Towards an Efﬁcient Multi-Generation System Providing Power, Cooling, Heating, and Freshwater for Residential Buildings Operated with Solar-Driven ORC

: In buildings, multi-generation systems are a promising technology that can replace discrete traditional energy production methods. A multi-generation system makes it possible to efﬁciently produce electricity, cooling, heating, and freshwater simultaneously. This study involved the numerical analysis of a modiﬁed proposed novel solar-driven multi-generation system (MGS-II) integrated with the Organic Rankine Cycle (ORC), Humidiﬁcation–Dehumidiﬁcation Desalination System (HDH), and Desiccant Cooling System (DCS) by using heat recovery and thermal energy storage (TES) units. In addition, a comparison study with the basic multi-generation system (MGS-I) is performed. The proposed system is designed to supply electricity, air conditioning, domestic heating, and fresh water to small/medium-sized buildings. How operating conditions affect system productivity and performance metrics have been investigated. The results show that the proposed multi-generation system (MGS-II) can produce electrical power, space cooling, domestic heating and fresh water while maintaining comfortable conditions inside the conditioned space. Moreover, the MGS-II outperforms the MGS-I system, and the maximum MGS-II system productivity; electricity production ( W • net ,), freshwater ( m • fresh ,), space cooling ( Q • cooling ), and domestic heating ( Q • heating ) are 102.3 kW, 141.5 kg/h, 20.77 kW, and 225 kW, respectively. In addition, the highest total gained output ratio (TGOR), speciﬁc total gained energy (STG), and speciﬁc total gained energy equivalent price (STGP) of the MGS-II sys-tem are 0.6303, 3.824 kWh/m 2 , and 0.149 USD/m 2 , respectively. The accepted ranges of comfortable space-supplied air conditions (temperature and humidity) are 15.5–18.2 ◦ C and 9.2–12.00 gv/kga for both systems, MGS-I and MGS-II. Finally, the current system (MGS-II) has the maximum of the system’s performance indicators and productivity (TGOR and . m fresh ) compared with the other reported systems.

