Optimizing Refrigeration Cycles to Enhance Capacity and Dew Regulation in VRF High Wall Systems

Optimizing Refrigeration Cycles to Enhance Capacity and Dew Regulation in VRF High Wall Systems | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Optimizing Refrigeration Cycles to Enhance Capacity and Dew Regulation in VRF High Wall Systems Atul M.Elgandelwar This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7250980/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract The growing demand for energy-efficient and environmentally sustainable HVAC solutions in residential buildings has driven the adoption of Variable Refrigerant Flow (VRF) systems. VRF technology, typically using R410A as the working fluid, provides simultaneous heating and cooling with enhanced part-load efficiency and greater operational flexibility than conventional central air conditioning systems. This study aims to optimize the refrigeration cycle of a VRF high wall indoor unit to improve cooling capacity and dehumidification performance. A combination of experimental and analytical methods was employed to evaluate system behavior under varying ambient temperatures and load conditions. Special emphasis was placed on assessing resistance to surface condensate formation (sweating), which is prevalent in high-humidity environments. Results indicate that specific cycle enhancements can significantly increase capacity utilization and improve control over dew point conditions. These improvements suggest that optimized VRF systems can better meet thermal comfort and moisture regulation requirements, particularly in tropical and sub-tropical climates where both energy efficiency and humidity control are critical. Mechanical Engineering Variable Refrigerant Flow Cycle optimization Cooling capacity enhancement Dehumidification performance Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 1. Introduction The primary objective of air conditioning systems is to ensure thermal comfort for building occupants by regulating indoor temperature and humidity levels. Modern HVAC (Heating, Ventilation, and Air Conditioning) technologies offer a wide spectrum of solutions, ranging from basic window units to advanced systems such as Variable Air Volume (VAV) and Variable Refrigerant Flow (VRF) systems. Among these, VRF systems have emerged as a prominent energy-efficient alternative due to their high Coefficient of Performance (COP), modular scalability, and precise load matching capabilities [ 5 ], [ 6 ], [ 8 ], [ 9 ]. VRF systems are designed to deliver individualized zone control and energy savings by modulating the refrigerant flow rate according to the thermal demands of each zone. These systems operate with one or more variable-speed compressors that dynamically adjust their speed to optimize energy usage and maintain desired comfort levels [ 6 ], [ 8 ], [ 10 ]. VRF technology is available in two main configurations: heat pump (cooling or heating only) and heat recovery systems, the latter of which enables simultaneous cooling and heating in different zones, making them particularly suitable for buildings with diverse thermal requirements [ 5 ], [ 9 ], [ 11 ]. Environmentally friendly refrigerants such as R-410A are widely adopted in VRF systems due to their favorable thermodynamic properties and zero ozone depletion potential [ 3 ], [ 7 ]. However, with rising concerns about global warming and the financial and environmental costs associated with fossil fuel-based electricity generation, further improvements in system efficiency and sustainability are essential [ 9 ]. One approach to achieving this is through cycle optimization, which enhances performance by refining the control strategy and operational parameters of the refrigeration cycle [ 6 ], [ 10 ]. This study investigates the potential for improving the performance of VRF high-wall indoor units through cycle optimization, with a focus on enhancing cooling capacity and managing moisture removal under high humidity conditions. The work also addresses the challenge of surface condensation (commonly referred to as "sweating") that can occur during extreme humid operation. By analysing system behavior under varied climatic and operational scenarios, the study aims to contribute to the development of more robust and efficient VRF systems for residential and commercial applications [ 9 ], [ 11 ]. 2. Cycle Optimization The fundamental objective of modern air conditioning (AC) systems is to minimize operational costs, enhance energy efficiency, and ensure optimal indoor air quality while maintaining thermal comfort for occupants [ 4 ], [ 10 ]. A wide range of AC technologies—such as window units, split systems, packaged units, dual-duct central systems, and Variable Refrigerant Flow (VRF) systems—are employed across residential and commercial buildings [ 2 ], [ 4 ], [ 6 ]. Among these, VRF systems have gained prominence due to their superior adaptability to dynamic thermal loads, zoned temperature control capabilities, and higher part-load efficiencies compared to conventional systems [ 5 ], [ 8 ], [ 9 ]. VRF systems offer several advantages, including the ability to modulate refrigerant flow precisely based on the real-time load of individual indoor units. This results in better occupant comfort, reduced energy consumption, and flexible operation across multiple zones, each with independent heating or cooling requirements [ 5 ], [ 6 ], [ 10 ]. However, key limitations include the relatively high initial capital cost and limited capacity for introducing fresh air during system operation. To overcome the latter, VRF systems are often supplemented with Heat Recovery Ventilation (HRV) systems. HRVs function by transferring heat between the exhaust and supply air streams, thereby reducing ventilation-related thermal loads and improving overall energy performance [ 5 ], [ 11 ]. According to ASHRAE Standard 62, VRF systems are characterized by their ability to control refrigerant flow across multiple indoor units or evaporators of varying capacities and configurations [ 5 ]. This enables features such as individualized comfort control, simultaneous heating and cooling in different zones, and inter-zonal heat recovery [ 5 ], [ 9 ], [ 11 ]. These attributes make VRF systems particularly suitable for complex building environments with variable and non-uniform load profiles. To further improve the performance and efficiency of VRF systems, cycle optimization is essential. This involves refining the thermodynamic cycle