Tunnel Ventilation Barns Open endwall on a tunnel-ventilated freestall barn. The goal is to provide approximately 1 sq. ft. of endwall opening per 400 cfm of in-place fan capacity. This goal is generally met by fully opening the endwall as shown. Notice that there are no major obstructions to block airflow at cow level. (Note, this barn was not in the tunnel ventilation mode when this image was taken.) Endwall opposite of the inlet. A large number of high capacity fans are used to draw air through the barn. Total fan capacity is determined by meeting the greatest of two criteria: 1) ensuring an average air velocity of 400 to 600 fpm in the tunnel barn, and 2) providing an air exchange (ventilation) rate 1,000 cfm per cow. Fans should be position ed as low as possible on the endwall to help keep airflow at cow level. The lowest fans should be on the primary (first) stage of ventilation if a stage ventilation control is used. Many times insufficient endwall space exists in order to mount all tunnel ventilation fans. Fans can be also located on the sidewall as shown here, although research as found that as much as 25 percent reduction of fan capacity is lost with fans mounted on the sidewall. Why? Because moving air has both mass and velocity, and therefore momentum. The momentum of the air moving longitudinally down the barn will tend to carry it past the sidewall fans. If fans are mounted on the sidewall, it is best to stack fans in vertical columns rather than position them in horizontal rows as is shown in this picture. An alternate way to mount fans is to build the endwall at an angle with respect to the sidewall as shown here. Field research has shown that fans mounted in this fashion function well with little loss in efficiency. Notice a panel fan is positioned in the gable endwall to tunnel ventilate the attic space. This is a floor plan for the barn shown above. Notice that additional length is added to the barn in order to mount fans in this fashion. This 3-row freestall barn has one less overhead door than is conventionally used for this barn configuration. Also notice that fans are positioned to enhance airflow in the animal zone of the barn. This is an inside image of the tunnel-ventilated 3-row barn described above. Notice that the barn has a flat ceiling with a continuous moisture barrier. A ceiling is used to reduce the overall required fan capacity for the barn by reducing the building's cross sectional area perpendicular to the direction of airflow. A ceiling also helps keep meaningful airflow at cow level when the barn is tunnel-ventilated (summer), but limits natural air exchange during natural ventilation times (fall, winter, and spring). Vertical baffles are sometimes positioned in a barn to help keep airflow at cow level. Baffles in this picture are placed approximately 40 feet apart and are made from curtain sidewall material. Baffles are not as effective as a ceiling in tunnel-ventilated barns but are more friendly during non-tunnel (natural) ventilation periods.