Pub Date : 2024-10-22DOI: 10.1016/j.ijrefrig.2024.10.014
Shuo Zhang , Huiming Zou , Mingsheng Tang , Fanchen Kong , Wencong Shao , Zhouhang Hu
The self-lubricating linear compressor with aerostatic bearings has good prospect for the scenario which has difficulties of oil returning. This study presents a novel oil-free linear compressor and establishes a frictional damping model by using equivalent circuit approach to evaluate the mechanical performance of the compressor. The changes in friction damping characteristics of VISLLC under different piston strokes and injection pressure are analyzed. The flow resistance coefficients within the porous medium and gas gap are obtained by experimental tests and modeling analysis. Simulation results indicate that the equivalent frictional damping coefficient can be reduced by 36.1 % comparing with that of the non-injection and the efficiency can improved the by 17.2 %. The frictional damping coefficient in the porous bearing thickness of 0.9 mm at 600 kPa injection pressure is 3.64 N·s·m−1.
{"title":"Study on the friction characteristics of a self-lubricating linear compressor using vapor injection","authors":"Shuo Zhang , Huiming Zou , Mingsheng Tang , Fanchen Kong , Wencong Shao , Zhouhang Hu","doi":"10.1016/j.ijrefrig.2024.10.014","DOIUrl":"10.1016/j.ijrefrig.2024.10.014","url":null,"abstract":"<div><div>The self-lubricating linear compressor with aerostatic bearings has good prospect for the scenario which has difficulties of oil returning. This study presents a novel oil-free linear compressor and establishes a frictional damping model by using equivalent circuit approach to evaluate the mechanical performance of the compressor. The changes in friction damping characteristics of VISLLC under different piston strokes and injection pressure are analyzed. The flow resistance coefficients within the porous medium and gas gap are obtained by experimental tests and modeling analysis. Simulation results indicate that the equivalent frictional damping coefficient can be reduced by 36.1 % comparing with that of the non-injection and the efficiency can improved the by 17.2 %. The frictional damping coefficient in the porous bearing thickness of 0.9 mm at 600 kPa injection pressure is 3.64 N·s·m<sup>−1</sup>.</div></div>","PeriodicalId":14274,"journal":{"name":"International Journal of Refrigeration-revue Internationale Du Froid","volume":"169 ","pages":"Pages 294-307"},"PeriodicalIF":3.5,"publicationDate":"2024-10-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142662958","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 : 2024-10-21DOI: 10.1016/j.ijrefrig.2024.10.025
Wenzhuo Li, Ivan Korolija, Rui Tang, Dejan Mumovic
Supermarket refrigeration systems adopting traditional refrigerants with high global warming potential (GWP) have impacts on global warming for indirect and direct greenhouse gases (GHG) emissions. CO2 is a popular low-GWP alternative. The transcritical operation of CO2 systems worsens their energy performance, but provides recoverable heat as a heat source to reduce gas consumption. To evaluate operation performance, data-driven models, trained by historical data, are weak in implementation with datasets outside the scope of training data; in contrast, theoretical models have better extrapolation ability to calculate all operation conditions of CO2 systems at supermarket. Existing theoretical modeling approaches often lack validation against the limited public-access data, which reduces model reliability for further applications, and adopt oversimplified inference methods for unmeasured variables, which increases the risks of breaking thermodynamic laws and lowering model accuracy. This study therefore develops a steady-state theoretical model for CO2 booster refrigeration systems validated against field measurements from three UK supermarkets. The available measurements are utilized to the best level to ensure model accuracy and physical interpretability. Proposed methods to infer missing variables in CO2 systems include condenser outlet temperature, evaporating temperature, compressor isentropic efficiency and compressor mass flow rate. Results show that proposed inference methods enhance the abilities of the proposed modeling approach to ensure data integrity, avoid breaking thermodynamic laws, and improve model accuracy by reflecting real-time actual values of unmeasured variables rather than rough assumptions. The proposed modeling approach provides satisfactory accuracy validated using high-resolution measurements across the whole year from three real supermarkets.
