Study of scroll compressors with vapor-injection for heat pumps operating in cold climates or in high-temperature water heating applications

Tesis por compendio[ES] Esta tesis doctoral presenta un estudio de compresores scroll con inyección de vapor (SCVI) para bombas de calor que operan en climas fríos o para aplicaciones de calentamiento de agua a alta temperatura. Para ello, se comparó experimentalmente un SCVI con un compresor de dos etapas de pistones (TSRC) trabajando con R-407C en condiciones extremas. La comparación se realizó en términos de eficiencias del compresor, capacidad, COP y rendimientos estacionales tanto para el modo calefacción como para el modo refrigeración. Los resultados proporcionan una idea general sobre el rango de aplicación de los compresores estudiados y sobre las diferencias en los rendimientos de los compresores. Sin embargo, se identificaron varias limitaciones en la caracterización de los compresores y en el análisis del ciclo. Esto motivó a profundizar en el estudio del ciclo de compresión de dos etapas y sus componentes. El siguiente paso fue realizar un análisis teórico de los ciclos de compresión de dos etapas para aplicaciones de calefacción, en donde se identificó a la presión intermedia y a la relación de inyección como los parámetros del sistema más influyentes sobre el COP. La presión intermedia se optimizó para dos configuraciones de inyección (tanque de separación y economizador) utilizando varios refrigerantes. Basándose en los resultados de la optimización, se propuso una correlación que permite obtener la presión intermedia óptima del ciclo, considerando la influencia del subenfriamiento a la salida del condensador. Además, se analizó la influencia del diseño de los componentes del sistema sobre el COP del ciclo. Posteriormente, el estudio se profundizó a nivel de componentes. El factor más crítico en el sistema es el rendimiento del compresor. Por lo tanto, el siguiente paso fue evaluar la influencia de varios sistemas de compresión con inyección de vapor sobre el COP. Se tomaron en cuenta tres tecnologías de compresores, un SCVI, un TSRC y un compresor scroll de dos etapas (TSSC). Estas tecnologías de compresores fueron caracterizadas y modeladas para estudiar su rendimiento. Para ello, se propuso una nueva metodología para caracterizar compresores scroll con inyección de vapor. Esta metodología permite evaluar el rendimiento del compresor independientemente del mecanismo de inyección que se utiliza en el ciclo. Se identificó una correlación lineal entre la relación de inyección de refrigerante y la relación de compresión intermedia. Esta correlación se utiliza para determinar el flujo másico de inyección en función de la presión intermedia. Posteriormente, se propuso un modelo semi-empírico de compresores scroll y una metodología para extender dicho modelo para compresores scroll con inyección de vapor. Los modelos fueron ajustados y validados usando datos experimentales de cuatro compresores scroll trabajando con R-290 y un SCVI trabajando con R-407C. Finalmente, se comparó un SCVI con dos compresores de dos etapas, un TSSC y un TSRC, trabajando en condiciones extremas. Se optimizó la relación de volúmenes de los compresores de dos etapas. Los resultados muestran que, en las condiciones nominales de funcionamiento (Te=-15 °C, Tc=50 °C), la relación de volúmenes óptima del TSSC es 0.58, y del TSRC es 0.57. El TSSC consigue un COP 6% mayor que el SCVI y un COP 11.7% mayor que el TSRC. Bajo un amplio rango de condiciones de operación, el SCVI presenta una mejor eficiencia y COP para relaciones de presión inferiores a 5. Para relaciones de presión más altas, el TSSC presenta mejor rendimiento y consigue una temperatura de descarga más baja. Se concluye que el SCVI es una solución fácil de implementar, desde el punto de vista del mecanizado, y que permite extender el mapa de trabajo de los compresores de una etapa. Sin embargo, los resultados muestran que la compresión en dos etapas consigue mejorar en mayor medida el COP del ciclo y la capacidad, con una mayor redu[CA] Aquesta tesi doctoral presenta un estudi de compressors scroll amb injecció de vapor (SCVI) per a bombes de calor que operen en climes freds o per a aplicacions d'escalfament d'aigua a alta temperatura. Per a això, es va comparar experimentalment un SCVI amb un compressor de dues etapes de pistons (TSRC) treballant amb R-407C en condicions extremes. La comparació es va realitzar en termes d'eficiències del compressor, capacitat, COP i rendiments estacionals tant per al mode calefacció com per al mode refrigeració. Els resultats proporcionen una idea general sobre el rang d'aplicació dels compressors estudiats i sobre les diferències en els rendiments dels compressors. No obstant això, es van identificar diverses limitacions en la caracterització dels compressors i en l'anàlisi del cicle. Això va motivar a aprofundir en l'estudi del cicle de compressió de dues etapes i els seus components. El següent pas va ser realitzar una anàlisi teòrica dels cicles de compressió de dues etapes per a aplicacions de calefacció, on es va identificar la pressió intermèdia i la relació d'injecció com els paràmetres del sistema més influents sobre el COP. La pressió intermèdia es va optimitzar per a dues configuracions d'injecció (tanc de separació i economitzador) utilitzant diversos refrigerants. Basant-se en els resultats de l'optimització, es va proposar una correlació que permet obtindre la pressió intermèdia òptima del cicle, considerant la influència del subrefredament a l'eixida del condensador. A més, es va analitzar la influència del disseny dels components del sistema sobre el COP del cicle. Posteriorment, l'estudi es va aprofundir a nivell de components. El factor més crític en el sistema és el rendiment del compressor. Per tant, el següent pas va ser avaluar la influència de diversos sistemes de compressió amb injecció de vapor sobre el COP. Es van prendre en compte tres tecnologies de compressors, un SCVI, un TSRC i un compressor scroll de dues etapes (TSSC). Aquestes tecnologies de compressors van ser caracteritzades i