parameters to achieve optimal energy utilization under different operating conditions [ 6 ]. In this study, CoolPack—a widely used refrigeration system simulation software developed by the Technical University of Denmark—is employed for cycle optimization [ 6 ]. CoolPack offers specialized simulation modules tailored to specific refrigeration and air conditioning cycles, allowing researchers to assess performance metrics without needing to model full system architectures. By inputting relevant operational conditions and selecting appropriate system configurations, CoolPack enables targeted analysis and optimization of VRF cycle behavior [ 6 ]. The optimization process focuses on enhancing cooling capacity, reducing energy consumption, and mitigating the formation of surface condensation, particularly under high humidity conditions [ 3 ], [ 10 ], [ 11 ]. The insights obtained from the simulation studies are utilized to develop advanced control strategies and recommend system-level enhancements for next-generation Variable Refrigerant Flow (VRF) high-wall indoor units. Figure 1 illustrates the optimized refrigeration cycle of the VRF system operating with R-410A as the working fluid. 3. Cooling Capacity Test The objective of the cooling capacity test is to evaluate the performance characteristics of the Variable Refrigerant Flow (VRF) high-wall unit under standardized operating conditions. Key performance indicators assessed during this test include the Energy Efficiency Ratio (EER), operating current (expressed as a current ratio), power consumption (watt ratio), and the net cooling effect delivered by the system. As part of the procedure, the rotational speed (RPM) of the indoor unit's fan motor is measured in fan-only mode, i.e., with the compressor switched off, after the room has reached a steady-state condition. This assessment is carried out at the motor’s rated voltage to ensure consistency and accuracy. The dry condition of the evaporator coil is verified during this phase through the RPM observation, confirming the absence of condensation and ensuring that no latent cooling is taking place. These measurements provide baseline operational data and help validate the system's performance prior to compressor engagement, serving as a reference point for evaluating cycle efficiency and cooling output under full-load and part-load conditions. Prior to initiating the cooling capacity test, the environmental conditions within the test chamber must be stabilized and maintained for a minimum duration of one hour to ensure thermal equilibrium. Following stabilization, data collection is performed in accordance with the test protocol. As presented in Table 1 , measurements are recorded at 10-minute intervals, resulting in a total of seven sets of readings. Table 1 Temperature conditions for capacity test [ 12 – 14 ] BIS ISO Domestic Indoor 27.+/-0.3 27.+/-0.3 27.+/-0.3 Indoor 19.+/-0.2 19.+/-0.2 19.+/-0.2 Outdoor 35.+/-0.3 35.+/-0.3 35.+/-0.3 Outdoor 24.+/-0.2 24.+/-0.2 24.+/-0.2 This systematic data acquisition approach ensures the reliability and repeatability of the test results. 4. Dew Formation Resistance Test This test is conducted to evaluate the air conditioner's ability to resist surface condensation (commonly referred to as "sweating" ) when operating under high-humidity conditions. The primary objective is to assess the effectiveness of the system in maintaining surface temperatures above the dew point, thereby preventing moisture accumulation on the unit’s external surfaces. Table 2 presents the controlled temperature and humidity conditions employed during the dew resistance evaluation. Table 2 Temperature conditions for dew improvement test. [ 12 – 14 ] BIS ISO Domestic Accelerate Test Indoor 27.+/-0.3 27.+/-0.3 27.+/-0.3 27.+/-0.3 Indoor 24.+/-0.2 24.+/-0.3 24.+/-0.3 24.+/-0.3 Outdoor 27.+/-0.3 27.+/-0.3 27.+/-0.3 27.+/-0.3 Outdoor 24.+/-0.2 24.+/-0.3 24.+/-0.3 24.+/-0.3 The Accelerated Dew Formation Test was performed under controlled environmental conditions, maintaining a relative humidity of 95%. Both the indoor unit (IDU) and outdoor unit (ODU) were subjected to identical dry-bulb/wet-bulb temperature conditions of 27°C / 26.35°C, respectively. 5. Experimental Setup Variable Refrigerant Flow (VRF) systems are commonly integrated with inverter-driven compressors, enabling variable-speed operation through the use of DC inverters. Unlike conventional systems that operate in an on/off manner, VRF systems adjust the compressor speed in real time to match the thermal load, thereby regulating refrigerant flow precisely. This results in substantial energy savings, particularly under partial load conditions. Studies suggest that VRF systems can achieve up to 55% greater energy efficiency compared to conventional unitary systems with fixed-speed compressors. Figure 2 illustrates the experimental setup developed to evaluate the performance of a Variable Refrigerant Flow (VRF) high wall indoor unit under various ambient and load conditions. The setup consists of a VRF outdoor unit connected to multiple indoor units via insulated refrigerant piping, with emphasis placed on the high wall unit being tested. Key instrumentation includes pressure gauges, thermocouples, a flow meter, and humidity sensors, all strategically positioned to capture critical system parameters such as suction and discharge pressures, refrigerant temperature at various points, and indoor air humidity levels. To simulate different operational scenarios, the setup allows for variation in refrigerant charge, airflow rates, and ambient temperature using a controlled test chamber. Data acquisition is managed through a digital data logger, which records real-time values during steady-state and transient operations. This configuration provides a reliable platform for analysing cooling performance, capacity utilization, and condensate behavior under typical conditions encountered in tropical and sub-tropical environments. VRF systems are typically categorized into two-pipe and three-pipe configurations. In a two-pipe heat pump system, all indoor units operate in either heating or cooling mode simultaneously, limiting zone-specific control. In contrast, heat recovery (HR) VRF systems allow for simultaneous heating and cooling across different zones, enhancing thermal comfort and system efficiency. Although traditionally implemented using a three-pipe system, some manufacturers (e.g., Mitsubishi and Carrier) have developed two-pipe HR systems that utilize branch