Energy efficiency of combined transcritical absorption cooling cycles

For citation: Sulin A.B., Efriushin D.M., Dmitriev D.O. Energy efficiency of combined transcritical absorption cooling cycles. Journal of International Academy of Refrigeration. 2026. No 2. p. 36-46. DOI: 10.17586/1606-4313-2026-25-2-36-46 (in Russian)

Abstract
The study analyses the energy efficiency of combined cooling systems that combine transcritical steam compression cycles on carbon dioxide (CO2/R744) with absorption refrigerating machines. The relevance of the study is due to the ratification of the Kigali Amendment, which requires a reduction in the use of synthetic refrigerants with high global warming potential, and the need to switch to natural refrigerants such as CO2. The problem of low energy efficiency of transcritical CO2 systems in warm climates due to high throttle losses and high potential heat dissipation is shown. The integration of these systems with absorption systems is considered as a solution for the utilization of heat from the gas cooler and its conversion into additional cold directed to supercooling CO2. Based on the analysis of scientific studies, it has been shown that combining a transcritical CO2 cycle with a bromistolithium absorption refrigerating machine (H2O-LiBr) provides a significant increase in the conversion coefficient of COP and exergetic efficiency, especially at low evaporation temperatures. However, it is noted that combining a transcritical CO₂ cycle with ammonia absorption refrigerating machines (NH3-H2O) is inefficient and impractical due to the incompatibility of the cycles’ optimal operating temperature ranges.  We conclude that the choice of the optimal configuration for the combined system critically depends on the operating conditions (primarily on the ambient temperature), and that the CO2/H2O-LiBr system is one of the promising areas for the development of highly efficient and environmentally friendly refrigeration systems.