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)

[EN] This paper presents the experimental results obtained from a new heat pump prototype for sanitary hot water production, in the application of heat recovery from water sources like sewage water or condensation loops (typical temperature condition between 10 degrees C and 30 degrees C). The system configuration is able to produce a high degree of subcooling in order to take advantage from the high water temperature glide (typical value for sanitary hot water production is 10 degrees C to 60 degrees C). Subcooling is made by using a separate heat exchanger from the condenser (subcooler). The obtained results have shown a high degree of improvement by making subcooling. COP is 5.61 in nominal conditions, which is about 31% higher than the same cycle working without subcooling (Nominal point: inlet/outlet water temperature at evaporator is 20 degrees C/15 degrees C and the water inlet/outlet temperature in the heat sink is 10 degrees C and 60 degrees C). (C) 2016 Elsevier Ltd and HR. All rights reserved.This work has been developed in the European Union Seventh Framework Programme by the project Next Generation of Heat Pump Technologies (NEXTGHP) grant agreement 307169. The authors give thanks for the given support. Part of the work presented was carried by Miguel Pitarch-Mocholi with the financial support of the Phd scholarship from the Universitat Politecnica de Valencia.Pitarch, M.; Navarro-Peris, E.; Gonzálvez-Maciá, J.; Corberán, JM. (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.2016.08.017S2262347

How to achieve full liquid conditions at the capillary tube inlet of a household refrigerator

[EN] The capillary tube with a liquid-to-suction heat exchanger (CT-LSHX) is a component that is widely used in household refrigerators. Recent works have indicated that even when measuring subcooled conditions at the condenser outlet, the condition at the capillary tube inlet is a two-phase flow. The present work was dedicated to analyzing the actual refrigerant conditions at the capillary tube inlet and to investigating how full liquid conditions could be achieved. The research was performed using a typical household refrigerator with corresponding fresh food and freezer compartments, replacing the original refrigerant-to-air condenser with a refrigerant-to-water condenser. This allowed, first, the condensation conditions to be controlled and, second, the estimation of the refrigerant conditions at the condenser outlet from the heat exchanger balance. The obtained results indicated the presence of a non-equilibrium two-phase flow, composed of subcooled vapor and subcooled liquid, at the capillary tube inlet, with both liquid and vapor entering the capillary tube as a vortex with small, fast fluctuations of the liquid level. This non-equilibrium indicated that the subcooling, evaluated from the pressure and temperature of the refrigerant at the condenser outlet, was only apparent and did not allow the evaluation of the actual enthalpy. Finally, by using a smaller capillary tube diameter and increasing the compressor speed, full liquid conditions at the capillary tube inlet were achieved. Furthermore, a performance comparison between the original and the new design revealed that the COP was higher with full liquid conditions.In this project, the work of Laetitia Bardoulet was partially supported by the Santiago Grisolia 2015 program, which is funded by the Generalitat Valenciana, with the reference number GRISOLIA/2015/021.Bardoulet, L.; Corberán, JM.; Santiago Martínez-Ballester (2019). How to achieve full liquid conditions at the capillary tube inlet of a household refrigerator. International Journal of Refrigeration. 100:265-273. https://doi.org/10.1016/j.ijrefrig.2019.02.006S26527310

