Energetic/exergetic study of Kalina and refrigeration bottoming cycles on different solar‐driven organic Rankine cycles

Combination of different power cycle scenarios is of prime importance in achieving maximum energy utilization from solar‐driven multigeneration systems. To fulfill such objective, the present article proposes a novel energy distribution system, leveraging a combination of direct‐fed organic Rankine cycle (ORC) and a bottom‐cycled arrangement of Kalina cycle system (KCS) and double‐effect absorption refrigeration cycle (DEARC) within a parabolic trough solar collector powered trigeneration system. The study explores three different ORC configurations: simple ORC; ORC equipped with internal heat exchanger (ORC‐IHE) and regenerative ORC (RORC). It is shown that although higher efficiencies are achievable from a larger portion of PTSC energy absorbed by the ORC, the ORC energy absorption is limited by ORC evaporator temperature differences, and there is unused energy that can be recovered by the KCS, based on the proposed energy system. The results indicate that the addition of bottoming KCS leads to a considerable increase in the exergy efficiency of ORC, ORC‐IHE and RORC‐based systems by 11.7%, 30.7% and 32.6%, respectively. The impact of different ORC configurations, key ORC parameters and various organic working fluids on the energetic/exergetic efficiencies is also examined to find the optimal configuration. In terms of overall energetic/exergetic efficiencies, the highest performance belongs to ORC (78.4%/30.4%) while the lowest energetic and exergetic efficiencies belong to ORC‐IHE and RORC, respectively (56.3% and 25.65%). On the basis of a comparative study with the available literature, these values are higher than what is already reported for similar solar‐driven multigeneration systems. Appropriate thermal match and lower exergy destruction in the KCS, and bottoming cycle arrangement of the DEARC are the main reasons for such enhanced performance. This research not only contributes valuable insights into efficient solar‐driven systems but also sets a new benchmark for performance metrics in the existing literature.


| INTRODUCTION
Rising energy demand, industrial dependence on fossil fuels and inefficient energy systems have resulted in air pollution and global warming.Substitution of fossil fuelbased energy conversion systems with clean and renewable energy alternatives is crucial to avoid or decline harmful global issues. 1Among renewable energy sources, solar energy is promising and available.
Parabolic trough solar collector (PTSC) is the most commonly used solar thermal technology for power generation.Stand-alone cycles suffer from low energy and exergy efficiencies.They can be enhanced by the integration of different cycles and simultaneous production of multiple outputs, like that in the combined cooling, heat and power (CCHP) systems. 2,3Numerous studies have analyzed PTSC-based energy systems for cooling, heat and power generation.In the following, previous studies regarding coupling of the PTSC with different CCHP systems are reviewed.
Organic Rankine cycle (ORC) is a suitable candidate for solar-driven power generation systems.This is because of low boiling point and low vaporization enthalpy of organic fluids that provide a suitable match for power cycles operating in low to medium temperatures (60-350°C). 4,5The optimal design of ORC powered by PTSC was investigated by Yu et al. 6 for various ORC configurations.Results indicated that recuperative ORC outperforms the basic ORC.][9][10] On the basis of dynamic conditions in low solar radiation zone (with radiation intensity lower than 400W/m 2 ), the maximum energy efficiency of the PTSCbased ORC system was 11.05%. 11Utilization of R245fa/ R500 pair as the working fluid of PTSC-based cascaded ORCs resulted in a higher energy efficiency of 12.76%. 12he Kalina cycle system (KCS) is a practical bottoming cycle that augments the energy conversion efficiency of hybrid systems.It provides an appropriate thermal match between the heat source and the working fluid temperature profiles, and therefore reduces irreversibilities induced by the heat recovery process. 13KCS11 employs the zeotropic mixture NH H O 3 2

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with zero ozone depletion and minimal global warming potential as the working fluid. 14Regarding the integration of PTSC and KCS, Zare and Moalemian 15 analyzed an innovative Kalina cycle (KCS123) and obtained an exergy efficiency of 14%.Mirjavadi et al. 16 compared the cascading of ORC and KCS in a PTSC-based steam Rankine cycle and found higher performance for the KCS cascaded system.Boyaghchi and Sabaghian 17 conducted a parametric study to show that the growth of solar irradiation declines both the energy and exergy efficiencies of the PTSC-driven KCS system.Investigation of PTSC with variable aperture area in solar-based KCS indicated that the efficiency of the variable concentration ratio pattern at the autumn equinox is higher than the design concentration ratio pattern. 18egarding solar-driven refrigeration systems, absorption refrigeration is the most usual mode. 19,20

