Thermal Performance of a Greenhouse Covered with Shading Material against Infrared Rays

Abstract

Infrared rays contained in the solar radiation are well known to contribute little to photosynthesis of plants and convert easily into heat in a material absorbed. Thus, the exclusion of infrared rays with covering materials of greenhouses is expected to be an effective method to enable greenhouse culture during a high temperature period and cut down the cooling load of greenhouses.
In this study, the thermal characteristics of a greenhouse covered with a new selective absorber of infrared rays which has been commercialized were measured from summer to autumn. The following results were obtained by comparisons of these characteristics with those measured in the same scale glasshouse during the same period.
1) The effect of the present covering material on suppression of temperature rise in a greenhouse with all windows closed was small for inside air but considerable for soil surface of floor.
2) The reason for the small effect on inside air temperature was that over-all heat transfer from inside air to outside air was weakened by temperature rise of the covering materials due to absorption of infrared rays.
3) Under the condition of natural ventilation with all windows open, the effect was less for inside air but relatively large for soil surface.
4) The covering material also affected leaf temperature and the effect on suppression of temperature rise in lettuce leaf under solution culture increased with increasing solar radiation.