Refrigerant Charge Research Articles

Natural refrigerant mixtures in low-charge heat pumps: An analysis of the potential for performance enhancements

The study investigated the characteristics of different natural refrigerants and their mixtures in a residential heat pump with low refrigerant charge. Three main evaluation criteria were utilized for comparing different mixtures: Coefficient of Performance (COP), Volumetric Heating Capacity (VHC), and a newly proposed indicator, the heating capacity at charge limit. Propane was used as a reference refrigerant. It was found that some mixtures significantly improved both COP and the heating capacity at charge limit while maintaining similar volumetric heating capacity and operating conditions. Alternative multi-criteria decision-making techniques were adopted to rank the best refrigerant mixtures. Mixtures rich in Dimethyl Ether (DME), such as DME-CO2 [0.96-0.04] and DME-Propylene [0.75-0.25] were found consistently among the best options. Those were followed by Propylene-rich mixtures such as Propylene-CO2, Propylene-Isobutane and Propylene-Butane. The levelized cost of heat (LCOH) could be improved by up to 12 %. To accelerate the transition to natural refrigerants, without compromises on efficiency and costs, further research and certification activities on non-fluorinated refrigerants based on Dimethyl Ether (R-E170), CO2 (R-744) and Propylene (R-1270) are recommended.

Optimization study of the circuitry for 5 mm small-diameter finned-tube heat exchanger in air-source heat pumps

Finned-tube heat exchangers (FTHXs) are currently extensively utilized in residential air-source heat pumps (ASHPs), but their escalating costs pose an urgent issue needing resolution. This study investigated the feasibility of replacing the 7 mm diameter FTHX in the outdoor unit of an ASHP with a 5 mm small-diameter FTHX, aiming to reduce material consumption without compromising performance. Based on the Intelligent System for Heat Exchanger Design (ISHED), a 6–3-1 circuitry (6 circuitries merging into 3 then 1) optimization scheme tailored for the 5 mm diameter FTHX was proposed under non-uniform airflow distribution. The performance differences between this circuitry and the baseline were then analyzed through numerical simulations. Finally, comparative tests were performed between the original FTHX and the modified 5 mm diameter FTHX. Overall, even with a 5.10 % reduction in total heat exchange area, its heat exchange capacity and efficiency still meet the performance standards for the initial ASHP. Notably, the proposed 5 mm diameter FTHX reduces the material costs and refrigerant charge by 19.76 % and 12.28 %, respectively. This phenomenon illustrates the considerable economic benefits of reducing the volume of FTHX. Additionally, it holds significant practical value in promoting the use of natural refrigerants including hydrocarbons according to the new international legislative framework.

Experimental investigation into the influence of different system configurations on charge optimization in an R410A chiller with a dedicated subcooler

The current study addresses the important issue of reducing the amount of refrigerant used in HVAC&R systems due to new regulations and the phase-down of high Global Warming Potential (GWP) refrigerants. Specifically, this research compares the optimal refrigerant charge for two distinct scroll compressors: a variable speed compressor and a single speed compressor, both operating within the same R410A chiller equipped with a condenser, receiver and dedicated subcooler. The nominal cooling capacity of this chiller is 8 kW. One novelty of this study lies in assessing the charge optimization not only at full load but also at part load conditions to determine if there is any effect of using continuous capacity modulation like a variable speed compressor on the optimum charge. The results reveal that the COP maximizing charge corresponds to when some part of the two-phase heat transfer happens in the dedicated subcooler and not when the receiver is partially filled with liquid refrigerant as expected. Interestingly, at part load conditions, the compressor lacking continuous capacity modulation demonstrates higher optimum subcooling and COP improvement potential compared to full load conditions. Moreover, the study also analyzes the impact of operating at peak COP charge on seasonal performance using a variable speed compressor. This seasonal performance investigation reveals that although cooling capacity obtained when the system is operating with COP maximizing charge is 6 % lower, the seasonal performance is 11 % higher when compared to typical operating charge. Notably, for the first time, charge optimization is conducted in the same experimental with different configurations of the condenser with/without receiver and with/without subcooler to understand the contribution of these components. This systematic comparison revealed the absence of abnormal COP peak in configurations without a dedicated subcooler.