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

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. T., Moreno, B., & Soares, I. (2016). Analyzing the sustainable energy development in the EU-15 by an aggregated synthetic index. Ecological Indicators, 60, 996-1007. doi:10.1016/j.ecolind.2015.07.006News and Developments – Architecture 20302018. https://architecture2030.org/news-and-developments/(Accessed 29 November 2018).Energy consumption in households - Statistics Explained2018. http://ec.europa.eu/eurostat/statistics-explained/index.php/Energy_consumption_in_households(Accessed 1 August 2018).Technical | Passive House energy reduection and efficiency2017. http://recoupwwhrs.co.uk/technical/passive-house/(Accessed 1 August 2018).Meggers, 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.2010.12.008Hepbasli, A., Biyik, E., Ekren, O., Gunerhan, H., & Araz, M. (2014). A key review of wastewater source heat pump (WWSHP) systems. 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. District cooling and heating with seawater as heat source and sink in Dalian, China. vol. 32. 2007. doi:10.1016/j.renene.2006.12.015.Torío, H., & Schmidt, D. (2010). Development of system concepts for improving the performance of a waste heat district heating network with exergy analysis. Energy and Buildings, 42(10), 1601-1609. doi:10.1016/j.enbuild.2010.04.002Lund, H., Werner, S., Wiltshire, R., Svendsen, S., Thorsen, J. E., Hvelplund, F., & Mathiesen, B. V. (2014). 4th Generation District Heating (4GDH). Energy, 68, 1-11. doi:10.1016/j.energy.2014.02.089Alnahhal S., Spremberg E.Contribution to exemplary in-house wastewater heat recovery in Berlin, 2016;40:35–40. doi:10.1016/j.procir.2016.01.046.Baek 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.Ni, L., Lau, S. K., Li, H., Zhang, T., Stansbury, J. S., Shi, J., & Neal, J. (2012). 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. Energy and Buildings, 59, 44-49. doi:10.1016/j.enbuild.2012.12.026Wong, L. T., Mui, K. W., & Guan, Y. (2010). Shower water heat recovery in high-rise residential buildings of Hong Kong. Applied Energy, 87(2), 703-709. doi:10.1016/j.apenergy.2009.08.008Postrioti, L., Baldinelli, G., Bianchi, F., Buitoni, G., Maria, F. D., & Asdrubali, F. (2016). An experimental setup for the analysis of an energy recovery system from wastewater for heat pumps in civil buildings. Applied Thermal Engineering, 102, 961-971. doi:10.1016/j.applthermaleng.2016.04.016Hervas-Blasco, E., Pitarch, M., Navarro-Peris, E., & Corberán, J. M. (2017). Optimal sizing of a heat pump booster for sanitary hot water production to maximize benefit for the substitution of gas boilers. Energy, 127, 558-570. doi:10.1016/j.energy.2017.03.131TRNSYS 17. 2009.Fischer, D., Wolf, T., Scherer, J., & Wille-Haussmann, B. (2016). A stochastic bottom-up model for space heating and domestic hot water load profiles for German households. 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Experimental study of a heat pump with high subcooling in the condenser for sanitary hot water production

[EN] The use of heat pumps in order to produce sanitary hot water have been demonstrated as a very efficient alternative to traditional boilers. Nevertheless, the high water temperature lift (usually from 10 degrees C to 60 degrees C) involved in this application has conditioned the type of used solutions. In order to overcome it, transcritical cycles have been considered as the most suitable solution. The current article analyzes a new heat pump prototype able to enhance the heat pump efficiency using a subcritical cycle. The proposed prototype is able to control the system subcooling and make it capable to work at different subcoolings in the condenser. That kind of mechanism has demonstrated its capability to increase the efficiency of the heat pump. The obtained results have shown that coefficient of performance depends strongly on subcooling. In nominal condition (inlet/outlet water temperature at evaporator is 20 degrees C/15 degrees C and the water inlet/outlet temperature in the heat sink is 10 degrees C and 60 degrees C), the optimal subcooling is 42 K with a heating coefficient of performance of 5.35, which is about 25% higher than the same cycle working without subcooling.Pitarch, M.; Navarro-Peris, E.; Gonzálvez-Maciá, J.; Corberán, JM. (2018). Experimental study of a heat pump with high subcooling in the condenser for sanitary hot water production. Science and Technology for the Built Environment. 24(1):105-114. https://doi.org/10.1080/23744731.2017.1333366S10511424

Error estimation of single phase effectiveness and LMTD methodologies when applied to heat exchangers with phase change

[EN] Single phase formulas based on logarithmic mean temperature difference (LMTD) or Effectiveness (E-NTU) are widely and wrongly used for the thermal analysis of evaporators and condensers. Those formulas do not take into account that temperature variation during phase change is due to pressure variation and/or concentration changes when using nonazeotropic refrigerant mixtures. This paper first presents the correct evaluation of the mean temperature difference and effectiveness, for parallel and counter flow arrangements, under the hypothesis of linear temperature variation, for both evaporator and condenser cases. Then, the analytical solution is employed to evaluate the error of applying the single phase formulas of LMTD and Effectiveness to the phase change part of evaporators and condensersCorberán, JM.; Martínez-Ballester, S.; Gonzálvez-Maciá, J.; La-Barbera, C. (2016). Error estimation of single phase effectiveness and LMTD methodologies when applied to heat exchangers with phase change. Journal of Physics: Conference Series (Online). 745(3):1-8. https://doi.org/10.1088/1742-6596/745/3/032125S18745

