Solar Energy Utilization in Closed Greenhouse Environment
Abstract
Closed greenhouses can in principle be free of fossil fuel use if excess solar energy gained is utilized through seasonal storage. In the fully closed greenhouse, there is no ventilation, and the excess heat in the summer can be stored using proper thermal storage system (TES). It can then be utilized later in order to supply heat load to the greenhouse as well as to neighbouring buildings. Although higher amount of solar energy can be harvested through fully closed greenhouse, in reality a semi-closed greenhouse concept is more common. In the semi-closed greenhouse, a large part of the available excess heat will be stored through TES. However, ventilation can still be integrated with TES in order to use fresh air as a rapid response indoor climate control system. The efficient climate control should be integrated with a proper insulation structure in order to minimize the heat loss from the greenhouse and facilitate an accurate indoor climate control system. Based on former studies, it is shown that the grower can control precisely the level of CO2 in the closed greenhouse, while in open greenhouses; around 90% of supplementary CO2 is lost due to opening of ventilation windows. This paper presents comparative analysis of heating and cooling demand for an ideally closed greenhouse and a closed greenhouse with infiltration considered. Furthermore, the effective utilization of excess solar energy through the integration of seasonal and short term thermal energy storage is assessed in a first basic design.