Modelling of the refrigerant distribution in a critically charged propane heat pump cycle for performance evaluation

The investigation of heat pumps employing natural refrigerants as working fluids has gained substantial momentum, driven by increasingly stringent regulations addressing the global warming potential (GWP) and ozone depletion potential (ODP) of refrigerants. Propane (R290) stands out as an attractive option due to its low GWP and zero ODP. However, a major drawback of propane lies in its flammability. When using propane as working fluid, it will therefore be necessary to limit the total refrigerant charge within the system, without compromising on the heat pump performance. This study endeavors to address this challenge by developing a model of the refrigerant charge distribution in a critically charged heat pump system consisting of an evaporator, a compressor, a condenser, and an expansion valve. In the model, the charge distribution in the two heat exchangers is modelled in detail using a suitable void fraction correlation. For the compressor and expansion valve, a simplified model is employed, in which no refrigerant charge is calculated. Using an iterative procedure, the model can then be used to determine the coefficient of performance (COP), evaporator- and condenser pressure for a heat pump with an established total charge and heat capacity. The influence of different design and operation parameters, such as the degrees of subcooling and superheat, the volume ratio of the evaporator and the condenser, etc., can be assessed.

Optimal charge amount for semiconductor chiller applying eco-friendly refrigerant R-744

The refrigerants used to cool the heat generated in semiconductor production are Freons, which are now subject to regulation because of their high ozone depletion potential (ODP) and global warming potential (GWP). Therefore, R-744 is considered an eco-friendly refrigerant. This study experimentally analyzed the effect of the refrigerant charge amount based on the temperature discharged after cooling objects when operating a brine chiller using R-744 under subcritical conditions. The results showed that the optimal charge amount in terms of the coefficients of performance (COP) differed from that in terms of the maximum cooling capacity. In case of the apparatus used in this study, the optimal refrigerant charge amount with maximum cooling capacity was estimated at 8.2 kg when the temperature of the cooling object was in the range of −20 °C and −10 °C and at 9.2 kg when the temperature of the cooling object was 0 °C. However, in terms of COP, the optimal refrigerant charge amount was estimated at 8.2 kg when the temperature of the cooling object was in the range of −20 °C and 0 °C. This difference was attributed to the variation in the required evaporation heat capacity with the target temperature of the cooling object.

Experimental investigation on the influence of electronic expansion valve opening on the performance of miniature refrigeration system

In the cooling of personnel and electronic equipment under specific conditions, the miniature refrigeration system needs to provide different cooling capacity to adapt to different working conditions. At present, most scholars use capillaries as throttling components. Compared with capillaries, miniature refrigeration systems using electronic expansion valves as throttling components can provide a wider range of cooling capacity adjustment. Therefore, this study constructed a miniature vapor compression refrigeration system based on electronic expansion valves as throttling devices, with a system weight of 3.0 kg and dimensions of 380 mm × 300 mm × 200 mm. The experiment investigated the impact of electronic expansion valve opening on compressor power, cooling capacity, and COP under different refrigerant charge conditions. Results indicated that at an electronic expansion valve opening of 90, within the experimental range, there was a relative change in cooling capacity of 39.85 % and a relative change in COP of 29.11 % as the refrigerant charge increased. Refrigerant charge had a significant effect on the cooling capacity and COP of the miniature refrigeration system. Under the optimal refrigerant charge of 70 g, within the experimental range, there was a relative change in cooling capacity of 88.14 % with varying electronic expansion valve opening. The use of electronic expansion valves as throttle components in miniature refrigeration systems allows for a wider range of cooling capacity adjustments, making them suitable for more cooling conditions.

Effect of the refrigerant charge on transcritical CO2 direct evaporation ice-making system

The low global warming potential and zero ozone depletion potential of CO2 make it highly suitable for application in ice rinks. The refrigerant charge prediction model of the transcritical CO2 direct evaporation ice-making system is proposed and compared. According to the predictive results, the performance of the ice-making system was experimentally studied at three predictive refrigerant charges. The results show that the ice-making system with the refrigerant charge predicted by the comprehensive model with GC + ECH (gas cooler refrigerant charge model and evaporator refrigerant charge model with Hughmark correlations) presents the optimum performance. The refrigerant charge in the pipeline accounts for 46.6 %–57.2 % of the total refrigerant charge, so proper pipeline arrangements are crucial to reduce the overall refrigerant charge, especially before and after the throttle valve. The experiment data shows that the optimal high-side pressure of the ice-making system is between 7.9 MPa and 8.3 MPa, and the optimal COP (coefficient of performance) is between 1.34 and 1.75. Excessive or insufficient refrigerant charge leads to overall superheating or overall unsaturation of the refrigerant at the outlet of the evaporator. At the proposed refrigerant charge, both cooling capacity and COP increase by 8.3 %–38.3 % and 21.5 %–30.6 % respectively compared to other charges tested. In addition, the ice-making time at the proposed refrigerant charge can be saved by 10.0 %–15.6 %.