circuit (BC) controllers. These controllers manage refrigerant distribution by recovering heat from cooling zones and redirecting it to heating zones, enabling efficient thermal energy redistribution. In such systems, an indoor unit operating in heating mode may act as a condenser, while another unit in cooling mode functions as an evaporator, enabling heat transfer within the refrigerant circuit. While HR systems typically involve higher initial installation costs, they offer superior zonal temperature control and improved seasonal energy performance. When heating and cooling demands within a building are balanced, the combined coefficient of performance (COP) of the system can exceed 7 , assuming typical COP values of 3.0 for cooling and 4.0 for heating. Although such load-balancing conditions may not occur frequently throughout the year, the capability of heat recovery significantly enhances the system’s overall energy efficiency and operational flexibility, making it highly suitable for complex multi-zone applications. The following experimental parameters were recorded to assess system performance: Total cooling capacity Rated cooling capacity Capacity ratio (actual/rated) Energy Efficiency Ratio (EER) Power input (kW) Power output (cooling effect, kW) Power ratio Evaporator inlet temperature for five indoor units Evaporator outlet temperature for five indoor units Dry Bulb Temperature (DBT) – entering and leaving air Wet Bulb Temperature (WBT) – entering and leaving air These parameters provide a comprehensive overview of the system's thermodynamic behavior and energy performance under various load and environmental conditions. 6. Results and Discussion The performance evaluation of the indoor and outdoor units was conducted within separate, environmentally controlled test chambers shown in Table 3 . System data was acquired using Multi V PHY CAL split-type diagnostic software, which enables real-time monitoring and analysis of operational parameters across multiple indoor units. Table 3 Experimental results of evaporator in and evaporator out temperature Unit Value EVA IN 1 0 C 7.1 EVA IN 2 0 C 6.5 EVA IN 3 0 C 6.8 EVA IN 4 0 C 6.7 EVA IN 5 0 C 7.7 Avg. 6.96 Unit Value EVA OUT 1 0 C 8.9 EVA OUT 2 0 C 12.7 EVA OUT 3 0 C 11.5 EVA OUT 4 0 C 9.5 Avg. 10.65 The influence of suction and discharge pressures on the refrigeration capacity per unit mass of refrigerant and the coefficient of performance (COP) is illustrated in Fig. 3 – 6 . The results demonstrate that a decrease in suction pressure and an increase in discharge pressure adversely affect both the refrigerating capacity and the system efficiency. Specifically, a lower suction pressure is necessary to maintain the evaporator temperature at desired low levels for effective cooling. However, this also results in reduced refrigerant mass flow rate and enthalpy difference across the evaporator, thereby lowering the net cooling effect. Similarly, an elevated discharge pressure, typically associated with higher condenser temperatures, increases compressor work input, leading to a decline in COP. The data clearly indicate that as evaporator capacity decreases—due to lower suction pressure—the operational energy cost of the system increases disproportionately. Therefore, optimizing suction and discharge pressures is critical for maintaining a balance between cooling performance and energy efficiency. 7. Conclusion This study employed CoolPack software, a suite of specialized refrigeration system simulation tools, to model and analyze the performance of a Variable Refrigerant Flow (VRF) system using R-410A as the working fluid. Experimental investigations were conducted to evaluate both cooling capacity and dew formation resistance, and the results were compared against theoretical predictions derived from simulation outputs. The findings indicate a strong correlation between experimental and theoretical performance trends. The system exhibited a maximum Coefficient of Performance (COP) of approximately 5.0 under optimal conditions. This performance was observed when the rate of heat transfer by air was equal to or greater than that of the refrigerant. Any imbalance—specifically when the refrigerant-side heat transfer lagged—led to increased power consumption and a corresponding decline in the Energy Efficiency Ratio (EER). These results underscore the importance of precise thermal load matching and refrigerant-side optimization for maximizing system efficiency. The study highlights the value of simulation-assisted cycle optimization in enhancing the design and control of next-generation VRF systems. Declarations Competing Interest Declaration A statement declaring “The authors declare that there are no competing interests” has been added to the manuscript. Funding Declaration A statement declaring “This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors” has been included in the manuscript. Data availability statement The data that support the findings of this study and software that implements the resulting model are available from the corresponding author, I Atul M. Elgandelwar, upon reasonable request. References Rajasekar P, Palanisamy P (2012) Design and analysis of triple tube heat exchangers with fins. IOSR J Mech Civil Eng 1(1):1–5. https://doi.org/10.9790/1684-011105 Rairker NB, Karmankar AV, Thombre RE (2014) Thermal analysis of fin and tube heat exchanger. International Journal of Engineering Research and Applications, 4 (6, Version 4), 1–5. https://doi.org/10.9790/9622-04644145 Tian Q, Cai D, Ren L, Tang W, Xie Y, He G, Liu F (2015) An experimental investigation of refrigerant mixture R32 as a drop-in replacement for HFC-410A in household air conditioners. Int J Refrig 57:216–228. https://doi.org/10.1016/j.ijrefrig.2015.04.003 Stoeker WF, Jones JW (1982) Refrigeration and air conditioning, 2nd edn. McGraw-Hill Strand RK, Fisher DE, Liesen RJ, Pedersen CO (2002) Modular HVAC simulation and the future integration of alternative cooling systems in a new building energy simulation program. ASHRAE Trans 108(2):1107–1117 Li YM, Wu JY, Shiochi S (2010) Experimental validation of the simulation module of the water-cooled variable refrigerant flow system under cooling operation. Appl Energy 87(5):1513–1521. https://doi.org/10.1016/j.apenergy.2009.10.009 Aprea M, Mastrullo R, Renno C (2007) Experimental analysis of R134a, R407C and R410A flow boiling inside a horizontal smooth tube. Appl Therm Eng 27(8–9):1311–1319. https://doi.org/10.1016/j.applthermaleng.2006.11.011 