Pub Date : 2025-12-16DOI: 10.1016/j.ijrefrig.2025.12.015
Hoang Minh Phan , Bert E. Verlinden , Maarten L.A.T.M. Hertog , Pieter Verboven , Bart M. Nicolai
The energy efficiency of ‘Conference’ pear storage was assessed for different storage strategies, including dynamic controlled atmosphere (DCA) at different temperatures and controlled atmosphere (CA) at varying temperatures and O2 levels. Storage at -1 °C in 3 kPa O2 and 0.7 kPa CO2 was used as a benchmark. Direct respiration measurements during the storage period showed that DCA reduced respiratory heat by 30–40 % compared with the benchmark, even at slightly elevated temperatures. A simulation-based energy assessment revealed that DCA could reduce the total heat load in a storage room by 8–16 %. Fan operation was found to account for the largest share of the total heat load (up to 50 %), while the respiratory heat contributed around 10–30 %. Among all experimental strategies, DCA at -1 °C reduced the total heat load by ∼8 %, and maintained good firmness and skin colour without inducing internal browning after long-term storage. This makes it the most optimal approach to balance fruit quality and energy savings.
{"title":"Improving energy efficiency in pear storage through dynamic controlled atmosphere (DCA)","authors":"Hoang Minh Phan , Bert E. Verlinden , Maarten L.A.T.M. Hertog , Pieter Verboven , Bart M. Nicolai","doi":"10.1016/j.ijrefrig.2025.12.015","DOIUrl":"10.1016/j.ijrefrig.2025.12.015","url":null,"abstract":"<div><div>The energy efficiency of ‘Conference’ pear storage was assessed for different storage strategies, including dynamic controlled atmosphere (DCA) at different temperatures and controlled atmosphere (CA) at varying temperatures and O<sub>2</sub> levels. Storage at -1 °C in 3 kPa O<sub>2</sub> and 0.7 kPa CO<sub>2</sub> was used as a benchmark. Direct respiration measurements during the storage period showed that DCA reduced respiratory heat by 30–40 % compared with the benchmark, even at slightly elevated temperatures. A simulation-based energy assessment revealed that DCA could reduce the total heat load in a storage room by 8–16 %. Fan operation was found to account for the largest share of the total heat load (up to 50 %), while the respiratory heat contributed around 10–30 %. Among all experimental strategies, DCA at -1 °C reduced the total heat load by ∼8 %, and maintained good firmness and skin colour without inducing internal browning after long-term storage. This makes it the most optimal approach to balance fruit quality and energy savings.</div></div>","PeriodicalId":14274,"journal":{"name":"International Journal of Refrigeration-revue Internationale Du Froid","volume":"182 ","pages":"Pages 447-455"},"PeriodicalIF":3.8,"publicationDate":"2025-12-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145786651","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-12-16DOI: 10.1016/j.ijrefrig.2025.12.017
Yue Zheng , Hua Han , Jun Xiong , Hua Zhang , Xun Cao , Bo Gu , Wenjie Dai , Xu Gao , Weiqi Yi
Refrigerant leakage significantly undermines the energy efficiency and operational safety of variable refrigerant flow (VRF) systems, making accurate prediction of refrigerant charge critically important. Conventional diagnostic approaches are often costly, reliant on complex models, non-quantitative, and lack generalization, which restricts their practical deployment. To address these limitations, a series of enhancements and intelligent integration were introduced to the virtual refrigerant charge (VRC) sensor. An operating-condition matching strategy was first employed to establish an exVRC sensor for condition extending. An exponentially weighted moving average (EWMA) control chart was then incorporated to construct an exVRC-E sensor for oscillation mitigation. Finally, a deep learning-based Residual Neural Network (ResNet) was established and coupled with the exVRC-E sensor to produce an AI-knowledge dual-driven intelligent sensor, exVRC-ER. Experimental validation on a 33.5 kW VRF system under one rated and fourteen off-rated conditions showed that compared with the original VRC sensor, the exVRC sensor reduces MAPE by 16.21 % under extreme off-rated conditions, corresponding to a 74 % relative reduction. The exVRC-E sensor further lowers oscillation amplitude by 84 % and reduces false-alarm risk during normal operation. Across all conditions, the final exVRC-ER intelligent sensor integrated with deep learning achieves the best performance, with a 71.8 % relative reduction in MAPE and a 1.21 kg decrease in root mean square error (RMSE) compared with the original VRC sensor. These results indicate a significant potential for precise quantification of refrigerant leakage, highlighting their importance for enhancing the efficient operation and intelligent maintenance of HVAC systems.
