DESIGNS FOR WINDBREAK WALLS FOR MITIGATING DUST AND ODOR EMISSIONS FROM TUNNEL VENTILATED SWINE BUILDINGS

Abstract

Although windbreak walls have traditionally been applied to reduce ground-level wind speeds and enhance snow deposition, windbreak walls have also recently been placed downwind of animal buildings in efforts to control emissions of dust and odors. In particular, windbreaks placed near exhaust fans on tunnel-ventilated livestock and poultry buildings appear promising, primarily because the air jets issuing from the exhaust fans are diverted upward. This effect promotes mixing of the odorous, dusty airflow with the wind passing over the building, so that the plumes of air pollutants originating from the fans are made larger (extend higher). Thus it is reasonable to expect that in some wind conditions the aerial concentration of odorous vapors, dust, and other air pollutants in the breathing space of downwind neighbors will be reduced by improvement in air mixing at the emission sources (the fans). Windbreak structures may either be designed to withstand the same wind speeds as the buildings and be insured with the buildings, or lower wind speeds at reduced cost. Relevant design considerations and low-cost designs using UV-resistant tarpaulin or plastic material, roofing, or wood fastened to anchored pipe frames or posts are discussed. If the windbreaks are not designed for maximum design wind speeds, a method of ensuring non-catastrophic failure is needed, such as breakaway ties fastening material to frames. The location of the windbreak affects the diversion of airflow from exhaust fans. Further modeling and field evaluations are needed to determine beneficial and potential adverse effects of fan plume deflection. Observations of windbreak action in several locations suggest that the windbreaks should be placed two to four fan diameters downwind from the fans to deflect fan airflow without back pressures, and extend high enough to fully intercept the plumes of airflow issuing from the fans (e.g. 4 m high for typical buildings).