Refrigerant Charge Research Articles

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.

The utilizability of non-flammable R471A with low-GWP in air-conditioning systems

<p class="15">The utilizability of non-flammable refrigerant R471A with low-GWP is theoretically investigated in an air-conditioning system. In this context, R410A, R32, and R471A are compared for the evaporation temperatures of 4, 8 and 12 ℃ with the condenser temperatures of 40 and 50 ℃. The results indicate that both the mass flow rate and power consumption of R471A are higher compared to R410A and R32. Although COP of R471A is determined to be smaller than R410A and R32 about by 19% and 22%, R471A can satisfy the restrictions for air-conditioning systems due to its considerable low-GWP compared to R410A and R32 (GWP of R471A is lower by 78% and 93% in comparison with R32 and R410A, respectively). Hence, it should be possible to suppress global warming through the reduction of carbon emissions as a result of using R471A in these systems<span style="font-family: 'Times New Roman';">.</span> Additionally, since R471A is non-flammable, it can be safely used for systems requiring a high amount of refrigerant charge without violating the restrictions.</p>

A novel control method for the automotive CO2 heat pumps under inappropriate refrigerant charge conditions

CO2 heat pumps are increasingly widely used in automotive air conditioning, and the demand for refrigerant charge varies greatly under different modes and operation conditions. However, due to the limited space in vehicles, the accumulator cannot fully meet the refrigerant balance requirements for the variable operating conditions, and states of inappropriate refrigerant charge were frequently observed. To enhance system performance and safety under inappropriate charge conditions, an experimental setup and a mathematical model with a maximum error of 6 % were established to investigate the operating characteristics under inappropriate charge conditions. An investigation into the interplay among discharge pressure, the appropriate refrigerant charge range, and refrigerant distribution was conducted. It elucidated how refrigerant charging states (undercharged, adequately charged, or overcharged) manifest in terms of refrigerant distribution and optimal discharge pressure. A novel control method based on refrigerant distribution regulation has been proposed. The proposed control logic could increase the system IPLV by 36.8 % when the refrigerant charge deviates from the appropriate range by 12.12 %, and the greater the dysregulation in the refrigerant charge, the greater the improvement. This control logic would be more enhanced if dysregulation was considered.

Influence on the Energy Conservation and Green Environment R152A Refrigeration with Various Nanorefrigerants

Global Warming Potential (GWP) has proven to be just as critical in determining a possible coolant in recent years as Ozone Depletion Potential (ODP). By lowering the refrigerant charge and enhancing the coolant containment systems, R152A emissions are now aggressively reduced. The option to use the R152A device must be discussed due to concerns about its global warming potential. Disperse the specified quantities of nanoparticles in the compressor oil using a magnetic stirrer for two hours, and then ultrasonic dissolve for four hours to prepare the necessary volume fractions. The experiments showed a performance improvement using CuOs with 0.5% volume fractions with a base refrigerant such as R152A. Experimental results from three different nanoparticles, such as CuO, ZnO and Al2O3, indicate strong miscibility of the nano-CuO lubricant and an increase in lubricity oil to two nanoparticles.

Experimental performance analysis of evacuated tube type direct-expansion solar-assisted heat pump system

ABSTRACT The direct-expansion solar-assisted heat pump (DX-SAHP) have proven to be one of the strategies in reducing energy consuming for domestic hot water supply. The poor pressure resistance of the collector, high heat loss from radiation for the traditional bare-plate type DX-SAHP limits its popularization and application. To solve this problem, a DX-SAHP system using evacuated tube type collector-evaporator was proposed in this post. System optimization can not only reduce operating costs, but also results in energy savings. Thus, a DX-SAHP prototype was established and tested under various running conditions to obtain the optimal running parameters. Based on experimental data, the impacts of refrigerant charge, solar radiation intensity, and ambient temperature on the performances of evacuated tube type DX-SAHP system are investigated and evaluated. The outcome indicates that this system coefficient of performance (COP) increases by 73.4% with the decrease of charge amount of refrigerant in the range of 5.66–6.67 kg. And, the average collector efficiency is 0.71 with a refrigerant charge of 5.66 kg. And, the optimal COP of this presented system is 5.27 when an ambient temperature, solar radiation intensity, and refrigerant charge are 26.3°C, 954.37 , and 5.56 kg, respectively.