modelades per a estudiar el seu rendiment. Per a això, es va proposar una nova metodologia per a caracteritzar compressors scroll amb injecció de vapor. Aquesta metodologia permet avaluar el rendiment del compressor independentment del mecanisme d'injecció que s'utilitza en el cicle. Es va identificar una correlació lineal entre la relació d'injecció de refrigerant i la relació de compressió intermèdia. Aquesta correlació s'utilitza per a determinar el flux màssic d'injecció en funció de la pressió intermèdia. Posteriorment, es va proposar un model semi-empíric de compressors scroll i una metodologia per a estendre aquest model per a compressors scroll amb injecció de vapor. Els models van ser ajustats i validats utilitzant dades experimentals de quatre compressors scroll treballant amb R-290 i un SCVI treballant amb R-407C. Finalment, es va comparar un SCVI amb dos compressors de dues etapes, un TSSC i un TSRC, treballant en condicions extremes. Es va optimitzar la relació de volums dels compressors de dues etapes. Els resultats mostren que, en les condicions nominals de funcionament (Te=-15 °C, Tc=50 °C), la relació de volums òptima del TSSC és 0.58, i del TSRC és 0.57. El TSSC aconsegueix un COP 6% major que el SCVI i un COP 11.7% major que el TSRC. Sota un ampli rang de condicions d'operació, el SCVI presenta una millor eficiència i COP per a relacions de pressió inferiors a 5. Per a relacions de pressió més altes, el TSSC presenta millor rendiment i aconsegueix una temperatura de descàrrega més baixa. Es conclou que el SCVI és una solució fàcil d'implementar, des del punt de vista del mecanitzat, i que permet estendre el mapa de treball dels compressors d'una etapa. No obstant això, els resultats mostren que la compressió en dues etapes aconsegueix millorar en major mesura el COP del cicle i la capacitat, amb una major reducció de la[EN] This Ph.D. thesis presents a study of scroll compressors with vapor-injection (SCVI) for heat pumps operating in cold climates or in high-temperature water heating applications. To do so, firstly, an SCVI was experimentally compared with a two-stage reciprocating compressor (TSRC) working with R-407C under extreme conditions. The comparison was made in terms of compressor efficiencies, capacity, COP, and seasonal COP, both for heating and cooling modes. The results give a general idea about the application range of the studied compressors and the differences in the compressors' performance. Nevertheless, several restrictions in the compressors' characterization and the cycle analysis were identified. This motivated us to deepen in the study of the two-stage compression cycle and its components. The next step was performing a theoretical analysis of two-stage compression cycles for heating applications, where the intermediate pressure and the injection ratio were identified as the most influential system parameters on the COP. The intermediate pressure was optimized for two vapor-injection configurations (flash tank and economizer) using several refrigerants. Based on the optimization results, a correlation was proposed that allows obtaining the optimal intermediate pressure of the cycle, considering the influence of the subcooling at the condenser outlet. In addition, a theoretical analysis of the influence of the design of the system components on the COP of the cycle was performed. Once the thermodynamic analysis of the two-stage cycle was carried out, the study was deepened at the component level. The most critical factor in the system is the compressor performance. Hence, the next step was evaluating the influence of several compression systems with vapor-injection on the COP. Three compressor technologies were taken into account, an SCVI, a TSRC and a two-stage scroll compressor (TSSC). These compressor technologies were characterized and modeled in order to study their performance. To do so, a new methodology to characterize SCVI was proposed. This methodology allows evaluating the compressor performance independently of the injection mechanism used in the cycle. A linear correlation was identified between the refrigerant injection ratio and the intermediate compression ratio. This correlation is used to determine the injection mass flow as a function of the intermediate pressure. Then, a semi-empirical model of scroll compressors and a methodology to extend the model for scroll compressors with vapor-injection was proposed. The models were adjusted and validated using experimental data from four scroll compressors working with R-290 and an SCVI compressor working with R-407C. Finally, an SCVI was compared with two two-stage compressors, a TSSC, and a TSRC, working in extreme conditions. The displacement ratio of the two-stage compressors was optimized. Results show that, at the nominal operating conditions (Te=-15 °C, Tc=50 °C), the optimal displacement ratio of the TSSC is 0.58, and of the TSRC is 0.57. The TSSC achieves 6% larger COP than the SCVI and 11.7% larger COP than the TSRC. Under a wide range of operating conditions, the SCVI presents a better efficiency and COP for pressure ratios below 5. For higher-pressure ratios, the TSSC presents better performance and achieves lower discharge temperature. It is concluded that the SCVI is an easy solution to implement from the point of view of machining, which allows extending the working map of the single-stage compressors. However, the results show that the two-stage compression technology gets further improve the COP of the cycle and the capacity, with a greater reduction of the discharge temperature operating under extreme conditions.I thank the financial support provided by the Secretaría de Educación Superior, Ciencia, Tecnología e Innovación (SENESCYT) of Ecuador, through the international scholarship program for postgraduate studies “Convocatoria Abierta 2013 Segunda Fase, Grant No 2015-AR37665”.Tello Oquendo, FM. (2019). Study of scroll compressors with vapor-injection for heat pumps operating in cold climates or in high-temperature water heating applications [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/120473TESISCompendi