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is more advantageous since it provides higher coefficient of performance (COP) at low generator temperatures. 21,22Bellos et al. 23 evaluated a solar-based ARC system based on thermodynamic and financial aspects to show the superiority of a PTSC-driven system compared with the systems powered by the evacuated tube or other types of collectors.Analysis of a PTSCbased single-effect ARC (SEARC) showed that the COP decreases as the absorber inlet temperature increases. 24nother parametric study of the PTSC-driven doubleeffect ARC (DEARC) system also revealed that COP decreases as solar collector area increases. 25Performance of various solar-powered ARC configurations was evaluated by Ratlamwala and Abid. 26They found that COP and exergy efficiency of the triple-effect ARC were higher than those of single-and double-effect ARCs.
The overall assessment is that ORC is compatible with low-to medium-temperature heat sources (60-350°C), KCS gives an appropriate thermal match between the heat source and the working fluid temperature profiles, and LiBr H O 2

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DEARC provides a higher COP at low generator temperatures.Therefore, these three are selected as the main subsystems of CCHP in the present study.
Within the domain of PTSC-driven CCHP systems, researchers have extensively investigated configurations incorporating ORC, KCS and ARC components.Keshavarzzadeh and Ahmadi 27 optimized a solar-driven trigeneration system based on PTSC, ORC and SEARC.They confirmed that electrical power generation in the DEHGHAN ET AL.
| 1615 solar mode is greater than that of the storage mode.On the contrary, Haghghi et al. 28 reported the highest cost per unit exergy in the storage mode.Analysis of a PTSCdriven CCHP system based on six ORC working fluids in another study resulted in the highest energetic and exergetic performances for n-pentane and toluene fluids. 29Zhao et al. 30 found that the sequential configuration was superior to the parallel configuration in terms of overall exergy efficiency.Dynamic evaluation of the same system for several locations in Greece led to the highest energy efficiency of 36.43% in Athene. 31afary et al. 32 analyzed two PTSC-driven trigeneration systems based on DEARC, one including an internal heat exchanger integrated with ORC (the ORC-IHE-based system) and the other including feed fluid heater as a regenerative ORC (the RORC-based system).The overall exergy efficiency of the ORC-IHE-based configuration (12.69%) was higher than that of the RORC-based system (6.64%).Eisavi et al. 33 reported a higher COP and an exergy efficiency of 12.8% in the solar-driven DEARCbased system as compared with the SEARC-based CCHP configuration.Chen et al. 34 implemented the PTSCdriven ORC-DEARC-based system for building demands and obtained an annual energy efficiency of 56.5%.This efficiency was raised up to 34.16% in another optimization study. 35Cao et al. 36 showed that the complexity of the PTSC-driven CCHP system does not necessarily enhance system output.They found higher power output and therefore higher electrical energy generation for the ORC-SEARC-based system in comparison with those of the RORC-DEARC-based configuration.
Regarding the integration of KCS with solar-based CCHP systems, the literature is scarce.Gogoi and Hazarika 37 examined four configurations of PTSCdriven trigeneration systems involving multiple ORCs, triple-effect ARC and KCS, and found a higher performance for the hybrid system including one KCS and one ORC.Almatrafi et al. 38 evaluated the PTSC-based CCHP system consisting of KCS and DEARC and obtained energy and exergy efficiencies of 13.8% and 6.55%, respectively.Tariq et al. 39 investigated a solar-driven trigeneration system based on ORC, DEARC and KCS and obtained the maximum energetic efficiency of 46.30%.
Comparison between various configurations of ARC in multigeneration cycles has indicated that higher energetic and exergetic efficiencies are achievable when the ARC system is arranged as a bottoming cycle fed by another cycle like ORC. 30,40,41 In Gogoi and Hazarika 37 and Tariq et al., 39 ARC was directly fed by solar heat transfer fluid (HTF).3][44][45][46] From another perspective, SEARC and DEARC systems can operate with hot fluid in the temperature ranges of 80-150°C and 100-205°C, respectively. 20,21,47,48Both of these temperature ranges are more consistent with bottom-cycled ARC compared with direct-fed ARC through the solar field which provides considerably higher temperatures.
The preceding discussion shows that integration of ORC as a direct-feed component plus utilization of bottoming power/refrigeration cycles can maximize the extraction of energy from the PTSC.Due to some limitations induced by the temperature of organic working fluid (OWF) at the ORC evaporator inlet and the pinch point temperature of the ORC evaporator, there is some unused heat that can be recovered.Incorporation of a Kalina bottoming cycle is proposed as a practical and novel solution to such unused energy.In this regard, the main contributions of the present study are as follows: • An Innovative energy distribution system, leveraging a combination of direct-fed ORC and a bottom-cycled arrangement of DEARC and KCS, is adopted for the PTSC-driven trigeneration system.Specifically, the contribution of Kalina cycle in augmenting the hybrid system's performance is examined.• On the basis of such configuration, three novel trigeneration systems involving three different ORC structures are proposed as test cases.This comprehensive exploration, coupled with an examination of various organic fluids, allows us to clarify the impact of ORC configurations on the thermodynamic performance of the overall system.
These topics are organized in the article as follows.Section 2 describes the three proposed hybrid systems.This is followed by thermodynamic modeling of the CCHP system and validation of its principal components in Sections 3 and 4, respectively.Finally, Section 5 presents the key results and discusses the findings of the article.

