scholarly journals Evaluating the Performance of Water Chillers Equipped with Constant- or Variable-Frequency Centrifugal Compressors

Processes ◽  
2021 ◽  
Vol 9 (6) ◽  
pp. 1039
Author(s):  
Chih-Neng Hsu ◽  
Shih-Hao Wang
Keyword(s):  
Energy Saving ◽  
Load Capacity ◽  
Operating Performance ◽  
Cooling Water ◽  
Variable Frequency ◽  
Inlet Temperature ◽  
Constant Frequency ◽  
Frequency Unit ◽  
The Difference ◽  
Better Than

The cooling coefficient of performance (COPR) and energy efficiency ratio (EER) of refrigerant R-134a compressors (single- and double-compressors) with different refrigerant tonnage (200, 250, 300, 380, 500, and 700 RT) for centrifugal and Maglev centrifugal compressors change with different operating performance load percentages (10%–100%), and constant-frequency and variable-frequency operation, resulting in performance differences. In particular, a water chiller can have a fixed cooling water inlet temperature of 32 °C and a variable cooling water inlet temperature between 18.33 °C and 32 °C. According to the actual test results, the commercial performance code program and parameter table of the water chiller were established. Based on the performance matching of different load chillers, the on-site load capacity was analyzed and the effective water chiller performance and model matching were determined as the best choice for the tonR number of the deicing machine and unit matching, providing a reference for a future large water chiller that cannot be used on site for a single unit tonR. To achieve energy-saving benefits, different types of compressors, different refrigeration tonR operation, constant-frequency unit and variable-frequency unit alternate operation, and different operating performance load percentage operation can be allocated. Finally, the results show that, when the cooling water inlet temperature is fixed, the Maglev variable-frequency centrifugal compressor water chiller is better than the constant-frequency centrifugal water chiller, and also better than the variable-frequency centrifugal water chiller. The larger the freezing tonR of the variable-frequency centrifugal water chiller, the smaller the difference between COPR and EER. When the cooling water inlet temperature changes, the Maglev variable-frequency centrifugal water chiller is better than the constant-frequency centrifugal water chiller, and it is also better than the variable-frequency centrifugal water chiller. The larger the freezing tonR of the variable-frequency centrifugal water chiller, the smaller the difference between COPR and EER. Moreover, the operating performance of the constant-frequency centrifugal water chiller is between 60% and 90%, which can maintain relatively high COPR and EER values. The operating performance of the variable-frequency centrifugal water chiller is between 40% and 70%, which can maintain relatively high COPR and EER values. Compared with the constant-frequency and variable-frequency, the Maglev variable-frequency centrifugal water chiller can maintain higher COPR and EER values when the operating performance is between 10% and 100%. When the operating performance is between 10% and 70%, it can maintain very high COPR and EER values. When the water chiller is selected in the field, the energy-saving of COPR and EER will be given priority. Therefore, the load capacity can be used to effectively manage the water chiller performance and model selection, so that the operation performance can reach the best percentage and energy saving can be achieved.

scholarly journals The Impact of Coolant Temperatures on Various Cycle Parameters of NH3-H2O Absorption Chiller from Solar Source

2021 ◽  
pp. 43-50
Author(s):  
Adel Akair ◽  
Hesham Baej
Keyword(s):  
Water Temperature ◽  
Temperature Increase ◽  
Cooling Water ◽  
Relative Difference ◽  
Inlet Temperature ◽  
Absorption Chiller ◽  
Ammonia Water ◽  
Solar Source ◽  
Cooling Water Temperature ◽  
The Difference

