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Positive-pressure ventilation systems for calf facilities

PD Editor Karen Lee Published on 17 January 2014

Better-managed calf barns are beginning to rival outdoor hutches – the long-held gold standard to calf housing.

Dr. Ken Nordlund explained that there are three reasons why interest in calf barns is growing: first, to avoid dealing with inclement weather; second, automatic calf feeders are not feasible for hutches; and third, emerging data shows properly ventilated calf barns are providing health results equivalent to hutches.

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At a Dairyland Initiative Workshop in Madison, Wisconsin, in November, Nordlund discussed the importance of positive-pressure ventilation systems and provided practical advice to keep in mind when designing a system.

Nordlund, with the University of Wisconsin School of Veterinary Medicine, estimated several thousand barns have been retrofitted with positive-pressure pressure tubes over the last few years in order to disperse fresh air in places where natural ventilation fails to reach.

Producers on those farms have reported a drop in respiratory disease by one-half to three-quarters of the rate they experienced before installing the tubes.

“That tells me that there are some major problems with natural ventilation by itself,” Nordlund said.

Natural ventilation is driven primarily by prevailing winds and a little by thermal buoyance (as animals heat the air which causes it to rise out the ridge opening).

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This system fails on calm days when the air is still and during a four-hour period of the day when the outside temperature is four to five degrees warmer than inside the barn. According to Nordlund, together that equates to 20 percent of the time, when there is little to no ventilation.

Some producers might remember ventilation tubes from the 1970s, but Nordlund said these are a new generation of tubes. The old tubes were essentially a recirculation system. They pulled air from within the barn itself.

Today’s tubes run from a fan directly mounted on the outside wall to bring in 100 percent fresh air.

“Initially, we had fears of taking frigid air into a tube and driving it non-stop at the calves,” Nordlund said.

After comparing two similar barns, one with the tube and one without, he found no difference in the average temperature. During the middle of the night, the barn with the tube was one to two degrees colder, but during the day it was one to two degrees warmer than the temperature in the other barn.

The new generation tubes evenly disperse air throughout the barn and do so by creating clouds of fresh air just above the calf level, as opposed to blowing air directly at the calves.

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These systems are a relatively low-cost expense. Fans typically range from $250 to $700. Tubing is $1 to $15 per linear foot. Cables, clamps, hangers and labor vary per job.

Overall, Nordlund said, “Many calf barns will install a system costing less than $1,500 that can transform their entire heifer operation.”

He touched on common issues that arise when designing these systems.

Fans
Fans will lose capacity over time. Belt-driven fans will need belt replacement, direct-drive fans lose efficiency, fan blades get dirty, and protective screens can get plugged.

Farms can expect a typical non-stop fan life of about five years.

Variable speed fans are fine, just as long as they only run at one speed. In general, Nordlund would formulate the system to match the tube at maximum fan capacity.

Hoods
Nordlund said he likes to install hoods on the outside of the fan to reduce the amount of rain and snow drawn in and blown down the tube.

Be careful not to undersize the hood, as that can reduce fan performance.

Relatively low-cost positive-pressure ventilation systems have been found to reduce the incidence of respiratory disease by one-half to three-quarters.

Tubes
There are a number of options when it comes to tube material.

Smooth polyethylene is the lowest-cost option, ranging from $2 to $3 per linear foot.

Hole locations on this material are usually limited to matched pairs (i.e., 3 o’clock and 9 o’clock) and 1 to 3 inches in size by half-inch increments.

It is usually suspended with a single row of clips to a cable and is known to twist. It can be easily damaged and is recommended for use in very enclosed locations.

Woven polyethylene and vinyl comes in several grades and varies in price from $5 to $12 per linear foot.

If the tube will be exposed to sunlight, vinyl is preferred, as the polyethylene will deteriorate.

Holes are cut by computer-control lasers, resulting in an infinite choice of hole sizes and configurations. Very small anti-condensation holes are also an option with this material.

Double cables prevent twisting and turning of the tube.

The most expensive option is hard PVC and drainage pipes. These typically range from $12 to $20 per linear foot.

Holes would need to be hand-drilled at any desired size.

This is a very durable material but needs to be suspended with a chain or set on a wood frame.

For the drainage pipe, Nordlund suggested finding a material with a smooth interior to reduce friction losses.

When attaching the tube to the fan, Nordlund recommended attaching it first with a bungee cord. This will leave working room to properly pleat the material before securing it with the worm gear clamp.

In general, the number of tubes is determined by the width of the barn. A good rule of thumb is one tube per 25 to 30 feet.

When it comes to length, Nordlund said he is comfortable sizing a tube up to 175 feet. Anything longer would require special calculations.

The tubes should be placed high enough to not interfere with labor and machines. Wind damage can be minimized if the tube is located within the truss structure.

Discharge holes and perforations
It is not necessary to place one hole per individual calf pen. If the right throw distance and air speed is achieved, the angle of entrainment of air from the tube widens and will cover more than one pen.

Extensions and side entrances

Barriers such as milk preparation and feed storage rooms are commonly located between the outside wall and the calves. Tubes, with or without discharge holes, can be run straight through the intermediate room.

Another option is a side access with right-angle turn. To do this, a fan can be mounted on the sidewall with a 90-degree corner in the tube, or a passive air access duct can be built from the side of the barn and the fan mounted into the duct wall. For the second scenario, the passive duct needs to be sized so it does not create negative pressure in the system.

Non-naturally ventilated barns
These systems, paired with a large-capacity positive-pressure tube located along the barn sidewalls that can change air 15 to 20 times, have been found to meet the year-round ventilation needs of a retrofitted stall barn.

Neither system will work well in a barn that has a wind tunnel running parallel to the tube.

For more information, visit the Dairyland Initiative website . It contains a listing of 250 graduates of the positive-pressure tube systems in calf barns workshop who can assist in the design process.

The website also has information on the next calf barn workshop set for Feb. 14. It will be held in conjunction with 100-pound Dairyland Initiative Farm Tours and a workshop on how to remodel dairy cattle housing to maximize cow comfort, which take place earlier in the week. PD

PHOTO
Relatively low-cost positive-pressure ventilation systems have been found to reduce the incidence of respiratory disease by one-half to three-quarters. Photo by Karen Lee.

Karen Lee


Karen Lee

Editor
Progressive Dairyman

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