| SYSTEM DESCRIPTION
The trigeneration systems in the present study consist of the PTSC as the prime mover and ORC, KCS and DEARC for electrical, heating and cooling.Three thermal configurations are proposed in the ORC cycle, namely, simple ORC, ORC-IHE and RORC systems.These configurations are derived based on a combination of the best practices reviewed in Section 1.The absorbed heat by HTF in the PTSCs flows towards the ORC and KCS systems.The ORC system provides thermal energy for the heating process subsystem and the remaining energy is sufficient for the high-pressure generator (HPG) of the DEARC system.The general heat flow of the proposed trigeneration systems is illustrated in Figure 1.The fluid at the turbine outlet (state 35) provides the required heating for the HP process as well as HPG of the ARC.

| ORC-based cycles
The ORC-IHE-based system is depicted in Figure 3. HPG-outlet fluid (state 32) is pumped to the heat exchanger (state 33) for preheating before passing through the evaporator and turbine.Turbine outlet fluid (state 36) supplies the energy input in IHE.The fluid leaving IHE provides the required thermal energy for the HP and DEARC systems.
Figure 4 illustrates the RORC-based system.The HPG-outlet fluid (state 32) is pumped to the feed fluid heater (FFH) and mixes with the high-pressure outlet vapor of the turbine (state 37) to increase fluid enthalpy at the FFH outlet (stage 34).This stream is then pumped towards the evaporator and turbine for power generation.The low-pressure expanded vapor at the second turbine outlet (state 38) provides the required heat for HP and DEARC systems.

| Kalina cycle system
The KCS11-type Kalina cycle is utilized in all three CCHP systems as shown in Figures 2-4.In each KCS system, after heat absorption from HTF in the evaporator (state 5), the working fluid passes through the separator and divides into rich ammonia-water saturated vapor (state 6) for power generation and poor ammonia-water saturated liquid (state 7) for regeneration.After throttling of poor ammonia-water liquid to the condenser pressure (state 10), it is mixed with the rich ammonia-water expanded from the turbine (state 8) before delivering to the condenser.The condenser outlet fluid (state 12) is then pumped towards the regenerator (for preheating) and the evaporator.

| DEARC system
A series-flow double-effect LiBr─H 2 O absorption chiller is utilized in all three trigeneration systems as illustrated in Figures 2-4.The weak solution leaving the absorber (state 28) is pumped to the low-temperature heat exchanger (LTHE) and high-temperature heat exchanger (HTHE) for preheating purpose before passing through the HPG (state 31).In the HPG, evaporation of a portion of water causes the production of primary refrigerant vapor (state 15) and medium solution (state 22).After F I G U R E 1 Schematic representation of heat flow from the solar mover to various subsystems of the proposed trigeneration system.DEARC, double-effect absorption refrigeration cycle; HTF, heat transfer fluid; KCS, Kalina cycle system; ORC, organic Rankine cycle; OWF, organic working fluid; SF, solar field.
passing through HTHE and the expansion valve EV-4, the medium solution enters the low-pressure generator (LPG).Condensation of primary refrigerant vapor in the LPG (state 16) causes the production of a secondary refrigerant vapor (state 18) and strong solution (state 25).
After throttling of condensed primary refrigerant vapor in the valve EV-2, it is mixed with the secondary refrigerant vapor in the condenser.Because of heat rejection in the condenser and throttling in the valve EV-1, refrigerant enters the evaporator with significant F I G U R E 2 Schematic diagram of the ORC-based trigeneration system.ab, absorber; cd, condenser; DEARC, double-effect absorption refrigeration cycle; ev, evaporator; EV, expansion valve; HP, heating process; HPG, high-pressure generator; HTHE, high-temperature heat exchanger; KCS, Kalina cycle system; LPG, low-pressure generator; ORC, organic Rankine cycle; PTSC, parabolic trough solar collector.temperature drop (state 20).The strong solution passes through LTHE and expansion valve EV-3, and then it mixes with the refrigerant vapor (state 21) in the absorber and produces the weak solution (state 28).

