Introduction to ORC–VCC Systems: A Review

Abstract

The increasing demand for sustainable energy solutions has spurred significant interest in cogeneration technologies. This study introduces a novel integrated organic Rankine cycle (ORC) and vapor compression cycle (VCC) system, specifically designed to enhance energy efficiency and reduce greenhouse gas emissions in industrial applications and district heating systems. The key innovation lies in the development of an advanced coupling mechanism that seamlessly connects the ORC and VCC, enabling more efficient utilization of low-grade heat sources. By optimizing working fluid selection and implementing a shared shaft connection between the ORC turbine and VCC compressor, the system achieves dual functionality—simultaneous electricity generation and cooling—with higher efficiency than conventional methods. Thermodynamic analyses and experimental results demonstrate that the proposed ORC–VCC system can significantly reduce operational costs and decrease reliance on fossil fuels by leveraging renewable energy sources and industrial waste heat. Additionally, the study addresses integration challenges by introducing specialized components and a modular design approach that simplifies installation and maintenance. This innovative system not only enhances performance but also offers scalability for various industrial applications. By providing a detailed evaluation of the ORC–VCC integration and its practical implications, this work underscores the system’s potential to contribute substantially to a sustainable energy transition. The findings offer valuable insights for future research and development, highlighting pathways to overcome existing barriers in cogeneration technologies.

1. Introduction

The escalating global demand for sustainable and efficient energy solutions has intensified research into advanced cogeneration systems. Among these, the integration of the organic Rankine cycle (ORC) and the vapor compression cycle (VCC) has emerged as a promising technology for enhancing energy efficiency and reducing greenhouse gas emissions [1,2]. This review article synthesizes recent advancements in ORC–VCC systems, focusing on their applications in various industrial sectors and district heating contexts. By exploring the integration and optimization of these systems, we aim to provide a comprehensive understanding of their capabilities and potential impact on sustainable energy practices.

Global environmental challenges, such as climate change and resource depletion, have highlighted the necessity for improving energy efficiency in industrial processes. The increasing demand for energy-intensive facilities, including refrigeration and air-conditioning equipment, has further emphasized this need [3]. Implementing energy recovery technologies that employ standalone and combined cycle configurations has garnered significant attention [4]. Utilizing industrial waste heat and renewable energy sources presents a viable strategy for enhancing industrial energy efficiency [5]. Due to technological advancements, low-grade waste heat and renewable energy sources are now prime candidates for various applications, including electricity generation, heating and cooling, hydrogen production, and water desalination [6].

Combined heat and power (CHP) systems are widely used for electricity production alongside simultaneous heating or cooling services [7]. These systems leverage renewable energies and waste heat recovery, exhibiting high potential in improving overall system performance by transforming otherwise wasted energy into useful outputs [8]. The expected increase in global energy demand—up to 80% by 2050 [4]—coupled with stringent regulations on greenhouse gas emissions, underscores the importance of such technologies. Implementing small-scale, renewable-energy-based cogeneration technologies in decentralized, off-grid areas can enhance socioeconomic conditions by providing energy independence and reducing costs [3]. This approach has become a driving force for economic development and sustainability.

The organic Rankine cycle (ORC) is a technology that enables the efficient use of low-temperature heat sources for electricity generation. Unlike the traditional Rankine cycle, ORC utilizes organic working fluids with low boiling points, allowing effective energy conversion from geothermal resources, industrial waste heat, solar energy, and biomass.

Geothermal energy, especially low-enthalpy sources, is ideal for ORC applications due to its constant availability and independence from weather conditions [9,10,11,12,13,14,15,16,17,18].

In the article by Li et al. (2023) [9], a thermo-economic model was developed for a 300 kW hybrid solar-geothermal ORC system, focusing on the impact of energy resource endowments on system efficiency across four Chinese locations. The results demonstrated a significant improvement in performance, with up to a 25.34% increase in energy output and a 16.28% reduction in the levelized cost of energy (LCOE) compared to standalone solar systems. This highlights the benefits of integrating geothermal preheating in regions with moderate solar resources. Wu et al. (2024) [10] investigated the dynamic behavior of an ORC coupled with an ejector expansion refrigeration cycle (EERC) driven by geothermal water. Two configurations, single and dual condensers, were modeled to evaluate system stability under disturbances in heat source flow. The dual-condenser setup was shown to better isolate the EERC subsystem from ORC-induced performance fluctuations. The study also proposed a multi-device cooperative control strategy, improving the system’s cooling capacity by up to 9.29% under variable heat source conditions. Semmari et al. (2024) [11] conducted a thermo-economic assessment of indirect heat ORC geothermal power plants in northeastern Algeria. The analysis revealed that geothermal electricity production is technically feasible, with the Meskhoutine site achieving a payback period of 10.8 years and an electricity cost of 0.21 $/kWh. However, the study noted that current energy subsidies in Algeria limit the economic attractiveness of these systems, emphasizing the need for policy revisions to support renewable energy adoption. Laghari et al. (2024) [12] analyzed the thermodynamic performance of a geothermal ORC system using mixtures of working fluids, specifically R245fa/R600a. Their simulations demonstrated that the mixture outperformed pure working fluids in terms of energy and exergy efficiency, achieving optimal performance at elevated evaporator pressures. The regenerative cycle provided a 20.72% energy efficiency, 67.76% exergy efficiency, and a net power output of 2326 kW. Mohammadi and Fallah (2023) [13] explored a novel combined system integrating a double-flash ORC, absorption cooling, and thermoelectric generators (TEGs) powered by geothermal energy. Advanced exergy analysis identified key components for improvement, such as the generator and low-pressure turbine, which together accounted for 35.35% of the total avoidable exergy destruction. The study demonstrated that targeted improvements could significantly enhance system efficiency, with an overall exergy efficiency of 55.83%. Cui and Aziz (2024) [14] evaluated the thermodynamic and economic viability of ORC-based geothermal hydrogen production systems. Using R236fa, R245fa, and R600a as working fluids, they found that R600a offered the lowest levelized cost of hydrogen (LCOH) at 5.22 $/kg and optimal economic performance at geothermal fluid temperatures of 300 °C. The study highlighted the importance of fluid selection and bespoke system configurations in optimizing geothermal hydrogen production. Lou et al. (2023) [15] proposed a combined ORC and thermoelectric generator (TEG) system utilizing geothermal energy through a coaxial casing well. The integrated model achieved a 9% increase in power output and a 4.3% improvement in overall system efficiency compared to standalone ORC systems. Key design variables, such as water flow rates and thermal insulation materials, were identified as critical to maximizing performance. Pandey et al. (2023) [16] designed a space cooling system powered by residual energy from an ORC-ground source heat pump (GSHP)-assisted geothermal plant in India. Experimental results over 90 days demonstrated the system’s effectiveness, achieving indoor temperatures of 18 °C under ambient conditions ranging from 19 to 46 °C. The GSHP exhibited a coefficient of performance (COP) between 1.6 and 4, indicating its suitability for both cooling and heating applications. Chitgar et al. (2023) [17] analyzed geothermal energy-driven ORC systems for desalination, comparing basic, parallel, and series configurations. Using a genetic algorithm coupled with an artificial neural network, the study optimized working fluid selection and system design. Parallel and series configurations achieved significant improvements in power generation and water production, with up to 150% and 60% enhancements, respectively, over the basic configuration. Liu et al. (2023) [18] explored the integration of a geothermal ORC system with a solid oxide fuel cell-gas turbine (SOFC-GT) system to enhance power generation. By utilizing SOFC waste heat, the combined system improved energy efficiency by 8.11% and increased output power by 7.95%. Under low-temperature geothermal conditions, the ORC power output improved by 22.64%, demonstrating the potential of cascade heat utilization to optimize geothermal energy applications.

Waste heat from industrial processes is another significant energy source. Many industrial facilities generate excess heat that can be recovered and used in ORC systems, increasing energy efficiency and reducing greenhouse gas emissions [19,20,21,22,23,24,25,26,27].

Tchanche et al. (2011) [19] reviewed the applications of ORC technology for converting low-grade heat into power. The study highlighted mature applications such as binary geothermal and biomass combined heat and power (CHP) systems and anticipated growth in waste heat recovery systems driven by legislative support. It also pointed out ongoing research in solar-powered modular ORC systems for cogeneration and offshore ocean thermal energy conversion (OTEC) systems. Vélez et al. (2012) [20] provided a comprehensive technical, economic, and market analysis of ORC systems. The study emphasized ORC’s versatility in converting low- and medium-grade heat into electrical or mechanical energy, suitable for isolated areas and desalination. It identified the optimization of working fluid selection as a critical research direction and presented the economic viability of small-scale systems (0.2–2 MWe) in a pre-commercial phase. Sauret and Gu (2014) [21] focused on the design and optimization of a radial-inflow turbine for ORC applications under geothermal conditions. Using R143a as the working fluid, the study employed 3D CFD simulations and thermodynamic analysis to validate turbine performance under nominal and off-design conditions. The results underscored the importance of coupled thermodynamic and turbine design optimization for improving system efficiencies. Bao et al. (2020) [22] compared single-fluid and dual-fluid ORC–VCC systems for geothermal heat-activated cooling applications. The study optimized system parameters and working fluids, finding that dual-fluid systems, particularly ORC–FTVIC configurations, outperformed others in cooling capacity and efficiency. R1234yf-R152a was identified as the optimal working fluid combination for the dual-fluid ORC–FTVIC system. Zhai et al. (2016) [23] categorized heat sources for ORC applications, including geothermal, solar, and biomass sources, emphasizing the impact of heat source characteristics on system design and performance. The study recommended performance metrics for evaluating ORC systems and outlined market opportunities for various heat source applications, identifying future development directions. Demierre et al. (2014) [24] explored a thermally driven heat pump concept based on a dual ORC system. Using an oil-free compressor-turbine unit, the study demonstrated the prototype’s effectiveness for heating applications with geothermal and other heat sources. The results highlighted the system’s adaptability to various thermal sources and its potential for efficient energy use. Song et al. (2020) [25] analyzed the thermo-economic performance of subcritical and transcritical ORC systems for geothermal applications. Through multi-objective optimization, the study demonstrated that transcritical systems offered better thermal matching and economic feasibility. Non-recuperated configurations with working fluids having critical temperatures close to the heat source temperature were the most favorable. Moloney et al. (2017) [26] performed a parametric analysis of regenerative supercritical ORC systems for medium-temperature geothermal reservoirs. The study identified optimal working fluids, such as cis-butene and pentane, achieving higher efficiencies under specific conditions. It also demonstrated the potential of supercritical cycles for improved energy conversion from low-grade geothermal resources. Zywica et al. (2017) [27,28] investigated the performance of a domestic CHP ORC system designed for single-family houses. The prototype, equipped with an oil-free turbogenerator, demonstrated reliable operation under varying thermal and electrical loads. The results confirmed the system’s adaptability and safety under transient operating conditions, making it suitable for small-scale energy applications.

Solar energy can also be harnessed in ORC systems through the use of solar collectors. Concentrating solar radiation allows for temperatures sufficient to drive the ORC cycle, enabling electricity production from a clean, renewable source [29,30,31,32,33,34,35,36,37].

Permana et al. (2024) [29] explored the integration of small-scale solar ORC systems with phase change materials (PCMs) in Indonesia, targeting backup electricity production. The study revealed that R134a provided the highest power output, while R245fa demonstrated the best efficiency at 7.45%. An inorganic PCM was selected for thermal energy storage due to its optimal heat capacity, enabling a daily ORC operation of 500 W. Xu et al. (2024) [30] investigated a 3 kW solar-ORC integrated power and heating system designed for household use. Using BY-3 as the working medium, experiments analyzed system performance under varying thermal and electrical conditions. The system achieved a power generation efficiency of 6.8% and a COP of 3.5, highlighting its potential for residential applications. Fatigati et al. (2023) [31] conducted experimental and theoretical analyses of a micro-cogenerative solar ORC unit featuring a sliding rotary vane expander. By varying the expander speed, the study optimized performance under off-design conditions, ensuring system adaptability. The results confirmed the suitability of the expander for enhancing electricity generation efficiency. Rahmdel et al. (2023) [32] proposed a solar ORC cogeneration system tailored for remote areas to produce electricity, freshwater, and heating energy. The system demonstrated flexibility in responding to varying environmental conditions, maintaining steady performance across different scenarios. Results emphasized the practicality of such systems in meeting diverse energy demands. Wang et al. (2024) [33] focused on thermal energy storage for solar-coupled ORC systems, comparing single-stage and cascade phase change storage. The study demonstrated that cascade systems improved thermal efficiency by up to 17.2% under fluctuating solar conditions, highlighting their potential for distributed power generation applications. Fatigati and Cipollone (2024) [34] evaluated the impact of recuperative layouts in solar-assisted ORC micro-cogeneration plants. The study showed that recuperative systems required lower working fluid flow rates, resulting in a 38% increase in electricity production compared to non-recuperative designs, justifying the investment in recuperative technology.