{"title":"High-fidelity model development of CO2 booster refrigeration systems in supermarkets using field measurements","authors":"Wenzhuo Li, Ivan Korolija, Rui Tang, Dejan Mumovic","doi":"10.1016/j.ijrefrig.2024.10.025","DOIUrl":"10.1016/j.ijrefrig.2024.10.025","url":null,"abstract":"<div><div>Supermarket refrigeration systems adopting traditional refrigerants with high global warming potential (GWP) have impacts on global warming for indirect and direct greenhouse gases (GHG) emissions. CO<sub>2</sub> is a popular low-GWP alternative. The transcritical operation of CO<sub>2</sub> systems worsens their energy performance, but provides recoverable heat as a heat source to reduce gas consumption. To evaluate operation performance, data-driven models, trained by historical data, are weak in implementation with datasets outside the scope of training data; in contrast, theoretical models have better extrapolation ability to calculate all operation conditions of CO<sub>2</sub> systems at supermarket. Existing theoretical modeling approaches often lack validation against the limited public-access data, which reduces model reliability for further applications, and adopt oversimplified inference methods for unmeasured variables, which increases the risks of breaking thermodynamic laws and lowering model accuracy. This study therefore develops a steady-state theoretical model for CO<sub>2</sub> booster refrigeration systems validated against field measurements from three UK supermarkets. The available measurements are utilized to the best level to ensure model accuracy and physical interpretability. Proposed methods to infer missing variables in CO<sub>2</sub> systems include condenser outlet temperature, evaporating temperature, compressor isentropic efficiency and compressor mass flow rate. Results show that proposed inference methods enhance the abilities of the proposed modeling approach to ensure data integrity, avoid breaking thermodynamic laws, and improve model accuracy by reflecting real-time actual values of unmeasured variables rather than rough assumptions. The proposed modeling approach provides satisfactory accuracy validated using high-resolution measurements across the whole year from three real supermarkets.</div></div>","PeriodicalId":14274,"journal":{"name":"International Journal of Refrigeration-revue Internationale Du Froid","volume":"169 ","pages":"Pages 152-165"},"PeriodicalIF":3.5,"publicationDate":"2024-10-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142593306","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-10-21DOI: 10.1016/j.ijrefrig.2024.10.024
Yanjie Zhao , Tonghe Zhang , Yongxing Song , Qiang Liu , Lin Liu , Ming Yu , Yi Ge
Under off-design conditions, scroll compressors can lead to reduced efficiency, motor damage, and even cause safety problems such as leaks or explosions. To solve the above problems, this paper analyzes the influence mechanism of different voltages on the spectrum of pressure pulsation signal and modulation signal and provides theoretical support for fault diagnosis and enhances the interpretability of the model. A voltage fault diagnosis method of scroll compressor based on Time-frequency Principal component Convolutional Network (TPCN) model is proposed. By demodulation analysis of the pressure pulsation signal of the low-pressure inlet and high-pressure outlet of the refrigerant in the scroll compressor, the spectrum information of the principal component modulation signal under different voltages is obtained. The pooling strategy is used to accurately identify and extract the fault information in the modulated signal spectrum as the input data of the model. The input data is divided into the training set and the test set according to the ratio of 8:2 to complete the training and testing of the fault diagnosis model. The experimental results show that the accuracy of TPCN model for the diagnosis of 5 types of faults reaches 100 %. The average accuracy of the model is 100 %, which indicates that the model has good stability.
{"title":"Characteristic analysis and diagnosis method optimization of scroll compressor pressure pulsation signal under voltage fluctuation","authors":"Yanjie Zhao , Tonghe Zhang , Yongxing Song , Qiang Liu , Lin Liu , Ming Yu , Yi Ge","doi":"10.1016/j.ijrefrig.2024.10.024","DOIUrl":"10.1016/j.ijrefrig.2024.10.024","url":null,"abstract":"<div><div>Under off-design conditions, scroll compressors can lead to reduced efficiency, motor damage, and even cause safety problems such as leaks or explosions. To solve the above problems, this paper analyzes the influence mechanism of different voltages on the spectrum of pressure pulsation signal and modulation signal and provides theoretical support for fault diagnosis and enhances the interpretability of the model. A voltage fault diagnosis method of scroll compressor based on Time-frequency Principal component Convolutional Network (TPCN) model is proposed. By demodulation analysis of the pressure pulsation signal of the low-pressure inlet and high-pressure outlet of the refrigerant in the scroll compressor, the spectrum information of the principal component modulation signal under different voltages is obtained. The pooling strategy is used to accurately identify and extract the fault information in the modulated signal spectrum as the input data of the model. The input data is divided into the training set and the test set according to the ratio of 8:2 to complete the training and testing of the fault diagnosis model. The experimental results show that the accuracy of TPCN model for the diagnosis of 5 types of faults reaches 100 %. The average accuracy of the model is 100 %, which indicates that the model has good stability.</div></div>","PeriodicalId":14274,"journal":{"name":"International Journal of Refrigeration-revue Internationale Du Froid","volume":"169 ","pages":"Pages 89-100"},"PeriodicalIF":3.5,"publicationDate":"2024-10-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142571572","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 : 2024-10-19DOI: 10.1016/j.ijrefrig.2024.10.017
Hua Zhong , Wei Zhao , Zhaodong Zhang , Che Wang , Keke Gao , Jianhua Wu
The rotary compressors are currently witnessing a trend towards high-speed operation, resulting in an increased frequency of valve motion and a higher mass flow rate through the discharge valve. Consequently, high-speed operation leads to intensified impact between the valve and both the valve stopper and valve seat, thereby posing challenges to the reliability of the valve. Simultaneously, the dynamic characteristics of the valve at high operating speeds exert a significant influence on the compressor's performance. This paper develops a three-dimensional fluid-structure interaction (FSI) model to investigate the dynamic characteristics and reliability of the valve in a high-speed rotary compressor while considering heat transfer during the flow process within the cylinder. The proposed model shows better agreement with the experiment. The study revealed that as the rotational speed increases, there is an obvious rise in over-compression loss and a pronounced valve closure delay, which increases the impact velocity of the valve. The valve experiences two peaks of equivalent stress within one cycle, rendering it susceptible to fail at high speeds. The adoption of a double-valve structure at a rotational speed of 12,000 rpm leads to a significant reduction in over-compression loss by 62.9 %, an increase in volumetric efficiency by 6.7 %, a maximum decrease in impact velocity by 54.5 %, and a maximum decrease in equivalent stress by 25.6 %. The reliability of the double-valve structure under 12,000 rpm was proved by an endurance experiment. Besides, the asymmetry in the opening process of the two valves has been unveiled for the first time.