A comprehensive study of two-stage vapor compression cycles with vapor-injection for heating applications, taking into account heat sink of finite capacity

[EN] This paper presents a comprehensive study of two-stage vapor compression cycles with vapor-injection for several refrigerants considering that the heat sink has a limited capacity. The key parameters of the cycle performance are identified and the influence of these parameters on the heating COP is analyzed. The optimum intermediate conditions of the cycle are evaluated using a general model of the cycle, considering two configurations (flash tank and economizer). Based on the optimization results, a correlation is proposed in order to estimate the optimum intermediate pressure, taking into account the temperature lift in the secondary fluid imposed by the application. The correlation uses cycle subcooling as an input, which is a novelty from the current correlations proposed in the literature. In addition, an optimum subcooling control strategy is proposed and finally, the influence of the size of the system components on the COP is studied.Fernando M. Tello-Oquendo acknowledges the financial support provided by the CONVOCATORIA ABIERTA 2013-SEGUNDA FASE program, which was funded by the SENESCYT (Secretaria de Educacion Superior, Ciencia, Tecnologia e Innovacion) (Grant no. 2015-AR37665) of Ecuador.Tello Oquendo, FM.; Navarro-Peris, E.; Gonzálvez-Maciá, J. (2018). A comprehensive study of two-stage vapor compression cycles with vapor-injection for heating applications, taking into account heat sink of finite capacity. International Journal of Refrigeration. 93:52-64. https://doi.org/10.1016/j.ijrefrig.2018.05.039S52649

