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Effect of refrigerant charge on the performance of air conditioning systems
International Journal of Energy Research
Abstract
An air conditioning system operates in an optimal condition if the system is fully charged with a specified amount of refrigerant. Poor field maintenance or refrigerant leakage causes low level of charge resulting in a lower thermal performance and higher operating cost. An experimental investigation was conducted to study the effect of low charge level of R-22 on the performance of a 3-ton residential air conditioning system. The experimental results show that if a system is undercharged to 90 per cent then the effect is small: a 3.5 per cent reduction in cooling capacity and a 2 per cent increase in the coefficient of performance (COP). However, the system performance suffers serious degradation if the level of charge drops below 80 per cent. An ice layer formed on the outer surface of the cooling coil impedes the heat transfer between the warm air and cold refrigerant vapour. An economic analysis shows that the cost of properly charging an under-charged system which is at an 85 per cent charge level, can pay for itself in savings in a short period of 3–4 months. Copyright © 2001 John Wiley & Sons, Ltd.
... 11 In addition, refrigerant overcharging increases the compressor power consumption that consequently decreases Energy Efficiency Ratio (EER). 12,13 Accordingly, determining the optimal refrigerant charge can reduce the electrical energy consumption and therefore the EER of refrigeration systems will be increased. Many studies have reported using alternative refrigerants, finding optimal operating conditions and their effects on the EER and the cooling capacity in refrigerating systems. ...
... In order to investigate the replacement of R22 with R417A and its effects on optimal operating conditions of refrigeration system, the above-mentioned experimental procedure was carried out for refrigerants overcharging and undercharging condition. Then the thermodynamic properties of R22 and R417A required for calculating Equations (1)- (12) were obtained using the thermodynamic tables and diagrams. Figure 5a,b gives temperature-entropy diagrams of experimental results for tested mass charges of R22 and R417A, respectively. ...
In this paper, the optimal refrigerant mass charge amount of R417A, as a substitute for R22, was experimentally investigated in a split‐type air‐conditioner with no changes in system configuration. Experiments were conducted for both refrigerants over a range of mass charge from 500 to 850 g in a 12,000 Btuh⁻¹ split air‐conditioner as the case study which is a conventional refrigeration system in residential sector of Iran. In order to study the effect of refrigerant mass charge on performance of refrigeration cycle, energy and exergy analysis were performed to determine cooling capacity, energy efficiency ratio (EER) and exergy efficiency. Results showed that the maximum EER for R22 and R417A are 2.48 and 2.41, and the maximum exergy efficiencies obtained for R22 and R417A are around 7.3% and 7%, respectively. Based on both EER and exergy efficiency, the optimum mass charge for R22 and R417A refrigerants are around 640 g and 650 g, respectively. In addition, it was found that under optimal charge conditions, the cooling capacity, EER and exergy efficiency of the system while working with R417A are lower than R22, just by 2.5%, 3%, and 4.5% respectively. Comparison results indicate that R417A can be considered as a suitable substitute for R22, which can almost provide the same performance without need to change the system components.
... For such system the COP was relatively insensitive to refrigerant charge -for R407C system maximum reduction of COP at charge conditions from -20% to +20% of full charge was 3.6%. The effect of refrigerant charge level on airconditioning systems was also examined by Goswami et al. [6]. The authors concluded that charge level has a significant effect on the performance of air-conditioning systems at levels below 80% of normal. ...
... The liquid subcooling is a large contributor to total charge since the subcooling region holds significant fraction of the total charge inventory. Experimental proof for this statement may be found in various sources, for example in [2][3][4][5][6][7]. In these works different systems were analyzed but similar conclusions were obtained. ...
This paper presents a review of refrigerant charge studies in a refrigerating system - sensitivity of system performance to charge levels, relationship of charge with superheat and subcooling, methodologies of charge measurement and calculation, existing charge reduction strategies and their applicability to transport refrigerating systems. For the low charge system one should not optimize the charge, but rather just ensure complete condensation. Such system could comprise of high pressure receiver, microchannel condenser and DX evaporator with TXV or EEV expansion device.
... Consequently, the compressor work increases, resulting to direct GHG emissions, significant energy loss due to long hours of operation at undercharged condition, and poor quality of stored products in cold storage (Tassou and Grace, 2005;Jain et al., 2019). According to experimental study by Goswami et al., (2001), 10% decrease in refrigerant level reduces the cooling capacity by 3.5%. Nevertheless, at over 20% charge losses, the system suffers serious degradation of perf ormance. ...
The purpose of this study is to investigate the challenges, needs, and the energy
savings resulting from energy efficient cooling opportunities in developing countries.
