Statistical Characteristics and Frequency Spectrum Analysis of Fan Induced Airflow Compared with Natural Winds

Abstract

Electric fans used for cooling or local ventilation are common household appliances around the world, especially in developing countries. They offer many advantages such as low cost and energy savings, as well as easy implementation. However, the airflow from fans is often considered to be less comfortable than the sensations produced by natural winds. In order to avoid the draught induced by fans, and to investigate dynamic airflow characteristics of household fans, an anemometer was utilized to measure the corresponding time series of the air velocity. Statistical parameters, wavelet transforms and power spectrum exponents of air velocity signals from different types of fans were analyzed.The results show that the standard deviation of actual, natural wind velocity profiles is slightly greater than that of mechanically produced wind. More importantly, we found that statistical parameters involving mean air velocity, standard deviation, skewness and kurtosis are insufficient to indicate completely, all the characteristics of mechanical wind. Power spectrum density exponent (β) also shows the frequency characteristics of airflow. Finally, based on the comparison of β with a variety of fans, it was found that inducing surrounding air can enhance β, and reduce the draught.

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“…The β values for the forest park and the naturally ventilated room, i.e., 1.22 and 1.70, were much higher than that for the mechanical wind which is 0.48. This is consistent with the results by Gao et al [43] and Ouyang et al [44].…”

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“…Figure 12 shows the velocity distribution and power spectral density functions for different conditions. 25,26 Ouyang et al 27 reported that the critical b value to distinguish mechanical wind from natural wind is 1.0-1.1 in human perceptual velocity range. Figure 13 presents power spectrum curves at different positions.…”