solid oxide fuel cell tri-generation system is determined to have the greatest tri-generation exergy efficiency at 64.5%.
Zare [11] provided a thermodynamic analysis and optimization comparison of two separate designs of geothermal energy-based tri-generation systems based on research involving geothermal energy (one using an ORC and the other using a Kalina cycle). The ORC and Kalina cycles are coupled to a LiBr/water absorption chiller and a water heater to provide cooling and heating loads, respectively. In addition, Azhar et al. [12] investigated a multigenerational system that utilizes geothermal, solar, and ocean thermal energy conversion as energy inputs to produce electrical power, fresh water, space cooling, and industrial heating. The energy and exergy efficiency of the entire system were determined to be 13.93% and 17.97%, respectively. Moreover, Gholizadeh et al. [13] developed a unique tri-generation system that generates potable water, electricity, and cooling utilizing a flashbinary geothermal heat source at 170 • C. It was discovered that optimization increases turbine output power, overall cooling load, tri-generation-based gain-output-ratio (TGOR), and exergy efficiency by approximately 77.08 percent, 87.01 percent, 8.18 percent, and 46.33 percent, respectively. In addition, Li et al. [14] described a novel geothermal-powered tri-generation layout based on a cascade power system and a CO 2 cooling system. A modified Kalina cycle (MKC), an (ORC), and a liquefied natural gas (LNG) subsystem are all components of the geothermal-powered cascade system. The net output power, cooling rate, and hydrogen rate of the system are 451.8 kW, 297.8 kW, and 2.27 kg per hour, respectively.
In another studies, Hands et al. [15] tested a tri-generation power plant with solar desiccant air conditioning. The solar-driven desiccant cooling system met roughly 35% of the total building cooling load under ideal ambient circumstances. Abdelhay et al. [16] conducted a thermodynamic analysis of a poly-generation system that included a solar power system (SPS), a multi-effect desalination (MED) system, and an absorption refrigeration system (ARS). The facility is powered by solar energy, with a natural gas heater for backup. The proposed integrated system has the lowest unit water price of 1247 USD/m 3 , cooling unit price of 0.003 USD/kWhr, and the maximum energy efficiency of 23.95%. Dabwan et al. [17] devised and implemented a conceptual analytic approach for finding the optimal integration of linear Fresnel reflector (LFR) technology with traditional cooling, fresh water, and electric power tri-generation systems. Yao et al. [18] designed and evaluated a new tri-generation plant for integrated cooling, heating, and power based on compressed air energy storage technology. It was discovered that choosing the best trade-off solution resulted in an overall exergy efficiency of 53.04% and a total product unit cost of 20.54 cents/kWh. Bellos and Tzivanidis [19] used several optimization parameters to optimize a tri-generation system for solar-powered building applications. According to the final results, the optimum system has an exergy efficiency of 11.26% and an energy efficiency of 87.39%, while the power outputs for electricity, cooling, and heating are 4.6 kW, 7.1 kW, and 59.4 kW, respectively. Recently, Fouda et al. [20] evaluated a unique tri-generation system for simultaneously generating electrical power, air conditioning, and desalinated water. The proposed system includes an ORC, a Humidification and Dehumidification (HDH) water desalination system, a Desiccant Cooling System (DCS), a solar system (including evacuated tube collectors and a thermal energy storage unit), and additional components. The proposed trigeneration system has the greatest electrical power, freshwater capacity, space cooling capacity, and Energy Utilization Factor (EUF) of 104.5kW, 72.37kg/h, 25.48kW, and 0.266%, respectively.
According to the literature review, few tri/multi-generation systems for power, fresh water, and cooling load combined with MED/SRC/ARS, HDH/ORC/ECC, and HDH/ORC/ DCS operated with solar, biomass, biogas, and geothermal energies. As a result, multigeneration systems have not been thoroughly investigated to date. Therefore, a new multi-generation set-up based on an ORC, DCS, and HDH unit to generate power, space cooling/domestic heating, and fresh water is aimed to small/medium-scale buildings. The low operating temperatures are suitable for ORC power generation [21]. HDH water desalination has several advantages, including low-temperature energy utilization (e.g., waste energy, solar energy), simplicity, and inexpensive operation and installation costs [22]. Desiccant air conditioners do not produce polluting gases such as chlorofluorocarbons, which are produced by traditional air conditioning systems. Therefore, these constraints motivate the authors to research the design, operation, and performance assessment of multi-generation systems capable of providing continuous daylight electrical power, fresh water, and space cooling/domestic heating using solar energy for small and mediumscale buildings.