| System specifications
The solar system consists of a regular array of LS-2 collectors in 40 rows, each with 13 collectors.Therminol VP-1 is F I G U R E 3 Schematic diagram of the ORC-IHE-based trigeneration system.ab, absorber; cd, condenser; DEARC, double-effect absorption refrigeration cycle; ev, evaporator; EV, expansion valve; HP, heating process; HPG, high-pressure generator; HTHE, hightemperature heat exchanger; IHE, internal heat exchanger; KCS, Kalina cycle system; LPG, low-pressure generator; LTHE, low-temperature heat exchanger; ORC, organic Rankine cycle; PTSC, parabolic trough solar collector.utilized as the HTF in the solar collectors because of its high thermal capacity, 27 reasonable temperature control 49,50 and operation up to 400°C. 20The main properties of the Therminol VP-1 are summarized in Table 1.The mass flow rate of HTF per single row of the solar collectors is set to 0.5 kg/s.n-Octane is chosen as the ORC working fluid due to its high critical temperature. 51The basic thermophysical properties of n-octane are listed in Table 2.

| General methodology and assumptions
The present study aims to evaluate the energy extraction share between different ORC cycles and the Kalina cycle based on thermodynamic characteristics.The overall procedure is presented in Figure 5.It starts by setting the input data for various parameters and states of the systems (input data of PTSC and various cycles is given in Tables 3 and 4, respectively).The next stage is to extract the thermodynamic states data based on the thermophysical properties of the working fluids.Then, the energy and exergy balance equations are solved to calculate various performance characteristics, namely, electrical/heating/cooling power and energy/exergy efficiency of each system.
A numerical code is developed in MATLAB to solve the governing equations and postprocess the results.It is linked with Engineering Equation Solver (EES) to extract the thermodynamic properties of various working fluids and states.In Section 3, the mathematical modeling of the proposed hybrid systems is described.The following assumptions are considered in the thermodynamic analysis: • steady-state condition, • the dead state pressure and temperature of 101.325 kPa and 298.15 K, respectively, • negligible pressure drop and friction in the piping and heat exchangers, • no variation of kinetic and potential energy/exergy, • predefined isentropic efficiencies for pumps and turbines, • saturated liquid state at condenser outlets and saturated vapor state at evaporator outlets, • negligible chemical exergy of the working fluid in DEARC, 53 the mixture temperature of 30°C at the KCS separator inlet, which is less than the dew point temperature.

| Parabolic trough solar collector
The useful solar heat gain can be calculated as follows 52 : where T in is the HTF temperature at the receiver inlet, T amb is the ambient temperature, and the coefficients K 1 and K 2 can be obtained from the relations listed in Table 5. Q ˙S represents the solar beam irradiation, defined as where A ap is the collector aperture area and G b notifies the solar beam intensity.Considering the energy balance on the solar collector with Q ˙u as the thermal input, the HTF outlet temperature is calculated as follows 52 : where m ˙and c P are the mass flow rate and constantpressure specific heat of HTF in the receiver, respectively.─ in the KCS) at steady-state condition are expressed as follows 54 :

| General analysis
T A B L E 1 Thermophysical properties of Therminol VP-1. 20rameter Properties
where m ˙denotes the mass flow rate and x represents the concentration of lithium bromide or ammonia in the solution.Considering the steady-state condition and neglecting the changes in kinetic and potential energies, Table 6 presents energy and exergy balance equations for various components of the proposed trigeneration systems.

| Thermodynamic analysis
Performance of the trigeneration systems is analyzed in terms of energetic and exergetic metrics of the overall system as well as various subsystems, as follows.

| Energy analysis metrics
The electrical energy efficiency of the ORC and KCS cycles are expressed as follows 37,55 : where Q ˙ev ORC and Q ˙ev KCS denote the heat transfer rate of the evaporator in these two cycles expressed as follows: ( ) ( ) W ˙net ORC and W ˙net KCS represent the net electrical power of ORC and KCS cycles.Generally, W ˙net for each arbitrary cycle or multigeneration system is calculated as follows 56 : where η g and η m denote the efficiencies of electrical generator and pump electromotor, respectively.
COP of the DEARC system is defined as follows 57 : where W ˙pump DEARC is the power consumption of the DEARC pump, Q ˙HPG DEARC represents input the energy to | 1623 the weak solution in HPG and Q ˙cooling is the cooling power provided by the evaporator, calculated as follows: ( ) ( ) where m ˙HPG ORC indicates the mass flow rate of the ORC fluid passing through HPG and m ˙ev DEARC denotes the evaporator mass flow rate in the DEARC system.
The overall energetic efficiency of the net electrical power is expressed as follows 33 : where Q ̇in is the input (solar) energy and W ˙net overall , indicates the net electrical power generated by the overall system, calculated as follows: ( ) The energetic efficiencies for combined heat and power system (η CHP ), combined cooling and power system (η CCP ) and CCHP system (η CCHP ) are defined as follows 33,58 : where Q ˙heating represents the heating power in the HP unit defined as follows:

| Exergy analysis metrics
The overall exergetic efficiency of the net electrical power is defined as follows 56 : where Ex ˙coll is the exergy of solar collectors calculated as 56 where T 0 is the surrounding temperature and T sun is the sun temperature which is considered as 6000 K. 56 The exergetic efficiencies for combined heat and power system (Ψ CHP ), combined cooling and power T A B L E 4 Input data for ORC (three arrangements), DEARC and KCS. 33,37cle/parameter Value ORC Turbine isentropic efficiency 0.9 Pump isentropic efficiency 0.9 system (Ψ CCP ) and CCHP system (Ψ CCHP ) are defined as follows 56 : where Ex ˙heating notifies the heating power exergy in the HP unit and Ex ˙cooling represents the exergy of cooling in the DEARC evaporator, expressed as follows 59 : where T ev DEARC denotes the temperature of DEARC evaporator.

