Open Access
Experimental assessment of a thermoelectric subcooler included in a transcritical CO2 refrigeration plant
(Elsevier, 2021-05-25) Aranguren Garacochea, Patricia; Sánchez, Daniel; Casi Satrústegui, Álvaro; Cabello, Ramón; Astrain Ulibarrena, David; Ingeniería; Ingeniaritza; Institute of Smart Cities - ISC
This study brings an experimental research that has tested a real transcritical CO2 vapor compression cycle that includes a thermoelectric subcooler at the exit of the gas-cooler of the refrigeration plant. The aforementioned technology hybridization increases the COP of refrigeration systems as long as the subcooling system is properly designed and operated. The experimental facility studied has been tested under constant ambient conditions (30 °C and relative humidity of 55%) and maintaining the evaporating temperature at -10 °C; while the voltage supplied to the thermoelectric modules and the thermal resistances of the heat exchangers located at the thermoelectric subcooler have been experimentally modified. The voltage supplied to the fans located at these heat exchangers was modified implying thermal performance deviation of the heat exchangers and a variation on the power consumption of the cooling facility. The results show an experimental increase on the COP of 11.3% while the cooling capacity increases a 15.3% when the thermoelectric modules are supplied with 2 V and the fans with 9 V. Moreover, the importance of optimizing the voltage supplied to the thermoelectric modules and to the auxiliary consumption of the thermoelectric subcooler is addressed along this research.
Open Access
Experimental evaluation of a transcritical CO2 refrigeration facility working with an internal heat exchanger and a thermoelectric subcooler: performance assessment and comparative
(Elsevier, 2022) Casi Satrústegui, Álvaro; Aranguren Garacochea, Patricia; Araiz Vega, Miguel; Sánchez, Daniel; Cabello, Ramón; Astrain Ulibarrena, David; Ingeniería; Ingeniaritza; Gobierno de Navarra / Nafarroako Gobernua; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
The use of carbon dioxide in transcritical state has become one of the most used solutions to comply with the F-Gas directive and reduce greenhouse gases emissions from refrigeration systems at high ambient temperatures. For low-medium power units, the commonly used solutions to improve the efficiency such as the ejector, multiple compressor arrangements, mechanical subcooler, etc., add complexity and increase the cost of the refrigeration facility, which is not ideal for small units. In this low-medium power range, two technologies stand out to increase the performance of a carbon dioxide transcritical cycle: the internal heat exchanger and the thermoelectric subcooler. This study brings a complete research in which both solutions have been tested in the same experimental transcritical carbon dioxide refrigeration facility under the same working conditions. It focuses on the real performance of both systems and discusses the strengths and weaknesses of using an internal heat exchanger or a thermoelectric subcooler. The results show that the thermoelectric subcooler outperforms the internal heat exchanger in both the coefficient of performance and the cooling capacity while also being a more controllable and flexible solution.
Open Access
Experimental enhancement of a CO2 transcritical refrigerating plant including thermoelectric subcooling
(Elsevier, 2020) Sánchez, Daniel; Aranguren Garacochea, Patricia; Casi Satrústegui, Álvaro; Llopis, R.; Cabello, Ramón; Astrain Ulibarrena, David; Ingeniería; Ingeniaritza
CO2 is an excellent natural refrigerant that can be used in almost any commercial cooling application thanks to its useful range of evaporative temperatures and excellent environmental properties. However, due to its low critical temperature, CO2 has an important issue related to the low performance of the simplest transcritical refrigeration cycle. To overcome it, the subcooling technique is a well-known method to improve the energy performance of any refrigeration cycle especially the CO2 transcritical one. The IHX is a widely used example of this method that is implemented in almost all standalone systems that use CO2 as a refrigerant. As an alternative of this element, in this work, a thermoelectric subcooling system is presented and tested in a CO2 transcritical refrigerating plant. The experimental tests have been performed at two ambient temperatures: 25 and 30 degrees C, maintaining a constant evaporating level at-10 degrees C and varying the voltage supply to thermoelectric modules and the heat rejection pressure. The results from these experimental tests revealed that the COP and the cooling capacity of the refrigerating plant can be enhanced up to 9.9% and 16.0%, respectively, operating at the optimum operating conditions. Moreover, the experimental tests corroborate the existence of an optimum voltage which maximizes the COP, and the almost linear capacity regulation easily adjustable by varying the voltage supply.

Casi Satrústegui, Álvaro

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