Open Access
Experimental development of a novel thermoelectric generator without moving parts to harness shallow hot dry rock fields
(2021) Alegría Cía, Patricia; Rodríguez García, Antonio; Catalán Ros, Leyre; Astrain Ulibarrena, David; Araiz Vega, Miguel; Ingeniería; Institute of Smart Cities - ISC; Ingeniaritza
Nowadays, geothermal energy in shallow hot dry rocks is not exploited enough due to the high economic and environmental impact as well as the lack of scalability of the existing technologies. Here, thermoelectricity has a great future potential due to its robustness, absence of moving parts and modularity. With this research, the feasibility of a novel and robust geothermal thermoelectric generator whose working principle is phase change has been experimentally demonstrated, as well as the importance of compactness to maximize its efficiency and thus, power generation.
Open Access
Effect of thermoelectric subcooling on COP and energy consumption of a propane heat pump
(Elsevier, 2024-12-01) Aranguren Garacochea, Patricia; Sánchez, Daniel; Haida, Michal; Smolka, Jacek; Cabello, Ramón; Rodríguez García, Antonio; Astrain Ulibarrena, David; Ingeniería; Ingeniaritza; Institute of Smart Cities - ISC; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
The building sector has an important impact on the environment, being responsible for 30 % of the total greenhouse gas emissions. Knowing that the energy consumption devoted to HVAC systems accounts for 50 % of the total energy consumption of buildings, it is paramount to develop environmentally friendly technologies able to provide green space heating to the building sector. To that purpose, this manuscript presents a computational study on propane vapor compression heat pumps which include thermoelectric subcooling to boost their operation. The combination of these technologies has been proven in the past to be very beneficial for refrigeration systems and this study concludes for the first time that propane heat pumps can highly benefit from thermoelectric subcooling. The widely conducted research includes the following parameters: ambient temperatures from -20 to 15 °C, voltage supplies to the thermoelectric modules from 0.5 to 10 VDC, number of thermoelectric subcooling blocks from 1 to 8 and two water inlet temperatures, 40 and 55 °C to study their influence on heating capacity, compressor and thermoelectric power consumptions, subcooling degree, propane mass flow, compressor capacity, COP, energy consumption and SCOP of the combined heat pump. The obtained results are very conclusive, COP enhancements up to 12.29 % are achieved when a thermoelectric subcooler with 16 modules is included in a propane heat pump already provided with an internal heat exchanger for an ambient temperature of -20 °C and a water inlet temperature of 55 °C. Additionally, improvements in Seasonal COP up to 9.98 % are achieved if the above-mentioned technologies integration between a vapor compression heat pump and a thermoelectric subcooler substitutes a conventional propane heat pump with an internal heat exchanger for space heating a single-story two-family house.
Open Access
Experimental development of a novel thermoelectric generator without moving parts to harness shallow hot dry rock fields
(Elsevier, 2022) Alegría Cía, Patricia; Catalán Ros, Leyre; Araiz Vega, Miguel; Rodríguez García, Antonio; Astrain Ulibarrena, David; Ingeniaritza; Institute of Smart Cities - ISC; Ingeniería
Nowadays, geothermal energy in shallow hot dry rock fields is not exploited enough due to the high economic and environmental impact as well as the lack of scalability of the existing technologies. Here, thermoelectricity has a great future potential due to its robustness, absence of moving parts and modularity. However, the efficiency of a thermoelectric generator depends highly on the heat exchangers. In this work, a novel geothermal thermoelectric generator is experimentally developed, characterizing different configurations of biphasic heat exchangers to obtain low thermal resistances that allow the maximum efficiency in the thermoelectric modules. As a result, robust and passive heat exchangers were obtained with thermal resistances of 0.07 K/W and 0.4 K/W in the hot and cold sides, respectively. The geothermal thermoelectric generator was built with the most effective heat exchangers and was experimented under different temperature and convection conditions, generating 36 W (17 W by a prototype with 10 modules and 19 W by a prototype with 6 modules) for a temperature difference of 160 °C between the heat source and the environment. Furthermore, the experimental development showed that it is possible to increase electricity generation with a more compact generator, since a decrease in the number of modules from 10 to 6 increases the efficiency from 3.72% to 4.06%. With this research, the feasibility of a novel and robust geothermal thermoelectric generator whose working principle is phase change has been experimentally demonstrated, as well as the importance of compactness to maximize its efficiency and thus, power generation.
Open Access
Influence of temperature and aging on the thermal contact resistance in thermoelectric devices
(Springer, 2020) Rodríguez García, Antonio; Pérez Artieda, Miren Gurutze; Beisti Antoñanzas, Irene; Astrain Ulibarrena, David; Martínez Echeverri, Álvaro; Ingeniaritza; Institute of Smart Cities - ISC; Ingeniería
During thermal design in the first phases development, thermoelectric systems, such as thermoelectric generators, the most important parameter affecting the performance is thermal resistance of the components. This paper focusses on the thermal contact resistance (TCR), analyzing the influence of aging and temperature on different thermal interface materials (TIMs), i.e., thermal paste, graphite and indium. In previous papers, TCR has been studied depending on parameters such as surface roughness, bonding pressure, thermal conductivity and surface hardness. However, in thermoelectric applications, a relevant aspect to consider when choosing a TIM is aging due to thermal stress. The exposure of this type of material to high temperatures for long periods of time leads to deterioration, which causes an increase in the TCR impairing the conduction of the heat flow. Therefore, there is a need to study the behavior of TIMs exposed to temperatures typical in thermoelectric generators to make a correct selection of the TIM. It has been observed that exposure to temperatures of around 180°C induces a significant increase in the thermal impedance of the three TIMs under study, although this effect is much more relevant for thermal paste. The contact, comprising steel, thermal paste and ceramic, presents a 300% increase in the thermal impedance after 70 days of aging, whereas that exceeds 185% for the contact of aluminum, thermal paste and ceramic. In the tests with exposure temperature of 60°C, there is no observed decrease in the thermal impedance.
Open Access
Advanced phase-change intermediate heat exchanger development for multistage thermoelectric heat pumps
(Elsevier, 2023) Erro Iturralde, Irantzu; Aranguren Garacochea, Patricia; Alegría Cía, Patricia; Rodríguez García, Antonio; Astrain Ulibarrena, David; Institute of Smart Cities - ISC; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
The need to reach a full energy decarbonisation is well known. Heating and cooling consumption is almost half of the global energy end-use. Thus, development of low-carbon and highly efficient power-to-heat technologies must be developed. In this work, the use of thermoelectric technology working as a heat pump is proposed to heat up an airflow of 38 m3/h. Two different prototypes of multistage thermoelectric heat pumps have been developed and compared based on monophasic and phase-change intermediate heat exchangers. The reduced thermal resistance obtained for the novel phase-change heat exchanger increases the heat flux supplied to the airflow and reduces the consumed power of the system, outperforming the operation of the monophasic thermoelectric heat pump between a 30 and a 67 %. The novel multistage phase-change heat pump obtains experimental COP values between 3.25 and 1.26 when the airflow rises its temperature from 3.5 °C to 23.5 °C. Additionally, this experimental study proves a new methodology to calculate the supplied heat flux to the airflow. The validation of this technology proves a discrepancy of ± 9 % when this novel technology is compared to the conventional one based on the airflow temperature rise.