| VALIDATION
The validity of mathematical modeling for each of the subsystems is evaluated in this section.Four different studies are employed: 1. PTSC system: The parabolic trough solar collector is validated by comparing its performance results with the empirical study of Bellos and Tzivanidis 52 for similar configuration and operating conditions.Table 7 presents the principal input data as well as the output temperature of the HTF and thermal efficiency of the panel.The relative errors calculated between our numerical results and those from measurements are less than 0.12% for the output temperature and lower than 2.55% for the thermal efficiency.2. ORC-based systems: Thermodynamic modeling of ORC, ORC-IHE and RORC cycles are validated by comparing performance results for the same operating conditions to those reported by Safarian and Aramoun. 60Table 8 presents the net output power and thermal efficiency of the cycles.Relative errors are lower than 1.6% for the net output power and less than 1.8% for the thermal efficiency.3. KCS system: Performance results of the KCS system in the present numerical model are compared with He et al. 61 Four different input data sets (including pressure and concentration of ammonia at the separator inlet) are employed to calculate net output power and thermal efficiency.According to Table 9, relative errors of the present study are less than 1.7% for the net output power and less than 1.8% for the thermal efficiency.4. DEARC system: A double-effect ARC, integrated into a solar-driven CCHP system 33 is used to validate the DEARC modeling of the present study.COP of the present modeling is identical to the reported value.

| RESULTS AND DISCUSSION
Study of the effects of the bottoming cycles on ORC systems in this article is based on energy divide between the ORC and KCS cycles.Two parameters are responsible for this energy divide: 1. OWF-HTF mass flow ratio (MR m m = ̇/ ȮWF HTF ), 2. Evaporator temperature difference which is directly related to evaporator pinch point temperature, or for a fixed HTF temperature, to the evaporator outlet temperature.
On the basis of these two terms, the fraction of energy extracted by the ORC cycle from the PTSC available energy can be determined.HTF temperature at the solar field outlet is calculated to be 339.75°C.This is also considered as the inlet temperature of the ORC evaporator in all three trigeneration systems (state 1) which provides an identical energy and exergy resource.
T A B L E 5 The definition of coefficients K 1 to K 5 used in the PTSC modeling. 52efficient Definition Abbreviation: PTSC, parabolic trough solar collector.a The parameter η opt in definition of K 1 is optimal efficiency of the collector, , where K θ ( ) represents the incident angle modifier coefficient, given as b The parameter ε′ r in definition of K 3 is expressed as

Cycle/ component
Energy rate balance Exergy rate balance where   In addition to this study, a sensitivity analysis is performed and different ORC systems are compared from energetic and exergetic points of view.Different OWFs are also examined for the three configurations to find the optimal performance.The input data for the simulation of ORC-based systems, KCS and DEARC are summarized in Table 4. | 1627

| Energy divide between subsystems
Figure 6 shows the effect of ORC evaporator heat absorption Q ˙ev ORC on the overall energy/exergy efficiencies.The horizontal axis represents the ratio between Q ˙ev ORC and the absorbed PTSC energy (Q ˙in ).This fraction changes as the OWF-HTF mass flow rate ratio varies.
There is a constant increase of both energetic and exergetic efficiencies for larger absorbed heat in the ORC evaporator Q ˙ev ORC .OWF inlet temperature and pinch point temperature of the ORC evaporator limit the minimum HTF outlet temperature to 137°C, 209.9°C and 208.8°C for the ORC, ORC-IHE and RORC systems, respectively.HTF outlet temperature should not be lower than OWF inlet temperature.This limits Q ˙ev ORC to 76%, 51% and 52% of the absorbed PTSC energy (Q ˙= 18, 878kW in ), for ORC, ORC-IHE and RORC cycles, respectively and leaves 24%, 49% and 48% unused energy to KCS.To evaluate the impact of the KCS on the performance of the proposed trigeneration systems, thermodynamic characteristics are examined for two distinct configurations: (1)  with KCS and (2) without KCS.The comparative results (Table 11) reveal a notable enhancement in the performance of the system across various thermodynamic criteria in the presence of KCS.Specifically, the addition of KCS leads to a considerable increase in the exergy efficiency of ORC-, ORC-IHE-and RORCbased systems by 11.7%, 30.7% and 32.6%, respectively.Overall, the present results justify the addition of KCS as the bottoming cycle to enhance the hybrid system performance.

