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Optimization of a non traditional cooling and dehumidifying method for a semi-closed organic tomato greenhouse

Activity summary

Canadian greenhouse production requires rigorous climate management and systems control, specifically temperature and humidity, in order to achieve high performance. In northern climates, the use of tightly sealed greenhouses with the aim of reducing energy loses leads to increased humidity in the greenhouse environment. To reduce this moisture, growers must ventilate the greenhouse to dehumidify, which can consume as much as 10% of total heating energy. However, dehumidification by natural ventilation has a significant disadvantage, as it increases heating costs. Nevertheless, when dehumidification is assured by using a heat pump, energy savings in the vicinity of 30% can be achieved ().

The objective of this activity is to develop an energy efficient system and a better understanding of the optimal climate management strategies for greenhouses when using a fan coil and heat pump as cooling and dehumidifying methods in a semi-closed greenhouse.

The main challenge in the optimization of climate control in greenhouses under semi-closed and closed environments is to balance the total cooling and dehumidification capacity to be equivalent to the heat and excess moisture present at a given time in the greenhouse, in order to remove this excess energy and humidity.

We have found that non-traditional cooling and dehumidifying systems, i.e. pumping water from a high water table, was sufficient to cool and dehumidify the greenhouse during high solar radiation levels, thus allowing the maintenance of high carbon dioxide levels in the greenhouse and stimulating photosynthesis. The previous production results are promising, as it was shown that a yield increase of ~6 kg/m² was reached when using the cooling system, compared to previous harvest years. This represents an increase of 15% in yields. During Organic Science Cluster II, more research is required to conclude the agronomic gains of the technology. As well, the technology must be optimized to run efficiently in order to reduce its energy requirements.

In order to be able to cool and dehumidify a larger scale greenhouse, it is necessary to find a method that is more water efficient. The use of a geothermal pump is to be considered. The geothermal pump can be used in different ways, and so the different options will be analyzed and the optimal use will be selected for the project.

This is the first study on semi-closed greenhouses in Canada in regards to organic crop production in soil. The research will stimulate photosynthesis by improving carbon dioxide injection, will improve yield and quality by improving the micro-climate in the greenhouse, and will lead to a better understanding of its effects on crop production. A better understanding of the specific agronomic gains that semi-closed greenhouses can deliver in a northern country is of high interest and financial value for the organic greenhouse market.

Materials and Results to Date

• • Acta Hort (2014) 1037: 611-616
• • Acta Hort (2014) 1037:237-241

• Geothermal and organic vegetables: Abri végétal

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