Comprehensive Review on Climate Control and Cooling Systems in Greenhouses under Hot and Arid Conditions

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.

Microclimatic Evaluation of Five Types of Colombian Greenhouses Using Geostatistical Techniques

“…On the other hand, the maximum mean values (T mh ) occur just between 11 and 14 h for TG, MG, SG, HGT1 and HGT2, where values of 21.4, 19.4, 24.3, 21.5 and 21.1 °C, respectively, were obtained. These T mh values, with the exception of SG, are not within the ranges established as optimal daily temperature values, which should range between 24 and 30 °C for the optimal growth and development of a great variety of ornamental and vegetable species cultivated in greenhouses [ 4 ]. For the case of the minimum mean values (Tml), these values were 11.3, 9.8, 10.1, 11.8 and 12.7 °C, representing thermal differentials between the indoor and outdoor environment of 1.1, 0.03, −0.7, 0.07 and 1.7 °C, for TG, MG, SG, HGT1 and HGT2, respectively.…”

“…In the case of relative humidity (RH), the hourly behavior can be observed for each greenhouse in Figure 2 . This variable is undoubtedly the most difficult to control within the greenhouse microclimate management since its value will depend on the psychrometric condition of the air and the mass contributions that occur via transpiration and water evaporation phenomena inside the greenhouse [ 4 , 38 ]. It can be observed that the humidity values in the greenhouses always show values higher than 67% for the average hourly value; the maximum humidity conditions inside the greenhouses occur during the night hours and generally exceed 90%, while the minimum values occur between 11 and 14 h and range between 67% and 75%.…”

“…One of the variables of interest for decision-making in climate and irrigation management inside the greenhouse is the VPD, a variable that relates the difference between the water vapor pressure at saturation and the actual water vapor pressure at a pressure from the greenhouse temperature [ 39 ]. VPD is a variable dependent on the temperature and RH of the greenhouse environment; its importance for climate management lies in the fact that this variable is the driving force of plant transpiration [ 4 ]. Its behavior in each of the greenhouses can be observed in Figure 3 ; it is observed that the maximum values of VPD occur during daytime hours, precisely in the periods where the temperature increases and the RH decreases, while the lowest values of VPD occur during the nighttime period, where the cold and saturated environments predominate in each of the greenhouses.…”

“…In crops grown under protective environment structures, microclimate management is undoubtedly one of the most relevant factors affecting crop production in terms of both quality and quantity [ 1 , 2 ]. Worldwide, there are more than 5.2 million hectares covered with different types of protective agriculture structures [ 3 , 4 ]. These structures present different technological levels, from a low technological level, such as that found in the small tunnels or structures typically used in tropical countries of Latin America and Asia [ 5 ], to an extremely high level, such as that found in the high-tech greenhouses found mainly in northern European countries, where it is possible to fully manage the variables that affect crop growth and development [ 6 ].…”

Experimental study of a pilot unit of a ground regenerator for greenhouses

“…ScienceRise ISSN 2313-8416 erators can be used to maintain the required temperature level in greenhouses [5]. The average temperature in a greenhouse should be between +16 and +25 degrees, and at night it should fall by no more than 5-8 degrees.…”