Open Access
Experimental study of a multistage thermoelectric heat pump using different internal heat exchangers
(2021) Erro Iturralde, Irantzu; Aranguren Garacochea, Patricia; Astrain Ulibarrena, David; Ingeniería; Institute of Smart Cities - ISC; Ingeniaritza
The current need to carry out an energy transition towards a 100 % renewable horizon places the energy storage as the key. Thermal energy storage has the potential to be an optimal technology. Nowadays electrical resistors are used to convert electrical energy to termal energy by heating an air flux which is stored afterwards. In this work, it is proposed to use a multistage thermoelectric heat pump (MS-TEHP) to do this energy conversion. It has been experimentally analyzed and compared the performance of two MS-TEHP with different internal heat exchangers. With this preliminary research, it has been demonstrated the feasibility of this novel thermoelectric technology which aim is to improve the energy conversión process for thermal energy storage.
Open Access
Experimental analysis of one and two-stage thermoelectric heat pumps to enhance the performance of a thermal energy storage
(Elsevier, 2023) Astrain Ulibarrena, David; Aranguren Garacochea, Patricia; Erro Iturralde, Irantzu; Chavarren Oroz, David; Alzuguren Larraza, Iñaki; Ingeniería; Ingeniaritza; Institute of Smart Cities - ISC
This experimental study demonstrates the possibility to enhance the performance of a low-temperature thermal energy storage system (~160 ¿C) based on airflow heating using electrical heaters by including thermoelectric technology. An improvement of the 17 % on COP is reached by using an optimized thermoelectric heat pump system to preheat the airflow, consisting of three one-stage and three pyramidal two-stage thermoelectric heat pumps sequentially installed along the airflow that is heating. This research experimentally analyses and compares the COP of three different configurations of thermoelectric heat pumps: one-stage, square two-stage, and pyramidal two-stage thermoelectric heat pumps. The experimental study aims to characterize the operation of each configuration for heating an airflow of 16.5 m3/h at 25 ¿C as ambient temperature. To that purpose, the airflow inlet temperature, voltage supply, and voltage ratio between stages have been modified. The experimental results show that for 25 ¿C as inlet temperature the one-stage thermoelectric heat pump has the best performance with a maximum generated heat of 78 W. Whereas, a two-stage thermoelectric heat pump is required when the inlet temperature increases. At 40 ¿C as inlet temperature, the square two-stage configuration provides the best performance with a voltage ratio of 2, which reaches a COP of 3.29 generating only 20 W of heat. However, the pyramidal two-stage configuration is able to achieve the maximum heat outputs with a voltage ratio of 1, generating 172; 161; 149 and 138 W, with corresponding COP values of 1.17; 1.16; 1.14 and 1.11 for inlet temperatures of 25; 40; 55 and 70 ¿C. This configuration is the one that achieves the greatest COP values with high inlet temperatures.
Open Access
Thermoelectrics working in favour of the natural heat flow to actively control the heat dissipation
(Elsevier, 2024) Alzuguren Larraza, Iñaki; Aranguren Garacochea, Patricia; Casi Satrústegui, Álvaro; Erro Iturralde, Irantzu; Rodríguez García, Antonio; Ingeniería; Ingeniaritza; Institute of Smart Cities - ISC; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
In sectors such as electronics, photonics and HVAC and refrigeration, heat dissipation has a major impact in their performance. However, there is generally not much control over this effect. Thus, one way of making these units more controllable would be to include thermoelectric technology in the heat dissipation systems. Therefore, in this work, a computational model based on the resistance-capacitance model to solve a thermoelectrically aided heat dissipation system is proposed, considering all the thermoelectric effects, temperature dependent thermoelectric properties and four temperature levels. Besides, an experimental prototype has been built to assess the real performance of thermoelectric modules (TEM) working under different operating conditions. Additionally, these results have been used to validate the computational model, obtaining maximum errors of ±6% in the main parameters. Moreover, the computational model has been used to simulate the effect of modifying the temperature difference between the hot and cold sources and the thermal resistances of the heatsinks located on both sides of the TEMs. The results show that the thermoelectrically aided dissipation system would be beneficial when working with low temperature differences and low thermal resistance values of the heatsinks, especially on the heatsink located on the hot side of the TEMs.
