Modeling and control of CHP generation for greenhouse cultivation including thermal energy storage

In recent decades, greenhouse energy consumption has been the object of a substantial literature. Attention has also been paid to the modeling of greenhouse climate simulation and energy sources to evaluate energy saving options. However, such models are not readily available in the literature. The goal of this work is therefore to propose an open modeling framework capable of simulating the complex interactions and energy flows relative to such systems. A detailed dynamic model of a greenhouse describing the indoor climate and the heating system components was implemented. A dynamic tomato crop yield model was also implemented to account for the effects of the indoor climate on the harvested dry matter. The models are written in the Modelica language, are released open-source and are run within the Dymola simulation platform. The use of the proposed simulation platform is then illustrated for a particular case. The limited electrical load of greenhouses implies an excess of electricity generation when using CHP units, which have a power-to-heat ratio close to one. In this work, the addition of a heat pump is proposed to foster electrical self-consumption. A control strategy is designed to optimize the operational cost of the system. The system includes thermal energy storage, which acts as a buffer and allows minimizing the electricity sold back to the grid. Performance-based models for each generation unit and the storage unit are developed. Results show that the gas consumption was reduced by 25%. The heat pump generated 25% of the thermal load, the rest being generated by the CHP. Only 42% of the generated electricity is sold back to the grid, 57% being consumed by the heat pump. In conclusion, the heat pump and the thermal energy storage significantly improve the self-consumption level and thereby reduce the system operational cost by 9%.