Zha Z, Wang H, Liu Y (2011) Performance analysis of a multi-evaporator VRF air-conditioning system under part-load conditions. Energy Build 43(4):904–910. https://doi.org/10.1016/j.enbuild.2010.12.010 Abdelaziz M, Munk J, Fricke B (2015) Performance comparison of low-GWP refrigerants R32, DR-5A, and DR-55 as alternatives to R-410A in split air conditioning systems. Sci Technol Built Environ 21(5):674–682. https://doi.org/10.1080/10789669.2014.990163 Li D, Chen S (2010) Energy performance evaluation of VRF systems using simulation and field data. Energy Build 42(4):544–551. https://doi.org/10.1016/j.enbuild.2009.10.017 Jin G, Spitler Z (2012) Improved modeling of variable refrigerant flow (VRF) systems using data-driven and physics-based approaches. HVAC&R Res 18(4):750–764. https://doi.org/10.1080/10789669.2011.640945 Bureau of Indian Standards (2017) IS 1391 (Part 1): Room Air Conditioners — Unitary Air Conditioners — Specification, 6th rev., New Delhi, India Bureau of Indian Standards (2017) IS 1391 (Part 2): Room Air Conditioners — Split Air Conditioners — Specification, 6th rev., New Delhi, India International Organization for Standardization (2017) ISO 5151: Non-ducted Air Conditioners and Heat Pumps — Testing and Rating for Performance Characteristics, Geneva, Switzerland Additional Declarations The authors declare no competing interests. Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. 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Introduction","content":"\u003cp\u003eThe primary objective of air conditioning systems is to ensure thermal comfort for building occupants by regulating indoor temperature and humidity levels. Modern HVAC (Heating, Ventilation, and Air Conditioning) technologies offer a wide spectrum of solutions, ranging from basic window units to advanced systems such as Variable Air Volume (VAV) and Variable Refrigerant Flow (VRF) systems. Among these, VRF systems have emerged as a prominent energy-efficient alternative due to their high Coefficient of Performance (COP), modular scalability, and precise load matching capabilities [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e], [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e], [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e], [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eVRF systems are designed to deliver individualized zone control and energy savings by modulating the refrigerant flow rate according to the thermal demands of each zone. These systems operate with one or more variable-speed compressors that dynamically adjust their speed to optimize energy usage and maintain desired comfort levels [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e], [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e], [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. VRF technology is available in two main configurations: heat pump (cooling or heating only) and heat recovery systems, the latter of which enables simultaneous cooling and heating in different zones, making them particularly suitable for buildings with diverse thermal requirements [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e], [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e], [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eEnvironmentally friendly refrigerants such as R-410A are widely adopted in VRF systems due to their favorable thermodynamic properties and zero ozone depletion potential [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e], [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. However, with rising concerns about global warming and the financial and environmental costs associated with fossil fuel-based electricity generation, further improvements in system efficiency and sustainability are essential [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eOne approach to achieving this is through cycle optimization, which enhances performance by refining the control strategy and operational parameters of the refrigeration cycle [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e], [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eThis study investigates the potential for improving the performance of VRF high-wall indoor units through cycle optimization, with a focus on enhancing cooling capacity and managing moisture removal under high humidity conditions. The work also addresses the challenge of surface condensation (commonly referred to as \"sweating\") that can occur during extreme humid operation. By analysing system behavior under varied climatic and operational scenarios, the study aims to contribute to the development of more robust and efficient VRF systems for residential and commercial applications [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e], [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e].\u003c/p\u003e"},{"header":"2. Cycle Optimization","content":"\u003cp\u003eThe fundamental objective of modern air conditioning (AC) systems is to minimize operational costs, enhance energy efficiency, and ensure optimal indoor air quality while maintaining thermal comfort for occupants [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e], [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. A wide range of AC technologies\u0026mdash;such as window units, split systems, packaged units, dual-duct central systems, and Variable Refrigerant Flow (VRF) systems\u0026mdash;are employed across residential and commercial buildings [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e], [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e], [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. Among these, VRF systems have gained prominence due to their superior adaptability to dynamic thermal loads, zoned temperature control capabilities, and higher part-load efficiencies compared to conventional systems [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e], [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e], [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eVRF systems offer several advantages, including the ability to modulate refrigerant flow precisely based on the real-time load of individual indoor units. This results in better occupant comfort, reduced energy consumption, and flexible operation across multiple zones, each with independent heating or cooling requirements [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e], [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e], [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. However, key