{"title":"Investigation of discharge valve in ultra-high-speed rotary compressors: An experimental and FSI simulation-based study","authors":"Hua Zhong , Wei Zhao , Zhaodong Zhang , Che Wang , Keke Gao , Jianhua Wu","doi":"10.1016/j.ijrefrig.2024.10.017","DOIUrl":"10.1016/j.ijrefrig.2024.10.017","url":null,"abstract":"<div><div>The rotary compressors are currently witnessing a trend towards high-speed operation, resulting in an increased frequency of valve motion and a higher mass flow rate through the discharge valve. Consequently, high-speed operation leads to intensified impact between the valve and both the valve stopper and valve seat, thereby posing challenges to the reliability of the valve. Simultaneously, the dynamic characteristics of the valve at high operating speeds exert a significant influence on the compressor's performance. This paper develops a three-dimensional fluid-structure interaction (FSI) model to investigate the dynamic characteristics and reliability of the valve in a high-speed rotary compressor while considering heat transfer during the flow process within the cylinder. The proposed model shows better agreement with the experiment. The study revealed that as the rotational speed increases, there is an obvious rise in over-compression loss and a pronounced valve closure delay, which increases the impact velocity of the valve. The valve experiences two peaks of equivalent stress within one cycle, rendering it susceptible to fail at high speeds. The adoption of a double-valve structure at a rotational speed of 12,000 rpm leads to a significant reduction in over-compression loss by 62.9 %, an increase in volumetric efficiency by 6.7 %, a maximum decrease in impact velocity by 54.5 %, and a maximum decrease in equivalent stress by 25.6 %. The reliability of the double-valve structure under 12,000 rpm was proved by an endurance experiment. Besides, the asymmetry in the opening process of the two valves has been unveiled for the first time.</div></div>","PeriodicalId":14274,"journal":{"name":"International Journal of Refrigeration-revue Internationale Du Froid","volume":"168 ","pages":"Pages 730-741"},"PeriodicalIF":3.5,"publicationDate":"2024-10-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142528179","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 : 2024-10-18DOI: 10.1016/j.ijrefrig.2024.09.028
Jan Albers
<div><div>The method of characteristic equations aims to describe the part-load behavior of sorption heat pumps and chillers as well as heat transformers as simply as possible but yet still accurately. Based on an approach by T. Furukawa for heat transformers, the method was further developed by F. Ziegler and others for absorption heat pumps and generalized for application in multistage processes. Clever simplifications were made, to represent the cooling capacity <span><math><mrow><mspace></mspace><msub><mover><mi>Q</mi><mo>˙</mo></mover><mi>E</mi></msub></mrow></math></span> of absorption chillers with a characteristic temperature difference <span><math><mrow><mspace></mspace><mstyle><mi>Δ</mi></mstyle><mstyle><mi>Δ</mi></mstyle><mi>t</mi></mrow></math></span> as a simple linear equation <span><math><mrow><mspace></mspace><msub><mover><mi>Q</mi><mo>˙</mo></mover><mi>E</mi></msub><mo>=</mo><msub><mi>s</mi><mi>E</mi></msub><mo>·</mo><mrow><mo>(</mo><mstyle><mi>Δ</mi></mstyle><mstyle><mi>Δ</mi></mstyle><mi>t</mi><mo>−</mo><mstyle><mi>Δ</mi></mstyle><mstyle><mi>Δ</mi></mstyle><msub><mi>t</mi><mrow><mi>min</mi><mo>,</mo><mi>E</mi></mrow></msub><mo>)</mo></mrow></mrow></math></span>. In <span><math><mrow><mspace></mspace><mstyle><mi>Δ</mi></mstyle><mstyle><mi>Δ</mi></mstyle><mi>t</mi></mrow></math></span>, the average hot, cooling, and chilled water temperatures are combined, and the slope and loss parameters, <span><math><mrow><mspace></mspace><msub><mi>s</mi><mi>E</mi></msub></mrow></math></span> and <span><math><mrow><mspace></mspace><mstyle><mi>Δ</mi></mstyle><mstyle><mi>Δ</mi></mstyle><msub><mi>t</mi><mrow><mi>min</mi><mo>,</mo><mi>E</mi></mrow></msub></mrow></math></span> are constant. However, in practical applications of this established method, inconsistencies arise. For example, the calculated slope parameter <span><math><mrow><mspace></mspace><msub><mi>s</mi><mi>E</mi></msub></mrow></math></span> does not match the slope when plotting simulated or measured cooling capacities against <span><math><mrow><mspace></mspace><mstyle><mi>Δ</mi></mstyle><mstyle><mi>Δ</mi></mstyle><mi>t</mi></mrow></math></span>. Furthermore, the loss parameter <span><math><mrow><mspace></mspace><mstyle><mi>Δ</mi></mstyle><mstyle><mi>Δ</mi></mstyle><msub><mi>t</mi><mrow><mi>min</mi><mo>,</mo><mi>E</mi></mrow></msub></mrow></math></span> is actually not constant.</div><div>In this work a more precise formulation of the characteristic equation is derived which takes into account that the solution entering the absorber and desorber is generally superheated or subcooled. By means of a domain-wise heat transfer calculation, these effects can be implemented into the method and explain the above mentioned inconsistencies. The new formulation allows for explicit consideration of different heat exchanger designs and cooling water configurations. No iterations or regression analyses are required. Thus, the calculation method can be easily implemented into industrial controlle
