Reduction in the Solar Radiation Transmittance of Greenhouses Covered with Plastic Films

Abstract

The reduction in solar radiation transmittance(SRT) because of dust and other foreignmaterials was experimentally tested in two types of greenhouses with the intent to obtain basicdata for establishing maintenance and management guidelines for greenhouse cover materials. The test results in the greenhouse in Gyehwa-do estimated the amount of removed dust at 16.8–1,021.6 mg·m-2(average: 520.7 mg·m-2), and the dust amount varied widely with the measurementpoints. The SRT measured in triplicate before and after dust removal ranged 68.5–80.9% and80.9–87.2%, respectively; thus, there was an improvement in SRT by about 8.1% after dusting. In contrast, the greenhouse in Gyeongsang National University did not exhibit great fluctuationsin the coefficient of determination(correlation coefficient) regardless of the daily total, average,or maximum horizontal surface radiation; the SRT gradually decreased over time. The SRTincreased or decreased, showing clearly different patterns in summer and winter half years, asdid the coefficients of determination(0.468–0.828). Dust was measured to be in the range 747.1–983.1 mg·m-2(average: 840.1 mg·m-2), without great differences between the measurement points,unlike in the case of the greenhouse in Gyehwa-do. The SRT measured before and after thedust removal ranged 73.0–80.5% and 81.0–88.6%, respectively, showing an average improvementof about 7.9%. The SRT measured after washing with water ranged 88.7–90.6%, demonstratinga greater improvement with an average increase rate of 13.0%, which is 5.1% higher than theincrease rate after dust removal. These results suggest that although washing with water ratherthan dust removal improves SRT to a greater extent(13.0% vs. 7.9%), dust removal alone isconsidered to provide considerable improvement in SRT. Comparison of the images of theunused film and pre-dusting film under the microscope revealed that foreign materials such asdust were adhered to the pre-dusting film, and variations were observed according to themagnification ratio and photographed area.