{"title":"Improvements and intelligence integration of virtual refrigerant charge (VRC) sensor","authors":"Yue Zheng , Hua Han , Jun Xiong , Hua Zhang , Xun Cao , Bo Gu , Wenjie Dai , Xu Gao , Weiqi Yi","doi":"10.1016/j.ijrefrig.2025.12.017","DOIUrl":"10.1016/j.ijrefrig.2025.12.017","url":null,"abstract":"<div><div>Refrigerant leakage significantly undermines the energy efficiency and operational safety of variable refrigerant flow (VRF) systems, making accurate prediction of refrigerant charge critically important. Conventional diagnostic approaches are often costly, reliant on complex models, non-quantitative, and lack generalization, which restricts their practical deployment. To address these limitations, a series of enhancements and intelligent integration were introduced to the virtual refrigerant charge (VRC) sensor. An operating-condition matching strategy was first employed to establish an exVRC sensor for condition extending. An exponentially weighted moving average (EWMA) control chart was then incorporated to construct an exVRC-E sensor for oscillation mitigation. Finally, a deep learning-based Residual Neural Network (ResNet) was established and coupled with the exVRC-E sensor to produce an AI-knowledge dual-driven intelligent sensor, exVRC-ER. Experimental validation on a 33.5 kW VRF system under one rated and fourteen off-rated conditions showed that compared with the original VRC sensor, the exVRC sensor reduces MAPE by 16.21 % under extreme off-rated conditions, corresponding to a 74 % relative reduction. The exVRC-E sensor further lowers oscillation amplitude by 84 % and reduces false-alarm risk during normal operation. Across all conditions, the final exVRC-ER intelligent sensor integrated with deep learning achieves the best performance, with a 71.8 % relative reduction in MAPE and a 1.21 kg decrease in root mean square error (RMSE) compared with the original VRC sensor. These results indicate a significant potential for precise quantification of refrigerant leakage, highlighting their importance for enhancing the efficient operation and intelligent maintenance of HVAC systems.</div></div>","PeriodicalId":14274,"journal":{"name":"International Journal of Refrigeration-revue Internationale Du Froid","volume":"182 ","pages":"Pages 456-468"},"PeriodicalIF":3.8,"publicationDate":"2025-12-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145786652","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-12-12DOI: 10.1016/j.ijrefrig.2025.12.013
Anjelina W Mwakosya, Graciela Alvarez, Fatou Toutie Ndoye
This study aims to investigate the microstructure changes of partially frozen beef under different superchilling storage conditions and relate these changes to quality degradation. Beef samples were partially frozen in an air blast freezer with a heat transfer coefficient of 112 W/m2K and an air temperature of ‒32 °C for 2 min following storage at ‒1.8 °C, ‒2.8 °C, ‒4 °C and ‒5 °C for 21 days. "X-ray micro-computed tomography (µCT), a non-destructive 3D imaging technique was used to visualize and quantify ice crystal characteristic, including ice volume fractions, ice crystal size, number and distribution". Recrystallization kinetics were modelled using the asymptotic Ostwald ripening equation and correlated with quality degradation rate through Pearson correlation analysis. Immediately after partial freezing, the average initial ice volume fraction, mean equivalent diameter, and crystal number were 31 ± 1 %, 36.0 ± 0.3 µm, and 421,182 ± 16,524, respectively. Over storage time, ice volume fraction and crystal size increased significantly (p < 0.05), while crystal number decreased, leading to increased drip loss, and reduced firmness of beef upon thawing. In addition, recrystallization rates increased significantly (p < 0.05) with decreasing storage temperature specifically within a range of ‒1.8 °C to ‒5 °C as lower temperatures resulted in higher ice fractions and more heterogeneous crystal size distributions, thereby promoting recrystallization. A high regression coefficient (R2 > 0.9) indicated a strong fit of the recrystallization rate’s temperature dependence to the Arrhenius model. Recrystallization rate was strongly correlated with all quality degradation rates (R2 > 0.9). Overall, this study demonstrates the critical role of recrystallization in driving deterioration of partially frozen beef and highlights the value of X‒ray µCT for non-invasive monitoring microstructure changes during superchilled storage.
