Estudio teórico-experimental de compresores de pistón herméticos con diferentes refrigerantes

[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 no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/135957TESI

Virtual sensor of insufficient lubrication in variable speed compressors

The ability to modulate the compressor’s speed and adapt the capacity to the load has permitted to decrease the annual energy consumption in many applications. However, in the compressor, having the correct lubrication at high speeds usually imply having insufficient lubrication at low speeds. This fact has to be considered by manufacturers as it limits the speed range of the compressor. In this study, a methodology to establish the working limit of a compressor is proposed. It is based on the specific consumption surface of the compressor and no oil circulation measurements are required. A compressor working between 6600 and 900rpm with propane and POE oil has been used to test the proposed methodology. The results show that lubricating issues in this compressor start at 1800rpm and rise as speed decreases.The authors would like to acknowledge the Spanish “MINISTERIO DE ECONOMIA Y COMPETITIVIDAD”, through the project ref- ENE2017-83665-C2-1-P “Maximización de la eficiencia y minimización del impacto ambiental de bombas de calor para la descarbonización de la calefacción/ acs en los edificios de consumo casi nulo” for the given support. In addition, Ruben Ossorio would like to thank the Spanish government for his PhD scholarship with reference PRE2018-083535

Influence of the Thermal Energy Storage Strategy on the Performance of a Booster Heat Pump for Domestic Hot Water Production System Based on the Use of Low Temperature Heat Source