To the authors' knowledge, no previous research into such advanced systems has been done. Therefore, a more efficient multi-generation system, including ORC, HDH, DCS, and with heat recovery systems is proposed, thermodynamically evaluated and compared with the basic system [20] in this study. The impact on the system's productivity and performance parameters is investigated using thermodynamics analysis and parametric study. The systems' cycles are thermodynamically simulated and analyzed using the EES (Engineering Equation Solver) software. The following points will be fulfilled: (i) extensive energy mathematical modeling, (ii) effects of various operating parameters on the system's productivity and performance, and (iii) assessing and evaluating the proposed system compared with basic system. It is expected that the findings of the proposed integrated ORC, HDH, and DCS multi-generation systems will attract attention and benefit researchers, solar multi-generation developers, power plant designers, and investors because of theor economic and environmental feasibility for producing electricity, space cooling, domestic heating, and fresh water for end users, especially for small and medium-scale buildings. Figure 1 depicts a schematic design of the basic system, and the modified suggested solar-driven multi-generation system with a heat recovery unit (MGS-I and MGS-II). By connecting solar ORC to a DCS and HDH desalination unit, the suggested system is designed to produce power, space cooling/domestic heating, and fresh water. An evacuated tube solar collector and a thermal storage tank are components of the solar system. A thermal oil (Therminol-VP1) is utilized as the working fluid for the solar field loop because of its capacity to maintain the liquid phase at temperatures up to 400 • C [23]. The basic system (MGS-I), which serves as a reference system, and the modified system are the systems that were investigated (MGS-II). As depicted in Figure 1, the MGS-I can produce energy, space cooling, and freshwater (a). The system has four major cycles: two closed cycles (the solar and the ORC) and two open cycles (air and water cycles). Appl. Sci. 2022, 12, x FOR PEER REVIEW water desalination has several advantages, including low-temperature energy u (e.g., waste energy, solar energy), simplicity, and inexpensive operation and ins costs [22]. Desiccant air conditioners do not produce polluting gases such as chlo carbons, which are produced by traditional air conditioning systems. Therefore, th straints motivate the authors to research the design, operation, and performanc ment of multi-generation systems capable of providing continuous daylight power, fresh water, and space cooling/domestic heating using solar energy for s medium-scale buildings.

Systems Description
To the authors' knowledge, no previous research into such advanced sys been done. Therefore, a more efficient multi-generation system, including ORC DCS, and with heat recovery systems is proposed, thermodynamically evalu compared with the basic system [20] in this study. The impact on the system's pr ity and performance parameters is investigated using thermodynamics analysis ametric study. The systems' cycles are thermodynamically simulated and analyz the EES (Engineering Equation Solver) software. The following points will be ful extensive energy mathematical modeling, (ii) effects of various operating param the system's productivity and performance, and (iii) assessing and evaluating posed system compared with basic system. It is expected that the findings of the p integrated ORC, HDH, and DCS multi-generation systems will attract attention efit researchers, solar multi-generation developers, power plant designers, and i because of theor economic and environmental feasibility for producing electrici cooling, domestic heating, and fresh water for end users, especially for small and m scale buildings. Figure 1 depicts a schematic design of the basic system, and the modified su solar-driven multi-generation system with a heat recovery unit (MGS-I and MG connecting solar ORC to a DCS and HDH desalination unit, the suggested syste signed to produce power, space cooling/domestic heating, and fresh water. An ev tube solar collector and a thermal storage tank are components of the solar sy thermal oil (Therminol-VP1) is utilized as the working fluid for the solar field cause of its capacity to maintain the liquid phase at temperatures up to 400 °C basic system (MGS-I), which serves as a reference system, and the modified sy the systems that were investigated (MGS-II). As depicted in Figure 1, the MGS-I duce energy, space cooling, and freshwater (a). The system has four major cy closed cycles (the solar and the ORC) and two open cycles (air and water cycles) (a) In the solar field cycle, evacuated tube solar collectors are used to charge th tank when it is sunny (state points t1 and t2), which is then used to provide the with constant energy demand through the ORC evaporator both during the day night (state points t3 and t4). The ORC cycle uses an evaporator to transfer heat fr thermal oil to the ORC fluid, which is then expanded through the turbine to produ tricity using a linked generator after becoming superheated to (f3) and evaporat maintain the same temperature at the state points (a8 and w3), the ORC fluid e turbine at (f4). It is delivered to the triple channel heat exchanger's condenser, wh condensed at (f1), and waste heat is recovered for the DCS and HDH units. The finished by pumping the ORC liquid to (f2) and then back to the evaporator. Th fluid leaves the turbine at position (f4). It is transported to the triple channel h changer's condenser, where it condenses at position (f1) and recovers waste heat DCS and HDH units to maintain the temperature at state points (a8 and w3). To co the cycle, the ORC liquid is subsequently piped to (f2) and finally pushed back evaporator.

