Radiometric and thermal properties of, and testing methods for, greenhousecovering materials

In this paper, the most critical physical properties for the greenhouse cov ering materials are reviewed. The physical properties considered include th e radiometric properties (transmissivity, reflectivity and absorptivity) ov er several radiation bands and also the K-value (the overall heat transfer coefficient). Only a few standard methods for testing these physical proper ties of covering materials for greenhouses exist. Usually, some of the test ing methods used for plastics in general, are also applied to greenhouse co vers despite important functional differences. These testing methods are re viewed with regard to their suitability for application to greenhouse cover ing materials. Also, reported values of the most important physical propert ies of greenhouse covering materials are presented and reviewed. The values presented are found to vary considerably among the materials considered. T hese variations are attributed mainly to the testing method employed and al so to the type of the material. Existing testing methods are used arbitrari ly and technical information is presented in a rather confusing way. Modifi cation of existing testing methods is required because, in most cases, they are insufficient for greenhouse covering materials. Also new testing metho ds should be elaborated, and specially designed for greenhouse covering mat erials. (C) 2000 Silsoe Research Institute.