Modeling and simulation of solar adsorption cooling systems for energy efficiency and cost reduction in Saudi Arabia

Abstract

Saudi Arabia is firmly committed to achieving ambitious renewable energy targets outlined in its Vision 2030 initiative. Within the framework of this vision, the nation aspires to generate 50% of its electricity from sustainable sources by the year 2030, ultimately striving for complete carbon neutrality by 2060. The Ministry of Energy in Saudi Arabia has set a specific target to incorporate renewable energy to meet 50 % of the cooling energy needs for buildings by 2030.

The achievement of these goals introduces fresh challenges for managing the equilibrium between energy supply and demand and providing the requisite operational flexibility to support energy networks fueled by renewable sources. In light of these challenges, the adoption of a solar thermal cooling system emerges as a promising solution to contribute to the desired flexibility. Such a system, seamlessly integrated with sustainable thermal energy sources, has the potential to efficiently respond to the cooling demand. While Saudi Arabia has recently directed its energy policy towards addressing these concerns, a notable shortfall remains in the location of advanced technology, specifically in the domain of solar thermal cooling systems. This deficiency continues to impede the realisation of the potential of solar thermal cooling systems in facilitating the integration of renewable energy sources into building cooling processes and establishing a sustainable source for cooling supply.

This thesis aims to address a knowledge gap in the assessment of climate impacts on cooling and heating demands by conducting an in-depth analysis of 44 cities across Saudi Arabia, each with different climates. The goal is to develop a comprehensive framework for assessing the resilience and sustainability of solar-driven adsorption chillers, particularly in Riyadh, the capital city and one of the hottest and driest cities in Saudi Arabia. However, the results regarding the cooling and heating demands of the remaining 43 cities can also be utilised to assess the feasibility of implementing district cooling and/or heating systems in those locations. Additionally, this research identified strategies for minimising the capital costs associated with adsorption chillers through the application of optimisation techniques. The research contributions are divided into four chapters.

First, in the context of comprehending the climate and its implications for Saudi Arabia, this study leverages meteorological data to conduct a thorough analysis of annual cooling and heating degree days for a comprehensive sample of 44 cities across the nation. Of particular significance is the discernible trend wherein the majority of cities, marked by hot and arid climates as well as hot and humid climates, prominently manifest heightened cooling requirements. This contrast is observed in comparison to cities with milder climates, where the demand for cooling remains consistently high, consequently leading to a notable upward trajectory in cooling energy consumption Chapter 3.

Second, within the context of residential cooling solutions, the implementation of an adsorption refrigeration system powered by solar thermal energy offers a sustainable and environmentally friendly alternative to the prevalent use of fossil fuels in the Middle East. This comprehensive approach takes into account various critical aspects, including energy efficiency, economic viability, and ecological impact. To gauge the efficacy of this approach, we juxtapose it with traditional compression chiller systems, employing a rigorous analysis conducted with the TRNSYS software tool. The findings of our study reveal an exceptional annual cost reduction exceeding 60 % for adsorption chillers when applied in Riyadh, Saudi Arabia Chapter 4.

Third, for minimising capital expenditures, the creation of a lumped-parameter dynamic model for a two-bed adsorption chiller system involved a comprehensive assessment of different isotherm and kinetic models pertaining to the adsorbent-water interaction. The validation of this model against existing experimental data culminated in a testament to its precision, revealing deviations that did not surpass the threshold of 5 % Chapter 5.

Finally, the study culminates in optimisation, targeting both the reduction of investment costs and the maximisation of specific cooling power for a two-bed adsorption chiller system. This optimisation encompasses the identification of parameters for the Dubinin-Astakhov isotherm model using nonlinear regression across various adsorbents. Following the formulation of the design equations for the chiller system, a genetic algorithm is employed for further optimisation. The findings indicate a remarkable 59 % decrease in investment costs for the optimised system relative to its benchmark counterpart. Additionally, the refined system boasts an inlet chilled water temperature of 20 oC, thereby amplifying its efficiency Chapter 6.