Moreover, it is aimed to identify the common leakage source in Refrigeration and Air-Conditioning (RAC) systems that are responsible for energy losses and refrigerant emissions. For doing so, a combined method of comprehensive desktop study and structured questionnaire survey methods were used. The study found that there are technical, technological, commercial, and policy and regulatory challenges ahead of transformation to energy efficient cooling industry in developing countries. The study suggests that adoption of best available technology (BAT) options through cooling market transformation along with wide adoption of Minimum Energy Performance Standard (MEPS) has up to 60% energy savings potential, while non-structured initiatives such as stringent Minimum Energy Performance Standards (MEPS) and accelerated energy efficiency programs may contribute in range between 43-45% energy saving potentials. The study results also indicates that good servicing, better monitoring, and maintenance have energy savings potential in range between 15-20 %. Thus, the study emphasizes the importance of optimization, monitoring, maintenance, and refrigerant leakage prevention as easy and at hand options in both existing RAC systems and new installations. It has been found that the common leakage areas in RAC systems are the flare and brazing joints which are areas that need particular attention during maintenance service. The study also identified three preventive pathways for minimizing refrigerant leakage which are adherence to best practices, strengthening standards, regulations, and codes, and the development and utilization of alternative joining methods in RAC systems.
... It has been found that a very high charge only affects the condenser, reducing the condensation area. Goswani et al.'s work 12 showed that a 10% reduction in total charge results in a 3.5% reduction in refrigeration capacity and a 2% increase in COP, compared to the charge giving the maximum COP. Kim et al. 13 found that COP is maximum when both single and cascade heat pump systems have optimal charge, resulting in reduced refrigerant leakage, reduced performance, and deterioration in thermal comfort. ...
With the increase in industrialization and the number of people and buildings, the need for refrigeration systems has also increased. Maintenance of these systems, malfunctions and their late detection cause time and cost problems. Therefore, in this study, a machine learning application is recommended to diagnose the refrigerant undercharge and refrigerant overcharge faults that may occur in the refrigeration system by using infrared images. Firstly, infrared images obtained from normal charge, undercharge and overcharge situations in the refrigeration system, are passed through the two-dimensional discrete wavelet transform (2D-DWT) and the images are decomposed. Then, statistical texture features from the original input images are obtained by separating infrared images. The dimensionality of the extracted features is reduced using the principal component analysis (PCA) and the ReliefF (RF) algorithm. Finally, these selected features are applied to the K nearest neighbor (k-NN), naive Bayes algorithm (NBA), decision tree (DT), and cascade forward neural network (CFNN) classifiers. It has been found that RF-based feature selection is useful in obtaining the optimal feature vector. The classification results revealed that CFNN outperforms k-NN, NBA, and DT. Compared to traditional electrical measurements and fault detection methods, it has been shown that the recommended system is feasible due to its features such as ease of use, remote measurement, and self-adaptive recognition.
... Numerous studies (e.g. Farzad, 1990;O'Neal and Farzad, 1990;Farzad andO'Neal, 1991, 1993;Neal and O'Neal, 1992;Goswami et al., 2001;Harms et al., 2003;Dooley, 2004;Kim et al., 2006Kim et al., , 2009Payne et al., 2009;Shen et al., 2006Shen et al., , 2009Raj and Lal, 2010;Kim and Braun, 2012;Cho et al., 2014;Domanski et al., 2014;Du et al., 2016;Qureshi and Zubair, 2014;Hu et al,.2021a;Hu and Yuill, 2022a) have investigated fault impacts on split residential air conditioning systems. However, few (Shen et al., 2011;Palmiter et al., 2011;Hu et al,.2021b, ...
Operating faults that degrade performance of residential airconditioning systems can be caused by problems during installation, and are believed to be quite common. When a problem occurs during installation, potentially from a lack of training or care by a technician, difficult work conditions, etc., it is likely that several faults can occur simultaneously. Many studies have investigated single-fault impacts on system performance during the past three decades. However, few of them studied simultaneous fault impacts, especially for more than two simultaneous faults. Therefore, the current study investigated four common installation fault impacts, both singly and in combination (up to 4 at a time), on the performance of a high-efficiency split heat pump system equipped with a thermostatic expansion valve and a standard-efficiency air conditioner equipped with a fixed orifice expansion device in cooling mode. These four faults are: improper evaporator airflow, improper refrigerant charge, liquid line restrictions, and the presence of non-condensable gas in the refrigerant. The fault intensities for each fault are varied, with limits selected based on practical considerations, and are imposed similarly on each system. The results are compared according to fault type and fault intensity imposed. For single faults, the air conditioner performs better than the heat pump when refrigerant overcharge (OC) or low evaporator faults are present. When simultaneous faults are present, the heat pump performs better for almost all fault combinations except for combinations that include OC.
... Fault impacts studies on air conditioning systems are usually carried out in a laboratory environment with a well-controlled indoor and outdoor thermal conditions. Some studies [12,29,13,14,27,15,32,22] investigated single refrigerant charge (CH) fault impacts. For instance, Farzad [12], O'Neal and Farzad [29], Farzad and O'Neal [13,14], and Neal and O'Neal [27] investigated CH faults on a 3-ton split residential air conditioner using R22 with three different metering devices: a thermostatic expansion valve (TXV), and two types of fixed orifice expansion devices (FXO). ...
