Data Filtering for Accurate Airflow Measurement in a Monoslope Beef Barn

Abstract

Livestock facilities are a source of aerial pollutants including ammonia, hydrogen sulfide, carbon dioxide (CO2), methane, and nitrous oxide. However, estimating pollutant emission depends on accurate measurements of highly variable pollutant concentrations and ventilation airflow rates. There is a need to refine and validate direct airflow measurements, especially through naturally-ventilated barns, and identify the environmental conditions that provide the best measurement results. The objective of this research was to measure the airflow through naturally-ventilated monoslope beef barns by direct and indirect (CO2 mass balance) methods, and determine filtering conditions when accurate airflow measurements are achievable. Direct airflow measurements were collected using ultrasonic anemometers and depended on wind direction perpendicular to the opening area of the inlet and outlet wall; therefore, some ranges of wind speed and direction were not suitable for accurate airflow measurements. Barn management decisions, such as the north side wall opening also changed and impacted airflow measurement accuracy. The results of this study suggested filtering data based on large north wall opening dimensions, wind speeds between 0.5 m/s to 6 m/s, and wind direction conditions ±45o from due south provide data suitable for predictable airflow measurements for monoslope beef barns. Based on a comparison of airflow through the north and south wall openings, when airflow was 200 – 400 m3/s per pen, the north wall opening airflow was within ±20% of the south wall opening airflow. Carbon dioxide method airflow estimates were generally lower than airspeed-based measurements.