| Sensitivity analysis
This section examines a sensitivity analysis focusing on key parameters concerning ORC-KCS integration that characterizes energy divide between them.These parameters include the ORC evaporator pinch point temperature (T PP ), the fluid temperature at the inlet of the ORC pump (T 32 ) that directly affects the fluid temperature at the ORC evaporator inlet, and the mass flow ratio of OWF to that of the solar HTF (MR m m = ˙/ ȮWF HTF ).Table 12 examines the effect of T PP , T 32 and MR on the heat transferred to each of ORC and KCS systems (Q ̇ev ORC and Q ̇ev KCS ) for three proposed systems, that is, the ORC-, ORC-IHE-and RORC-based systems.For all the systems, increase of T PP decreases the heat transferred to ORC which in turn enhances the thermal heat towards | 1629 the KCS system.In other words, although a greater pinch point temperature causes a higher heat transfer potential, it also corresponds to a lower heat exchanger surface area that diminishes the exploitation of this potential for heat transfer enhancement.This reduces the OWF outlet temperature, decreases the temperature difference between the inlet and outlet of OWF, and consequently declines the heat transfer from HTF to OWF in the ORC evaporator.
In the case of ORC-and ORC-IHE-based systems, Table 12 indicates that an increase of T 32 reduces the heat absorption by the ORC evaporator leading to enhanced input energy to the KCS evaporator.A higher temperature at the ORC evaporator inlet and a lower temperature difference between the inflow and outflow of OWF (by a constant outflow temperature) are responsible for such a trend.Because of the constant pressure of FFH in the RORC-based system, the OWF temperature at the RORC evaporator inlet is independent of the pump inlet temperature.Therefore, the heat transferred to the RORC cycle (and in turn the heat flow towards the KCS) is unchanged by variation of T 32 .
The contribution of the mass flow rate ratio between OWF and HTF on the subsystems heat resources is also examined in Table 12 considering four different flow rate configurations.All three proposed systems confirm that by increasing MR, the thermal energy received by the ORC system is enhanced, while a lower share of energy is transferred to the KCS system.

| Comparison between the three ORC systems
Figure 7 compares the energetic and exergetic efficiencies of the three trigeneration systems.The input energy (Q ˙in ) and exergy (Ex ˙coll ) for all systems are the same.
Figure 7 indicates higher overall electrical efficiencies for the ORC-IHE system (14.7% for η el overall , and 18.3% for ψ el overall , ) which is due to larger electrical power generated by this system.The ORC-IHE system also results in higher energetic/exergetic CCP efficiencies (18.4%/18.6%)than those of ORC (16.1%/15.6%)and RORC (15.3%/16.1%)hybrid systems.This is due to the dominance of and W Ex ˙+ ṅet overall cooling , in the ORC-IHE system.
Regarding the CHP and CCHP efficiencies, the ORCbased configuration leads to a higher performance in either energy or exergy viewpoints (energetic/exergetic efficiencies of 74.6%/30% for CHP and 78.4%/30.4% for CCHP configurations).The reason is significant heating | 1631 best and the worst performances (15% and 12%), respectively.Among cooling, heating and electrical power, heating has the major contribution on these systems.The ORC-based system consumes a larger portion of the HTF energy in the heating process ) as compared with those of ORC-IHE-and RORC-based systems (38% and 41%, respectively).The ORC-based system directly uses the energetic flow through the turbine to generate power.In contrast, regenerative cycles consume a portion of turbine energy to enhance cycle efficiency.Regarding the cooling capacity, although the enthalpy drop of OWF through the HPG is identical for all three trigeneration systems, bleeding of a considerable portion of vapor and smaller fluid mass flow rate in the RORC-based system, reduce both Q ˙HPG and Q ˙cooling for this system in comparison with ORC-IHE-based system.Cooling and exergy capacities for the ORCbased systems are directly proportional to the heat absorbed in the evaporator.
Finally, among these three configurations, ORC produces the largest heat and cooling powers and generates the least electrical power, while ORC-IHE produces the least heat and the highest electrical power.According to the above discussion and based on the overall net electrical and heating powers, the ORC-based system can be a suitable choice for cold climate in which heating is the most desirable requirement.In contrast, according to the trends observed for the overall net electrical and cooling powers, the ORC-IHE-based system can be recommended for regions with warm weather condition where cooling is required.