Split system air conditioners are widely used to cool residential buildings, because of their low cost and simplicity. However, their efficiency is impacted by installation faults, which include: improper refrigerant charge (undercharge or overcharge), improper evaporator airflow, liquid line restrictions (LL), and the presence of non-condensable gas (NC) in the refrigerant. No known previously published research has studied the effect of these four faults on a system equipped with a microtube condenser, which has smaller tube size than a traditional condenser and therefore holds less refrigerant charge, but has a different configuration than a microchannel. Furthermore, very few have studied the impacts of LL and NC. This paper describes laboratory fault tests of a microtube-equipped system, compares the fault impacts with those of a traditional system, and considers the characteristic fault features. The tested system uses R-410A refrigerant and has a scroll compressor, a fixed orifice expansion device, and two fin-tube heat exchangers. The tests were carried out under steady operation with a range of fault intensities and operating conditions. The microtube system’s performance degradation from faults is similar to systems with traditional heat exchangers, despite the reduced capacity to hold refrigerant charge.
... Improper refrigerant charge (CH), including undercharge (UC) and overcharge (OC), is an important fault that can occur in air conditioning systems. To evaluate the impacts of CH faults on the performance of the system, several laboratory experimental studies (Farzad, 1990;O'Neal and Farzad, 1990;Farzad andO'Neal, 1991, 1993;Neal and O'Neal, 1992;Rossi and Braun, 1997;Breuker and Braun, 1998a, b;Braun, 2000, 2001;Goswami et al., 2001;Harms et al., 2003;Shen et al., 2006Shen et al., , 2009Shen et al., , 2011Kim et al., 2006Kim et al., , 2009Payne et al., 2009;Raj and Lal, 2010;Yoon et al., 2011;Palmiter et al., 2011;Kim and Braun, 2012;Mowris et al., 2012;Cho et al., 2014;Domanski et al., 2014;Du et al., 2016;Hu et al., 2021a, b) have investigated this fault. Mehrabi and Yuill (2017) analyzed the previous studies to generalize the effects of CH faults across systems, and found the effects to be quite homogeneous. ...
The effects of refrigerant charge (CH) faults have been intensively investigated over the past three decades. However, the effect of CH faults in the presence of other faults, like the presence of non-condensable gas (NC), has been seldom studied. The patterns of the effect of CH faults on a system with other faults could be different from that on a fault-free system, which could degrade the performance of fault diagnostic tools and cause improper charging by technicians during installation or service of systems in the field. To address this problem, four common installation faults-improper evaporator airflow (EA), liquid line restrictions (LL), CH, and NC faults were imposed on an 18 SEER residential heat pump with a TXV metering device both individually and simultaneously, and the system was tested in a laboratory. First, the individual impacts of undercharge (UC) and overcharge (OC) on the performance of the system were evaluated under four different operating conditions. Then, the impacts of CH faults in the presence of the other three faults, both singly and in combinations, were examined at one operating condition. Under single CH fault conditions, the cooling capacity decreased for UC faults but was almost unchanged for OC faults, while the COP decreased for both UC and OC faults. In combination with other faults, the trend for UC faults is the same as those for the fault-free system. However, the OC fault can ameliorate the impacts of other faults on capacity, particularly a severe LL fault (LL32). The effect on COP for OC faults depends on fault type and intensity. For example, the COP with an OC fault decreased in the presence of light LL fault (LL22) but increased in the presence of a more severe LL fault (LL32). The variations of indicator variables such as refrigerant temperatures under different fault conditions are also presented.
... The authors presented a thorough review on refrigerant charges in refrigeration systems and the strategies of charge reduction. The majority of cited works leading with the study of refrigerant charge influence on refrigerating, air conditioning and heat pump system's parameters are experimental [41][42][43][44][45][46], with few works using steady-state models [47,48]. Recent works continue to address the same problematic through the development of experimental and numerical studies. ...
In this work, two transient mathematical models are presented for simulating a vapor compression refrigeration system of domestic refrigerator using R134a. One, the thermal model, is based on the application of the first law of thermodynamics and the second, capacitive model, adds the evaluation of the refrigerant mass distribution in the system. An experimental procedure to calculate the thermal conductance and capacity of system components (compressor, condenser, capillary tube, evaporator, cabinet) is presented. Experimental data describing the transient behavior of the refrigeration system are also obtained to validate the simulation procedures. The domestic refrigerator studied is a vertical two compartments refrigerator. The simulation results follow the measured experimental trends and are very satisfactory when compared to the transient and time averaged experimental data. The maximum relative error obtained for simulated temperatures was about 5.65%. Parametric analyses were conducted to identify the influence of refrigerant charge and ambient temperature on the refrigeration system performance. The optimum refrigerant charge has distinct values regarding the operational condition of the system. In the pull-down operation the highest COP is attained for 105g and 140g of refrigerant for transient and the steady-state regimes, respectively. In the on-off operation the optimum refrigerant charges are 105g for transient operation (placing goods inside the compartments) and around 70g to 95g for stationary condition (without goods). Excepting for small refrigerant charges ∼50g, the higher quantity of refrigerant during the entire system operation is in the evaporator. For low refrigerant charges, 50-70g, it is also shown a refrigerant migration between condenser and evaporator under the effects of thermal loads when compressor is turned on. Ambient temperature augmentation by 18°C decreases refrigerator COP without thermal load in 10% and 16% for pull-down and on/off operations, respectively. The presented experimental results are new and can be used by other researchers for validating their own simulation models. The developed models can considerably improve the design of domestic refrigeration systems by manufacturers.
... The refrigerant charge amount is one of the main parameters that affect the performance and energy consumption of heat pumps [4][5][6][7]. When the refrigerant charge exceeds 90% of the rated charge, the effect on the COP and cooling capacity is small. ...
