Tube ventilation

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When a fire destroyed the calf barn at Hanke Farms four years ago, they did not hesitate to rebuild and install the same positive-pressure ventilation system in the new calf barn.

VentilationThis group-housing calf barn with automatic feeders features a supplemental positive pressure ventilation system. The tube is made of a flexible woven plastic material. “I knew I wanted to put the positive-pressure tubes back in — that was a no-brainer for me because we had such good results in our previous barn,” says Heidi Hanke, herdsperson at the 700-cow dairy in Sheboygan Falls, Wis. “You are giving the calves fresh air without creating a draft on the calves,” she says.

This is one of the hallmarks of positive-pressure systems that have spurred their increased use in nursery and grower barns within the last five years or so, particularly in cooler regions of the country.

But, as with any ventilation system, they are not without their share of challenges, as Hanke knows.

“We didn’t have enough cables suspending (the ventilation tubes) from the rafters,” she says.

When the wind came from a certain direction or the barn was wide open, the tubes tended to bounce around a lot, especially on windy days. The tubes broke, and consequently, did not perform like they should.

“We added a few more cables, and now it doesn’t blow around as much on windy days,” Hanke says.

Fixing the problem has helped maintain good respiratory health among the calves. Here is some design and installation advice to help you head off problems with tube ventilation that can jeopardize calf health.

Focus on fan capacity, not diameter

Essentially, there are three primary components in a positive-pressure ventilation system: a fan, a tube and cables that suspend the tube from the rafters.

During the design phase, it is important to account for three key physical properties within the tube: static pressure, aperture ratio and discharge coefficient. Without going into a lot of detail, just remember that if the system is not designed with these factors in mind, you can end up with a poor match between the fan and the tube. Ultimately, this can result in insufficient air flow through the tube and uneven air distribution at calf level.

“We don’t fix the problem that we set out to fix (i.e., poor air quality at calf level) without accounting for those properties,” says Becky Brotzman, veterinarian and associate outreach specialist at the University of Wisconsin-Madison School of Veterinary Medicine.

To ensure proper air quality, base the diameter of the tube on the fan’s air-throwing capacity, not its size, says Brotzman, who works with fellow veterinarian Ken Nordlund and UW-Madison agricultural engineering colleagues to provide farms with design specifications for supplemental positive-pressure ventilation systems.

One farm they worked with did not follow the design specs they were given. They ended up with the tube being the same diameter as the fan.

“So if the fan was a 12-inch fan, they put a 12-inch tube in (which wasn’t) designed to meet the air produced by that fan,” Brotzman recalls. “Although another 12-inch fan may have worked, that one was producing more air than what should have gone through that type of tube.”

Bottom line: When you’re going over the blueprints with the builder or ordering fans yourself, focus on the cubic feet per minute of airflow provided by the fan, not its diameter in inches.

“We certainly recommend that they go to someone who’s been through one of our training programs or come to our group (at the vet school) to have a system designed,” Brotzman says.

Find out more at: www.thedairylandinitiative.vetmed.wisc.edu

Tube talk

The tubes used in a positive-pressure ventilation system have holes in them. Making sure these holes are properly sized and spaced is important for good air distribution along the entire length of the tube.

Again, this goes back to making sure that you account for static pressure, aperture ratio and discharge coefficient during the design process.

“The holes need to be designed so that we have a balanced discharge speed throughout the whole length of the tube and so the air coming from the tube goes a certain distance,” Brotzman says.

The material that the tube is made of is an important consideration, too.

Tubes can be made of hard-walled material, like a PVC duct or a smooth-interior drain tile duct, or a flexible plastic or cloth-like material. However, when the wind is whipping around, the tubes — particularly those made of flexible material — tend to sway more and thus become more prone to breaking or developing tears.

Hasel Farms in Lake Mills, Wis., headed off this problem by hanging an extra chain in the center of each tube, says Heather Schuld, calf manager at the farm. This has helped keep the tube from swaying so much.

“We ordered the two-cable tube and added a chain at the center of each tube which went from each cable to the rafters to help (stabilize) the tube,” Schuld says. “If the tube is swinging in the wind,” Schuld says, “it’s not going to be doing 100 percent of the job.”

Installation tweaks to consider

The connection between the fan and the tube is one of the first areas where you may encounter wear-and-tear with the system.

Schuld says they double-folded some extra tubing (it was part of the packaging material) and placed this at the connection of the fan to make it stronger. They put the tubing over the top of that and fastened it with a strap.

Where and how the fans are mounted is also important. If the fans aren’t mounted onto the exterior wall, they end up re-circulating air rather than drawing in fresh air, Brotzman says. Be mindful of this during installation.

Nate Elzinga of Daybreak Dairy in Zeeland, Mich., learned the hard way just how important installation is.

“We didn’t know a lot about it when we did it, and we did it wrong,” he says. “We ended up not being able to run it when it was cold.”

They have since built a new barn with group housing and an automatic feeder, and despite the not-so-good results the first time around, they still included positive-pressure tubes in this barn.

“We put them in the new barn right from the get-go because we knew it was important,” Elzinga says. A few tweaks may be needed, but overall, he is pleased with the system’s performance.

“It does us a good service, especially through the winter.”





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