Performance of hybrid electric vehicle air-conditioning using SiO2/POE nanolubricant

The automobile air-conditioning (AAC) system uses the most energy among all auxiliary components in hybrid electric vehicles (HEV) with an electrically-driven compressor (AAC-EDC). Incorporating nanolubricant improves AAC-EDC performance and reduces battery and AAC component size. This study aims to assess the performance of an AAC-EDC system by employing SiO2/POE nanolubricants. The performance of the AAC-EDC was examined using SiO2/POE with a volume concentration of up to 0.01 %, a refrigerant charge of 120–160 g, and a compressor speed of 1200–3840 rpm. The performance of the AAC system was measured by its heat absorption, compressor work, coefficient of performance (COP), and EDC power consumption. The SiO2/POE was stable for 30 days with a zeta potential of 102.5 mV. The SiO2/POE demonstrated superior performance over the pure POE lubricants. The compressor work and power consumption were reduced to 26.17 % and 11.97 %, respectively. The lowest expansion valve discharge temperature of 9.6 °C was achieved at 160 g refrigerant charge and compressor speed of 3840 rpm. The nanolubricant attained the highest COP of 3.36 at 1860 rpm speed and 160 g charge. The SiO2/POE nanolubricant with a volume concentration of 0.01 % is highly recommended for optimal performance in the AAC-EDC system.

Tube bundle evaporators with LGWP refrigerant R1234ze(E)

With new low-GWP HFO refrigerants, the heat transfer performances and methods for decreasing system refrigerant inventory are receiving increasing interest. In shell-and-tube heat exchangers, refrigerant distribution via pressurized liquid spray has the potential for high heat transfer performance while reducing refrigerant charge. However, no published studies have investigated LGWP refrigerants with spray evaporation on tube bundles. A test apparatus was constructed to measure the shell-side heat transfer coefficients of R1234ze(E) on bundles of tubes with two different enhanced-surface types and in two different bundle geometries at various refrigerant saturation temperatures. The results showed strong dependence on refrigerant properties, tube heat flux, enhanced-surface type, bundle geometry, and refrigerant inlet subcooling. The bundle heat transfer coefficients of R1234ze(E) were similar to that of R134a in the same test setup, usually within ±15% for similar conditions. In both cases, they first increased with the heat flux until a local maximum value was achieved. A localized dryout of the tubes at the bottom of the bundle penalized the overall bundle heat transfer coefficient at very high heat flux. For the condensing surface, bundle heat transfer coefficients rarely exceeded 10 kW/m2-K, whereas values in excess of 30 kW/m2-K were sometimes seen for the evaporating surface.

Using Charge Determination Design of Experiments to Develop A Refrigerant Charge Health Status Model for Heat Pump Systems

Refrigerant based heat pump systems are becoming an integral system in electric vehicle architectures due to their high efficiencies in providing heating and cooling to people and components within the car. An important component in heat pump systems that determines optimal efficiency is the amount of refrigerant. As such, the capability to model refrigerant charge helps quantify the health status of the heat pump system, whereby the lack or over abundance of refrigerant in a heat pump refrigerant system leads to various other component failures, e.g., liquid slugging, compressor overheating, material fatigue in heat exchanger, and degraded/stuck expansion valves. In designing a heat pump system, engineers need to perform a set of design of experiments to determine an optimal refrigerant charge based on a set of performance metrics in the presence of certain noise factors. This optimal refrigerant charge provides conditions where the heat pump system operates efficiently in both heating and cooling, in addition to facilitating operational conditions that will not lead to secondary component degradation or damage. The search for optimal refrigerant charge is classified as refrigerant charge determination, whereby engineers incrementally increase the refrigerant in the heat pump system in operation of heating/cooling and collect data about performance metrics. Some of the key performance metrics used to determine efficiency of a heat pump system include i) compressor inlet superheat temperature, ii) condenser outlet subcool temperature, iii) compressor high side pressure, iv) compressor low side pressure, v) condenser outlet pressure, and vi) condenser quality estimate. Furthermore, this process follows design of experiments concepts and is performed for both heating and cooling modes of operation. In this paper, we leverage refrigerant charge determination as a training data source to develop refrigerant charge models, where several performance metrics are health indicators used as model inputs and the amount of refrigerant added to the heat pump system are ground truth refrigerant charges used as model outputs. In this paper we develop regression models to estimate the total refrigerant charge, which is used to classify different health states of refrigerant based on levels of performance degradation corresponding to specific refrigerant charge thresholds. We trained a robust linear regression model using this charge determination data and found that the worst case estimation error was less than 10% with respect to the refrigerant charge grouth truth.