Mohseni et al. (2024) [35] designed a solar–natural gas ORC-based trigeneration system for residential applications in Khuzestan, Iran. The system provided cooling, heating, and electricity, achieving energy and exergy efficiencies of 186.6% and 27.81%, respectively. The results highlighted the potential of integrating renewable and conventional energy sources. Zhao et al. (2024) [36] optimized a solar-powered ORC–VCR–CCHP system using a ternary refrigerant selection model. The system achieved an exergoeconomic efficiency of 42.49%, with R245fa/R41/R1336mzz(z) emerging as the optimal refrigerant blend. This approach emphasized the importance of refrigerant selection for efficiency and environmental performance. Fatigati et al. (2024) [37] presented a dynamic analysis of a micro-scale ORC unit powered by solar flat panels and thermal energy storage. The study identified optimal operating strategies to maximize electricity production while maintaining thermal needs. Results demonstrated the significance of regulating working fluid mass flow rates to prolong operating time.

Biomass and biogas are additional renewable heat sources for ORC. The combustion of biomass or the heat generated during biogas fermentation provides thermal energy that can be converted into electricity in ORC systems [38,39,40,41,42,43,44,45,46,47,48].

Mascuch et al. (2021) [38] shared insights from the pilot operation of a biomass-fired ORC micro-cogeneration unit. Operating for over 3000 h, the unit provided 125 MWh of heat and 2.34 MWh of electricity. While initial issues, particularly with the expander, were noted, these were mitigated during operation. The authors emphasized that economic performance should not be the sole evaluation criterion, highlighting the broader benefits of μCHP systems. Braimakis et al. (2021) [39] conducted a techno-economic assessment of a biomass-fired ORC plant for district heating applications. Analyzing various scenarios across Europe, the study revealed that high electricity and heat prices, along with long operating hours, were essential for economic viability. Challenges such as high specific costs and limited operating hours impacted payback periods, ranging from 5 to 7 years under favorable conditions. Pina et al. (2021) [40] designed and analyzed a hybrid solar-biomass ORC-based polygeneration system for a commercial center in Zaragoza, Spain. While the system achieved high renewable energy use, it faced economic limitations, with electricity production costs exceeding purchase prices. However, it significantly reduced CO₂ emissions (by 96.1%) and non-renewable energy consumption (by 85.6%) compared to conventional systems. Hasanzadeh et al. (2023) [41] proposed a novel biomass-gas turbine-ORC system with electrochemical amine regeneration for CO₂ capture. This hybrid system achieved high energy efficiency (up to 33.65%) while integrating near-zero CO₂ emissions. However, the CO₂ capture reduced system efficiency by 6–8%, highlighting a trade-off between environmental benefits and energy performance. Permana et al. (2024) [42] performed a analysis of a 150 kWe biomass-ORC plant in Bologna, Italy. The study demonstrated the plant’s economic competitiveness with a net present value (NPV) of EUR 238,000 and a levelized cost of energy (LCOE) of 0.93 EUR/kWh. Despite a 24-year payback period, the system was deemed a viable renewable energy solution for small-scale applications. Kalina and Świerzewski (2019) [43] analyzed operational data from a biomass-fired ORC cogeneration system in a municipal heating network. The study used regression-based models to identify off-design performance characteristics, providing valuable insights for maintenance planning and system diagnostics in real operational conditions. Świerzewski and Kalina (2020) [44] optimized biomass-fired ORC cogeneration plants integrated with coal-fired district heating systems. The study revealed that optimal ORC unit sizes range from 1–2 MW for a 30 MW heating network. While thermal energy storage slightly improved economic performance, anticipated increases in electricity and emission allowance prices significantly enhanced financial outcomes. Carraro et al. (2020) [45] investigated an innovative biomass-fired micro-ORC system for isolated microgrids. Through experimental analysis, the study identified optimal operational conditions, achieving an ORC electrical efficiency of 7.3% and an expander efficiency of 57%. These findings highlight the potential of micro-ORC systems in distributed energy generation. Morais et al. (2020) [46] proposed a hybrid solar–biomass ORC system integrated with an absorption cooling unit for a Brazilian industrial plant. Among the tested fluids, cyclohexane demonstrated the best energy, exergy, and economic performance, with an internal rate of return (IRR) of 6%. The study underscored the influence of electricity costs and solar collector expenses on system viability. Cao et al. (2021) [47] compared waste heat recovery via ORC and compressor inlet cooling for a biomass-fueled gas turbine. Results indicated that compressor inlet cooling outperformed ORC-based power generation, achieving 11.2% higher exergy efficiency and 12.3% lower electricity costs under optimal conditions. Georgousopoulos et al. (2021) [48] assessed waste heat recovery using ORCs in biomass-fueled IGCC plants. The integration of syngas cooling provided the best thermodynamic and economic outcomes, with efficiency improvements of 2.81% and a discounted payback period of 5.7 years. While zeotropic ORCs offered thermodynamic advantages, their economic benefits were marginal compared to pure fluid cycles.

Additionally, ocean thermal energy conversion (OTEC) systems utilize temperature differences between surface and deep waters for ORC applications, offering potential for coastal regions with significant thermal gradients.

ORC–VCC systems are designed to harness low-temperature heat sources, such as solar energy, industrial waste heat, and biomass, to generate both electricity and refrigeration [49]. The ORC is particularly effective in converting low-grade thermal energy into electricity due to its use of organic working fluids with lower boiling points than water [50,51,52]. The robustness and simplicity of the ORC make it versatile, from small-scale power generation to industrial waste heat recovery [53]. Complementing the ORC, the VCC employs refrigerants like ammonia or hydrofluorocarbons (HFCs) for cooling through mechanical compression and expansion processes. Integrated with the ORC, the VCC utilizes the electricity produced to power its compressor, reducing dependency on external power sources [54,55]. This synergy enables ORC–VCC systems to meet power and cooling demands efficiently.

The versatility of ORC–VCC systems extends across industries. In industrial settings, they recover waste heat to produce power and cooling, reducing emissions and enhancing efficiency. In district heating networks, these systems improve heat distribution and provide additional cooling, optimizing overall network performance. Their ability to operate efficiently with low-temperature heat sources, such as solar thermal and geothermal energy, reduces reliance on fossil fuels and supports the transition to a sustainable energy future [56,57].

In light of these considerations, this review examines the latest research on ORC–VCC systems, including thermodynamic analyses, working fluid selections, and system optimizations. By consolidating findings from recent studies, we aim to identify opportunities for improving system performance and contributing to sustainable energy solutions.

2. Overview of the ORC–VCC Integration

The integration of the organic Rankine cycle (ORC) with the vapor compression cycle (VCC) represents a highly innovative approach to energy recovery and efficient utilization, capitalizing on low-temperature waste heat sources for the cogeneration of both electricity and cooling. This combined ORC–VCC system is specifically designed to enhance energy efficiency while simultaneously minimizing environmental impact by effectively repurposing waste heat that would otherwise be lost.

The fundamental operating principle of the ORC–VCC system involves leveraging waste heat—commonly sourced from industrial processes or renewable energy inputs such as geothermal or solar thermal energy—to drive the ORC. Within this configuration, the ORC converts the captured low-temperature thermal energy into mechanical energy. This mechanical energy is then utilized to operate the VCC, which subsequently provides refrigeration and cooling.

The synergistic nature of this integrated system allows for the simultaneous generation of electricity and cooling from a single heat source, thereby achieving a high level of energy efficiency and resource utilization. The ORC is particularly well-suited for converting low-grade heat due to its use of organic working fluids, which have lower boiling points than water, facilitating efficient energy conversion at reduced temperatures. The mechanical energy produced by the ORC is harnessed directly by the VCC, which uses it to drive a compressor and generate cooling output. As a result, the ORC–VCC integration forms a unified energy system capable of addressing both thermal power generation and cooling requirements from the same energy input, effectively reducing overall energy waste and contributing to a lower carbon footprint.

Such systems are increasingly recognized for their potential applications in industrial settings, district heating, and renewable energy installations, where their ability to maximize energy recovery and deliver multiple forms of energy output is essential for advancing sustainability and achieving higher operational efficiency.

2.1. Basic Schematic of the ORC–VCC System

Figure 1, derived from the work of Witanowski et al. [52], illustrates the schematic of the ORC–VCC system. In this design, low-temperature waste heat sources drive the ORC, which generates mechanical energy. This mechanical energy, in turn, drives the VCC, producing cooling. The cooling water system and air cooling facilitate the heat rejection processes.

The ORC–VCC system employs various components and processes to achieve efficient energy recovery and conversion. The low-temperature waste heat source, which may originate from industrial waste heat, geothermal energy, or solar thermal energy, is captured and used to evaporate the working fluid within the organic Rankine cycle (ORC). The ORC uses organic fluids with low boiling points, such as R600a (isobutane) or ammonia, to efficiently convert thermal energy into mechanical energy at temperatures lower than those typically used in conventional steam Rankine cycles. In this process, the working fluid is vaporized by the captured waste heat and subsequently expands through an expander to produce mechanical work. After expansion, the working fluid is condensed and then pumped back to the evaporator, completing the cycle.

The mechanical energy generated by the ORC, often referred to as shaft work, is employed to drive the compressor in the vapor compression cycle (VCC). This mechanical coupling is a fundamental aspect of the integrated ORC–VCC system, enabling it to simultaneously produce electricity and cooling. In the VCC, the mechanical energy from the ORC is used to compress a refrigerant, which then absorbs heat during evaporation, thereby providing the desired cooling effect. The refrigerant used in the VCC is typically ammonia or another suitable substance known for its thermodynamic efficiency and environmentally favorable properties.

To sustain the efficiency of the ORC–VCC system, heat rejection mechanisms such as cooling water systems and air cooling units are employed. These systems are crucial for rejecting excess heat from both the ORC condenser and the VCC condenser, respectively. Effective heat rejection ensures that the system operates efficiently and that all components are protected from overheating, thereby maintaining overall system performance and reliability.

For the above example of an ORC–VCC system, where the ORC expander and VCC compressor are coupled by a common shaft, the process looks like the following (Figure 2):

Processes in the ORC cycle:

• Process (1→2): The actual expansion of the working fluid in the ORC expander.
• Process (2→3): Regeneration process.
• Process (4→5): The isentropic compression process of the working fluid in the ORC pump.
• Process (5→6): Regeneration process.
• Process (3→4): Actual pumping work, which raises the pressure of the fluid in the ORC cycle.
• Process (4→1): Heat addition in the generator (e.g., solar collector), causing the working fluid to evaporate in the ORC cycle.
• Processes in the VCC cycle:
• Process (11→12): The actual compression of the working fluid in the VCC compressor.
• Process (12→13): The condensation of the working fluid in the condenser, where heat is rejected; this process is shared by both the ORC and VCC cycles.
• Process (13→14): Expansion across the throttle valve in the VCC cycle, where the pressure of the working fluid decreases without heat exchange.
• Process (14→11): Heat absorption in the VCC evaporator, where the working fluid vaporizes, creating the cooling effect.

2.2. Thermodynamic Analysis

Thermodynamic analysis is a cornerstone of evaluating the performance and efficiency of energy systems, providing a quantitative foundation for understanding their operational potential and limitations. In this review, the analysis serves several key purposes. By applying mass, energy, entropy, and exergy balance equations, the thermodynamic analysis establishes baseline efficiency metrics for integrated ORC–VCC systems. These metrics are essential for comparing the performance of various configurations and identifying areas for improvement.

Mass Balance

The mass balance equation is fundamental to any thermodynamic analysis, ensuring that the mass flow entering the system is equal to the mass flow exiting it [59]:

$$\sum {\dot{m}}_{in}=\sum {\dot{m}}_{ex},$$

(1)

here, ṁ denotes the mass flow rate, with the subscripts ‘_in’ and ‘_ex’ referring to the inlet and outlet of the system, respectively. This equation assumes steady-state conditions, where the mass accumulation within the system is negligible.

Energy Balance

The energy balance equation is a cornerstone of thermodynamic analysis, reflecting the conservation of energy principle [60]:

$$\sum {\dot{m}}_{in}{h}_{in}+\sum {\dot{Q}}_{in}+\sum {\dot{W}}_{in}=\sum {\dot{m}}_{ex}{h}_{ex}+\sum {\dot{Q}}_{ex}+\sum {\dot{W}}_{ex},$$

(2)

where, h represents the specific enthalpy, $\dot{Q}$ denotes the heat transfer rate, and $\dot{W}$ is the work transfer rate. The terms on the left side of the equation account for the energy inputs to the system, while those on the right side represent the energy outputs. This balance is crucial for determining the net energy performance of the system.

Entropy Balance

Entropy balance is used to quantify the irreversibilities within the system, which are crucial for understanding the efficiency losses [61]:

$$\sum {\dot{m}}_{in}{s}_{in}+\sum \left({\displaystyle \frac{{\dot{Q}}_k}{T_k}}\right)=\sum {\dot{m}}_{ex}{s}_{ex}+{\dot{S}}_{gen},$$

(3)

where s is the specific entropy, $T_k$ is the absolute temperature at which heat transfer ${\dot{Q}}_k$ occurs, and ${\dot{S}}_{gen}$ represents the rate of entropy generation due to irreversibilities. This equation is pivotal in assessing the second law efficiency of the system.