limitations include the relatively high initial capital cost and limited capacity for introducing fresh air during system operation. To overcome the latter, VRF systems are often supplemented with Heat Recovery Ventilation (HRV) systems. HRVs function by transferring heat between the exhaust and supply air streams, thereby reducing ventilation-related thermal loads and improving overall energy performance [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e], [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eAccording to ASHRAE Standard 62, VRF systems are characterized by their ability to control refrigerant flow across multiple indoor units or evaporators of varying capacities and configurations [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. This enables features such as individualized comfort control, simultaneous heating and cooling in different zones, and inter-zonal heat recovery [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e], [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e], [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]. These attributes make VRF systems particularly suitable for complex building environments with variable and non-uniform load profiles.\u003c/p\u003e\u003cp\u003eTo further improve the performance and efficiency of VRF systems, cycle optimization is essential. This involves refining the thermodynamic cycle parameters to achieve optimal energy utilization under different operating conditions [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. In this study, CoolPack\u0026mdash;a widely used refrigeration system simulation software developed by the Technical University of Denmark\u0026mdash;is employed for cycle optimization [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. CoolPack offers specialized simulation modules tailored to specific refrigeration and air conditioning cycles, allowing researchers to assess performance metrics without needing to model full system architectures. By inputting relevant operational conditions and selecting appropriate system configurations, CoolPack enables targeted analysis and optimization of VRF cycle behavior [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eThe optimization process focuses on enhancing cooling capacity, reducing energy consumption, and mitigating the formation of surface condensation, particularly under high humidity conditions [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e], [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e], [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]. The insights obtained from the simulation studies are utilized to develop advanced control strategies and recommend system-level enhancements for next-generation Variable Refrigerant Flow (VRF) high-wall indoor units. Figure\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e illustrates the optimized refrigeration cycle of the VRF system operating with R-410A as the working fluid.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e"},{"header":"3. Cooling Capacity Test","content":"\u003cp\u003eThe objective of the cooling capacity test is to evaluate the performance characteristics of the Variable Refrigerant Flow (VRF) high-wall unit under standardized operating conditions. Key performance indicators assessed during this test include the Energy Efficiency Ratio (EER), operating current (expressed as a current ratio), power consumption (watt ratio), and the net cooling effect delivered by the system. As part of the procedure, the rotational speed (RPM) of the indoor unit's fan motor is measured in fan-only mode, i.e., with the compressor switched off, after the room has reached a steady-state condition. This assessment is carried out at the motor\u0026rsquo;s rated voltage to ensure consistency and accuracy. The dry condition of the evaporator coil is verified during this phase through the RPM observation, confirming the absence of condensation and ensuring that no latent cooling is taking place. These measurements provide baseline operational data and help validate the system's performance prior to compressor engagement, serving as a reference point for evaluating cycle efficiency and cooling output under full-load and part-load conditions. Prior to initiating the cooling capacity test, the environmental conditions within the test chamber must be stabilized and maintained for a minimum duration of one hour to ensure thermal equilibrium. Following stabilization, data collection is performed in accordance with the test protocol. As presented in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e, measurements are recorded at 10-minute intervals, resulting in a total of seven sets of readings.\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eTemperature conditions for capacity test [\u003cspan additionalcitationids=\"CR13\" citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"4\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\"\u0026minus;\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\"\u0026minus;\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\"\u0026minus;\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eBIS\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eISO\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eDomestic\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eIndoor\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026minus;\" colname=\"c2\"\u003e\u003cp\u003e27.+/-0.3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026minus;\" colname=\"c3\"\u003e\u003cp\u003e27.+/-0.3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026minus;\" colname=\"c4\"\u003e\u003cp\u003e27.+/-0.3\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eIndoor\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026minus;\" colname=\"c2\"\u003e\u003cp\u003e19.+/-0.2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026minus;\" colname=\"c3\"\u003e\u003cp\u003e19.+/-0.2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026minus;\" colname=\"c4\"\u003e\u003cp\u003e19.+/-0.2\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eOutdoor\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026minus;\" colname=\"c2\"\u003e\u003cp\u003e35.+/-0.3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026minus;\" colname=\"c3\"\u003e\u003cp\u003e35.+/-0.3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026minus;\" colname=\"c4\"\u003e\u003cp\u003e35.+/-0.3\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eOutdoor\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026minus;\" colname=\"c2\"\u003e\u003cp\u003e24.