[EN] Energy recovery from a low temperature heat source using heat pump technology is becoming a popular application. The domestic hot water demand has the characteristic of being very irregular along the day, with periods in which the demand is very intensive and long periods in which it is quite small. In order to use heat pumps for this kind of applications efficiently, the proper sizing and design of the water storage tank is critical. In this work, the optimal sizing of the two possible tank alternatives, closed stratified tank and variable-water-volume tank, is presented, and their respective performance compared, for domestic hot water production based on low temperature energy recovery in two potential applications (grey water and ultra-low temperature district heating). The results show that the efficiency of these kind of systems is very high and that variable-water-volume tanks allow a better use of the energy source, with an 8% higher exergy efficiency and around 3% better seasonal performance factor (SPF), being able to provide similar comfort levels with a smaller system size"Vicerectorado de Investigacion, Innovacion y Transferencia of the Universitat Politecnica de Valencia (Spain)" throught the project "REDUCCION DE LAS EMISIONES DE CO2 A ALTA TEMPERATURE A PARTIR DE LA RECUPERACION DE CALOR RESIDUAL MEDIANTE EL USO DE UNA BOMBA DE CALOR"with the reference SP20180039 from the program "Primeros proyectos de investigacion (PAID-06-18)".Masip, X.; Navarro-Peris, E.; Corberán, JM. (2020). Influence of the Thermal Energy Storage Strategy on the Performance of a Booster Heat Pump for Domestic Hot Water Production System Based on the Use of Low Temperature Heat Source. Energies. 13(24):1-24. https://doi.org/10.3390/en13246576S12413242050 Long-Term Strategy https://ec.europa.eu/clima/policies/strategies/2050_enEnergy Consumption Buildings https://ec.europa.eu/energy/en/topics/energy-efficiency/buildingsEnergy Consumption in Households http://ec.europa.eu/eurostat/statistics-explained/index.php/Energy_consumption_in_householdshttps://www.google.com.hk/url?sa=t&rct=j&q=&esrc=s&source=web&cd=&cad=rja&uact=8&ved=2ahUKEwip0ubH48ztAhUEMN4KHRmLA0kQFjABegQIAxAC&url=https%3A%2F%2Feur-lex.europa.eu%2FLexUriServ%2FLexUriServ.do%3Furi%3DOJ%3AL%3A2009%3A140%3A0016%3A0062%3Aen%3APDF&usg=AOvVaw10tSQ3SpiUkxpXKuCB6R0nCecchinato, L., Corradi, M., Fornasieri, E., & Zamboni, L. (2005). Carbon dioxide as refrigerant for tap water heat pumps: A comparison with the traditional solution. International Journal of Refrigeration, 28(8), 1250-1258. doi:10.1016/j.ijrefrig.2005.05.019Pitarch, M., Navarro-Peris, E., Gonzálvez-Maciá, J., & Corberán, J. M. (2017). Experimental study of a subcritical heat pump booster for sanitary hot water production using a subcooler in order to enhance the efficiency of the system with a natural refrigerant (R290). International Journal of Refrigeration, 73, 226-234. doi:10.1016/j.ijrefrig.2016.08.017Pitarch, M., Hervas-Blasco, E., Navarro-Peris, E., Gonzálvez-Maciá, J., & Corberán, J. M. (2017). Evaluation of optimal subcooling in subcritical heat pump systems. International Journal of Refrigeration, 78, 18-31. doi:10.1016/j.ijrefrig.2017.03.015Hervas-Blasco, E., Pitarch, M., Navarro-Peris, E., & Corberán, J. M. (2018). Study of different subcooling control strategies in order to enhance the performance of a heat pump. International Journal of Refrigeration, 88, 324-336. doi:10.1016/j.ijrefrig.2018.02.003Meggers, F., & Leibundgut, H. (2011). The potential of wastewater heat and exergy: Decentralized high-temperature recovery with a heat pump. Energy and Buildings, 43(4), 879-886. doi:10.1016/j.enbuild.2010.12.008Liu, L., Fu, L., & Jiang, Y. (2010). Application of an exhaust heat recovery system for domestic hot water. Energy, 35(3), 1476-1481. doi:10.1016/j.energy.2009.12.004Baek, N. C., Shin, U. C., & Yoon, J. H. (2005). A study on the design and analysis of a heat pump heating system using wastewater as a heat source. Solar Energy, 78(3), 427-440. doi:10.1016/j.solener.2004.07.009Bertrand, A., Aggoune, R., & Maréchal, F. (2017). In-building waste water heat recovery: An urban-scale method for the characterisation of water streams and the assessment of energy savings and costs. Applied Energy, 192, 110-125. doi:10.1016/j.apenergy.2017.01.096High Efficiency Heat Pump for Domestic Hot Water Generation http://docs.lib.purdue.edu/iracc%0Ahttp://docs.lib.purdue.edu/iracc/953Østergaard, P. A., & Andersen, A. N. (2018). Economic feasibility of booster heat pumps in heat pump-based district heating systems. Energy, 155, 921-929. doi:10.1016/j.energy.2018.05.076Fischer, D., Toral, T. R., Lindberg, K. B., Wille-Haussmann, B., & Madani, H. (2014). Investigation of Thermal Storage Operation Strategies with Heat Pumps in German Multi Family Houses. Energy Procedia, 58, 137-144. doi:10.1016/j.egypro.2014.10.420Han, Y. M., Wang, R. Z., & Dai, Y. J. (2009). Thermal stratification within the water tank. Renewable and Sustainable Energy Reviews, 13(5), 1014-1026. doi:10.1016/j.rser.2008.03.001Haller, M. Y., Haberl, R., Mojic, I., & Frank, E. (2014). Hydraulic Integration and Control of Heat Pump and Combi-storage: Same Components, Big Differences. Energy Procedia, 48, 571-580. doi:10.1016/j.egypro.2014.02.067Liu, F., Zhu, W., Cai, Y., Groll, E. A., Ren, J., & Lei, Y. (2017). Experimental performance study on a dual-mode CO2 heat pump system with thermal storage. Applied Thermal Engineering, 115, 393-405. doi:10.1016/j.applthermaleng.2016.12.095Castell, A., Medrano, M., Solé, C., & Cabeza, L. F. (2010). Dimensionless numbers used to characterize stratification in water tanks for discharging at low flow rates. Renewable Energy, 35(10), 2192-2199. doi:10.1016/j.renene.2010.03.020Armstrong, P., Ager, D., Thompson, I., & McCulloch, M. (2014). Domestic hot water storage: Balancing thermal and sanitary performance. Energy Policy, 68, 334-339. doi:10.1016/j.enpol.2014.01.012Hervás-Blasco, E., Navarro-Peris, E., & Corberán, J. M. (2019). Optimal design and operation of a central domestic hot water heat pump system for a group of dwellings employing low temperature waste heat as a source. Energy, 188, 115979. doi:10.1016/j.energy.2019.115979Next Generation of Heat Pumps Working with Natural Fluids (NxtHPG) http://www.nxthpg.eu/Transient Systems Simulation Homepage http://www.trnsys.comMasip, X., Cazorla-Marín, A., Montagud-Montalvá, C., Marchante, J., Barceló, F., & Corberán, J. M. (2019). Energy and techno-economic assessment of the effect of the coupling between an air source heat pump and the storage tank for sanitary hot water production. Applied Thermal Engineering, 159, 113853. doi:10.1016/j.applthermaleng.2019.11385