The cycles’ structure was based on recently published technical information of low-temperatures powered Ammonia-water (NH3-H2O) absorption chiller.  The cycle was completely modeled using different components available within the refrigeration library of IPSEpro software package.  Using the model a cold-water ammonia-water absorption chiller was examined and validated in accordance to the relevant thermodynamic laws and charts. A low-grade temperature solar resource was modeled to energise the proposed model. For water-cooled cycles, the rejected heat from the absorbers and the condensers was carried out by water, at an average fixed temperature of 25°C, pumped out from ground water. The results obtained show that when the Coefficient of performance (COP), heat inputs into the generator, and cooling mass flow rates are fixed, the cycle parameters are highly affected by variation of coolant temperature. For instance when cooling water temperature decreases. Also when cooling water temperature increase, the cycle pressure, usable chilled water temperature difference and desorber outlet temperature increase whereas mass concentration and refrigeration capacity decrease. The effectiveness of the generator inlet temperature (solar source) is a factor of the largest effect to the COP. The difference was 0.1401, 27.4%. The chilled water inlet temperature (underground water) is the second largest effect to the COP. The difference between the maximum and the minimum value is 0.0865 and the relative difference is 18.9% with cooling capacity 12 kW. The influence of evaporator temperature to the COP is also minimal with only 2.2% difference. The influence of absorber temperature and condenser temperature to the COP are almost identical, the relative difference is 19.2% and 18.9% respectively.

Energy Analysis of Cooling Water Pump for Variable Loading in Air-Conditioning System

2013 ◽  
Vol 421 ◽  
pp. 66-71
Author(s):  
Yung Chung Chang ◽  
Kai Chun Peng ◽  
Ching Liang Chen
Keyword(s):  
Regression Analysis ◽  
Power Consumption ◽  
Energy Saving ◽  
Linear Regression Analysis ◽  
Cooling Water ◽  
Variable Frequency ◽  
Second Phase ◽  
Operational Mode ◽  
Water Pump ◽  
Analysis Model

This study used linear regression analysis model to explore chilled water system of central air conditioning for energy saving of cooling water pump based on frequency conversion control of pumped. Research and analysis is divided two phases, the first phase is recording approach temperature and load rate (PLR; Partial Load Ratio) of cooling tower in variable frequency operational mode, then using linear regression analysis model to built the power consumption equation (KW/RT) of cooling water pump. Second phase will be to non-variable frequency operation modes to establish the same relationship equation, and then will be used the first phase record data that its wet bulb temperature and cooling towers PLR limits are in accordance with the second phase of the same range conditions, you can explore the power consumption difference of cooling water pump in variable frequency and non-variable frequency operational mode.Through this research and analysis, was informed that power consumption model error rate of less than 1%, also informed that variable frequency operational mode than non-variable frequency operational mode can save 782.8 kW (19.64%) in the quadratic regression analysis results. In three times regression analysis results can be saved 919.38 kW (22.3%). Accordingly, the present research findings and theoretical models can be used as cooling water pump energy saving, also can serve as the theoretical basis for other energy saving.

scholarly journals Comparison investigation on the load capacity of octagonal, circular and square concrete filled steel tubes

2018 ◽  
Author(s):  
Tak-Ming Chan ◽  
Jiong-Yi Zhu
Keyword(s):  
Cross Sections ◽  
Load Capacity ◽  
Comparative Investigation ◽  
Axial Stiffness ◽  
Steel Tubes ◽  
Cross Sectional ◽  
Total Cross Sectional Area ◽  
The Difference ◽  
Concrete Filled Steel Tubes ◽  
Better Than

This paper presents a comparative investigation on the load capacity of octagonal concrete filled steel tubes (CFST) with that of the commonly used circular and square CFST. Existing experimental data of octagonal CFST were collected and based on the cross-sectional properties of the existing octagonal specimens, the corresponding circular and square cross-section were generated under three different control parameters: total cross-sectional area of column, confinement ratio and axial stiffness. Those circular and square cross-sections were used in the numerical analysis of CFST to obtain the load capacity for the comparative investigation. Validated finite element models were built for the modeling of the circular and square CFST. The outcome of comparison shows that the confinement ratio is the crucial parameter to the difference of axial behaviour between octagonal and circular CFST. Under the same confinement ratio, octagonal CFST has a very close axial bearing performance to that in circular CFST and are much better than the square CFST.