Lean Feed 조건에서의 NGL/LNG 통합공정에 대한 최적 설계와 경제성평가에 관한 연구

학위논문 (박사)-- 서울대학교 대학원 : 공과대학 조선해양공학과, 2019. 2. 임영섭.최근 호주와 미국을 비롯한 국가들의 비 전통가스전 개발이 증가함에 따라 lean 가스필드에 대한 수요가 점차 증가하고 있으며 따라서 조성이 lean 한 조건하에서의 NGL 회수공정 및 LNG 공정에 대한 성능 및 경제성 재평가가 필요할 것으로 예상된다. 본 논문은 다양한 NGL 회수 공정과 액화공정 그리고 NGL/LNG 통합 공정에 대하여 HHV 스펙을 고려한 공정최적화 및 경제성평가를 진행하고 비교 분석하였다. NGL회수공정은 네 가지 서로 다른 공정들에 대하여 다양한 lean가스조성 하에서 공정성능 및 경제성평가를 진행하였다. 그 중 ISS 와 IPSI 공정은 전통 feed 조건하에서의 대표적인 공정인 반면에 HHC separator 와 scrub column 은 장치수를 최소화하여 단순한 공정도를 가진 공정들로 feed 조성이 lean 할 경우 강점을 가질 것으로 예상되는 공정이다. 공정성능평가 결과 비교적 많은 장치를 사용하여 복잡한 공정도를 가지고 있는 IPSI 공정이 가장 좋은 분리효율을 가지고 있으므로 다른 공정들에 비해 가장 적은 재료비를 사용하였다. 그러나 상대적으로 높은 자본투자가 IPSI 공정의 전체적인 경제성에 더 큰 영향을 주었다. 가장 단순한 공정인HHC separator 공정은 다른 공정들 대비 가장 적은 자본투자비를 보였지만 상대적으로 좋지 않은 분리효율로 인하여 가장 많은 재료비를 사용하였다. 자본투자비용 및 운전비용 등 전반적인 경제성을 고려 했을 경우 ISS 공정이 feed GPM 값이 2.5로 근접할 때 가장 좋은 경제성을 보였고 scrub column 공정은 feed 조성이 일정하게 lean 할 경우 다른 공정들 대비 가장 좋은 경제성을 보였다. 이는 전반적인 경제성측면에서 봤을 때 조성이 일정하게 lean 할 경우에는 상대적으로 복잡한 ISS 공정이나 IPSI 공정보다도 scrub column 공정을 NGL 회수 공정으로 사용하는 것이 더 유리함을 보여 준다. 해상용 천연가스 액화공정의 경우 제한된 공간 및 안전성 등 원인으로 인하여 일반적으로 육상보다 더 복잡한 선정기준을 가지고 있다. 예를 들어 육상에서 최대 점유율을 보이고 있는 C3MR 액화공정은 상대적으로 많은 공간 필요 및 공정안전성에 영향을 주는 많은 양의 프로판 성분을 필요로 하고 있으며 이로 인하여 해양 플랫폼에는 실제 사용 된 경우가 없다. 본 논문은 해상에서 사용 가능한 하나의 N2 엑스펜다 공정, 두 가지 종류의 단일혼합냉매 공정 (SMR) 및 세가지 타입의 듀얼혼합냉매 공정 (DMR) 등 총 6가지 타입의 공정들에 대해 공정성능 및 경제성평가를 진행하였다. N2 엑스펜다 공정은 비가연성인 질소를 단일냉매로 사용하므로 플랜트 운전측면 및 안전성 측면에서 강점을 가지고 있지만 다른 공정들 대비 가장 좋지 않은 효율을 보이는 것으로 알려져 있다. DMR 공정은 두 개의 혼합냉매를 사용하므로 N2 엑스펜다 및 SMR 공정보다 더 좋은 효율을 보이고 트레인당 용량도 가장 크므로 상대적으로 큰 용량의 액화공정 선정에 사용가능하다. 반면에 상대적으로 많은 장치를 사용하므로 복잡한 공정도를 가지고 있고 따라서 가장 큰 투자비를 필요로 한다. SMR 공정은 N2 엑스펜도 와 DMR 공정의 사이의 공정성능을 보인다. 성능 및 경제성평가 결과 N2 엑스펜더 공정이 다른 공정들 대비 가장 낮은 효율과 수익성을 보였다. SMR 2 공정은 가장 적은 투자비와 payout time 을 보였고 DMR base 공정이 다른 공정들 대비 높은 액화효율을 보여주었고 따라서 가장 높은 수익성과 가장 적은 운전비용을 필요로 하였다. SMR 2 공정은 투자비측면에서 가장 좋은 경제성을 보였고 DMR base 공정은 상대적으로 복잡한 공정도를 가지고 있어 높은 초기 투자비를 보이지만 높은 액화효율을 가지고 있어 운전비용 측면에서 다른 공정들 대비 강점을 가지고 있으므로 해상용 액화공정 선정 시 프로젝트 상황에 따라 SMR 2 공정 또는 DMR base 공정을 액화공정 후보로 고려할 수 있다. 통합공정은 본 논문에서 제안 한 두 개의 최대한 장치수를 간소화 한 NGL/LNG 통합공정과 전통적인 통합공정을 feed 가 lean 한 조성 하에서 LNG HHV 스펙을 고려하여 성능 및 경제성을 비교 분석하였다. 액화공정 파트는 SMR 2 공정과 DMR base 공정을 각각 사용하였고 유전자 알고리즘을 공정 글로벌 최적화에 적용하여 공정 최적운전조건을 도출하였다. 공정 최적화 결과 제안 한 Case 1 공정이 전통공정에 대비 액화효율은 조금 낮았지만 NGL회수 공정부분 장치를 최대한 줄임으로 인하여 상당히 낮은 자본투자비를 보였다. 또한 전반적인 경제성 측면에서도 Case 1 공정이 가장 좋은 성능을 보여주었다. 액화공정에 SMR 를 사용한 Case 2 공정의 경우에는 비교 분석한 세 개의 공정 중에서 가장 낮은 자본투자비를 보였으나 운전비 측면에서 다른 공정들 대비 비교적 큰 차이를 보여 전반적인 경제성 측면에서는 좋지 않았다. 하지만 플랜트 운영기간이 15개월보다 짧을 경우에는 가장 좋은 수익성을 보여주었다. 그러므로 제안된 Case 2 공정은 플랜트 운전기간이 짧은 peak shaving 플랜트 또는 feed reservoir 수명이 짧은 해양플랜트에 적용하면 전체 투자비를 줄일 수 있을 뿐만 아니라 전체 수익성 측면에서 유리하여 NGL/LNG 통합 공정 선정 시 하나의 좋은 공정옵션으로 고려할 수 있음을 보여주었다.In recent years, the demand for lean gas fields has increased due to the development of unconventional gas reservoirs in Australia and U.S. Therefore, the re-evaluation of natural gas liquid (NGL) recovery and NGL/LNG integrated processes under lean feed conditions are required. This dissertation performs process optimization and economic evaluation for the various representative NGL recovery, natural gas liquefaction and NGL/LNG integrated processes considering the liquefied natural gas (LNG) higher heating value (HHV) specification. Four different NGL recovery process schemes were evaluated under various lean feed conditions. The ISS and IPSI (A company name who owns it) processes are the representative processes in the conventional NGL recovery feed conditions. On the other hand, heavy hydrocarbons (HHC) separator and scrub column schemes are the simplified processes which may have advantages for lean feeds. The results indicate that IPSI process requires lowest raw material cost due to high process efficiency. However, its high total capital cost offset its overall economic performance. The HHC separator scheme shows the lowest total capital cost because of a simplified configuration, but requires the highest raw material cost among the processes due to the poor separation efficiency compared with the other processes. ISS scheme shows best economic performance when the feed GMP value reaches 2.5. The scrub column scheme shows the best overall economic performance among the process schemes in the wide range of lean feed conditions. The results demonstrate that scrub