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[en] A Study of Noise has been carried out in 17 private offices, with window-type room air-conditioners, to assess noise levels in these offices. A-Weighted equivalent sound-pressure levels (dB(A) LAeq) and equivalent octave-band sound-pressure levels (dB Leq) were measured in each office, and Preferred Speech Interference Levels (PSIL) evaluated. The results show that the interior noise-levels in these offices vary from 59.6 to 72.2 dB(A) LAeq. which are very high and much above the interior noise limits, recommended for offices by some individual workers. Some ways and means to limit its emission of high level of noise from the air conditioners are also discussed. (author)
[en] R134a is the most widely used refrigerant in domestic refrigerators. R134a is a Hydrofluorocarbon (HFC) with high GWP of 1430 and hence, it must be phase out soon under the Kyoto protocol. Hydrocarbon (HC) refrigerants have zero ODP and very low GWP. In the present work, an experimental investigation has been made with HC refrigerant R600a (isobutane) and Hydrocarbon mixture (HCM) refrigerant R436a (composed of R290 and R600a in the ratio of 54:46 by weight) as an alternative to R134a refrigerant in 170 L domestic refrigerator. The performance characteristics such as coefficient of performance (COP), energy consumption, pull down time, discharge temperature, pressure ratio and evaporator inlet temperature of R600a and R436a were compared with those of R134a. The system was modified by replacing HFC compressor with HC compressor and using optimized capillary. In the modified system, for 45g of R436a, the power consumption reduces by 41.66% as compared to R134a in original system also it reduces by 15.66% than optimized charge of R600a in modified system. COP for optimized charge of R436a with modified system increases by 60.25% than R134a and 27.11% R600a.Pull down time for R436a also reduces considerably than R134a and R600a. The overall performance has proved that the R436a refrigerant could be the best long term alternative to phase out R134a. (paper)
[en] Capillary tubes are simple narrow tubes but the phase change which occurs inside the capillary tubes is complex to analyze. In the present investigation, an attempt is made to analyze the flow of Isobutane (R-600a) inside the coiled capillary tubes for different load conditions by Homogeneous Equilibrium Model. The Length and diameter of the capillary tube not only depend on the pressure and temperature of the condenser and evaporator but also on the cooling load. The present paper investigates the change in dimensions of the coil capillary tube with respect to the change in cooling load on the system for the constant condenser and evaporator conditions. ANSYS CFX (Central Florida Expressway) software is used to study the flow characteristics of the refrigerant. Appropriate helical coil is selected for this analysis. (paper)
[en] Highlights: • We proposed a method to evaluate the dynamic energy performance of VRF systems. • Dynamic energy benchmarks were established based on data mining techniques. • Nine power consumption patterns were classified using DT analysis. • Energy consumption rating system was developed to provide quantitative energy evaluation. • Case study was conducted under various refrigerant charge faults of the VRF system. - Abstract: The variable refrigerant flow (VRF) system has extremely different energy performance at various operation conditions. Its power consumption is inconsistent even under the steady operation condition. In order to accurately evaluate the VRF system’s dynamic energy performance, this study proposed a data-mining-based method to benchmark and assess its energy uses. The correlation analysis is used for key factors selection and the interquartile range rule is employed to remove outliers of the database. In addition, the power consumption patterns are classified using decision tree (DT) method. The classification results are validated by the ANOVA analysis and post hoc test. Nine energy benchmarks are established based on the classified power consumption patterns. Moreover, an energy consumption rating system is established to provide quantitative assessment on the power consumption of the VRF system. A case study is conducted by comparatively analyzing the energy performance of the VRF system at multiple refrigerant charge fault cases. Results show that both the PLR and OT significantly affected the power consumption of the VRF system. However, the degree to which the refrigerant charge fault affects system power consumption varies with the power consumption patterns. For different patterns, the power consumptions of the VRF system were either lower, higher or similar to each other at various RCLs. Results also suggest that the energy benchmarking process provide reasonable classification criteria, and the grading process provide quantitative assessment on the energy consumption. Therefore, the proposed dynamic energy benchmarks are reliable and reasonable to evaluate the dynamic energy performance of VRF systems.