Systems Description
Process air enters the desiccant wheel (DW) at (a1) in the air cycle, where it i midified and heated to (a2) before passing via the heat exchanger (HE-1), whe cooled to (a3). The process air enters the direct evaporative cooler (DEC-1), which is and humidified at (a4) before entering the air-conditioned chamber. The return a the conditioned space at (a5) is directed to the direct evaporative cooler (DEC-2), w is cooled and humidified before leaving at (a6). The heat exchanger (HE-1) is then heat the return air (a7). The return air (regeneration air) then passes through a h changer (HE-2) to recover some of the waste ORC condenser heat to reach the ne regeneration temperature (a8) before passing through DW (reactivation part), wh cooled and humidified to the required regeneration temperature (a9). Finally, th system delivers the humidified and cooled regeneration air from the DW to the h fier, where it is humidified and cooled at (a10) before being given to the dehumidif is dehumidified at (a11). Figure 2a for the basic multi-generation system shows t chrometric cycle of the air (MGS-I).  In the solar field cycle, evacuated tube solar collectors are used to charge the TES-1 tank when it is sunny (state points t1 and t2), which is then used to provide the system with constant energy demand through the ORC evaporator both during the day and at night (state points t3 and t4). The ORC cycle uses an evaporator to transfer heat from the thermal oil to the ORC fluid, which is then expanded through the turbine to produce electricity using a linked generator after becoming superheated to (f3) and evaporating. To maintain the same temperature at the state points (a8 and w3), the ORC fluid exits the turbine at (f4). It is delivered to the triple channel heat exchanger's condenser, where it is condensed at (f1), and waste heat is recovered for the DCS and HDH units. The cycle is finished by pumping the ORC liquid to (f2) and then back to the evaporator. The ORC fluid leaves the turbine at position (f4). It is transported to the triple channel heat exchanger's condenser, where it condenses at position (f1) and recovers waste heat for the DCS and HDH units to maintain the temperature at state points (a8 and w3). To complete the cycle, the ORC liquid is subsequently piped to (f2) and finally pushed back to the evaporator.
Process air enters the desiccant wheel (DW) at (a1) in the air cycle, where it is dehumidified and heated to (a2) before passing via the heat exchanger (HE-1), where it is cooled to (a3). The process air enters the direct evaporative cooler (DEC-1), which is cooled and humidified at (a4) before entering the air-conditioned chamber. The return air from the conditioned space at (a5) is directed to the direct evaporative cooler (DEC-2), where it is cooled and humidified before leaving at (a6). The heat exchanger (HE-1) is then used to heat the return air (a7). The return air (regeneration air) then passes through a heat exchanger (HE-2) to recover some of the waste ORC condenser heat to reach the necessary regeneration temperature (a8) before passing through DW (reactivation part), where it is cooled and humidified to the required regeneration temperature (a9). Finally, the HDH system delivers the humidified and cooled regeneration air from the DW to the humidifier, where it is humidified and cooled at (a10) before being given to the dehumidifier and is dehumidified at (a11). Figure  In the water cycle, seawater at (w1) is pumped through the water treatment unit (TU) to remove turbidity, bacterial content, and total dissolved solids, which cause fouling and scaling in the tubes and then passes through the dehumidifier coil to dehumidify the humid air that came from the humidifier to produce desalinated water at (w5). The desalinated water is sent through a chemical treatment unit (CTU) to make it fresh/potable water with a salinity of 500 ppm, which is the WHO's (World Health Organization) approved value. It is then gathered and stored in the FWST. The saltwater is heated to (w2) when it leaves the dehumidifier, and it then flows via an ORC condenser, where it is partially warmed using waste heat from the ORC condenser to reach (w3) before passing through a humidifier to moisten the air coming from the DW of DCS. The incoming air carries some of the pure water out to the dehumidifier as it evaporates, and the remaining pure water is drained as a brine at the end of the process (w4).
The schematic of the modified system (MGS-II) is shown in Figure 1b. The system can generate electricity, space cooling/domestic heating, and fresh water. The system consists of the same components and operations as the MGS-I. In addition, the system is improved by adding second stage dehumidification (2nd Deh.), a heat recovery system (HR), and a thermal energy storage unit to recover (TES-2) heat from brine and desalinated water to use in domestic heating applications. In MGS-II, the air leaves the first stage dehumidifier at (a11) and enters the second stage dehumidifier to reach (a12). The desalinated water yields at (w6) mix with the desalinated water produced from the first stage dehumidification (w7) to give the total desalinated water yields at (w8). After that, a heat recovery system is used to recover the heat energy from desalinated water (w8) and brine water (w4) to obtain heating water used for domestic applications via TES-2 to recover most of the waste heat. This helps to achieve system optimization and more efficient operation. The psychrometric cycle describing the processes of air through MGS-II is shown in Figure 2b.