Experimental Research on Heat Transfer of Closed Cooling Tower with Packing

2014 ◽  
Vol 960-961 ◽  
pp. 614-620 ◽  
Author(s):  
Ya Su Zhou ◽  
Xiao Ding ◽  
Wei Xie
Keyword(s):  
Water Flow ◽  
Flow Rate ◽  
Cooling Tower ◽  
Water Flow Rate ◽  
Cooling Water ◽  
Cocurrent Flow ◽  
Inlet Temperature ◽  
Cooling Performance ◽  
Cooling Water Flow Rate ◽  
Better Than

Three different structural types of closed cooling tower (CCT) and two cooling water flow directions were considered. The experimental study were done on the cooling performance of influences of inlet air dry and wet bulb temperature, cooling water flow rate and inlet temperature, air flow rate and spray density. The experimental results show that the cooling performance of CCT with packing is obviously better than non-packing cooling tower in 7%~18.4%. And the cooling performance of CCT with packing on top and coil underneath is slightly better than CCT with coil on top and packing underneath in 4.9%. In the same conditions the cooling performance of CCT with packing under cooling water cocurrent-flow is better than that cooling water countercurrent-flow in 3.2%~9.6%. Therefore, the closed cooling tower structure with the cooling water path in bottom and out top, and with packing on top and coil underneath is recommended.

Performance Corrections for Steam Turbines With Multi-Pressure Condensers

2014 ◽  
Author(s):  
Thomas P. Winterberger ◽  
Ioannis Tzagkarakis
Keyword(s):  
Cooling Water ◽  
Critical Parameters ◽  
Inlet Temperature ◽  
Steam Turbines ◽  
Factors Affecting ◽  
Pressure Correction ◽  
Cooling Water Temperature ◽  
The Difference ◽  
Tube Plugging ◽  
Performance Results

An accurate correction methodology is essential when analyzing test data and trending performance. One of the most critical parameters for steam turbines, which can result in large corrections, is condenser back-pressure or exhaust pressure. Many large fossil and all nuclear steam turbines are configured with either two or three low pressure condensing exhaust hoods. All exhaust hoods may not operate with the same condenser pressure. Factors affecting condenser pressures between hoods could include the cooling water arrangement, uneven fouling, tube plugging, air removal effectiveness, etc. The biggest impact is likely due to the cooling water arrangement. In a parallel arrangement, the condenser cooling water splits between the shells with each shell receiving an equal amount of flow at the same inlet temperature. In a series arrangement, all cooling water enters and exits the first shell before entering the next shell. In this arrangement the cooling water temperature entering the second shell is higher than the temperature entering the first shell resulting in the condensers operating at different exhaust pressures. One common practice is to apply a single exhaust pressure correction factor based on the average exhaust pressure of all condenser shells. In cases where the differences in condenser pressure are small, this practice can provide accurate corrected turbine performance. As the difference in condenser pressures increases, the potential for introducing error in the corrected performance results also increases. This paper will discuss the mechanism of why multi-pressure operation can result in correction errors if not modelled correctly and will also quantify the potential impact of these errors on the corrected performance results. In addition, guidance will be given on how exhaust pressure correction curves should be created and applied to most accurately model the performance of the turbine cycle when multi-pressure operation exists.

Removal of inelastically scattered electrons substantially increases phase contrast on frozen-hydrated molecules

1987 ◽  
Vol 45 ◽  
pp. 652-653
Author(s):  
John P. Langmore ◽  
Brian D. Athey
Keyword(s):  
Electron Diffraction ◽  
Phase Contrast ◽  
Low Dose ◽  
Dark Field ◽  
Biological Structure ◽  
Bright Field ◽  
Low Contrast ◽  
Negative Stain ◽  
The Difference ◽  
Better Than

Although electron diffraction indicates better than 0.3nm preservation of biological structure in vitreous ice, the imaging of molecules in ice is limited by low contrast. Thus, low-dose images of frozen-hydrated molecules have significantly more noise than images of air-dried or negatively-stained molecules. We have addressed the question of the origins of this loss of contrast. One unavoidable effect is the reduction in scattering contrast between a molecule and the background. In effect, the difference in scattering power between a molecule and its background is 2-5 times less in a layer of ice than in vacuum or negative stain. A second, previously unrecognized, effect is the large, incoherent background of inelastic scattering from the ice. This background reduces both scattering and phase contrast by an additional factor of about 3, as shown in this paper. We have used energy filtration on the Zeiss EM902 in order to eliminate this second effect, and also increase scattering contrast in bright-field and dark-field.

