Energy Analysis of the Closed Greenhouse Concept : Towards a Sustainable Energy Pathway
Abstract: The closed greenhouse is an innovative concept in sustainable energy management. The closed greenhouse can be considered as a large commercial solar building. In principle, it is designed to maximize the utilization of solar energy through seasonal storage. In a fully closed greenhouse, there are not any ventilation windows. Therefore, the excess sensible and latent heat must be removed, and can be stored using seasonal and/or daily thermal storage technology. The available stored excess heat can be utilized later in order to satisfy the heating demand in the greenhouse, and also in neighbouring buildings.A model for energy analysis of a greenhouse has been developed using the commercial software TRNSYS. With this model, the performance of various design scenarios has been examined. The closed greenhouse is compared with a conventional greenhouse using a case study to guide the energy analysis. In the semi-closed greenhouse, a large part of the available excess heat will be stored through thermal energy storage system (TES). However, a ventilation system can still be integrated in order to use fresh air as a rapid response indoor climate control system. The partly closed greenhouse consists of a fully closed section and a conventional section. The fully closed section will supply the heating and cooling demand of the conventional section as well as its own demand. The results show that there is a large difference in heating demand between the ideal closed and conventional greenhouse configurations. Also, it can be concluded that the greenhouse glazing type (single or double glass) and, in the case of the semi-closed and partly closed greenhouse, the controlled ventilation ratio are important for the thermal energy performance of the system. A thermo-economic analysis has been done in order to investigate the cost feasibility of various closed greenhouse configurations. From this analysis, it was found that the load chosen for the design of the seasonal storage has the main impact on the payback period. In the case of the base load being chosen as the design load, the payback period for the ideal closed greenhouse might be reduced by 50% as compared to using peak load. Thus, future studies should explore innovative combinations of short term and seasonal storage.Finally, several energy management scenarios have been discussed in order to find alternatives for improving the energy performance of the closed greenhouses. However, no specific optimal solution has so far been defined.
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