1,721,108 research outputs found
Fault detection and diagnosis algorithm for multiple simultaneous faults in residential air-conditioning systems: Development, validation study and critical analysis
Get PDF[EN] Detecting and diagnosing faults in residential air conditioning (AC) systems is crucial for preventing critical failures and ensuring efficient operation. Some of these soft faults are refrigerant undercharge (UC), overcharge (OC), inadequate evaporator airflow (EA), or liquid line restrictions (LL). Data-driven methodologies have proven effective in achieving reliable detection but require a large amount of data. This paper proposes utilizing a model based on vapor compression cycles capable of simulating a wide range of indoor/outdoor operating conditions and faults imposed individually and several co-occurring (multiple combinations) for a residential AC unit. This simulated dataset is used to train a Support Vector Machine (SVM) classification algorithm to distinguish between fault, non-fault, and multiple fault states. The SVM uses features obtained from a small number of sensors, making this methodology adequate for residential AC units that typically have limited instrumentation. The proposed method is applied to the same simulated unit, which is experimentally tested in the laboratory with imposed faults, resulting in a balanced accuracy of 82% and a weighted F1-score of 84%. These results demonstrate the feasibility of training a fault detection and diagnosis algorithm with simulation data without requiring an extensive experimental campaign.The authors gratefully acknowledge the financial support provided by the project "Decarbonizacion de edificios e industrias con sistemas hibridos de bomba de calor", funded by "Ministerio de Ciencia e Innovacion" of Spain, with project code: PID2020-115665RB-I00. Belen Llopis-Mengual extends her appreciation to the Ministry of Universities of Spain through the "Formacion de Profesorado Universitario" programme ref. FPU19/04012 and the funding to conduct a research stay EST23/00752.Llopis-Mengual, Belén;Yuill, D.;Navarro-Peris, Emilio (2025). Fault detection and diagnosis algorithm for multiple simultaneous faults in residential air-conditioning systems: Development, validation study and critical analysis. Applied Thermal Engineering. 269. https://doi.org/10.1016/j.applthermaleng.2025.125975S26
Time series analysis of field data for soft faults detection and degradation assessment in residential air conditioning systems
No full text[EN] Residential Air Conditioning units are significant contributors to energy consumption. Soft faults in these units, such as refrigerant leakage and inadequate condenser airflow, can lead to reduced equipment life, decreased cooling capacity, and increased energy consumption. While extensive research has been conducted on Fault Detection and Diagnosis (FDD) in AC systems, most studies rely on laboratory-imposed faults or simulations, which may not reflect real-world conditions. Thus, long-term field data analyses remain scarce. This study develops and validates a time-series analysis-based methodology for detecting and diagnosing these faults in residential air conditioning units. Virtual refrigerant charge is used to detect refrigerant leakage, while the difference between condensing and ambient temperatures is used to detect inadequate condenser airflow. The methodology is tested on a dataset of 81 units across the US and Canada, monitored over a full cooling season (2¿7 months). Results show that 2 units exhibited degraded condenser airflow and 5 had refrigerant leakage. Refrigerant leakage resulted in a monthly Coefficient of Performance (COP) reduction of 4¿10% and an increase in daily energy consumption by 4¿26% over a faulty period of 6.5 to 15 weeks. Similarly, units with degraded condenser airflow experienced a COP reduction of 4¿7% per month, and daily electricity consumption increased by 15¿17% over a faulty period of 8¿8.5 weeks. This study quantifies fault performance degradation under residential conditions by analyzing real-world operational data, offering a field-tested approach for identifying and assessing soft faults. This work highlights the importance of timely fault detection and maintenance in residential Air Conditioning