Study on the discharge coefficient of wind-driven naturally ventilated Chinese solar greenhouses

The Chinese solar greenhouse(CSG)is a prevalent feature in agricultural practices within China.Nevertheless,the regulation of natural ventilation within this architectural structure remains suboptimal.Consequently,the development of a natural ventilation model becomes imperative for the effective management of the greenhouse environment.Of particular significance within these models is the consideration of the discharge coefficient as a pivotal parameter.Conducting a multi-case investigation into the variable-dependent discharge coefficient is crucial for both practical application and model advancement.This research delved into the impact of various factors,including the upper-lower vents area ratio(A_(up)/A_(low)),vent-greenhouse area ratio(A_(low)/A_(greenhouse)),lower vent position height(h/H),the incident angle of the external wind,and altitude,on the discharge coefficient(C_(d))of CSG.A CFD model was developed for a scaled CSG with validation conducted through field experiments and wind tunnel tests.Results indicated a 61.6%reduction in C_(d)on average corresponding to an 80%decrease in A_(up)/A_(low).C_(d)levels remained consistent following the attainment of an A_(up)/A_(low)ratio of 1.0.Besides,there was an average increase of 52.5%in C_(d)levels for every 0.09 decline in h/H,attributed to the blocking effect of the cover.Moreover,the ventilation rate and the pressure coefficient difference were utilized to construct a model of C_(d)pertaining to greenhouse design and ventilation operation,exhibiting a notable accuracy level of R^(2)=0.95.Furthermore,the blocking effect of higher h/H was relieved as the incident angleθdecreased under the windward conditions.The increase in A_(up)/A_(low)and the decrease in A_(low)/A_(greenhouse)were identified as crucial factors contributing to the growth of C_(d)under leeward conditions.Ultimately,the high-altitude environment led to a rise in C_(d)levels in contrast to the low-altitude region.The increasing rate of C_(d)correlated positively with A_(low)/A_(greenhouse)and h/H initially,but exhibited a decline once A_(low)/A_(greenhouse)reached 0.036,remaining stable thereafter once h/H reached 0.18.In summary,a comprehensive examination of the discharge coefficient of CSG was undertaken,addressing a significant knowledge deficiency and laying the groundwork for advancements in the natural ventilation model and the intelligent control system for CSG.

Analysis of solar radiation changes in Chinese solar greenhouses with different roof structures based on a solar radiation model

Chinese solar greenhouses(CSGs)are important agricultural production facilities.Under non-artificial heating conditions,solar radiation is the only CSGs energy source.It is highly important to optimally obtain solar energy in greenhouse construction and production.In this study,a solar radiation model for solar greenhouses was adopted to explore the quantities of solar radiation in greenhouses considering different front roof forms and angles.Herein,the solar radiation amounts corresponding to five roof forms,namely,double-section arc,parabolic,oval,arc,and linear roofs,are compared and analyzed during the four solar periods(beginning of spring,vernal equinox,beginning of winter,and winter solstice).It was found that the solar radiation of oval roof greenhouses on the ground was the largest and was 4.44%-23.68%higher than that of parabolic roofs.In addition,the cumulative sum of light on the linear roof greenhouse wall is also the largest and was 6.02%to 12.08%higher than the parabolic roof greenhouse in the four solar terms.Moreover,the solar radiation in CSGs was compared with front roof angles of 25°,30°,and 35°.It was observed that the solar radiation amount gradually increases with increasing angles.Notably,the variation at an angle of 35°influences the solar radiation of the paraboloidal CSGs ground and elliptical CSGs north wall to the greatest extent,which increased by 8.23%and 12.74%,respectively.This study confirms the role of front roof form and inclination angle in enhancing the greenhouse solar radiation level.

Development and test verification of air temperature model for Chinese solar and Spainish Almeria-type greenhouses

Growth can be defined as an increment in biomass or an increment in weight or height of the organs of the plant influenced by physiological processes.Many of these processes have their limits genetically determined,but climate and irrigation play an important role.Because of its importance,microclimate has been extensively studied in the modeling as a surrounding condition which is imposed by the exterior climate.The main objective of this work was to develop a temperature model based on the energy balance dynamics at two different greenhouse locations-South-eastern Spain and Northern China,and the traditional structures of Chinese solar greenhouse and Almería-type multi-span greenhouse were taken into account.The final model was developed by combining the external conditions,the actuator influence and the crop growth,where the temperature is influenced by soil,crop,cover,actuators,back wall and greenhouse geometry.The model took into account the energy lost by convective and conductive fluxes,as well as the energy supplied by solar radiation and heating systems.The soil and the back wall are the main media for energy storage.The temperature dynamic was determined by a physical model,which considered the energy balance from a holistic point of view-as a sub-model for a customizable interface among the external climate,the plant and the greenhouse system.The influences of different subsystems included in the temperature model were analyzed and evaluated.The results showed a high R^(2)value of 0.94 for Beijing and 0.95 for Almeria,and the average error was low,of which the MAE and RMSE were 0.71 and 1.365 for Almeria and 0.62 and 1.102 for Beijing,respectively.Thus,the model can be considered as a powerful tool for control design purposes in microclimate systems.