Enhancing Greenhouse Efficiency in Semi-Arid Climates: Humidity Control and Water Recovery Using Liquid Desiccant Systems

Semi-arid climate greenhouses are increasingly faced with high internal humidity, due to climate change impacts, despite the generally arid external climate. The unintended rise in humidity results from irrigation, plant transpiration, and limited ventilation, and it negatively affects crop growth, yield, and susceptibility to pests and diseases, especially during summer. This study investigates the application of an open-cycle liquid desiccant dehumidification system using calcium chloride (CaCl₂) for humidity control and water harvesting in a greenhouse located in the Dhiban/Madaba region of Jordan. A numerical model based on the effectiveness (ε-NTU) method was used to study the system's performance under local climatic and operating conditions. Results show that the system kept the relative humidity of the greenhouse below 60% effectively, which is optimal for plant growth. Moreover, it achieved significant water recovery: 19,757 kg in June, 20,849 kg in July, and 21,317 kg in August, based on 8-hour daily operation. This condensed water represents a valuable resource for supplemental irrigation. The findings underscore the dual advantage of the liquid desiccant system for reducing excessive humidity as well as water scarcity in a complementary way towards improving sustainable cultivation in the greenhouse in arid and semi-arid regions.