Design and development of hot water production system using high-temperature heat pumps for decarbonization of industrial process heat

Abstract High Temperature Heat Pumps (HTHPs) are promising devices for reducing carbon emissions and replacing fossil fuel boilers in industries requiring hot water and steam. This study focuses on developing an HTHP system capable of achieving refrigerant temperatures above 100 °C through two stages: (1) process modeling and simulation, and (2) design, construction, and testing of the experimental device. In the modeling stage, the HTHP was designed as a two-stage cascade refrigeration system using R-134a as the working fluid in both cycles. Internal heat exchangers were incorporated to enhance efficiency via regeneration. Tap water at 25-35 °C was used as a heat source. DWSIM, an open-source process modeling tool, was employed, with thermodynamic properties sourced from CoolProp. The simulation achieved a refrigerant temperature of 109 °C, total energy consumption of 2.72 kW, a heat capacity of 6.8 kW, and a COP of 2.5. In the experimental stage, the HTHP prototype was constructed based on DWSIM design and sizing, with SolidWorks used for equipment layout and piping. The prototype successfully increased water temperature from 25-35 °C to 85-90 °C, achieving a temperature uplift of 50-60 °C. It reached a refrigerant temperature of 104.82 °C, with total energy consumption of 3.90 kW, a heating capacity of 8.90 kW, and a COP of 2.28. Comparison of simulation and experimental results showed good agreement, demonstrating DWSIM’s effectiveness in HTHP design. The payback period of the device was 1.17 years, with an initial cost of 207,366.6 Baht and annual savings of 176,862.5 Baht. The system reduced electricity consumption by 2.28 times and carbon emissions by 23.91 tCO2e annually compared to an electric hot water boiler.