Critical analysis of the design of atmospheric water generators based on vapour compression refrigeration cycle: A numerical study

Abstract

Water scarcity is a problem affecting millions of people in the world, which is amplified by climate change, pollution and population growth. To address this problem, an Atmospheric Water Harvesting system is evaluated, introducing a novel critical analysis using five refrigerants typically used by manufacturers and broadens the current spectrum of ambient conditions. The system is mathematically modelled by integrating semi-empirical models of every component. Each semi-empirical model is individually validated, with errors ranging from 2.5% to 6%. The system is evaluated through a) a parametric analysis and b) an annual analysis using climate conditions of seven cities and five refrigerants. From the parametric analysis it is concluded that the trend of the main indicators is similar for the five refrigerants. The best operating conditions are located at ambient temperatures lower than 25 °C with relative humidities within 40% and 80%. The results are highly influenced by the control system. Cities, such as Beijing and Kabul, having low temperatures during winter, present almost 5000 non-operating hours. In terms of water collection, Sao Paulo presents the highest values, ranging from 3.58 L h⁻¹ for R1234yf to 4.54 L h⁻¹ for R407C. For the SEC, the best performance is also obtained in Sao Paulo, with R407C having the best SEC of 0.34 kWh L⁻¹ and refrigerants R134a and R1234yf having the worst SEC of 0.43 kWh L⁻¹. According to the limitations found for this technology, it is recommended to consider a system with an adaptive control and to combine it with sorption systems.