## 2 Modelling, Analysis and Optimization of a System
### Modelling of the System  
For the real operational Sinem GPP, some control volumes are identified and thermodynamic balance equations are applied to these control volumes. These control volumes are the vaporizers (VAP 1 and VAP 2) and pre-heaters (PREHE 1 and PREHE 2) allowing heat exchange between the geofluid and \(n\)-pentane as working fluid, condensers (CON 1 and CON 2) allowing heat exchange between the air and \(n\)-pentane, and the recuperator (RECUP) using only \(n\)-pentane, turbines (TURB 1 and TURB 2), pumps (PU 1 and PU 2) and fans (FAN 1 and FAN 2), as seen in Figure 1. The basic aim of the model is to research the interactions between the components mentioned above on performance of the whole system, the potentials to improvement and energy saving aspects and potentials. Additionally, some parametric studies are completed to investigate the effect of some important parameters on the performance of the air-cooled binary geothermal ORC (see Figure 2). The thermodynamic properties of the pure water for geofluid (brine), n-pentane as working fluid and air as an ideal gas in each control volume is determined from the COOLPROP software [47; 48]. The MATLAB software [49] is used for thermodynamic balance equations and numerical calculations. In this way, the thermodynamic fluid properties in COOLPROP may be included in MATLAB software (2015b, MathWorks, Natick, MA, USA). Shortly, an algorithm is used for thermodynamic analysis and modelling of Sinem GPP in the MATLAB software. For simplicity, the balance equations for the algorithm models are not given in the text; however they are given in Appendix A Tables A1 and A2. The basic assumptions of the integrated model system in exergy analysis are as follows:* System and its components work in stable state and stable volume conditions,
* Kinetic and potential losses are ignored,
* Heat losses from components are collected in a single location,
* Pressure drops in evaporators, condensers, valves and pipes are collected in a single location,
* For geofluid (brine), the thermodynamic properties of water are used. By doing so, any possible effects of salts and incondensable gases that might be present in the geofluid are neglected [50]. * The pressure losses due to the liquid flow friction were considered negligible. * In air-cooled condensers, air is accepted as an ideal gas with homogenous distribution,
* Isentropic efficiencies of turbines, pumps and fans are only fixed for the optimization process. In order to build a model that will simulate the Sinem GPP completely, an algorithm working in accordance with the T-s flow diagram in Figure 2 using the real data in Table 1 is designed. The algorithm is modelled with a construct created between components using data collected from the real system. This construct is presented in Figure 3. During modelling, for each piece of components on the T-s flow diagrams (Figure 2), values of parameters, effectiveness coefficient (\(\widetilde{\epsilon}_{\text{k}}\)) and isentropic efficiency (\(\eta_{\text{k}}\)), are changed and attempts are made to bring the model output parameters (temperature and pressure) closest to or to the same value as the operation parameters (temperature and pressures) (in Table 1) collected from the Sinem GPP. Thus, the developed model will imitate the real GPP system. As can be seen in Figure 3 and Appendix A Table 1, \(\widetilde{\epsilon}_{\text{k}}\) and \(\eta_{\text{k}}\) are effectiveness coefficient associated with \(\varepsilon\)-NTU method for heat exchangers (vaporizers, condensers, pre-heaters and recuperator) and isentropic efficiency for turbines and pumps, respectively. These are clearly defined as the parameters used to try to make the model match the operational state of the GPP. Their constants used to match the real system to the model are within the boundaries defined by the equipment manufacturer. Their values are 0.82 and 0.88 for VAPs, 0.92 and 0.95 for PREHEs, 0.49 for RECUP, 0.68 and 0.75 for CONs, 0.92 and 0.81 for TURBs, 0.96 and 0.97 for PUs, respectively.