Comparison of solar transmittance through a small single-span greenhouse covered by diffusive and clear films
This study was conducted to clarify, as basic information, the difference in solar radiation in greenhouses used widely throughout Japan covered by diffusive film and clear film (ethylene-tetrafluoroethylene copolymer, Fluororesin; AGC Green-Tech Co., Ltd.). Global and diffused solar radiation (global solar radiation is direct solar radiation plus diffused solar radiation) were measured to compare the transmittance characteristics of these films. Each 6.0-m-wide greenhouse had 1.8 m eave height, 3.0 m ridge height, and a 9.0-m frontage. According to the films' manufacturer, the global solar radiation transmittance of each film is 90%. In each greenhouse, to investigate whether solar radiation is increased by reflection closer to a surface covered with film, a solar radiation sensor was set at equal intervals on the north side, the center, and the south side. Variation of the three measurement results was less for solar radiation using the diffusive film than that using the clear film. Comparison of solar radiation effects on the clear film and diffusive film on a day with high direct solar radiation revealed that the overall solar radiation for the clear film became higher than that for the diffusive film; the difference between them reached approximately 10%. In contrast, when the proportion of diffused solar radiation was high, the solar radiation for the diffusive film was higher than that for the clear film.
Tamaki, M., Usui, T. and Takakura, T. (2018). Comparison of solar transmittance through a small single-span greenhouse covered by diffusive and clear films. Acta Hortic. 1227, 213-220
diffuse solar radiation, direct solar radiation, reflection, solar radiation sensor