+/-0.2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026minus;\" colname=\"c3\"\u003e\u003cp\u003e24.+/-0.2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026minus;\" colname=\"c4\"\u003e\u003cp\u003e24.+/-0.2\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003eThis systematic data acquisition approach ensures the reliability and repeatability of the test results.\u003c/p\u003e"},{"header":"4. Dew Formation Resistance Test","content":"\u003cp\u003eThis test is conducted to evaluate the air conditioner's ability to resist surface condensation (commonly referred to \u003cb\u003eas\u003c/b\u003e \"sweating\"\u003cb\u003e)\u003c/b\u003e when operating under high-humidity conditions. The primary objective is to assess the effectiveness of the system in maintaining surface temperatures above the dew point, thereby preventing moisture accumulation on the unit\u0026rsquo;s external surfaces. Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e presents the controlled temperature and humidity conditions employed during the dew resistance evaluation.\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eTemperature conditions for dew improvement test. [\u003cspan additionalcitationids=\"CR13\" citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"5\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\"\u0026minus;\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\"\u0026minus;\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\"\u0026minus;\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\"\u0026minus;\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eBIS\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eISO\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eDomestic\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003eAccelerate Test\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eIndoor\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026minus;\" colname=\"c2\"\u003e\u003cp\u003e27.+/-0.3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026minus;\" colname=\"c3\"\u003e\u003cp\u003e27.+/-0.3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026minus;\" colname=\"c4\"\u003e\u003cp\u003e27.+/-0.3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026minus;\" colname=\"c5\"\u003e\u003cp\u003e27.+/-0.3\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eIndoor\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026minus;\" colname=\"c2\"\u003e\u003cp\u003e24.+/-0.2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026minus;\" colname=\"c3\"\u003e\u003cp\u003e24.+/-0.3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026minus;\" colname=\"c4\"\u003e\u003cp\u003e24.+/-0.3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026minus;\" colname=\"c5\"\u003e\u003cp\u003e24.+/-0.3\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eOutdoor\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026minus;\" colname=\"c2\"\u003e\u003cp\u003e27.+/-0.3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026minus;\" colname=\"c3\"\u003e\u003cp\u003e27.+/-0.3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026minus;\" colname=\"c4\"\u003e\u003cp\u003e27.+/-0.3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026minus;\" colname=\"c5\"\u003e\u003cp\u003e27.+/-0.3\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eOutdoor\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026minus;\" colname=\"c2\"\u003e\u003cp\u003e24.+/-0.2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026minus;\" colname=\"c3\"\u003e\u003cp\u003e24.+/-0.3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026minus;\" colname=\"c4\"\u003e\u003cp\u003e24.+/-0.3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\"\u0026minus;\" colname=\"c5\"\u003e\u003cp\u003e24.+/-0.3\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003eThe Accelerated Dew Formation Test was performed under controlled environmental conditions, maintaining a relative humidity of 95%. Both the indoor unit (IDU) and outdoor unit (ODU) were subjected to identical dry-bulb/wet-bulb temperature conditions of 27\u0026deg;C / 26.35\u0026deg;C, respectively.\u003c/p\u003e"},{"header":"5. Experimental Setup","content":"\u003cp\u003eVariable Refrigerant Flow (VRF) systems are commonly integrated with inverter-driven compressors, enabling variable-speed operation through the use of DC inverters. Unlike conventional systems that operate in an on/off manner, VRF systems adjust the compressor speed in real time to match the thermal load, thereby regulating refrigerant flow precisely. This results in substantial energy savings, particularly under partial load conditions. Studies suggest that VRF systems can achieve up to 55% greater energy efficiency compared to conventional unitary systems with fixed-speed compressors.\u003c/p\u003e\u003cp\u003eFigure \u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e illustrates the experimental setup developed to evaluate the performance of a Variable Refrigerant Flow (VRF) high wall indoor unit under various ambient and load conditions. The setup consists of a VRF outdoor unit connected to multiple indoor units via insulated refrigerant piping, with emphasis placed on the high wall unit being tested. Key instrumentation includes pressure gauges, thermocouples, a flow meter, and humidity sensors, all strategically positioned to capture critical system parameters such as suction and discharge pressures, refrigerant temperature at various points, and indoor air humidity levels. To simulate different operational scenarios, the setup allows for variation in refrigerant charge, airflow rates, and ambient temperature using a controlled test chamber.\u003c/p\u003e\u003cp\u003eData acquisition is managed through a digital data logger, which records real-time values during steady-state and transient operations. This configuration provides a reliable platform for analysing cooling performance, capacity utilization, and condensate behavior under typical conditions encountered in tropical and sub-tropical environments.