The Energy Strategy 2020 of the European Commission calls for increased use of renewable resources in the energy system, thus pushing the technology of wood biomass system for space heating of the greenhouses, since this resource is considered as 'greenhouse gas' (GHG) neutral when converted to heat, excluding the GHG generation during harvesting, transportation, and pre-processing of raw materials. The Italian greenhouse vegetable industry is an important sector that requires thermal energy as much as 0.74 Mtoe, derived mostly from fossil fuels, which corresponds to 2 MtCO 2 emissions. While this is obvious, the quantification of the effect as demonstrated here is of great interest to growers, and is essential for the development of the second part of the system. Relaxing the temperature and humidity bounds decreases the energy input to the greenhouse. The prominent role of the bounds was clearly demonstrated. This potential was related to the definition of lower and upper bounds, less natural ventilation at colder days, and more natural ventilation and less heating at warmer days. It was shown that over twelve selected days, distributed over the entire year, the energy saving potential as compared to the actual grower’s practice is substantial. A relatively simple crop transpiration model was validated separately, with very good results. The underlying dynamic model of temperature and humidity, based on known physical principles and parameters, compared very well with unique, year round high frequent data from a commercial rose greenhouse.
By giving the grower the lead in defining the bounds, the method stays as closely as possible to the grower’s daily practice and experience, and no crop production models and market prices are needed. A dynamic optimization tool based on optimal control theory was used to obtain time trajectories of the energy flux that minimizes total external energy input over the year, while maintaining greenhouse air temperature and humidity between grower defined bounds. The current paper describes the energy minimization part. A novel management system is proposed, consisting of an energy input minimizing module, and a module to realise the determined input with the available equipment.
In a modern greenhouse there are a number of alternative systems that can be deployed to control the climate, and the choice what to use and when is not easy for the grower.
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