Abstract
Decarbonization of the industrial sector is one of the most important keys to reducing global warming. Energy demands and associated emissions in the industrial sector are continuously increasing. The utilization of high temperature heat pumps (HTHPs) operating with natural fluids presents an environmentally friendly solution with great potential to increase energy efficiency and reduce emissions in industrial processes. Ammonia-water absorption–compression heat pumps (ACHPs) combine the technologies of an absorption and vapor compression heat pump using a zeotropic mixture of ammonia and water as working fluid. The given characteristics, such as the ability to achieve high sink temperatures with comparably large temperature lifts and high coefficient of performance (COP) make the ACHP interesting for utilization in various industrial high temperature applications. This work reviews the state of technology and identifies existing challenges based on conducted experimental investigations. In this context, 23 references with capacities ranging from 1.4 kW to 4500 kW are evaluated, achieving sink outlet temperatures from 45 °C to 115 °C and COPs from 1.4 to 11.3. Existing challenges are identified for the compressor concerning discharge temperature and lubrication, for the absorber and desorber design for operation and liquid–vapor mixing and distribution and the choice of solution pump. Recent developments and promising solutions are then highlighted and presented in a comprehensive overview. Finally, future trends for further studies are discussed. The purpose of this study is to serve as a starting point for further research by connecting theoretical approaches, possible solutions and experimental results as a resource for further developments of ammonia-water ACHP systems at high temperature operation.
Highlights
This study identifies the existing challenges and future trends for the utilization of the absorption–compression heat pumps (ACHPs) at high temperature operation against the background of recent research activities and findings
This study identifies the existing work related to the described cycle modifications and the identification of existingchallenges chaland future trends for the utilization of the ACHP at high temperature operation against lenges
Despite the lower temperature lift and required pressure ratio, the achieved cooling coefficient of performance (COP) at 0.9 is smaller than the cooling COP obtained for the ACHP with two-stage solution circuit
Summary
The required compression ratio can be reduced, when compared with conventional vapor compression heat pumps (VCHPs) utilizing single fluid refrigerants, by adjusting the concentration to the given boundary conditions These characteristics, combined with the ability to achieve high sink temperatures above 100 ◦ C at large temperature lifts and high coefficients of performance (COP), make the ACHP system a valuable solution for high temperature heat supply in the industry [18]. The lean solution passes through an internal heat exchanger (IHX) to that only vapor entersincrease the compressor (2) to compressed toperformance the high-pressure side liquid temperature andbe improve overall cycle (5,6). The vapor compression cycle with solution circuit and desorber/absorber heat exchange (DAHX) cycle, as shown, was investigated by Groll and Radermacher (1994) [42] In this approach, the gliding temperature intervals of desorber and absorber are further increased, allowing them to overlap.
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