## 2 Methodology  
### Description of the System  
The schematic diagram of the proposed tri-generation system is shown in Figure 1. The system is able to simultaneously generate heating, power and cooling for various purposes in different seasons. The system consists of three parts: the power section which produces electricity, the adaptable cooling part which is applied as absorption refrigeration in summer days and heat pump in winter days (by switching the evaporator) and the domestic heat exchanger (DHE) is used to supply heat demand. As shown in Figure 1, the geothermal hot water (state 21) is divided into two parts; one part provides the required heat input to satisfy the heat demand (state 24) via the DHE. The other part is coupled to the power section by the boiler (BOI) (state 22). The required heat for the generator (GEN) is supplied by stream 26 which is the combination of the two returning geothermal water streams coming from DHE (state 25) and BOI (state 23). The description of the tri-generation system is started with the ammonia-water solution in the power section. A saturated liquid ammonia-water solution (state 4) is pumped through pump 2 (PU2) (state 8) to the high pressure of the system. The stream is delivered to separator (SEP) after heating in the boiler via geothermal water (state 9). In the SEP, the liquid-vapor stream is separated to saturated liquid (state 10) and saturated vapor phases (state 11). The stream 12 is expanded via the turbine (TUR) and is mixed with the stream leaving the solution heat exchanger (SHE) via expansion valve 2 (EX2). This stream (stream 15) is led through \(\text{CON}_{2}\) and then to absorber (ABS) (stream 17) through PU3. The ammonia-water solution at the outlet of the ABS (state 1) is forced to the medium pressure level (state 2) by PU1 and is led to SHE. This stream at the outlet of the SHE (stream 3) which is heated in the SHE via saturated liquid (state 11) from SEP. The stream 3 goes to GEN to heat with the geothermal water following to divide into two saturated liquid and vapor streams (stream 4 and 5). The vapor stream coming from the GEN (state 5) is cooled through rectifier (REC) and again the stream is divided into liquid and vapor phase to provide a strong ammonia solution (stream 7). The pure ammonia is saturated in the \(\text{CON}_{1}\) (stream 18) and is led through the evaporator (EVA) via \(\text{EX}_{1}\). In the EVA, the pure ammonia solution is heated by absorbing heat and can produce a cooling demand in the summer condition (stream 39-40). The stream coming from EVA (stream 20) leads to ABS and is mixed with stream 17 via PU3 and the proposed system is completed. The heat sink streams (streams 31-36) are used as coolant and the water- ethylene glycol streams 39 and 40 are utilized to cover the cooling demand. The water streams 29 and 30 are used to produce heating demand. Moreover, it is worthwhile to indicate that in the proposed system, two different evaporators are applied in summer and winter. In summer days, when the tri-generation mode is required, the evaporator for cooling is applied to the system. In winter days, when no cooling demand is required, the geothermal fluid coming from GEN (stream 27) is led through the evaporator for heating. In this regard, the useful productions in the tri-generation system are outlined as follows:  
- heating via domestic heat exchanger  
- power generation via turbine  
- cooling via evaporator