[en] In this study, experimental research is carried out on two different class of refrigerants at three varied ambient conditions viz. (30°C, 35ºC and 40ºC) and three different air velocities viz. (1.25, 1.00, 0.75 m/s) in air cooled and evaporative cooled condenser. The first class is of low temperature refrigerant (R-134a) and the second is of high temperature refrigerant (R-410a). The results described that COP of high temperature refrigerant is greater than that of low temperature refrigerant. The COP increased with increasing air speed in air cooled and evaporative cooled condenser and decreased with increasing the ambient temperatures. For a fixed ambient temperature and air velocity, the COP of R-410a turned out to be greater than the COP of R-134a.Thus proving that high temperature refrigerant is better in performance than low temperature refrigerant. (paper)
[en] R22 is a hydrochloroflurocarbon (HCFC) refrigerant widely used in air conditioning. R22 is an ozone depleting substance. Due to ozone layer depletion, HCFC will be phased out in near future. R290 is hydrocarbon (HC) refrigerant is an alternative to R22. This paper presents outcomes of this comparative study. A 1 ton capacity window air conditioner was used to experiment. R22 was used for baseline refrigerant. R290 refrigerant using air cooled condenser coefficient of performance (C.O.P.) lowered by 6.91%, 6.28% & 1.38% at different set point temperatures 16°C, 20°C& 25°C. The system is optimized to increase in thermodynamic performance by using evaporative cooling condenser with R290 refrigerant. C.O.P. of system is improved by 15.84%, 18.23% & 22.92% at different set point temperature and power consumption reduces by almost 50% than the baseline system. The amount of refrigerant charge of R290 refrigerant is 70% less than that of R22 refrigerant. Experimental results show that implementation of the evaporative cooled air condenser by using R290 refrigerant has a significant effect on performance improvement of window air conditioner. (paper)
[en] This study aims to determine the reduction in power consumption of refrigerators by using parallel expansion. A refrigerator with a capacity of 120 litters has been used as a test instrument and R134a acts as a working fluid. Recording of refrigerator energy consumption is based on changes in cooling load temperature from range 3C to -3 C. The parameters observed during the test include suction pressure, discharge pressure, electric current, and weight of refrigerant circulated. The results indicate that installation of parallel expansion device on the refrigerator generates a decreased 1.5% - 4% of the electrical power consumption (ECP) so that it implicates for the save on power consumption required a refrigerator. (paper)
[en] Highlights: • Real gas theoretical model is used to get ejector performance at critical/sub-critical modes. • The model has a better accuracy against the experiment results compared to ideal gas model. • The overall performances of two refrigerants are analyzed based on the parameter analysis. - Abstract: The ejector refrigeration integrated in the air-conditioning system is a promising technology, because it could be driven by the low grade energy. In the present study, a theoretical calculation based on the real gas property is put forward to estimate the ejector refrigeration system performance under overall modes (critical/sub-critical modes). The experimental data from literature are applied to validate the proposed model. The findings show that the proposed model has higher accuracy compared to the model using the ideal gas law, especially when the ejector operates at sub-critical mode. Then, the performances of the ejector refrigeration circle using different refrigerants are analyzed. R290 and R134a are selected as typical refrigerants by considering the aspects of COP, environmental impact, safety and economy. Finally, the ejector refrigeration performance is investigated under variable operation conditions with R290 and R134a as refrigerants. The results show that the R290 ejector circle has higher COP under critical mode and could operate at low evaporator temperature. However, the performance would decrease rapidly at high condenser temperature. The performance of R134a ejector circle is the opposite, with relatively lower COP, and higher COP at high condenser temperature compared to R290.
[en] Variable Refrigerant Flow (VRF) systems are refrigerant systems, which are generally comprised of an outdoor unit serving multiple indoor units connected by a refrigerant piping network. It is important to evaluate the performance of VRF systems, which can help the design and operate of VRF systems. Performance test done by manufactory can reveal the performance of VRF systems in designed conditions. However, it is hard to reveal effective performance in real buildings. The field test is complicated compared with the test in the laboratory and can only conduct on typical samples rather than large scale samples. However, typical samples are not enough for reflecting the performance of large scale VRF systems samples. A simple method of evaluating the performance of large scale VRF systems samples is necessary. This paper proposed and calculating model for electricity consumption and cooling demand of VRF systems based on measured operating data in the laboratory. The paper used the calculating model combined with 344 samples operating data from real residential buildings to calculate the performance of a large scale VRF. This paper analyzed the VRF systems’ performance with different influencing factors such as climate zones, cooling duration and outdoor temperature for the recommendation for VRF systems’ designing and operation. (paper)
[en] Highlights: • COP was improved due to plate-type LSHX utilization. • R1234ze(E) with low-GWP was determined as a good alternative refrigerant. • Smaller Tc and greater Te caused an improvement in both COP and ε. • ηv was reduced with PH/PL and it was better for R1234ze(E) compared to R134a and R1234yf. • ηv was further increased as a result of using plate-type LSHX. This study is directed to propose a method for enhancing the energy parameters of the refrigeration systems operating with R134a which generally presents low performance of the units. Hence, R134a was experimentally compared with HFO-based refrigerants of R1234yf and R1234ze(E) having low-GWP. Additionally, plate-type liquid to suction heat exchanger (LSHX) was utilized in order to determine its effect on the system's energy performances. The evaporation temperatures were −9, −4.5 and 0 °C while the condenser temperatures were 40, 45, and 50 °C in the experimental work. The cooling capacity and power consumption of R1234ze(E) were noticed lower, however its COP was higher compared to R1234yf. It was also figured out that COP of the system with LSHX using R1234ze(E) was better about by 3% than that without LSHX which operated with R134a. The results of the present study indicated that the presence of LSHX caused improved COP and lower power consumption of the refrigeration system.