Thermoelectric (TE) air conditioning is a viable solid-state cooling technology which can potentially compete with conventional air conditioning systems. TE air conditioning technology offers many advantages that are required for next-generation air conditioning, such as demand-flexible operation, low noise, no moving parts, no harmful gas emissions, and scalability with a modular structure. A TE cooling device can pump heat from one side to the other using electrical energy based on the physical phenomenon called the Peltier effect, and it comprises multiple TE legs that are connected electrically in series and thermally in parallel. In the past few decades, a number of experiments have been done to compare the performance of TE cooling systems with conventional vapor compression-based air conditioning, and the coefficient of performance (COP) of the former has been found to be lower [1]. The COP of TE cooling devices for a given current is limited by the TE figure of merit (zT) of the TE material used, which depends on the Seebeck coefficient, electrical resistivity, and thermal conductivity. At the same time, the COP also depends inversely on the current input while the actual air temperature drop along a TE module, or the cooling capacity of the TE cooling system, depends directly on the current input. Due to the trade-off between the COP and the cooling capacity of the TE cooling module, a TE cooling system operates typically with a relatively high current for high cooling capacity in sacrifice of COP.In the present work, we propose a modular approach by which one can achieve both a high COP and a high cooling capacity in a TE air conditioning system. In our approach, small TE cooling modules are connected in series for sequential cooling to achieve sufficient air temperature drop (ΔT) in one row, and multiple parallel rows are configured to achieve sufficient cooling capacity for the air. Each of the cooling modules operates at a relatively small current to maintain a high COP per module, such that the overall system COP remains very high, exceeding the COP of conventional air conditioning systems. One of the drawbacks of this small-current operation is that the parasitic heat losses could be significant compared to the cooling power. For this, we develop a rigorous theoretical model with major parasitic heat losses and three-dimensional heat contraction effects taken into account. Realistic external air convection heat transfer and parasitic thermal and electrical contact resistances have been modelled. Variation of cooling capacity, COP, and power consumption are systematically studied using the theoretical model by varying the key parameters such as electric current, air inlet flow rate, material zT, TE leg thickness, and fill factor. [2] Our results show that TE cooling can be a competitive technology for small-scale air conditioning with existing materials, provided that parasitic losses are reasonably reduced and cooling modules are optimally designed. Additionally, the results will be compared with Ansys simulations using coupled models of convection, conduction, and TE heat transfer in terms of COP, cooling capacity, and power consumption.[1] D. Zhao et al. Appl. Therm. Engg. 66, 15-24 (2014).[2] A. Saini et al. Energy Build. 240, 110931 (2021).

Theoretical Modeling and Modular Approach for High-Cop Thermoelectric Air Conditioning System

Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2021/volume/85543

ASME 2021 International Mechanical Engineering Congress and Exposition (IMECE2021)

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