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

Ahmed Abdel-Ghany,Mohamed Shady,Pietro Picuno,Abdullah Alsadon,Abdullah Ibrahim,Ibrahim Al-Helal

doi:10.3390/en81212404

Ahmed Abdel-Ghany, Mohamed Shady + Show 4 more

Open Access

https://doi.org/10.3390/en81212404

Copy DOI

Journal: Energies	Publication Date: Dec 8, 2015
Citations: 54	License type: CC BY 4.0

Affiliation: King Saud University, University of Basilicata

Abstract

Shading the greenhouses is necessary in summer to reduce the solar radiation load. This however generates a considerable amount of thermal radiation heat load that needs to be removed via cooling systems. This study aimed to evaluate the effect of different shading configurations on the solar and thermal radiation in a greenhouse. Nets at four different locations were employed to shade the roof and side-walls of a polycarbonate, mechanically ventilated greenhouse. The spectral radiative properties of all these plastic materials were measured in short and long wave spectrum bands. The net solar and thermal radiations and air temperature were measured outside and inside two identical shaded and unshaded greenhouses. The results showed that external roof-shading is desirable, as it reduced the generated thermal radiation in the greenhouse by 21% and 15% during the day and night time, respectively and reduced the greenhouse air temperature during the day. The internal shading (roof and side walls) is undesirable, since it drastically increased the generated thermal radiation in the greenhouse by 147% and strongly increased the greenhouse air temperature during the day. Shading the side-walls is not recommended because it significantly reduces the transmitted solar radiation in the morning and afternoon (when the outside irradiance is low) and is useless at around noon when the outside irradiance is extremely high.

Highlights

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]
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]
It reduced the average greenhouse transmittance to solar radiation by about 50%; it is washed away if rains fall on the greenhouse and its shading density cannot be changed once applied [5,6]

Summary

Introduction

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]. This is accomplished by using commercial shading devices (curtains, clothes, or plastic nets). Whitening the roof is inexpensive; it can be used for reducing the heat load during summer. It reduced the average greenhouse transmittance to solar radiation by about 50%; it is washed away if rains fall on the greenhouse and its shading density cannot be changed once applied [5,6]

Objectives

Methods

Conclusion