Experimental investigation on the performance of a cascaded heat pump with steam supply temperature up to 100 °C

Under the context of achieving carbon neutrality goals, high-temperature heat pumps (HTHPs) have achieved an improvement in thermal energy grade driven by low-carbon electricity. This study developed a high-temperature cascaded heat pump (HTCHP) using R134a and R245fa as the working fluids, aiming to generate steam within the temperature range of 100–110 °C. A wide cascade pressures were tested under 25 °C ∼ 55 °C heat source temperatures. The results demonstrate that, at a condition of 55 °C heat source temperature and 112 °C condensation temperature, the system produced steam at 109.4 °C with a mass flow rate of 0.27 t/h, delivering a heating capacity of 196 kW and achieving a coefficient of performance of 2.26. Additionally, the high-stage compressor exhibited superior operational stability under variable operating conditions. Based on experimental results, an exergy analysis was performed for both the system and individual components. It is found that the high-temperature compressor, low-temperature compressor, and high-temperature expansion valve are the dominant sources of exergy loss, collectively accounting for 74% of the total destruction. Furthermore, increasing the heat source temperature remarkably improves the exergy efficiency of the system, with a maximum value of 54.9%. With increasing steam production, the specific electricity consumption dropped to 321.59 kW·h/t, raising the steam production cost-saving ratio to 26.5%. The result provides practical insights for optimizing operating conditions and enhancing component-level performance in HTCHPs.