A critical analysis of the AHRI polynomials for scroll compressor characterization

[EN] This paper presents the analysis of the energy consumption and mass flow rate of scroll-type compressors. The study has included the data of several AHRI reports (especially AHRI 11 and AHRI 21) and data from other sources. A total of 7 different scroll compressors of different sizes have been considered in the study, some of them tested with various refrigerants (R134a, R32, R410A, R404a¿). For all the studied compressors and refrigerants, the compressor energy consumption and mass flow rate values have been analyzed. The main objective is to better understand the dependence of these variables on the operating conditions and the refrigerant used. The analyzed data include tests following different superheat control, i.e., constant superheat or constant return temperature, so the effect of the inlet temperature on these variables is also discussed. As the main novelty of this study, the analysis of the response surfaces has allowed the authors to evaluate the most suitable correlation to use, including an analysis of the necessary experimental tests and where to place them to increase the model's accuracy. It was found that using the condensing and evaporating pressure terms is more universal than the classical temperature domain. In scroll compressors, AHRI polynomials overfits the compressor performance introducing significant deviations in the interpolation and extrapolation capabilities if the experimental data are not properly selected. Finally, it was found that lower degree polynomials are more suitable for this kind of compressor and has also the advantage of requiring fewer experimental point measurements to characterize the compressor with the corresponding cost-savings.The present work has been supported by the project "DECARBONIZACION DE EDIFICIOS E INDUSTRIAS CON SISTEMAS HIBRIDOS DE BOMBA DE CALOR", funded by "Ministerio de Ciencia e Innovacion", MCIN, Spain, with code number: PID2020-115665RB-I00 and by the Ministerio de Educacion, Cultura y Derporte inside the program "Formacion de Profesorado Universitario (FPU15/03476)".Marchante-Avellaneda, J.; Corberán, JM.; Navarro-Peris, E.; SHRESTHA (2023). A critical analysis of the AHRI polynomials for scroll compressor characterization. Applied Thermal Engineering. 219(A):1-18. https://doi.org/10.1016/j.applthermaleng.2022.119432118219

Optimal sizing of a heat pump booster for sanitary hot water production to maximize benefit for the substitution of gas boilers

[EN] Heat recovery from water sources such as sewage water or condensation loops at low temperatures (usually between 10 and 30 °C) is becoming very valuable. Heat pumps are a potential technology able to overcome the high water temperature lift of the Sanitary Hot Water (SHW) application (usually from 10 °C to 60 °C with COPs up to 6). This paper presents a model to find the optimal size of a system (heat pump and recovery heat exchanger) based on water sources to produce SHW compared to the conventional production with a gas boiler in order to maximize the benefit. The model includes a thermal and economic analysis for a base case and analyzes the influence of a wide set of parameters which could have a significant influence. Even the uncertainties involved, results point out considerable benefits from this substitution based on the capacity of the system. Thus, demonstrating the importance of the optimal size analysis before an investment is done.Part of the work presented was carried by Estefania Hervas Blasco with the financial support of a PhD scholarship from the Spanish government SFPI1500X074478XV0. Part of the work presented was carried by Miguel Pitarch-Mocholi with the financial support of a PhD scholarship from the Universitat Politecnica de Valencia. The authors would like also to acknowledge the Spanish 'MINISTERIO DE ECONOMIA Y COMPETITIVIDAD', through the project ref-ENE2014-53311-C2-1-P-AR "Aprovechamiento del calor residual a baja temperatura mediante bombas de calor para la produccion de agua caliente" for the given supportHervas-Blasco, E.; Pitarch, M.; Navarro-Peris, E.; Corberán, JM. (2017). Optimal sizing of a heat pump booster for sanitary hot water production to maximize benefit for the substitution of gas boilers. Energy. 127:558-570. https://doi.org/10.1016/j.energy.2017.03.13155857012

Exergy analysis on a heat pump working between a heat sink and a heat source of finite heat capacity rate