units to ensure efficiency, minimize energy waste, and prevent system damage.The authors would like to acknowledge Alert Labs for sharing the data from the monitored air conditioning units with Sentree. Belen Llopis-Mengual extends her acknowledgment to the Ministry of Universities of Spain through the "Formacion de Profesorado Universitario" program ref. FPU19/04012 and the funding to conduct a research stay ref. EST23/00752.Llopis-Mengual, Belén;Yuill, D.;Navarro-Peris, Emilio (2025). Time series analysis of field data for soft faults detection and degradation assessment in residential air conditioning systems. Applied Thermal Engineering. 269. https://doi.org/10.1016/j.applthermaleng.2025.126104S26
Experimental study about frost formation and growth in the evaporator of an air-to-water heat pump
No full text[EN] Frost formation in the evaporator of air-to-water heat pumps (AWHPs) is one of the most crucial aspects that affect the efficiency of these systems. This paper analyzes the frost formation and growth in a finned-tube evaporator to monitor the degradation of a commercial heat pump's performance. The analysis includes the characterization of the various frost formation processes that may occur in real operating conditions, as well as a detailed examination of the water vapor sublimation process as a function of evaporation temperature and relative humidity. The results are presented in terms of the air-side pressure drop, evaporation temperature evolution, and the amount of condensed water recovered. From these results, key factors in the evolution of this process, like the frost structure, are critical in the system performance degradation, and parameters like air-side pressure drop are not enough to determine the optimum time for initiating the defrost process.This work has been funded by the project " Investigacion en la proxima generacion de bombas de calor aerotermicas para edificios integradas en los sistemas de calefaccion/refrigeracion y agua caliente sanitaria ", Ref. PID2023-148964OB-I00, by the Spanish Ministry of Science, Innovation and Universities. The authors are grateful for the support given.Marchante-Avellaneda J. would like to acknowledge the Universitat Politecnica de Valencia (UPV) for the grants for contracts for research personnel access (Ref. PAID-10-23) ; and initial research projects (Ref. PAID-06-24) .Alarcón-Gallén, David;Marchante-Avellaneda, Javier;Hassan, Abdelrahman;Navarro-Peris, Emilio (2025). Experimental study about frost formation and growth in the evaporator of an air-to-water heat pump. International Journal of Refrigeration. 179:295-303. https://doi.org/10.1016/j.ijrefrig.2025.08.013S29530317
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Estudio teórico-experimental de compresores de pistón herméticos con diferentes refrigerantes
Get PDF[EN] This thesis is included within the objectives of the project of the Ministerio de Ciencia yTecnologia DICORE.Within the frame of this project, the thesis is focused in the study of hermetic piston compressors for refrigeration systems to attend their adaptation and use with new refrigerants.
Firstlyaseriesoffivereciprocatingcompressorsofdifferentcapacitieslubricated with POE working with propane and R407C were analyzed. Since traditionally the compressors working with propane have being lubricated with mineral oil of high viscosity, an additionally a comparative study between a MO of high viscosity and the used POE were developed to evaluate the possible convenience of using POE of lower viscosity with propane. These tests included a compressor characterization with both oils, OCR measurement (Oil Circulation Rate) and finally thedesignofaproceduretomeasuretheoilexpelledbythecompressorinthestartup.
Once verified the reliability in the experimental level of propane as refrigerant with this compressors. A general semi-empirical compressor model which allows on the one hand to analyze from a theoretical point of view the observed differences between both refrigerants and on the other hand to asses the design of compressors working with other refrigerants. The obtained model allows obtaining an estimation of the volumetric efficiency and the compressor when the refrigerant with an error lower than 3% in most of the tested working conditions.
