Design and performance of a direct and continuous ventilation measurement system for variable-speed pit fans in a pig building

Manure pit ventilation is a common design in commercial pig-rearing buildings. However, determining accurate pit ventilation rates is technically challenging. A new pit exhaust airflow measurement assembly (PEAMA) was developed to directly and continuously measure airflow rates for tube-mounting variable-speed pit fans. The PEAMA consists of a PVC pipe, a flow straightener, and an impeller anemometer. A laboratory study revealed good linear correlations between the PEAMA signal outputs and the fan rotational speeds (R 2  > 0.999). The ventilation rates measured with the PEAMA were calibrated against those with the standardised traverse measurement with a highly linear correlation (R 2  > 0.996). In 2011, 24 PEAMA units were installed in twenty-four 250-mm diameter pit fans in a state-of-the-art pig research building. Multi-year field performance showed that the PEAMA greatly improved data quality during pit fan airflow monitoring compared with previously adopted techniques. This system enabled continuous and real-time ventilation outputs to be determined in volume time −1 . It was easy to maintain due to the simple design and outdoor installation. The cost of the 24 units accounted for only a small portion of a comprehensive air quality monitoring setup at the pig research building.