[EN] The optimum performance of a pure subcritical refrigeration cycle depends significantly on the temperature lift of the heat source and sink. Therefore, the maximization of the system efficiency has to be linked to them. This paper shows an exergy analysis of each heat pump component (condenser, evaporator, expansion valve and compressor) considering that the heat source and sink are not at constant temperature. The performed study shows the components with more possibilities for improvement. Based on this analysis, the optimization of cycle parameters like subcooling and superheat as a function of the external conditions have been done. In addition, this work has demonstrated that the components having a higher influence in the system irreversibility's depends significantly on the temperature lift of the secondary fluids. Finally, the obtained results show potentials improvements of the efficiency up to 23% if the system is able to operate in the optimal subcooling and superheat.Part of the results of this study were developed in the mainframe of the FP7 European project 'Next Generation of Heat Pumps workingwith natural fluids' (NxtHPG). Part of the work presented was carried by Miquel Pitarch with the financial support of a PhD scholarship from the Universitat Politecnica de Valencia. Part of the work presented was carried by Estefania Hervas-Blasco with the financial support of a Ph.D. scholarship from the Spanish government SFPI1500X074478XV. The authors would like also to acknowledge the Spanish 'MINISTERIO DE ECONOMIA Y COMPETITIVIDAD', through the Project ENE2017-83665-C2-1-P, "Maximizacion de la Eficiencia y Minimizacion del Impacto Ambiental de Bombas de Calor para la descarbonizacion de la calefaccion/ACS en los proximos edificios de consumo energetico casi nulo" for the given support.Pitarch, M.; Hervás-Blasco, E.; Navarro-Peris, E.; Corberán, JM. (2019). Exergy analysis on a heat pump working between a heat sink and a heat source of finite heat capacity rate. International Journal of Refrigeration. 99:337-350. https://doi.org/10.1016/j.ijrefrig.2018.11.044S3373509

Visualization of the Refrigerant Flow at the Capillary Tube Inlet of a Houseold Refrigeration System

Capillary tube-suction line heat exchangers (CT-SLHX) introduce complex phenomena due to simultaneous 2-phase flow expansion and heat transfer such as: reverse heat transfer, flow hysteresis and flow oscillations. Some of the negative consequences of these phenomena are: noise due to re-condensation, which is becoming an important quality issue; and reduction of the SLHX effectiveness, which also affects the global efficiency. Studies about how to solve the noise problem show that it disappears when there is enough subcooling at the capillary tube inlet. This fact also supports the idea that two-phase flow at the capillary tube inlet contributes to re-condensation phenomenon in the CT-SLHX. Different reasons may explain it, e.g. the small compressor capacity compared the expansion device capacity of the capillary tube used. Another important consequence would be wasting condenser surface due to the two-phase outlet. Therefore, the main objective of this work is to assess experimentally the actual conditions taking place at the capillary tube inlet and find a solution to the problems mentioned above. An innovative test bench has been designed in order to visualize and analyze the phenomena occurring at the condenser outlet, along the filter and at the capillary tube inlet. This experimental bench test is connected to an A+++ no-frost household refrigerator equipped with a fin-and-tube evaporator, a tube and wire condenser and a variable-speed 7.24 cm³ hermetic reciprocating compressor. The refrigerant used is isobutane (R600a). In order to determine the refrigerant temperature, a set of thermocouples has been placed along the refrigerant loop, while a pressure transducer is installed at the condenser outlet. The mass flow rate is measured with a Coriolis meter installed at the compressor discharge line. The final part of the condenser and the filters were built with PFA (Perfluoroalkoxy) transparent pipes. Three different positions of identical filters were tested to analyze their influence on the flow configuration. The first filter is horizontally oriented, second and third ones are in a vertical position but with opposite flow directions. A system composed of three manual solenoid valves enables to test each of the three configurations independently from the two others. The transparent filters make possible the visualization of the refrigerant flow pattern at the capillary inlet. An adjustable system has been designed to modify the length of the capillary inside the filters. The set of experiments were tested in steady conditions, by using electrical heaters inside the cabinets to keep the setting point constant. Results show the description of the flow pattern at the capillary tube inlet and condenser outlet with the different capillary tubes and filter arrangements. The condenser outlet conditions were analyzed and the energy efficiency of the refrigerator was compared with a system with actual subcooled outlet conditions. Once characterized the refrigerant flow at the condenser outlet, a configuration has been proposed to ensure an effective subcooling and thus an improvement of the refrigerator performance