{"title":"Impact of superchilling storage temperatures on beef quality: Micro-CT analysis of ice recrystallization kinetics in partially frozen samples","authors":"Anjelina W Mwakosya, Graciela Alvarez, Fatou Toutie Ndoye","doi":"10.1016/j.ijrefrig.2025.12.013","DOIUrl":"10.1016/j.ijrefrig.2025.12.013","url":null,"abstract":"<div><div>This study aims to investigate the microstructure changes of partially frozen beef under different superchilling storage conditions and relate these changes to quality degradation. Beef samples were partially frozen in an air blast freezer with a heat transfer coefficient of 112 W/m<sup>2</sup>K and an air temperature of ‒32 °C for 2 min following storage at ‒1.8 °C, ‒2.8 °C, ‒4 °C and ‒5 °C for 21 days. \"X-ray micro-computed tomography (µCT), a non-destructive 3D imaging technique was used to visualize and quantify ice crystal characteristic, including ice volume fractions, ice crystal size, number and distribution\". Recrystallization kinetics were modelled using the asymptotic Ostwald ripening equation and correlated with quality degradation rate through Pearson correlation analysis. Immediately after partial freezing, the average initial ice volume fraction, mean equivalent diameter, and crystal number were 31 ± 1 %, 36.0 ± 0.3 µm, and 421,182 ± 16,524, respectively. Over storage time, ice volume fraction and crystal size increased significantly (<em>p</em> < 0.05), while crystal number decreased, leading to increased drip loss, and reduced firmness of beef upon thawing. In addition, recrystallization rates increased significantly (<em>p</em> < 0.05) with decreasing storage temperature specifically within a range of ‒1.8 °C to ‒5 °C as lower temperatures resulted in higher ice fractions and more heterogeneous crystal size distributions, thereby promoting recrystallization. A high regression coefficient (R<sup>2</sup> > 0.9) indicated a strong fit of the recrystallization rate’s temperature dependence to the Arrhenius model. Recrystallization rate was strongly correlated with all quality degradation rates (R<sup>2</sup> > 0.9). Overall, this study demonstrates the critical role of recrystallization in driving deterioration of partially frozen beef and highlights the value of X‒ray µCT for non-invasive monitoring microstructure changes during superchilled storage.</div></div>","PeriodicalId":14274,"journal":{"name":"International Journal of Refrigeration-revue Internationale Du Froid","volume":"182 ","pages":"Pages 418-429"},"PeriodicalIF":3.8,"publicationDate":"2025-12-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145786653","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-12-11DOI: 10.1016/j.ijrefrig.2025.12.011
P.L.Pavan Kumar , B.J. Gireesha , P. Venkatesh
The presents study investigates transient thermal analysis of porous dovetail fin made of copper () and aluminium () under dehumidification condition, where simultaneous heat and mass transfer occurs through surface condensation when the fin temperature drops below the ambient dew point. The flow and transport through the porous structure are modelled using Darcy’s law and the nonlinear governing equations are solved numerically using Finite Difference Method (FDM) with results showing good agreement with existing literature confirming the model’s accuracy and reliability. Results reveal that fin demonstrate superior heat dissipation and efficiency exhibiting a 119.09 % rise in temperature distribution compared with 178.10 % for attributed to higher thermal conductivity and enhanced heat diffusion capability. The dovetail configuration yields better thermal performance than the rectangular fin with temperature rises of 178.10 % () and 119.09 % () owing to its tapered profile that reduces axial thermal resistance and promotes effective condensation. Parametric evaluation reveals that increasing Relative Humidity () by 400 % decreases temperature distribution by 131.58 % in and 81.65 % in due to intensified latent heat absorption, while a 200 % variation in taper ratio () alters it by 14.50 % and 10.06 %, respectively. These results confirm that dovetail fin achieve higher efficiency and more stable condensation dynamics, offering practical applicability for compact heat exchangers, air-cooling units and dehumidification-based thermal management systems.
{"title":"Simultaneous heat and mass transfer in transient dovetail metallic porous fin made of aluminium and copper metals: Analysing efficiency and thermal dynamics under dehumidification","authors":"P.L.Pavan Kumar , B.J. Gireesha , P. Venkatesh","doi":"10.1016/j.ijrefrig.2025.12.011","DOIUrl":"10.1016/j.ijrefrig.2025.12.011","url":null,"abstract":"<div><div>The presents study investigates transient thermal analysis of porous dovetail fin made of copper (<span><math><mrow><mi>C</mi><mi>u</mi></mrow></math></span>) and aluminium (<span><math><mrow><mi>A</mi><mi>l</mi></mrow></math></span>) under dehumidification condition, where simultaneous heat and mass transfer occurs through surface condensation when the fin temperature drops below the ambient dew point. The flow and transport through the porous structure are modelled using Darcy’s law and the nonlinear governing equations are solved numerically using Finite Difference Method (FDM) with results showing good agreement with existing literature confirming the model’s accuracy and reliability. Results reveal that <span><math><mrow><mi>C</mi><mi>u</mi></mrow></math></span> fin demonstrate superior heat dissipation and efficiency exhibiting a 119.09 % rise in temperature distribution compared with 178.10 % for <span><math><mrow><mi>A</mi><mi>l</mi></mrow></math></span> attributed to <span><math><mrow><mi>C</mi><mi>u</mi></mrow></math></span> higher thermal conductivity and enhanced heat diffusion capability. The dovetail configuration yields better thermal performance than the rectangular fin with temperature rises of 178.10 % (<span><math><mrow><mi>A</mi><mi>l</mi></mrow></math></span>) and 119.09 % (<span><math><mrow><mi>C</mi><mi>u</mi></mrow></math></span>) owing to its tapered profile that reduces axial thermal resistance and promotes effective condensation. Parametric evaluation reveals that increasing Relative Humidity (<span><math><mrow><mi>R</mi><mi>H</mi></mrow></math></span>) by 400 % decreases temperature distribution by 131.58 % in <span><math><mrow><mi>A</mi><mi>l</mi></mrow></math></span> and 81.65 % in <span><math><mrow><mi>C</mi><mi>u</mi></mrow></math></span> due to intensified latent heat absorption, while a 200 % variation in taper ratio (<span><math><mi>C</mi></math></span>) alters it by 14.50 % and 10.06 %, respectively. These results confirm that <span><math><mrow><mi>C</mi><mi>u</mi></mrow></math></span> dovetail fin achieve higher efficiency and more stable condensation dynamics, offering practical applicability for compact heat exchangers, air-cooling units and dehumidification-based thermal management systems.</div></div>","PeriodicalId":14274,"journal":{"name":"International Journal of Refrigeration-revue Internationale Du Froid","volume":"182 ","pages":"Pages 430-446"},"PeriodicalIF":3.8,"publicationDate":"2025-12-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145786650","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-12-10DOI: 10.1016/j.ijrefrig.2025.12.012
