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Optimal control of humidity can reduce energy consumption in greenhouse nurseries

Commercial horticultural greenhouses in Denmark have in recent years been good at saving energy and in this way protect the environment from emission of greenhouse gases. Scientists and the industry are now joining forces to develop technology based on knowledge of plant physiology to further reduce energy consumption through the optimal control of humidity.

[Translate to English:] Ved at optimere fugtstyringen i væksthuse kan der spares yderligere på energien. Foto: Flemming Nielsen

When you put the teeth into a Danish tomato or decorate your coffee table with a Danish potted rose, you consume products created under glass in Danish commercial nurseries. In Denmark it is necessary to cultivate products such as these in climate-controlled greenhouses, because the Danish climate has many cool and dark days during the year. But there are problems associated with this type of production.


The use in greenhouses of advanced climate control and good insulation creates the optimum lighting and temperature conditions for the plants. The dilemma is that this may also create moisture, which is removed by using more energy than necessary for heating. This is a waste of precious energy. This is a problem that scientists from Aarhus University will help to solve.


- In a normal intensive production of greenhouse plants that uses artificial lighting and highly insulating thermal screens, the humidity is regulated by heating and by the opening of windows. The result is a high consumption of electricity and heat. The problem is that the control is preventive – in other words before the need actually arises – to avoid the precipitation of dew in the humid zones in the greenhouse, even if you shortly after will reach a lower humidity anyway, explains Associate Professor Carl-Otto Ottosen from the Department of Food Science at Aarhus University. He leads a project in collaboration with the University of Copenhagen, the nursery Knud Jepsen A/S and manufacturer FlexTechnic to develop a technology for the optimum control of moisture based on knowledge about plant physiology.


Several approaches to energy savings

In most greenhouse nurseries between 25-35 percent of the annual energy consumption is used for dehumidification to prevent fungal attacks. The humidity is due to evaporatranspiration from soil and plants. The process moves water to the air and is affected by temperature, humidity and light.


- This means that late in the afternoon and at night there are often critically high humidity levels, which automatically trigger an energy-intensive climate regulation. There can also be periods of the year when the humidity outside is very high and it would not be possible to regulate the humidity in the greenhouse without heating it, says Carl-Otto Ottosen.


Much of the energy can be saved by using a combination of methods adapted to different plant species and systems installations. One way is to reduce plant transpiration using active climate control with existing climate methods. Another approach is to assess the different dehumidifying methods and ventilation systems in both practical and economic terms. They can be passive systems or they can recapture part of the energy used for humidity management.


The scientists involved in the project will additionally develop models that predict the times and periods when the humidity actually reaches a level where it has to be reduced. This requires knowledge of how plant stomata respond to combinations of climatic conditions; this is knowledge that scientists at Aarhus University have accumulated from previous experiments.


Knowledge put to practical use

The project partners’ combination of research knowledge, technical knowledge, practical experience and close contact with the horticultural industry ensures that the results can be implemented broadly and effectively.


- We expect that a reduction in the consumption of energy and fungicides of at least 10 percent can be achieved, with minimal risk to the horticultural industry. This will also strengthen innovative and technological development. It will be a gain for both the individual nursery, the environment and the climate, says Carl-Otto Ottosen.


The project has a total budget of 12 million DKK with 7.6 million DKK of this funded by the Green Development and Demonstration Programme of the Ministry of Food, Agriculture and Fisheries over the next two years.


For further information please contact:

Associate Professor Carl-Otto Ottosen, Department of Food Science, email: coo@food.au.dk, telephone: +45 8715 8373, mobile: +45 2290 3105