Design principles and functions of glass greenhouses

Due to the low thermal inertia of the covering layer and enclosure structure, as well as the high transmittance of glass, the distribution of indoor thermal environment is well coupled with the external environment in a glass greenhouse. Therefore, studying the spatiotemporal distribution of greenhouse thermal environment under different climatic conditions is of great significance for controlling and optimizing crop growth environment, scientifically and reasonably configuring greenhouse facilities and irrigation systems, optimizing greenhouse structural design and ventilation layout. Simply put, the function of a glass greenhouse is insulation (for rooms that require insulation in planting or cold weather, etc.). The principle of a glass greenhouse: The main form of solar radiation is shortwave radiation (ultraviolet radiation with shorter wavelengths). When it reaches the ground, it generates heat that becomes longwave radiation, while glass can block the entry and exit of longwave radiation, causing the indoor environment temperature to continuously rise.

The glass greenhouse adopts an environmental control system, which has the functions of distributed control system collection, storage, communication, and processing, and compensates for the shortcomings of large, expensive, and inconvenient application of distributed systems. Therefore, it has been widely applied in industrial and agricultural automation systems. At present, the environmental monitoring and control of developed glass greenhouses in the world mainly rely on computer monitoring and control systems.

[System Functions of Glass Greenhouses]

At present, greenhouse automatic control systems can be divided into digital control instrument control systems, controller control systems, and computer control systems. Choosing different control systems can achieve single control and multiple comprehensive control of the greenhouse environment.

The computer control system for a glass greenhouse consists of hardware facilities and software systems such as a greenhouse controller, outdoor weather station, communication unit display, and output unit. Monitoring, data display, and collection of indoor and outdoor environments can be achieved through sensors; Through a computer integrated monitoring system, precise control can be carried out on the skylights, side windows, sunshades, micro fog, wet curtains, heaters and other equipment of the greenhouse based on changes in indoor and outdoor climate conditions, completing functions such as ventilation and cooling, dehumidification, humidification, shading and insulation, automatic heating, air circulation, light supplementation, scientific irrigation, fertilization, detection and adjustment of wind, rain and snow, pH value, EC value, fault alarm, etc. Provide an easy to manage and easy to operate method for greenhouse planting.

With the development of computers, the computational simulation ability of computational fluid dynamics software has been improved, bringing changes to the field of design. The application of computational fluid dynamics methods in greenhouse research has broadened the thinking of greenhouse structural design, and has good research value and practical application prospects.

[Application Principles of Glass Greenhouse System]

We analyzed the indoor environment model of a glass greenhouse under mechanical ventilation conditions, and studied the main factors that affect the indoor environment of the greenhouse. We reasonably solved the problem of selecting the computational domain for CFD numerical simulation, selecting the form of flow field control equations, turbulence and radiation models, and solving the control equation. We conducted cooling experiments on the greenhouse under mechanical ventilation conditions in summer, The temperature distribution in the vertical and horizontal directions of the greenhouse and the meteorology of the surrounding environment were tested to provide data sources for the parameter setting of the CFD model. Based on experimental analysis, the CFD validation model was established and the simulated boundary conditions were set. CFD numerical simulation was conducted on the greenhouse environment under experimental conditions to compare the simulation results with the measured results, verifying the effectiveness of the simulated boundary conditions and the effectiveness of the CFD model.

On the basis of the above research, the key links in the greenhouse cooling system, such as the setting of internal shading, the installation degree of fans and wet curtains, the degree of wet curtains, and the coordinated configuration of greenhouse length, were studied. With the goal of greenhouse cooling, the optimization design of the overall structural parameters of the greenhouse was preliminarily explored, providing a theoretical basis for the optimization of greenhouse structure.