Customize your cross-vent

December 6, 2008 10:13 AM
 


Dan Little
Cross-ventilated barns may be the greatest single factor in improving the ability to produce low-cost milk in the Upper Midwest. While the advantages related to labor, cooling and subzero winter temperatures are obvious, cross-ventilated buildings also offer design opportunities for added improvements in ventilation and cow comfort.

Intake curtain area. The total square feet of intake curtain wall must be calculated for each building based on the width of the barn. The increased barn width requires greater surface area of intake to maintain airflow at a low negative static pressure.

Therefore, the same 8' sidewall does not fit all cross-vent barns. A common problem is the gap between a top and bottom evaporation pad, as well as the amount of wall from the top or bottom of the pad that is not used. Higher sidewalls (and larger evaporation pads) are necessary for wider barns.

Air intake. This is especially important as barn width increases. Since the evaporation pad is covered during winter weather, some allowance must be made for an even flow of fresh air during the winter months.

An open slot from end to end of the evaporative cooling wall may meet these needs. However, dairy producers are experimenting with other methods of introducing fresh air into the middle of the barn during the winter months. Simple inlet tubes from the roof may be all that is needed to provide sufficient fresh air without creating drafts or freezing conditions at the point of intake.

Holding pen ventilation. When properly designed, cross-vent barns do an excellent job of providing fresh air to the building. However, since the milking parlor is usually off the side of the main building, ventilation of the holding pen is often a problem. My preference is to ventilate the holding pen with a combination of tunnel and cross-ventilation.

Minimum ventilation should be provided by fresh air entering the parlor area and moving in tunnel fashion to the rear of the pen. This helps control the buildup of ammonia and gases in the milking pit from footbath chemicals and manure.

To have true cross-ventilation in the holding pen for maximum cooling, the exterior and interior walls must be properly designed. Internal fencing must be open to allow airflow across the holding pen. This is a challenge for contractors—many prefer to pour solid concrete walls to support the crowd gate rather than dig individual posts connected with a beam.

The combination cross-tunnel ventilation for the holding pen results in a bank of fans on one wall of the holding pen and a bank of fans at the back of the holding pen.

Minimizing overhead doors. It is becoming more common to add length to the barn to allow tractors, etc., to enter though one door. The breakeven point depends on:
• the cost of additional square footage;
• your staff's ability to fix broken doors;
• the number of doors destroyed by your equipment operators per year!

Hopefully, these considerations will assist you with the customization of your barn to maximize cow comfort.

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