Transient investigation of solar-powered absorption heat transformers for process heat production in industries

This study investigates a solar-driven absorption heat transformer (AHT) with the LiBr/H₂O pair. Four different solar thermal technologies are examined for producing useful heat which is then stored in a tank and feeds the AHT for industrial heat production. The examined solar thermal collectors are the simple flat plate collector (SFPC), the advanced flat plate collector (AFPC), the evacuated flat plate collector (EFPC), and the evacuated tube collector (ETC). Practically, the heat transformer upgrades the solar useful output through a thermochemical absorption cycle. This work uses a validated thermodynamic program created in Engineering Equation Solver, while the unsteady investigation is carried out through TRNSYS software by connecting the tools properly, exploiting their interoperability. During this analysis, the impact of some critical parameters on the system behavior is studied to calculate the industrial heat production and the system efficiency by conducting a dynamic simulation of a typical summer typical week in Athens (Greece). Specifically, the impact of the solar collectors' mass flow rate, the load mass flow rate, the solar field area, and the tank's volume are defined for all the collector types. Finally, a yearly simulation is conducted for the main scenario (100 m² solar field with a tank of 8 m³) indicating that the selection of EFPC is the best choice energetically and economically compared to others. Specifically, in this scenario, the yearly industrial heating production is calculated at 36879 kWh, the yearly system energy efficiency at 21.17 %, the yearly system exergetic efficiency at 5.86 %, the levelized cost of heating at 0.0702 €/kWh, and the yearly CO₂ emissions avoidance at 8504 kg CO₂. The reported data shows that the proposed systems are more sustainable compared to a benchmark scenario with a natural boiler system. Finally, it is useful to state that the use of ETC and AFPC are also sustainable choices, but they are less effective compared to EFPC.