# New Developments and Progress in Absorption Chillers for Solar Cooling Applications
## 6 Concluding Remarks  
The use of solar energy for space cooling applications is an attractive green solution that can reduce the strain on the electrical grid, especially at peak hours, while decreasing fossil fuel consumption and associated greenhouse gas emissions. Another main driver for the use of a solar cooling system is the concurrence of solar radiation and air conditioning needs in most buildings. Solar absorption cooling systems can considerably reduce the adverse global environmental effect of the demand for space cooling. However, most conventional market available absorption chillers cannot effectively use the solar resource because they are costly, bulky, and consume a significant amount of electrical energy for the parasitic loads.  
Recently, new water/LiBr absorption chillers with unique technical features have emerged on the global market. They were described and thoroughly discussed in the present article. Among these newly developed chillers are an air-cooled small capacity chiller of 2.5 kW; compact chillers designed using asymmetric plate heat exchangers (15, 30, and 65 kW nominal capacities); highly-efficient compact absorption heat pumps for cooling and heating applications (50, 160, and 500 kW nominal cooling capacities); single-effect double-lift chillers (with 40 K and above temperature glide in the driving heat); and solar-gas-fired single/double-effect absorption chillers. Besides, pre-industrial and laboratory prototypes of ammonia/LiNO\({}_{3}\) absorption chillers using typical symmetrical plate heat exchangers have been developed and tested in different operating conditions. Furthermore, water/LiBr chillers are enabled to adapt to extreme operating conditions (e.g., high heat rejection temperatures, >35 \({}^{\circ}\)C) using R718 turbo compressor boosted absorption chiller configurations. This concept was applied and tested using a 15 kW exclusively designed water/LiBr single-effect absorption chiller with a turbo compression booster and showed the desired operational flexibility.  
Additionally, because of the intermittent nature of the solar resource and the variation in the cooling load during the day (and also the year), absorption chillers need to be controlled and operated safely if they are to perform optimally in full and partial load operations. Thus, active control strategies based on the variable volume flow rates of the external heat carrier fluid circuits, mainly for heat rejection, can reduce the parasitic electricity consumption of the overall system (i.e., higher electrical COP). Finally, using these newly developed absorption chillers with an advanced control strategy could help develop highly efficient, cost-effective, and robust solar thermal cooling solutions which can mitigate the unsustainable impact of the future global demand for space cooling.  
Review of literature, writing--original draft preparation, writing-review and editing, D.S.A.; supervision, review, resources, A.C. All authors have read and agreed to the published version of the manuscript.  
Universitat Rovira i Virgili: Marti-Franques postdoctoral research fellowship 2018 (Ref.: 2017 PMF-POST2).  
[PERSON] gratefully acknowledges the Universitat Rovira i Virgili for the Marti-Franques postdoctoral research fellowship 2018 (2017 PMF-POST2). [PERSON], coordinator of the language service at the Universitat Rovira i Virgili, is acknowledged for his editing contribution to the final version of the manuscript.  
The authors declare no conflict of interest.