## 3 Results and Discussion
### Seasonal Energy Performance and TEWI  
In Table 2, a summary of the yearly energy and environmental performance of the studied system configurations is reported as a function of the heat pump typology and refrigerant fluid. If we consider the results of the heat pumps operating with R-410A, it is confirmed that, on a seasonal basis, the heat pump energy performance can be improved by up to 20% in heating mode and even more than 40% in cooling mode when a GCHP is considered, due to the more favorable heat source/sink. However, also taking into account the energy consumption of auxiliaries, the advantage of ground-coupled units drops to 10% and 15%, respectively. Indeed, the overall energy consumption of the circulating pumps increases by about 150%, lowering the global performance of the system. Finally, if the annual performance factor (\(APF\)) is considered, it is confirmed that the GCHP has a higher efficiency, with an increase of 25% in this KPI compared to that of the ASHP. In addition, on an annual basis, the advantage of a GCHP-based system is reduced only to 11% when the energy demand of pumps and auxiliaries is considered. It is important to mention that the effective energy penalization mainly depends on the complexity of the hydronic piping, dominant building thermal load among the heating and cooling seasons, operating fluid (pure or glycol water), circulating pump size and its control strategy (fixed-speed, constant or proportional pressure control). For instance, [PERSON] et al. (2018) showed that with a predominant heating load, energy penalization can reach about 12% and 3% in winter and summer, respectively. On the other hand, analyzing the influence of the adopted refrigerant on the seasonal and annual efficiency, it can be observed that, with the fluid R-454B, a slight decrease in heat pump performance is present and, consequently, in the performance of the entire system. More in detail, the data reported in Table 2 highlight that the performance of the heat pumps operating with R-454B is similar to that achieved with R-410A during the winter period: a slight reduction in \(SCOP_{n}\) is observed, equal to 2%, with both external sources, whereas, considering the auxiliary components, the seasonal efficiency (\(SCOP\)  
Figure 7: Monthly energy performance of the geothermal and aerothermal heat pumps with R-454B and of the whole HVAC system in the heating (**a**) and cooling (**b**) seasons. drops by 3% in ground-mode. A slightly greater penalization is noticed during the cooling season. The GCHP and the ASHP \(SEER_{n}\) values drop by about 3% and 6%, respectively; this penalization becomes 3% in both modalities when the auxiliaries (\(SEER\)) are taken into account. These results are due to a slight drop in heat pump thermal and cooling capacity when the unit operates with the low GWP refrigerant R-454B (see Figures 4 and 5). Indeed, the heat pump operating time rises, and, consequently, the electricity absorbed by the circulating pumps and other auxiliaries increases slightly. More in detail, in winter, the compressor energy consumption increases by about 1%, whereas in summer, this figure rises by 3.5% and 6% for the GCHP and ASHP, respectively. Considering the overall electric consumption, the heat pump system based on R-454B consumes in the heating season 2% and 0.5% more in ground- and air-mode, respectively, while in the cooling season, these values increase to 3% and 6%.To summarize, it is noticed that, on an annual basis, switching from R-410A to R-454B implicates a rise in overall electricity consumption of about 1-2%, with a consequent \(APF\) reduction of 2-3%. Nevertheless, the analysis of the system environmental performance by means of the TEWI index highlights how the use of a low-GWP refrigerant leads to a significant reduction in GHG emissions across the whole life cycle of the HVAC plant.