Accuracy requirements and limitations for low velocity measurements.

Recommendations for the characteristics of anemometers that will ensure accurate velocity measurements are specified in the present standards. Recent research shows, however, that the requirements in the standards are based on incorrect assumptions and are insufficient to perform draught discomfort assessment that meets the accuracy requirements for human comfort specified in the indoor climate standards. Further, the accuracy of low velocity anemometers with omnidirectional velocity sensors available on the market and commonly used for indoor velocity measurements in practice is not sufficient and needs to be improved. In this paper, results from a recently completed European research project on calibration and requirements for accuracy of thermal anemometers for indoor velocity measurements are presented. The impact of static calibration and dynamic behaviour of thermal anemometers, directional sensitivity of the velocity sensor, free convection flow from the sensor, design of the sensor and the instrument, etc., on the accuracy of low velocity measurements indoors is assessed. New test methods and updated requirements that will improve the accuracy of the velocity measurements are proposed. Further research that will identify the accuracy limitations of thermal anemometers for low velocity measurements indoors is outlined.