Sujie Liu , Jiaxuan Pu , Jiaxing Li , Huan Zhang , Tianzhen Ye , Xinyu Zhang , Zhihao Wan , Zhaoying Wang , Xianwang Fan , Wandong Zheng
The ongoing integration of renewable energy into power grids is driving a transition towards distributed and multi-source energy frameworks in building energy systems. Solar-assisted heat pumps, as the emerging distributed multi-source heating systems, face persistent challenges including operating instability, seasonal limitations, and complex control requirements. To address these shortcomings, this study develops a novel integrated unglazed solar-air dual-source heat pump (USAHP) system. The system synergistically harnesses dual renewable energy sources by incorporating high-efficiency finned tubes with absorbing coating and reflectors into a compound solar air collector-evaporator. The integration could maximize evaporator output within a constrained area. Experimental investigations are conducted to evaluate and analyze the system performance, specifically examining the effects of operating parameters and collector-evaporator configuration on thermal collection efficiency. Results demonstrate that among three key parameters, solar irradiance and ambient air temperature exert significantly positive influences on system performance, while relative humidity exhibits weak correlation. The reflector-equipped collector-evaporator enhances solar irradiance absorption by 27–54 %. The proposed USAHP achieves superior frost suppression and enhanced energy efficiency by elevating the evaporation temperature. The evaporation temperature of USAHP increases by up to 3.2 °C under experimental conditions, and COP improves by up to 19.3 % compared to conventional air-source and solar-air assisted heat pump systems. Furthermore, a payback period of 3.18 years demonstrates the economic viability of USAHP. This research represents key advancement in frost mitigation mechanisms and demonstrates substantial improvements in energy efficiency, thereby advancing heat pump technology for multi-source energy applications.
{"title":"Thermo-economic performance of an integrated unglazed solar-air dual-source heat pump: an experimental investigation","authors":"Sujie Liu , Jiaxuan Pu , Jiaxing Li , Huan Zhang , Tianzhen Ye , Xinyu Zhang , Zhihao Wan , Zhaoying Wang , Xianwang Fan , Wandong Zheng","doi":"10.1016/j.ijrefrig.2025.12.012","DOIUrl":"10.1016/j.ijrefrig.2025.12.012","url":null,"abstract":"<div><div>The ongoing integration of renewable energy into power grids is driving a transition towards distributed and multi-source energy frameworks in building energy systems. Solar-assisted heat pumps, as the emerging distributed multi-source heating systems, face persistent challenges including operating instability, seasonal limitations, and complex control requirements. To address these shortcomings, this study develops a novel integrated unglazed solar-air dual-source heat pump (USAHP) system. The system synergistically harnesses dual renewable energy sources by incorporating high-efficiency finned tubes with absorbing coating and reflectors into a compound solar air collector-evaporator. The integration could maximize evaporator output within a constrained area. Experimental investigations are conducted to evaluate and analyze the system performance, specifically examining the effects of operating parameters and collector-evaporator configuration on thermal collection efficiency. Results demonstrate that among three key parameters, solar irradiance and ambient air temperature exert significantly positive influences on system performance, while relative humidity exhibits weak correlation. The reflector-equipped collector-evaporator enhances solar irradiance absorption by 27–54 %. The proposed USAHP achieves superior frost suppression and enhanced energy efficiency by elevating the evaporation temperature. The evaporation temperature of USAHP increases by up to 3.2 °C under experimental conditions, and COP improves by up to 19.3 % compared to conventional air-source and solar-air assisted heat pump systems. Furthermore, a payback period of 3.18 years demonstrates the economic viability of USAHP. This research represents key advancement in frost mitigation mechanisms and demonstrates substantial improvements in energy efficiency, thereby advancing heat pump technology for multi-source energy applications.</div></div>","PeriodicalId":14274,"journal":{"name":"International Journal of Refrigeration-revue Internationale Du Froid","volume":"182 ","pages":"Pages 383-398"},"PeriodicalIF":3.8,"publicationDate":"2025-12-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145786747","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-12-09DOI: 10.1016/j.ijrefrig.2025.12.008
Weijia Jiang , Ke Chen , Aikun Tang , Tao Cai , Shuangyuan Xiong , Zhikun Liu
To address the challenges of high energy consumption during winter heating and limited driving range in electric vehicles, a transcritical CO2 secondary throttling heat pump system, which integrates an internal heat exchanger and dual expansion valves, is proposed in this study. By optimizing the dual indoor heat exchangers and a staged throttling, the refrigerant heat exchange efficiency of the system within the heating cycle is enhanced. A 1D thermal management simulation model incorporating both cabin and battery is first developed, whose accuracy is demonstrated to be quite satisfactory by comparing numerical results with experimental data. Subsequently, a comparative analysis between the secondary throttling system and a conventional heat pump reveals a heating capacity increase of 50.88 % at 0 °C. Further parametric studies are conducted under varying valve openings, indoor/outdoor airflow rates, and compressor speeds, demonstrating that the coordinated control of dual EXVs effectively regulates the intermediate pressure. Additionally, airflow parameters and compressor speed significantly influence overall system performance. Under optimized operating conditions, the system achieves significant improvements in both heating capacity and coefficient of performance, demonstrating the effectiveness of the proposed design. This investigation provides a viable technical pathway for optimizing CO2 heat pump air conditioning systems.
