Triple-curtain buildings used to be a hot topic when people talked about finishing units. But you don’t hear much about them anymore.
Why not? Is the concept less viable today? Or has the industry simply latched onto new fads like wean-to-finish?
It may be more of the latter than the former. The triple-curtain building is still providing advantages in summer ventilation. That’s especially true on hot, still days when the lack of a breeze makes standard double-curtained buildings a less effective natural ventilation option, says Terry Feldmann of Animal Environment Specialists, East Peoria, Ill.
The theory behind the triple-curtain unit: A large ridge-vent opening offers more opportunity for thermal buoyancy to pull warm air up and out of the building as cool air fills from the side curtains.
And that cooler air encourages pigs to maintain feed intake, thereby improving growth rates during hot weather. Keeping pigs eating may also reduce the rate of ulcers. Finally, reducing temperature fluctuation in spring and fall helps improve finishing pig health.
All ridge-vent systems aim to draw out warm air and replace it with cool, outside air. Triple-curtain buildings may take better advantage of the effect, Feldmann says. “It offers simpler automation than most ridge-vent systems,” he notes.
While other ridge-vent systems may cool a building within 10 degrees of the outside temperature, a triple-curtain unit may cool it within 5 degrees. “A triple-curtain building provides a larger opening to exhaust a lot more air in warm and hot weather, even at slow air speeds,” Feldmann explains.
If you have a 24-inch clear opening for the curtain with air moving at 150 feet per minute, you can exhaust 3,000 cubic feet per minute every 10 feet of opening, he says. You’re not accelerating air movement; you’re simply letting thermal buoyancy pull out large volumes of warm air.
The triple-curtain design also accommodates a quicker shift to natural ventilation in spring, and a smoother transition back to minimal mechanical ventilation in the autumn, Feldmann says.
Temperature logs show ridge-vent systems cool buildings quicker on hot, still days than flat-ceiling units.
Feldmann cites a producer who had a flat-ceiling, double-curtain building next to a ridge-vent, double-curtain building. On a still but cold spring day, the curtains in the flat-ceiling unit opened halfway, letting in cold air and widening temperature fluctuations. The curtains on the ridge-vented building only opened 4 inches, keeping a more consistent temperature while still providing adequate ventilation.
A common complaint about triple-curtain units is winter performance. With a high ceiling, they can be a challenge to heat. You may have to seal the upper and sidewall curtains to keep the environment warm enough for feeder-sized pigs.
Carl Swinford has seen this aspect of the triple-curtain buildings firsthand. He is a partner in Swinford & Frantz Farm, a 1,700-sow, farrow-to-finish operation located near Hillsdale, Ind.
Swinford and Frantz built two triple-curtain buildings in spring 1994. During summer, pigs in these buildings perform better than those in the flat-ceiling finishers or chimney-ventilated units.
Swinford says direct comparisons are difficult to make because he and partner Steve Frantz built an off-site nursery and adopted segregated early weaning at the same time they built the new triple-curtain finishers.
He is a bit discouraged by the supplemental heating required in the triple-curtain buildings during the winter.
“We decided if we built another triple-curtain building we might make it 50 feet wide instead of 60 feet to reduce the air mass we’d have to heat,” Swinford says. “That large air mass makes it hard to warm up the buildings, especially when a room is empty between pig groups.”
Trying their hands at wean-to-finish buildings, Swinford and Frantz have built two units with flat ceilings. Swinford says they’re getting better performance with these buildings than with the other finishers. Pigs always do best in new buildings, but after multiple turns the results in the wean-to-finish units look promising.
“The place for the triple-curtain building,” he concludes, “is in southern areas with a long summer, high temperatures and less wind.”
Feldmann agrees that areas with less wind likely will benefit most from thermal buoyancy in summer. But he still says triple-curtain buildings are viable in the lower and upper Midwest.
He likes them for breeding/gestation units. Sows and boars get more relief in summer and need less warmth in winter due to the heat their bodies produces.
Feldmann also notes they work well in a pure finisher setting. If you bring pigs in at 100 or 110 pounds instead of 40 pounds, you have less worry in winter about keeping the building warm.
“If you put pigs weighing less than 55 pounds into a triple-curtain finisher, it can be a challenge to keep them warm in winter,” Feldmann admits. “You may need to close it up and use a little minimal mechanical ventilation. It makes a big difference if those pigs go in at 45 pounds or 65 pounds.”
The cost of a triple-curtain building ought to be considerably less than a wean-to-finish building. From a materials and labor standpoint, it should be somewhat less than a flat-ceiling building, Feldmann says. But he notes some contractors who aren’t used to the concept may charge as much to build a triple-curtain unit as a traditional flat-ceiling finisher.
While chimney-ventilation, ridge-vent and triple-curtain buildings all are based on sound theories, the design is the key to making them work.
Swinford suggests getting professional help to design a building suited to your site and pig flow. He will continue to run the off-site nurseries and grow/finish buildings that he has, but he would prefer to bring weaned pigs into one unit and finish them there.
As for triple-curtain buildings, they still offer consistent natural ventilation from spring to fall. The only fly in the ointment is how well you design and manage the building to withstand winter conditions in your area.