column scheme can be seen as a good candidate of the NGL recovery processes for economically when the feed is in the considerably lean conditions. An offshore platform has limited deck area different from onshore liquefaction plants. So the selection criteria for a liquefaction process is different compared to the onshore liquefaction processes. In this study, six types of liquefaction processes that applicable for offshore units were selected and analyzed both the process efficiency and economic performance. The six types of processes are a dual N2 expander, two single mixed refrigerant (SMR) and three kinds of dual mixed refrigerant (DMR) processes. The N2 expander process uses nonflammable pure nitrogen as the refrigerant that has advantages of safety and relatively simple operation. However, the liquefaction efficiency is the lowest one compared with the other processes. The DMR process includes two mixed refrigerant cycles that owns the highest liquefaction efficiency and per train capacity than the N2 expander and SMR processes. However, it has more complex process configuration than the other processes that normally used in the large scale liquefaction plants. On the other hand, the process performance of a SMR process is between the N2 expander and DMR processes. The results present that dual N2 expander process has the lowest process efficiency and net profit among the compared processes. The SMR process 2 shows the lowest capital expenditure and payout time. The DMR base case scheme indicates the highest profitability and lowest operating cost among the processes because of the highest liquefaction efficiency. The results show that both SMR process 2 and DMR base processes have advantages in terms of some aspects compared with the other processes. The proposed two simple integrated NGL/LNG processes and a conventional LNG and NGL coproduction process were also investigated with consideration of LNG HHV specification under the lean feed condition. The SMR process 2 and DMR base cycles were selected for the liquefaction part and the genetic algorithm (GA) method was used for the process optimization. The results show that the proposed integrated process, case 1, has overall economic advantages compared to the conventional base case scheme. The capital cost reduced remarkably by simplifying NGL recovery part, and only a little loss of liquefaction efficiency (less than 1%). The proposed process case 2, which adopts SMR process 2 as the liquefaction process, shows the lowest total capital cost and best profitability when a plant operating time is less than a certain period. Therefore, it could be a good process option when a plant reservoir lifetime is relatively short such as some peak shaving plants and special offshore applications in terms of economic aspect.Abstract i Contents iv List of Figure vi List of Tables viii CHAPTER 1. Introduction 1 1.1. Research motivation 1 1.2. Research objectives 3 1.3. Outline of the thesis 3 CHAPTER 2. Economic evaluation of the conventional NGL recovery and liquefaction processes 5 2.1. Evaluation of the representative NGL recovery processes considering LNG HHV specification 5 2.1.1. Overview 5 2.1.2. Process selection and description 9 2.1.3. Design criteria and specifications 19 2.1.4. Economic evaluation 23 2.1.5. Profitability analysis 28 2.1.6. Total annualized cost (TAC) optimization 28 2.1.7. Results and discussion 41 2.1.8. Summary 48 2.2. Optimization and economic analysis of natural gas liquefaction processes for offshore units 49 2.2.1. Overview 49 2.2.2. Process description 51 2.2.3. Results and discussion 65 2.3. Evaluation of a representative NGL/LNG integrated process considering LNG HHV specification 81 2.3.1. Overview 81 2.3.2. A conventional integrated process description 84 CHAPTER 3. The proposed integrated processes under the lean feed conditions 87 3.1 Overview 87 3.2 The proposed integrated process description 88 3.2.1. The proposed integrated process with DMR cycle 88 3.2.2. The proposed integrated process with SMR cycle 91 3.3 Feed compositions and specification 93 3.4 Liquefaction efficiency analysis 96 3.5 Economic evaluation 99 3.6 Results and discussion 99 3.7 Summary 109 CHAPTER 4. Concluding Remarks 111 4.1. Conclusions 111 4.2. Future works 113 References 114 Nomenclature 123 Abstract in Korean (국문초록) 125Docto

