Experimental investigation and performance analysis of an industrial high-temperature cascade heat pump using R134a and R245fa

Geopolitical tensions have intensified concerns over energy security, highlighting the crucial role of high-temperature heat pumps (HTHPs) in regional electrification. This study developed an R134a/R245fa high-temperature cascade heat pump (HTCHP) for direct steam generation at 100∼110 °C. Experiments at heat source temperatures of 30∼45 °C investigated the effects of intermediate condensation temperatures (T_c,LT) on performance. The results indicate that, increasing T_c,LT from 50 °C to 70 °C leads to an average reduction of 22.5% in volumetric efficiency of the high-temperature compressor and 8.6% in adiabatic efficiency. Meanwhile, the heating capacity increases by 17% on average, and the coefficient of performance (COP) decreases by an average of 11.4%. Compared with the constant condensation temperature control, the high-temperature compressor load-priority strategy resulted in lower steam stability but reduced average energy consumption by 47.54 kW h per ton of steam (approximately 14.1%). At an intermediate condensation temperature of 70 °C, refrigerant-cooled lubricating oil scheme improved the heating COP by only 4.9% compared to water-cooled scheme, which yielded negligible results. These results provide practical insights for the engineering design and operational control of HTCHP systems.