Direct entry of solar radiation through the covers into the greenhouse enclosure is the primary source of heat gain. The amount of radiation (or light) entering the greenhouse can be controlled by shading and/or reflecting the incident radiation. In this study, the effect of a novel shading technique which is named Water Injected Polycarbonate Shading (WIPS) was investigated. In this method to create shading, the ducts in between the two-layer polycarbonate sheet were used to pass and maintain a suitable liquid (e.g. water) flow to the roof of the greenhouse. However, the use of water does not cause any barrier for the light passing the greenhouse roof which can reduce plants photosynthesis. This is the most important parameter for shadings that has to be used in greenhouses. Due to the ability to absorb infrared radiation by water, the proposed shading system absorbs about 14% of the solar spectrum and hence helps greenhouse cooling, with less side effect on other solar spectrum and hence photosynthesis. The results of statistical analysis revealed that WIPS system can decrease greenhouse temperature in the range of about 1 to atmost 3 °C at the peak of the ambient temperature. Also, using water in the WIPS shading does not create an obstacle to ultraviolet light. Comparison of mean with “t” test showed that there is a significant difference between the temperature and infrared light transmission in two greenhouses without shading and with WIPS greenhouse, at the 5% and 1% probability level, respectively. However, no significant difference in UV and visible light observed between the two greenhouses, implying shading performance of WIPS with no serious obstacle for photosynthesis.

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