Thermodynamic and Annual Performance Assessment of a Cascaded Air-Source Heat Pump for Industrial Steam Generation: a Mediterranean Case Study

Industrial heat decarbonization is a key challenge for the energy transition, particularly in applications requiring high-temperature steam when industrial waste heat is unavailable. This study presents a thermodynamic and annual performance assessment of a steam-generating heat pump system using ambient air as the external low-temperature heat source. The system combines cascaded low- and medium-temperature heat pumps with a mechanical vapor recompression unit. Steady-state thermodynamic models, parameterized using assumptions consistent with representative commercial components, are used to evaluate the system under nominal and annual operating conditions. The annual assessment is applied to the continuous steam demand of a real paper-production facility under Mediterranean climatic conditions. A grid-supported photovoltaic and battery energy storage system is included as the electricity supply framework for characterizing the operation of the steam-generating heat pump under time-varying ambient and renewable-generation conditions. Under the adopted modeling assumptions, the system produces saturated steam at 5–25 bar with design COP values of 1.35–1.49. As steam pressure increases, mechanical vapor recompression becomes the dominant electricity-consuming stage, resulting in a moderate reduction in COP while decreasing the sensitivity of overall system performance to ambient temperature variations. Full-year simulations show that the operating COP exceeds the design-point value for the investigated location because ambient temperatures are generally more favorable than the nominal design condition. The results of the preliminary economic analysis performed for three PV-BESS configurations show that the economic feasibility strongly depends on the electricity purchase price. None of the studied configurations recovers its additional investment at 50 €/MWh, whereas discounted payback periods range from 6.9 to 16.5 years at 100 €/MWh and from 4.2 to 7.3 years at 150 €/MWh. As the integrated system has not been experimentally validated, the results should be interpreted as model-based estimates.