# New Developments and Progress in Absorption Chillers for Solar Cooling Applications
## 1 Introduction  
According to an International Energy Agency (IEA) [1] report, the global energy required for space cooling applications will increase three-fold over the next 30 years (i.e., it will rise to 6200 TWh by 2050) if the current policies and targets are continued. This projected energy demand is mainly due to the fact of economic growth and population increases in the hotter regions of the world, 50% of which is contributed to by three countries (i.e., China, India, and Indonesia). Also, more people are interested in comfort cooling due to the fact of rising living standards and increases in the income of the burgeoning middle classes in these countries. Thus, the total number of air conditioners in buildings will increase by approximately 250% between 2016 and 2050, from 1.6 billion to 5.6 billion units [1,2]. In addition, the global electrical power capacity needed to meet these space cooling demands will also increase from 850 GW in 2016 to 3350 GW in 2050 [1]. In 2018, the use of air conditioners and electric fans to satisfy cooling demand accounted for nearly 20% of the total electricity consumed in buildings (equivalent to 10% of the world's electricity consumption) [2]. Moreover, air conditioning will account for approximately 37% of the world's growth in electricity demand by 2050 [3]. The global air conditioning market is dominated by technologies based on vapor-compression refrigeration cycles driven by electricity and uses synthetic refrigerants (with considerable global warming potential). The current air conditioning systems comprise packaged air conditioners,split-system air conditioners, and various types of compression chillers (e.g., centrifugal, reciprocating, or screw-type compression chillers). Packaged air conditioners include window units, terminal air conditioners, portable units, and rooftop units. In addition, split-system air conditioners range from small single room units to large systems that can supply cold to large buildings. Solar thermal energy-driven systems for space cooling and refrigeration applications are attractive solutions for three main reasons [1; 3; 4]: (1) they use natural refrigerants (such as ammonia and water) which have recently been pushed by national and international regulations (e.g., European F-gas regulation No. 517/2014); (2) they consume less electricity and reduce peak electricity demand, which is especially beneficial in countries with significant cooling needs and electric grid constraints; and (3) the concurrence of solar radiation and the cooling demands of most buildings can save costly electricity in peak periods. Hence, they help to reduce the consumption of fossil fuels and their associated greenhouse gas (GHG) emissions. They can also be an option for storing solar heat for cooling in the evenings, nights, and mornings [3]. Globally, an estimated 1800 solar cooling systems have been installed by 2018, of which 70% were small- and medium-capacity (<350 kW (100 TR)) systems in Europe [3]. Most of these systems use relatively mature technologies: non-tracking solar thermal collectors and absorption chillers. Large-scale systems (>350 kW cooling capacity) that use absorption chillers continue to improve their performance and decrease capital investment costs. This is due to the significant increase in the performance of flat-plate solar collectors (up to 120 \({}^{\circ}\)C) and economies of scale for the cost competitiveness of solar cooling applications (e.g., for large office buildings, hotels, and hospitals). The world's largest solar cooling system with a nominal capacity of 1750 kW was installed and commissioned in Arizona (USA) in 2014. This system uses a single-effect water/LiBr chiller driven by a 4865 m\({}^{2}\) roof-mounted solar collector field with a thermal capacity of 3400 kW [3]. However, only three large solar absorption cooling systems were deployed in 2018, of which two were driven by evacuated tube collectors and installed in Italy. Another system using Fresnel collectors was installed in Jordan.