Agrilab continues its research efforts to modify and monitor all aspects of its heating system to enhance performance in heat generation, transfer, and distribution for consistency and reliability in field operations.

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