Cross ventilation has potential

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A free-stall barn under construction near Harlan, Iowa, is amazing by its sheer size.

The 420-foot-by-1,350-foot facility will cover 12 acres, house 5,040 cows and move copious amounts of air for proper ventilation.  

“It’s pretty much given that a building of that size and magnitude has to be mechanically ventilated,” says Joe Harner, agricultural engineer at Kansas State University.

Then, it’s a choice between tunnel-ventilation (with fans pulling air down the length of the barn) and cross-ventilation (with fans pulling air across the width of the barn). The farm has chosen the latter. 

Although there is much to learn about cross-ventilation in dairy barns, the technology has a lot of potential, according to John Smith, extension dairy specialist at Kansas State University, who with Harner and others helped design the system in Harlan. 

Q: How many cross-ventilated barns are there?

Only seven at this point — all located in the Upper Midwest. The one that’s gained the most attention is at MCC Dairy in North Dakota (managed by Rick Millner). That barn (at 210-feet-by-420 feet) isn’t as large as the barn in Harlan, Iowa. But the principle is the same: Evaporative cooling pads located on one side of the barn cool incoming air, and fans located on the other side pull the cooled air across the building.    

Q: Do the buildings work?

Data from the North Dakota barn show that cross-ventilation can have a significant impact on cow-comfort. The benefit is most pronounced on warm days with low humidity. For example, Smith found the temperature-humidity index (THI) — a common indicator of cow-comfort — improved five points during the late afternoon and early evening one day last July when the outdoor temperature reached 85 degrees F and the relative humidity was about 50 percent: 

Improvement in temperature–humidity index

Air coming into building

 

   77.5

 

Air leaving building

 

   72.5

 

 

“That’s a huge difference in a cow’s life,” Smith says.

But three days later, when the outdoor temperature approached 90 degrees F and relative humidity fluctuated between 70 percent and 80 percent, THI in the North Dakota barn improved only two points during the late-afternoon and early-evening hours.

“High humidity limits our ability to take advantage of evaporative cooling to cool the air,” Smith says. “This technology will work the best in climates where we consistently have low relative humidity in the afternoon.”

Q: What are some of the other considerations?

Air speed is controlled by metal baffles that hang from the ceiling. The barn in Harlan, Iowa, has seven baffles positioned across its 420-foot width — parallel to lanes where the free-stalls are located. Air flows beneath the baffles, causing it to pick up speed and provide extra comfort to the cows lying in their stalls.  

Baffles are more easily adapted to a cross-ventilated barn than a tunnel-ventilated barn. In a tunnel-ventilated barn, baffles run perpendicular to the feed lanes, so their height must conform to the height of feed trucks and other equipment using those lanes. But, in a cross-ventilated barn, baffles run parallel to the feed lanes, making the issue of height much more flexible.

When installing baffles, it’s extremely important that the producer consult an engineer who knows how to calculate the number of baffles and proper baffle height, Smith says.  In addition:

  • Sand bedding is needed in enclosed cross-ventilated barns, because other bedding types, such as sawdust or composted dairy-waste solids, might generate too much particulate matter in the air. 
  • The electric bill for an eight-row, cross-ventilated barn with 70 fans would run $16,097 per year, Smith has calculated, compared to $19,845 for a four-row, naturally ventilated barn with 140 fans. (This assumes the fans in the cross-ventilated and naturally ventilated barns are 51 inches and 36 inches in diameter, respectively. Half of the 70 fans in the cross-ventilated barn would run at one time, on average. And 140 fans in the naturally ventilated barn would run 24 hours a day, 150 days a year.)
  • Yet, the sight of these large, totally enclosed barns may evoke images of a “factory farm.” That’s why more research is needed — not only as it relates to ventilation, but animal-behavior as well. Anecdotally, the owners of cross-ventilated barns have commented to Smith that the cows are “extremely comfortable (and) using stalls and eating aggressively.” Upwards of 1,000 people have toured the North Dakota facility, he adds, and their comments have been positive. 

 



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