Exergy Balance

Exergy analysis provides insights into the quality of energy, focusing on the work potential rather than just the quantity of energy [62]:

$$\sum {\dot{m}}_{in}{e}_{in}+\sum {\dot{E}}_{Q,in}+{\dot{E}}_{W,in}=\sum {\dot{m}}_{ex}{e}_{ex}+\sum {\dot{E}}_{Q,ex}+{\dot{E}}_D.$$

(4)

In this equation, ex is the specific exergy, ${\dot{E}}_Q$ is the exergy associated with heat transfer, and ${\dot{E}}_W$ is the exergy related to work. The term ${\dot{E}}_D$ represents the exergy destruction rate, which is a measure of the irreversibilities within the system.

Exergy Destruction Rate

The exergy destruction rate, which is a direct consequence of system irreversibilities, is calculated as follows [63]:

$${\dot{E}}_D=T_0{\dot{S}}_{gen},$$

(5)

where $T_0$ is the reference environmental temperature, and ${\dot{S}}_{gen}$ is the rate of entropy generation. This equation highlights the thermodynamic losses that reduce the efficiency of the system.

Exergy Related to Work

The exergy associated with work, which is the maximum useful work obtainable as the system comes into equilibrium with its surroundings, is given by the following:

$${\dot{E}}_W=\dot{W}.$$

(6)

Exergy Related to Heat Transfer

Exergy related to heat transfer accounts for the quality of heat energy at different temperatures [62]:

$${\dot{E}}_Q=\dot{Q} \ast \left(1-{\displaystyle \frac{T_0}{T}}\right).$$

(7)

Specific Flow Exergy

Specific flow exergy, which is the maximum useful work obtainable from a fluid as it flows through a system, is expressed as follows [63]:

$${ex}_{ph}=\left(h-h_o\right)-T_0\left(s-s_0\right).$$

(8)

COP of the System

The coefficient of performance (COP) of the system, which is a measure of the efficiency of energy usage, is defined as follows [60]:

$$\mathrm{C}\mathrm{O}\mathrm{P}={\displaystyle \frac{\sum \mathrm{u}\mathrm{s}\mathrm{e}\mathrm{f}\mathrm{u}\mathrm{l} \mathrm{o}\mathrm{u}\mathrm{t}\mathrm{p}\mathrm{u}\mathrm{t} \mathrm{e}\mathrm{n}\mathrm{e}\mathrm{r}\mathrm{g}\mathrm{y}}{\sum \mathrm{i}\mathrm{n}\mathrm{p}\mathrm{u}\mathrm{t} \mathrm{e}\mathrm{n}\mathrm{e}\mathrm{r}\mathrm{g}\mathrm{y}}}.$$

(9)

ORC System Efficiency

The efficiency of the organic Rankine cycle (ORC) system is determined by the following [64]:

$${\mathsf{\eta }}_{ORC}={\displaystyle \frac{{\dot{W}}_{turbine}-{\dot{W}}_{pump}}{{\dot{Q}}_{in}}},$$

(10)

where the symbol η is used to denote the thermal efficiency of the ORC system. This symbol is commonly used to represent the efficiency of a thermodynamic cycle, particularly in systems where work output and heat input are the primary considerations.

VCC System Efficiency

The efficiency of the vapor compression cycle (VCC) system, often expressed as a coefficient of performance, is given by the following [60]:

$${\mathsf{\psi }}_{VCC}={\displaystyle \frac{{\dot{Q}}_L}{{\dot{W}}_{compressor}}}.$$

(11)

The symbol ψ is used here to denote the exergetic efficiency of the VCC system. While η is typically used for thermal efficiency, ψ is often reserved for exergetic efficiency, which accounts for the quality of energy conversions in systems where work and exergy play significant roles.

Total System Efficiency

The overall efficiency of the combined ORC–VCC system is calculated by the following [65]:

$$\mathsf{\beta }={\mathsf{\eta }}_{ORC}x{COP}_{VCC}$$

(12)

3. Literature Survey

Research into ORC–VCC systems experienced a significant slowdown after the mid-1990s, largely due to the lack of environmentally friendly working fluids and technical challenges related to component performance and control systems [8]. In the past decade, however, the development of new eco-friendly refrigerants and advancements in component technologies have revitalized interest in ORC systems. These advancements have been extensively reviewed by numerous authors [66,67,68,69,70]. Despite the remarkable progress in ORC technology, interest in ORC–VCC systems has only recently been rekindled and remains relatively limited. The following is a literature review of notable advancements in ORC–VCC since the early 21st century.

The selection of a working fluid plays a pivotal role in the design and optimization of ORC–VCC systems, as it directly impacts thermodynamic performance, environmental sustainability, and operational safety. Working fluids differ in their physical and chemical properties, such as boiling point, critical temperature, thermal conductivity, and viscosity, which determine their suitability for specific operating conditions. Environmental considerations, such as global warming potential (GWP) and ozone depletion potential (ODP), are also critical due to regulatory restrictions, including the Montreal Protocol and F-Gas regulations.

Table 1. Properties of selected working fluids used in ORC–VCC systems [71,72,73].

Working Fluid	Boiling Point (°C)	Critical Temperature (°C)	Critical Pressure (MPa)	GWP	ODP	Thermal Conductivity (W/mK)	Application Contexts
R134a	−26.1	101.1	4.06	1430	0	0.084	VCC cycles; moderate-temperature applications; high GWP phase-out.
R245fa	15.3	154.0	3.65	950	0	0.073	ORC systems; low- to medium-temperature sources; stable but regulated.
HFO-1234yf	−29.4	94.7	3.38	4	0	0.086	Automotive air-conditioning; low-GWP alternative for R134a.
HFO-1234ze(E)	−19.0	109.4	3.36	7	0	0.085	Medium-temperature ORC/VCC; low environmental impact.
Ammonia (R717)	−33.3	132.4	11.33	0	0	0.023	Industrial refrigeration; high efficiency, toxic handling.
Isobutane (R600a)	−11.7	134.7	3.64	3	0	0.100	Small-scale ORC; household refrigeration; flammable.
R410A	−51.6	72.5	4.95	2088	0	0.072	Air-conditioning; high GWP phase-out.
HFO-1336mzz(Z)	33.4	171.3	3.47	2	0	0.064	High-temperature ORC systems; promising low-GWP fluid.
Propane (R290)	−42.1	96.7	4.25	3	0	0.091	Refrigeration; low-temperature ORC; environmentally friendly but flammable.

summarizes the most commonly used working fluids in ORC–VCC systems, highlighting their key properties, including boiling point, critical temperature, GWP, ODP, thermal conductivity, viscosity, and application contexts. This comparison provides a comprehensive overview of fluid characteristics to aid in the understanding of their suitability for various system configurations and use cases.

3.1. Theoretical Studies on ORC–VCC Systems

Many theoretical studies have been carried out on coupled ORC and VCC systems, with a primary focus on selecting the working fluid, optimizing system structure, and refining operational parameters.

Kim and Blanco (2015) [74] analyzed the thermal efficiency of several working fluids—namely R143a, R22, R134a, R152a, propane, ammonia, isobutane, and butane—when applied in an organic Rankine cycle (ORC) system combined with a vapor compression cycle (VCC) for standalone cooling and power-cooling applications. In their setup, both the ORC with recuperation and the VCC relied on a shared refrigerant, connected through a common condenser. Their study investigated the effects of varying turbine inlet temperature, input pressure, and flow division ratios on multiple performance metrics, including specific cooling capacity, net power output, thermal and exergy efficiency, total heat transfer units, system size parameters, and the turbine’s volumetric flow ratio. Fluids with high critical temperatures, such as isobutane and butane, showed enhanced efficiency in refrigeration-focused applications, while isobutane stood out for dual power and cooling purposes due to its superior thermal efficiency. The findings highlighted that integrating ORC and VCC can be an effective approach for utilizing low-temperature heat sources.

Yilmaz (2015) [75] explored the potential of a transcritical ORC–VCC setup designed to deliver 30 kW of cooling in intercity buses by recovering engine waste heat. R134a and R245fa served as the refrigerants across both cycles, employed in a shared configuration. The study examined how variations in compressor, pump, and turbine isentropic efficiencies and fluctuating engine loads influenced the system’s coefficients of performance (COPs), including cooling output per heat input (COPH) and cooling output per ORC pump work (COPW). Results indicated that the ORC–VCC system could meet cooling needs even at half engine load, demonstrating both refrigerants as viable for this purpose.

Molés et al. (2015) [76] conducted a thermal assessment of an ORC–VCC model using different refrigerants in each cycle. The team evaluated low-global-warming-potential (GWP) fluids, such as HCFO-1233zd(E) and HFO-1336mzz(Z) in the ORC, and HFO-1234yf and HFO-1234ze(E) in the VCC, as alternatives to traditional HFC refrigerants. Four fluid pairings were tested, with ORC evaporator temperatures between 97 °C and 147 °C and VCC evaporator temperatures from −13 °C to 7 °C. The range of thermal and electrical COP values was broad, with thermal COPs ranging from 0.30 to 1.10 and COPW ranging from 15 to 110, depending on the configuration. HFO-1234ze(E) in the VCC and HFO-1336mzz(Z) in the ORC showed slightly superior outcomes.

Li et al. (2014) [77] performed an energy and exergy analysis on a transcritical ORC paired with a VCC for power and refrigeration cogeneration. R22, R134a, and R290 were tested as shared refrigerants in both cycles with a common condenser. The study emphasized key variables such as flue gas inlet and turbine inlet temperatures, and condensation temperature, assessing their impact on system performance. Results showed that electricity and refrigeration capacities were strongly linked, with R134a emerging as the preferred fluid under partial load conditions.

Yue et al. (2016) [78] investigated the thermal and economic feasibility of an ORC–VCC system that used engine exhaust in vehicles, comparing it with traditional waste heat recovery systems. Testing fluids like n-propane, cyclopentane, R134a, and R245fa, they varied VCC evaporator, ORC–VCC condenser, and ORC evaporator temperatures across specified ranges. Efficiency improvements between 9.2% and 9.8% and fuel savings from 1.1 to 1.3 L/h were recorded, with R134a identified as the optimal refrigerant due to its balance between efficiency and cost-effectiveness.

Aneke et al. (2012) [79] compared a waste-heat-driven ORC–VCC system using R245fa and NH₃ with an NH₃-H₂O absorption cycle, utilizing the IPSEpro PSE simulation tool. The system used flue gases at 164 °C to cool ambient air from 25 °C to −18 °C. The ORC–VCC system achieved better second-law efficiency and lower operating pressures than the absorption cycle under similar conditions. With minor modifications, the system could also produce electricity, further enhancing its cost-effectiveness.

Demierre et al. (2012, 2014) [24,80] developed a prototype featuring a supercritical R134a ORC connected with an R134a VCC for heating outputs of 20 kW and 40 kW, respectively. Their unique compressor–turbine unit (CTU), comprising a centrifugal compressor and radial inflow turbine on a shared shaft with self-acting vapor bearings, was analyzed for COP sensitivity to CTU speed. Exergetic efficiency varied from 0.37 to 0.45, highlighting the performance of their double-tube coil supercritical evaporator.

Wang et al. (2011) [81] contributed key insights into ORC–VCC designs. In 2012, they created a prototype with R245fa in the ORC and R134a in the VCC, using a hot oil loop at 200 °C to simulate waste heat. The system produced up to 4.4 kW of cooling, with a COP of 0.48 under off-design conditions. A 2013 theoretical study evaluated different ORC–VCC configurations, focusing on ORC recuperation and VCC subcooling, achieving a peak COP of 0.66 with R245fa as the common refrigerant.

Aphornratana and Sriveerakul (2010) [82] analyzed an ORC–VCC unit featuring a single-piston expander–compressor arrangement, sharing refrigerants through a common condenser. They tested R22 and R134a with generator temperatures between 60 °C and 90 °C, condenser temperatures from 30 °C to 50 °C, and evaporator temperatures from −10 °C to 10 °C. R22 exhibited optimal performance with COP values ranging from 0.1 to 0.6.

Jeong and Kang (2004) [83] evaluated an ORC–VCC configuration both with and without ORC regeneration, using R123, R245ca, and R134a as shared refrigerants through a common condenser. R123 achieved the highest performance, but environmental considerations led them to recommend R245ca, with recuperation potentially improving performance by about 47%.

Zhou et al. (2023) [84] present a study on a dynamically modeled, mechanically coupled organic Rankine–vapor compression cycle (ORVC) system aimed at efficient heat recovery from compression units in cryogenic air separation. The ORC–VCC system was designed to enhance energy savings by coupling an ORC expander directly to a VCC compressor using a single-shaft expander–compressor unit. With R245fa as the working fluid, the system operated effectively across various environmental conditions. The system’s thermal efficiency averaged 19.7%, recovering up to 76.4% of compression heat. Dynamic performance simulations indicated an annual energy savings of approximately 13.75 GWh, equivalent to reducing CO₂ emissions by around 9.9 Mt, demonstrating substantial environmental benefits and efficiency gains.