Finally, the development of the model has pointed out the possibility of the existence of an effect of condensation of the refrigerant during the compression process. Thiseffectthathabituallyisnotcontemplatedinthemodelsofthebibliographywould allow to explain the discrepancy between the dead volume of the compressor considered by the manufacturer and the obtained dead volume with the model.[ES] La presente tesis se encuentra englobada dentro de los objetivos del proyecto del Ministerio de Ciencia y Tecnología DICORE. En este contexto este trabajo se centra en el estudio de compresores de pistón herméticos para sistemas de refrigeración con el fin de asistir a su adaptación y uso con nuevos refrigerantes. Inicialmente se procedió a analizar una serie de cinco compresores de pistón de distintas capacidades lubricados con POE funcionando con propano y con R407C, observando a nivel experimental las diferencias observadas en su comportamiento. Puesto que tradicionalmente los compresores que han utilizado propano han venido siendo lubricados con aceite mineral de viscosidad alta, se realizó adicionalmente un estudio comparativo entre aceite MO clavus GV 68 y POE ISO 32 con el fin de determinar la posible aparición de algún problema relacionado con la lubricación y el aceite POE de menor viscosidad. En estas pruebas se procedió a caracterizar un compresor funcionando con ambos tipos de aceite, a realizar medida de OCR (Oil Circulation Rate) y por último se diseño un procedimiento de medida del aceite expulsado por el compresor en el arranque.
Una vez comprobada la viabilidad a nivel experimental del propano como refrigerante en este tipo de compresores se procedió a realizar un modelo semiempírico general de compresor que permitiese por un lado analizar desde un punto de vista teórico las diferencias de funcionamiento de ambos refrigerantes. Dicho modelo permitiríaasíasistiraldiseñodecompresoresfuncionandoconotrosrefrigerantes. El modeloasíobtenidoproporcionaobtenerunaestimacióndelrendimientovolumétrico y del compresor cuando se sustituye el refrigerante con un error inferior al 3% en la mayoría de las condiciones de trabajo evaluadas.
Porúltimo,eldesarrollodelmodelohaapuntadolaposibilidaddelaexistenciade una condensación de parte del fluido frigorígeno durante el proceso de compresión. Dicho efecto que no es habitualmente contemplado en los modelos de la bibliografía permitiríaexplicarladiscrepanciaentreelvolumenmuertoestimadoporelfabricante del compresor y el volumen muerto obtenido con el modelo.[CA] La present tesi es troba englobada dins dels objectius del projecte del Ministeri de Ciència i Tecnologia DICORE. Dins d’aquest context este trevall es centra en l’estudidecompressorsdepistóhermèticsperasistemesderefrigeracióperaassistir a la seua adaptació i ús amb nous refrigerants.
Primerament es va procedir a analitzar una sèrie de cinc compressors de pistó de distintescapacitatslubricatsambPOEfuncionantambpropàiambR407C,observant a nivell d’experimental les diferències observades en el seu comportament. Ja que tradicionalment els compressors que han utilitzat propà han vingut sent lubricats amb oli mineral de viscositat alta, es realitze addicionalment un estudi comparatiu d’estos dos olis a fi depoder establir l’existència d’algun problema relacionat amb la lubricació i l’oli POE de menor viscositat. En estes proves es va procedir a caracteritzar un compressor funcionant amb estos dos tipus d’oli, a realitzar mesura d’OCR (Oil Circulation Rate) i finalment se disseny un procediment de mesura de l’oli expulsat pel compressor en l’arrancada.
Una vegada comprovada la viabilitat a nivell experimental del propà com a refrigerant es va procedir a realitzar un model semi-empiric general de compressor que permetera d’una banda analitzar des d’un punt de vista teòric les diferències de funcionament d’estos dos refrigerants permetent així assistir al disseny de compressors funcionant amb altres refrigerants. El model així obtingut permet obtindre una estimació del rendiment volumètric i del compressor quan se substituïx el refrigeren-te amb un error inferior al 3% en la majoria de les condicions de treball avaluades.
Finalment, el desenrotllament del model ha apuntat la possibilitat de l’existència d’una condensació de part del fluid frigorigen durant el procés de compressió. Dit efecte que no és habitualment contemplat en els models de la bibliografia permetria explicar la discrepància entre el volum mort estimat pel fabricant del compressor i el volum mort obtingut amb el model.Dar gracias también al Ministerio de Educación y Ciencia que concediéndome la beca FPI asociada al proyecto DICORE me proporcionó el apoyo económico suficiente para poder realizar esta tesis.Navarro Peris, E. (2006). Estudio teórico-experimental de compresores de pistón herméticos con diferentes refrigerantes [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/135957TESI
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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