Mathematical Model and Thermodynamics Analysis
The utilization of solar energy for the desalination of water, air conditioning, electricity generation, and hot water generation is being investigated and deployed in multi- In the water cycle, seawater at (w1) is pumped through the water treatment unit (TU) to remove turbidity, bacterial content, and total dissolved solids, which cause fouling and scaling in the tubes and then passes through the dehumidifier coil to dehumidify the humid air that came from the humidifier to produce desalinated water at (w5). The desalinated water is sent through a chemical treatment unit (CTU) to make it fresh/potable water with a salinity of 500 ppm, which is the WHO's (World Health Organization) approved value. It is then gathered and stored in the FWST. The saltwater is heated to (w2) when it leaves the dehumidifier, and it then flows via an ORC condenser, where it is partially warmed using waste heat from the ORC condenser to reach (w3) before passing through a humidifier to moisten the air coming from the DW of DCS. The incoming air carries some of the pure water out to the dehumidifier as it evaporates, and the remaining pure water is drained as a brine at the end of the process (w4).
The schematic of the modified system (MGS-II) is shown in Figure 1b. The system can generate electricity, space cooling/domestic heating, and fresh water. The system consists of the same components and operations as the MGS-I. In addition, the system is improved by adding second stage dehumidification (2nd Deh.), a heat recovery system (HR), and a thermal energy storage unit to recover (TES-2) heat from brine and desalinated water to use in domestic heating applications. In MGS-II, the air leaves the first stage dehumidifier at (a11) and enters the second stage dehumidifier to reach (a12). The desalinated water yields at (w6) mix with the desalinated water produced from the first stage dehumidification (w7) to give the total desalinated water yields at (w8). After that, a heat recovery system is used to recover the heat energy from desalinated water (w8) and brine water (w4) to obtain heating water used for domestic applications via TES-2 to recover most of the waste heat. This helps to achieve system optimization and more efficient operation. The psychrometric cycle describing the processes of air through MGS-II is shown in Figure 2b.

Mathematical Model and Thermodynamics Analysis
The utilization of solar energy for the desalination of water, air conditioning, electricity generation, and hot water generation is being investigated and deployed in multigeneration systems intended for domestic applications. The multi-generation system is split into three subsystems, ORC, HDH, and DCS, to determine each subsystem's thermo-dynamic characteristics and the entire system's performance. During the simulation model phase, the first and second laws of thermodynamics are applied to each system component. In the current model, the following assumptions have been considered:

•
All system processes are assumed to be in a steady state. • Air/water leakage in system components is ignored.

•
The kinetic and gravitational energies are not considered.

•
The air wet-bulb temperature and the blowdown water temperature leaving the humidifier are the same. • Process air, return air, and water has the same mass flow rate.

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The cold outlet streams from ORC condenser are assumed to be the same (t s1 = t w3 ) to distribute the condenser capacity on HDH and DCS cycles.

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At the dehumidifier's exit, the fresh water and the air wet-bulb temperatures are the same.

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The ORC fluid's states at the turbine inlet are dry-saturated and superheated based on the different values of t evap and degree of superheating.

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Based on the pressure of the condenser, the ORC fluid state at the pump inlet is saturated liquid.

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In DCS and HDH systems, the special power of auxiliary components (power consumed by fans) is ignored.

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Organic fluid (n-Octane) is selected to carry out the comparative study of the proposed systems due to its performance and thermodynamic properties [24].

•
The studied and operating parameters values, ranges, and relevant efficiencies for the system's components are given in Tables 1 and 2

. •
Superheat degree at ORC turbine inlet and ORC evaporation temperature were selected based on the maximum temperature (200 • C) that can be obtained from the evacuated tube solar collectors and critical temperature of organic working fluids. • ORC condensation temperature was selected based on the temperature of refrigerant in the condenser that should be greater than the heated air (t a7 ) and sea water (t w2 ) condensation temperature where the heat transfer process occurs in the right direction • Mass flow rate ratio (0-0.4) was selected based on previously published work for HDH systems • Ambient air inlet temperature, ambient air inlet humidity, seawater inlet temperature and average solar intensity were selected based on average climatic conditions of the Jeddah city, Saudi Arabia • Conditioned space air temperature, and humidity were selected based on average inside design human comfort conditions.