Modeling and validation of the effects of soft faults on the operation of an air source heat pump in cooling mode

Some faults in heat pumps cannot be easily detected and diagnosed, as the system appears to function correctly, but it is working with lower efficiency. These soft faults occur either due to faults during installation or slowly over time, letting the heat pump operate without maintenance. It is relevant to acquire data from heat pumps operating with soft faults to develop techniques for detecting and diagnosing these faults. As this is a difficult task, we have modeled an air source heat pump in cooling mode, and performed simulations under different conditions of faults such as inadequate refrigerant charge, evaporator fouling, and compressor valve leakage. We validate them with available data from experimental tests fault-free and tests in which these faults have been imposed. Based on the model, we calculate the effects of soft faults when they appear at different levels and their impact on the Seasonal Energy Efficiency Ratio (SEER).The authors would like to acknowledge the Spanish “Ministerio de Ciencia e Innovación”, through the project ref: PID2020-115665RB-I00 “Decarbonización de edificios e industrias con sistemas híbridos de bomba de calor” for the given support. Belén Llopis-Mengual acknowledges the Spanish “Ministerio de Universidades” through the “Formación de Profesorado Universitario” program ref. FPU 19/04012

Closing the residential energy loop: Grey-water heat recovery system for domestic hot water production based on heat pumps