特征方程法旨在尽可能简单但准确地描述吸收式热泵和冷却器以及热变压器的部分负荷行为。该方法以 T. Furukawa 用于热变压器的方法为基础，由 F. Ziegler 等人针对吸收式热泵进一步开发，并推广应用于多级工艺中。通过巧妙的简化，吸收式制冷机的制冷量 Q˙E 在特性温差 ΔΔt 的情况下，可以用一个简单的线性方程来表示 Q˙E=sE-（ΔΔt-ΔΔtmin,E）。在 ΔΔt 中，热水、冷却水和冷冻水的平均温度合并计算，斜率和损耗参数 sE 和 ΔΔtmin,E 保持不变。然而，在实际应用这种既定方法时，会出现不一致的情况。例如，在绘制模拟或测量的冷却能力与 ΔΔt 的关系图时，计算出的斜率参数 sE 与斜率不一致。此外，损耗参数ΔΔtmin,E 实际上并不是恒定的。在这项工作中，考虑到进入吸收器和解吸塔的溶液通常是过热或过冷的，因此得出了一个更精确的特性方程公式。通过全域传热计算，可以将这些影响纳入计算方法，并解释上述不一致之处。新方法可以明确考虑不同的热交换器设计和冷却水配置。无需进行迭代或回归分析。因此，该计算方法可以很容易地应用到工业控制器中，例如用于吸收式冷却器和热泵的模型预测控制。
{"title":"Enhanced characteristic equation method for single-stage absorption heat pumps","authors":"Jan Albers","doi":"10.1016/j.ijrefrig.2024.09.028","DOIUrl":"10.1016/j.ijrefrig.2024.09.028","url":null,"abstract":"<div><div>The method of characteristic equations aims to describe the part-load behavior of sorption heat pumps and chillers as well as heat transformers as simply as possible but yet still accurately. Based on an approach by T. Furukawa for heat transformers, the method was further developed by F. Ziegler and others for absorption heat pumps and generalized for application in multistage processes. Clever simplifications were made, to represent the cooling capacity <span><math><mrow><mspace></mspace><msub><mover><mi>Q</mi><mo>˙</mo></mover><mi>E</mi></msub></mrow></math></span> of absorption chillers with a characteristic temperature difference <span><math><mrow><mspace></mspace><mstyle><mi>Δ</mi></mstyle><mstyle><mi>Δ</mi></mstyle><mi>t</mi></mrow></math></span> as a simple linear equation <span><math><mrow><mspace></mspace><msub><mover><mi>Q</mi><mo>˙</mo></mover><mi>E</mi></msub><mo>=</mo><msub><mi>s</mi><mi>E</mi></msub><mo>·</mo><mrow><mo>(</mo><mstyle><mi>Δ</mi></mstyle><mstyle><mi>Δ</mi></mstyle><mi>t</mi><mo>−</mo><mstyle><mi>Δ</mi></mstyle><mstyle><mi>Δ</mi></mstyle><msub><mi>t</mi><mrow><mi>min</mi><mo>,</mo><mi>E</mi></mrow></msub><mo>)</mo></mrow></mrow></math></span>. In <span><math><mrow><mspace></mspace><mstyle><mi>Δ</mi></mstyle><mstyle><mi>Δ</mi></mstyle><mi>t</mi></mrow></math></span>, the average hot, cooling, and chilled water temperatures are combined, and the slope and loss parameters, <span><math><mrow><mspace></mspace><msub><mi>s</mi><mi>E</mi></msub></mrow></math></span> and <span><math><mrow><mspace></mspace><mstyle><mi>Δ</mi></mstyle><mstyle><mi>Δ</mi></mstyle><msub><mi>t</mi><mrow><mi>min</mi><mo>,</mo><mi>E</mi></mrow></msub></mrow></math></span> are constant. However, in practical applications of this established method, inconsistencies arise. For example, the calculated slope parameter <span><math><mrow><mspace></mspace><msub><mi>s</mi><mi>E</mi></msub></mrow></math></span> does not match the slope when plotting simulated or measured cooling capacities against <span><math><mrow><mspace></mspace><mstyle><mi>Δ</mi></mstyle><mstyle><mi>Δ</mi></mstyle><mi>t</mi></mrow></math></span>. Furthermore, the loss parameter <span><math><mrow><mspace></mspace><mstyle><mi>Δ</mi></mstyle><mstyle><mi>Δ</mi></mstyle><msub><mi>t</mi><mrow><mi>min</mi><mo>,</mo><mi>E</mi></mrow></msub></mrow></math></span> is actually not constant.</div><div>In this work a more precise formulation of the characteristic equation is derived which takes into account that the solution entering the absorber and desorber is generally superheated or subcooled. By means of a domain-wise heat transfer calculation, these effects can be implemented into the method and explain the above mentioned inconsistencies. The new formulation allows for explicit consideration of different heat exchanger designs and cooling water configurations. No iterations or regression analyses are required. Thus, the calculation method can be easily implemented into industrial controlle","PeriodicalId":14274,"journal":{"name":"International Journal of Refrigeration-revue Internationale Du Froid","volume":"169 ","pages":"Pages 124-139"},"PeriodicalIF":3.5,"publicationDate":"2024-10-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142593234","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-10-16DOI: 10.1016/j.ijrefrig.2024.10.018
Chengxuan Wei , Xiuming Li , Mengyi Li , Zongwei Han , Shuangquan Shao , Bo Zhou
Multi-split backplane cooling, a typical rack-level cooling technology, has the advantage of solving local hot-spot problems with huge energy-saving potential. These systems adopt the multi-split mode, and the operation effect is affected by terminal control performance. However, there are factors in the operation process, such as superheat degree (SH), rack airflow, evaporating/condensing pressures, etc., which improve the control complication, particularly under large head load differences among different terminals. Therefore, appreciative control strategies for outlet air temperatures of terminal evaporators, including single-loop control limited by minimum stable superheat degree (SLC) and fan/electronic expansion valve (EEV) double-loop control (DLC), are proposed considering that cooling performance can be affected by both refrigerant flow and airflow. Then, comparative simulation studies are carried out to evaluate energy efficiency, control effect, and feasibility under the condition of different server heat distribution characteristics. Results indicate that the DLC strategy achieves 23 % higher energy efficiency than the SLC strategy with a better temperature control effect when the inlet air temperature (IAT) difference between terminal evaporators is within ±5K. The SLC strategy has better reliability by more stable control of SH at IATs below 42°C, but it may lead to cooling failure when IATs exceed 42°C. An insufficient liquid supply problem may happen to the evaporator adopting the DLC strategy when the IAT is too high, which can be solved by adjusting the pressure differential between the evaporator and condenser. Moreover, the DLC system exhibits intense coupling effects, and how to decouple it is worthy of further study.
