Incorporating Evapotranspiration of Plants in Thermal Modelling of Greenhouses in Cold Regions

Abstract

The energy consumption of greenhouse in cold regions, especially for the space heating, is still large and needs to be diminished either by reducing heat loss or by increasing the percentage of renewable energy usage. In order to predict the performance of different energy-saving designs, a greenhouse model with better accuracy and reduced complexity is needed. The main objectives of this paper are: 1. give a comprehensive review about the energy-saving design and operation strategies of greenhouses from previous studies. 2. provide detailed descriptions about important parameters of plants that should be used in greenhouse modelling. 3. develop a simplified greenhouse modelling method. 4. test three advanced design concepts: insulated north wall, cyclic lighting, transparent and vertical ceiling. The concepts and some other background information of plants’ parameters are given, and the relationships between these parameters and greenhouse modelling are explained. Before building the mathematical models, the thermal networks were simplified by dividing a greenhouse into three kinds of areas: middle, edge, and corner areas. The corner areas were not modelled because of their small proportion. When compared to the conventional ways of doing greenhouse modelling, the difficulty of the new modelling method is diminished by dividing a complex greenhouse thermal network into simpler subnetworks, which can be combined to form a complete network. In addition, the accuracy of new modelling method is also higher, since the interior air is modelled in more than one control volumes in middle and edge areas within a greenhouse, and the air node is separated from the plant node. The modelled results showed that the insulated north wall gave rise to a significant increase in air temperature (around 3.5 ℃) and resulted in greatest thermal energy saving.