Refrigerants for eutectic refrigerating systems–Experimental results and future consideration

The new European F-Gas and PFAS Directives threaten to dramatically reduce quotas or even outright ban synthetic refrigerants, and transition to natural refrigerants in the near future seems inevitable. This article examines eutectic refrigerating systems used in low-temperature transport refrigerators for retail distribution considering transition to natural refrigerants. The main limitation for the operation of eutectic systems is the low evaporation pressure, and various designs addressing this limitation were already tried in the last few years during transition from R507A to R452A and other alternatives. In this article 5 systems with R452A, two with R290 and two with R1270 are compared. The greatest effect was demonstrated by addition of roll-bond plates – it reduced the difference between the inside air and evaporation temperatures by about 3 K. However, this solution is not promising with hydrocarbons due to the higher refrigerant charge. All other solutions together give no more effect than roll-bond plates in terms of evaporation temperature at the end of pull-down. Based on experimental results, the prospects of eutectic refrigeration system with natural refrigerants are reviewed. R290 is not suitable for such systems, but R1270 could be used in systems where eutectic plates just need to be crystallized. However, in weight-optimized systems used in refrigerated vans, the evaporation pressure of R1270 would be lower than atmospheric, which is considered unacceptable due to safety requirements. If this provision remains, the eutectic refrigerators with a single-stage vapour compression refrigerating system become impossible, and more complicated cascade system has to be developed.

Research on refrigerant charge determination under different compressor speed and its effects on the performance of transcritical CO2 air-conditioning heat pump system in electric vehicle

CO2 is assumed to be one of the most potential refrigerant alternatives for electric vehicles for its excellent properties. However, the charge determination of CO2 in current studies remain controversial. In this study, a transcritical CO2 air-conditioning heat pump system was established and experimentally tested to analyze the optimal charge amount. Based on two conflicting methods of charge determining proposed by the preceding research, this paper substantiated the existing controversy and subsequently proposed a more comprehensive method. The effects of different refrigerant charge on the system characteristics were investigated. The influence of the compressor speed on the optimal refrigerant charge and system characteristics was also analyzed. It was found that the optimal charge plateau occurred from refrigerant of 500 g–580 g at the compressor speed of 3000 r·min−1. However, the optimal charge declined with the increment of compressor speed from 3000 r·min−1 to 4500 r·min−1. Among three models, Hughmark's model was proved to be the most appropriate for the theoretical calculation of optimal charge within an error of 6.09%. Further study illustrates that refrigerant mass in high-pressure pipe and intermediate heat exchanger/accumulator (IHX/A) accounted for the main proportion about 52.6%–55.14%.

Dynamic modeling of a centrifugal chiller with hybrid falling film evaporator including pressure drop computation

Over the last decade, the introduction of new technologies such as falling film evaporators and advanced control techniques has significantly enhanced chiller efficiency while reducing refrigerant charges. However, the complexity of the involved transport phenomena poses significant challenges in simulating the behavior of these devices, resulting in very few validated models that encompass such advances. This study introduces a novel dynamic model for centrifugal liquid chillers with a hybrid evaporator (one that combines features of falling film and flooded designs). Employing the moving boundary method, the model incorporates the intricacies of the transport phenomena, including the pressure drop across the tube bank, with relatively low computational requirements. Implemented in OpenModelica, the model was validated using performance data from a 550 TR centrifugal chiller, yielding normalized residual errors of less than 0.5% for values of supply water temperature and power consumption. This provides a comprehensive tool suitable for analyzing chiller performance as a function of the evaporator geometric characteristics and enabling optimal dynamic control of central cooling systems incorporating this kind of chillers, as long as contributes to the development of dynamic and steady state models of vapor compression centrifugal chillers with falling film evaporators.