Temperature and Pressure Drop Analysis of Automobile Minichannel Condenser using CFD

Refrigeration and air conditioning plays a vital role in domestic and industrial heating, cooling, refrigerating and ventilation but they are contributing to ozone layer depletion and global warming due to unfriendly refrigerants and consume 33% of the world energy. The condenser is an important component of the vapor compression system which contained 30% of the refrigerant charge. The versatile one ton of refrigeration system is designed, developed for testing minichannel condenser for different condenser temperature and pressure by providing artificial condenser compartment with three air heaters of 2.2 kW capacity each with a multispeed condenser fan for controlling air velocity. Thus, the condensation temperature is reduced by 2 to 3°C due to its special geometry, passes provided, efficient cooling and the coefficient of performance increased by 10 to 15% for condensation temperature varying from 40 to 55°C whereas evaporation temperature varies from -10 to +15°C. Computational Fluid Dynamics (CFD) simulation for different sections of the minichannel condenser such as a single minichannel, single tube with 10 minichannels, first, second, third, fourth passes with varying tubes and entire condenser with all four passes for different inlet and exit temperature are performed using ANSYS FLUENT-20 CFD turbulence models and validated with the experimental results. The pressure and temperature counters for all the sections are studied and plotted. It is found that the temperature difference between experimental and CFD results are within ±15% for all the simulations along the condenser.

Numerical simulation of flow characteristics of falling-film evaporation of R32/R134a non-azeotropic refrigerant outside a horizontal tube

Horizontal-tube falling-film evaporator is regarded as an effective alternative to full-liquid evaporator because of its higher heat transfer coefficient and lower refrigerant charge. In the process of falling-film evaporation, the thin liquid film thickness (δ) is an important parameter for characterizing the hydrodynamics, and accurate prediction of δ can effectively prevent the reduction in heat transfer efficiency caused by local wall dryout. In this study, non-azeotropic refrigerant R32/R134a was taken as the research object. By incorporating the multi-component phase change model and contact angle model into the governing equations, a two-dimensional numerical model of falling-film evaporation outside a horizontal circular tube was established. The effects of the spray height (H), tube diameter (d), Reynolds number (Re), inlet temperature (Tinlet), and mass fraction of R32 in the liquid-phase mixture (MR32_liquid) on δ were analyzed under sheet flow. The results show that an increase in Tinlet, H, and d is favorable for increasing the average δ (δave), whereas an increase in MR32_liquid and Re leads to a reduction in δave. Besides, the decreasing rate of the δave decreases gradually as H and d increase. When H is 4 mm, the local δ (δlocal) first decreases and then increases as the circumferential angle (Φ) increases. When H ranges from 6 mm to 13 mm, as Φ increases, δlocal first increases slightly, then decreases, and finally increases significantly near the wake region. The δlocal of a larger tube diameter is thicker than that of a smaller tube diameter near the impact region, whereas in the subsequent regions, the δlocal of a larger tube diameter is thinner than that of a smaller tube diameter. The minimum δlocal occurs at Φ between 130° and 140°, and with an increase in H and d, Φ corresponding to the minimum δlocal decreases.