Organic Rankine Cycle (ORC)
The organic working fluid (n-Octane), which has a low boiling temperature and an appropriate operating pressure within the parameter range of the solar energy heat source in the ORC system, is evaporated using solar energy. The governing equations (Equations (1)-(11)) of the evaporator, condenser, turbine, pump, and ORC thermal efficiency are presented in the following manner based on the energy and mass balance [20]: The current work takes the total daily average solar intensity [8]. Whereas the average annual value of the thermal efficiency of the evacuated tube solar collector is 63.2%, [27] • Condenser energy balance • Turbine power • Pump power • ORC net power and thermal efficacy

Desiccant Cooling System (DCS)
The desiccant wheel is the main component of the DCS, and the model established by Panaras et al. [25] is used to simulate the desiccant wheel in this study. The following are the associated energy balances and governing equations for the DCS components: • The combined potential of the desiccant wheel • Desiccant wheel's efficiency • Energy and mass balances of the desiccant wheel where, C min = min m • P,a c p,ma , m • R,a c p,ma • Direct evaporative coolers: • Regeneration energy, space cooling capacity and coefficient of performance

Humidification Dehumidification Water Desalination System (HDH)
The energy balance of the humidifier [20] is given as where, The mass flow rate of the makeup water (sea or brackish water) supplied to the system [20] is given as The energy balance and freshwater productivity of the first dehumidifier in the basic system [20] are given as where, h w5 = c p,w t a11 C min = min{m • w c p,w , m • R,a c p,ma } The energy balance, freshwater productivity of the second dehumidifier, and total freshwater productivity for MGS-II systems [20] are given as The gain output ratio (GOR) for MGS-I and MGS-II systems [20] is given by

System Performance Parameters and Evaluation
The tri-generation total gained output ratio (TGOR), tri-generation gained output ratio for independent systems (TGO Rind ), specific total gained energy (STG), and specific total gained energy equivalent price (STGP) of the proposed basic, IS-I, and IS-II multi-generation systems [20] are as follows.
∆τ: daylight time (12 h) WUR: water unit rate USD/kg EUR: Energy unit rate USD/kWh The prices for energy and freshwater units vary from one city to another. In the present study, typical values of energy and water unit prices of 0.05 USD/kWh and 2.5 USD/m 3 of Gulf cities [8,28] are taken. The system governing equations (Equations (1)-(46)) are simulated by using C++ and EES software based on energy and mass balances for all system components to calculate the system performance and productivity parameters for different ranges of design and operating conditions as given in Table 1.

Results and Discussion
The thermodynamics analysis was carried out to assess the performance of proposed multi-generation systems (MGS-I and MGS-II) for electricity production, freshwater and space cooling, and domestic heating through the integration of solar ORC with DCS and HDH subsystems. The effects of the controlling parameters (∆t sup , t f1 , t w1 , and MR) on /Q cooling ) and the system's performance indicators (η ORC , GOR HDH , COP DCS , TGOR, STG, and STGP) are investigated, discussed, and evaluated using n-Octane as an organic fluid.

Model Validation
To confirm the developed thermodynamic models in the present study, model validation is implemented, and the results of the current work are compared with those reported in the literature to determine their degree of accuracy. Table 3 illustrates the validation of the current thermodynamic models with previously published data in [28][29][30] for the HDH, ORC, and DCS subsystems. In Table 3, a good agreement is observed between the results obtained in the current work and those reported previously in the literature.

Systems' Productivities
The influences of operating parameters (∆t sup , tf1, tw1, and MR) on the systems' productivities; electrical power generation, freshwater productivity (  Table 4 and Figures 3 and 4. Table 4 and Q heating improve with increasing ∆t sup . Such a trend is the same for the proposed systems (MGS-I and MGS-II). This is attributed to the increase in turbine work, solar energy needed, and the heat liberated at the ORC condenser as the turbine inlet temperature increases. This reflects the increase in the needed area of solar collectors, air humidification capacity inside the humidifier, space cooling capacity, and domestic heating capacity.    Q cooling . Such a trend is similar for MGS-I and MGS-II. Increasing the condensation temperature reduces the turbine power due to the reduction in enthalpy difference across the turbine, which also results in a decreasing freshwater rate. This is a result of reducing the heat recovered from the condenser to water and air streams before entering the humidifier, which reduces the amount of water evaporation and consequently reduces the dehumidifier capacity. In addition, increasing the condenser pressure reduces the regeneration temperature of DCS, which, in turn, causes a reduction in space cooling capacity. Furthermore, Figure 3b and Table 4 show that increasing tw1 has an adverse and negligible effect on . m f resh and . W net , respectively. Decreasing . m f resh is due to decreasing the air dehumidification capacity through the dehumidifier, which leads to a lower freshwater production rate. Nevertheless, the increase in water inlet temperature has no impact on . W net (see Table 4). This is because of the independence of the ORC heat supply and liberated to the seawater inlet temperature. The space cooling of the three proposed systems is shown in Figures 4a,b. The space cooling capacity of both the MGS-II and MGS-I systems show similar space cooling capacities. Such a trend is the same at any Δtsup, tf1, tw1, or MR. This is a result of the regeneration heat recovery for DCS not affected by the improvements applied to the MGS-II system (i.e., second stage dehumidification, brine and freshwater heat recovery at HE-3 and HE-4, respectively). The proposed multi-generation systems produce the same turbine power (see Table 3). Such a trend is the same at any Δtsup, tf1, tw1, or MR. The improvements of the MGS-II system are not affected by the turbine power compared to the MGS-I system (i.e., adding second stage dehumidification and brine and freshwater heat recovery). As shown in Figures 3,4 and    Q heating due to the decrease in evaporation rate in the humidifier due to reducing the seawater flow rate with increasing MR. This results in a lower freshwater yield and domestic heating capacity. Figure 4a displays the increase of . Q cooling with increasing MR until it attains a maximum value and then starts to drop with increasing MR. Increasing MR has two opposing effects: it reduces air flow rate and increases the enthalpy difference across the conditioned space. In the first interval of MR, the increase in enthalpy difference across the space dominates the reduction in air mass flow rate, which leads to improved . Q cooling and vice versa in the second interval of MR. W net and that this is because the ORC heat source and rejected heat are independent of MR. Comparing the proposed multi-generation systems (MGS-I and MGS-II), Figure 4a-c shows that the freshwater productivity of the MGS-II system is higher than that of the MGS-I system. The trend is consistent across all ∆t sup , tf1, tw1, and MR values. This is due to adding a second stage to the dehumidifier of the MGS-II system.
The space cooling of the three proposed systems is shown in Figure 4a,b. The space cooling capacity of both the MGS-II and MGS-I systems show similar space cooling capacities. Such a trend is the same at any ∆t sup , tf1, tw1, or MR. This is a result of the regeneration heat recovery for DCS not affected by the improvements applied to the MGS-II system (i.e., second stage dehumidification, brine and freshwater heat recovery at HE-3 and HE-4, respectively). The proposed multi-generation systems produce the same turbine power (see Table 3). Such a trend is the same at any ∆t sup , tf1, tw1, or MR. The improvements of the MGS-II system are not affected by the turbine power compared to the MGS-I system (i.e., adding second stage dehumidification and brine and freshwater heat recovery). As shown in Figure 3, Figure 4 and Table 4, for the MGS-II system, the maximum system productivity of

