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

Currently, High Temperature Heat Pump (HTHP) is considered a device that helps reduce carbon emissions and could potentially replace fossil fuel boilers in various industrial sectors that require the use of hot water and steam for process heats. This research presents the development of a hot water production system using high-temperature heat pumps capable of achieving refrigerant temperatures greater than 100 °C. The work is divided into two stages: (1) process modelling and simulation and (2) design, construction, and testing of the experimental HTHP devices. In the modelling and simulation stage, the HTHP device was designed as a two-stage cascade refrigeration system using R-134a as the working fluid in both the upper and lower cycles. Internal heat exchangers were added to improve system efficiency through regeneration. Tap water at the temperature of around 25 to 35 °C was considered as a heat source. The open-source process modelling software, DWSIM, was primarily employed as a development tool in this work. The thermodynamic properties of all working fluids came from CoolProp packages. The HTHP model in DWSIM achieved a working fluid temperature of up to 109 °C with a total energy consumption of 2.72 kW, a heat capacity of 6.8 kW, and a COP (Coefficient of Performance) of 2.5. In the construction and testing stages, the experimental HTHP prototype was constructed based on the design and equipment sizing from DWSIM with the assistance from SolidWorks for equipment layout and piping arrangement. The experimental results showed that the HTHP could increase water temperature from around 25 to 35 °C to a range of 85 to 90°C, providing a temperature uplift of around 50-60 °C from the source. The developed device was also capable of upgrading the refrigerant temperature up to 104.82°C, with a total energy consumption of 3.90 kW. This system has a heating capacity of 8.90 kW with COP of 2.28. The comparison between the simulation and experimental results showed a good agreement and demonstrated DWSIM as a powerful tool for design of HTHP. The payback period for the experimental device was approximately 1.17 years, with an initial cost of 207,366.6 Baht and a cost saving potential of 176,862.5 Baht per year. It could reduce electricity consumption by 2.28 times and also reduce carbon emissions by 23.91 tCO₂e per year when compared to that of an electric hot water boiler.