A review of current and future district cooling (DC) technologies, operational, economic, and environmental aspects, and analysis and optimization methodologies is presented, focusing on the demands of cooling-dominated regions. Sustainable energy sources (i.e., renewable, waste/excess electricity and heat, natural/artificial cold) and cooling/storage technology options with emphasis on heat-driven refrigeration, and their integrations in published DC design and analysis studies are reviewed. Published DC system analysis, modeling, and optimization methodologies are analyzed in terms of their objectives, scope, sustainability-related criteria, and key findings. The current and future development of DC in the Gulf Cooperation Council (GCC) region, a major developing cooling-dominated market, is examined more specifically in terms of current and future energy sources and their use, and economic, environmental, and regulatory aspects, with potential technical and non-technical solutions identified to address regional DC sustainability challenges. From the review of published DC design and analysis studies presented, collective research trends in key thematic areas are analyzed, with suggested future research themes proposed towards the sustainability enhancement of DC systems in predominantly hot climates.

At present, novel, small-to-large capacity absorption chillers with unique technical features have emerged on the global market, and laboratory and pre-industrial prototypes have also been developed. These chillers have been designed for the efficient use of low-grade heat sources; some are air-cooled, small capacity systems; compact water/LiBr chillers; or solar-gas-fired single/double-effect chillers. Also, some advanced commercial absorption chillers have an extensive temperature glide in the driving heat stream (>30 K) which extracts approximately twice as much heat (~200%) as the single-effect chiller. This large temperature glide means that the chillers are well suited to solar thermal collector installations and district heating networks, and the extra driving heat increases cold production. Moreover, recent advances in R718 turbo compressor technologies have helped to solve the problems water/LiBr absorption chillers have in adapting to extreme operating conditions (e.g., high ambient temperature, >35 °C) by using a compressor-boosted absorption chiller configuration. This review paper presents and discusses the developments and progress in these absorption chiller technologies. In summary, the new absorption chillers may be useful for developing efficient, cost-effective, and robust solar cooling solutions that are needed to mitigate the unsustainable impact of the rising global demand for space cooling.