| Organic fluid selection
OWF is a key factor affecting the performance of ORC and other systems equipped with it for warm and cold climates.Among common OWFs, six of them including n-hexane, n-heptane, cyclohexane, n-octane, benzene and toluene are selected to evaluate their impact on the ORC and the overall hybrid system.Thermodynamic properties of the selected OWFs are presented in Table 13.ORC evaporator pinch point temperature and OWF mass flow rate are kept the same for all OWFs (14°C and 20kg/s, respectively).ORC-and ORC-IHE- based systems are considered for this analysis due to their higher general performance compared with the RORC-based system.Figure 9A illustrates the overall efficiencies of these two systems for the selected OWFs.The maximum exergy efficiency of ORC-and ORC-IHEbased systems corresponds to n-octane and toluene, respectively, while in terms of energy efficiency, n-hexane and benzene are the superior fluids for ORC-and ORC-IHE-based systems, respectively.
Figure 9B presents the overall electrical, heating and cooling powers of ORC and ORC-IHE systems for the six selected OWFs.For both systems, toluene leads to generate higher electrical output, and benzene results in higher cooling power.Regarding the heating power, n-hexane is the superior fluid for the ORC-based system, while benzene is suitable for the ORC-IHE system.Considering the overall net electrical and heating powers, n-hexane is the most appropriate fluid for the ORC-based system to be used in cold climate.In contrast, for utilization of ORC-IHE system in warm climate, toluene is the optimal choice since it produces the highest overall net electrical and cooling powers.The final conclusion is that there is no single OWF which would be preferable for all systems and optimization depends on the application.

| Performance comparison with the literature
To compare the performance of the proposed configurations in the present study with the related results of the previous studies, two PTSC-driven hybrid systems are considered: 1. Eisavi et al. 33 investigated a PTSC-driven system consisting of an ORC integrated with a DEARC as the bottoming cycle, and two heating processes, one of them was fed by ORC (HP1) and the other was supplied by solar HTF after leaving the ORC evaporator (HP2).Electrical, CHP and CCP exergy efficiencies of this hybrid system were 4.4%, 12.8% and 4.5%, respectively, which are lower than the respective efficiencies of the proposed ORC-based system in the present study, that is, 15.3%, 30% and 15.6%.The main reason for the enhanced performance of the current study is the substitution of HP2 with the KCS system.On the one hand, adding the KCS system increases overall electrical power and efficiency of the multigeneration system and on the other hand, the KCS evaporator leads to lower exergy destruction than HP2, because ammonia-water mixture in the KCS evaporator has a better thermal consistency with the heat source (solar HTF) in comparison with thermal match of pure water and the heat source in HP2. 622. Tariq et al. 39 examined a hybrid system consisting of PTSC-driven ORC and DEARC cycles integrated with KCS as the bottoming system.The highest energetic efficiency was 46.30%, which is lower than those obtained in the present study for ORC-, ORC-IHEand RORC-based systems, that is, 78.4%, 56.3% and 56.7%, respectively.This is because of changing the DEARC configuration from direct feeding by solar HTF (the study of Tariq et al.) to a bottom-cycle arrangement feeding by ORC system (the current study).Although such configuration may decrease the cooling power, it provides more input energy for both ORC and KCS systems and enhances net electrical power and overall efficiency of the trigeneration system.Improvement of multigeneration cycle efficiency by utilizing the ARC system as a bottoming cycle (instead of direct feeding) has also been reported in the literature. 30,40,41nally, the above evaluation shows that the proposed hybrid systems in the current study have better thermodynamic performances than previous related research.Further assessment of these systems in terms of environmental and economic aspects is in progress and will be presented in our future study.

| CONCLUSION
The present study proposed a novel arrangement of energy system components by utilizing bottom-cycled KCS and DEARC in a PTSC-driven ORC trigeneration system to extract maximum energy from the solar field.The optimum configuration was achieved when the ORC system absorbed the highest possible share of PTSC energy and left the remaining for the KCS.The share of ORC absorbed energy from the PTSC available energy was dependent on the combination of OWF-HTF mass flow ratio and evaporator temperature difference.In other words, OWF inlet temperature and pinch point temperature of the ORC evaporator limited the minimum HTF outlet temperature delivering towards the KCS.Accordingly, depending on the ORC hybrid system, 24%-49% of PTSC energy remained unused for the KCS.
The comparative results revealed a notable enhancement in the performance of the system across various thermodynamic criteria in the presence of KCS.Specifically, the addition of KCS led to a considerable increase in the exergy efficiency of ORC-, ORC-IHE-and RORCbased systems by 11.7%, 30.7% and 32.6%, respectively.Examination of the three PTSC-driven trigeneration systems indicated that: • From energy (exergy) perspectives, the highest electrical and CCP efficiencies were achieved by the ORC-IHE-based system as 14.7% (18.3%) and 18.4% (18.6%), respectively, while the highest CHP and CCHP efficiencies were obtained for the ORC-based system as 74.6% (30%) and 78.4% (30.4%), respectively.Accordingly, the ORC-and ORC-IHE-based systems can be represented as suitable candidates for cold and warm climates, respectively.• On the basis of a comparative study, all energetic and exergetic performance metrics of the proposed hybrid systems were higher than the reported values in the literature.Better thermal match and lower exergy destruction in the KCS evaporator, and bottom-cycle arrangement of the DEARC were the main reasons for such enhanced performance in the current study.• Concerning the net electrical and heating powers normalized by the input PTSC energy, ORC-IHE-and ORC-based systems provided the highest generation rates, respectively (15% and 62%).In terms of normalized cooling power, ORC capacity (3.8%) was higher than that of ORC-IHE-and RORC-based configurations (3.7% and 2.5%, respectively).• Sensitivity analysis for all the systems indicated that an increase of pinch point temperature of the ORC evaporator decreases the heat transferred to ORC.This highlights the importance of the bottoming KCS in recovering the augmented unused thermal energy leaving the ORC.
As a future research scope, we are extending beyond the thermodynamic analysis by delving into economic and environmental aspects.Such a study will incorporate a multicriteria decision-making framework to identify the optimal configuration of the proposed systems.