Refrigerant charge faults, which occur frequently, increase the energy loss and may fatally damage the system. Refrigerant leakage is difficult to detect and diagnose until the fault has reached a severe degree. Various techniques have been developed to predict the refrigerant charge amount based on steady-state operation; however, steady-state experiments used to develop prediction models for the refrigerant charge amount are expensive and time-consuming. In this study, a prediction model was established with dynamic experimental data to overcome these deficiencies. The dynamic models for the condensation temperature, degree of subcooling, compressor discharge temperature, and power consumption were developed with a regression support vector machine (r-SVM) model and start-up experimental data. The dynamic models for the condensation temperature and degree of subcooling can predict the distinct start-up characteristics depending on the refrigerant charge amount. Moreover, the estimated root mean square error (RMSE) of the condensation temperature and degree of subcooling of the test data are 0.53 and 0.84°C, respectively. The refrigerant charge is one of the predictors that defines the dynamic characteristics. The refrigerant charge can be estimated by minimizing the RMSE of the predicted values of the dynamic models and experimental data. When the dynamic characteristics of the two predictor variables, “condensation temperature” and “degree of subcooling” are used together, the average prediction error of the test data is 2.54%. The proposed method, which uses the dynamic model during start-up operation, is an effective technique for predicting the refrigerant charge amount.
... A handful of experimental studies have been done. Most commonly they have examined one or two fault types on a particular air conditioner [12,29,13,14,28,15,9,16,8,26,33,[35][36][37]31,21,32], but a few exceptions have studied several faults [34,4,5,2,3,19,20,30,38,27,6,7,10]. Refrigerant charge is the most commonly studied fault, followed by evaporator airflow. ...
Faults are believed to be common in split system air-conditioner and heat pump systems, due to operating degradation or installation problems. Common faults include improper refrigerant charge, reduced evaporator airflow, liquid line restrictions, and the presence of non-condensable gas. Laboratory tests were used to quantify fault impacts on performance of a heat pump system, and impacts on indicator variables such as refrigerant temperatures and pressures. This paper describes a large set of laboratory tests implemented on a high efficiency heat pump operating in cooling mode. This system uses R-410A refrigerant and has a rotary compressor, TXV, two accumulators, and a compensator. A small number of previous experimental studies have been done previously to study the effects of some operating faults, but none has examined a modern system with these components. The tests were conducted with a range of fault intensities and driving conditions. The results are compared to previous researchers' experimental results. The system's performance was found to be quite robust in the presence of faults. The TXV, accumulators, and compensator significantly reduce sensitivity to refrigerant charge and liquid line restriction faults, and other faults to a lesser extent.
... The degradation becomes significant at -20% of the designed charge. Goswani et al. (1997) have also studied the effect of the R-22 ...
L'objectif de ce travail de thèse est la caractérisatiorn du comportement dymamique de machines frigorifiques lors des différentes phases transitoires intervenant durant leur utilisation. Une étude expérimentale a été réalisée sur deux machines : la première d'une puissance utile de 60 kW est dotée d'échangeurs à tubes et calandre ; la seconde, ayant une puissance utile de 10 kW, est équipée d'échangeurs àplaques à chevrons. Les deux installations utilisent le réfrigérant R-407C. L'étude du groupe froid de puissance moyenne équipé d'échangeurs à tubes et calandre a souligné la sensibilité du comportementtransitoire à la durée de l'arrêt avant le démarrage et à la valeur de la consigne de surchauffe imposée au détendeur thermostatique. De plus, il est apparu que la réponse transitoire à une sollicitation quelconque (démarrage, variation de puissance ou variation de débit de réfrigérant) entraîne un comportement transitoire plus marqué et perturbé dans la zone à basse pression. Enfin, concernant l'emploi du réfrigérant R-407C, un changement de composition significatif a été mesuré lors des phases de démarrage et d'arrêt de la machine.L'étude du groupe froid de petite puissance, dotée d'échangeurs à plaques, a d'abord été axée sur le comportement général del'instauration. Puis l'étude locale de l'évaporateur a été menée grâce à une instrumentation fine des canaux. Le comportement de ce groupe froid diffère fortement du premier étudié. Les instabilités de surchauffe apparaissent entre deux valeurs de débit, et un effet prépondérant de la distribution du fluide diphasique dans l'évaporateur influence le comportement transitoire. En outre, la mesure du coefficient d'échange local en évaporation indique que les corrélations usuelles sous estiment fortement les échanges thermiques, notamment dans la zone de post assèchement, à cause d'un effet de primage de liquide important.
... In this condition, the mass flow rate in the system is not sufficient and therefore the cooling effect is not high. A further increase of mass charge increases the cooling capacity and EER reaches its maximum value [4][5][6]. Again, increase of the mass charge leads to more power consumption of compressor, and as a result EER decreases. ...
