## 3 Results  
In this study, an air-cooled binary geothermal organic Rankine cycle (ORC) power plant is thermodynamically modelled to observe, test and check its thermodynamic performance more accurately and rapidly. Additionally, to increase the modelled system performance, the artificial bee colony (ABC) method is used to maximize system exergy efficiency. With this aim, real operating data (flow rate, pressure and temperature values from input and output lines of system components) from an existing power plant were collected by the system's Supervisory Control and Data Acquisition (SCADA) program on 14 April 2013. This date is a transitional period between winter and summer seasons for data from the Sinem GPP. The environmental temperature and pressure on that date were recorded as 18 \({}^{\circ}\)C and 1 bar, respectively. Later the operational data according to state numbers of Figure 1 are presented in Table 1 and the equations given in the Thermodynamic Analysis section are used to complete exergy analysis. The results of the exergy analysis for the real GPP are shown as the Grossman flow diagram in Figure 4. The exergy efficiency of the power plant is calculated as 39.1% based on the exergy input of geofluid (brine) and its steam entering the system. However, the power consumed in the operation of turbines, pumps, fans, auxiliary equipment of the GPP is met by the gross power generated by the plant. When this was deduced, the system exergy efficiency was found to be 14.52%. Turning to Figure 4, the result is that 60.9% of the exergy input rate entering the system is lost as waste heat (exergy loss and destruction). Of the exergy input rate of the geofluid entering the system, 23.7% and 0.5% is lost in the re-injection phase and in the phase of releasing NCGinto the atmosphere as exergy loss (heat loss-waste heat), respectively. Of the remaining exergy input rate, 20.6% and 15.6% are consumed as exergy destruction on levels I and II, respectively. The highest exergy destruction percentages for components are 4.6% from condenser CON 2 and vaporizer VAP 2, 3.7% from condenser CON 1 and then 3.6% from pumps and separators on level I and II. As observed in Figure 4, there is approximately 53,772 kW exergy input rate into the system from the geofluid and its steam. Of this total exergy input rate, 12,740 kW is calculated as the exergy rate spent on re-injection, 11,102 kW is exergy destruction rate occurring in system components on level I, 8388 kW is exergy destruction rate of those in level II and 275 kW is the exergy loss rate from NCG. The highest exergy destruction rate in the GPP occurs in the condenser CON 2 in level II of the binary cycle. This is followed by VAP 2 on level II and then CON 1 on level I. In this situation the priority components requiring improvement are CON 2, VAP 2 and CON 1. As described in the Modelling of the System section, modelling is based on the exergy analysis of a real GPP. The data (mass flow rate, temperature and pressure on steam lines in Figure 1) entering and exiting the system and its components are recorded momentarily. Thus, all the data are dynamic over time. Two parameters (\(\bar{\epsilon}_{\rm k}\) and \(\eta_{\rm k}\)) with these data are established a relationship between the system components, so an integrated system model has been created. As a result, the behaviour of the model is very close to that of the real system and simulates it accurately. Therefore, the convergence behaviour of the model for modelling the real system according to the exergy efficiency is presented in Figure 5. Note that the exergy efficiency of the real system is 14.52%. It can be seen that the exergy efficiency of the model fluctuates with an increase in iteration number and varies between 14.42% and 14.55%. This fluctuation occurs during the matching process between the real system and the model.