Figure 2
Figure2illustrates the trigeneration system equipped with a simple ORC cycle (termed as the ORC-based system).The leaving fluid from the HPG (state 32) is pumped towards the evaporator and passes through the turbine to generate mechanical power.The fluid at the turbine outlet (state 35) provides the required heating for the HP process as well as HPG of the ARC.The ORC-IHE-based system is depicted in Figure3.HPG-outlet fluid (state 32) is pumped to the heat exchanger (state 33) for preheating before passing through the evaporator and turbine.Turbine outlet fluid (state 36) supplies the energy input in IHE.The fluid leaving IHE provides the required thermal energy for the HP and DEARC systems.Figure4illustrates the RORC-based system.The HPG-outlet fluid (state 32) is pumped to the feed fluid heater (FFH) and mixes with the high-pressure outlet vapor of the turbine (state 37) to increase fluid enthalpy at the FFH outlet (stage 34).This stream is then pumped towards the evaporator and turbine for power generation.The low-pressure expanded vapor at the second turbine

Mass, energy and 2 ─
exergy balances are applied to various components of trigeneration systems to evaluate plant performance.The mass balance equations for singlecomponent streams and two-component mixtures (LiBr H O in the DEARC and the NH H O3 2

6
h fm in the definition of K 4 is the convective heat transfer coefficient for the internal flow inside the absorber pipe, expressed as h Energy and exergy balance equations for various components of each cycle of the proposed trigeneration systems.

F I G U R E 7
Energetic and exergetic efficiencies of various combinations (net power, CHP, CCP and CCHP) for the three trigeneration configurations.CCHP, combined cooling, heat and power; CCP, combined cooling and power; CHP, combined heat and power; IHE, internal heat exchanger; ORC, organic Rankine cycle; RORC, regenerative organic Rankine cycle.F I G U R E 8 Power output of three trigeneration systems in terms of electrical, heating and cooling effects.IHE, internal heat exchanger; KCS, Kalina cycle system; ORC, organic Rankine cycle; RORC, regenerative organic Rankine cycle.

Table 10
52mparison of PTSC system results with experimental data reported by Bellos and Tzivanidis.52 presents the calculated states for three different ORC configurations, and KCS and DEARC components.The states data are extracted using EES.Abbreviations: DEARC, double-effect absorption refrigeration cycle; EV, expansion valve; FFH, feed fluid heater; HPG, high-pressure generator; HTF, heat transfer fluid; HTHE, high-temperature heat exchanger; IHE, internal heat exchanger; KCS, Kalina cycle system; LPG, low-pressure generator; LTHE, low-temperature heat exchanger; ORC, organic Rankine cycle; PTSC, parabolic trough solar collector; RORC, regenerative organic Rankine cycle.T A B L E 7

out η (%) en G b (W/m ) 2 T amb (K) T in (K) V ̇min (L/ )
61mparison of the results of the three ORC-based cycles with the results reported by Safarian and Aramoun.60Comparison of KCS cycle results with data reported by He et al.61 T A B L E 8 net η (%) net η (%) Abbreviation: KCS, Kalina cycle system.TA B L E 10 Thermodynamic states for different cycles.
: IHE, internal heat exchanger; KCS, Kalina cycle system; ORC, organic Rankine cycle; RORC, regenerative organic Rankine cycle.Effect of ORC evaporator heat absorption on the overall energy/exergy efficiencies.CCHP, combined cooling, heat and power; IHE, internal heat exchanger; ORC, organic Rankine cycle; RORC, regenerative organic Rankine cycle.Thermodynamic performance of trigeneration systems with and without KCS for the solar intensity G = 800W/m Effect of T PP , T 32 and MR on the heat transferred to each of ORC and KCS systems for the ORC-, ORC-IHE-and RORC-based systems.
AbbreviationsF I G U R E 6