Open Access
Simulation of thermoelectric heat pumps in nearly zero energy buildings: why do all models seem to be right?
(Elsevier, 2021) Martínez Echeverri, Álvaro; Díaz de Garayo, Sergio; Aranguren Garacochea, Patricia; Araiz Vega, Miguel; Catalán Ros, Leyre; Ingeniería; Ingeniaritza; Institute of Smart Cities - ISC
The use of thermoelectric heat pumps for heat, ventilation, and air conditioning in nearly-zero-energy buildings is one of the most promising applications of thermoelectrics. However, simulation works in the literature are predominately based on the simple model, which was proven to exhibit significant deviations from experimental results. Nine modelling techniques have been compared in this work, according to statistical methods based on uncertainty analysis, in terms of predicted coefficient of performance and cooling power. These techniques come from the combination of three simulation models for thermoelectric modules (simple model, improved model, electric analogy) and five methods for implementing the thermoelectric properties. The main conclusion is that there is no statistical difference in the mean values of coefficient of performance and cooling power provided by these modelling techniques under all the scenarios, at 95% level of confidence. However, differences appear in the precision of these results in terms of uncertainty of the confidence intervals. Minimum values of uncertainty are obtained when the thermal resistance ratio approaches 0.1, being ±8% when using temperature-dependent expressions for the thermoelectric properties, ±18% when using Lineykin's method, and ± 25% when using Chen's method. The best combination is that composed of the simple model and temperature-dependent expressions for the thermoelectric properties. Additionally, if low values of resistance ratio are anticipated, empirical expressions from the literature can be used for the thermal resistance of the heat exchangers; for high values, though, experimental tests should be deployed, especially for the heat exchanger on the hot side.
Open Access
Prototype of an air to air thermoelectric heat pump integrated with a double flux mechanical ventilation system for passive houses
(Elsevier, 2021) Díaz de Garayo, Sergio; Martínez Echeverri, Álvaro; Aranguren Garacochea, Patricia; Astrain Ulibarrena, David; Ingeniería; Ingeniaritza; Institute of Smart Cities - ISC
This paper describes the design of an air-to-air thermoelectric heat pump for its integration with a double flux mechanical ventilation system for domestic use in Passive House standard. The prototype has been built and thermally characterized in a test bench reproducing winter and summer conditions, with different gaps between indoor and outdoor temperatures. In addition, two different integration possibilities have been analyzed and tested: a stand-alone installation and the combination with a heat recovery unit. This prototype is composed of 10 thermoelectric modules and finned heat pipes to transfer the heat between the modules and the incoming and outgoing ventilation flows. The maximum heating capacity with 12 V supply was proven to be 1,250 W for heating and 375 W for cooling, with COPs ranging 1.5–4 and 0.5–2.5 respectively. Results show the variations in the performance of the thermoelectric heat pump depending on the voltage supply (3–12 V), the air flows (55–130 m3/h) and the temperature gaps between them. This paper demonstrates the convenience of combining passive and active heat recovery technologies (thermoelectric pump coupled to a heat recovery unit), bringing improvements on the thermal power higher than 25% for heating and 10% for cooling, with respect to the thermoelectric heat pump working directly between the incoming and outgoing air flows. The COP is also increased, especially for low energy demands, when the voltage is 3–6 V. In these cases, the COP might be improved by 50% for heating and 30% for cooling.
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 %.

Martínez Echeverri, Álvaro

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