Bu et al. (2013, 2013) [85,86] extensively examined ORC–VCC systems in geothermal air conditioning, solar-powered ice production, and marine waste heat recovery for ice production. Their findings highlighted isobutane and butane as effective for geothermal and marine applications, with R123 being competitive in solar-based systems.

Li et al. (2013) [86] explored hydrocarbon-based fluids, including propane, butane, isobutane, and propylene, as working fluids for ORC–VCC systems using a common condenser. They tested boiler temperatures from 60 °C to 90 °C, condenser temperatures between 30 °C and 55 °C, and evaporator temperatures from −15 °C to 15 °C. Butane was identified as the most suitable fluid, with propylene showing limited compatibility.

Aphornratana and Sriveerakul (2010) [82] analyzed a combined Rankine–vapor–compression refrigeration cycle using R22 and R134a. Key operating conditions included generator temperatures of 60–90 °C, condenser temperatures of 30–50 °C, and evaporator temperatures of −10–10 °C. COP values ranged from 0.1 to 0.6, with R22 performing better due to its higher vapor density, enhancing cooling capacity. Adding a liquid preheater reduced energy input, increasing COP. COP improved with higher evaporator and lower condenser temperatures. A smaller expander piston area further boosted efficiency, making this system suitable for low-temperature heat sources, ideal for small-scale, waste-powered, or solar-powered refrigeration.

Liang, Yu, and Li (2019) [87] examined an ORC–VCC system for waste heat recovery from marine engines. They tested a belt drive (independent operation) and a common shaft (direct coupling) configuration. The belt drive achieved a maximum cooling capacity of 9823 kW (EER 2.74) with R245ca at 3500 kPa, while the common shaft setup reached 6902 kW (EER 3.06) using R1233zd at 900 kPa, favoring compact design. Exergy analysis identified ORC evaporator losses due to high temperature gradients, suggesting efficiency gains by reducing these. This compact ORC–VCC design supports efficient marine waste heat recovery.

Salim and Kim (2019) [6] optimized an ORC–VCC system for waste heat at 120–150 °C, using NSGA II to balance cost (UAtotal, SPtotal) and efficiency (ηth, IR). R245ca yielded high efficiency with the lowest IR, while R245fa provided a balanced performance at 150 °C (UAtotal 99.6 kW/K, ηth 35.8%, IR 54.2%). Sensitivity analysis showed higher evaporator pressures boosted ηth by 107.9% and reduced IR by 25.1%. The study concluded that R245fa is effective for cost-efficient waste heat recovery systems.

Qureshi et al. (2024) [88] analyzed a solar-based ORC–VCR for low evaporation temperatures. The regenerative ORC–CRS configuration, using n-Dodecane and isopentane, achieved the highest COP overall of 1.017, outperforming the simple ORC–VCR setup (with a COP overall of 0.7174). Parametric analysis showed a 61.7% COP boost with increased ORC evaporation temperatures, underscoring the value of optimized settings in efficient, sustainable cooling.

Ngangué et al. (2023) [89] optimized an ORC–VAC–VCC system for tropical climates with low-GWP fluids. R717 reached a 1201 kW cooling capacity, 126.5 kW net power, and 62.59% thermal efficiency. Optimization improved these metrics to 1205 kW, 158.3 kW, and 64.32%. Exergy analysis identified the main destruction sources in the steam generator and ORC/VCC condenser.

Xu et al. (2024) [30] conducted a thermodynamic simulation of a solar-powered air-conditioning system utilizing a combined organic Rankine cycle and vapor compression cycle (ORC–VCC). They evaluated working fluids R134a, R123, and R290 under various operational temperatures. R123 proved most efficient, achieving a cooling coefficient of performance (COPc) of 0.85 and a total system efficiency (ηt) of 76.2%. The optimal cooling power per collector area was 390 W/m² at 120 °C. Both COPc and ηt increased with working fluid temperature to a peak before declining. Lower condensation temperatures (40 °C water-cooled) enhanced ηt and Pc, especially with R123. Higher evaporator temperatures (up to 15 °C) also improved performance. The study highlights ORC–VCC’s potential for efficient solar-powered cooling in high irradiance regions, emphasizing optimal fluid and temperature selection for maximum efficiency.

Xia et al. (2023) [90] performed an energy and exergy analysis of a low-grade waste heat-driven ORC–vapor compression refrigeration (ORC–VCR) system. The system achieved a coefficient of performance (COP) of 0.44 and an exergy efficiency of 14.97%. Exergy analysis revealed that the condenser was the largest source of exergy destruction, accounting for 39.32% (44,148 W) of total losses, followed by the generator (26.2%) and evaporator (11.47%). The condenser exhibited the highest avoidable exergy destruction at 43.39%. The study identified the condenser, turbine, and compressor as key components for efficiency improvements through internal optimization. Advanced exergy analysis proved effective in pinpointing areas for enhancing overall system efficiency, making the ORC–VCR more viable for industrial waste heat recovery applications.

Ashwni and Sherwani (2021) [91] analyzed a hybrid organic Rankine cycle with flash tank vapor compression refrigeration (ORC–FTVCR) system powered by solar and biomass energy. Five hydrocarbon working fluids—hexane, heptane, octane, nonane, and decane—were evaluated. Heptane achieved the highest performance, with a system COP of 0.551 and an exergetic efficiency (ηoex) of 4.21%. The solar collector and biomass burner accounted for 88% of exergy destruction due to temperature differentials between heat sources and the working fluid. Incorporating a flash tank increased COP by 10% and ηoex by 9%, under solar radiation of 800 W/m² and a biomass burner temperature of 150 °C. The study underscores the potential of integrating solar and biomass energy in hybrid refrigeration systems, highlighting the need to minimize exergy losses in key components to enhance overall efficiency.

Eisavi et al. (2021) [92] investigated a solar-driven mechanical vapor compression (MVC) desalination system integrated with an organic Rankine cycle (ORC). The system operated under solar irradiance of 500 W/m², generating 43.43 kW from solar panels and 33.27 kW from the ORC. The MVC unit consumed 38.7 kW to produce 141 m³ of distilled water daily. The ORC achieved a thermal efficiency of 11.36%, and the specific power consumption for desalination was 6.49 kWh/m³. Major exergy losses occurred in photovoltaic-thermal (CPVT) panels (84.8%) and the evaporator/condenser unit (6.9%). Economic analysis showed electricity costs of 0.044 USD/kWh and water production costs of 1.02 USD/m³. The study concludes that integrating ORC with MVC desalination is energetically and economically viable, especially in high solar irradiance regions, with further optimization of CPVT panels recommended for enhanced performance.

Ashwni and Sherwani [91] (2022) conducted a thermodynamic and environmental analysis of a hybrid system that combines an organic Rankine cycle (ORC) with a vapor compression cycle (VCC), integrated with an N-series photovoltaic thermal compound parabolic collector (PVT-CPC) system. The study investigates the efficiency of this solar-driven ORC–VCC system using a zeotropic mixture of heptane and R245fa as the working fluid. With an expander inlet temperature optimized at 423 K, the system achieved a maximum coefficient of performance (COP) of 1.81 and exergy efficiency of 5.8%. The results showed that adjusting the number of PVT-CPC collectors increased both energy savings and exergy efficiency, with the highest recorded exergy efficiency at 17.4% when using five collectors. This study demonstrates the system’s viability for sustainable cooling and power generation with solar energy, with an additional environmental benefit of reducing CO₂ emissions.

Ashwni and Sherwani (2022) [93] examined a multi-evaporator vapor compression refrigeration (VCR) system driven by an organic Rankine cycle (ORC) for commercial applications. They used a zeotropic mixture of hexane and R245fa to enhance thermodynamic performance. The system achieved a maximum coefficient of performance (COP) of 0.425 and an exergy efficiency of 31.1%. Optimization via a genetic algorithm resulted in an optimal exergy efficiency of 58%, with operating parameters set at an ORC evaporator temperature of 388 K and VCR evaporator temperatures of 268 K. Exergetic destruction primarily occurred in the evaporator and condenser. The study emphasizes the benefits of zeotropic mixtures in improving cooling efficiency for multi-zone refrigeration, highlighting significant gains in system performance through optimized operating conditions.

Evangelos Bellos and Christos Tzivanidis (2021) [94] developed a solar-driven trigeneration system using a parabolic trough collector (PTC) to power an organic Rankine cycle (ORC) and a vapor compression cycle (VCC). The system produced 10 kW of cooling at 5 °C and 10 kW of heating at 60 °C, while generating 6.14 kW of electricity. The energy efficiency was 37.34% and exergy efficiency was 12.14%. Sensitivity analysis showed that increasing turbine inlet superheat enhanced overall efficiency, with optimal solar input achieved at a 100 m² collector area. Operating for 2500 h annually, the system had a simple payback period of 8.5 years, indicating economic viability for building energy applications. The study demonstrates the effectiveness of integrating PTC-driven ORC–VCC systems for combined electricity, heating, and cooling in sunny regions.

Ashwni Goyal et al. (2023) [95] explored a dual-evaporator VCR system powered by an ORC, assessing five working fluids: butane, pentane, isopentane, hexane, and R245fa. Butane was optimal, achieving a COP of 0.377, exergy efficiency of 10.91%, and total cost of $33,091 with a payback period of 5.8 years. Advanced exergy analysis indicated significant avoidable exergy destruction in the boiler, compressor, and condenser. Optimal conditions included boiler and condenser temperatures of 120 °C and 40 °C, respectively, with pinch-point temperature differences of 3 °C and 10 °C in the condenser and boiler. The study highlights butane’s economic and environmental suitability for dual-temperature refrigeration applications, suggesting potential for substantial performance improvements through exergy optimization.

Xia Zhou et al. (2021) [96] proposed an ORC-assisted air compression system (ORVC-ACS) for cryogenic air separation units (ASUs), aiming to recover compression waste heat to pre-cool compressor inlet air. The system achieved an energy saving ratio (ESR) of 4.2%, resulting in annual energy savings of 7500 MWh for a 60,000 Nm³/h ASU. Operating with feed air temperatures between 5.35 and 22.5 °C and relative humidity up to 0.8, the system reduced compression power consumption while maintaining humidity constraints. Economic analysis indicated a discounted payback period of 3.1 years and a reduction in annual CO₂ emissions by 5400 tons. The study demonstrates strong economic and environmental potential for implementing waste heat recovery in industrial ASUs.

Ashwni et al. (2021) [97] conducted an exergy, economic, and environmental analysis of a low-grade heat-driven ORC–vapor compression refrigeration (ORC–VCR) system using R602 as the working fluid. The system achieved an exergetic efficiency of 28.4%, total cost of $69,949, and environmental cost savings of $3491 from reduced CO₂ emissions. Optimal operating conditions included compressor and expander isentropic efficiencies of 75% and 85%, an ORC evaporator inlet temperature of 393 K, and a cooling water inlet temperature of 313 K. The study highlighted R602’s balance of performance and environmental costs but noted high initial costs limit commercial competitiveness. The system showed substantial environmental benefits, with annual CO₂ reductions saving $3491, emphasizing potential for sustainable refrigeration applications.

Bounefour and Ouadha (2017) [98] developed a cascade ORC–vapor compression cycle (VCC) system for waste heat recovery from marine diesel engines, utilizing hydrocarbon refrigerants propane, butane, and isobutane. The cascade evaporation design increased the expander’s power output by 10% and enhanced the system’s COP by improving heat recovery. Exergy analysis identified the evaporator and compressor as major sources of irreversibility. Recommendations included optimizing these components to further boost efficiency. This cascade approach supports effective onboard cooling and energy recovery in maritime applications, contributing to fuel savings and emission reductions, particularly for ships operating under variable thermal conditions.

Bao et al. (2020) [22] compared single-fluid and dual-fluid ORC–vapor compression cycle (VCC) systems with a flash tank vapor injection cycle (FTVIC) for geothermal heat sources at 140 °C. Dual-fluid configurations, especially R1234yf-R152a, achieved the highest cooling capacity of 2282.0 kW and superior COP compared to single-fluid systems. The dual-fluid ORC–FTVIC utilized two-stage throttling, minimizing exergy losses and making it optimal for high cooling demands with heat source temperatures between 100 °C and 150 °C. The study suggests that dual-fluid systems offer significant performance improvements for industrial and energy sector refrigeration applications utilizing geothermal heat.

Molés et al. (2015) [76] assessed the thermodynamic performance of an ORC–vapor compression cycle (VCC) system using low-grade heat sources and low-GWP refrigerants. The system’s thermal COP ranged from 0.30 to 1.10, and electrical COP from 15 to 110, depending on operating conditions. HFO-1336mzz(Z) delivered the best thermal and electrical performance due to its favorable thermodynamic properties. The study demonstrated the feasibility of ORC–VCC systems in eco-friendly applications, showing that HFO-1336mzz(Z) can effectively replace higher-GWP refrigerants, reducing environmental impacts without sacrificing efficiency. This underscores the potential for sustainable refrigeration technologies in compliance with global emissions regulations.

