Analysis and optimization of different two-stage transcritical carbon dioxide cycles for heating applications

[EN] Increased interest in the environmental impact of refrigeration technology is leading toward design solutions aimed at improving the energy efficiency and use of eco-friendly refrigerants with low GWP. The aim of this paper is to theoretically analyse R744 air to water heat pump cycles for heating applications up to 80 °C. This work studies the following cycle configurations: two-stage with injection (with and without intermediated cooling between compressors) and a single-stage circuit coupled with an auxiliary circuit. Internal heat transfer among the different streams of refrigerant is included, and the cycles have been optimized with regards to COP in terms of the intermediate conditions and gas cooler pressure. Finally, these cycles have been compared and analysed among each other and with a subcritical injection cycle working with R134a and a single-stage R744 cycle. The improved cycle with R744 can represent a global improvement of 15% in terms of COP.This work has been developed in the 7 framework program of the European Union by the project Next Generation of Heat Pump Technologies (NEXTGHP) grant agreement 307169. The authors give thanks for the given support. Part of the work presented was carried by Miquel Pitarch-Mocholi with the financial support of the Phd scholarship from the Universitat Politecnica de Valencia.Pitarch Mocholí, M.; Navarro-Peris, E.; Gonzálvez Maciá, J.; Corberán Salvador, JM. (2016). Analysis and optimization of different two-stage transcritical carbon dioxide cycles for heating applications. International Journal of Refrigeration. 70:235-242. https://doi.org/10.1016/j.ijrefrig.2015.08.0132352427