Operation Parameters Variation of Air Source Heat Pump According to the Outdoor Temperature

Air source heat pumps (ASHP), known as energy efficient systems, emerge as environmentally friendly and economical solutions for building heating. Unfortunately, the operating parameters of ASHPs and accordingly their performance are directly affected by the daily and seasonal temperature changes of the outside air. In this study, change in operation parameters of a selected ASHP with 3.4kW nominal heating capacity is investigated with a calculation method based on the logarithmic mean temperature difference, between -10°C to 18°C outdoor temperature range with 2°C steps, at constant compressor power. The study is verified with published COP data of the manufacturer. Results are shared with graphs that give the variation of refrigerant evaporation and condensation temperature and pressure, COP, and condenser heating load according to outdoor air temperature. A raise from -10°C to 18°C in outdoor temperature, increases the COP value from 3.38 to 5.49. Detection of the increase in evaporation pressure in parallel with the outdoor temperature may allow easy control of the refrigerant charge level with a manometer. This study can be a useful guide for researchers who aim to determine the outdoor temperature dependent operating parameters of an ASHP and for technical personnel who need this information in fields.

Performance enhancement and optimization of residential air conditioning system in response to the novel FAl2O3-POE nanolubricant adoption

This paper aims to evaluate residential air conditioning systems' performance enhancement and optimization by adopting a novel functionalized Al2O3 (FAl2O3)–Polyolester (POE) nanolubricant. Comprehensive discussions were conducted on key performance parameters, including heat absorption, compressor work, cooling capacity, coefficient of performance (COP), and power consumption. Novel FAl2O3 nanoparticles were dispersed into the POE lubricant using a two-step method. The findings reveal that FAl2O3–POE nanolubricant exhibits superior heat absorption compared to pure POE. Heat absorption decreases with an increased initial refrigerant charge, while cooling capacity performance improves with an increased initial refrigerant charge. The COP shows an increasing trend at all concentrations of FAl2O3–POE nanolubricant when operating with R32. FAl2O3–POE/R32 demonstrates an enhanced range of 3.12%–32.26% for COP. The results suggest that applying novel FAl2O3–POE nanolubricant with R32 can reduce electrical power consumption by 13.79%–19.35%. The central composite design (CCD) offers an optimal condition for FAl2O3–POE nanolubricant with a concentration of 0.11 vol%, an initial refrigerant charge of 0.442 kg, resulting in a COP of 3.982, a standard error of 0.019, and a desirability of 1.0.

Numerical simulation of heat transfer characteristics of falling-film evaporation of R32/R134a non-azeotropic refrigerant outside a horizontal tube

In response to the restrictions of the international community on the utilization of refrigerants with high GWP, the replacement of high-GWP refrigerants with non-azeotropic refrigerants and reduction in refrigerant charge have gradually become important research topics in academia. In this study, based on the VOF method, a 2D model of a sheet flow pattern was developed by considering the thermophysical properties and multicomponent phase change of a mixture. The falling-film evaporation of a non-azeotropic refrigerant composed of R32 and R134a outside a horizontal tube was numerically simulated. The effects of the spray height (H), tube diameter (d), inlet temperature (Tinlet), Reynolds number (Re), heat flux (q), and mass fraction of R32 in the liquid-phase mixture (MR32_liquid) on the heat transfer coefficient (HTC) were studied. The results indicate that with the increase of circumferential angle (Φ), the local HTC exhibits a trend of decreasing, increasing, decreasing, and increasing in sequence. The largest contribution to the increase in the average HTC comes from the impact and fully developed regions. An increase in H, Tinlet, and MR32_liquid is beneficial to the expansion of the fully developed region, whereas a decrease in d leads to expansion of the fully developed region. An increase in Re does not affect the extent of the fully developed region. The increase in H, Re, Tinlet, and MR32_liquid increases the average HTC, but the effect of Tinlet is not significant. Under the conditions of d = 24 mm, H = 13 mm, Re = 4000, MR32_liquid = 0.5, and q = 10 kW/m2, as the inlet temperature increases from 243.15 K to 283.15 K, the average HTC increases by 2.5%. An increase in q does not affect the average HTC, whereas an increase in d does not improve the average HTC.