In this paper the effects of refrigerant charge amount and ambient air temperature on performance and thermodynamic condition of refrigerating cycle in the split type air-conditioner have been investigated. Optimum mass charge is the point at which the energy efficiency ratio (EER) of refrigeration cycle becomes the maximum. Experiments have been conducted over a range of refrigerant mass charge from 540 to 840 g and a range of ambient temperature from 27 to 45 °C, in a 12,000 Btu/h split air-conditioner as case study. The various parameters have been considered to evaluate the cooling rate, energy efficiency ratio (EER), mass charge effect and thermodynamic cycle of refrigeration system with R22 refrigerant gas. Results confirmed that the lack of appropriate refrigerant mass charge causes the refrigeration system not to reach its maximum cooling capacity. The highest cooling capacity achieved was 3.2 kW (11,000 Btu/h). The optimum mass charge and corresponding EER of studied system have been obtained about 640 g and 2.5, respectively. Also, it is observed that EER decreases by 30% as ambient temperature increases from 27 °C to 45 °C. By optimization of the refrigerant mass charge in refrigerating systems, about 785 GWh per year of electric energy can be saved in Iran’s residential sector.
... The fault frequency, Frequ Fault , range of 40% to 80% reflects the authors' synthesis of field measurements of packaged unitary AC charge levels from several sources (Downey and Proctor, 2002;Modera and Proctor, 2002;Jacobs et al., 2003;Goody et al., 2003;Davis et al., 2002;Hewett et al., 1992;Carl and Smilie, 1992;Hoover, 2001). The average percent increase in energy consumption due to the fault, Degrade fault , comes from analytical estimates for EER degradation (Davis et al., 2002;Jacobs et al., 2003;Modera and Proctor, 2002) and laboratory testing to evaluate how different refrigerant levels effect the EER and SEER ratings of small (around 3-ton) packaged unitary AC (Farzad and O'Neal, 1993;Breuker and Braun, 1998;Goswami et al., 2001). The data sources estimated different values for the energy impact of different refrigerant charge levels, and the energy impact range of 5% to 15% reflects the authors' evaluation of the universality of the different sources. ...
Variable refrigerant flow (VRF) systems faults are inevitable due to installation errors, degradation, and other reasons. It is of great value to quantitatively understand the impact of faults on VRF systems performance and to clarify the changing trends of variables under different types of faults through experiments. In particular, the experimental analysis of simultaneous faults situations is helpful to improve the fault detection and diagnosis technology of VRF systems. There have been some previous experimental studies on the impact of faults, but none of them concerns modern VRF systems and their simultaneous faults. This paper presents results from a laboratory study of a VRF system with different types of faults. It provides the first published results of combinations of triple simultaneous faults, in addition to previously untested types of double simultaneous faults. The quantitative impact of the three crucial performance parameters, e.g. cooling capacity, system power, and COP, of the system under different faults has been analyzed. In addition, the quantitative influence and variation trend of system parameter variables during single fault and simultaneous fault are summarized. Results show that the outdoor fouling fault has the greatest impact, which can cause a 47.6% COP drop and 80.27% cooling capacity reduction. The influence of the simultaneous fault on the variable trend is superimposed and offset, but the trend influence of some faults also has a dominant characteristic.
Heat pumps are often operated with nonoptimal amounts of refrigerant charge under various operating conditions; this results in excessive energy consumption by the air-conditioning systems in buildings. This paper proposes a novel variable liquid-line length system (VLLS) to improve the performance of heat pumps by optimizing the amount of refrigerant charge under various operating conditions. The feasibility of the VLLS is experimentally verified by proving that changes in the condensing and evaporating pressures afford the same effects as those of varying the amount of refrigerant charge. The performance improvement in the heat pump using the VLLS was evaluated by varying the heat sink and source temperatures under a fixed electronic expansion valve (EEV) opening and fixed superheat. The results indicate that the VLLS with a fixed EEV opening enhances the maximum capacity and coefficient of performance (COP) of the heat pump by appropriately controlling superheat and subcooling under various operating conditions. Furthermore, the heat pump adopting the VLLS with a fixed superheat exhibits substantial improvements in the heating and cooling COPs by varying the optimal amount of refrigerant charge.
Air conditioning systems are known to experience operating faults, often caused by problems in their installation. To understand the impacts of these faults on system-wide performance requires laboratory tests with faults imposed, and many such experimental results have been published. However, it is likely that multiple simultaneous faults occur, but published results from testing with two simultaneous faults are very limited. This paper presents results from a laboratory study of an air-to-air heat pump system with combinations of: refrigerant charge (CH) too high or too low, evaporator airflow (EA), non-condensable gas (NC) in the refrigerant, and liquid line restrictions (LL). It provides the first published results of combinations of three and four simultaneous faults, in addition to previously untested types of double fault combinations. The impacts on cooling capacity and coefficient of performance (COP) are analyzed. COP reductions up to 34% occur within operation safety limits, meaning that such fault combinations would go unnoticed. An additional analysis examines the extent to which the superposition principle applies to combined fault impacts. The superposition principle is shown to have up to 25% error, indicating that there are synergistic effects – and sometimes cancelling effects – in the impacts from fault combinations.