He et al. (2017) [99] evaluated a mechanical vapor compression (MVC) desalination system driven by an organic Rankine cycle (ORC) using R245fa as the working fluid. The system produced freshwater at a rate of 1.09 kg/s and achieved a gained output ratio (GOR) of 3.15. Performance improved with higher boiler outlet temperatures, enhancing energy efficiency. Under optimal ambient and boiler conditions, the system effectively produced freshwater, indicating its potential for sustainable desalination. The study highlights the benefits of integrating ORC technology with desalination processes, reducing energy costs and emissions compared to traditional methods. Future work may focus on optimizing operational parameters and assessing different working fluids’ impacts on system performance.

Nasir et al. [100] (2021) examined a biomass-powered trigeneration system integrating an organic Rankine cycle (ORC) with a vapor compression cycle (VCC) to provide cooling, heating, and electricity. The system comprises a primary ORC (using M-Xylene as the working fluid) and a secondary ORC (using R245fa) directly coupled with the VCC cycle, where isobutane is employed as the refrigerant. The primary ORC converts biomass heat at 450 °C into electrical power, and its waste heat is subsequently utilized to drive the secondary ORC at 130 °C. This heat cascades down to the VCC system for cooling purposes. At peak performance, the system achieved a cooling capacity of 30 kW, a heating output of 528 kW, and an exergy efficiency of 71.1%. Optimization via a genetic algorithm demonstrated the system’s potential for robust energy and cooling output, making it suitable for localized energy applications.

Table 2. Overview of theoretical studies on ORC–VCC systems.

Year [Source]	Heat Source Temperature	ORC–VCC Configuration	Working Fluids	Highest Performance Obtained
Kim and Blanco (2015) [72]	150 °C	ORC with recuperation and VCC with shared condenser	R143a, R22, R134a, R152a, propane, ammonia, isobutane, and butane	-
Kosmadakis et al. (2017) [74]	100 °C	Open-drive scroll expander for small-scale ORC	R-404a	Thermal efficiency of 6%
Yilmaz (2015) [75]	-	Transcritical ORC–VCC setup for intercity buses	R134a and R245fa	-
Molés et al. (2015) [76]	97–147 °C	ORC–VCC model with low-GWP refrigerants	HCFO-1233zd(E), HFO-1336mzz(Z), HFO-1234yf, and HFO-1234ze(E)	-
Li et al. (2014) [77]	-	Transcritical ORC paired with VCC	R22, R134a, and R290	-
Yue et al. (2016) [78]	-	ORC–VCC system for vehicles	n-propane, cyclopentane, R134a, and R245fa	Efficiency improvements between 9.2% and 9.8%
Aneke et al. (2012) [79]	164 °C	Waste-heat-driven ORC–VCC system	R245fa and NH3
Demierre et al. (2012, 2014) [24,73]		Supercritical R134a ORC connected with R134a VCC	R134a	Exergetic efficiency of 0.37–0.45
Wang et al. (2011) [80]	200 °C	Prototype with ORC recuperation and VCC subcooling	R245fa and R134a	COP of 0.66
Aphornratana and Sriveerakul (2010) [81]	60–90 °C	Single-piston expander–compressor arrangement	R22 and R134a	COP values of 0.1 to 0.6
Jeong and Kang (2004) [82]	-	ORC–VCC configuration with or without ORC regeneration	R123, R245ca, and R134a	-
Zhou et al. [83] (2023)	-	Single-shaft expander–compressor unit for ORC–VCC	R245fa	Thermal efficiency of 19.7%
Bu et al. (2013, 2013) [84,85]	-	Geothermal air conditioning and marine waste heat recovery	isobutane, butane, and R123	-
Li et al. (2013) [85]	60–90 °C	ORC–VCC with a common condenser	propane, butane, isobutane, and propylene	-
Ashwni and Sherwani (2021) [90]	120–150 °C	NSGA II optimized ORC–VCC system	R245ca and R245fa	-
Evangelos Bellos and Christos Tzivanidis (2021) [93]	-	Solar-driven ORC–VCC system with parabolic trough collector	heptane and R245fa	-
Ashwni Goyal et al. (2023) [94]	120 °C	Dual-evaporator VCR system powered by ORC	Butane, pentane, isopentane, hexane, and R245fa	COP of 3.54
Xia Zhou et al. (2021) [95]	-	ORC-assisted air compression system	R1233zd	-
Ashwni et al. (2021) [96]	-	ORC–VCR system with R602	R602	-
Bounefour and Ouadha (2017) [97]	140 °C	Cascade ORC–VCC system for marine engines	propane, butane, and isobutane	-
Bao et al. (2020) [22]	-	Dual-fluid ORC–VCC with flash tank vapor injection cycle	R1234yf-R152a	-
He et al. (2017) [98]	-	ORC–MVC desalination system	R245fa	GOR of 3.15
Nasir et al. (2021) [99]	450 °C	Trigeneration ORC with VCC using biomass heat	M-Xylene, R245fa, and isobutane	Exergy efficiency of 71.1%

highlights key aspects of the process, including the heat source, system configuration, working fluids, and efficiency metrics.

Theoretical studies on ORC–VCC systems provide valuable insights into the advancements, challenges, and opportunities in this innovative field of energy technology. While the environmental impact of hydrocarbon and HFC working fluids has driven global efforts to phase them out due to their high global warming potential (GWP), they remain a focus of research due to their favorable thermodynamic properties, particularly in low-temperature applications. These fluids, such as R245fa, continue to offer high energy efficiency and operational reliability, making them essential benchmarks for comparison with newer alternatives.

A notable trend is the increasing adoption of low-GWP fluids, such as hydrofluoroolefins (HFOs), which provide a sustainable balance between environmental performance and system efficiency. Studies show that these fluids, while environmentally friendly, require additional optimization to achieve comparable or superior performance in ORC–VCC systems.

Theoretical analyses have demonstrated the complexity of system optimization, involving careful consideration of working fluid properties, cycle configuration, and component efficiency. Configurations with recuperation, transcritical cycles, and innovative coupling mechanisms, such as mechanically shared shafts or belt-driven systems, have shown potential to significantly enhance performance by reducing irreversibilities and improving energy recovery from waste heat. However, the integration of these components often introduces design challenges, such as maintaining operational stability and minimizing energy losses at the interfaces.

A key area of focus in these studies is the reduction of exergy losses, particularly in critical components such as condensers and heat exchangers. Thermodynamic modeling has underscored the importance of minimizing irreversibilities to improve system efficiency and sustainability. Furthermore, the development of compact, high-performance components, such as microchannel heat exchangers and advanced expanders, has been identified as a priority for enabling widespread adoption.

3.2. Experimental Studies on ORC–VCC Systems

Despite the significant contributions of earlier theoretical studies in deepening our understanding of organic Rankine cycle–vapor compression cycle (ORC–VCC) systems, these methods often depend on idealized assumptions and simplified models to facilitate analysis. Such simplifications are necessary for theoretical work but can lead to considerable differences between predicted outcomes and actual system performance in real-world settings. Recognizing this disparity, several researchers have moved towards conducting experimental investigations of ORC–VCC systems. These experimental studies are designed to validate theoretical models, provide empirical data, and ultimately enhance the accuracy of performance predictions by aligning them more closely with practical observations.

Wang et al. (2011) [81] conducted an experimental study on the performance of a combined organic Rankine cycle (ORC) and vapor compression cycle (VCC) system, aimed at utilizing waste heat for cooling. The ORC utilized R245fa as the working fluid, while the VCC employed R134a, with waste heat supplied at 200 °C. A key component of the system was a scroll expander, which achieved an impressive isentropic efficiency of 84%. The system demonstrated a cooling capacity of 4.4 kW with a heat-activated COP of 0.48. These results highlight the potential of integrating ORC and VCC technologies for effective heat recovery in both stationary and mobile applications. The study emphasizes the scalability of the system and the use of scroll expanders to enhance cooling efficiency through the direct mechanical coupling of the expander and compressor.

The study by Roumpedakis et al. (2015) [101] investigates a small-scale experimental trigeneration system that combines a supercritical organic Rankine cycle (SORC) and a vapor compression cycle (VCC) powered by a biomass boiler. The SORC uses R227ea as the working fluid, with the system designed to generate 5 kWe of electrical power, a 4 kW cooling load, and approximately 70 kWth of heat recovery. The system leverages high-pressure supercritical conditions with a biomass boiler heat input of 85 kWth, achieving maximum pressures and temperatures up to 30.4 bar and 110 °C, respectively. The innovative integration of a scroll expander with an open-drive configuration and supercritical plate heat exchangers demonstrates the feasibility of SORC–VCC systems for sustainable, multipurpose applications. This work underscores the potential of ORC-based trigeneration systems in efficiently utilizing renewable heat sources while achieving a high level of operational flexibility and environmental sustainability.

Garland et al. (2018) [102] present a turbo-compression cooling system (TCCS) designed to recover waste heat from power plants using a combined Rankine and vapor compression cycle. The TCCS utilizes HFE-7000 as the working fluid in the Rankine cycle and R134a in the cooling cycle, with a nominal cooling output of 250 kWth at a heat source temperature of 106 °C. The system achieves a coefficient of performance (COP) of 1.74 to 1.80, varying based on ambient temperature and other conditions. Key design elements include a hermetically sealed turbo-compressor operating at 30,000 RPM, with the turbine and compressor coupled via a magnetic drive for high transmission efficiency (93%). The study validates a UA-based scaling model for off-design performance prediction, achieving results within ±2.0% of experimental data. This work underscores the effectiveness of turbo-compression technology for low-grade waste heat recovery and offers a model for optimizing such systems across diverse operating conditions in power plant applications.

Liang et al. (2021) [103] explore the performance of a thermally driven cooling system based on a combined organic Rankine cycle (ORC) and vapor compression cycle (VCC), developed to recover waste heat from internal combustion engines in transport applications. The prototype utilizes R245fa as the working fluid in the ORC and R134a in the VCC, achieving an approximate cooling output of 1.8 kW at −4 °C, with a heat-to-cooling efficiency of 0.18. The system includes an oil-free scroll expander, belt-driven compressor, and a water heater to simulate engine cooling water at 95 °C. This design allows for an independent optimization of ORC and VCC operating speeds, enhancing efficiency under various load conditions. The study demonstrates the effectiveness of ORC–VCC systems for waste heat recovery in mobile applications, with potential improvements suggested through optimal component selection and advanced control mechanisms.

Sleiti et al. (2021) [104] present an experimental study on a thermo-mechanical refrigeration (TMR) system using an organic Rankine cycle (ORC) and vapor compression cycle (VCC) designed to utilize ultra-low temperature waste heat, specifically in the range of 50–85 °C. The system employs a full-scale expander–compressor unit (ECU) with refrigerants R134a, R410A, and R407C to optimize performance. At 85 °C, the ORC achieved an energy efficiency of 9.85%, while the VCC showed a COP of 3.99, with an evaporator temperature reaching as low as −20 °C using R407C in the cooling loop. These results underscore the ECU-based TMR system’s capability to convert low-grade heat into cooling, highlighting its potential for efficient waste heat recovery in various industrial applications.

Jiang et al. (2023) [105] present an experimental study of a compression heat recovery system that integrates an organic Rankine cycle (ORC) with a vapor compression cycle (VCR), aiming to reduce power consumption in air separation units. The ORC–VCR system uses R245fa as the working fluid for both cycles, with a high-temperature water source operating at 95 °C and a low-temperature evaporator at 32 °C. The system’s expander–compressor unit achieved a COP of 0.63 and a cooling capacity of 14.2 kW at 14.6 °C, operating at a speed of 25,822 rpm. Findings emphasize the system’s ability to maintain stable operation while achieving significant efficiency in low-grade waste heat recovery applications, showcasing its potential in energy-intensive industrial processes.

Grauberger et al. (2024) [106] introduce an organic Rankine–vapor compression cycle (ORVC) aimed at recovering low-grade waste heat to improve energy efficiency and reduce greenhouse gas emissions. The ORVC integrates an organic Rankine power cycle with a vapor compression cooling cycle, utilizing a shared shaft for both the turbine and compressor. The system was tested using waste heat at 91 °C, achieving a cooling capacity of 264 kW and a coefficient of performance (COP) of 0.56 during steady-state operation. The Rankine cycle demonstrated a thermal efficiency of 7.7%, while the vapor compression cycle exhibited a COP of 5.25. Challenges related to pressure drops in the system were noted, along with the impact of condenser glycol outlet temperature on overall performance. Adjustments to simulation models based on experimental data suggested a potential COP of 0.66, indicating room for optimization.

Wang et al. (2024) [2] conducted an experimental study on an ORC–VCC system using a zeotropic mixture of R245fa and R134a (0.9/0.1) as the working fluid. The system was designed to investigate off-design performance using a shared condenser for both ORC and VCC subsystems. The system was powered by low-grade waste heat at 104 °C, and the cooling subsystem employed a modified scroll expander. The results indicated that the system could achieve a maximum cooling capacity of 3.3 kW with a COP of 0.21 at an optimal evaporation temperature of 21 °C. Furthermore, the isentropic efficiency of the expander reached 74.8%, while the compressor achieved 72.5% efficiency. The study emphasizes the impact of cooling water conditions and flow rates on system performance, particularly the variation in condensation pressure and cooling capacity.

