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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] 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] 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] This study deals with energy and irreversibility analysis of a cascade refrigeration system employing various refrigerant couples, namely R152a-R23, R290-R23, R507-R23, R234a-R23, R717-R23 and R404a-R23, using a computer code developed for this aim. It is assumed that the refrigeration load is 1 kW, the refrigerated space temperature is -40 deg. C, and the environment temperature is 300 K, while the degrees of condenser subcooling and evaporator superheat are 5 and 7 deg. C, respectively, for all cases. Furthermore, the polytropic efficiencies of the compressors are assumed to be equal. It has been determined that the COP of the cascade refrigeration system increases and the irreversibility decreases with rising evaporator temperature and polytropic efficiency for all studied refrigerant couples. On the other hand, the COP of the cascade refrigeration system decreases and the irreversibility increases on increasing the condenser temperature and the difference between the saturation temperatures of the lower and higher temperature systems in the heat exchanger (ΔT). In all cases, the refrigerant couple R717-R23 has the highest COP and lowest irreversibility except for the limited ranges of polytropic efficiency (50-60%) and ΔT (13 K-16 K), while R507-R23 has the lowest COP and highest irreversibility. The refrigerant couple R152a-R23 has been found to be an alternative couple to R717-R23 for the above mentioned ranges of polytropic efficiency and ΔT. The refrigerant couples R134a-R23 and R290-R23 have placed in the middle range, and R404a-R23 can be considered as a replacement couple for R507-R23 in all cases.
[en] Highlights: ► Experimental study on the positions of pinch points and maximum temperature differences along a tube-in-tube evaporator. ► The positions of pinch points determined by the experiments and theoretical modeling were found to agree reasonably well. ► Results show that decreasing heat transfer fluid flow rate moves the pinch point closer to the refrigerant inlet. - Abstract: An experimental investigation is conducted on the occurrence and location of either a pinch point (PP) or maximum temperature difference (MTD) between a zeotropic refrigerant mixture and a heat transfer fluid (HTF) in a tube-in-tube evaporator. The zeotropic refrigerant used in the PP investigation is a R290/R600 mixture with a 0.15/0.85 mass fraction; the refrigerant used in the MTD investigation is a R245fa/R152a mixture with a 0.6/0.4 mass fraction. The inlet HTF temperature and the HTF and refrigerant flow rate were chosen as variable parameters at several sets of different working conditions to observe their effects on the location of a PP or MTD. The collected experimental data was then analyzed to determine the position of the PP or MTD. The position of the PP or MTD from the experiments did not show good agreement compared to predictions using existing available theoretical methods. The disagreement between theoretical and experimental results can be attributed in part to the nonlinear temperature change of the HTF along the evaporator which is not accounted for with existing theoretical methods.
[en] This paper discusses the use of propane (HC-290) as a safe and energy efficient alternative to HCFC-22 in a typical split air conditioner with nominal cooling capacities up to 5.1 kW. Initially split air conditioner performance is simulated for cooling capacity, energy efficiency ratio (EER), and refrigerant charge. Tests were conducted for different test cases in a psychrometric test chamber with HCFC-22 and HC-290. The test conditions considered are as per Indian Standards, IS 1391 (1992) Part I. The various parameters considered were based on simulated performance with the objective to achieve maximum EER for the desired cooling capacity. As the flammability is an issue for HC-290, the reduction of HC-290 charge was another objective. Two different types of condensers, first with smaller size tubing and another parallel flow condenser (PFC) or minichannel condenser were used in order to reduce HC-290 charge. For HC-290, the highest EER achieved was 3.7 for cooling capacity 4.90 kW for a refrigerant charge of 360 g. The important safety aspects of using HC-290 in air conditioner are discussed. The refrigerant charge as per EN 378 for different cooling capacities and room sizes is also considered. -- Highlights: • Simulation for performance of split air conditioner has been done using HC-290 as a replacement to HCFC-22. • The safety aspects of HC-290 are discussed when used in split air conditioner. • HC-290 was tested in psychrometric test chamber as per IS 1391 part 1. • With PFC, HC-290 gave highest EER of 3.7 which was 37% higher than that of HCFC-22. • The lowest HC-290 charge used in test was 340 g which is well below LFL
[en] Highlights: • A 3D numerical simulation is developed for the phase separation of refrigerants. • Effects of inlet parameters on the phase separation at a T-junction are studied. • Two small recirculation regions are found in the branch pipe of a T-junction under different mass fluxes. - Abstract: This paper describes a 3D numerical simulation to model the two-phase separation of refrigerants in a horizontal run-type T-junction. The computations are based on the Eulerian method with the k-ε turbulence model. Compared with data from existing experiments and phenomenological models, the average deviation of the established model is less than 5% when the liquid mass flow rate ratio is in the range 0.2–0.6. The effect of multiple parameters on phase separation is investigated using the validated model. The results show that the inlet qualities (0.3–0.7), saturation temperatures (279.15–284.15 K), and working fluids of R22 and R134a have little influence on the phase separation at the T-junction, whereas the gas mass flow rate ratio increases with the increase in inlet mass flux (100–500 kg m−2 s−1). Furthermore, it is found that two symmetric recirculation regions occur directly after the junction at the entrance to the branch.