{"title":"Heating performance analysis and operation optimization of CO2 secondary throttle heat pump system for electric vehicles","authors":"Weijia Jiang , Ke Chen , Aikun Tang , Tao Cai , Shuangyuan Xiong , Zhikun Liu","doi":"10.1016/j.ijrefrig.2025.12.008","DOIUrl":"10.1016/j.ijrefrig.2025.12.008","url":null,"abstract":"<div><div>To address the challenges of high energy consumption during winter heating and limited driving range in electric vehicles, a transcritical CO<sub>2</sub> secondary throttling heat pump system, which integrates an internal heat exchanger and dual expansion valves, is proposed in this study. By optimizing the dual indoor heat exchangers and a staged throttling, the refrigerant heat exchange efficiency of the system within the heating cycle is enhanced. A 1D thermal management simulation model incorporating both cabin and battery is first developed, whose accuracy is demonstrated to be quite satisfactory by comparing numerical results with experimental data. Subsequently, a comparative analysis between the secondary throttling system and a conventional heat pump reveals a heating capacity increase of 50.88 % at 0 °C. Further parametric studies are conducted under varying valve openings, indoor/outdoor airflow rates, and compressor speeds, demonstrating that the coordinated control of dual EXVs effectively regulates the intermediate pressure. Additionally, airflow parameters and compressor speed significantly influence overall system performance. Under optimized operating conditions, the system achieves significant improvements in both heating capacity and coefficient of performance, demonstrating the effectiveness of the proposed design. This investigation provides a viable technical pathway for optimizing CO<sub>2</sub> heat pump air conditioning systems.</div></div>","PeriodicalId":14274,"journal":{"name":"International Journal of Refrigeration-revue Internationale Du Froid","volume":"182 ","pages":"Pages 357-369"},"PeriodicalIF":3.8,"publicationDate":"2025-12-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145786743","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-12-08DOI: 10.1016/j.ijrefrig.2025.12.010
Tongzhi Yang , Xi’an Liu , Yifan Zhao , Weixing Yuan , Hao Cheng , Kexian Ren
Conventional data center air-conditioners consume excessive energy. Rack-level hybrid cooling systems combining a pump-driven heat pipe (PHP) and a vapor-compression (VC) cycle provide a promising alternative but often encounter refrigerant starvation in evaporators. Therefore, we previously proposed a novel rack-level hybrid cooling system adopting gas–liquid separation in all modes and a subcooler. However, prior work studied its energy efficiency ratio (EERcp) only at fixed vapor quality, leaving key operating characteristics unexplored. To address these gaps, this paper experimentally investigated the novel system’s response characteristics under varying vapor quality, condenser-side disturbances, and non-uniform cooling loads, including variations in mode-switching temperatures, EERcp, and refrigerant state. Experiments were conducted on a prototype setup with five plate heat exchangers representing rack-level evaporators, at evaporating temperatures of 23.5–24.0 °C to match the ASHRAE-recommended 27 °C server room. Results show that reducing the evaporator outlet vapor quality from 0.76 to 0.58 decreased EERcp by 13–30 %, shifted mode-switching temperatures by 2–4 °C, and increased evaporator inlet subcooling by 1.6–2.9 °C. The 6 °C disturbances in the condenser inlet water temperature (Tcon,win) caused transient fluctuations in evaporator inlet subcooling, yet it still remained above 0 °C to maintain the flow distribution among evaporators. Under severe non-uniform cooling loads, the system effectively prevented local hotspots, with EERcp decreasing by only 0.1–0.2 in vapor-compressor-driven and hybrid-driven modes, and remaining 127 in liquid-pump-driven mode. Although based on prototype experiments, these findings provided useful insights into strategies for operating the novel system in practical applications.