{"title":"A comparative performance study of terminal control strategy for the multi-split backplane cooling system in data centers","authors":"Chengxuan Wei , Xiuming Li , Mengyi Li , Zongwei Han , Shuangquan Shao , Bo Zhou","doi":"10.1016/j.ijrefrig.2024.10.018","DOIUrl":"10.1016/j.ijrefrig.2024.10.018","url":null,"abstract":"<div><div>Multi-split backplane cooling, a typical rack-level cooling technology, has the advantage of solving local hot-spot problems with huge energy-saving potential. These systems adopt the multi-split mode, and the operation effect is affected by terminal control performance. However, there are factors in the operation process, such as superheat degree (SH), rack airflow, evaporating/condensing pressures, etc., which improve the control complication, particularly under large head load differences among different terminals. Therefore, appreciative control strategies for outlet air temperatures of terminal evaporators, including single-loop control limited by minimum stable superheat degree (SLC) and fan/electronic expansion valve (EEV) double-loop control (DLC), are proposed considering that cooling performance can be affected by both refrigerant flow and airflow. Then, comparative simulation studies are carried out to evaluate energy efficiency, control effect, and feasibility under the condition of different server heat distribution characteristics. Results indicate that the DLC strategy achieves 23 % higher energy efficiency than the SLC strategy with a better temperature control effect when the inlet air temperature (IAT) difference between terminal evaporators is within ±5K. The SLC strategy has better reliability by more stable control of SH at IATs below 42°C, but it may lead to cooling failure when IATs exceed 42°C. An insufficient liquid supply problem may happen to the evaporator adopting the DLC strategy when the IAT is too high, which can be solved by adjusting the pressure differential between the evaporator and condenser. Moreover, the DLC system exhibits intense coupling effects, and how to decouple it is worthy of further study.</div></div>","PeriodicalId":14274,"journal":{"name":"International Journal of Refrigeration-revue Internationale Du Froid","volume":"168 ","pages":"Pages 742-757"},"PeriodicalIF":3.5,"publicationDate":"2024-10-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142528180","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 : 2024-10-16DOI: 10.1016/j.ijrefrig.2024.10.001
Gabriele Toffoletti , Riley B. Barta , Steven M. Grajales , Haotian Liu , Davide Ziviani , Eckhard A. Groll
To reduce the direct global warming impact of refrigerants in HVAC&R applications, low-global warming potential (GWP) refrigerants, including natural refrigerants, have been extensively investigated as alternatives to hydrofluorocarbon (HFC) refrigerants. Among the natural refrigerants, Carbon Dioxide (CO2) offers several advantages, such as excellent transport and thermo-physical properties, being neither toxic nor flammable, and having a low price and high availability around the world. However, the high critical pressure and low critical temperature of CO2 often lead to transcritical operation, resulting in lower efficiency due to the additional compressor power necessary to achieve transcritical operation relative to subcritical HFC cycles. Therefore, a number of cycle modifications are used to enhance the coefficient of performance (COP) of transcritical CO2 cycles to meet or surpass those of HFC cycles. This paper provides a systematic experimental investigation of four such cycle architectures by employing the same multi-stage, two-evaporator CO2 refrigeration cycle test stand, 3 of these configurations in transcritical and 1 in subcritical conditions. The four cycles architectures included intercooling, open economization, an internal heat exchanger and two different ejector control approaches. Specifically, a variable-diameter motive nozzle and a variable-speed liquid CO2 pump located directly upstream of the ejector motive nozzle inlet were analyzed. Based on the experimental data, the maximum COP improvements are 4.64 % and 9.47 % when the ejector and the internal heat exchanger are used, respectively. The CO2 pump, once successfully stabilized, can control the ejector, increase its efficiency by up to 15 % and increase the cooling capacity to a maximum of 6.2 %. Nevertheless, a reduction in COP is measured when the pump is in use; however, unlike the other three different configurations, it was only analyzed under subcritical conditions.