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eVRF systems are typically categorized into two-pipe and three-pipe configurations. In a two-pipe heat pump system, all indoor units operate in either heating or cooling mode simultaneously, limiting zone-specific control. In contrast, heat recovery (HR) VRF systems allow for simultaneous heating and cooling across different zones, enhancing thermal comfort and system efficiency. Although traditionally implemented using a three-pipe system, some manufacturers (e.g., Mitsubishi and Carrier) have developed two-pipe HR systems that utilize branch circuit (BC) controllers. These controllers manage refrigerant distribution by recovering heat from cooling zones and redirecting it to heating zones, enabling efficient thermal energy redistribution. In such systems, an indoor unit operating in heating mode may act as a condenser, while another unit in cooling mode functions as an evaporator, enabling heat transfer within the refrigerant circuit. While HR systems typically involve higher initial installation costs, they offer superior zonal temperature control and improved seasonal energy performance. When heating and cooling demands within a building are balanced, the combined coefficient of performance (COP) of the system can exceed \u003cb\u003e7\u003c/b\u003e, assuming typical COP values of 3.0 for cooling and 4.0 for heating. Although such load-balancing conditions may not occur frequently throughout the year, the capability of heat recovery significantly enhances the system\u0026rsquo;s overall energy efficiency and operational flexibility, making it highly suitable for complex multi-zone applications.\u003c/p\u003e\u003cp\u003eThe following experimental parameters were recorded to assess system performance:\u003c/p\u003e\u003cp\u003e\u003col\u003e\u003cspan\u003e\u003cli\u003e\u003cp\u003eTotal cooling capacity\u003c/p\u003e\u003c/li\u003e\u003c/span\u003e\u003cspan\u003e\u003cli\u003e\u003cp\u003eRated cooling capacity\u003c/p\u003e\u003c/li\u003e\u003c/span\u003e\u003cspan\u003e\u003cli\u003e\u003cp\u003eCapacity ratio (actual/rated)\u003c/p\u003e\u003c/li\u003e\u003c/span\u003e\u003cspan\u003e\u003cli\u003e\u003cp\u003eEnergy Efficiency Ratio (EER)\u003c/p\u003e\u003c/li\u003e\u003c/span\u003e\u003cspan\u003e\u003cli\u003e\u003cp\u003ePower input (kW)\u003c/p\u003e\u003c/li\u003e\u003c/span\u003e\u003cspan\u003e\u003cli\u003e\u003cp\u003ePower output (cooling effect, kW)\u003c/p\u003e\u003c/li\u003e\u003c/span\u003e\u003cspan\u003e\u003cli\u003e\u003cp\u003ePower ratio\u003c/p\u003e\u003c/li\u003e\u003c/span\u003e\u003cspan\u003e\u003cli\u003e\u003cp\u003eEvaporator inlet temperature for five indoor units\u003c/p\u003e\u003c/li\u003e\u003c/span\u003e\u003cspan\u003e\u003cli\u003e\u003cp\u003eEvaporator outlet temperature for five indoor units\u003c/p\u003e\u003c/li\u003e\u003c/span\u003e\u003cspan\u003e\u003cli\u003e\u003cp\u003eDry Bulb Temperature (DBT) \u0026ndash; entering and leaving air\u003c/p\u003e\u003c/li\u003e\u003c/span\u003e\u003cspan\u003e\u003cli\u003e\u003cp\u003eWet Bulb Temperature (WBT) \u0026ndash; entering and leaving air\u003c/p\u003e\u003c/li\u003e\u003c/span\u003e\u003c/ol\u003e\u003c/p\u003e\u003cp\u003eThese parameters provide a comprehensive overview of the system's thermodynamic behavior and energy performance under various load and environmental conditions.\u003c/p\u003e"},{"header":"6. Results and Discussion","content":"\u003cp\u003eThe performance evaluation of the indoor and outdoor units was conducted within separate, environmentally controlled test chambers shown in Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e. System data was acquired using Multi V PHY CAL split-type diagnostic software, which enables real-time monitoring and analysis of operational parameters across multiple indoor units.\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eExperimental results of evaporator in and evaporator out temperature\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"3\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eUnit\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eValue\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eEVA IN 1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u003csup\u003e0\u003c/sup\u003eC\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e7.1\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eEVA IN 2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u003csup\u003e0\u003c/sup\u003eC\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e6.5\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eEVA IN 3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u003csup\u003e0\u003c/sup\u003eC\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e6.8\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eEVA IN 4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u003csup\u003e0\u003c/sup\u003eC\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e6.7\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eEVA IN 5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u003csup\u003e0\u003c/sup\u003eC\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e7.7\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cb\u003eAvg.\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e\u003cb\u003e6.96\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u003cb\u003eUnit\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e\u003cb\u003eValue\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eEVA OUT 1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u003csup\u003e0\u003c/sup\u003eC\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e8.9\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eEVA OUT 2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u003csup\u003e0\u003c/sup\u003eC\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e12.7\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eEVA OUT 3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u003csup\u003e0\u003c/sup\u003eC\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e11.5\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eEVA OUT 4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u003csup\u003e0\u003c/sup\u003eC\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e9.5\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cb\u003eAvg.