A Comparative Study of R134a and Propane (R290) as Refrigerants in Heat Pump Water Heaters

In the context of decarbonization efforts, heat pump water heaters (HPWHs) offer an attractive solution over conventional electric resistance type hot water systems due to their 2-3 times higher efficiency. However, the high manufacturing costs and taxes associated with using hydrofluorocarbon (HFC) refrigerant make HPWHs expensive. As a means to tackle this issue, this paper explores the use of propane (R290) as a refrigerant in HPWHs. The study involves an experimental comparison of R290 and R134a, with refrigerant charges optimized for the unit at different ambient temperatures. This current work demonstrates that R290 achieves a 10% improvement in coefficient of performance (COP) at ambient temperatures beyond 20°C. However, at 10°C ambient temperature, the study shows that R290 offers no advantage over R134a, and the COP is lower. These results indicate that the compressor is the largest source of inefficiency, and this aligns well with experimental results on system performance. Additionally, simulation tests using compressors designed for R290 did not predict better COP values than the test unit. Overall, the study suggests that R290 is a viable refrigerant option for HPWHs, but further research is necessary to optimize it’s use.

Theoretical and experimental investigation on the effects of internal heat exchangers on a reversible automobile R744 air-conditioning system under various operating conditions

This paper presents a theoretical cycle analysis and an experimental study of the effects of internal heat exchangers (IHXs) on reversible automobile R744 air conditioning systems. The cycle analysis shows that the system efficiency benefits most with a high-efficiency IHX in the transcritical mode where the gas cooler exit temperature is high, while the IHX generally has a trivial or even negative effect on the system performance in the subcritical mode. The experimental results reveal that with the IHX, the optimal refrigerant charge is reduced from 1450 g to 1300 g, and the optimal high-side pressure is reduced by 0.24 to 0.67 MPa. Moreover, for both basic and IHX systems, it is experimentally confirmed that one linear control equation can relate the COP-maximizing high-side pressure with the gas-cooler/condenser exit temperature and functions well in both trans- and subcritical modes. That reveals the potential of combing the high-side pressure control in the transcritical mode and the subcooling control in the subcritical mode. Agreed with the theoretical analysis, the IHX has a negligible effect on COP in the subcritical mode in the experiments, while it improves the system efficiency by up to 13.8% in the transcritical mode. The highest benefit is gained in the pull-down condition that has high ambient and cabin temperatures and requires fast cooling.

Improved convolutional neural network chiller early fault diagnosis by gradient-based feature-level model interpretation and feature learning

For chillers, fault diagnosis (FD) is important for maintaining system reliability and performance. Deep learning methods, such as convolutional neural network (CNN), have been widely studied for chiller FD for its more significant diagnosis accuracy. But CNN model with deep layers and complex structures is black-box and difficult to interpret, which would greatly limit its practical FD applications for chillers. Traditional CNN model interpretation method may be not sensitive to interpret the chillers systematic faults especially at their early stages. Hence, to further obtain better interpretation of the CNN FD model, this study proposed a high-sensitivity gradient-based interpretation method. The proposed method adopts a softsign-forward-ReLU-backward manner to interpret the CNN model from the prospective of fault-discriminative feature, which localizes the fault-related feature variables and visualizing the diagnosis criteria for the CNN identified faults. The ASHRAE research project 1043 (RP-1043) chiller fault dataset was used to validate the proposed model interpretation and explanation method with higher feature-level sensitivity for the incipient fault. Based on the feature-level explanation and feature learning results, different feature combinations were investigated to improve diagnosis accuracy of some early-stage faults. If only small sizes of training data were available for modelling, 17 fault-related features were selected from the original 64 features to re-develop the CNN model and achieved diagnosis accuracy improvement of 9% for the early-stage improper refrigerant charge faults at most.

Experimental study on performance improvement of a household refrigerator with a flying-wing evaporator

In order to improve the performance of a household refrigerator, a flying-wing evaporator (FWE) is to replace the original finned tube evaporator (FTE). Different from the FTE, the fins of the FWE are formed directly on the tube by shoveling movement. Therefore, the FWE has high efficient heat transfer performance due to no thermal contact resistance between the tubes and the fins. According to different combinations of fin pitch and number of tube rows, three different structures of FWE are designed and tested in comparison with the original FTE on a double-door household refrigerator. The results show that the FWE shortens the cooling duration by 0.32 h (9.3%) and reduces the annual energy consumption by 4.28% with a 25% reduction in volume and a 13.5% reduction in refrigerant charge. This study proves that applying a FWE into a household refrigerator instead of the traditional FTE is one of the effective ways to decrease the volume of evaporator, reduce the energy consumption of refrigerator and enhance the effect of food preservation.

