## 4 Results
The amount of renewable energy supplied by the reversible heat pump, \(\Theta_{RES,RHP}\), shall be calculated with the following formula:  
\[\Theta_{RES,RHP}=\Theta_{RHP}\bigg{(}1-\frac{1}{SCOP_{RHP}}\bigg{)} \tag{35}\]  
where \(\Theta_{RHP}\) is the total thermal energy delivered by the heat pump, both heat and cooling. As a result, around 70% of the energy produced by the reversible heat pump can be considered renewable, for a total of 570 MWh. Instead, in the traditional configuration, the electric chiller can be considered to produce only 190 MWh of renewable energy. Figures 6 and 7 summarizes the annual share of production and consumption of the different energy services (i.e., electricity, heating, and cooling) for the two configurations under analysis. The share of electricity produced by the PV panels increases from the 31.8% to 36.6% when the reversible heat pump is included. Moreover, the amount of electricity sold to the grid remains approximately the same, despite the increase of RES installed capacity. Overall, the reversible heat pump plays a key role in covering the heating and cooling demands, with an increase of around 18% compared to the share covered by the boiler and the non-reversible electric chiller in the traditional configuration. \begin{table}
\begin{tabular}{c c c} \hline Energy System Configuration & \
\begin{tabular}{c} **Novel Configuration with** \\ **Reversible Heat Pump** \\ \end{tabular} &
\begin{tabular}{c} **Traditional Configuration with** \\ **Boiler and Non-Reversible** \\ **Electric Chiller** \\ \end{tabular} \\ \hline Investment Cost & 1199.0 k\& & 1138.0 k\& \\ Equivalent Annual Cost & **288.8 k\&** & **310.8 k\&** \\ Annual Carbon & **580.7 ton** & **694.9 ton** \\ Dioxide Emissions & \multicolumn{1}{c}{} & \\ \hline \end{tabular}
\end{table} 
Table 3: Cont. Figure 6: Sankey diagrams of the annual electricity balance for (**a**) traditional and (**b**) novel configurations. Finally, Figures 8-11 show how the energy demands (electricity, heating, and cooling) are met, in typical winter and summer weeks, with the novel configuration of the energy system. The internal combustion engine is generally continuously on to cover the electric base-load, except when the PV production is particularly high. To meet peak-demands, electricity is bought from the grid, while the sale of electricity to the grid only occurs with high PV production. The heating and cooling base-loads are covered by the ICE and the absorption chiller, respectively, while peak-demands are covered by the reversible heat pump during both winter and summer. Figure 7: Sankey diagrams of the annual thermal energy balances for (**a**) traditional and (**b**) novel configurations. Figure 8: Optimal operation: electricity flows in a typical winter week. Figure 10: Optimal operation: electricity flows in a typical summer week. Figure 9: Optimal operation: heating demand and load shares in a typical week. Obviously, the performance of the proposed configuration is strongly dependent on weather conditions and demand profiles of the case study. More specifically, a sufficiently high RES availability is needed, so that investment on PV panels or wind turbine is justified. Moreover, both peak and average heating and cooling demands must be comparable, so that the capacity of the reversible heat pump is suitable for both energy services. In summary, the proposed configuration is especially suitable for climates where the heating and cooling seasons are comparable in terms of duration and intensity and the RES electricity production is significant.