Yearly numerical evaluation of greenhouse cover materials

• Published in: Computers and electronics in agriculture 2018-06, Vol.149, p.54-70
• Main Authors: Baxevanou, Catherine, Fidaros, Dimitris, Bartzanas, Thomas, Kittas, Constantinos
• Format: Article
• Language: English
• Subjects: CFD; Cover materials; Greenhouse; Radiation
• ISSN: 0168-1699; 1872-7107
• DOI: 10.1016/j.compag.2017.12.006

•Assessment of cover material performance for naturally ventilated tunnel type greenhouse.•Development of CFD model, modeling of solar radiation in four wave length bands.•Modeling the crop as porous materials considering the optical properties in all wave length bands.•Unsteady simulation of aerodynamic, heat and radiation transfer, for 8 characteristic days along the year.•Cover materials’ evaluation in terms of temperature and available in PAR in plants level. The greenhouse internal microclimate, and consequently the plants growth, is formed from the combination of available solar radiation and ventilation. Transpiration and photosynthesis are affected by the PAR levels, as well as by the temperature, the wind velocity, and the air humidity etc. factors that vary along a day and along a year. The appropriateness of cover materials in a greenhouse depends on the crop as well as on the season of the year. Cover materials with high transmissivity in Photosynthetically active radiation (PAR) spectrum are desired during the winter but require significant ventilation during summer. Conversely covers with low transmissivity reduce the cooling requirements during summer but may prevent appropriate PAR to reach the plants during the winter. Consequently the evaluation of cover materials performance should be done along the whole year. In the present work the performance of four cover materials namely: Three-layer co-extruded film (3L), Ethylene vinyl acetate film (EVA), Thermal polyethylene film (TPE) and Rose Polyvinylchloride-based fluorescent (VPVC) were examined in terms of available PAR, temperature and air velocity in the plants’ level, for a tunnel type tomato greenhouse with side openings sited in the Central Greece. In order to evaluate the importance of the above mentioned parameters, the Ansys Fluent Computational Fluid Dynamic (CFD) code was used for a 2D simulation of transport phenomena inside the greenhouse like, the aerodynamics and the heat and radiation transfer in four wave length bands (Ultra Violet (UV), PAR, Near Infrared Radiation (NIR) and Infrared Radiation (IR)), using the method of finite volumes. The solar radiation was modeled with the Discrete Ordinates (DO) model and the daily variation of external solar radiation was introduced via User Defined Functions (UDFs) written in source code form. Plants were approached as porous materials. Unsteady simulations concerning eight characteristic days of the year (equinoxes, solstices and fo