[en] Highlights: ► We design ejector area ratio for higher back pressure (air-cooled condenser). ► Six ejector area ratios are designed by replaceable nozzles. ► The optimum area ratios are from 3.69 to 4.76. ► Optimum primary flow pressures increase along with area ratios. ► Cooling capacities are related to area ratios as well as nozzle diameters. - Abstract: In this paper, the key ejector geometry parameters for an air-cooled ejector cycle using R134a with cooling capacity of 2 kW are designed by 1D analysis. Through enlarging the designed area ratios by connecting the replaceable nozzles with a main body, optimum area ratios under air-conditioning working conditions are studied experimentally. Three parameters, namely, the entrainment ratio, COP and cooling capacity are evaluated, and the results show that the optimum area ratios are from 3.69 to 4.76 that are lower than those mentioned in other studies. With a fixed area ratio, experiments also show that the influence of the ejector area ratio on the ejector performance largely depends on the operating conditions. Consequently, the effects of operating conditions such as primary flow pressures on the ejector system performance are evaluated.
[en] Low noise of air-conditioners is one of the most important issues because of the users' strong demand. The main source of noise in an air-conditioner is the compressor. Therefore, noise reduction in a compressor is quite significant as an element technology in the air-conditioner field. Recently, scroll compressors are widely used, because they feature low noise, due to less pulsation of gas pressure, than that of rotary compressors. For reduction of noise, the source of noise must be identified. This paper presents a detailed analysis to identify the noise source and shows the dominant factors of noise of the scroll compressor, which will make it possible to design a scroll compressor with low noise
[en] Highlights: • There exists a maximum COP at optimum condenser temperature of LTC (T_4_o_p_t). • The input power of R41/R404A CRS is lower than that of R23/R404A CRS. • COP_o_p_t of R41/R404A CRS is higher than that of R23/R404A CRS. • R41/R404A is a more potential refrigerant couple than R23/R404A in CRS. - Abstract: This study presents a comparative analysis of thermodynamic performance of cascade refrigeration systems (CRSs) for refrigerant couples R41/R404A and R23/R404A to discover whether R41 is a suitable substitute for R23. The discharge temperature, input power of the compressor, coefficient of performance (COP), exergy loss (X) and exergy efficiency (η) are chosen as the objective functions. The operating parameters considered in this paper include condensing temperature, evaporating temperature, superheating temperature and subcooling temperature in both high-temperature cycle (HTC) and low-temperature cycle (LTC). The results indicate that an optimum condenser temperature exists for LTC (T_4_o_p_t) at which COP acquires maximum value. Under the same operation condition, the input power of R41/R404A CRS is lower than that of R23/R404A CRS, and COP_o_p_t is higher than that of R23/R404A CRS. The maximum exergy efficiency of R41/R404A and R23/R404A CRSs are 44.38% and 42.98% respectively. The theoretical analysis indicates that R41/R404A is a more potential refrigerant couple than R23/R404A in CRS.