Subjective Time Preference and Willingness to Pay for an Energy-Saving Durable Good

2001 ◽  
Vol 32 (3) ◽  
pp. 133-141 ◽  
Author(s):  
Gerrit Antonides ◽  
Sophia R. Wunderink
Keyword(s):  
Willingness To Pay ◽  
Energy Saving ◽  
Subjective Time ◽  
Durable Good ◽  
Discount Function ◽  
Hyperbolic Discount ◽  
The One ◽  
Two Parameter ◽  
Difference Effect ◽  
Better Than

Summary: Different shapes of individual subjective discount functions were compared using real measures of willingness to accept future monetary outcomes in an experiment. The two-parameter hyperbolic discount function described the data better than three alternative one-parameter discount functions. However, the hyperbolic discount functions did not explain the common difference effect better than the classical discount function. Discount functions were also estimated from survey data of Dutch households who reported their willingness to postpone positive and negative amounts. Future positive amounts were discounted more than future negative amounts and smaller amounts were discounted more than larger amounts. Furthermore, younger people discounted more than older people. Finally, discount functions were used in explaining consumers' willingness to pay for an energy-saving durable good. In this case, the two-parameter discount model could not be estimated and the one-parameter models did not differ significantly in explaining the data.

PENERAPAN MODEL PEMBELAJARAN KOOPERATIF TIPE STAD DENGAN PENDEKATAN RME UNTUK MENINGKATKAN HASIL BELAJAR MATEMATIKA SISWA KELAS IX SMP MUHAMMADIYAH PADANG LUAS KECAMATAN TAMBANG KABUPATEN KAMPAR

2018 ◽  
Vol 2 (5) ◽  
pp. 744
Author(s):  
Zainur Zainur
Keyword(s):  
Action Research ◽  
Cooperative Learning ◽  
Student Learning ◽  
Learning Outcomes ◽  
Mathematics Learning ◽  
Student Learning Outcomes ◽  
Learning Model ◽  
Research Instrument ◽  
The Difference ◽  
Better Than

This research was motivated by the low learning outcomes of grade IX SMP Muhammadiyah Padang LuasKecamatan Tambang Kabupaten Kampar. This study aims to improve learning outcomes in mathematicslearning through STAD type cooperative learning with the RME approach in class IX SMP MuhammadiyahPadang Luas Kecamatan Tambang Kabupaten Kampar. The subjects of this study were all classes IX in SMPMuhammadiyah Padang Luas Kecamatan Tambang Kabupaten Kampar totaling 26 people. The form ofresearch is classroom action research. This research instrument consists of performance instruments and datacollection instruments in the form of teacher activity observation sheets and activities. The results of the studystated that there were significant differences between students' mathematics learning outcomes before applyingthe STAD type cooperative learning model with the RME approach with after applying the STAD typecooperative learning model with the RME approach. The difference shows student learning outcomes after theaction is better than before the action with completeness reaching 80.77% or 21 completed. Based on the resultsof the study and discussion it can be concluded that the application of STAD type learning model with RealisticMathematic Education (RME) approach can improve the learning outcomes of grade IX students of SMPMuhammadiyah Padang Luas Kecamatan Tambang Kabupaten Kampar on statistical material.

scholarly journals Six ultraviolet minutes for cleaner operating theatres

2020 ◽  
Vol 30 (Supplement_5) ◽  
Author(s):  
R Bosco ◽  
S Gambelli ◽  
V Urbano ◽  
G Cevenini ◽  
G Messina
Keyword(s):  
Cross Sectional Study ◽  
Cross Sectional ◽  
Before And After ◽  
Operating Theatres ◽  
Cleaning Procedures ◽  
The Difference ◽  
Contamination Levels ◽  
Different Levels ◽  
Better Than ◽  
Final Cleaning