为了减少制冷剂在暖通空调与制冷应用中对全球变暖的直接影响，人们对包括天然制冷剂在内的低全球升温潜能值（GWP）制冷剂进行了广泛研究，将其作为氢氟碳化合物（HFC）制冷剂的替代品。在天然制冷剂中，二氧化碳（CO2）具有多种优势，如优异的运输和热物理性能，既无毒也不易燃，而且价格低廉，在世界各地的供应量很大。然而，二氧化碳的临界压力高、临界温度低，通常会导致跨临界运行，与亚临界氢氟碳化物循环相比，实现跨临界运行需要额外的压缩机功率，因此效率较低。因此，许多循环改造被用来提高跨临界 CO2 循环的性能系数 (COP)，以达到或超过 HFC 循环的性能系数。本文通过使用相同的多级双蒸发器 CO2 制冷循环试验台，对四种此类循环结构进行了系统的实验研究，其中三种配置在跨临界条件下，一种在亚临界条件下。这四种循环结构包括中冷、开放式节约、内部热交换器和两种不同的喷射器控制方法。具体来说，分析了位于喷射器喷嘴入口上游的可变直径喷嘴和变速液态二氧化碳泵。根据实验数据，使用喷射器和内部热交换器时，COP 的最大改善率分别为 4.64 % 和 9.47 %。二氧化碳泵一旦成功稳定，就能控制喷射器，将其效率提高 15%，并将冷却能力最大提高 6.2%。不过，在使用该泵时，COP 会有所降低；但与其他三种不同配置不同的是，该泵仅在亚临界状态下进行分析。
{"title":"Experimental comparison of cycle modifications and ejector control methods using variable geometry and CO2 pump in a multi-evaporator transcritical CO2 refrigeration system","authors":"Gabriele Toffoletti , Riley B. Barta , Steven M. Grajales , Haotian Liu , Davide Ziviani , Eckhard A. Groll","doi":"10.1016/j.ijrefrig.2024.10.001","DOIUrl":"10.1016/j.ijrefrig.2024.10.001","url":null,"abstract":"<div><div>To reduce the direct global warming impact of refrigerants in HVAC&R applications, low-global warming potential (GWP) refrigerants, including natural refrigerants, have been extensively investigated as alternatives to hydrofluorocarbon (HFC) refrigerants. Among the natural refrigerants, Carbon Dioxide (CO<sub>2</sub>) offers several advantages, such as excellent transport and thermo-physical properties, being neither toxic nor flammable, and having a low price and high availability around the world. However, the high critical pressure and low critical temperature of CO<sub>2</sub> often lead to transcritical operation, resulting in lower efficiency due to the additional compressor power necessary to achieve transcritical operation relative to subcritical HFC cycles. Therefore, a number of cycle modifications are used to enhance the coefficient of performance (COP) of transcritical CO<sub>2</sub> cycles to meet or surpass those of HFC cycles. This paper provides a systematic experimental investigation of four such cycle architectures by employing the same multi-stage, two-evaporator CO<sub>2</sub> refrigeration cycle test stand, 3 of these configurations in transcritical and 1 in subcritical conditions. The four cycles architectures included intercooling, open economization, an internal heat exchanger and two different ejector control approaches. Specifically, a variable-diameter motive nozzle and a variable-speed liquid CO<sub>2</sub> pump located directly upstream of the ejector motive nozzle inlet were analyzed. Based on the experimental data, the maximum COP improvements are 4.64 % and 9.47 % when the ejector and the internal heat exchanger are used, respectively. The CO<sub>2</sub> pump, once successfully stabilized, can control the ejector, increase its efficiency by up to 15 % and increase the cooling capacity to a maximum of 6.2 %. Nevertheless, a reduction in COP is measured when the pump is in use; however, unlike the other three different configurations, it was only analyzed under subcritical conditions.</div></div>","PeriodicalId":14274,"journal":{"name":"International Journal of Refrigeration-revue Internationale Du Froid","volume":"169 ","pages":"Pages 226-240"},"PeriodicalIF":3.5,"publicationDate":"2024-10-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142662954","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-10-16DOI: 10.1016/j.ijrefrig.2024.10.020
Po-Ching Hsu , Lei Gao , Yunho Hwang
The optimized control of variable refrigerant flow (VRF) system requires an accurate time series forecast model for power consumption. Currently, physics-based and black-box models widely used for forecasting power consumption may not be able to capture the dynamic and non-linear behavior of such complex systems. This study presents a long-short-term memory (LSTM), deep learning-based model to accurately predict the power consumption of a VRF system with heat recovery units. The model training used one year of VRF system field test data. The feature selection through the Pearson correlation coefficient was implemented to improve the model's accuracy and computational efficiency. The sensitivity analysis of feature selection was performed by preparing three feature sets, including different levels of relationship with the predicted target. Additionally, the hyperparameters of the models were optimized by Bayesian optimization with the Tree-structured Parzen Estimator algorithm. The deep learning model, LSTM model, was compared to the baseline machine learning model, Artificial Neural Network (ANN) and decision tree. The results show that LSTM-30feat with input time step 4 has the best testing performance of Coefficient of the Variation of the Root Mean Square Error (CvRMSE) 23.3%. The best ANN model is ANN-10feat with input time step 8, which has a CvRMSE of 27.8% in testing and 13,569 trainable parameters. However, LSTM-10feat with input time step 4 has the CvRMSE of 24.8% in testing, and the trainable parameters are 1,809. A higher number of trainable parameters in models might result in increased memory usage on the computer and be computationally expensive.
