## 3 Results and Discussion
### Comparison with a Conventional System  
At this point, it is important to compare the present system with another conventional one in order to investigate the sustainability of the suggested unit. The conventional system includes an oil boiler of 85% and an electric heat pump for cooling with \(\mathrm{COP}_{\mathrm{cool}}=2.8\), while the lower heating value of the oil was selected at the typical value of 42000 kJ/kg [25]. The cost of the oil was estimated at 2 \(\mathrm{\upxi}\)/Lt, according to the recent economic trends, the electricity price at 0.2 \(\mathrm{\upxi}\)/kWh, the biomass cost at 0.65 \(\mathrm{\upxi}\)/kg, and the oil density selected at 0.86 kg/Lt. The primary energy factors for oil, electricity, and biomass were selected at 1.1, 2.9, and 1.0, respectively [25]. The specific \(\mathrm{CO}_{2}\) emissions coefficients were selected at 0.264 kg\({}_{\mathrm{CO2}}\)/kWh\({}_{\mathrm{th}}\) for oil [25] and 0.487 kg\({}_{\mathrm{CO2}}\)/kWh\({}_{\mathrm{el}}\) for electricity [37]. \begin{table}
\begin{tabular}{c c} \hline \hline
**Parameter** & **Value** \\ \hline Cooling load & 8168 kWh \\ Heating load & 9136 kWh \\ Biomass demand for cooling & 10870 kWh \\ Biomass demand for heating & 6989 kWh \\ Total biomass demand & 17859 kWh \\ Mass of the consumed biomass for cooling & 2119 kg \\ Mass of the consumed biomass for heating & 1644 kg \\ The total mass consumed biomass & 3763 kg \\ Yearly system cooling energy performance & 0.751 \\ Yearly system heating energy performance & 1.307 \\ Yearly exergy efficiency for cooling & 6.31\% \\ Yearly exergy efficiency for heating & 14.48\% \\ Cooling period & 2627 h \\ Heating period & 3041 h \\ Heating period without heat pump operation & 1126 h \\ Heating period with heat pump operation & 1915 h \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Final results of the yearly performance. According to the results, the yearly operating cost of the present system is 2446 \(\upxi\), while the conventional system leads to 2726 \(\upxi\). Therefore, there is a decrease of 10.3% in the yearly operating costs. The primary energy consumption of the present system is 19,303 kWh per year, while the conventional system consumes 20284 kWh. Therefore, there are 4.8% savings in primary energy during the year. Additionally, the yearly CO\({}_{2}\) avoidance with the exploitation of biomass in the present systems was found to be 4258 kgc02 per year. The aforementioned values show that the suggested system has significant advantages in terms of economic gain, primary energy, and CO\({}_{2}\) emissions avoidance. Figure 14 depicts the cumulative primary energy demand during the year for the present system and the conventional one. It is clear that the absorption heat pump is significantly more efficient during the heating period, while it is less efficient during the winter period. However, the final primary energy demand is lower for the absorption heat pump and thus it is the preferable system energetically. Moreover, Figure 15 illustrates the cumulative operating costs of the two examined cases. The absorption heat pump is again a more viable choice during the winter, while during the summer the conventional electric heat pump is the best choice. However, the overall year period makes clear that the absorption heat pump leads to lower operating costs and thus it is the optimum choice financially. At this point, some limitations of the suggested system have to be discussed. Biomass is an environmentally friendly fuel sometimes its use is associated with a smell which makes some users avoid it. However, its use is safe and there is not any danger. Moreover, the biomass boilers in the households need a relatively often cleaning from the ash, something that has to be taken into consideration. Additionally, another aspect that has to be taken into account is the availability of biomass, when it is needed in huge quantities, something that can be a possible issue if its utilization is dramatically expanded.