{"title":"Experimental study of operating characteristics of a novel rack-level hybrid cooling system for data centers","authors":"Tongzhi Yang , Xi’an Liu , Yifan Zhao , Weixing Yuan , Hao Cheng , Kexian Ren","doi":"10.1016/j.ijrefrig.2025.12.010","DOIUrl":"10.1016/j.ijrefrig.2025.12.010","url":null,"abstract":"<div><div>Conventional data center air-conditioners consume excessive energy. Rack-level hybrid cooling systems combining a pump-driven heat pipe (PHP) and a vapor-compression (VC) cycle provide a promising alternative but often encounter refrigerant starvation in evaporators. Therefore, we previously proposed a novel rack-level hybrid cooling system adopting gas–liquid separation in all modes and a subcooler. However, prior work studied its energy efficiency ratio (<em>EER</em><sub>cp</sub>) only at fixed vapor quality, leaving key operating characteristics unexplored. To address these gaps, this paper experimentally investigated the novel system’s response characteristics under varying vapor quality, condenser-side disturbances, and non-uniform cooling loads, including variations in mode-switching temperatures, <em>EER</em><sub>cp</sub>, and refrigerant state. Experiments were conducted on a prototype setup with five plate heat exchangers representing rack-level evaporators, at evaporating temperatures of 23.5–24.0 °C to match the ASHRAE-recommended 27 °C server room. Results show that reducing the evaporator outlet vapor quality from 0.76 to 0.58 decreased <em>EER</em><sub>cp</sub> by 13–30 %, shifted mode-switching temperatures by 2–4 °C, and increased evaporator inlet subcooling by 1.6–2.9 °C. The 6 °C disturbances in the condenser inlet water temperature (<em>T</em><sub>con,win</sub>) caused transient fluctuations in evaporator inlet subcooling, yet it still remained above 0 °C to maintain the flow distribution among evaporators. Under severe non-uniform cooling loads, the system effectively prevented local hotspots, with <em>EER</em><sub>cp</sub> decreasing by only 0.1–0.2 in vapor-compressor-driven and hybrid-driven modes, and remaining 127 in liquid-pump-driven mode. Although based on prototype experiments, these findings provided useful insights into strategies for operating the novel system in practical applications.</div></div>","PeriodicalId":14274,"journal":{"name":"International Journal of Refrigeration-revue Internationale Du Froid","volume":"182 ","pages":"Pages 323-333"},"PeriodicalIF":3.8,"publicationDate":"2025-12-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145733326","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-12-08DOI: 10.1016/j.ijrefrig.2025.12.005
Matthias Heselmann , Steffen Folkers , Sebastian Schuster , Dieter Brillert , Andreas Brümmer
A major challenge in designing and evaluating thermodynamic cycles that include compression processes lies in accurately estimating compressor efficiency. To obtain reliable efficiency assumptions, the compressors would need to be at least partially designed. To simplify compressor design for given stationary cycle parameters, this study introduces a novel inverse design method that enables direct determination of the maximum achievable compressor internal isentropic efficiency (“process maps”) and the corresponding optimal machine parameters (e.g., number of stages, rotor geometry, internal volume ratio) based on a specified set of dimensionless cycle parameters. To ensure broad applicability, both positive displacement compressors (twin-screw compressors) and centrifugal compressors are considered, and corresponding “process maps” of the best possible efficiencies are developed. For positive displacement machines, the inverse design approach becomes feasible for the first time, as traditional methods implicitly constrain the design through empirical parameters such as delivery rate. Moreover, for centrifugal compressors within the ”process maps” developed in this study, the number of stages is inherently represented – enabling a fully inverse machine design without prior stage definition. This provides a new means of determining the optimal stage configuration directly from the cycle parameters.
{"title":"Inverse design: Process dependent efficiency of compressors for use in thermodynamic cycle simulations","authors":"Matthias Heselmann , Steffen Folkers , Sebastian Schuster , Dieter Brillert , Andreas Brümmer","doi":"10.1016/j.ijrefrig.2025.12.005","DOIUrl":"10.1016/j.ijrefrig.2025.12.005","url":null,"abstract":"<div><div>A major challenge in designing and evaluating thermodynamic cycles that include compression processes lies in accurately estimating compressor efficiency. To obtain reliable efficiency assumptions, the compressors would need to be at least partially designed. To simplify compressor design for given stationary cycle parameters, this study introduces a novel inverse design method that enables direct determination of the maximum achievable compressor internal isentropic efficiency (“process maps”) and the corresponding optimal machine parameters (e.g., number of stages, rotor geometry, internal volume ratio) based on a specified set of dimensionless cycle parameters. To ensure broad applicability, both positive displacement compressors (twin-screw compressors) and centrifugal compressors are considered, and corresponding “process maps” of the best possible efficiencies are developed. For positive displacement machines, the inverse design approach becomes feasible for the first time, as traditional methods implicitly constrain the design through empirical parameters such as delivery rate. Moreover, for centrifugal compressors within the ”process maps” developed in this study, the number of stages is inherently represented – enabling a fully inverse machine design without prior stage definition. This provides a new means of determining the optimal stage configuration directly from the cycle parameters.</div></div>","PeriodicalId":14274,"journal":{"name":"International Journal of Refrigeration-revue Internationale Du Froid","volume":"182 ","pages":"Pages 370-382"},"PeriodicalIF":3.8,"publicationDate":"2025-12-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145786745","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-12-08DOI: 10.1016/j.ijrefrig.2025.12.009
Lingeng Zou , Fukang Yu , Tao Bai , Ye Liu
The integration of solar-driven ejector refrigeration cycles with conventional vapor-compression refrigeration cycles (VCRC) offers significant potential for energy conservation in air-conditioning systems. To enhance VCRC performance, this study proposes a solar-assisted hybrid ejector-compression refrigeration cycle (ECRC) that employs a subcooler to couple the ejector cycle with the VCRC, using the low-global-warming-potential (GWP) refrigerant R290. The ECRC employs a solar-driven ejector cycle to enhance the primary vapor compression cycle by increasing the subcooling degree, thereby improving system performance. This work theoretically investigates the ECRC performance compared to the standard VCRC via a comprehensive 4E (energy, exergy, economic, environmental) analysis. Results show that at the optimal intermediate temperature, optimized via the Particle Swarm Optimization algorithm, the ECRC achieves a 9.0 % improvement in coefficient of performance (COP) and a 15.1 % increase in volumetric cooling capacity (Qev) over the VCRC. Exergy analysis reveals that the generator accounts for approximately 47.4 % of total exergy destruction, indicating optimization potential. Economically, the ECRC reduces exergy production cost by 7.9–12.7 %, demonstrating better returns. Environmentally, the ECRC with R290 cuts carbon emissions by 7.90 % compared to the VCRC. Overall, the ECRC exhibits strong potential for sustainable air-conditioning applications.