Development and Application of a Digital Twin for Chiller Plant Performance Assessment

As the complexity of industrial equipment continues to increase, the management of the individual machines and integrated operations becomes difficult without computer tools. The availability of streaming data from manufacturing floors, plant operations, and deployed fleets can be overwhelming to analyze, although it provides opportunities to improve performance. The use of dedicated monitoring systems in the plant and field to troubleshoot machinery can be integrated within a product lifecycle management (PLM) architecture to offer greater features. PLM offers virtual processes and software tools for the design, analysis, monitoring, and support of engineering systems and products. Within this paradigm, a digital twin can estimate system behavior based on the assembled physical models and the operating data for preventive maintenance efforts. PLM software can store computer-aided-design, computer-aided-engineering, advanced manufacturing, and data in cloud form for remote access. Integrating physical and performance data into a single database provides flexibility and adaptability while allowing distant commanding and health monitoring of dynamic systems. The recent attention on global warming, and the minimization of energy consumption can be partially addressed by examining those economic sectors that use large quantities of electric power. Across the United States, heating, ventilation, and air conditioning (HVAC) systems use a collective $14 Billion of resources to control the temperature of commercial and residential spaces. A typical commercial HVAC system consists of a chiller plant, water pumps for fluid circulation, multiple heat exchangers, and iii forced air blowers. In this research project, a digital twin is created for a single compressor chilled water-based HVAC system using a multi-disciplinary CAE software package. The system level models are assembled to describe a 1400 ton chiller located in the East-side chiller plant on the Clemson University (Clemson, SC) campus. The dynamic models that estimate the fluid pressures, temperatures, and flow rates, as well as the electrical and mechanical power consumption, are validated against the operating data streamed through the OptiCX System. To demonstrate the capabilities of this digital twin tool in a preventive maintenance mode, various degradations are virtually investigated in the chiller plant\u27s components. The mechanical pump efficiency, electric pump motor friction, pipe blockage, air flow rate sensor, and the expansion valve opening were degraded by 3% to 5%, which impacted component behavior and system performance. The analysis of these predicted plant signals helped to establish preventive maintenance thresholds on these components, which should promote improved plant reliability. A digital twin provides additional flexibility than stand-alone monitoring technologies due to the capability of simulating customized scenarios for analyzing failure-prone conditions and overall equipment effectiveness (OEE). The PLM-based digital twin offers a design and prognostic platform for HVAC systems

Feasibility Study of Jet-Ejector Refrigeration Systems as a Mechanism for Harnessing Low-Grade Thermal Energy from Different Sources

