Study Of Pneumatic Ventilation-window Opener And Temperature Control System For Intelligent Greenhouses

The natural ventilation widely used in greenhouse has advantages of saving energy and reducing expense, but it is difficult to be managed. For China lack in energy source, it is significant to study roof and side vent opener, principle of natural ventilation and position control system of vent opening.Natural ventilation equipment includes roof-vent and side-vent opener. Based on types of greenhouse and its region, ventilation openers are selected. At present, almost all greenhouses apply gear-rack roof-opener driven by electric units. Research of pneumatic roof-vent opener is in initial stage. Although foreign experts had made deep research for natural ventilation model, they did not compare roof ventilation and combined roof and side ventilation, and did not use these models to greenhouse climate control. Developing prediction and analysis model of temperature and applying it to a natural ventilation multi-span plastic greenhouse equipped with insect-proof screen, determining opening height of ventilation window according to environment parameters and plant needs, and developing position control system for greenhouse pneumatic roof-vent opener are keeping ahead in horticulture.To get rid of the disadvantages, such as slow response, easy to rust and short life span of traditional gear-rack mechanism driven by electric units, pneumatic roof-vent openers for multi-span plastic and glass greenhouse were designed. In order to provide information for climate control of greenhouse, a model was developed to predict the variation of air temperature in the naturally ventilated greenhouse equipped with insect-proof screen. Used pulse-width modulation and fuzzy technology, position control system of roof-vent opener was simulated and developed. Research contents are as follows:(1) Based on statics analyzing of pneumatic four-connecting lever roof-window mechanism applied to multi-span plastic greenhouse, optimizing model taking for minimal pneumatic cylinder output as object was established. For the first time, intensity requirement, installation error, boundary and other restrictions were considered in the optimizing model. Pneumatic cylinders were selected according to optimizing results. Checking showed that the present system meets stability requirements. The optimum programme can be used to design four-connecting lever pneumatic roof-window mechanism of all kinds of multi-span plastic greenhouses by changing load and structure parameters. The equipment cost and running effect were compared with a traditional gear-rack one. Running the new system indicates that the opening angel increase by 20° , electricity energy cost decrease by 20%, and response time is faster compared with the traditional one.(2) A track-type pneumatic roof-vent opener applied to multi-span glass greenhouse was innovated and designed. Load of roof vents was calculated based on the greenhouse design standard of USA. Relationship of roof-vent opening, output force of cylinder and forces imposing on push rod with displacement of piston were analyzed by kinetic and kinematic dynamic simulation. The cylinder stroke and piston diameter were determined on the basis of analyzing and calculating. Results indicate that there exists a maximal opening as for a specific pneumatic roof vent opener; requisite thrust of cylinder is markedly influenced by horizontal force between link rod and push rod, whereas friction influence is...