{"title":"Comparative study of LSTM and ANN models for power consumption prediction of variable refrigerant flow (VRF) systems in buildings","authors":"Po-Ching Hsu , Lei Gao , Yunho Hwang","doi":"10.1016/j.ijrefrig.2024.10.020","DOIUrl":"10.1016/j.ijrefrig.2024.10.020","url":null,"abstract":"<div><div>The optimized control of variable refrigerant flow (VRF) system requires an accurate time series forecast model for power consumption. Currently, physics-based and black-box models widely used for forecasting power consumption may not be able to capture the dynamic and non-linear behavior of such complex systems. This study presents a long-short-term memory (LSTM), deep learning-based model to accurately predict the power consumption of a VRF system with heat recovery units. The model training used one year of VRF system field test data. The feature selection through the Pearson correlation coefficient was implemented to improve the model's accuracy and computational efficiency. The sensitivity analysis of feature selection was performed by preparing three feature sets, including different levels of relationship with the predicted target. Additionally, the hyperparameters of the models were optimized by Bayesian optimization with the Tree-structured Parzen Estimator algorithm. The deep learning model, LSTM model, was compared to the baseline machine learning model, Artificial Neural Network (ANN) and decision tree. The results show that LSTM-30feat with input time step 4 has the best testing performance of Coefficient of the Variation of the Root Mean Square Error (CvRMSE) 23.3%. The best ANN model is ANN-10feat with input time step 8, which has a CvRMSE of 27.8% in testing and 13,569 trainable parameters. However, LSTM-10feat with input time step 4 has the CvRMSE of 24.8% in testing, and the trainable parameters are 1,809. A higher number of trainable parameters in models might result in increased memory usage on the computer and be computationally expensive.</div></div>","PeriodicalId":14274,"journal":{"name":"International Journal of Refrigeration-revue Internationale Du Froid","volume":"169 ","pages":"Pages 55-68"},"PeriodicalIF":3.5,"publicationDate":"2024-10-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142553701","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}
The refrigerated transportation industry's growth necessitates addressing energy consumption and greenhouse gas emissions. This study estimates a photovoltaic system's energy and environmental benefits to power a vapour compression refrigeration (VCR) system serving a light-duty commercial refrigerated van. A comprehensive energy model encompassing thermal, electrical, and battery sub-models simulating the system's dynamic behaviour is calibrated with real-world data referring to an urban single-delivery mission. The potential benefits are estimated for a long-distance single-delivery mission starting from the University of Salerno (Italy) and ending at the Jaume I University in Castellon de la Plana (Spain). The results have shown that the system can reduce fuel consumption for refrigeration by more than 88 % during summer months and allows neutral refrigeration during winter months, leading to on-wheel emission savings between 4 and 8 gCO2,e/km. When considering total emissions, including electrical energy from the power grid and the increased weight due to the PV system, a 33–47 % reduction is obtained, corresponding to 1–5 gCO2,e/km. In detail, PV panels can cover up to 19 % of the total energy requirements. In economic terms, the system allows a cost-saving between 0.1 and 0.3 c€/km. The low complexity and promising results suggest the hybrid PV solution is a viable path towards decarbonising refrigerated transport.
