## 3 Results and Discussion
### Seasonal Energy Performance and TEWI
Although the use of R-454B corresponds to a small increase in indirect emissions, due to the higher electric energy consumption linked to the penalization of heat pump efficiency, the direct emissions of the system decrease dramatically by almost 80%. As evidenced by Table 2, the adoption of a low-GWP refrigerant allows for the reduction, for both ASHP and GCHP configurations, in CO\({}_{2}\) emissions of about 2500 kg (\(-\)26%) over the whole system's life cycle. Another important result is that, in both cases, switching to the fluid with the lower environmental impact, the contribution of indirect emissions grows in relative terms. In fact, indirect GHG emissions represent about 63% of the overall CO\({}_{2}\) emissions in the configurations based on R-410A, while this percentage increases up to 90% adopting R-454B. It is important to mention that the contribution of indirect emissions in the TEWI can be limited in different ways. As an example, the heat pump can be directly powered by PV panels installed on the building; in this way, the electricity absorbed from the grid and thus the indirect emissions would be significantly reduced. Obviously, more efficient heat pump technologies can contribute to reduce electric energy needs and, consequently, indirect GHG emissions. Moreover, taking into account the current energy transition aimed at the complete decarbonization of the electric power system, it is reasonable to expect a continuous drop in the emission factor of the electricity drawn from the grid. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Refrigerant** & \multicolumn{2}{c}{**R-410A**} & \multicolumn{2}{c}{**R-454B**} \\ \hline Heat pump typology & GCHP & ASHP & GCHP & ASHP \\ \(Q_{h}\) (kWh) & 5280 & 5203 & 5241 & 5145 \\ \(Q_{c}\) (kWh) & 2435 & 2443 & 2438 & 2435 \\ \(E_{d,comp,heat}\) (kWh) & 980 & 1162 & 992 & 1166 \\ \(E_{d,comp,heat}\) (kWh) & 285 & 398 & 295 & 421 \\ \(E_{d,pump,heat}\) (kWh) & 148 & 66 & 159 & 68 \\ \(E_{d,temporal}\) (kWh) & 87 & 31 & 88 & 32 \\ \(SCOP_{n}\) & 5.39 & 4.48 & 5.28 & 4.41 \\ \(SCOP\) & 4.68 & 4.24 & 4.55 & 4.17 \\ \(SEER_{n}\) & 8.53 & 6.14 & 8.26 & 5.79 \\ \(SEER\) & 6.54 & 5.70 & 6.36 & 5.53 \\ \(APF_{n}\) & 6.10 & 4.90 & 5.97 & 4.78 \\ \(APF\) & 5.14 & 4.62 & 5.00 & 4.53 \\ Direct GHG emissions (kgCO2) & 3383 & 3383 & 740 & 740 \\ Indirect GHG emissions (kgCO2) & 5738 & 6338 & 5869 & 6453 \\ TEWI (kgCO2) & 9120 & 9721 & 6609 & 7193 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Energy and environmental performance of the considered HVAC system configurations. In order to evaluate the expected environmental impact of the studied heat pump systems during the next decades, the TEWI trend associated with the analyzed configurations has been calculated up to 2050, taking into account the upcoming energy transition scenario. The Italian emission coefficient \(\beta\) of the last 30 years has been imported from the Higher Institute for Environmental Protection and Research (ISPRA) database [34]. The analysis of the reported data outlines that the value of \(\beta\) was more than halved from 1990 to 2020, decreasing from 577.9 g\({}_{\text{CO2}}\) kWh\({}^{-1}\) to 255 g\({}_{\text{CO2}}\) kWh\({}^{-1}\), thanks to a deep penetration of renewable energy sources into the national energy mix. In addition, a decreasing trend in the emission factor has been estimated during the next years on the basis of the ambitious European goals set by the European Green Deal [2], aimed at the complete decarbonization of the energy sector by 2050. In particular, the emission factor in 2050 has been considered null, and its reduction with respect to the value of 2020 has been set equal to 15%, 33%, 50%, 66% and 85% for the years 2025, 2030, 2035, 2040 and 2045, respectively. In order to clarify, the \(\beta\) values during the analyzed years are reported in Table 3.  
Figure 8 shows the trend of TEWI for the HVAC system based on the GCHP operating with R-410A (Figure 8a) and R-454B (Figure 8b), with the share of direct and indirect emissions out of the total.