[ES] Los sistemas de refrigeración por eyección activados por calor de origen renovable o fuentes de calor residual tienen el potencial de alcanzar ahorros energéticos significativos al sustituir o asistir a los sistemas de refrigeración tradicionales. Su campo de aplicabilidad es muy amplio y el presente trabajo se ha centrado en un estudio detallado de dos aplicaciones con gran potencial siguiendo un enfoque computacional: (i) generación de aire acondicionado activado por energía solar térmica y (ii) refrigeración de la admisión de un motor de combustión reutilizando la energía térmica disponible en la línea de escape de este. Las actividades de investigación han estado dirigidas a mitigar dos de los principales puntos débiles que caracterizan a los ciclos de refrigeración por eyección: su eficiencia relativamente baja y la incapacidad mostrada por la configuración base del ciclo de eyección para operar de forma robusta en condiciones de operación alejadas de las de diseño. La primera cuestión ha sido abordada principalmente diseñando geometrías de eyector altamente optimizadas usando técnicas de mecánica de fluidos computacional y optimizando la integración del eyector en el conjunto del sistema de refrigeración. La segunda cuestión se ha abordado caracterizando el comportamiento del sistema en condiciones de diseño y fuera de diseño. Se han propuesto dos estrategias avanzadas para hacer frente a la caída de prestaciones que sufre el sistema al operar en condiciones fuera de diseño, como son la utilización de eyectores de geometría ajustable o la implementación de tanques de almacenamiento térmico. La respuesta del sistema se ha analizado en condiciones fuera de diseño con dos aproximaciones temporales complementarias. Los modelos estacionarios se han usado para optimizar las diferentes arquitecturas de eyector y la operación global del sistema en ciertas condiciones de operación representativas, mientras que el análisis transitorio representa un enfoque más realista y tiene en cuenta la naturaleza impredecible e inestable de la climatología. El estudio se ha concluido con un análisis termoeconómico, el cual ha sido útil para discernir si los diseños altamente optimizados son competitivos al ser comparados con las soluciones de refrigeración que se encuentran actualmente consolidadas en el mercado. La principal conclusión del análisis en condiciones estáticas para la aplicación termosolar es que la transformación de potencia térmica a potencia de refrigeración puede alcanzar un rendimiento del 37.7%, mientras que el rendimiento global del sistema alcanza el 20.1% con diseños altamente optimizados de eyector para unas condiciones de evaporación y condensación de 13°C y 40°C, respectivamente. En condiciones dinámicas, la implementación de la geometría variable mejora en torno a un 40% el rendimiento del sistema de refrigeración, además de incrementar su operatividad. El tanque de almacenamiento térmico juega un papel relevante en este aspecto y, para una envergadura de colector parabólico de 7.1 m, un consumo nominal de 13.3 kW de potencia térmica del tanque ha resultado ser una solución de compromiso para mantener en equilibrio los principales indicadores de prestaciones. El análisis termoeconómico de la arquitectura más prometedora sugiere que el ahorro de coste operativo está lejos de poder compensar la elevada inversión inicial en equipamiento (16.905€ para una capacidad de refrigeración aproximada de 5.6 kW), destacando la dificultad del sistema para competir con las soluciones de refrigeración actualmente consolidadas en el mercado y resaltando la necesidad de considerar soluciones híbridas. La principal conclusión de la aplicación en motor de combustión es que la reducción de temperaturas en la línea de admisión por debajo de 4°C es factible, produciendo mejoras en el rendimiento volumétrico de en torno al 11%, no obstante, el sistema muestra vulnerabilidades al operar en puntos de motor diferentes al de diseño.[CA] Els sistemes de refrigeració per ejecció activats per calor d'origen renovable o fonts de calor residual tenen el potencial d'assolir estalvis energètics significatius al substituir o assistir als sistemes de refrigeració tradicionals. El seu camp d'aplicabilitat es ampli i el present treball s'ha centrat en un estudi detallat de dos aplicacions amb gran potencial seguint un enfocament computacional: (i) generació d'aire condicionat activat per energia solar tèrmica i (ii) refrigeració de l'admissió d'un motor de combustió reutilitzant l'energia tèrmica disponible en la línia d'escapament d'aquest. Les activitats d'investigació han estat dirigides a mitigar dos dels principals punts dèbils que caracteritzen als cicles de refrigeració per ejecció: la seua eficiència relativament baixa i la incapacitat mostrada per la configuració base del cicle d'ejecció per a operar de forma robusta en condicions d'operació allunyades de les de disseny. La primera qüestió ha sigut abordada principalment dissenyant geometries d'ejector altament optimitzades usant tècniques de mecànica de fluids computacional i optimitzant la integració de l'ejector en el conjunt del sistema de refrigeració. La segona qüestió s'ha abordat caracteritzant el comportament del sistema en condicions de disseny i fora de disseny. S'han proposat dos estratègies avançades per a fer front a la caiguda de prestacions que pateix el sistema quan opera en condicions fora de disseny, com són la utilització d'ejectors de geometria ajustable o la implementació de tancs de emmagatzemament tèrmic. La resposta del sistema s'ha analitzat en condicions fora de disseny amb dos aproximacions temporals complementàries. Els models estacionaris s'han usat per a optimitzar les diferents arquitectures d'ejector i l'operació global del sistema en certes condicions d'operació representatives, mentre que l'anàlisi transitori representa un enfocament més realista i té en compte la natura impredictible i inestable dels canvis en les condiciones climàtiques. L'estudi s'ha conclòs amb un anàlisi termoeconòmic, el qual ha sigut útil per a discernir si els dissenys altament optimitzats són competitius quan es comparen amb les solucions de refrigeració que es troben actualment consolidades al mercat. La principal conclusió de l'anàlisi en condicions estàtiques per a l'aplicació termosolar és que la transformació de potència tèrmica a potència de refrigeració pot arribar a un rendiment del 37.7%, mentre que el rendiment global del sistema arriba al 20.1 % amb dissenys altament optimitzats d'ejector per a unes condicions d'evaporació i condensació de 13°C i 40°C, respectivament. En condicions dinàmiques, la implementació de la geometria variable millora al voltant d'un 40% el rendiment del sistema de refrigeració, a més d'incrementar la seua capacitat de romandre en funcionament. El tanc d'emmagatzemament tèrmic juga un paper rellevant en aquest aspecte i, per a una llargària de col·lector parabòlic de 7.1 m, un consum nominal de 13.3 kW de potencia tèrmica del tanc ha resultat ser una solució de compromís per a mantenir en equilibri els principals indicadors de prestacions. L'anàlisi termoeconòmic de l'arquitectura més prometedora suggereix que l'estalvi de cost operatiu està lluny de poder compensar l'elevada inversió inicial en equipament (16.905€ per a una capacitat de refrigeració aproximada de 5.6 kW), posant de manifest la dificultat del sistema per a competir amb les solucions de refrigeració actualment consolidades al mercat i ressaltant la necessitat de considerar solucions híbrides. La principal conclusió de l'aplicació en motor de combustió és que la reducció de temperatures a la línia d'admissió per baix de 4°C és factible, produint millores en el rendiment volumètric de al voltant de l'11%, no obstant això, el sistema mostra vulnerabilitats a l'hora d'operar en punts de motor diferents al de disseny.[EN] Jet-ejector refrigeration systems powered by renewable heat or waste heat sources have the potential to achieve significant primary energy savings when substituting or aiding traditional refrigeration systems. Their field of applicability is vast and the present work has been focused on a detailed study of two applications with great potential following a computational approach: (i) air-conditioning generation powered by solar thermal energy and (ii) internal combustion engine intake air refrigeration powered by its exhaust line waste heat. The research efforts have been directed towards mitigating the negative effect of two of the main weak points of jet-ejector refrigeration systems: their relatively low efficiency and the incapacity of the baseline configuration to operate robustly away from the design conditions. The first issue has been addressed mainly by designing highly optimized jet-ejector geometries using computational fluid dynamics techniques and optimizing the jet-ejector integration in the overall system. The second one has been addressed by carrying out complete characterizations of the refrigeration system response in design and off-design conditions. Advanced strategies to face the refrigeration system performance decay away from design conditions have been proposed, like the utilization of adjustable jet-ejector architectures or the implementation of hot thermal storage tanks. The system response has been analyzed in off-design conditions with two complementary temporal schemes. The steady-state models have been used to optimize the jet-ejector architectures and the overall system operation for representative operating scenarios, while the transient analysis represents a more realistic approach and accounts for changes in climatic conditions, which have an unpredictable and unstable nature. The study has been concluded with a thermoeconomic analysis, which has been useful to discern if the highly optimized designs are competitive when compared to existing refrigeration solutions consolidated in the market. The main conclusions of the steady-state analysis for the solar application are that the transformation from thermal power to refrigeration power can achieve an efficiency of 37.7%, while the global efficiency achieves 20.1% when highly optimized jet-ejectors are used for an evaporating and condensing conditions of 13°C and 40°C, respectively. In dynamic conditions, the implantation of an adjustable jet-ejector brings improvements in refrigeration system efficiency of around 40%, besides improving its capacity to remain in operation. The thermal storage system plays a relevant role in this sense and, for a fixed parabolic trough collector span of 7.1 m, a nominal thermal power consumption of 13.3 kW represents a trade-off between the performance indicators subject to analysis. The thermoeconomic assessment of the most promising system architecture suggests that the operating cost savings are far from compensating for the capital expenditures (16,905€ for a refrigeration capacity of approximately 5.6 kW), evidencing the difficulties of the system to compete against refrigeration solutions currently consolidated in the market and outlining the interest in hybrid solutions. The main conclusion of the automotive application is that it is feasible to achieve in the engine intake line temperatures below 4°C, bringing improvements in volumetric engine efficiency of around 11%. Nevertheless, the system shows vulnerabilities when operating in engine operating points different from the design one.My most sincere acknowledgment to the whole CMT-Motores Térmicos team for giving me the opportunity of being part of it and the grant program Subvenciones para la contrataci ́on de personal investigador predoctoral for doctoral studies (reference ACIF/2018/124), awarded by Generalitat Valenciana, Conselleria de Innovación, Universidades, Ciencia y Sociedad Digital and the European Union for funding this project.Ponce Mora, A. (2022). Feasibility Study of Jet-Ejector Refrigeration Systems as a Mechanism for Harnessing Low-Grade Thermal Energy from Different Sources [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/18171

