Multi-objective optimization and off-design performance analysis on the ammonia-water cooling-power/heating-power integrated system

Abstract

The utilization of ammonia-water as a working fluid in energy conversion systems presents a promising approach for efficient geothermal energy development. In this paper, a novel ammonia-water cooling-power/heating-power integrated system is presented, a structure design method suitable for the integrated thermal system is developed, and a comprehensive analysis of system performance using thermodynamic, economic, and off-design analytical methods is conducted. This study explores the impact of various variables on system design and off-design performance. The results demonstrate that optimal design performance is achieved at evaporation temperatures of 3.5 °C (cooling-power) and 20 °C (heating-power), and the hot-part temperature difference is 21 °C. Lower mass flow rate and ambient temperature lead to improved off-design performance. Due to the influence of pressure on the phase transition temperature of geothermal water, the position of the phase transition zone has shifted, resulting in a change in the mass flow rate of ammonia-water. When the pressure ratio drops below 0.9, the heat release during the phase transition of geothermal water is incomplete, leading to a significant decrease in pump speeds by 44.76 % and 41.14 % in the two modes respectively. This work provides valuable insights and references for the design and optimization of integrated thermal systems.