Validating a Multi-Port, Averaging Pitot Tube for Measuring Fan Airflow Rates

Abstract

A multiport averaging Pitot tube (MAPT) system was evaluated for measuring airflow rates from large agricultural fans in confined poultry facilities. The MAPT system consisted of a copper tube with multiple pressure ports along its length to respond to the velocity pressure profile across the full fan diameter. The tube was connected to a low-pressure transducer that provided a differential voltage signal, which was recorded by a data logger, in response to fan airflow. The best performance was observed when the tubes were positioned on the intake of a test fan and operated with pressure ports facing the downstream direction of the fan. The responses of two tube lengths were calibrated in measuring airflow delivered by a 91- or 122-cm diameter wall-mounted exhaust fan by comparing measurements to a Fan Assessment Numeration System (FANS) used as a reference. There was a strong linear relationship between the square root of voltage outputs from the MAPT pressure sensor and the reference FANS air velocity readings. Linear regression equations were used to compute flow rates of additional fans using MAPT measurement. Airflow rates based on MAPT measurement were highly correlated with the reference FANS values with mean deviation less than 3% and 9% for 91- and 122-cm diameter fans, respectively. The MAPT system is particularly useful for applications such as farm energy audits that require fast and easy estimates of airflow from large, wall-mounted agricultural exhaust fans.