[EN] Passive houses linked to more efficient heating and cooling technologies have been one of the focus in last years. However, to close the loop of the building sector, there is still one open source: wasted heat from grey water. This paper addresses the potentiality of the wasted heat from grey water as a heat source to produce domestic hot water (DHW) based on a heat pump system (HP). A heat pump optimized for these applications, a heat recovery heat exchanger and two variable volume storage tanks compose the system. The main objective of this work is to determine the potential recovery of the wasted heat in order to minimize the building energy consumption. Design guidelines of the components and the analysis of an optimum operation algorithm of the system have been performed in order to minimize CO2 emissions. In addition, an evaluation of the potential heat recovery of the wasted heat is included. As an example, that methodology has been applied to 20 dwellings. Based on that case, the obtained results demonstrate that by recovering 80% of the available recovery heat, the total demand of DHW is satisfied with high levels of comfort and efficiency.Part of the work presented was carried out by Estefania Hervas Blasco with the financial support of a PhD scholarship from the Spanish government SFPI1500 x074478XV0. The authors would like also to acknowledge the Spanish `Ministerio de Economia Y Competitividad', through the project "Maximizacion de la Eficiencia Y Minimizacion del Impacto Ambiental de Bombas de Calor Para la Descarbonizacion de la Calefaccion/ACS EN Los Edificios de Consumo Casi Nulo" with the reference ENE2017-83665-C2-1-P for the given support.Hervás-Blasco, E.; Navarro-Peris, E.; Corberán, JM. (2020). Closing the residential energy loop: Grey-water heat recovery system for domestic hot water production based on heat pumps. Energy and Buildings. 216:1-15. https://doi.org/10.1016/j.enbuild.2020.109962S115216García-Álvarez, M. 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Energy Conversion and Management, 88, 700-722. doi:10.1016/j.enconman.2014.08.065Spriet, J., & McNabola, A. (2019). Decentralized drain water heat recovery from commercial kitchens in the hospitality sector. Energy and Buildings, 194, 247-259. doi:10.1016/j.enbuild.2019.04.032Baek, N. C., Shin, U. C., & Yoon, J. H. (2005). A study on the design and analysis of a heat pump heating system using wastewater as a heat source. Solar Energy, 78(3), 427-440. doi:10.1016/j.solener.2004.07.009Nehm G., Nehme G., Palandre L., Clodic D.Purdue e-Pubs high efficiency heat pump for domestic hot water generation2008.Dar, U. I., Sartori, I., Georges, L., & Novakovic, V. (2014). Advanced control of heat pumps for improved flexibility of Net-ZEB towards the grid. Energy and Buildings, 69, 74-84. doi:10.1016/j.enbuild.2013.10.019Cecchinato, L., Corradi, M., Fornasieri, E., & Zamboni, L. (2005). Carbon dioxide as refrigerant for tap water heat pumps: A comparison with the traditional solution. International Journal of Refrigeration, 28(8), 1250-1258. doi:10.1016/j.ijrefrig.2005.05.019Kharagpur Indian Institute of Technology. Lesson 10 - Vapour Compression refrigeration systems. Refrig. Air Cond. Lect.2005:1–18.Gluesenkamp K.R., Patel V., Abdelaziz O., Mandel B., Dealmeida V.High efficiency water heating technology development-final report, part II: CO2 and absorption-based residential heat pump water heater development. 2017.Miquel Pitarch i Mocholí. High capacity heat pump development for sanitary hot water production. 2017.Hervás-Blasco, E., Navarro-Peris, E., Barceló-Ruescas, F., & Corberán, J. M. (2019). Improved water to water heat pump design for low-temperature waste heat recovery based on subcooling control. International Journal of Refrigeration, 106, 374-383. doi:10.1016/j.ijrefrig.2019.06.030Tammaro, M., Montagud, C., Corberán, J. M., Mauro, A. W., & Mastrullo, R. (2017). Seasonal performance assessment of sanitary hot water production systems using propane and CO 2 heat pumps. International Journal of Refrigeration, 74, 224-239. doi:10.1016/j.ijrefrig.2016.09.026Jensen, J. B., & Skogestad, S. (2007). Optimal operation of simple refrigeration cycles. Computers & Chemical Engineering, 31(5-6), 712-721. doi:10.1016/j.compchemeng.2006.12.003Pitarch, M., Navarro-Peris, E., Gonzálvez-Maciá, J., & Corberán, J. M. (2017). Evaluation of different heat pump systems for sanitary hot water production using natural refrigerants. Applied Energy, 190, 911-919. doi:10.1016/j.apenergy.2016.12.166Koeln, J. P., & Alleyne, A. G. (2014). Optimal subcooling in vapor compression systems via extremum seeking control: Theory and experiments. International Journal of Refrigeration, 43, 14-25. doi:10.1016/j.ijrefrig.2014.03.012Hervas-Blasco, E., Pitarch, M., Navarro-Peris, E., & Corberán, J. M. (2018). Study of different subcooling control strategies in order to enhance the performance of a heat pump. International Journal of Refrigeration, 88, 324-336. doi:10.1016/j.ijrefrig.2018.02.003Chow, T. T., Pei, G., Fong, K. F., Lin, Z., Chan, A. L. S., & He, M. (2010). Modeling and application of direct-expansion solar-assisted heat pump for water heating in subtropical Hong Kong. Applied Energy, 87(2), 643-649. doi:10.1016/j.apenergy.2009.05.036Baek N.C., Shin U.C., Yoon J.H.A study on the design and analysis of a heat pump heating system using wastewater as a heat source2004. doi:10.1016/j.solener.2004.07.009.REULENS, W., ‘Natural refrigerant CO2 edited by Walter Reulens October 2009 (Leonardo project)’ http://www.atmosphere2009.com/files/NaReCO2-handbook-2009.pdf.Tammaro, M., Montagud, C., Corberán, J. M., Mauro, A. W., & Mastrullo, R. (2015). A propane water-to-water heat pump booster for sanitary hot water production: Seasonal performance analysis of a new solution optimizing COP. International Journal of Refrigeration, 51, 59-69. doi:10.1016/j.ijrefrig.2014.12.008Spriet, J., & McNabola, A. (2019). Decentralized drain water heat recovery: A probabilistic method for prediction of wastewater and heating system interaction. Energy and Buildings, 183, 684-696. doi:10.1016/j.enbuild.2018.11.036Hervás-Blasco, E., Navarro-Peris, E., & Corberán, J. M. (2019). Optimal design and operation of a central domestic hot water heat pump system for a group of dwellings employing low temperature waste heat as a source. Energy, 188, 115979. doi:10.1016/j.energy.2019.115979Ferrantelli, A., Ahmed, K., Pylsy, P., & Kurnitski, J. (2017). Analytical modelling and prediction formulas for domestic hot water consumption in residential Finnish apartments. Energy and Buildings, 143, 53-60. doi:10.1016/j.enbuild.2017.03.021Zhen L., Lin D.M., Shu H.W., Jiang S., Zhu Y.X. 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Feasibility study of a localized residential grey water energy-recovery system. Applied Thermal Engineering, 39, 53-62. doi:10.1016/j.applthermaleng.2012.01.031Bertrand, A., Aggoune, R., & Maréchal, F. (2017). In-building waste water heat recovery: An urban-scale method for the characterisation of water streams and the assessment of energy savings and costs. Applied Energy, 192, 110-125. doi:10.1016/j.apenergy.2017.01.096Liu, L., Fu, L., & Jiang, Y. (2010). Application of an exhaust heat recovery system for domestic hot water. Energy, 35(3), 1476-1481. doi:10.1016/j.energy.2009.12.004Chen, W., Liang, S., Guo, Y., Cheng, K., Gui, X., & Tang, D. (2013). Investigation on the thermal performance and optimization of a heat pump water heater assisted by shower waste water. Energy and Buildings, 64, 172-181. doi:10.1016/j.enbuild.2013.04.021McNabola, A., & Shields, K. (2013). Efficient drain water heat recovery in horizontal domestic shower drains. 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Comparison of the performance of a vapor-injection scroll compressor and a two-stage scroll compressor working with high pressure ratios