{"title":"A modified solar-enhanced hybrid ejector-vapor compression cycle: Energy, exergy, economic, and environmental assessment","authors":"Lingeng Zou , Fukang Yu , Tao Bai , Ye Liu","doi":"10.1016/j.ijrefrig.2025.12.009","DOIUrl":"10.1016/j.ijrefrig.2025.12.009","url":null,"abstract":"<div><div>The integration of solar-driven ejector refrigeration cycles with conventional vapor-compression refrigeration cycles (VCRC) offers significant potential for energy conservation in air-conditioning systems. To enhance VCRC performance, this study proposes a solar-assisted hybrid ejector-compression refrigeration cycle (ECRC) that employs a subcooler to couple the ejector cycle with the VCRC, using the low-global-warming-potential (GWP) refrigerant R290. The ECRC employs a solar-driven ejector cycle to enhance the primary vapor compression cycle by increasing the subcooling degree, thereby improving system performance. This work theoretically investigates the ECRC performance compared to the standard VCRC via a comprehensive 4E (energy, exergy, economic, environmental) analysis. Results show that at the optimal intermediate temperature, optimized via the Particle Swarm Optimization algorithm, the ECRC achieves a 9.0 % improvement in coefficient of performance (COP) and a 15.1 % increase in volumetric cooling capacity (<em>Q</em><sub>ev</sub>) over the VCRC. Exergy analysis reveals that the generator accounts for approximately 47.4 % of total exergy destruction, indicating optimization potential. Economically, the ECRC reduces exergy production cost by 7.9–12.7 %, demonstrating better returns. Environmentally, the ECRC with R290 cuts carbon emissions by 7.90 % compared to the VCRC. Overall, the ECRC exhibits strong potential for sustainable air-conditioning applications.</div></div>","PeriodicalId":14274,"journal":{"name":"International Journal of Refrigeration-revue Internationale Du Froid","volume":"182 ","pages":"Pages 334-348"},"PeriodicalIF":3.8,"publicationDate":"2025-12-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145733331","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-12-07DOI: 10.1016/j.ijrefrig.2025.12.007
Türkan Üçok Erkek , Mehmet Erkek , Mehmet Bora Aydın , Koray Gezer
Data center cooling accounts for a substantial fraction of facility energy consumption, with environmental pressures driving the transition from high-GWP refrigerants to sustainable alternatives. However, rigorous experimental comparisons of next-generation refrigerants under realistic operational conditions remain limited, and existing benchmarking protocols often fail to account for ambient variability across test conditions. This study addresses these gaps by conducting a comprehensive experimental evaluation of an in-rack air-conditioning unit, comparing the conventional refrigerant R410A with the low-GWP alternative R454B (GWP = 466) across 24 tests spanning varied server loads and thermal conditions. The methodology integrates a transparent steady-state detection algorithm for time-series measurement processing, normalized Energy Efficiency Ratio (EER) calculations at fixed reference conditions to enable equitable cross-test comparison, and sensitivity analyses quantifying the influence of ambient and evaporator-side temperatures on system performance. Cooling capacity, raw and normalized EER, facility-level Power Usage Effectiveness (PUE), and Total Equivalent Warming Impact (TEWI) were derived for each refrigerant. Results demonstrate that R454B exhibits load-dependent performance advantages: under high-load conditions (9 kW), R454B achieved 38 % higher EER (∼5.8 vs. ∼4.2) and superior cooling capacity (13 kW vs. 9.5 kW median) compared to R410A, with reduced operational variability. However, under supply-air matched baseline conditions (16–20 °C), both refrigerants exhibited equivalent performance, confirming that R454B's efficiency gains emerge primarily under elevated thermal stress and higher refrigerant flow rates. PUE analysis showed equivalent facility-level efficiency, enabling R454B as a direct drop-in replacement. TEWI analysis revealed that indirect emissions dominate climate impact (>90 %), establishing operational efficiency optimization as the primary environmental lever, with refrigerant selection providing secondary benefits through GWP reduction. These findings support the adoption of R454B in high-load data center environments, while the transparent methodological framework provides a reproducible benchmark for condition-aware refrigerant evaluation in mission-critical cooling systems.