Alshammari et al. (2023) [107] presented an analysis of an organic Rankine cycle–vapor compression refrigeration (ORC–VCR) system featuring a novel single-rotor expander–compressor device. The study evaluated the system’s thermal performance at varying ORC evaporation temperatures (62.75–89.7 °C), VCR evaporation temperatures (−20 to 5 °C), and a constant heat source temperature of 95 °C. Results indicated that the new single-rotor device achieved a maximum cooling effect of 5.38 kW, with a heat-to-cooling efficiency of 56% and an exergy efficiency of 63%. The single-rotor expander–compressor allowed efficient energy transfer between the ORC and VCR cycles, and the system demonstrated robustness under different operational conditions.

This detailed analysis of key studies on ORC–VCC systems highlights the diverse approaches and methodologies employed across different regions and institutions. The experimental investigations span various working fluids, heat source temperatures, and expander technologies, offering valuable insights into the potential for optimizing ORC–VCC systems for different industrial applications. Each study contributes uniquely to the advancement of ORC–VCC technology, from small-scale trigeneration systems to large-scale industrial cooling applications. The comparative analysis of all of these experimental studies, including performance metrics such as cooling capacity, COP, thermal efficiency, and expander efficiency, is summarized in

Table 3. Overview of experimental studies on ORC–VCC systems conducted after the year 2000.

Working Fluids	Heat Source/Temperature	Mass Flow Rate/ Pressure	Type of Expander	Conclusion	Ref. Year
R245fa (ORC)/R134a (VCC)	Waste heat/200 °C	-	Scroll expander	Achieved a cooling capacity of 4.4 kW with a heat activated COP of 0.48 and expander isentropic efficiency of 84%.	[81] 2011
R227ea	85 kWth biomass boiler/ up to 120 °C	Mass flow: 0.699 kg/s/Pressure: 30.4 bar	Open-drive scroll expander	Achieved an electrical power output of 5 kWe and a cooling load of 4 kWth, with 70 kWth heat recovery.	[101] 2015
R134a (VCC)/HFE7000 (ORC)	Waste heat/106 °C	Mass flow: 0.35–0.5 kg/s	Turbo-compressor (magnetic drive)	Achieved 250 kW cooling capacity, and a COP of 1.74 to 1.80 with a cooling load of 145 kWth.	[102] 2018
R245fa (ORC)/R134a (VCC)	Waste heat from IC engine/95 °C	Mass flow: 0.04 kg/s	Belt-driven scroll expander	Generated 1.8 kW of cooling at −4 °C with a heat-to-cooling efficiency of 0.18.	[103] 2021
R134a/R407C/R410A	Ultra-low temperature/85 °C	Mass flow: 0.43–0.88 kg/s	Isobaric expander–compressor	Achieved an energy efficiency of 9.85% with a COP of 3.99 at 85 °C. Evaporation temperature below −20 °C.	[104] 2021
R245fa	Hot water/95 °C	Mass flow: 0.5 kg/s (ORC), 0.44 kg/s (VCR)	Coaxial turbine-expander	Achieved a cooling capacity of 14.2 kW and a COP of 0.63 with a cooling temperature of 14.6 °C.	[105] 2023
R1234ze(E)	Waste heat/91 °C	-	Centrifugal turbo-compressor	Achieved a cooling capacity of 264 kW ± 3.5 kW with a COP of 0.56 ± 0.01. Thermal efficiency of the Rankine cycle was 7.7%.	[106] 2024
Zeotropic mixture R245fa/R134a (0.9/0.1)	Electrically heated steam boiler/105 °C	-	Open-drive scroll expander	Achieved a COP of 3.24–3.78 and maximum isentropic efficiencies of 74.8% and 72.5 %. Achieved the highest cooling capacity of 3.3 kW with a COP of 0.21.	[2] 2024
R245fa (ORC)/R134a (VCR)	Hot water/95 °C	Not specified	Single-rotor expander–compressor	Achieved a max cooling effect of 5.38 kW, heat-to-cooling efficiency of 56%, and exergy efficiency of 63%	[107] 2023

.

A comprehensive review of experimental studies on organic Rankine cycle–vapor compression cycle (ORC–VCC) systems highlights their technological versatility and adaptability across diverse applications and operational scenarios. The wide range of working fluids—such as R245fa, R134a, and the environmentally friendly R1234ze—combined with various expander configurations, including scroll expanders, radial turbines, and turbo-compressors, enables system customization to meet specific temperature and efficiency requirements.

The efficiency and coefficient of performance (COP) of ORC–VCC systems vary significantly depending on system design and fluid choice. For example, Wang et al. (2011) [81] achieved a cooling COP of 0.48 with R245fa at a high heat source temperature of 200 °C, demonstrating potential for high-temperature applications. Conversely, Roumpedakis et al. (2015) [101] reported a COP of 0.56 in a biomass-powered system, emphasizing the adaptability of ORC–VCC for low-temperature renewable applications. Sleiti et al. (2021) [104] achieved an impressive COP of 3.99 and 9.85% efficiency at ultra-low temperatures (85 °C), showcasing the technology’s suitability for low-temperature waste heat recovery. Differences in reported COP values often stem from variations in performance metrics and indicator definitions.

Working fluid selection emerges as a critical factor influencing both system efficiency and environmental sustainability. Low-GWP fluids like R1234ze are increasingly preferred for their balance of high performance and reduced environmental impact. Additionally, advancements in expander configurations—whether scroll, turbo, or isobaric—enhance system flexibility, facilitating effective heat recovery over a broad temperature range (80 °C to 200 °C). Recent experimental studies, such as those by Jiang et al. (2023) [105] and Liang et al. (2021) [103], demonstrate the efficiency of ORC–VCC systems in utilizing low-grade heat for power and cooling, particularly in transportation and industrial sectors with substantial waste heat potential.

The adoption of low-GWP working fluids aligns ORC–VCC systems with global environmental objectives, supporting energy-efficient practices without sacrificing performance. As innovations in fluid selection and component design advance, ORC–VCC systems are poised to play a pivotal role in energy conservation and emissions reduction across industries.

In conclusion, ORC–VCC systems offer exceptional flexibility due to their customizable configurations, diverse working fluids, and advanced expander technologies. They are highly effective in applications such as industrial cooling, transportation, and energy recovery. Continued progress in sustainable fluid adoption and efficiency enhancement will likely broaden the applicability of ORC–VCC technology, strengthening its role in sustainable development and energy efficiency.

However, it is surprising that significant research still focuses on working fluids like HFCs and hydrocarbons, which are being phased out or face regulatory limitations due to their environmental impact. Meanwhile, there is a noticeable scarcity of studies exploring natural refrigerants such as ammonia, propane, or isobutane, which are environmentally friendly and hold great promise for sustainable energy applications. Addressing this gap could further align ORC–VCC technology with long-term environmental and regulatory goals.

4. Mechanisms of Energy Transfer in Integrated ORC–VCC Systems

The integration of organic Rankine cycle (ORC) and vapor compression cycle (VCC) systems is a highly effective solution for utilizing low-grade waste heat, enabling simultaneous power generation and cooling. Energy transfer between the ORC and VCC systems can be achieved through various coupling methods, each tailored to the specific needs of an application and system configuration. These methods, whether mechanical or thermal, play crucial roles in optimizing system efficiency, ensuring operational flexibility, and simplifying structural design.

Among the most effective and widely discussed methods are the following:

• Shared shaft connection between ORC turbine and VCC compressor: The direct mechanical coupling of the ORC expander and the VCC compressor via a common shaft allows efficient power transmission without the need for intermediate components. This method enhances energy efficiency and results in a compact system design.
• Magnetic coupling between the ORC turbine and the VCC compressor: Mechanical power is transferred using magnetic forces through a hermetically sealed shaft. This enables each cycle to operate with optimal working fluids without cross-contamination, reducing mechanical wear and maintaining high transmission efficiency.
• Belt-driven coupling between ORC expander and VCC compressor: Mechanical power generated by the ORC expander is transferred to the VCC compressor through a belt transmission. The adjustable expander-to-compressor speed ratio allows for operational flexibility between the two cycles, enabling each subsystem to operate closer to its optimal efficiency.
• Common condenser connection between ORC and VCC: A thermal coupling method where the ORC and VCC systems share a condenser facilitates direct heat exchange between the cycles. This minimizes energy losses, reduces space requirements, and simplifies the system by combining heat exchangers.
• Expander–compressor unit (ECU) integration between ORC and VCC.

This section will review these five connection techniques, drawing on studies that demonstrate their application and efficiency. Each method’s detailed setup will be illustrated, along with examples where available. By examining the advantages and disadvantages of each coupling method, we aim to provide a comprehensive understanding of the mechanisms of energy transfer in integrated ORC–VCC systems.

4.1. Shared Shaft Connection Between ORC Turbine and VCC Compressor

In the discussed solution presented by Jiang et al., an organic Rankine cycle (ORC) system is integrated with a vapor compression refrigeration (VCR) system for compression heat recovery. This integration is achieved through the mechanical coupling of the ORC expander and the VCR compressor via a common shaft utilizing a coaxial design.

Figure 3 illustrates the system layout, depicting four circuits: the high-temperature water (HTW) circulation loop (shown in brown), the low-temperature water (LTW) circulation loop (shown in blue), and the ORC and VCR circuits (shown in grey).

Figure 4 presents the prototype of the integrated expander–compressor unit. This critical component employs a common shaft to directly transfer mechanical energy from the expander to the compressor, eliminating the need for additional power transmission elements. The coaxial design enhances power transmission efficiency and allows for a more compact structure. A single condenser is employed for both the ORC and VCR cycles, which not only saves space but also facilitates process control, as both cycles operate at the same condensing temperature. The condenser is a large-surface-area heat exchanger equipped with variable frequency drives on the fans, enabling precise control of the condensing temperature by adjusting the cooling air flow rate.

The advantages of this solution include enhanced energy efficiency due to the direct mechanical coupling of the expander and compressor, which reduces power transmission losses; a compact design resulting from the coaxial configuration and shared components; space savings by utilizing a single condenser for both cycles; and the use of a unified working fluid (R245fa) in both the ORC and VCR circuits, eliminating issues related to potential leakage between the systems. The disadvantages, if mentioned in the publication, may involve complex control requirements, as the mechanical coupling can complicate the individual control of the ORC and VCR systems, necessitating precise matching of operating parameters, and the risk of system-wide failure, since a malfunction in either the expander or compressor could affect the entire system due to the shared shaft.

In contrast to previous configurations, Alshammari et al. (2023) [107] present an innovative single-rotor expander–compressor device within a hermetically sealed casing for use in a combined organic Rankine cycle (ORC) and vapor compression refrigeration (VCR) system. This computational study utilizes modeling and simulation to assess the performance of the integrated device. The rotor simultaneously handles both the expansion and compression processes using R245fa as the working fluid. The device comprises two symmetrical chambers mounted on a common spherical rotor enclosed in a single casing, as depicted in Figure 5.

One chamber functions as the expander for the ORC, while the other serves as the compressor for the VCR, allowing each process to occur without the need for separate valving. This compact, hermetically sealed design reduces thermal losses by enabling direct heat transfer between the expansion and compression chambers, thereby enhancing overall thermodynamic efficiency. The absence of valves and close fluid sealing minimize leakage, making it a highly efficient and space-saving solution. The rotation of the rotor is designed to properly open and close the inlet and outlet ports on both sides, ensuring precise valveless operation and the synchronization of the cycles.

Compared to the previous work employing separate expander and compressor units connected via a shared shaft, this single-rotor design further integrates the components into a single device, enhancing compactness and potentially improving efficiency due to reduced thermal and mechanical losses. Figure 6 illustrates the schematic diagram of the combined ORC–VCR system with the integrated single-rotor expander–compressor device, highlighting the differences from the prior configuration.

Advantages of this configuration include high efficiency due to the elimination of intermediate conversion components, such as electric motors, which minimizes conversion losses; a compact design that simplifies the system architecture and reduces its footprint, advantageous in applications with space constraints; and enhanced reliability, as direct coupling minimizes potential points of failure and reduces maintenance requirements, with close fluid sealing reducing leakage and wear, thereby enhancing system longevity.

Disadvantages include challenges with speed matching, as the shared rotor necessitates precise speed alignment between the ORC and VCR cycles. Alshammari et al. note that differing optimal speeds could lead to performance losses if not properly managed; potential for mechanical wear, since continuous operation may increase wear on the rotor and impact system longevity, and even though the design minimizes wear, variable loads can pose challenges; and sensitivity to temperature fluctuations, where thermal variations within the shared rotor can affect performance, requiring additional monitoring and control to maintain stable conditions.

A further advancement in the group of integrated systems combining ORC and VCC technologies with a shared shaft is presented in the publication by Wang et al. [81], which details an innovative approach aimed at utilizing low-temperature waste heat for cooling applications. This integration is achieved through a unique direct mechanical coupling between the ORC and VCC, wherein a scroll expander (Figure 7) in the ORC drives a scroll compressor in the VCC. This mechanical linkage eliminates the need for electrical conversion, thus reducing energy losses typically associated with intermediate conversion steps.

