Assessment of Uncertainty in Measurements with Low Velocity Thermal Anemometers

The important error sources associated with measurements using low velocity thermal anemometersincorporating an omnidirectional velocity sensor (LVTA) are identified and quantified. The impact of natural convection, directional sensitivity and dynamic response of the anemometer are modelled. The developed models, together with a database of instantaneous velocity records obtained by means of a Laser Doppler Anemometer are used to estimate the uncertainty of mean velocity and standard deviation of velocity measurements by LVTA. The uncertainty is due to the separate and the combined impact of natural convection and directional sensitivity of omnidirectional velocity sensors as well as the dynamic response of the anemometers. The total uncertainty due to all error sources is estimated. Comparison of measurements performed with a LVTA and a 3-D Laser Doppler Anemometer served to test the method developed and showed good agreement. The results of this study make it possible to improve the quality of validation of CFD predictions of room air movement based on measurement results. The results of this study allow for the determination of realistic requirements in future standards regarding the characteristics of LVTA and indices for the prediction of human response based on indoor velocity measurements. The method developed can be used by manufacturers of LVTA devices to optimize the LVTA design.