## 3 Results and Discussion
### The Optimized Quasi-Steady State Results For Different Typical Days
In the typical day of WSF, in the first scenario the system is run under part load of 90% with net produced power of 1517 kW. However, in the typical day of TSF with the net produced power of 986.1 kW the system is run under part load of 58%. In minimizing the total exergy destruction rate, the \(\delta\)T\({}_{\text{CON1}}\), \(\delta\)T\({}_{\text{ABS}}\) and \(\delta\)T\({}_{\text{CON2}}\) select their lowest values. The TIP and T\({}_{\text{gen}}\) are considered as the variable parameters. In this regard, in the second scenario the annual mean exergy destruction rate is 2980.32 kW. In addition, the annual mean exergy and energy efficiencies in the second scenario are calculated to be 40.95% and 42.59%, respectively. It is observed that the highest mean exergy destruction rate occurs in the typical day TWC of 3747 kW. The lowest mean exergy achieves a value of 2433 kW in the typical day TSF. In the winter days, the total exergy destruction rate in the work days is lower than the one in the Sundays, however, in the transient and summer days this value in the workdays is higher than the one in the Sundays. In addition, a comparison between cloudy and fine days in the winter days shows that in the fine days the total exergy destruction rate takes higher value than the one in the cloudy days in the winter conditions. In the transient condition, this value in cloudy days in lower than the one in the fine days. In this  
Figure 8: The mean energy and exergy efficiencies as well as the mean total exergy destruction rate of each typical day under optimization condition based on minimum total exergy destruction rate. regard, the performances of tri-generation system have been changed with variation in the weather conditions. The system works under part load of 35.35% and 70.32% in the typical day of WWF and SWX, respectively. Comparing two optimization cases, the reduction in the total exergy destruction rate in the second scenario is achieved at the expense of 8.32% decrease in the exergy efficiency. In addition, the higher mean exergy efficiency in the first scenario is obtained at the expense of 14.52% increase in the total exergy destruction rate. In this regard, the optimization results for minimizing the total exergy destruction rate bring about a better performance enhancement. In detail discussion, the on-design exergy efficiency in [17] driven by geothermal heat source of 173 \({}^{\circ}\)C was 52.8% in winter days, however it was calculated to be 49.5% in summer days. However as seen in the Figures 7 and 8, the exergy efficiency in the winter days is varied between 38.79-53.21%. In the summer days, it varies between 25.2-36.16%. In addition, in the transient conditions, it is in the range of 36.08-41.16%. Furthermore, in Ref. [17] the ambient temperature was taken constant values of in summer and winter days 22.3 \({}^{\circ}\)C and 10.1 \({}^{\circ}\)C, respectively. However, in the present study it varies in different typical day categories according to an existing geothermal district heating network in the German Molasse basin, which makes the investigation more practical. Referring to Tables 13 and 14 in the Appendix A, the turbine isotropic efficiency in the off- design mode in different typical day categories varies between 56-85%, however it took almost in the previous works constant value of 85%. It is important to mention that the turbine isotropic efficiency in the off-design calculation in the second scenario is almost 5-20% lower than the one in the first scenario. In addition, the pinch point difference temperature in the boiler in previous works always took a constant value of 10 \({}^{\circ}\)C. However, as shown in Tables 13 and 14, it varies between 14.22-25.47 \({}^{\circ}\)C for maximizing the exergy efficiency. It is obvious that the pinch point difference temperature in the boiler takes higher values in order to minimizing the total destruction rate in comparison to maximizing the exergy efficiency.