During Summer conditions, dairy facilities need adequate ventilation AND air velocity. Adequate ventilation is 1000 cfm / cow. Desired air velocity is 550 feet per minute which is approximately 6.2 miles per hour. By multiplying the cross section of your barn by 550 you can determine the total cubic feet per minute required.

Of the two calculations use which ever number is greater. For example if you have 600 cows, adequate ventilation is 600,000 cubic feet per minute. But if the building is 150' wide by 15' high x velocity of 550 fpm the required air amount 1,237,500 cubic feet per minute.

Divide the required amount of air by the performance of the fan to determine the number of fans. For example, Schaefer model 523CF112-3 moves 28,100 cfm at .05 static pressure.

1,237,500 cubic feet per minute divided by 28,100 means you need 44 fans.

The building must be "closed up" in order for tunnel ventilation to be effective. All roof vents, chimneys, side vents, windows, doors, and openings other than the air inlet area opposite of the fan wall must be closed for an effective air flow.

Buildings with open ceilings require baffles. Baffles should be equally spaced throughout the length of the building and hung as low as possible without affecting the daily routine of machinery. Baffles ensure that the air movement maintains the velocity.

The air inlet end of the building should provide 800 feet per minute. 1,237,500 cfm from the example above divided by 800 equals 1547. This is the square feet of opening required.

Frequently we recommend evaporative cooling systems for the air inlet end of tunnel ventilation system. Please contact us if you are interested in learning more about adding this very effective added cooling strategy.

During winter you can run a few of the fans to remove gases, keep air fresh, and humidity low. The winter rate should be approximately 50 to 100 cfm per cow.

These are general "rules of thumb". Please contact us if you would like us to design a tunnel ventilation system for your buildings.

Cross Ventilation for Dairy Barns

Cross ventilation is very similar to tunnel ventilation. The difference is that we change the direction of the air flow. Instead of drawing the airflow the length of the building, we draw it through the width of the building.

There are benefits to using a cross ventilation strategy instead of a tunnel ventilation strategy. The building ends are used for necessary overhead doors as opposed to fans and pads.

Baffles run parallel to the roof line. This is very important because when baffles run perpendicular, the height is limited to the size of feed trucks and equipment. The lower the baffle height, the better the velocity at cow level.

Please contact us if you would like us to design a cross ventilation system for your buildings.