Flow boiling heat transfer characteristics and correlation development of R290/R600a mixtures in an internally threaded tube

Excessive hydrofluorocarbons (HFCs) usage significantly contributes to the global warming. Therefore, there is a widespread shift toward natural refrigerants with low global warming potential (GWP). Among these alternative refrigerants, R290, R600a, and their mixtures have gained considerable attention. However, their flammability limits the charge. To decrease the equipment volume and reduce the refrigerant charge, internally threaded tubes have been introduced to enhance the heat transfer. Therefore, in this study, flow boiling experiments were conducted on R290, R600a, and mixtures inside an internally threaded tube, obtaining heat transfer data under a pressure of 0.216–0.416 MPa, heat flux of 10.5–73.0 kW m−2, mass flux of 70–190 kg m−2 s−1. To quantitatively discern the dominant heat transfer mechanism, a dimensionless number Nz was introduced. In the nucleate boiling dominant region, an increase in the heat flux markedly enhances the heat transfer, with pressure and mass flux playing minor roles. Furthermore, the heat transfer deterioration trend of the mixtures aligns with the variation trends of concentration slip and boiling range. In the convective heat transfer dominant region, a rise in the mass flux significantly increases the heat transfer coefficient, while the pressure and heat flux have minor effects. Additionally, at high R290 mole fraction and vapor quality, high surface tension maintains a continuous liquid film, enhancing the heat transfer. Furthermore, new heat transfer correlations for flow boiling inside the internally threaded tubes were established, which exhibit a mean relative deviation of −2.30 % and 8.80 % for the obtained experimental results and collected data, respectively.

Research on the effect of the refrigerant charge in a variable capacity heat pump

Current energy efficiency regulations have led to the development of heat pumps equipped with variable speed compressors (VSC) and electronic expansion valves (EEV). To reduce the amount of refrigerant charge, heat pump manufacturers are developing units without a liquid receiver. As a result, the amount of refrigerant charge has a direct impact on the unit performance and needs to be optimized. Previous studies have shown the existence of an optimum refrigerant charge that maximizes the COP at a given operating condition. However, with VSC it is not clear if the optimum charge at a given compressor speed is the adequate one at other speed values. This paper analyzes the effects of the refrigerant charge amount on the performance of a brine-to-water heat pump equipped with a VSC and an EEV. For a given compressor speed, the variation of the COP with the charge showed similar trends and an optimum refrigerant charge could be identified. The charge for the maximum COP changes slightly with the compressor speed. The seasonal coefficient of performance (SCOP) is proposed as a better metric for evaluating the optimum charge. Results show that the SCOP is quite stable with the refrigerant charge.

Experimental investigation of air-conditioning electrical compressor using binary TiO2–SiO2 polyol-ester nanolubricants

As electric vehicles (EVs) continue to replace conventional gasoline vehicles, maintaining thermal comfort within the car requires additional energy to operate the automotive air-conditioning (AAC) system. This work aims to optimise the electrically driven compressor (EDC) system utilising polyol-ester (POE)-based binary nanolubricants to enhance performance and minimise the size of the EV battery and AAC components. A binary nanolubricant was formulated using a two-step method of formulation. The TiO2–SiO2/POE binary nanolubricant was prepared at different volume concentrations ranging from 0.01 to 0.1 %. The experiment was conducted for the 1200–3840 rpm compressor speed with different initial refrigerant charges between 120 and 160 g. The heat absorption rose by up to 44.2 % while utilising the binary nanolubricant at a volume concentration of 0.03 %. The coefficient of performance (COP) reached its maximum value of 2.43 at a refrigerant charge of 160 g and compressor speed of 1860 rpm. Furthermore, the binary nanolubricant significantly reduced the expansion valve discharge temperature, exhibiting a substantial decrease of up to 51.6 %. The highest COP increment, up to 23.4 %, was achieved at a volume concentration of 0.03 %. Hence, it is recommended to utilise 0.03 % TiO2–SiO2/POE binary nanolubricant to achieve optimal performance in the AAC-EDC system.

