Double absorption-compression heat pump system for waste‑heat recovery: conceptual design and thermodynamic assessment

• An enhanced hybrid heat pump cycle and its open–loop variant are proposed. • Compressor pressure ratio drops by 70.3%, power input slashed by up to 59%. • Maximum temperature lifts greatly enhanced, notably for outlet temperature. As one of the most promising clean heating technologies to replace fossil-fuel boilers, heat pumps face significant challenges in large-scale industrial applications due to their limited temperature lift capability. The hybrid absorption–compression heat‑pump (ACHP) cycle, featuring pre-absorption followed by compression, has been shown to outperform conventional vapor‑compression heat pumps in both overall efficiency and achievable temperature lift. Nevertheless, it faces performance deterioration and excessively high compressor pressure ratios under high-temperature lift conditions. To address these issues, this study proposes a double absorption-compression heat pump (DACHP) structure, along with its corresponding open-loop variant. Results show that the introduction of the double absorption heat transformer sub-cycle significantly enhances the temperature lift capability on the absorption side, thereby reducing compressor power consumption and broadening the operational temperature range. Compared to the ACHP system, under reference conditions (cooling water temperature of 10 ℃, waste heat temperature of 65 ℃, and output temperature of 180 ℃), DACHP extends the permissible operating boundaries, raising the maximum condensation temperature from 5 ℃ to 25 ℃, lowering the minimum waste heat temperature from 70 ℃ to 55 ℃, and increasing the maximum output temperature from 170 ℃ to 230 ℃. The work-equivalent COP considering thermal input ranges from 2.18 to 1.4. In addition, DACHP reduces the compressor pressure ratio by 70.3% and electrical energy consumption by 49.4%; the open-loop configuration further lowers power consumption by up to 59%. Overall, the proposed DACHP structure achieves notable improvements in output temperature, temperature lift capacity, operational stability, and energy performance, highlighting its strong potential for widespread application in industrial low temperature waste heat recovery.