Greenhouses covering materials: a comparative study

Greenhouse covering material is the most governing member of the construction which controls two major parameters, the amount of light and heat diffused from the surrounding environment into the internal space. In hot areas, balancing between optimum temperature and maximum light intensity inside the greenhouse consumes most of the energy spent in vegetable production systems. In this research, a special testing stand was fabricated to simulate the structure of a typical greenhouse provided with a 400W full spectrum light as a source of light and heat. Tests were carried out to investigate the effectiveness of different commercial covering material in light and heat diffusion. Twenty one combinations of Fiberglass, Polyethylene, Polycarbonate, Plexiglass and Agril (PP nonwoven fabric) were tested. It was concluded that Plexiglass was the highest in light transmittance of 87.4%, while the lowest was 33.03% and 34.24% for Fiberglass sheets. The enthalpy of the air moving through the testing rig was calculated according to air temperature differences between inlet and outlet openings. The highest enthalpy value was recorded for one layer of Fiberglass where it was 0.81 kJ/kg air while it was 0.2 kJ/kg air for blocked Plexiglass (60mm).