Crop based climate regimes for energy saving in greenhouse cultivation

Key words: Biocides, cut chrysanthemum, Chrysanthemum grandiflorum , CO 2 , crop photosynthesis, DIF , energy saving, fungal diseases, humidity control, plant quality, simulation model, stem elongation, temperature integration.Sustainability is one of the major aims in greenhouse horticulture. According to agreements between the Dutch grower association and the government, energy consumption and the use of chemical biocides have to be reduced. More advanced greenhouse technique is being developed to reach the target to decrease the energy efficiency-index by 65 % between 1980 and 2010. However, this could also be achieved with existing technology by using more advanced climate regimes. The present thesis aimed at that, through designing and analysing climate regimes while employing existing climate control possibilities. Theoretical temperature and humidity regimes were designed to decrease energy consumption and a photosynthesis maximisation procedure was implemented to maximise growth.The basis for a crop gross photosynthesis model for control purposes was created. Crop photosynthesis models were evaluated at conditions expected to occur with more sustainable climate regimes. It was shown with experimental evidence that theoretical assumptions on the temperature - CO 2 effects in a crop that are based on theoretically models scaling up leaf photosynthesis to the crop level are valid and that simplified existing models could be applied up to 28 ° C. With higher temperatures new designs are needed and this can probably be achieved with an improved stomata-resistance model.The well known temperature integration principle was modified with two nested time-frames (24-hour and six days) and a temperature dose-response function. In a year round tomato cultivation, energy consumption was predicted to decrease with up to 9 % compared to regular temperature integration.The potential for energy saving with temperature integration is limited by humidity control when as usual fixed set points are maintained, because it counteracts temperature integration. Vents open at lower temperatures and heating is switched on at higher temperatures than required for optimal effects of temperature integration. A new approach to control relative humidity on the underlying processes (crop growth and development, plant water stress, calcium deficiencies and the major fungal diseases) by controlling relative humidity through maximum leaf wetness duration, minimum transpiration and transpiration integral was designed for cut chrysanthemum. This idea is based on earlier formulations to use set points for transpiration. In the current approach, general rules were formulated. From that, a control regime was designed. Simulations showed that with this humidity regime, yearly energy consumption could be reduced by 18 % (compared to a fixed setpoint of 80 % relative humidity).When the two climate control principles, modified temperature integration and process based humidity control, were merged, annual energy consumption was predicted to decrease by more than 33 % and cut chrysanthemum plant dry weight increased with 39 % in experiments compared to a normal climate regime.Cut chrysanthemum was used as a central crop. Here, short compact stems is one of the main quality aspects. This is commonly controlled with chemical growth retardants. An alternative is to control temperature according to the DIF concept (difference between average day and average night temperature). A negative DIF value decreases stem elongation. Therefore, temperature integration without DIF restriction was extensively compared to temperature integration with DIF restriction. Energy consumption with different settings was quantified. It was shown that an optimisation problem existed in spring and summer. For that purpose, a joined temperature integration and DIF regime over several days was designed and tested. The use of an average DIF over several days rather than a DIF within 24-hours was proposed. In times and climate regions when cold and warm days interchange, this approach can increase energy saving and decrease final plant stem length simultaneously. This however, was a compromise. An optimisation problem between the two regimes aiming at sustainable greenhouse horticulture remained (less energy consumption versus reduction in application of biocides). This can only be solved when detailed models for crop quality, development and growth will become available.The regimes could be applied in commercial greenhouses with only little adjustment. The only additional expense is a computer functioning as set point generator, and a suitable interface with the existing climate computer. In addition, the achieved degrees of freedom for two main states (temperature and humidity) form a promising perspective for future optimal greenhouse climate control. The regimes, however, were based on many arbitrary assumptions. More research is needed for parameterisation.