Abstract Background Sanitizing the operating theatres (OT) is important to minimize risk of post-operative infections. Disinfection procedures between one operation and another is less aggressive than final cleaning procedures, at the end of the day. Aim was assessing the difference of contamination: i) between different levels of disinfection; ii) before and after the use of a UVC Device (UVC-D). Methods Between December 2019/February 2020 a cross sectional study was conducted in OT in a real clinical context. 94 Petri dishes (PD) were used in 3 OT. Three different sanitation levels (SL1-3) were compared pre- and post-use of UVC-D: i) No cleaning after surgery (SL1); ii) after in-between cleaning (SL2); iii) after terminal cleaning (SL3). UVC-D was employed for 6 minutes, 3 minutes per bed side. PD were incubated at 36 °C and colony forming unit (CFU) counted at 48h. Descriptive statistic, Wilcoxon and Mann-Whitney tests were performed to assess the contamination levels in total, pre/post use of UVC-D, and between different sanitation levels, respectively. Results In total we had a mean of 3.39 CFU/PD (C.I. 2.05 - 4.74) and a median of 1 CFU/PD (Min. 0 - Max. 39), after UVC-D use we had a mean of 2.20 CFU/PD (C.I. 0.69 - 5.09) and a median of 0 CFU/PD (Min. 0 - Max. 133). The UVC-D led to a significant reduction of CFU (p < 0.001). Without UVC-D we had a significant CFU drop (p < 0.05) between SL1 and SL3. Using UVC-D, we observed significant reductions of contamination (p < 0.05) between SL3 and SL1. Comparing SL1 (median 0) post UVC-D use vs SL2 pre UVC-D use (median 0.5), and SL2 post UVC-D use (median 0) vs SL3 pre UVC-D use (median 1) we had a significant reduction of contamination (p < 0.05). Conclusions UVC-D improved environmental contamination in any of the three sanitation levels. Furthermore, the use of UVC-D alone was better than in-between and terminal cleaning. Although these encouraging results, the cleaning procedures executed by dedicated staff has to be considered. Key messages UVC are efficient to decrease contamination in operating theatres regardless of sanitation levels. The additional use of UVC technology to standard cleaning procedures significantly improves sanitation levels.

Effects of activation frequency and force on low-frequency fatigue in human skeletal muscle

1999 ◽  
Vol 86 (4) ◽  
pp. 1337-1346 ◽  
Author(s):  
Stuart A. Binder-Macleod ◽  
David W. Russ
Keyword(s):  
Healthy Subjects ◽  
Human Skeletal Muscle ◽  
Low Frequency ◽  
Variable Frequency ◽  
Activation Pattern ◽  
Constant Frequency ◽  
Mean Frequency ◽  
Before And After ◽  
Low Frequency Fatigue ◽  
Force Time

No comparison of the amount of low-frequency fatigue (LFF) produced by different activation frequencies exists, although frequencies ranging from 10 to 100 Hz have been used to induce LFF. The quadriceps femoris of 11 healthy subjects were tested in 5 separate sessions. In each session, the force-generating ability of the muscle was tested before and after fatigue and at 2, ∼13, and ∼38 min of recovery. Brief (6-pulse), constant-frequency trains of 9.1, 14.3, 33.3, and 100 Hz and a 6-pulse, variable-frequency train with a mean frequency of 14.3 Hz were delivered at 1 train/s to induce fatigue. Immediately postfatigue, there was a significant effect of fatiguing protocol frequency. Muscles exhibited greater LFF after stimulation with the 9.1-, 14.3-, and variable-frequency trains. These three trains also produced the greatest mean force-time integrals during the fatigue test. At 2, ∼13, and ∼38 min of recovery, however, the LFF produced was independent of the fatiguing protocol frequency. The findings are consistent with theories suggesting two independent mechanisms behind LFF and may help identify the optimal activation pattern when functional electrical stimulation is used.

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