To baffle or not to baffle
Most cross-ventilated dairy barns have four baffles that block airflow from the roof down to about 6 to 7 feet above the floor. Some people have begun to question the need for baffles in cross-ventilated barns.
Most baffles are constructed of rigid materials. Some barns have canvas baffles that can be rolled up so that the barn can be naturally ventilated in cold and mild weather. So are baffles needed in cross-ventilated barns? As of now, there has not been research comparing cross-ventilated barns with baffles with barns without baffles.
When thinking about ventilation and airflow it is important to remember that air is lazy. Air takes the easiest path it can. So if you install an exhaust fan next to an open window, the air will take the easiest and shortest path going in through the window and out the fan. The air entering through the window will not flow over to the far side of the barn before coming back and exiting through the fan. The air will take the easiest path zipping in through the window and out through the fan. If you want uniform airflow through a barn, you need to uniformly distribute inlets throughout the barn or in the far wall opposite exhaust fans. The key to uniform ventilation is uniform inlet distribution.
Obstructions inside dairy barns will also impact airflow through the barn. One of the weaknesses of tunnel ventilation is that cows, waterers and walls upstream of the stalls block airflow past cows in downstream stalls. The blockages push the air to flow down feed and manure alleys or up above the cows. Early research in tunnel ventilated freestall barns without ceilings noted that a lot of the air flowed high above the cows. Baffles were recommended in the trusses. Unfortunately baffles cannot be brought much lower than the trusses in tunnel ventilated barns because of the feed and manure handling equipment that need to move down alleys and pass under the baffles.
Cross-ventilated barns can bring baffles down to 6 or 7 feet above the floor because baffles can be located over the freestalls. Cross-ventilated barn with drover lanes and equipment lanes at one or both ends of the pens can have a lot of air bypass the freestall pens if the lanes do not have baffles or freezer strips. A lane without a baffle represents a big smooth path for the air to take rather than flow through the cows and squeeze under the baffles in the freestall area.
Baffles do make the exhaust fans work harder which reduces the fan airflow rates a small amount. Baffles force the ventilation air to speed up to squeeze through a 6 to 7 feet tall space. Squeezing the air and increasing the air velocity under the baffle requires energy that reduces the airflow rate.
Baffles in cross-ventilated freestall barns serve three purposes. Baffles increase the air velocity under the baffle which helps cool cows near the baffles in hot weather. Secondly, baffles produce more uniform air flow through the barn from end to end if the baffles go from one end to the other. Finally, baffles prevent air from flowing high above the cows where cows get little benefit from the airflow.
There is little published research on cross-ventilated barns. Research on an early eight row cross-ventilated freestall dairy barn with baffles found, as expected, that barn static pressure increased as the ventilating rate increased. At the high ventilating rate, each baffle added about 0.015 inches of H2O static pressure to the total barn static pressure. Air velocities under the baffles were around 590 feet per minute (fpm) and around 180 fpm near a feed alley away from the baffles at the hot weather high ventilating rate. This work documented the role baffles have on static pressure and how they increased air velocity under the baffles.
A University of Minnesota study measured air velocities in six cross-ventilated barns during four visits over a 12-month period. The air velocities averaged 256 fpm under the baffles and 120 fpm near the feed bunk away from the baffles. This work also documented that air velocities under the baffles were higher than in areas away from baffles.
Heat stress modeling work at the University of Minnesota indicated that increasing the air velocity past a high producing cow from 60 fpm to 177 fpm to 530 fpm helped the cow lower her respiration rate (i.e., 83, to 76 to 66 breaths per minute, respectively) and her body temperature (i.e. 102.6, 102.5 and 101.8 F, respectively) during hot weather.
Baffles are expected to help cows with cooling during hot weather, create more uniform conditions and reduce the amount of air that passes far above the cows. Research is needed to document these expectations.