Experimental analysis of a tri-partite brazed plate gas cooler for CO2 heat pump water heaters

Gas cooler is a crucial component in CO2 systems, and its performance significantly influences the overall efficiency of the CO2-based heat pump system. Brazed plate heat exchangers feature a compact design, reduced refrigerant charge, enhanced heat transfer coefficient, and lower pressure drop, resulting in space savings and improved system performance. This experimental study investigates a water-cooled tri-partite brazed plate gas cooler in a CO2 heat pump. The tri-partite brazed plate gas cooler has a double effect: it allows matching the temperature glide of CO2 with that of water and meeting the requirements for both domestic hot water and space heating simultaneously. The experiments are conducted in only domestic hot water and combined space and domestic hot water operative modes. The effects of different operating parameters on heat duty, supply temperature, temperature approach, and pinch point location are evaluated. The actual conductance of gas coolers is calculated, and a new definition is adopted to determine the ϵ−NTU of gas coolers. Results show that preheating gas cooler (GC3) has a higher heat duty at pressures near the critical pressure. As the inlet pressure increases, the domestic hot water supply temperature increases, the pinch point moves to the cold end of GC3, and the temperature approach decreases. The LMTD method may result in an undersized or oversized CO2 gas cooler by up to ±50% for different pressures. The errors reach their maximum values when the temperature difference is low at the cold end and high at the hot end. The effectiveness ranges from 0.56 to 0.94 and the NTU ranges from 2.64 to 5.41. The gas cooler shows promising performance. The outcomes of this research are anticipated to serve as a valuable reference for enhancing the design and optimization of transcritical CO2 systems.

A validated model for variable-speed multi-chillers to assess different operation modes

Environmental protection drives the replacement of environmentally harmful refrigerants with potentially flammable alternatives, necessitating efficient cooling strategies for varying loads. Legislation limits flammable refrigerant charge, leading to the adoption of multi-chiller systems with smaller charges and therefore also smaller loads per chiller. However, operating such systems requires complex strategies, addressable through fast and reliable models. This study presents a semi-empirical model predicting the behaviour of variable-speed multi-chiller systems. The model focuses on predicting cooling capacity and coefficient of performance (COP) for cooling, with input parameters of evaporation and condensation temperatures, and compressor speed. Experimental validation of the parameterized model shows COP predictions within 3 % for a two-module system using R-290 (propane) under different conditions and compressor speeds. The model assesses various operation strategies, including the conventional mode with fewer chiller modules running at high speed, compared to modes where all chillers run but at reduced speeds. Comparing COP values in these modes reveals energy-saving potentials of up to 14.57 % for constant condensation temperatures. Moreover, strategies involving condensation temperature reduction, or a combination with compressor speed reduction are analysed for energy-saving potentials. Reducing the condensation temperature by 3 K results in savings of up to 13.25 % and combined with the compressor speed reduction savings of up to 23.54 % are feasible. These findings emphasize the importance of considering compressor speed when operating multi-chiller systems to maximize energy savings. The presented model effectively evaluates various strategies and implements variable-load control in multi-chiller systems, serving as a valuable tool for optimising energy efficiency and promoting environmentally friendly cooling practices.

Development and validation of a model for an air-to-air air conditioner

Air conditioning units are responsible for a significant amount of global warming, with demand predicted to triple by 2050. Mathematical models aid in designing energy efficient air conditioners that can contribute to climate change mitigation. This study presents a steady-state model for a air-to-air air conditioner. The proposed model can assist in reducing the number of experiments and optimizing the efficiency of air conditioning systems. It utilizes a bottom-up approach to solve for compressor, condenser, capillary tube, and evaporator sub-models. The compressor is modelled using polynomial equations to determine refrigerant mass flow rate and power consumption based on operating temperatures. Heat exchanger models are solved using finite volume approach and reliable correlations are used for void fraction, friction factor, and heat transfer coefficient calculations. The closing equations are the mass conservation, i.e. constant refrigerant charge, and the equivalence between the mass flow rate sucked by the compressor and the one that flows through the capillary tube, while the evaporating and condensing pressures are the independent variables. The capillary tube is modelled using semiempirical correlations. The model is validated against experimental data at various operating conditions and shows a ±7% agreement for predicted cooling capacity.

