Design and Development, Via Prototype Testing and Multiphysics Modelling, of a Thermoelectric Generator (TEG) for Integration in Autonomous Gas Heaters

A wide range of technical solution based on gas combustion is available for heating of both residential and industrial environment. While in most cases the gas combustion is localized in a central heating unit (the boiler) and the generated heat is transferred to an intermediate fluid (e.g. water) which is circulated through heat radiators located in the rooms, in some relevant cases each heat-radiating unit includes the gas combustor and operates autonomously with local gas and electrical feeding. The latter approach applies more frequently in industrial or commercial environments, where localized heating may be more effective than uniform heating of the whole environment: in such situation, the use of autonomous units is characterized by higher flexibility of design and operation. For autonomous gas heaters, a cogenerating thermoelectric generator (TEG) can be integrated within the heater. Locally produced electrical power may allow unit's installation and operation without the need of a connection to the electrical grid, reducing installation constraints and also increasing the overall efficiency, through reduction or elimination of electrical power supply for fans (or pumps), safety and monitoring, control devices and accessory functions (e.g. illumination). A self standing gas heater for heat radiation in outdoor commercial environments has been selected as a test case for verifying feasibility and profitability of such technical solution. A TEG device has been designed and prototyped, and integrated in the heater (Figure 1), (co-)generating an amount of electrical power and providing autonomous operation from electrical connection to grid and power for accessory functions (high efficiency LED illumination). A prototype has been built and tested. On the basis of empirical data from the prototype testing, a numerical multiphysics model was built using COMSOL Multiphysics, to allow incremental optimization of the design and extrapolation of the performance of modified designs. Approaches for modeling each sub-problem, specially the equations of Seebeck/Peltier physics and the joint calculation of the thermal and electrical fields, for integration of each sub-model in a complex multiscale model representing the device's operation, are discussed. Apart of the mentioned design optimization needs, the problem was modeled with the purpose to extend its application towards a range of larger and/or more complex designs of gas-heaters integrating thermoelectric co-generation technology, aiming to extend and reinforce its impact for improvement of energy efficiency of gas-combustion heating devices.