Covering Materials Incorporating Radiation-Preventing Techniques to Meet Greenhouse Cooling Challenges in Arid Regions: A Review

Abstract

Cooling greenhouses is essential to provide a suitable environment for plant growth in arid regions characterized by brackish water resources. However, using conventional cooling methods are facing many challenges. Filtering out near infra-red radiation (NIR) at the greenhouse cover can significantly reduce the heating load and can solve the overheating problem of the greenhouse air. This paper is to review (i) the problems of using conventional cooling methods and (ii) the advantages of greenhouse covers that incorporate NIR reflectors. This survey focuses on how the cover type affects the transmittance of photosynthetically active radiation (PAR), the reflectance or absorptance of NIR and the greenhouse air temperature. NIR-reflecting plastic films seem to be the most suitable, low cost and simple cover for greenhouses under arid conditions. Therefore, this review discusses how various additives should be incorporated in plastic film to increase its mechanical properties, durability and ability to stand up to extremely harsh weather. Presently, NIR-reflecting covers are able to reduce greenhouse air temperature by no more than 5°C. This reduction is not enough in regions where the ambient temperature may exceed 45°C in summer. There is a need to develop improved NIR-reflecting plastic film covers.

Radiometric Characterization, Solar and Thermal Radiation in a Greenhouse as Affected by Shading Configuration in an Arid Climate

“…In regions characterized by an arid climate with brackish water resources such as in the Arabian Peninsula, preventing heat from entering the greenhouse is the most appropriate technique for cooling greenhouses in hot summer seasons [1,2]. Through appropriate heat prevention methods, the radiation heat load can be eliminated or reduced before entering the greenhouse by cutting-off (via absorption or reflection) a portion of the incident radiation on the greenhouse cover [2][3][4].…”

“…Through appropriate heat prevention methods, the radiation heat load can be eliminated or reduced before entering the greenhouse by cutting-off (via absorption or reflection) a portion of the incident radiation on the greenhouse cover [2][3][4]. This is accomplished by using commercial shading devices (curtains, clothes, or plastic nets).…”

“…This is accomplished by using commercial shading devices (curtains, clothes, or plastic nets). Shading the roof of a greenhouse is usually performed by various conventional methods such as: (i) whitening by spraying the exterior cover surface with an aqueous solution of hydrated calcium oxide [Ca(OH) 2 ] as in [5,6]; (ii) external shade cloths as in [7][8][9]; (iii) deploying fixed or movable refractive screens or curtains as in [10][11][12][13] and (iv) deploying fixed or movable plastic nets of various types and colors as in [14][15][16][17][18]. Whitening the roof is inexpensive; it can be used for reducing the heat load during summer.…”

“…Plastic nets are widely used all over the world for shading residential buildings to reduce heating and cooling loads [19][20][21] and in agricultural sectors for plant and animal protection purposes. This is because plastic nets offer many environmental and economical advantages [1][2][3][4]18,22]. Protection from heavy meteorological actions (i.e., hail, wind, snow, or strong rainfall) in fruit-farming and ornamentals, as well as shading the greenhouses in sunny regions for modifying the micro-environment through the realization of confined airspaces with better microclimatic conditions, are the most common cases.…”

Effects of climatic control on tomato yield and nutritional quality in Mediterranean screenhouse

“…The climate in Mediterranean regions is characterised by long, hot summers, high solar radiation flux, dusty and dry weather and limited water resources . These stressful conditions require environmental control devices to improve the production and quality of tomato fruits.…”