[EN] This paper presents a comparative analysis of the performance of a vapor-injection scroll compressor (SCVI) and a two-stage scroll compressor (TSSC) working with high pressure ratios in heat pump applications. Semi-empirical models of the compressors are implemented. The models are adjusted with experimental data obtained in a calorimetric test bench. The optimum displacement ratio (DR) is analyzed considering two criteria, COP maximization, and discharge temperature minimization. Once defined the optimum DR, a systematic comparison of the compressors is performed in terms of compressor efficiencies, heating capacity, COP, and discharge temperature. Finally, the intermediate pressure is optimized for a high-temperature water heating application, taking into account heat sink of finite capacity. Results show that the optimum DR of TSSC is around 0.58 and the COP is 6% larger than that the SCVI at the nominal point. Considering a wide range of operating conditions, the SCVI presents better efficiency and COP for pressure ratios below 5. For higher-pressure ratios, the TSSC presents better performance and achieves lower discharge temperature. The heating capacity of the TSSC can be improved by 7% by varying the swept volume of the high-stage compressor compared with the SCVI, with a minimum effect on the COP and on the discharge temperature from the optimum conditions.Fernando M. Tello-Oquendo acknowledges the financial support provided by the CONVOCATORIA ABIERTA 2013-SEGUNDA FASE program, which was funded by the SENESCYT (Secretaría de Educación Superior, Ciencia, Tecnología e Innovación) (Grant No. 2015-AR37665) of Ecuador. The authors would like to acknowledge Emerson Commercial and Residential Solutions for the given support to obtain the experimental data of scroll compressors and testing. In addition, the authors acknowledge the Spanish MINISTERIO DE ECONOMIA Y COMPETITIVIDAD , through the project ref-ENE2017-83665-C2-1-P Maximización de la eficiencia y minimización del impacto ambiental de bombas de calor para la descarbonización de la calefacción/ACS en los edificios de consumo casi nulo for the given support.Tello-Oquendo, FM.; Navarro-Peris, E.; Gonzálvez-Maciá, J. (2019). Comparison of the performance of a vapor-injection scroll compressor and a two-stage scroll compressor working with high pressure ratios. Applied Thermal Engineering. 160:1-15. https://doi.org/10.1016/j.applthermaleng.2019.114023S11516