Realistic performance predictions are required for efficient operation strategy of air conditioners. In this study, the application of a cost effective and non-intrusive black box model utilizing artificial neural networks (ANN) to predict the cooling capacity of air conditioning systems is investigated, while considering the effect of fouling and leakage that may occur after prolonged operation. The effect of various leakage and fouling combinations on the output cooling capacity were numerically simulated. The training data set is first generated for a system that is ideally operating without any fouling or leakage. The developed ANN model is tested to predict cooling capacity in “faulty” systems. The results indicated that, as long as leakage and fouling are limited below 10% and 4% respectively, the ANN model trained by the data generated with the ideal system, can predict cooling capacity with a relative averaged cooling capacity difference (ΔQ-e,rel) of approximately 13%. Moreover, the inclusion of data with different leakage and fouling combinations in the training set enables accurate predictions of the cooling capacity of the air conditioning system during the entire timespan of its operation. It suggests that cooling capacity under the fouling and leakage phenomena can be predicted using limited input information.
Soğutma sistemlerinde soğutucu akışkan kaçakları montaj ve servis hatalarından kaynaklanabildiği gibi, zaman içinde boru ve
bağlantılardaki titreşime ve malzeme yıpranmasına bağlı olarak oluşabilmektedir. Bu durum, soğutma sisteminin çalışma verimini
engelleyerek, soğutma/ısıtma kapasitesini düşürme ve sistemde kızgınlık artışına neden olmaktadır. Ayrıca, emme hattında vakum
düşüşü gerçekleşeceği için sisteme hava ve nem girişinden dolayı iç kirlenme ve tıkanma oluşmaktadır. Soğutucu akışkan kaçaklarının
tespitinde köpükleme ve akışkan kaçak dedektörü ile algılama kullanılan en yaygın yöntemlerdir. Bu çalışmada, bir soğutma sisteminde
oluşabilecek kaçakların tespiti için, kızılötesi görüntü işleme tekniğine dayalı yeni bir yöntem önerilmiştir. Bunun için ilk olarak, R22
soğutucu akışkan kullanılarak hazırlanan deney düzeneğinde, 7 farklı noktada, farklı zamanlarda yapay kaçaklar oluşturulur. Daha sonra,
sağlam sistem kızılötesi görüntüsü ile yapay kaçak yapılmış sistem görüntüleri üzerinden daha önceden tespit edilmiş 12 alt bölgeden
öznitelik verileri çıkartılmaktadır. Öznitelik özellik verilerinin elde edilme işleminde, belirlenen 12 bölgenin yüzey sıcaklık bilgileri
kullanılmıştır. Yüzey sıcaklık bilgileri minimum, maksimum, ortalama ve en yoğun sıcaklık bilgisi olarak dört farklı şekilde
çeşitlendirilmiştir. Kızılötesi görüntü analizi işlemini gerçekleştirmek için elde edilen öznitelik verileri Pearson Korelasyon Benzerlik
Analizi (PKBA) işlemine sokulmaktadır. Son olarak, izlenmesi gereken 12 alt bölgenin PKBA sonuçları bir eşik değere tabi tutularak,
eşik değerin altında kalan bölgelerde “Kaçak vardır” tespiti yapılmaktadır. Diğer bir olası durum ise, eğer sağlam ve kaçak kızılötesi
karşılaştırmasında, benzerlik değerinin çok yüksek bir değer oluşmasında, bu bölgeler için “Kaçak yoktur” sonucunu vermektedir.
Kızılötesi görüntü işleme tekniği kullanılarak gerçekleştirilen PKBA ile kaçak tespit işlemi, kullanım kolaylığı, hızlı ve eş zamanlı
kaçak tespit etme noktasında daha avantajlı olduğunu göstermiştir.
Accurate refrigerant charge fault estimation is important to ensure the efficient operation of air conditioning systems. This paper presents a novel hybrid model based refrigerant charge estimation approach. Firstly, an improved gray box model is presented, which integrates the key characteristic variables of subcooling temperature, superheat temperature, quality and pressure drop. Secondly, three extra variables having highest maximal information coefficients with the prediction residual are used to extend the gray box, and the robust machine learning model is developed using the gradient boosting decision tree algorithm. Then, a hybrid model is presented by combining the improved gray box and machine learning models. Finally, the prediction and generalization capacities of the proposed models under various operation conditions are validated using the experimental data. The results show that the hybrid charge fault estimation model has the best performance. Its overall prediction and generalization MREs are 2.53% and 3.09%, respectively.
Several laboratory experiments have studied the effect of faults on vapor compression cycle air-conditioning systems. There has been a particular focus on refrigerant charge variation, which is believed to be quite common in air conditioners, and a lesser focus on heat exchanger fouling. The majority of the published results evaluate the fault effects on particular system operating parameters in one unit. For example, the effect on capacity and efficiency are typically evaluated. The results differ from one study to the next. The current paper summarizes the effects for all of the results available in the literature for condenser fouling and refrigerant charge variation, and provides normalized relationships. The normalizations are provided for ANSI/AHRI 210/240 standard test conditions and are provided separately for fixed orifice and thermostatic expansion valve equipped systems. The level of variation found in the summary shows that for many applications, it is reasonable to the use normalized relationships to estimate the effect of faults on systems that have not been tested in a laboratory.
Building performance models most typically do not account for equipment faults, even though such faults are believed to significantly impact performance. One reason is that fault effects on performance are not very well understood, and can be quite complex to model. To address this situation, the current paper provides a summary of known empirical studies of fault effects on air-cooled unitary equipment. The summary includes three important performance parameters-capacity, efficiency, and sensible heat ratio-for three common fault types. Statistical analyses have been used to provide simplified models that can be programmed into building simulation software.