Energy impact of the Internal Heat Exchanger in a horizontal freezing cabinet. Experimental evaluation with the R404A low-GWP alternatives R454C, R455A, R468A, R290 and R1270

This work analyses the influence of the Internal Heat Exchan ger (IHX) on the energy performance of a vapor compression cycle associated with a freezing cabinet using different R404A low-GWP alternatives. Among them, the refrigerants R454C (GPW100=146), R455A (GPW100=146), R468A (GPW100=146), R290 (GPW100=5) and R1270 (GPW100=1.8) have been tested in a horizontal freezing cabinet maintaining a product target temperature of -20°C at the heat rejection temperatures of 20, 30 and 40°C. The results from tests show that the use of the IHX reduces energy consumption in all scenarios without significantly increasing the compressor's discharge temperature. For a test period of 16 hours, the refrigerants that offer better reductions are R404A and R1270, followed by R455A, R290, R454C and R468A. The maximum energy saving is rated to 9.2% at the heat rejection temperature of 40°C, demonstrating that the enhancement of the IHX is better as higher the heat rejection conditions are.Funding for open access charge: CRUE-Universitat Jaume

Screening of energy efficient technologies for industrial buildings' retrofit

This chapter discusses screening of energy efficient technologies for industrial buildings' retrofit

Predictive Controller for Refrigeration Systems Aimed to Electrical Load Shifting and Energy Storage

The need to reduce greenhouse gas emissions is leading to an increase in the use of renewable energy sources. Due to the aleatory nature of these sources, to prevent grid imbalances, smart management of the entire system is required. Industrial refrigeration systems represent a source of flexibility in this context: being large electricity consumers, they can allow large-load shifting by varying separator levels or storing surplus energy in the products and thus balancing renewable electricity production. The work aims to model and control an industrial refrigeration system used for freezing food by applying the Model Predictive Control technique. The controller was developed in Matlab® and implemented in a Model-in-the-Loop environment. Two control objectives are proposed: the first aims to minimize total energy consumption, while the second also focuses on utilizing the maximum amount of renewable energy. The results show that the innovative controller allows energy savings and better exploitation of the available renewable electricity, with a 4.5% increase in its use, compared to traditional control methods. Since the proposed software solution is rapidly applicable without the need to modify the plant with additional hardware, its uptake can contribute to grid stability and renewable energy exploitation