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

Khalid Hamid, Shuai Ren, Ignat Tolstorebrov, Armin Hafner, Chi-Chuan Wang, Uzair Sajjad and Trygve M. Eikevik

Applied Energy, 2025, vol. 383, issue C, No S0306261925000820

Abstract: 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.

Keywords: High temperature heat pump; Absorption–compression; Oil free twin-screw compressor; NH3/H2O mixture; Osenbrück cycle (search for similar items in EconPapers)
Date: 2025
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DOI: 10.1016/j.apenergy.2025.125352

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