In this study, an existing laboratory heat pump is converted to a refrigeration unit in order to evaluate efficiency, power consumption, pressure and temperature variations and optimal charge amount of the system in new mode using refrigerant R-407C. Refrigerant charge amount has a key role in the terms of performance, operating cost (regarding to the charge reduction and energy consumption) and environmental concerns in all heat pump and refrigeration systems, which work on the same principles. Heat pump charge amount is the subject of many research, but less studies have been done in the case of refrigerators and freezers where the system works in the transient condition, on the contrary to the heat pump units. Although this study has been devoted to a detailed attempt to examine the possibility of converting the heat pump into the refrigerator, energy aspects of the whole system and the compressor have been analyzed under different working conditions. In the installed setup, the COP value of the system is tested with charge amount between 1 kg and 7 kg, but obtained results show that, this value is so lower than that of heat pump unit due to restricted energy source in cooling chamber.
The effects of the refrigerant charge on the performance of a portable propane air conditioning system have been evaluated and compared to nonportable systems in which the surrounding temperatures of the evaporator and condenser are not equal. This study aims to determine the similarities and differences in the performance of the two types of propane air conditioners under different charge levels, and to serve as a source of reference for future designs of portable air conditioners. The refrigerant charge was changed from −12.3% to +30% of its normal charge at several room temperatures ranging from 20 °C to 35 °C. The performance parameters include the refrigerant temperature, mass flow rate, maximum velocity of refrigerant, maximum pressure, cooling capacity, compressor work, specific cooling capacity, and coefficient of performance of the system. It has been found that an increase in charge level was found to increase the cooling capacity, coefficient of performance, and maximum velocity of refrigerant in the system while decreasing specific cooling capacity. The increase in the charge caused a relatively insignificant rise in the maximum pressure of the system and useful work of the compressor.
Performance degradation of air conditioners and heat pumps due to faults has been studied in several experiments reported in the literature. Among the faults, refrigerant charge variation is believed to be very common, and has been the focus of experiments by many researchers. In the current paper, using all available results in the literature, the effect of refrigerant charge faults on single-speed air-cooled air-conditioners and heat pumps is summarized. Generalized relationships have been developed to describe the fault effects, and these are provided for equipment operating at ANSI/AHRI 210/240 standard test conditions. Results are presented separately for fixed orifice (FXO) and thermostatic expansion valves (TXV), for both cooling and heating modes. The variation level of the results indicates that for many applications, it is reasonable to use these generalized relationships to estimate the effect of refrigerant charge variation on systems that have not been tested in a laboratory.
Several laboratory experiments have studied the effect of faults on vapor compression cycle air-conditioning
systems. There has been a particular focus on refrigerant charge variation, which is believed to be quite common in air conditioners, and a lesser focus on heat exchanger fouling. The majority of the published results evaluate the fault effects on particular system operating parameters in one unit. For example, the effect on capacity and
efficiency are typically evaluated. The results differ from one study to the next. The current paper summarizes the effects for all of the results available in the literature for condenser fouling and refrigerant charge variation, and provides normalized relationships. The normalizations are provided for ANSI/AHRI 210/240 standard test
conditions and are provided separately for fixed orifice and thermostatic expansion valve equipped systems. The level of variation found in the summary shows that for many applications, it is reasonable to the use normalized relationships to estimate the effect of faults on systems that have not been tested in a laboratory.
The extended use of cooling and refrigeration systems in industrial, building and transport sectors may have a negative impact on the climate change and ozone depletion. Thus, important aspects related to these systems, such as refrigerant charge level, malfunction, or refrigerant leakage, must be taken into account. In this sense, the study of refrigeration system performance under different conditions can be very useful. In this paper, a novel methodology for modelling a simple compression refrigeration system is described. Starting from three input parameters, i.e. the ambient air temperature, the cold room air temperature, and the degree of superheating, a calculation algorithm based on iterative loops is used in the model to determine the operating point of the system. An experimental set-up consisting of a walk-in freezer unit was used for the development and validation of the model. The model is system dependent, i.e. empirical correlations must be derived for determining some of the features of system components. The numerical results are in good agreement with the experiment, therefore the model can be a reliable tool for the detection of a system malfunction.
This paper presents the results of a study carried out to elucidate the influence of the source and sink temperatures on the optimal charge of a propane water-to-water 16 kW heat pump which does not incorporate any liquid receiver. The unit had been fully tested along a previous experimental study, at various refrigerant charges and different condensing temperatures. A detailed mathematical model was then employed to simulate the unit performance. The predicted results were in very good agreement with the experiments, and furthermore, showed the same trends found in a similar unit tested at the KTH (Sweden) when the evaporation temperature was progressively decreased. Then, the model was employed to study the influence of the source and sink temperatures on the optimal charge of the unit. The simulation showed that the great variation of the optimal charge with the variation of the evaporation temperature is mainly due to the variation of the amount of refrigerant in the compressor oil.
