INVESTIGATION OF SUSTAINABLE COOLING TECHNOLOGIES WITH THERMAL MANAGEMENT FOR AGRICULTURAL GREENHOUSES IN HOT ARID CLIMATES

Abstract

The rapid population growth, increased global demand for crops, challenges posed by climate change, and heavy reliance on food imports led to many countries facing food insecurity. In hot arid regions, the combination of high ambient temperatures, intense solar irradiation, limited freshwater resources, and lack of fertile soil create a harsh environment for agriculture production. Without sustainable and innovative solutions, cultivation in hot arid regions will become energy-intensive, expensive, and susceptible, if not entirely unattainable. Therefore, this dissertation models, simulates, and analyzes innovative greenhouse technologies for hot arid climates. This dissertation initially evaluates alternative cooling approaches in contrast to conventional refrigeration systems. It presents investigations into the development of a sustainability performance index for comprehensively and accurately comparing different cooling approaches. Twenty-one different cooling cycles and refrigerants were assessed based on three main groups: vapor-compression cycles, thermally-driven cycles, and emerging cycles. Secondly, this research investigates the thermoeconomic performance of four different passive-cooled greenhouse configurations in hot arid climates based on natural ventilation, shading, and buried greenhouse structure. Assessments of thermal performance, water requirements, and detailed economic analyses were conducted. Significant reductions in greenhouse inside temperature and water requirements were computed. However, passive cooling was found to be insufficient to maintain adequate interior temperatures in the summer. Consequently, the third part of this research proposes innovative, resilient, and sustainable integrated greenhouse systems for controlling indoor climate within the cultivation range. The systems utilized advanced renewable energy, cooling, desalination, and storage technologies to sustainably produce cooling, electricity, and irrigation water. Four greenhouse configurations were simulated: closed, shaded, buried, and buried and shaded. The research work revealed significant reductions in cooling demand and water usage and provided a comprehensive life cycle cost analysis of the integrated systems. Finally, the research introduced two novel greenhouse designs optimized for hot arid regions. The first design incorporated four cost-effective and innovative techniques: (1) a fully sunken greenhouse, (2) a fully shaded roof with openings for diffuser lenses, (3) a thermally insulated roof, and (4) a horizontal earth-to-air heat exchanger. Computational modeling (CFD simulations) involved developing a ray-tracing model and a heat transfer model. The results demonstrate that the proposed greenhouse achieves sufficient and well-distributed solar irradiation for plant growth, with a remarkable 85.5% reduction in cooling load and a 67.8% reduction in the lifetime cost of greenhouse cooling. The second innovative design integrated three energy- and cost-efficient techniques: (1) wind tower natural ventilation, (2) a sunken greenhouse structure, and (3) evaporative cooling downdraught. A comprehensive computational model was developed. The results showed efficient ventilation rates and great improvement of the greenhouse's internal microclimate in terms of temperature and relative humidity, reducing interior temperatures by up to 12.9°C from the ambient and increasing humidity by up to 54%. Comparatively, a non-sunken greenhouse faced temperatures up to 8.9°C higher and humidity 39.4% lower.

Date of Award	2024
Original language	American English
Awarding Institution	HBKU College of Science and Engineering