Experimental study on falling film evaporation heat transfer outside a horizontal tube in refrigeration system

Experimental study on falling film evaporation heat transfer outside a horizontal tube in refrigeration system

A new defrosting model for microchannel heat exchanger heat pump system considering the effects of drainage and water retention

Microchannel heat exchangers (MCHX) have been widely used in heat pump systems due to their advantages of higher efficiency and lower refrigerant charge. However, when the MCHX heat pump system works under defrosting conditions, there are problems of poor defrosting performance and long defrosting time. To study the transient characteristics of the MCHX heat pump system during defrosting, a new defrosting model was developed. The defrosting process was divided into five stages based on the variation characteristics of the frost thickness and the water film. The drainage stage was first proposed in the defrosting model to consider the influence of melted frost. In addition, the impact of retained water was also assessed in the dry heating stage. The deviation of the model and experimental data is within the acceptable range, and the transient characteristics can be accurately predicted. The visualization of the frost melt showed that defrosting was an uneven process from the top down, and the frost layer was almost completely melted at 250 s. In this study, indoor air supplied the most energy at 68.8 %. Furthermore, melting frost consumed the largest amount of energy at 33.7 %, and heating ambient air consumed the second largest amount of energy at 29.1 %. Metal energy storage (MES) had a negative impact of −7.5 % on defrosting efficiency due to a large amount of energy required to heat MCHX. Moreover, the negative influence of frost melt water and retained water on defrosting efficiency was −9.5 % and −1.9 %, respectively. It can be concluded that the key measure to improve the defrosting performance of MCHX is to reduce the effect of melted frost. This work can provide helpful insights into the defrosting simulation model development of MCHX and guide defrosting strategy optimization.

Multi-criteria refrigerant screening and performance optimization comparison of a basic and composition-adjustable dual cooling source system

Climate variability and staff mobility have exacerbated the vulnerability of the indoor environment, which calls for air-conditioning units capable of adapting to the active regulation demand of the changing heat and humidity loads. The identification of the refrigerant constitutes an essential sector of the air-conditioning system design. A composition-adjustable dual cooling source (CADCS) chiller has been proposed utilizing the characteristics of inefficient condensation of the non-azeotropic mixture. Separated flows of the working fluid with flexible mass fraction and flow rate respectively treat the waste heat and moisture. Multi-criteria screening mechanism for the working fluid is established involving: i) application field. The critical temperature is better restricted within 300 K to 400 K for application in air-conditioning. ii) environmental impact. The GWP of the candidate cannot exceed 800. iii) cycle architecture adaptability. The boiling point difference preferably exceeds 20 K. iv) liquid separation potential. The obvious temperature glide and substantial separation range allow for the integration of liquid separation technology. Thermodynamic performance optimization indicates that propane/isobutane outperforms all the candidates at a mass fraction of 0.5:0.5 characterized by obvious temperature glide and close to temperature change of the heat transfer medium. The maximum coefficient of performance (COP) is found to be up to 5.2 for the BDCS cycle and 4.42 during separation at vapor quality 0.436 for the CADCS cycle. The exergy loss of the evaporator is reduced by 17.1 %-73.7 % while the exergy efficiency is improved by 3 %-59.7 % due to temperature match refinement in the CADCS cycle. The refrigerant charge in the CADCS cycle can be saved by 5.54 %-15 %. The accumulating waste heat demands a lower vapor quality during separation, while the moisture load barely exerts an effect. Moreover, the effect of the subcooling degree on the cycle performance is analyzed and suggested at 1 °C. The CADCS cycle constitutes a promising prospect of dynamic treatment for thermal and humidity load in the air-conditioning room due to its flexible function and improved heat transfer match.

Performance analysis of automotive air conditioning systems with electric compressors using R1234yf refrigerant: Insights into power consumption, cooling capacity, and energy efficiency

R1234yf, a low global warming potential (GWP) refrigerant, offers a promising alternative to traditional refrigerants like R134a. This study analyzes automotive air conditioning systems (AAC) equipped with electric compressors and utilizing R1234yf refrigerant. The interrelationships between refrigerant charge, compressor speed, power consumption, cooling capacity, and energy efficiency are examined. The results show that increasing refrigerant charge and compressor speed leads to higher power consumption due to increased compressor work. However, higher refrigerant charges and compressor speeds improve cooling capacity in line with heat transfer principles. As refrigerant charge and compressor speed increase, the energy efficiency, measured by the Coefficient of Performance (COP), tends to decrease, indicating a trade-off between cooling capacity and energy efficiency. Optimizing refrigerant charge and compressor speed is crucial to strike a balance between cooling performance and energy efficiency. R134a outperforms R1234yf, with an average percent difference in COP approximately 25% higher at all compressor speeds. This study contributes to the understanding of AAC system performance and guides the development of energy-efficient automotive air conditioning. Future research can further explore system components and conditions to enhance energy efficiency and advance air conditioning technology.