{"title":"Performance evaluation of a hybrid photovoltaic-vapor compression system serving a refrigerated van","authors":"Angelo Maiorino , Fabio Petruzziello , Claudio Cilenti , Rodrigo Llopis , Ciro Aprea","doi":"10.1016/j.ijrefrig.2024.10.021","DOIUrl":"10.1016/j.ijrefrig.2024.10.021","url":null,"abstract":"<div><div>The refrigerated transportation industry's growth necessitates addressing energy consumption and greenhouse gas emissions. This study estimates a photovoltaic system's energy and environmental benefits to power a vapour compression refrigeration (VCR) system serving a light-duty commercial refrigerated van. A comprehensive energy model encompassing thermal, electrical, and battery sub-models simulating the system's dynamic behaviour is calibrated with real-world data referring to an urban single-delivery mission. The potential benefits are estimated for a long-distance single-delivery mission starting from the University of Salerno (Italy) and ending at the Jaume I University in Castellon de la Plana (Spain). The results have shown that the system can reduce fuel consumption for refrigeration by more than 88 % during summer months and allows neutral refrigeration during winter months, leading to on-wheel emission savings between 4 and 8 gCO<sub>2</sub>,e/km. When considering total emissions, including electrical energy from the power grid and the increased weight due to the PV system, a 33–47 % reduction is obtained, corresponding to 1–5 gCO<sub>2</sub>,e/km. In detail, PV panels can cover up to 19 % of the total energy requirements. In economic terms, the system allows a cost-saving between 0.1 and 0.3 c€/km. The low complexity and promising results suggest the hybrid PV solution is a viable path towards decarbonising refrigerated transport.</div></div>","PeriodicalId":14274,"journal":{"name":"International Journal of Refrigeration-revue Internationale Du Froid","volume":"168 ","pages":"Pages 720-729"},"PeriodicalIF":3.5,"publicationDate":"2024-10-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142528178","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-10-16DOI: 10.1016/j.ijrefrig.2024.10.019
Zhixiang Liao , Bin Peng , Yubo Zhang , Xiaoliang Yang , Youxin Zhou , Pengcheng Zhang , Bingguo Zhu
The combined algebraic spiral (CAS) effectively maximizes the geometric performance of a scroll compressor; however, its dynamic behavior remains inadequately explored. Utilizing the geometric model of the CAS scroll compressor, this study derived the functional relationship between the meshing point and the rotation angle, and calculated the working chamber volume using the discrete Green's theorem method. A dynamic model of the CAS scroll compressor was developed, and the influence of various parameters on its dynamic characteristics was analyzed. The findings indicate that when the polar angle interval is <0.01π, the discrete Green's theorem method accurately computes the working chamber volume. Among the gas forces acting on the CAS scroll compressor, the axial gas force is the most significant, followed by the tangential gas force, while the radial gas force is considerably smaller. The tangential gas force predominantly influences the overturning and rotational moments. Notably, when the polar angles of the connection points between the higher-order curve and the starting and ending algebraic spirals are set at 1.5π and 3π, the gas force remains low while maintaining geometric performance. This configuration results in reduced variation in gas force and enhanced dynamic performance. The spiral coefficient and spiral index of the starting algebraic spiral should be set as intermediate values to ensure optimal geometric and dynamic performance of the CAS scroll compressor.
组合代数螺旋（CAS）能有效地将涡旋式压缩机的几何性能最大化，但对其动态行为的研究仍显不足。本研究利用 CAS 涡旋式压缩机的几何模型，得出了啮合点与旋转角度之间的函数关系，并利用离散格林定理方法计算了工作腔容积。建立了 CAS 涡旋式压缩机的动态模型，并分析了各种参数对其动态特性的影响。研究结果表明，当极角间隔为 0.01π 时，离散格林定理方法能准确计算工作腔容积。在作用于 CAS 涡旋式压缩机的气体力中，轴向气体力最为显著，切向气体力次之，而径向气体力则小得多。切向气体力主要影响倾覆力矩和旋转力矩。值得注意的是，当高阶曲线与代数螺旋起点和终点的连接点的极角分别设置为 1.5π 和 3π 时，气体力保持在较低水平，同时还能保持几何性能。这种配置减少了气体力的变化，提高了动态性能。起始代数螺旋的螺旋系数和螺旋指数应设置为中间值，以确保 CAS 涡旋式压缩机具有最佳的几何和动态性能。
{"title":"Dynamic model and characteristic analysis of a combined algebraic spiral scroll compressor","authors":"Zhixiang Liao , Bin Peng , Yubo Zhang , Xiaoliang Yang , Youxin Zhou , Pengcheng Zhang , Bingguo Zhu","doi":"10.1016/j.ijrefrig.2024.10.019","DOIUrl":"10.1016/j.ijrefrig.2024.10.019","url":null,"abstract":"<div><div>The combined algebraic spiral (CAS) effectively maximizes the geometric performance of a scroll compressor; however, its dynamic behavior remains inadequately explored. Utilizing the geometric model of the CAS scroll compressor, this study derived the functional relationship between the meshing point and the rotation angle, and calculated the working chamber volume using the discrete Green's theorem method. A dynamic model of the CAS scroll compressor was developed, and the influence of various parameters on its dynamic characteristics was analyzed. The findings indicate that when the polar angle interval is <0.01π, the discrete Green's theorem method accurately computes the working chamber volume. Among the gas forces acting on the CAS scroll compressor, the axial gas force is the most significant, followed by the tangential gas force, while the radial gas force is considerably smaller. The tangential gas force predominantly influences the overturning and rotational moments. Notably, when the polar angles of the connection points between the higher-order curve and the starting and ending algebraic spirals are set at 1.5π and 3π, the gas force remains low while maintaining geometric performance. This configuration results in reduced variation in gas force and enhanced dynamic performance. The spiral coefficient and spiral index of the starting algebraic spiral should be set as intermediate values to ensure optimal geometric and dynamic performance of the CAS scroll compressor.</div></div>","PeriodicalId":14274,"journal":{"name":"International Journal of Refrigeration-revue Internationale Du Froid","volume":"169 ","pages":""},"PeriodicalIF":3.5,"publicationDate":"2024-10-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142553699","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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