Analytical and experimental performance analysis of thermoelectric generators for low-grade water stream heat recovery

Thermoelectric generators (TEGs) present a promising technology for recovering thermal energy from waste heat in water streams; however, their performance under low-grade heat and continuous-flow conditions has not yet been fully characterized. This study presents a combined analytical and experimental investigation of a custom-designed thermoelectric energy recovery system integrated into a boiler–chiller water loop, representative of waste-heat recovery applications in water streams such as HVAC and industrial wastewater. The system maintains a controlled flow temperature difference, ΔT flow , between the hot and cold-water streams under steady-state operation. The effects of operating conditions, including flow rates and inlet temperatures, on heat transfer, electrical power generation, and conversion efficiency are systematically evaluated. Experimental results show that increasing ΔT flow from 33 to 63 °C increases the generated power from approximately 0.12 to 0.33 W. An analytical model based on thermoelectric relations and thermal resistance networks is developed to evaluate the influence of thermal losses on system performance. Incorporating both thermal contact and conduction resistances significantly improves agreement between theoretical predictions and experimental measurements compared with the ideal model. At a fixed TE temperature difference of 34 °C, the analytical model predicts a TE power of 0.7 W without accounting for losses, whereas the experimental measurement yields 0.33 W. However, including thermal contact and conduction resistances reduces the analytical model's TE power to 0.38 W. These findings highlight the critical role of thermal resistances in limiting harvested energy and the performance of practical thermoelectric systems and provide guidance for optimizing heat recovery in water-based systems.