To further improve system compactness and efficiency, microchannel heat exchangers are used in both the boiler and recuperator. These specialized exchangers are designed to minimize the system’s size and weight while maximizing heat transfer efficiency. Initial tests revealed that the system achieves a cooling capacity of 4.4 kW with a coefficient of performance (COP) of 0.48, and the scroll expander reached an isentropic efficiency of 84% under optimal conditions. The ORC utilizes HFC-245fa, chosen for its favorable thermodynamic properties and low environmental impact, while the VCC uses HFC-134a, commonly employed in air conditioning applications.

However, the system faces certain limitations. Laboratory conditions, which differed from the intended design conditions, led to reduced cooling capacity and performance, highlighting the system’s sensitivity to external environmental factors. Additionally, challenges with integrating microchannel heat exchangers arose, with issues such as internal leaks in custom microchannel designs, requiring the replacement of some units with standard plate heat exchangers during testing. Nonetheless, the high isentropic efficiency of the scroll expander and the elimination of electrical conversion losses represent significant advantages.

This integrated ORC–VCC system holds promising potential for both stationary and mobile applications, especially where compactness, efficient waste heat utilization, and cooling are essential. Future optimization and refinement could further enhance system performance and adaptability in various industrial and transport cooling applications. The system’s layout and performance features, including the scroll expander and detailed installation schematic, are visually illustrated in Figure 8 [81].

In the study [91], Ashwni and Sherwani develop an integrated system that combines an organic Rankine cycle (ORC) with a vapor compression refrigeration (VCR) system, powered by a series of fully covered photovoltaic thermal-compound parabolic collectors (PVT-CPC). The primary objective is to simultaneously produce electrical power and cooling by harnessing solar energy (Figure 9).

The integration between the ORC and VCR systems is achieved through the direct mechanical coupling of the expander and compressor. Specifically, the expander of the ORC is directly connected to the compressor of the VCR system via a shared shaft. This configuration allows the mechanical work generated by the expanding working fluid in the ORC to drive the compressor in the VCR without intermediate energy conversions, thereby minimizing energy losses and enhancing overall system efficiency.

The working fluid used in both the ORC and VCR cycles is a zeotropic mixture of heptane and R245fa. The use of a zeotropic mixture enables temperature glides during phase change processes in the heat exchangers, improving thermal matching between the heat source and the working fluid, and thus enhancing thermal efficiency.

The PVT-CPC system operates by absorbing solar radiation through semi-transparent photovoltaic (PV) modules fully covering the top of the collector tubes. These PV modules generate electrical power from the absorbed sunlight. Simultaneously, the thermal energy is captured by the heat transfer fluid (HTF), which is pressurized water circulating through the collector tubes beneath the PV modules. This dual functionality allows for the simultaneous generation of electricity and collection of thermal energy.

The heated HTF exits the PVT-CPC system and transfers its thermal energy to the ORC working fluid in the evaporator, causing it to vaporize. The vaporized working fluid then expands through the expander, producing mechanical work. Because the expander is directly coupled to the VCR compressor, this mechanical work is immediately used to compress the refrigerant vapor in the VCR system. Similar systems have been studied extensively for optimizing energy collection and utilization. Recent works, such as the performance evaluation of parabolic trough collectors by [108,109], demonstrate the potential of dual-function systems in achieving high thermal efficiency and energy conversion rates.

After expansion and compression, the streams from both the ORC expander and the VCR compressor are merged in a mixer and enter a common condenser. In this shared condenser, the mixed working fluid rejects heat to a cooling water stream and condenses back to liquid form. The condensed fluid is then split into two streams using flow-regulating valves:

• Stream 1: Pumped back to the ORC evaporator to continue the ORC cycle.
• Stream 2: Undergoes an isenthalpic expansion through an expansion valve before entering the VCR evaporator, where it absorbs heat from a low-temperature environment to provide cooling.

This configuration allows for efficient energy utilization by leveraging the thermal and mechanical interactions between the ORC and VCR systems, with the shared condenser facilitating heat rejection for both cycles.

The advantages of this integrated system include the simultaneous production of electricity and cooling, maximizing the utility of the captured solar energy, and enhanced thermal efficiency due to the use of a zeotropic mixture of heptane and R245fa, which allows for better thermal matching in the heat exchangers through temperature glides. Additionally, the system offers environmental benefits by reducing greenhouse gas emissions through the use of renewable solar energy, and the direct mechanical coupling of the ORC expander and VCR compressor reduces energy conversion losses and mechanical complexity. However, the disadvantages involve increased system complexity due to the integration of multiple advanced components and the need for precise control and coordination, higher initial investment costs owing to the additional collectors and specialized equipment, and challenges in optimizing the system to balance energy, exergy, environmental, and economic considerations for commercial viability. Maintenance requirements may also be higher due to potential issues with fluid composition and mechanical alignment, and the system’s efficiency may decrease under partial load conditions or fluctuating solar inputs, affecting its reliability in consistently meeting energy demands. The implementation of dynamic solar tracking systems, similar to those analyzed in [110], can help minimize the drop in optical efficiency under varying incident angles. Such solutions are critical for improving the performance of ORC systems powered by solar energy.

4.2. Magnetic Coupling Between the ORC Turbine and the VCC Compressor

In the study conducted by Garland et al. [102], a thermally driven refrigeration system is developed that integrates an organic Rankine cycle (ORC) with a vapor compression cycle (VCC) to utilize waste heat for cooling applications. This system, known as a recuperative turbo-compression cooling system (TCCS), employs a magnetic coupling to directly transfer mechanical power from the ORC turbine to the VCC compressor via a hermetically sealed shaft. The basic process flow diagram of the TCCS is depicted in Figure 10, illustrating the integration of the ORC and VCC cycles through the magnetic coupling mechanism.

The ORC subsystem absorbs heat at the waste heat boiler, vaporizing the working fluid HFE7000, which then expands through a centrifugal turbine. The mechanical power generated by the turbine is transferred directly to a centrifugal compressor in the VCC via the magnetic coupling, as shown in Figure 11.

The magnetic coupling integration in the turbo-compression cooling system (TCCS) presents several advantages and disadvantages. One of the primary advantages is the hermetic separation provided by the hermetically sealed shaft, which allows the ORC and VCC to operate independently with optimal working fluids, maximizing the efficiency of both the turbine and compressor; this design eliminates cross-contamination between the working fluids and enables each cycle to function under conditions best suited to its specific thermodynamic requirements. Additionally, the elimination of mechanical seals results in reduced mechanical wear, enhancing the reliability and longevity of the system by reducing friction and the likelihood of component failure. The magnetic coupling achieves a high transmission efficiency, maintaining a shaft efficiency of around 93%, ensuring efficient power transfer with minimal losses. Furthermore, the use of separate working fluids and cycles provides operational flexibility, enabling the system to adapt to varying operating conditions and optimize performance for different waste heat sources. However, there are disadvantages and limitations associated with this integration method. The complexity and cost of designing and fabricating the magnetic coupling and hermetically sealed shaft involve higher initial expenses and engineering challenges compared to conventional mechanical couplings. The air gap required for the magnetic coupling can introduce slight transmission losses, necessitating precise alignment and high-quality materials to maintain strong magnetic fields and minimize efficiency reductions. Moreover, the performance of the magnetic coupling and the overall system can be sensitive to operating conditions such as temperature and pressure changes, requiring careful control and monitoring to ensure stable operation under different conditions.

4.3. Belt-Driven Coupling Between the ORC Expander and VCC Compressor

Liang et al. (2021) [103] present a belt-driven coupling mechanism that flexibly integrates the ORC expander with the VCC compressor, enabling waste heat utilization for cooling applications. In this configuration, the ORC subsystem, powered by R245fa as the working fluid, generates mechanical power via an expander, which is transferred to the VCC compressor through a belt transmission (Figure 12). A distinctive feature of this setup is the adjustable expander-to-compressor speed ratio, achieved by altering pulley sizes within the belt drive, allowing operational flexibility between the two cycles. The VCC employs R134a, a common refrigerant, enabling its compressor speed to adapt based on the ORC expander’s output. By adjusting the mass flow rate and rotational speeds through the belt-driven mechanism, the system accommodates variable load demands and optimizes cooling capacity.

Visual representations of the system are essential for understanding the practical arrangement and placement of the belt transmission. The system schematic (Figure 12) illustrates the interconnection between the ORC and VCC, indicating the belt-driven transmission and the flow paths of R245fa and R134a.

An image of the expander and compressor setup (Figure 13) highlights the practical implementation of the belt-driven mechanism. This integrated ORC–VCC configuration exemplifies an innovative solution for waste heat recovery, with potential applications in sectors requiring mobile and efficient cooling solutions, such as transportation.

This belt-driven ORC–VCC coupling presents several advantages. The operational flexibility afforded by the belt-driven transmission allows the expander and compressor to operate at independent speeds, permitting each cycle to function closer to its optimal efficiency. This flexibility leads to improved cooling output, as each subsystem can adjust to varying thermal loads. The system also achieves a higher heat-to-cooling efficiency compared to direct shaft connections, where rotational speed synchronization could hinder performance; such efficiency improvements are particularly useful in mobile applications where space and energy conservation are critical. Additionally, the integration avoids the need for complex fluid-coupling mechanisms, and the straightforward design using commercially available components simplifies maintenance.

However, there are disadvantages and limitations associated with this setup. Mechanical losses inherent to belt-driven systems, though negligible in experimental setups, could affect long-term performance and reduce overall system efficiency if not optimized. The performance of the system is sensitive to the expander-to-compressor speed ratio; excessive or inadequate ratios can lead to suboptimal cooling, as the VCC compressor might either exceed or lag behind the required operational range for effective condensation, impacting cooling capacity. Furthermore, the prototype experiences fluctuations in cooling output under dynamic load changes, which could be mitigated by substituting the thermostatic expansion valve (TEV) with an electronic expansion valve (EEV) for improved regulation.

4.4. Common Condenser Connection Between the ORC and VCC

In the study by Zhar et al. (2021) [111], a common condenser mechanism is used to integrate the ORC and VCC systems. This approach enables effective heat transfer between the cycles, transforming waste heat into cooling energy, thereby enhancing system efficiency in a compact design.

In this setup, a shared condenser enables the heat discharged from the ORC system to drive the VCC compressor. The ORC system uses a low-grade heat source to vaporize a working fluid in the boiler. The fluid, typically R123 for high efficiency, is expanded through a turbine, generating mechanical energy, which is then directed toward the VCC compressor. After expansion, the ORC working fluid enters the shared condenser, where it releases heat to the VCC cycle before being pressurized and recirculated by a pump. In the VCC system, R134a is used as the working fluid, passing through an expansion valve and evaporator, where it absorbs heat and then moves to the compressor. This shared condenser setup, leveraging a steady-state heat transfer interface, allows both cycles to operate efficiently without intermediate components, reducing system complexity and energy losses (Figure 14).

This ORC–VCC system design is well-suited for applications in industrial waste heat recovery, building climate control, and other settings where waste heat can be efficiently repurposed for cooling. Zhar et al. demonstrated the performance of this configuration with notable thermodynamic results: using R123 in the ORC cycle yielded a thermal efficiency of approximately 58% and an exergy efficiency of 26.6%, outperforming alternative configurations. The system achieved a coefficient of performance (COP) around 0.58 and delivered a cooling capacity of 3.7 kW under optimal conditions, indicating that the setup is capable of stable operation and high efficiency with waste heat inputs of 150 °C and condenser temperatures of 37 °C. The economic assessment revealed a payback period of approximately 4.9 years, with a levelized cost of energy (LCOE) at 0.06 $/kWh.

The shared condenser minimizes intermediate energy losses, achieving a thermal efficiency of up to 58% and exergy efficiency of 26.6% in the system’s optimal state. By integrating both cycles within a single condenser, the system’s footprint is reduced, making it advantageous for applications with spatial constraints. This configuration simplifies installation and reduces material costs associated with separate heat exchangers. The steady-state heat exchange provided by the shared condenser maintains cooling capacity despite variable heat inputs, a valuable feature in industrial applications where waste heat is often inconsistent.

The shared condenser requires precise thermal control, as fluctuations in condenser temperature can impact both ORC and VCC performance. Zhar et al. noted a decline in system efficiency when condenser temperatures exceed 37 °C, requiring additional monitoring and control. Continuous operation with a shared condenser, especially under variable loads, may accelerate wear on the system’s components. Regular maintenance is necessary to manage wear, particularly on the condenser and compressor, which are prone to degradation under high thermal loads.

In the publication by Roumpedakis et al. [101], a trigeneration system integrates an organic Rankine cycle (ORC) with a vapor compression cycle (VCC) through the use of a shared condenser, as illustrated in Figure 15. In this configuration, the ORC is powered by thermal energy from a biomass boiler, generating electrical power via an expander or turbine, which then drives the compressor of the VCC system. After passing through the expander, the working fluid in the ORC releases its residual thermal energy into the shared condenser where condensation occurs. Simultaneously, the VCC system absorbs this thermal energy from the condenser to facilitate efficient cooling. This innovative coupling allows for direct heat exchange without the need for additional mechanical connections between the ORC expander and the VCC compressor, effectively combining power generation, heating, and cooling within a single integrated system.