Comparison of Transcritical and Subcritical Heat Pump Systems for Domestic Hot Water Production in Energy Recovery Applications

Water-to-Water heat pump (WtWHP) is an efficient alternative to the current technologies used in Domestic Hot Water (DHW) production. However, this application is characterized by high secondary temperature lifts and irregular demands that define critically its design. In order to maximize the efficiency, transcritical cycles coupled to stratified storage tank has been the preferred solution. Nevertheless, recently subcritical cycles with a subcooling control system has been also considered also as a promising alternative because of the cost with the right desing the efficiencies could be in the range of transcritical system. The objective of this work is to compare the performance of both heat pump systems for DHW production in a heat recovery application where there is no restriction in the low temperature energy source availability. This situation could correspond to a source coming from sewage water or a system of low temperature district heating. The comparison has been made for the optimum configuration of both system which has implied the definition of the proper control strategy, proper sizing of the WtWHP and the tank and incorporation of a primary recovery heat exchanger in order to compare both systems in what is considered as the optimum working conditions. Results show that while both systems are able to operate with similar SCOPs, the CO2 system is more sensitive to water temperature lifts variations and temperature of the heat source than the propane WtWHP resulting in lower performances

Analysis of variable speed vapor injection scroll compressors working with several refrigerants: Empirical correlation for the characterization and optimization of the intermediate conditions

Vapor-injection scroll compressors (SCVI) are present in the market since many years. There are several studies in the literature dealing with their proper characterization and the development of correlation in order to estimate properly its intermediate working conditions. The main objective of these correlations is the prediction of the compressor behavior for any condition based on a reduced number of test. Derived from that a correlation would be better as less parameter it will require, as this will imply less number of test in order to determine it. Nowadays, variable speed SCVI are being installed more widely but not so much studies are available for these type of compressors. In this work, based on previous correlations obtained for constant speed SCVI, a correlation for variable SCVI has been obtained. In order to do that, a set of experimental calorimetric test has been conducted for different condensing and evaporating temperatures and 4 different compressor speeds. From these data, it has been possible to obtain a correlation depending in four parameters able to predict the intermediate conditions (pressure and temperature), the mass flow rates and the energy consumption with an error lower than 3%. The correlation has been checked with other sources of data available in the public literature obtaining similar deviations from the measured values. Finally and based on these results, the optimum intermediate operation conditions for an injection heat pump with an economizer has been determined in different external conditions. From the optimization process an improvement in COP up to 5% could be expected from the theoretical analysis