For some years, European regulation concerning refrigerating systems has become more and more severe. Because of their design and technology, refrigeration units cannot avoid refrigerant leaks, and can thus have a harmful impact on the environment. Many studies aimed at minimizing the charge in a refrigerating machine were thus developed. On a global level, reduction of refrigerant charges must not affect energy aspects while respecting environmental constraints [Montreal 1987, Kyoto 1997]. The architecture and refrigerant charge distribution in the systems are of particular importance; their analyses permit the determination of the target elements and thus define those in which the refrigerant charge could be reduced (heat exchangers, liquid pipes, receivers, ...). This paper presents a review of the refrigerant charge studies in a refrigerating plant (methodologies of charge measurement, void fraction correlations and characteristic values for various technologies). It also evaluates the influence of the refrigerant charge on the coefficient of performance (COP) and on the cooling capacity. Finally, it inventories the different means that allow the charge in a refrigerating system to be minimized. (C) 2007 Elsevier Ltd and IIR.
The existence of faults in vapour compression chillers plays a significant role in terms of energy efficiency loss, performance degradations, and even environmental implications. In this paper, a dynamic model-based fault detection technique suitable for real-time implementation is proposed. The main objective is to obtain a reliable and automated tool for fault detection in vapour compression chillers, which can be applied in steady-state or transient operation. The fault detection methodology is based on comparing actual and expected performance using an adaptative model and operating variables dynamic thresholds. The technique has been successful applied for on-line refrigerant leakage detection with experimental tests involving the artificial introduction of the fault in a laboratory vapour compression plant, showing the results its capability of detecting incipient leakage failure conditions avoiding false alarms.
An experimental study was conducted in which the performance of three blends of R134a and R32 were compared to R22. The effect of refrigerant charge and the size of expansion device on the performance of these refrigerants in an air-to-air heat pump operating in the air-conditioning mode was quantified. All tests were conducted according to ASHRAE Standard 116 (1983). The mixtures consisted of 60%/40%, 70%/30% and 80%/20% ratios by mass of R134a and R32. Charge levels of 5, 5.45, 5.90 and 6.00 kilograms (11, 12, 13 and 14 pounds) were tested. At each charge level, outdoor room conditions of 27.8°C, 35.0°C and 40.6°C (82°F, 95°F and 105°F) were tested. For each combination of charge level and outdoor room temperature, orifice diameters of 1.64, 1.78, 1.96 and 2.07 millimeters (0.0645, 0.0700, 0.0770 and 0.0815 inches) were tested. Three variables were used to quantify refrigerant performance: total capacity, total electrical power consumption and coefficient of performance (COP). Several other variables such as mass flow rate, compressor suction pressures and differential pressures were also used to determine system characteristics. The performance of the three mixtures was not as good as the R22. The capacities were between 7 and 17% lower than R22. The energy efficiency ratios were IV within three percent in some cases but the corresponding capacities at these EERs were more than 12% lower than the R22 base case. The best results for a mixture was the 60/40 blend. The capacity was 7.3% lower than the base case and the EER was 8.5% lower.
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D. Y. GOSWAMI E¹ A¸ AÇ 2001 John Wiley & Sons, Ltd. Int. J. Energy Res. 2001; 25:741}750 D. Y. GOSWAMI E¹ A¸ AÇ 2001 John Wiley & Sons, Ltd. Int. J. Energy Res. 2001; 25:741}750 REFERENCES ANSI/ARI Standard 210/240-89. 1989. ;nitary Air Conditioning and Air Source Heat Pump Equipment. ANSI/ASHRAE Standard 37-1988. Methods of ¹esting for Rating ;nitary Air-Conditioning and Heat Pump Equipment, ASHRAE Inc., Atlanta, GA, U.S.A. ASHRAE. 1993. Handbook of Fundamentals. American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE) 1791 Tullie Circle, NE, Atlanta, GA, U.S.A. Damasceno GS, Domanski PA, Rooke S, Goldschmidt VW. 1991. Refrigerant charge e!ects on heat pump performance. ASHRAE transactions: research, part 1, pp. 304}310. Engineering Weather Data. 1978. Departments of The Air Force, The Army, and The Navy, Washington DC, AFM 88-29, TM 5-785, NAVFAC P-89, 1 July.
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An airconditioning system test facility and test procedures for system performance
- D Y Goswami
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- S A Sherif
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- M Leung
- S Gupta
- W Kuo
Goswami DY, Mathur GD, Sherif SA, Klausner JF, Davanagere BS, Leung M, Gupta S, Kuo W. 1993. An airconditioning system test facility and test procedures for system performance. Solar Energy and Energy Conversioņ
aboratory Report No. ;FME/SEEC¸9310, University of Florida, Gainesville, FL, U.S.A.
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Departments of The Air Force, The Army, and The Navy
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Engineering Weather Data. 1978. Departments of The Air Force, The Army, and The Navy, Washington DC, AFM
88-29, TM 5-785, NAVFAC P-89, 1 July.
The e!ect of improper refrigerant charging on the performance of a residential heat pump with "xed expansion devices (Capillary tube and short tube ori"ce)
- M Farzad
- O Neal
Farzad M, O'Neal DL. 1994. The e!ect of improper refrigerant charging on the performance of a residential heat pump
with "xed expansion devices (Capillary tube and short tube ori"ce). 29th Intersociety Energy Conversion Engineering
Conference, vol. 2, 921}926.