Tri-State Neighbor: South Dakota Farm Newspaper

Some northwest Iowans harness the wind with a turbine.

Tom Olsen uses a double-curtained hog building in his finishing operation.

Olsen farms with his father, Marvel, and son Mark, near Newell, Iowa. For the better part of the year, Olsen uses the wind to keep his pigs cool.

“Our goal is to cool down the pigs, and the double-curtained, naturally ventilated buildings work very well,” said Olsen, who also works full-time as an Extension farm management specialist for Iowa State University.

Hogs come into the operation at about 40 pounds, he says. Olsen and his son use a 150-day production plan in their operation.

Each day, they record daily high and low temperatures. Ventilation settings are determined ahead of time and programmed into the automated control system.

“I really think you need to set up a plan and stick to it to make natural ventilation work,” Olsen said.

At this time of the year, he says there is also a financial savings when it comes to double-curtained buildings.

His utility bill is about $100 per month, compared to about $500 per month for a mechanically ventilated building.

“We believe pig performance is similar with both styles of buildings,” Olsen said. “Recently, the cost of electricity in this area has gone up significantly compared to the cost of propane, so we really have to pay attention to that.”

Curtained buildings are a hybrid, notes Larry Jacobsen, Extension ag engineer with the University of Minnesota.

He says natural ventilation is used in the summer, then the building is switched to mechanical ventilation in the winter.

A true naturally ventilated building would have an open ridge at the top, Jacobsen explains, but most buildings have flat ceilings that depend on the wind.

“The wind is really a dominant force, and it blows most of the time in the Midwest,” he said.“If you are in an area that has little wind, it would be problematic to have a naturally ventilated building. If you are in the right location, a curtained barn works very well.”

Jacobsen says any ventilation system must also control moisture inside a building. Buildings must include an insulated shell to help reduce condensation in the winter and keep surface temperatures down in the summer, he adds.

Inlets are a crucial part of any building design, Jacobsen says. In a naturally ventilated building, air should flow upward into an open ridge, or across the building.

“You want these inlets evenly distributed down the length of a barn,” he said.

An automated control system is also a necessity, he says.

“You have to be able to rely on that system to keep moving the curtains,” Jacobsen said. “It needs to have regular maintenance along with the rest of the ventilation system.”

Most buildings run east and west, he says, allowing the prevailing summer winds to flow through a building.

In some areas, a north-south building could work as well. Jacobsen says exhaust fans provide very little benefit in a naturally ventilated building.

“Circulation fans can provide some benefit in naturally ventilated systems by being hung inside the barn and creating air movement over the animals in the summer,” he said.

He says producers must look at economics, too, before putting up a naturally ventilated building.

“There is more labor and more management involved with a curtained barn,” Jacobsen said. “There is also very little wind from 2 to 5 a.m., so it won't take pigs long to get uncomfortable. You may see less feed efficiency as well, so you have to decide if it's worth the extra days it may take to get a pig ready for market.”

Olsen believes if a producer keeps detailed records for the building, a naturally ventilated system can work very well.

“It does require maintenance and management, and you will have to replace the curtains periodically because of the mice and bird issues,” he said. “We believe if you have a good plan and you can stick to that plan, naturally ventilated buildings can work very well in a grow/finish operation. If we were going to put up another finisher, it would be a double-curtained building.”