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In a conventional arrangement of the airflow pathway in nonunidirectional airflow cleanrooms with wall return schemes, the supply air is introduced from ceiling air grills and the return air, close and vertical to the floor, is extracted from the wall air grills. However, such a wall return ventilation system is theoretically not an optimal design for removing heat and particles released from processing machinery. The conventional wall return system currently used in cleanrooms aims to create an environment with diluted particle concentration in which downward cold supply air from ceiling filters encounters upward air currents generated by drifted particles from processing machinery. To solve the problem, we introduced a new design called fan dry coil units (FDCUs). In this article, we compare the performances of both innovative and traditional ventilation systems in a full-scale cleanroom. For each return air ventilation system, we investigated the effects of air change rates on the removal of 0.1∼5 μm particles. Based on the results, it is noted that the FDCU-return system eliminates about 60% more particles from the cleanrooms, compared with conventional wall-return system. [ABSTRACT FROM AUTHOR]

A statistical model was established in this article for predicting the broadband turbulent noise of axial flow fans. First, an integral formula was deduced based on the Ffowcs Williams-Hawkings (FW-H) equations for the purpose of calculating the sound power spectrum of aeroacoustic sources with low rotating speed. The auto-correlation spectrum of the fluctuating pressure on the fan blades was modeled by a two-section exponential function. The characteristic aerodynamic parameters, such as boundary layer thickness, external flow velocity, wall shear stress, and average static pressure gradient on blade surfaces, were obtained by solving the steady Reynolds-averaged Navier-Stokes equations and used to normalize the auto-correlation spectrum. Then, the unknown coefficients in the exponential function were determined by fitting the experimental noise spectra for two typical and commercially available axial flow cooling fans. Finally, under the conditions of retaining the similar aerodynamic performances of the two baseline fans, a new fan design was developed and optimized using this method, of which the overall noise level was 2 dB lower than the quieter of the two baseline fans. The predicted noise spectra for all three fans agreed very well with the experimental data. [ABSTRACT FROM AUTHOR]

In a warm environment, air movement with elevated velocity is a well-known cooling strategy. The local air movement is typically generated by cooling fans (e.g., ceiling fan, table fans, etc.). Appearance, power input, and price are the main parameters considered today when purchasing cooling fans, while cooling capacity and efficiency of energy use are unknown. To address this knowledge gap, this paper introduces the cooling-fan efficiency (CFE) index, defined as the ratio between the cooling effect (measured with a thermal manikin) generated by the device and its power consumption. The index was determined for a ceiling fan, a desk fan, a standing fan, and a tower fan in a real office at three room air temperatures and at different fan speed levels. The results reveal that the index is sensitive enough to identify differences in the performance of the cooling devices. A standard method for testing fan cooling effect and an index for determining fan efficiency, such as the CFE index proposed in this study, need to be developed. The cooling fans generate a nonuniform velocity field around occupants, which cannot be described with a single air-velocity value. Therefore, it is not clear how to apply in practice the recommended elevated velocities in warm environments presented in the present standards. The standards need to be revised. [ABSTRACT FROM AUTHOR]

In this study, aerodynamic performance was measured experimentally for three propeller fans subjected to systematic variation of inlet flow components. The inlet conditions were intended to simulate installations of fans typically encountered in the field. The aerodynamic performance penalties associated with the various appurtenances were characterized in terms of system effect factor (SEF). [ABSTRACT FROM AUTHOR]

A hybrid chiller plant employs a combination of chillers that are ‘powered’ by electricity and natural gas. This paper presents an algorithm for determining cooling tower fan settings in hybrid plants in response to loadings on individual chillers. Parameters of the algorithm are evaluated using design information for the chillers and cooling tower fans. In addition to reducing operating costs, use of the open-loop control strategy simplifies the control and improves the stability of the tower control compared with the use of a constant condenser water supply or approach to wet-bulb. Simulated plant cooling costs associated with the algorithm were compared with costs for optimized settings and were within 1% of the minimum costs. The control method is general, in the sense that it also applies to cooling plants that have all electric or all natural gas chillers. [ABSTRACT FROM AUTHOR]

The purpose of shaft power matching of contra-rotating axial flow fans (CRAFF) is to ensure the best utilization of the motors at their rated power while not to overload them at the operation. Usually it requires a lot of time and effort due to lack of theoretical guidance and, thus, becomes a major problem for the application of CRAFF. Through analyzing velocity triangle, the authors have found a nondimensional parameter k, defined as the tangential ratio of two relative outflow angles for two impellers, to be critical for successful shaft power matching and aerodynamic design. The authors then performed a numerical simulation of the flow field for a design of CRAFF, of which the performance prediction was validated very well by test data. Based on the analysis of the flow filed data, the result obtained from the velocity triangle analysis is further improved and some values for k and deviation angle δ are recommended. In order to determine the approximate optimum of blade pitch angles of two impellers, a guideline for shaft power matching is then presented. Finally, a comparison of the blade pitch angles obtained from the guideline with that obtained from the optimum using numerical simulation are carried out for six designs of CRAFF. The errors are only within 2 degrees. [ABSTRACT FROM AUTHOR]

Effects of the entrance parameters and their interactions on the noise reduction, static head, mass flow rate, rotational speed, and efficiency of a backward-curved centrifugal fan have been studied experimentally. Design of Experiment (DoE) method has been performed to analyze the results and their effects. Three different levels for the entrance curvature and two levels for the shape of blades passage, shroud, number of blades, and inlet bell position have been selected to design and construct different fans for the aero-acoustic experimental measurements. The results analysis shows that to have a lower noise and higher efficiency, higher entrance curvature, hyperbolic profile for the shape of shroud, and inlet bell position 1 (no radial clearance) must be selected. However, based on the priority of the noise reduction or efficiency increase, constant deceleration for the blade passage or a logarithmic profile for the blades passage should be chosen. The interactions of these selections have a positive effect on noise reduction as well as on efficiency. [ABSTRACT FROM AUTHOR]

Nonintrusive load monitoring (NILM) is accomplished by sampling voltage and current at high rates and reducing the resulting start transients or harmonic contents to concise "signatures." Changes in these signatures can be used to detect, and in many cases directly diagnose, equipment and component faults associated with rooftop cooling units. Use of the NILM for fault detection and diagnosis (FDD) is important because (1) it complements other FDD schemes that are based on thermo-fluid sensors and analyses and (2) it is minimally intrusive (one measuring point in the relatively protected confines of the control panel) and therefore inherently reliable. This paper describes changes in the power signatures of fans and compressors that were found, experimentally and theoretically, to be useful for fault detection. [ABSTRACT FROM AUTHOR]

Numerical simulation of the flow field was carried out for a whole centrifugal fan to consider the interaction of three parts—inlet, impeller, and scroll. A modern optimum design method for a centrifugal fan has been presented using a computational fluid dynamics (CFD) technique to replace the conventional method. A sample fan based on the optimum design was manufactured and tested. The numerical prediction agrees well with the test data. The excellent performance of the sample fan has proved the validity of the method adopted. Moreover, the effects of the blade inlet angle and the gap between impeller and inlet on the fan performance are quantitatively analyzed. Particularly the energy loss in every passage, including the gap loss and the leakage flow rate in the gap, are discussed in detail in the paper. It is found that the blade inlet angle and the impeller gap play an important role for fan performance. [ABSTRACT FROM AUTHOR]