![]() ![]() The transpiration rate of plants is affected by the amount of moisture in the air, which inhibits plant health, growth, and development. ![]() ![]() Similarly, at high levels of relative humidity, which are commonly occurring inside greenhouses in hot countries, especially during the night period, the risk for condensation on the leaves is high, and, therefore, the risk of botrytis and fungal and bacterial diseases is increased. Nonetheless, the traditional cooling processes, which involve natural ventilation and passive cooling techniques, were difficult to control, and no ideal climate conditions were guaranteed for the crops, which prohibited the cultivation of many crops, especially those that were not resistant to the high levels of temperature. Hence, traditional cooling systems in greenhouse agriculture have been adopted in regions of harsh and variable weather conditions, and they have improved the related climatic greenhouse parameters. In hot climate regions, such as in the Middle East and North African (MENA) regions, and the Gulf Cooperation Countries (GCC), where the protected crop areas reached 13,000 ha and 71,297 ha, respectively, in 2014, efficient greenhouse cooling is required during the hot seasons to bring the internal temperature to levels that are suitable for crop growth. Finally, the recommended energy-efficient approaches of the desiccant dehumidification systems for greenhouse farming are pointed out, and the future trends in cooling systems, which include water recovery using the method of combined evaporation–condensation, as well as the opportunities for further research and development, are identified as a contribution to future research work. Subsequently, the different cooling technologies that provide the required ranges of temperature and humidity inside the greenhouse are detailed, namely, the systems using heat exchangers, ventilation, evaporation, and desiccants. ![]() Climate control processes in the greenhouse by means of manual and smart control systems are investigated first. Hence, the main objective of this work is to provide a detailed review of the research studies that have been carried out during the last few years, with a specific focus on the technologies that allow for the enhancement of the system effectiveness under hot and arid conditions, and that decrease the energy and water consumption. Nevertheless, most of the commonly used systems are either highly energy or water consuming. In hot climates, the cooling systems, which are assisted by an effective control technique, constitute a suitable path for maintaining an appropriate climate inside the greenhouse, where the required temperature and humidity distribution is maintained. The climate control inside the greenhouse constitutes an efficient methodology for maintaining a satisfactory environment that fulfills the requirements of high-yield crops and reduced energy and water resource consumption. The main challenge is to provide a suitable greenhouse indoor environment, with sufficiently low costs and low environmental impacts. This work is motivated by the difficulty of cultivating crops in horticulture greenhouses under hot and arid climate conditions. ![]()
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