\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e\u003cb\u003e10.65\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003eThe influence of suction and discharge pressures on the refrigeration capacity per unit mass of refrigerant and the coefficient of performance (COP) is illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e\u0026ndash;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e. The results demonstrate that a decrease in suction pressure and an increase in discharge pressure adversely affect both the refrigerating capacity and the system efficiency. Specifically, a lower suction pressure is necessary to maintain the evaporator temperature at desired low levels for effective cooling. However, this also results in reduced refrigerant mass flow rate and enthalpy difference across the evaporator, thereby lowering the net cooling effect. Similarly, an elevated discharge pressure, typically associated with higher condenser temperatures, increases compressor work input, leading to a decline in COP. The data clearly indicate that as evaporator capacity decreases\u0026mdash;due to lower suction pressure\u0026mdash;the operational energy cost of the system increases disproportionately. Therefore, optimizing suction and discharge pressures is critical for maintaining a balance between cooling performance and energy efficiency.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003c/p\u003e"},{"header":"7. Conclusion","content":"\u003cp\u003eThis study employed CoolPack software, a suite of specialized refrigeration system simulation tools, to model and analyze the performance of a Variable Refrigerant Flow (VRF) system using R-410A as the working fluid. Experimental investigations were conducted to evaluate both cooling capacity and dew formation resistance, and the results were compared against theoretical predictions derived from simulation outputs.\u003c/p\u003e\u003cp\u003eThe findings indicate a strong correlation between experimental and theoretical performance trends. The system exhibited a maximum Coefficient of Performance (COP) of approximately 5.0 under optimal conditions. This performance was observed when the rate of heat transfer by air was equal to or greater than that of the refrigerant. Any imbalance\u0026mdash;specifically when the refrigerant-side heat transfer lagged\u0026mdash;led to increased power consumption and a corresponding decline in the Energy Efficiency Ratio (EER).\u003c/p\u003e\u003cp\u003eThese results underscore the importance of precise thermal load matching and refrigerant-side optimization for maximizing system efficiency. The study highlights the value of simulation-assisted cycle optimization in enhancing the design and control of next-generation VRF systems.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eCompeting Interest Declaration\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eA statement declaring \u0026ldquo;The authors declare that there are no competing interests\u0026rdquo; has been added to the manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding Declaration\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eA statement declaring \u0026ldquo;This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors\u0026rdquo; has been included in the manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData availability statement\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe data that support the findings of this study and software that implements the resulting model are available from the corresponding author, I Atul M. Elgandelwar, upon reasonable request.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eRajasekar P, Palanisamy P (2012) Design and analysis of triple tube heat exchangers with fins. 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HVAC\u0026amp;R Res 18(4):750\u0026ndash;764. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1080/10789669.2011.640945\u003c/span\u003e\u003cspan address=\"10.1080/10789669.2011.640945\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eBureau of Indian Standards (2017) IS 1391 (Part 1): Room Air Conditioners \u0026mdash; Unitary Air Conditioners \u0026mdash; Specification, 6th rev., New Delhi, India\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eBureau of Indian Standards (2017) IS 1391 (Part 2): Room Air Conditioners \u0026mdash; Split Air Conditioners \u0026mdash; Specification, 6th rev., New Delhi, India\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eInternational Organization for Standardization (2017) ISO 5151: Non-ducted Air Conditioners and Heat Pumps \u0026mdash; Testing and Rating for Performance Characteristics, Geneva, Switzerland\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":true,"highlight":"","institution":"Dr Vishwanath Karad MIT World Peace University ","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Variable Refrigerant Flow, Cycle optimization, Cooling capacity enhancement, Dehumidification performance","lastPublishedDoi":"10.21203/rs.3.rs-7250980/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7250980/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThe growing demand for energy-efficient and environmentally sustainable HVAC solutions in residential buildings has driven the adoption of Variable Refrigerant Flow (VRF) systems. VRF technology, typically using R410A as the working fluid, provides simultaneous heating and cooling with enhanced part-load efficiency and greater operational flexibility than conventional central air conditioning systems. This study aims to optimize the refrigeration cycle of a VRF high wall indoor unit to improve cooling capacity and dehumidification performance. A combination of experimental and analytical methods was employed to evaluate system behavior under varying ambient temperatures and load conditions. Special emphasis was placed on assessing resistance to surface condensate formation (sweating), which is prevalent in high-humidity environments. Results indicate that specific cycle enhancements can significantly increase capacity utilization and improve control over dew point conditions. These improvements suggest that optimized VRF systems can better meet thermal comfort and moisture regulation requirements, particularly in tropical and sub-tropical climates where both energy efficiency and humidity control are critical.\u003c/p\u003e","manuscriptTitle":"Optimizing Refrigeration Cycles to Enhance Capacity and Dew Regulation in VRF High Wall Systems","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-07-31 04:03:20","doi":"10.21203/rs.3.rs-7250980/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"c284eccf-2fdc-4509-9536-67e5e852ebf8","owner":[],"postedDate":"July 31st, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[{"id":52359649,"name":"Mechanical Engineering"}],"tags":[],"updatedAt":"2025-07-31T04:03:21+00:00","versionOfRecord":[],"versionCreatedAt":"2025-07-31 04:03:20","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-7250980","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7250980","identity":"rs-7250980","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}