Abstract
This work is motivated by the difficulty of cultivating crops in horticulture greenhouses under hot and arid climate conditions. The main challenge is to provide a suitable greenhouse indoor environment, with sufficiently low costs and low environmental impacts. 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. 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. Nevertheless, most of the commonly used systems are either highly energy or water consuming. 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. Climate control processes in the greenhouse by means of manual and smart control systems are investigated first. 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. 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.
Highlights
Introduction published maps and institutional affilProtected agriculture is a growing activity that is spreading throughout all the world continents, and that covers an area that was estimated to be 5.2 million ha in 2014 [1].Greenhouses that are covered either by plastic films in mild climates, or by glass or rigid plastic in temperate and cold climates, extend over an area that averages 4.7 million ha in the temperate regions of Europe, Asia, and America, and over an area that averages364,000 ha in the Mediterranean, as well as over an area that averages 156,000 ha in the tropical and subtropical regions [1].Hot and dry areas are characterized by hot summers, with high solar radiation and air temperatures
Forced ventilation ensures the control of the indoor the indoor environment to prevent overheating in greenhouse growing environments, environment to prevent in greenhouse growingfor environments, and it can and it can either replaceoverheating other common cooling systems, instance, fans and padeither sysreplace common cooling systems, for instance, fans and pad systems, or contribute tems, orother contribute to lowering their energy consumption
The present paper provides an updated literature review of the climate control methods and cooling systems, with a particular focus on their reliability under hot and arid climate conditions
Summary
The climate management of the greenhouse environment depends on many parameters, such as the solar radiation, the air temperature (T), the relative humidity (RH), and the carbon dioxide (CO2 ) concentration. The relative humidity is dependent on the amount of moisture that is continuously being released by the plants, on the soil evaporation, as well as on the temperature, which is, in turn, reliant on the solar radiation and the meteorological conditions. Monitoring such parameters is a real challenge in greenhouse climate control
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