Tunnel Ventilation Tips for Hot Weather Dairy Farms

By Blake Jackson

Providing adequate hot weather comfort for dairy cows relies on the principles of Shade, Air exchange, Airflow, and Water (SAAW). When temperatures exceed 70°F, cows must either reduce heat intake by seeking shade or eating less or increase heat loss through higher respiration, standing in a breeze, evaporating moisture from the skin, or moving to cooler areas.

Heat stress can rapidly reduce milk production and negatively affect reproduction, fetal growth, and young animal performance. Behavioral changes from heat stress can also lead to herd health problems.

Tunnel ventilation is an effective summer system designed to deliver high air exchange and fast airflow over cows, helping them shed body heat. These systems are typically suited for two-row tie-stall barns with more than 40 cows but are not ideal for year-round use due to inadequate winter ventilation.

Fan capacity for tunnel systems is determined by the barn’s cross-sectional area and desired airspeed, independent of cow numbers. Recommended airflow is 300-440 feet per minute (3.5-5 mph), with axial circulation fans added over the cows for localized speed, spaced no more than ten fan diameters apart.

Proper tunnel ventilation requires calculating fan capacity, selecting suitable fans, sizing inlets, and determining optimal fan and inlet placement. Inlets are sized at 2-2.5 square feet per 1,000 cfm of fan capacity.

Fans should operate efficiently, delivering at least 20 cfm per watt at 0.05 inches of static pressure, and be protected with fuses or circuit breakers. High-quality fans save electricity and reduce long-term maintenance costs.

Fans should be installed to minimize interference with people, cows, and equipment while ensuring safety and secure mounting.

Controls may include manual switches or thermostats, activating fans above 65°F and fully operating them above 70°F. Inlets and fans are ideally located on opposite barn ends at cow level, though obstructions may require adjustments.

Emergency ventilation plans, alarm systems, and winter insulation for inlets and fans are crucial to maintain cow comfort and barn safety year-round. Proper design ensures uniform airflow, preventing overheating and maximizing animal performance.

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