This trigeneration system is particularly suited for industrial applications where waste heat recovery is a priority. By utilizing thermal energy from renewable sources like biomass, the system simultaneously produces electricity, cooling, and heating, enhancing overall energy utilization and sustainability. The publication reports that the system achieves a thermal efficiency of approximately 58% and a coefficient of performance (COP) of 0.58, while producing 4 kWh of cooling and 70 kWh of heating. The system’s flexibility allows for switching between trigeneration mode during warmer months, providing cooling alongside power and heat, and cogeneration mode during colder months, focusing on power and heat generation. This adaptability optimizes performance according to seasonal demands and enhances the system’s overall efficiency and versatility.

The integrated use of a shared condenser offers several advantages. High efficiency is achieved by minimizing energy losses through direct heat exchange, optimizing resource utilization, and enhancing thermal efficiency. The compact design reduces space requirements and the number of components, lowering installation and maintenance costs, which is particularly beneficial in industrial settings with limited space. Operational flexibility allows the system to adapt to varying energy needs and waste heat availability, improving its applicability across different industries and conditions.

However, there are disadvantages to consider. The shared condenser requires precise temperature management to maintain optimal performance in both the ORC and VCC cycles; fluctuations in condensation temperature can negatively impact efficiency. The complexity of operation increases, as managing variable thermal loads can lead to accelerated wear of components like the condenser and VCC compressor, necessitating regular maintenance and careful monitoring to ensure system longevity and reliability. These factors underscore the need for meticulous design and operational strategies to fully realize the benefits of the integrated trigeneration system.

In the study by Aphornratana and Sriveerakul [82], the organic Rankine cycle (ORC) and vapor compression cycle (VCC) are integrated using an innovative expander–compressor unit (ECU), which combines the expander and compressor in a single, unified device. This ECU allows direct mechanical energy transfer from the ORC to the VCC without additional mechanical or electrical linkages, enhancing system compactness and operational efficiency (Figure 16).

The system operates with R134a or R22 as the working fluid shared between the two cycles, simplifying design and facilitating low-temperature operation. The ORC is powered by low-grade thermal energy from a generator (operating between 60 and 90 °C), producing high-pressure vapor that enters the expander section of the ECU. The ECU’s free-piston mechanism enables the simultaneous expansion of vapor in the ORC and compression in the VCC. As shown in the schematic diagram in Figure 15, the expander piston drives the compressor piston within the ECU, compressing the VCC working fluid and maintaining a cooling load with temperatures as low as −10 °C.

This design eliminates the need for additional components like shared shafts or belts, leading to reduced system complexity and footprint. It also allows for more precise control over temperature and pressure conditions in each cycle, making the system adaptable to a wider range of thermal inputs compared to traditional methods. Aphornratana and Sriveerakul reported a coefficient of performance (COP) between 0.1 and 0.6, demonstrating the ECU’s potential as an efficient solution for small-scale refrigeration systems driven by low-temperature heat sources.

Table 4. Comparison of integration methods between ORC and VCC systems [84,91,100,101,102,103,105,107,111,112].

Parameter	Shared Shaft Connection	Magnetic Coupling	Belt-Driven Coupling	Common Condenser Connection
Energy efficiency	High efficiency due to direct mechanical coupling; eliminates transmission losses.	High efficiency with transmission efficiency ~93%; hermetic separation allows optimal fluids, enhancing efficiency; slight losses due to air.	Moderate efficiency; mechanical losses inherent in belts; adjustable speed ratios can optimize efficiency but may introduce losses if mismanaged.	High thermal efficiency by direct heat exchange; minimizes energy losses; thermal efficiencies up to 58%.	ECU’s direct energy transfer reduces transmission losses.
Operational flexibility	Limited flexibility; both cycles must operate synchronously; requires precise matching of operating parameters.	High flexibility; cycles can operate independently; allows different optimal working fluids and conditions.	High flexibility; adjustable speed ratios allow each cycle to operate closer to optimal efficiency.	Limited flexibility; cycles are thermally coupled; fluctuations in one cycle affect the other.	ECU adapts to varying thermal inputs and conditions, suitable for different operating environments.
Reliability	Risk of system-wide failure if one component malfunctions; shared components may impact overall reliability.	Enhanced reliability; reduced mechanical wear due to non-contact transmission; hermetic separation prevents fluid cross-contamination.	Potential reliability issues due to mechanical wear of belts and pulleys; requires regular maintenance.	Reliability depends on precise thermal control; potential accelerated wear due to thermal stresses.	Fewer external components reduce wear, with periodic piston seal checks needed.
Mechanical complexity	Moderate complexity; requires precise mechanical alignment; fewer components simplify the system.	High complexity due to the design and fabrication of magnetic coupling; requires precise alignment and high-quality materials.	Low to moderate complexity; uses standard mechanical components; simpler to implement and adjust.	Low mechanical complexity; fewer mechanical parts; simplifies system design by combining heat exchangers.	Compact ECU design simplifies overall system with fewer external parts.
Maintenance requirements	Moderate maintenance due to mechanical wear on shared shaft components; requires monitoring of shaft alignment and seals.	Low maintenance due to non-contact transmission; reduced wear extends maintenance intervals.	Higher maintenance due to wear of belts and pulleys; requires regular inspection and replacement of belts.	Low mechanical maintenance; requires careful monitoring of thermal performance; potential for contamination in shared condenser.	Periodic checks on pistons and seals ensure reliability at high pressures.
Cost	Lower initial cost due to fewer components; cost-effective for simple, integrated systems.	Higher initial cost due to complex design and materials; investment justified by operational benefits.	Moderate cost with standard components; cost-effective adjustments and maintenance.	Lower cost by sharing equipment; reduces installation and material costs.	ECU’s compact design reduces installation and long-term maintenance costs.
Compactness	High compactness due to integrated design; suitable for space-constrained applications.	Compact design with hermetically sealed units; slightly larger due to magnetic coupling assembly.	Moderate compactness; belt transmissions require space for pulleys and belts; less compact than direct coupling methods.	Highly compact by combining heat exchangers; reduces overall system footprint.	Single ECU unit reduces footprint, ideal for small applications.

summarizes and compares the integration methods between the organic Rankine cycle and vapor compression cycle systems, taking into account the key advantages and disadvantages of each method.

Summary:

• A shared shaft connection offers high energy efficiency and compactness but has limited operational flexibility and potential reliability issues due to shared components. It is suitable for simple, integrated systems where both cycles can operate synchronously.
• Magnetic coupling provides high efficiency and operational flexibility with enhanced reliability due to reduced mechanical wear. However, it has higher mechanical complexity and cost. It is ideal for systems requiring optimal working fluids and hermetic separation.
• Belt-driven coupling allows for high operational flexibility with adjustable speeds, making it suitable for applications with variable load conditions. It has moderate mechanical complexity and cost but requires regular maintenance due to mechanical wear.
• A common condenser connection achieves high thermal efficiency and compactness by minimizing energy losses through direct heat exchange. It has low mechanical complexity but limited operational flexibility and requires precise thermal control. This method is ideal for applications with stable thermal loads and space constraints.

5. Techno-Economic Problems

The ORC–VCC (organic Rankine cycle–vapor compression cycle) technology, while offering substantial potential for enhanced energy efficiency and operational flexibility, faces several significant techno-economic challenges that must be effectively addressed to facilitate broader adoption. These challenges are deeply rooted in the system’s inherent complexity, which arises from the integration of two advanced thermodynamic cycles. This integration necessitates the use of specialized components, such as custom-designed compressors and turbines, which substantially increase the initial capital costs. As highlighted in several studies, the high upfront costs associated with these components are a primary barrier to the widespread deployment of ORC–VCC systems. For instance, Liang et al. [87] noted that the cost of specialized equipment and the custom nature of the system’s design are major contributors to the overall economic burden of implementing ORC–VCC technology, particularly in small-scale applications.

In addition to the high capital costs, operational and maintenance expenses are also elevated. The need for specialized knowledge to manage the complex interplay between the ORC and VCC cycles further compounds these costs. Khatoon et al. [5] discussed the operational challenges associated with maintaining system stability and efficiency, particularly when dealing with organic working fluids that require careful handling to avoid environmental and safety issues. The study emphasized that the efficiency of ORC–VCC systems is highly sensitive to the performance of compressors and turbines, especially under partial load conditions. This sensitivity means that any inefficiency in these components can significantly impact overall system performance, leading to higher operational costs and reduced economic returns.

Another critical challenge is achieving an optimal thermal match between the ORC and VCC cycles, which is crucial for maximizing system efficiency. The thermal match determines how effectively the heat rejected by the ORC cycle can be utilized by the VCC cycle. However, as Bounefour et al. [113] pointed out, any mismatch in thermal integration can lead to energy losses, thereby diminishing the economic benefits of the system. This issue is particularly pronounced in systems designed for variable load conditions, where the thermal requirements of the ORC and VCC cycles may not always align perfectly.

Market and economic uncertainties further complicate the adoption of ORC–VCC technology. The relative novelty of the technology means that established supply chains are lacking, which contributes to higher costs and slower adoption. Saleh [114] highlighted that the absence of a robust supply chain and the high costs of components like advanced compressors and expanders are significant barriers to market entry for ORC–VCC systems. These economic challenges are exacerbated by uncertainty surrounding the availability of economic incentives, such as subsidies or tax breaks, which are often crucial for offsetting the high initial investment required for these systems.

Regulatory and environmental compliance also add layers of complexity to the deployment of ORC–VCC systems. The use of organic working fluids, which are integral to the operation of these systems, must comply with stringent environmental regulations. The European Union’s F-Gas Regulation (EU Regulation No 517/2014) imposes limits on the use of high-GWP (global warming potential) fluids, compelling developers to either adopt lower-GWP alternatives or face potential restrictions. For example, the use of fluids such as R245fa (GWP of 1030) and R227ea (GWP of 3220) may be limited by future regulatory changes, as indicated by Delibaş and Kayabaşı [115]. This regulatory pressure adds to the complexity of selecting appropriate working fluids that not only perform well thermodynamically but also meet environmental standards.

Despite these challenges, ORC–VCC technology holds significant promise, particularly in regions where the demand for cooling and efficient energy recovery is high, such as Southern Europe and the Middle East. If the techno-economic hurdles can be addressed through innovation in component design, cost-reduction strategies, and the establishment of supportive market and regulatory environments, ORC–VCC systems have the potential to become a viable and widespread solution in the refrigeration and energy sectors. Ongoing research aimed at improving the thermal integration of the cycles, developing more efficient and environmentally friendly working fluids, and reducing overall system costs will be critical in determining the future success and adoption of ORC–VCC technology.

6. Conclusions

While ORC–VCC systems have shown great potential in enhancing energy efficiency and enabling sustainable industrial applications, significant challenges remain, particularly in optimizing component efficiency and regulatory compliance. A core challenge lies in the selection of working fluids, which must balance thermodynamic performance and environmental impact. Compliance with the EU’s F-Gas Regulation restricts high-GWP refrigerants, necessitating alternatives that are both efficient and eco-friendly. The trend toward low-GWP refrigerants, such as R1234ze and R600 (isobutane), addresses these regulatory demands but also introduces trade-offs, such as flammability, which require careful risk management.

The studies reviewed underscore the importance of regional application, particularly in hot climates where the cooling demand and availability of waste heat sources drive the adoption of ORC–VCC systems. Research in Southern Europe and the Middle East highlights how these systems meet the unique energy demands of these regions, enhancing cooling efficiency and optimizing waste heat utilization.

Anomalies in fluid performance, such as the efficacy of R123 and propane in high-temperature conditions despite regulatory limitations, suggest that future research must refine these fluid options or develop new alternatives that align with both performance and environmental goals. Similarly, while fluids like R245fa and R227ea offer high performance, their high GWP limits their long-term viability under current and future EU regulations.

Finally, the ORC–VCC technology’s complexity, including the need for specialized compressors and expanders, drives up costs, hindering its widespread adoption. Addressing these economic barriers through improved thermal integration, advanced control systems, and enhanced supply chains is essential.

Future research directions include integrating ORC–VCC systems with renewable energy sources, such as photovoltaic or wind energy, to offer hybrid power and cooling solutions that remain effective under varying environmental conditions. Additionally, developing novel heat exchanger materials with improved thermal conductivity and corrosion resistance, exploring low-GWP working fluids, and enhancing system scalability through modular designs are critical for advancing the technology. These efforts should be complemented by real-world testing and cost-reduction strategies to accelerate practical adoption.

In conclusion, the ORC–VCC systems reviewed demonstrate strong potential for efficient energy recovery and cooling in energy-demanding environments. Moving forward, the focus on low-GWP refrigerants, improved thermal integration, and cost-effective components will be central to advancing ORC–VCC technology, ensuring its adaptability to regulatory landscapes and its contribution to sustainable energy practices.