Development and experimental assessment of oil free combine absorption-compression heat pump with NH₃/H₂O mixture working fluid

The urgent adoption of clean heating technologies in industrial processes is essential to address critical challenges posed by climate change and comply with environmental regulations. The combined absorption-compression heat pump, using a natural working fluid based on the Osenbrück cycle, emerges as a promising high-temperature heating solution. However, its industrial application is hindered by excessive compressor discharge temperatures under large temperature lifts. This study experimentally evaluates the performance of a combined absorption-compression heat pump system using an oil-free standard twin-screw compressor under various operational conditions. The system uses a natural working fluid, an NH₃/H₂O mixture, and standard components to analyze performance parameters, including heat sink and source loads, temperature glides, temperature lift, and heat transfer coefficients in the absorbers. With a constant 60 °C inlet temperature for the heat sink and heat source, the system achieves a temperature lift of 35 °C. Heat sink and source loads rise to 60 kW and 30 kW, with glides of 35 °C and 15 °C, respectively, as the temperature lift increases. Higher temperature lifts reduce the COPs of Carnot and Lorenz cycles, though their efficiencies improve. Increasing the weak solution mass flow rate from 0.24 kg/s to 0.36 kg/s decreases temperature lift and heat sink capacity, while increasing weak solution injection flow rate (0–0.03 kg/s) lowers compressor discharge temperature from 140 °C to 126 °C. Absorber 1 (bubble mode) performs better than absorber 2 (falling-film mode), achieving a maximum heat transfer coefficient of 1.39 kW/m²K. The study provides comprehensive insights into system behavior, identifying key areas for improvement.