Systems' Performance
The effects of operating parameters (∆t sup , tf1, tw1, and MR) on the systems' performance indicators (η ORC , GOR HDH , COP DCS , TGOR, STG, STGP) of the three proposed multi-generation systems (MGS-I and MGS-II) are given in Table 4 and Figures 5-8. Systems' performance indicators for the proposed systems at operating conditions of tf1 = 50 • C, tw1 = 20 • C, and MR = 0.25 are slightly decreased with increasing ∆t sup . Heat input to ORC, HDH, and DCS increases with increasing turbine inlet temperature, which results in a drop in η ORC , GOR HDH , and consequently lower TGOR, STG, and STGP, for MGS-I and MGS-II proposed systems, the solar area, A solar , increases as ∆t sup increases (see Table 4). Increasing the amount of superheat at the turbine inlet requires increasing the solar input heat of the ORC. Appl

Systems' Performance
The effects of operating parameters (Δtsup, tf1, tw1, and MR) on the systems' performance indicators (ηORC, GORHDH, COPDCS, TGOR, STG, STGP) of the three proposed multigeneration systems (MGS-I and MGS-II) are given in Table 4 and Figures 5-8. Systems' performance indicators for the proposed systems at operating conditions of tf1 = 50 °C, tw1 = 20 °C, and MR = 0.25 are slightly decreased with increasing Δtsup. Heat input to ORC, HDH, and DCS increases with increasing turbine inlet temperature, which results in a drop in ηORC, GORHDH, and consequently lower TGOR, STG, and STGP, for MGS-I and MGS-II proposed systems, the solar area, Asolar, increases as Δtsup increases (see Table 4). Increasing the amount of superheat at the turbine inlet requires increasing the solar input heat of the ORC.
A comparison between the proposed multi-generation systems, Figure 5a, b shows that the system performance parameters (GORHDH, TGOR) of the MGS-II system are higher than those of the MGS-I system. Such a trend is the same at any Δtsup. Improving TGOR, STG, and STGP of the MGS-II system rather than the MGS-I system is attributed to the increase in total output system energy due to brine and freshwater heat recovery. This heat recovery increases heating capacity in domestic applications ( ), which improves the TGOR of MGS-II rather than MGS-I and consequently improves the STG and STGP. The MGS-II system has better GORHDH than that of the MGS-I. System.  Table 4 and Figure 6a, b show the values of the system performance indicators ηORC, TGOR, and STG at operating temperatures of Δtsup = 45 °C, tw1 = 20 °C, and MR = 0.25. All performance parameters are slightly decreased with increasing tf1. Such a trend is the same for the proposed systems. The decrease in ηORC with the increase in condensation temperature (see Table 4) is due to the reduction in enthalpy difference across the turbine with the same heat energy input. While the reduction of TGOR and STG is attributed to the increase in the amount of input heat energy to HDH and DCS. Increasing the tf1 leads to a reduction in TGOR and STG. Solar area, Asolar, decreases with increasing tf1 (see Table  4) for all proposed systems. This is because of reducing the required solar input heat to the ORC with increased condensation temperature. When comparing the proposed multigeneration systems, the MGS-II system has a higher performance than the MGS-I systems.  A comparison between the proposed multi-generation systems, Figure 5a, b shows that the system performance parameters (GOR HDH , TGOR) of the MGS-II system are higher than those of the MGS-I system. Such a trend is the same at any ∆t sup . Improving TGOR, STG, and STGP of the MGS-II system rather than the MGS-I system is attributed to the increase in total output system energy due to brine and freshwater heat recovery. This heat recovery increases heating capacity in domestic applications ( . Q heating ), which improves the TGOR of MGS-II rather than MGS-I and consequently improves the STG and STGP. The MGS-II system has better GOR HDH than that of the MGS-I. System. Appl. Sci. 2022, 12,  This is attributed to the increase in total output system energy as a result of brine and freshwater heat recovery used for . The effect of seawater temperature, tw1, on systems' performance indicators is also shown in Figure7 and Table 4 at Δtsup = 45 °C, tf1 = 50 °C, and MR = 0.25. As shown in Figure 7a, b, the STG and STGP decrease as tw1 increases. Such a trend is the same for proposed systems. The increase in the water inlet temperature has no impact on the ηORC and Asolar (see Table 4). This is because of the independence of the solar heat source of the ORC and the heat liberated to the seawater inlet temperature. Similarly, comparing the two proposed multi-generation systems, Figure 7a and b show that the MGS-II system has the best system performance among the three systems within the studied range of tw1.  This is attributed to the increase in total output system energy as a result of brine and freshwater heat recovery used for . The effect of seawater temperature, tw1, on systems' performance indicators is also shown in Figure7 and Table 4 at Δtsup = 45 °C, tf1 = 50 °C, and MR = 0.25. As shown in Figure 7a, b, the STG and STGP decrease as tw1 increases. Such a trend is the same for proposed systems. The increase in the water inlet temperature has no impact on the ηORC and Asolar (see Table 4). This is because of the independence of the solar heat source of the ORC and the heat liberated to the seawater inlet temperature. Similarly, comparing the two proposed multi-generation systems, Figure 7a and b show that the MGS-II system has the best system performance among the three systems within the studied range of tw1.  Table 4 and Figure 6a,b show the values of the system performance indicators η ORC , TGOR, and STG at operating temperatures of ∆t sup = 45 • C, tw1 = 20 • C, and MR = 0.25. All performance parameters are slightly decreased with increasing tf1. Such a trend is the same for the proposed systems. The decrease in η ORC with the increase in condensation temperature (see Table 4) is due to the reduction in enthalpy difference across the turbine with the same heat energy input. While the reduction of TGOR and STG is attributed to the increase in the amount of input heat energy to HDH and DCS. Increasing the tf1 leads to a reduction in TGOR and STG. Solar area, A solar , decreases with increasing tf1 (see Table 4) for all proposed systems. This is because of reducing the required solar input heat to the ORC with increased condensation temperature. When comparing the proposed multi-generation systems, the MGS-II system has a higher performance than the MGS-I systems. This is attributed to the increase in total output system energy as a result of brine and freshwater heat recovery used for . Q heating .
The influence of mass flow rate ratio, MR, on the systems' performance indicators is displayed in Figure 8 and Table 4 at Δtsup = 45 °C, tf1= 50 °C, and tw1= 20 °C. As shown in Figure 8a-c, the performance indicators (GORHDH, TGOR and STG) declined with increasing MR for the two proposed systems. Increasing MR, as a result of decreasing both air and seawater mass flow rates, with fixed leads to a lower rate of evaporation in the humidifier and, consequently, a lower rate of condensation in the dehumidifier. Hence, lower values of GORHDH are obtained, as shown in Figure 8a. Moreover, increasing MR has no impact on the ηORC and Asolar (see Table 4). In other words, it becomes independent of the solar heat source of ORC and the heat liberated to the seawater inlet temperature. In addition, Figure 8a-c show that the MGS-II system has the best performance rather to the MGS-I system within the studied range of MR. As shown in Figures 5-8 and Table 4, The maximum GORHDH, ηORC, Asolar, TGOR, STG, and STGP of the MGS-II system within the ranges of all studied parameters are 0.21,15.34 %, 1273 m 2 , 0.6303, 3.824 kWh/m 2 , and 0.149 USD/m 2 , respectively. The effect of seawater temperature, tw1, on systems' performance indicators is also shown in Figure 7 and Table 4 at ∆t sup = 45 • C, tf1 = 50 • C, and MR = 0.25. As shown in Figure 7a,b, the STG and STGP decrease as tw1 increases. Such a trend is the same for proposed systems. The increase in the water inlet temperature has no impact on the η ORC and A solar (see Table 4). This is because of the independence of the solar heat source of the ORC and the heat liberated to the seawater inlet temperature. Similarly, comparing the two proposed multi-generation systems, Figure 7a,b show that the MGS-II system has the best system performance among the three systems within the studied range of tw1.
The influence of mass flow rate ratio, MR, on the systems' performance indicators is displayed in Figure 8 and Table 4 at ∆t sup = 45 • C, t f1 = 50 • C, and t w1 = 20 • C. As shown in Figure 8a-c, the performance indicators (GOR HDH , TGOR and STG) declined with increasing MR for the two proposed systems. Increasing MR, as a result of decreasing both air and seawater mass flow rates, with fixed . m ORC leads to a lower rate of evaporation in the humidifier and, consequently, a lower rate of condensation in the dehumidifier. Hence, lower values of GOR HDH are obtained, as shown in Figure 8a. Moreover, increasing MR has no impact on the η ORC and A solar (see Table 4). In other words, it becomes independent of the solar heat source of ORC and the heat liberated to the seawater inlet temperature. In addition, Figure 8a-c show that the MGS-II system has the best performance rather to the MGS-I system within the studied range of MR. As shown in Figures 5-8 and Table 4, The maximum GOR HDH , η ORC , A solar , TGOR, STG, and STGP of the MGS-II system within the ranges of all studied parameters are 0.21,15.34 %, 1273 m 2 , 0.6303, 3.824 kWh/m 2 , and 0.149 USD/m 2 , respectively.

