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The general objective of this research activity is to evaluate the economic feasibility and the performance of a (semi) closed greenhouse under nordic (northern) conditions in the east of Canada by the use of geothermal and heat exchangers.  This innovative concept will permit:

• Achieving an optimal control of the temperature and humidity in the greenhouse throughout the production season.
• Increasing the CO₂ concentration in the greenhouse during the period of strong solar radiation and as a consequence, the fruit output.
• Reduce the use of fossil fuels and increase the efficacy of energy utilisation (EUE) of the growing.
• Reduce the environmental imprint connected to greenhouse growing.

Greenhouse crop production is a very important segment of the Canadian agricultural industry with a farm value of $2 B and a greenhouse area of ~2000 ha. However, this very energy-intensive industry consumed more than 40 PJ of fossil fuels ($260 M, 12% of the total agricultural energy use in Canada, Statistics Canada, 2005) and released about 2 million tonnes of CO2 and other air pollutants into the atmosphere. Energy is primarily used for temperature control, reduction of air humidity, increase of light intensity and CO2 supply. With the sharp increase in energy prices over last few years, energy cost has become the largest cost component in greenhouse crop production (20-40%), reducing the profitability and severely threatening the sustainability of the greenhouse industry.

In the last 10 years, several strategies have been investigated to reduce use of fossil energy and improve the energy use efficiency (EUE) of greenhouse crops:

• new greenhouse cover materials and new structures
• better greenhouse insulation
• thermal screens
• heat placement and distribution methods
• intelligent climate control based on crop and microclimate monitoring
• temperature integration
• use of alternative energy such as solar, biomass, biogas and windmills.

Substantial literature has shown that the use of geothermal energy for greenhouse production, as well as recent developments of closed or semi-closed greenhouses, may contribute to significant reductions of the environmental footprint associated with this industry, and increase Canadian competitiveness by energy saving. In Canada, greenhouse production of soil-grown organic vegetables generates high humidity during the cold season due to substantial soil water evaporation. Consequently, energy cost related to air humidity control is higher for organic producers than conventional growers using soilless growing media.

Even though some geothermal systems were installed recently for greenhouse production, little is known about the real performance of these systems on a year-round basis. Because of low expertise for the greenhouse industry, most of the geothermal systems are not optimized in terms of design, exchange surface, air flow and temperature. Heat distribution within the organic crop and humidity control are also not optimized. The main objective of this activity is to study the efficiency of using open water/air heat exchanger (water droplet curtain) and geothermal systems to control air humidity and temperature. This system will then allow the closing or semi-closing of the greenhouse to increase the EUE via higher CO2 content during high light conditions (higher yield), prevent heat losses which occur when ventilating excess humidity (energy saving), protect plants from outside pathogens and pests (higher yield), and to heat and cool the crops with heat exchangers (energy saving).

More specifically, the goals of this project are to:

1. Reduce the environmental footprint related to organic greenhouse production by the use of geothermal energy
2. Study the impact of a semi-closed greenhouse on CO₂ level, VPD and plant performance (growth and yield)
3. Study the effect of using an open water/air heat exchanger (droplet curtain) to control temperature and humidity
4. Evaluate the economics of both technologies for a soil organic closed or semi-closed greenhouse.

Experiments will be conducted at two pilot commercial greenhouses to ensure immediate technology transfer and adaptation of our sustainable organic growing system to real life. At the first commercial site, L’Abri vegetal (2000 m²), a geothermal system has been installed recently providing 220kWh and a theoretical performance coefficient of 4.0. Characterization of the real efficiency of the system will be studied in the first year in order to improve its performance in the following years. At Les Serres Jardins-Nature, one of the leading North American soil organic tomato producers (1.3 ha) that also has its own in house R&D division, an innovative system using the heat of their nearby water table (2 m) combined with a water droplet curtain will be developed and validated during three growing seasons. This enterprise has been, since its start-up, looking for ways to reduce its impact on the environment, either through the choice of heating systems used or through the management of fertilization or irrigation. Being proactive, it first began to use residual energy from a neighboring pulp and paper mill, and since 2005 it is now assuring its heating through biomass combustion. True to its objectives it now is exploring other possibilities of reducing its impact on the environment. Linked to these technologies are economic advantages such as low operating cost, long life, flexibility, as well as sustainability. Results from this activity would determine if the semi- or closed greenhouses under Canadian growing conditions can answer the economical demand of energy saving, the reduction of GGE and yield increase.

• [PDF - 31 kB]
  • Canadian Organic Science Conference. 2012
• [PDF - 3.6 MB]
  • The Canadian Organic Grower. 2012

• • Acta Horticulturae (2008) 801: 49-62
• • Acta Horticulturae (2008) 801: 1355-1362

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