Meeting the cooling and freshwater needs of arid countries

According to the 2022 Chilling Prospects report published by Sustainable Energy for All, the Middle East and North Africa (MENA) region is on the frontlines of the climate crisis. In many MENA countries, increasing temperatures and rapid urbanisation are leading to fast-growing demand for cooling.^[1] The total market size of RAC technologies in the region was estimated to be around EUR 8 billion in 2018, with an expected annual growth rate of 5% until 2024. ^[2] 

In addition, increasing global temperatures will have devastating effects such as more intense heat waves, severe droughts and reduced rainfall. This would mean a rise in demand for water desalination along with air conditioning, in a region that is one of the most water-stressed in the world.^[3] Sustainable Energy for All believes that creating an equitable, low-energy, low-impact cooling sector is vital for the MENA region.^[1] It should be noted that some countries in the MENA region (i.e. Morocco, Tunisia, Yemen, Lebanon and State of Palestine) have agreed to use 100% renewable energy by 2050, although not all countries have a roadmap in place.^[3] 

Most commercial desalination plants currently operating worldwide are powered by fossil fuels. It is estimated that the equivalent CO₂ emissions from these plants will reach about 218 million tonnes annually by 2040.^[4] Increasing the energy efficiency of current cooling and desalination technologies, while relying on renewable energy sources to supply the required electricity and heat for these technologies, is considered one solution to the greenhouse gas emissions and global warming problem.^[4]  

In recent decades, renewable energy-based hybrid desalination/cooling technologies have received much attention from researchers. Studies suggest that using these integrated hybrid systems helps increase the efficiency of  driving energy utilization and improve energy and exergy efficiency. Moreover, powering hybrid systems with renewable energy sources, such as solar or wind power, could also be an ultimate answer to meeting cooling and freshwater demands in a sustainable and green way.^[4] 

In a recent review article, the authors summarised research efforts in meeting cooling and freshwater demands using available solar resources. Various solar desalination technologies and their integration with different cooling technologies are reported.^[4] According to the review, a solar-driven hybrid system combining humidification-dehumidification desalination and air conditioning (HDH-AC system) had the highest COP of 4.35, at a low specific cost of fresh water production (0.7 cent/kg).  

The HDH system comprises a humidifier, in which the air is moistened by direct contact with hot saline water. In the dehumidifier, the air is cooled by indirect contact with the cool saline water before it enters the humidifier, leading to the condensation of the freshwater. Many researchers have attempted to integrate HDH with different cooling technologies to increase heat recovery in such systems and increase energy efficiency, while producing freshwater. Compared with traditional systems in hot and humid regions, the results indicate that the hybrid HDH-AC system has higher water production, cooling capacity, COP, as well as lower power consumption.  

For a more detailed comparison of the reported hybrid desalination/cooling systems, please read the study. 

Sources 

[1] Sustainable Energy for All. Chilling Prospects 2022: Putting natural refrigerants on the map in the Middle East and North Africa. https://www.seforall.org/data-stories/natural-refrigerants-in-mena-region  

[2] Cool up programme. MENA Region Cooling Status Report. Progress, Opportunities, and Insights. May 2022. 

https://www.coolupprogramme.org/knowledge-base/reports/mena-region-cooling-status-report-issue-1/  

[3] Aghahosseini, A., Bogdanov, D., & Breyer, C. (2020). Towards sustainable development in the MENA region: Analysing the feasibility of a 100% renewable electricity system in 2030. Energy Strategy Reviews, 28, 100466. https://doi.org/10.1016/j.esr.2020.100466  

[4] Alsaman AS, et al. Hybrid Solar-Driven Desalination/Cooling Systems: Current Situation and Future Trend. Energies. 2022; 15(21):8099. https://doi.org/10.3390/en15218099