Maximum Proposed Systems' Productivity
In light of previous discussions, the evaluation of the currently proposed systems will be based on the number of needed productivities (electrical power, fresh water, and cooling/heating capacity).

Maximum Proposed Systems' Productivity
In light of previous discussions, the evaluation of the currently proposed systems will be based on the number of needed productivities (electrical power, fresh water, and cooling/heating capacity).  Correspondingly, systems evaluation can also be measured by space-supplied air conditions (ta4 and wa4) to maintain human comfort conditions inside the conditioned space. Figure 10 illustrates all available air-conditioned space supply conditions on the psychrometric charts for all studied parameter ranges relative to the space condition (25 °C and 12 gv/kga). The accepted conditions of space-supplied air are shown in the figures to be ta4 = 15.5-18.2 °C and wa4 = 9.2-12.00 gv/kga for systems MGS-I and MGS-II. Oth- Correspondingly, systems evaluation can also be measured by space-supplied air conditions (ta4 and wa4) to maintain human comfort conditions inside the conditioned space. Figure 10 illustrates all available air-conditioned space supply conditions on the psychrometric charts for all studied parameter ranges relative to the space condition (25 • C and 12 gv/kga). The accepted conditions of space-supplied air are shown in the figures to be ta4 = 15.5-18.2 • C and wa4 = 9.2-12.00 gv/kga for systems MGS-I and MGS-II. Otherwise, the conditions outside are not desirable.  Figure 11a shows the limits of supplied conditions (ta4 and wa4) of conditioned space for two proposed systems (MGS-I and MGS-II) at any for all studied parameter ranges. Moreover, Figure 11b displays the values and limitations of at any for two systems and all studied parameter ranges. Figure 11 can help researchers, solar multi-generation developers, power plant designers, and investors relate the proposed systems' productivities (electricity, space cooling, freshwater) in the design stage to select the suitable multi-generation system based on the needed application.  Q cooling at any . m f resh for two systems and all studied parameter ranges. Figure 11 can help researchers, solar multi-generation developers, power plant designers, and investors relate the proposed systems' productivities (electricity, space cooling, freshwater) in the design stage to select the suitable multi-generation system based on the needed application. Appl. Sci. 2022, 12, x FOR PEER REVIEW 21 of 25 Figure 11. System assessment and evaluation: (a) Space-supplied air conditions versus produced fresh water rate, (b) power output and space cooling capacity versus produced fresh water rate.

Comparisons with Other Reported Systems
For more contribution and to prove the current proposed systems' capability, reliability, applicability, and practical use the current systems' results are compared with the related results in other published works. The maximum TGOR and maximum freshwater productivity of co-generation and tri-generation systems are chosen as performance and productivity indicators for comparison to the currently proposed systems. However, they differ in operating conditions from our chosen conditions, as shown in Table 5. As shown in Table 5, the current system (MGS-II) has maximum TGOR and freshwater productivity better than the comparable systems.

Comparisons with Other Reported Systems
For more contribution and to prove the current proposed systems' capability, reliability, applicability, and practical use the current systems' results are compared with the related results in other published works. The maximum TGOR and maximum freshwater productivity of co-generation and tri-generation systems are chosen as performance and productivity indicators for comparison to the currently proposed systems. However, they differ in operating conditions from our chosen conditions, as shown in Table 5. As shown in Table 5, the current system (MGS-II) has maximum TGOR and freshwater productivity better than the comparable systems.

Conclusions
Thermodynamics analysis of a more efficient novel solar-driven multi-generation system (MGS-II) combined with ORC, HDH, and DCS with heat recovery systems have been investigated and presented for producing electricity, space cooling/domestic heating, and freshwater production. The effect of different system operating and design parameters on the systems' productivities and performance indicators was studied. In addition, a comparison study with the basic multi-generation system (MGS-I) is performed. Moreover, the validated system models have been applied to the performance evaluation when operating conditions are varied. Consequently, the following conclusions can be drawn:

•
The proposed multi-generation systems can produce electricity, fresh water, and cooling/domestic heating while maintaining human thermal comfort conditions inside the buildings. Q cooling improves with increasing MR until it reaches a maximum value and decreases with increasing MR. • MGS-II system has higher GOR HDH , TGOR, STG, and STGP than the MGS-I system. • GOR HDH , TGOR, STG, and STGP for two proposed systems drop with increasing tw1.
• . Q cooling improves with an increase in MR until they reach peak values, decreasing considerably.

•
The accepted ranges of systems input studied parameter were determine based on the accepted ranges comfortable space-supplied air conditions (temperature and humidity) at t a4 = 15.5-18.2 • C and w a4 = 9.2-12.00 gv/kga for systems MGS-I and MGS-II. Otherwise, the conditions outside are not desirable. Finally, we acknowledge that the current work presented in this paper is just a start for poly-generation systems; using different improvements of ORC, types of A/C (adsorption and absorption) and desalination (RO, MED) systems in addition to transient analysis are recommended as a future work for poly-generation systems.
LBSE lithium bromide-water simple effect MR Mass flow rate ratio MED Multi-effect desalination ORC Organic Rankine cycle RO Reverse osmosis SOFC Solid oxide fuel cell STG Specific total gained energy, kWh/m 2 STGP Specific total gained energy equivalent price, USD/ m 2 TGOR Total gained output ratio