数据中心冷却占设施能源消耗的很大一部分，环境压力推动了从高gwp制冷剂向可持续替代品的转变。然而，在实际操作条件下对下一代制冷剂进行严格的实验比较仍然有限，现有的基准测试协议往往无法考虑测试条件下的环境变化。本研究通过对机架式空调机组进行全面的实验评估，将常规制冷剂R410A与低GWP替代R454B （GWP = 466）进行了24次测试，涵盖了不同的服务器负载和热条件，从而解决了这些差距。该方法集成了用于时间序列测量处理的透明稳态检测算法，固定参考条件下的归一化能效比（EER）计算，以实现公平的交叉测试比较，以及量化环境温度和蒸发器侧温度对系统性能影响的敏感性分析。每种制冷剂的制冷量、原始和标准化EER、设施级功率使用效率（PUE）和总等效变暖影响（TEWI）均得到了推导。结果表明，R454B具有负载相关的性能优势：与R410A相比，在高负载条件下（9 kW）， R454B的EER比R410A高38% (~ 5.8 vs. ~ 4.2)，冷却能力更强（13 kW vs. 9.5 kW中值），同时降低了运行变异性。然而，在送风匹配的基线条件下（16-20°C），两种制冷剂表现出相同的性能，这证实了R454B的效率提高主要是在更高的热应力和更高的制冷剂流量下实现的。PUE分析显示，R454B具有相同的设施级效率，可以直接替代R454B。TEWI分析显示，间接排放主导了气候影响（> 90%），将运行效率优化作为主要的环境杠杆，制冷剂选择通过降低全球升温潜能值提供次要效益。这些发现支持在高负载数据中心环境中采用R454B，而透明的方法框架为关键任务冷却系统的状态感知制冷剂评估提供了可重复的基准。
{"title":"Experimental performance characterization of R-454B and R-410A in data center server rack mount cooling unit: Energy efficiency and environmental impact assessment","authors":"Türkan Üçok Erkek , Mehmet Erkek , Mehmet Bora Aydın , Koray Gezer","doi":"10.1016/j.ijrefrig.2025.12.007","DOIUrl":"10.1016/j.ijrefrig.2025.12.007","url":null,"abstract":"<div><div>Data center cooling accounts for a substantial fraction of facility energy consumption, with environmental pressures driving the transition from high-GWP refrigerants to sustainable alternatives. However, rigorous experimental comparisons of next-generation refrigerants under realistic operational conditions remain limited, and existing benchmarking protocols often fail to account for ambient variability across test conditions. This study addresses these gaps by conducting a comprehensive experimental evaluation of an in-rack air-conditioning unit, comparing the conventional refrigerant R410A with the low-GWP alternative R454B (GWP = 466) across 24 tests spanning varied server loads and thermal conditions. The methodology integrates a transparent steady-state detection algorithm for time-series measurement processing, normalized Energy Efficiency Ratio (EER) calculations at fixed reference conditions to enable equitable cross-test comparison, and sensitivity analyses quantifying the influence of ambient and evaporator-side temperatures on system performance. Cooling capacity, raw and normalized EER, facility-level Power Usage Effectiveness (PUE), and Total Equivalent Warming Impact (TEWI) were derived for each refrigerant. Results demonstrate that R454B exhibits load-dependent performance advantages: under high-load conditions (9 kW), R454B achieved 38 % higher EER (∼5.8 vs. ∼4.2) and superior cooling capacity (13 kW vs. 9.5 kW median) compared to R410A, with reduced operational variability. However, under supply-air matched baseline conditions (16–20 °C), both refrigerants exhibited equivalent performance, confirming that R454B's efficiency gains emerge primarily under elevated thermal stress and higher refrigerant flow rates. PUE analysis showed equivalent facility-level efficiency, enabling R454B as a direct drop-in replacement. TEWI analysis revealed that indirect emissions dominate climate impact (>90 %), establishing operational efficiency optimization as the primary environmental lever, with refrigerant selection providing secondary benefits through GWP reduction. These findings support the adoption of R454B in high-load data center environments, while the transparent methodological framework provides a reproducible benchmark for condition-aware refrigerant evaluation in mission-critical cooling systems.</div></div>","PeriodicalId":14274,"journal":{"name":"International Journal of Refrigeration-revue Internationale Du Froid","volume":"182 ","pages":"Pages 469-481"},"PeriodicalIF":3.8,"publicationDate":"2025-12-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145836495","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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