Integration of booster heat pumps in ultra-low temperature district heating network: Prototype demonstration and refrigerant charge investigation

Decentral booster heat pumps (BHPs) integrated in ultra-low temperature district heating (ULTDH) systems are deemed a sustainable solution for low-carbon building systems. The performance of BHPs is critical for the implementation of ULTDH systems. In this study, we experimentally investigate the effect of refrigerant charge on temperature, pressure, system coefficient of performance (COP), and heating capacity to evaluate the operability and sensitivity of ULTDH. A performance-guaranteed range of refrigerant charge is proposed to ensure the feasibility of the system. We also analyse the component-level exergy destruction and the system-level exergetic efficiency of a BHP prototype. The exergetic efficiencies range from 24.9 % to 33.4 % under operational conditions for ULTDH. The condenser and evaporator's exergy destruction is influenced by the temperature profiles on both sides, suggesting the potential to improve BHP performance by tailoring operating parameters. Additionally, the return water temperature significantly affects the system COP when the domestic hot water supply temperature is fixed. Within the allowable range of return water temperature, BHP operation with high evaporator outlet water temperature can improve the overall efficiency of the ULTDH system.

Environmental impact assessment of an air-to-water heat pump through the expanded total equivalent warming impact index based on experimental data

The Total Equivalent Warming Impact (TEWI) index is conventionally used to evaluate emissions from heating, ventilation, air conditioning and refrigeration (HVAC&R) systems. However, a more comprehensive indicator, the Expanded Total Equivalent Warming Impact (ETEWI), has been proposed to overcome the limits of TEWI index and to consider additional environmental impacts such as the effects of urban heat island and the natural gas losses along high-pressure pipelines supplying gaseous fuel to natural gas-fired power plants. In this study, TEWI and ETEWI metrics are applied to an air-to-water electric heat pump (EHP) serving a university building in Benevento (Southern Italy). Real data on EHP electricity consumption have been derived from the entire building's electric load and compared to measured data. ETEWI index has been estimated in two scenarios, one considering the impact of refrigerant charge variation on the performance of the EHP and its environmental impact and the other disregarding it. Additionally, carbon dioxide emission factors for electricity production have been forecasted from 2021 to 2033 to determine the indirect term of ETEWI index. Over the lifetime of the EHP, ETEWI increases by 4.8% compared to TEWI when the variation of refrigerant charge level is not considered. However, this percentage growth is equal to 6.5% when the impact of refrigerant charge change is accounted too. In the latter scenario, the indirect term of ETEWI decreases from 22.7 tCO2 in 2015 to 12.0 tCO2 in 2033 when the forecast of the carbon dioxide emission factors for electricity production is taken into account.

Development and demonstration of a method to detect refrigerant charge level for variable refrigerant volume systems

Unlike traditional direct expansion systems, variable refrigerant flow (VRF) systems have longer routing, more complicated setup, and sophisticated controls and require much more refrigerant for proper operation. Proper refrigerant charge becomes more critical to their operations. Intensive studies have investigated refrigerant charge faults for VRF systems. Due to the daunting complexity, few studies use knowledge-based fault detection and diagnosis (FDD) methods. Most of them use data-driven FDD methods to study this fault. Although they seem promising, these methods can only handle single faults and are not scalable or interpretable. This paper proposes a decoupling-based FDD method to detect and diagnose improper refrigerant charge in VRF systems. This method was originally proposed by our previous work for rooftop units (RTUs) and split systems, which has been tested and validated by extensive studies. Due to the differences between VRF and RTU, the original method – virtual refrigerant charge sensor (VRC) for VRF is modified, analyzed, and investigated in detail. Data filter criteria were implemented to eliminate noisy data. The modified VRC, when combined with a data filter, was tested on two systems in the field. The results demonstrated its effectiveness in detecting an undercharged system, specifically a 30 % undercharge.