Open Access
Development and experimental validation of a two-stage thermoelectric heat pump computational model for heating applications
(Elsevier, 2024) Erro Iturralde, Irantzu; Aranguren Garacochea, Patricia; Martínez Echeverri, Álvaro; Astrain Ulibarrena, David; Ingeniería; Ingeniaritza; Institute of Smart Cities - ISC; Universidad Pública de Navarra - Nafarroako Unibertsitate Publikoa
The utilisation of thermoelectric technology as a heat pump in heating applications necessitates comprehensive investigation. The scalable nature of thermoelectric technology enables its operation at elevated temperatures without the requirement of refrigerants. In this work, an accurate computational model that can simulate one- and two-stage thermoelectric heat pumps is developed. This model uses the electric-thermal analogy and the finite difference method, including the thermoelectric effects, temperature dependent properties, thermal contact resistances and all heat exchangers, even the intermediate heat exchanger in the case of a two-stage configuration. Moreover, the model has been experimentally validated by built and tested prototypes, being the first time that a two-stage thermoelectric heat pump model is experimentally validated. The discrepancy between the simulated and experimental results is below the ± 10 % for , ± 8 % for generated heat and temperature lift in the airflow, and less than the ± 6 % for consumed power. Additonally, the model simulates real tendencies under different operating conditions, proving the reliability of the developed thermoelectric heat pump model. Finally, the model is used to optimise a thermoelectric system combining one- and two-stage thermoelectric heat pumps, and hybridising them with electric resistances. An airflow of 16.5 m3/h is heated from 25 °C to 160 °C, achieving a maximum of 1.21. Lastly, the importance of considering the thermal resistances of the heat exchangers is computationally modelled and demonstrated. Not taking them into account would overestimate the performance of the TEHP system by more than the 7 %.
Open Access
Enhancement of the power-to-heat energy conversion process of a thermal energy storage cycle through the use of a thermoelectric heat pump
(Elsevier, 2024) Erro Iturralde, Irantzu; Aranguren Garacochea, Patricia; Sorbet Presentación, Francisco Javier; Bonilla-Campos, Íñigo; Astrain Ulibarrena, David; Institute of Smart Cities - ISC; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
The principal strategy for achieving a neutral climate entails enhancing the share of renewable energies in the energy mix, in conjunction with promoting innovation in efficient technologies. Thermal energy storage systems have the potential to efficiently handle the intermittent nature of renewable energy sources. Furthermore, these systems can effectively handle shifts in both heat and electrical demand. Thus, efficient power-to-heat technologies are needed to boost thermal energy storage. This manuscript explores the potential of utilising a thermoelectric heat pump system in conjunction with electric resistances for charging a thermal energy storage. In order to achieve elevated temperatures, the thermoelectric system integrates thermoelectric heat pump blocks in a two-stage configuration. Air has been employed as a heat transfer medium for sensible heat storage. Higher airflow rates improve the performance of thermoelectric heat pump system. Moreover, its impact on the optimal voltage supply of the thermoelectric system is observed when it is combined with an electric resistance to achieve elevated temperatures. In comparison to the basic charging process that solely relies on the electric resistance of a thermal energy storage at 120 °C, a significant 30 % increase in power-to-heat energy conversion has been achieved by including the thermoelectric heat pump system. In fact, it efficiently elevates the temperature from the initial ambient temperature of 25 °C to a remarkable 113.1 °C, achieving a coefficient of performance of 1.35 with an airflow rate of 23 m3/h. Therefore, the use of this technology to enhance a complete process of storing excess renewable energy in the form of heat for subsequent use in both heat and electricity through a combined heat and power cycle is demonstrated.
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.