## 1 Introduction
Other research topics have also been investigated, such as the impact of ambient temperature on the system [40] or the type of thermodynamic cycle (subcritical, supercritical) followed by the working fluid in the ORC [41]. Currently, most ORC systems use the classical working fluids. However, environmental concerns on global warming and ozone destruction impact ORC systems, and are linked to the evolution of refrigerant fluid legislation, the Montreal Protocol, the Kyoto Protocol, and the Kigali Agreement [42; 43]. Hence, the use of and research on less-polluting and replacement fluids has tended to increase [44; 45; 46]. Two types of low global warming potential (GWP) working fluids have appeared, namely Hydrofluorolefin (HFO) [44; 47] and Hydrofluorolether (HFE) [45; 48], as potential replacement working fluids for the ORC. The interest in these fluids issues from their null ozone depletion potential (ODP) and their low or very low GWP. The low-GWP fluid HFO-1336 mzz is an interesting R-245 fa replacement fluid, and the two isomers (Z) and (E) of this fluid show similar performances to the R-245 fa. [PERSON] et al. [49] studied HFO-1336 mzz-Z, and the experimental results obtained with this fluid in comparison to those obtained with the R-245 fa for the same ORC show a similar range of net electrical efficiency. [PERSON] et al. [50] studied the other isomer HFO-1336 mzz-E, and obtained similar performances trends as those obtained with R-245 fa. Another HFO replacement fluid for the R-245 fa is the HFO-1234 [50; 51]; for this HFO fluid, the two isomers (ze) and (yf) present comparable performances with R-245 fa. However, the operating conditions and parameters, and the experimental facility of an ORC system, are important, as illustrated with the performances of HFO-1234. Although similar performances for these two HFO fluids ((ze) and (yf)) to R-245 fa were obtained in studies [50]and [51], slightly higher performance than R-245 fa was obtained in the study of [PERSON] et al. [50] and slightly lower performance in the study of [PERSON] et al. [51]. [PERSON] et al. [51] also demonstrated the good performances of HFO-1234 ze and HFO-1234 yf in comparison with the HFC fluid R-134a. The second low-GWP type of working fluids, HFE fluids, are described as attractive ORC fluids; however, just a few theoretical and experimental investigations have been done to date. [PERSON] et al. [52] presented a biomass-fired, ORC-based micro-CHP for domestic applications with HFE7000 as the working fluid for the ORC system. Their preliminary results, lower than previous expected simulations, highlight the interest of this type of global conversion system for domestic use on a small scale of heat source temperature and power production. [PERSON] et al. [53], [PERSON] et al. [54], and [PERSON] et al. [55] investigated HFE7100 in a small ORC with, respectively, a scroll expander, a radial turbine, and an axial turbine. For each of them, the global ORC performance results are moderate but show the sustainability of this working fluid. Two other HFE fluids [56], HFE245 fa2 and HFE245 cb2, present interesting ORC performances; however, their GWP is higher than HFE7000 and HFE7100 and closest to the classical HFC fluid R-245 fa (GWP\({}_{\text{R-245 fa}}\) = 1030). However, HFO fluids represent a potential problem due to their atmospheric decomposition to trifluoroacetic acid (TFA). Concerning HFE fluids, with a lower GWP than HFC fluids, their value remains around 500, which leads us to pay specific attention to their utilization in the close future. In addition to HFO and HFE, Hydrochlorofluoroolerin (HCFO) [50; 57] has been investigated. The interest in natural refrigerants as ORC working fluids is making a comeback due to their strong environmental friendly aspect, although their flammable potential remains high [58; 59]. Finally, another new low-GWP fluid, NovecTM649, seems to be an interesting working fluid according to the preliminary literature [20; 60; 61].