Designing for ventilation
By Diane Mettler
By Diane Mettler
If the next barn you see has a flattened roof and looks more like a
warehouse, it’s likely to be a LPCV (low profile cross ventilation)
A new low profile cross ventilation (LPCV) barn design could mean significant improvements for dairy cows
If the next barn you see has a flattened roof and looks more like a warehouse, it’s likely to be a LPCV (low profile cross ventilation) barn. The first barn of this design was stocked with cows in November of 2005 and, because the improved atmosphere is helping to improve productivity, LPCV barns are starting to take hold.
The idea started with Rick Milner out of Veblen, South Dakota, who had been working with John Smith, the Extension dairy specialist from the Kansas State University (KSU), on cross ventilating a proposed four or six row freestall building as part of an expansion project. Previously, Milner was operating a dairy where cross ventilation was used on an existing freestall building. Their discussion lead to the question: What would happen if two buildings were side by side? Could cross ventilation still work?
|Figure 1 shows an end view of an eight-row LPCV building. An evaporative cooling system is located along one side of the building and fans are placed on the opposite side. More space is available for fan placement and the cooling system parallel to the ridge rather than perpendicular because the equipment doors are located in the end walls.
They contacted Joe Harner, the Extension engineer for livestock and grain systems at KSU to help answer the questions. “The normal barn would have four to six rows, but side-by-side the building would have eight to 12 rows and would be 200 feet wide,” he says. “Nobody had ever really built a dairy building more than about 120 feet wide. So the question was, when you start expanding to 200, 300, 400 feet wide, how do you make sure the ventilation is adequate?”
The answers to these questions resulted in the conceptual idea of a LPCV freestall facility. The design objectives were to maintain desirable air velocities in the cow freestall space and prevent accumulation of gases and heat in the housing area.
The layout didn’t change much. The space between the two buildings was removed, but the manure handling and other elements remained the same. What did change was the roof line. It was lowered substantially.
“We changed the roof slope from a 3/12 or 4/12 pitch to a 0.5/12 pitch,” explains Harner. “That allowed us to have a 400-foot wide building that’s not as tall as a naturally ventilated 100-foot wide building.” And all the ventilation is mechanical, using 50- to 54-inch diameter fans.
|Figure 2 shows a layout of an eight-row LPCV building with tail-to-tail freestalls. From a top view, this design simply places two four-row freestall buildings side-by-side and eliminates the space between the buildings, necessary with natural ventilation. One potential advantage of the LPCV, or tunnel ventilated, buildings is that cows are exposed to near-constant wind speeds. Inside the building, the air velocity, or wind speed, is normally less than eight miles per hour (mph) during peak airflow. The ventilation rate is reduced during cold weather with the wind speed decreasing to less than two mph.
Harner explains that with tunnel ventilation barns, fans are often placed on one end of a 400-foot long building and air is pulled across the cows. In addition, fans are also placed at the outlets around the end wall doors.
This is not ideal, he says. “The stalls are where you want the airflow, but (in a regular barn) the air will take a path of least resistance. There will be higher air velocities in the feed lane and cow alleys rather than in the freestall area. The optimum environment may not be where the cows are hopefully resting 12 to 14 hours per day.
“In a cross ventilation system, we go ahead and enclose the ends. But we use one side of the building as the inlet and the other side as the outlet or where the fans are placed,” he says. “So, in a 400-foot wide building, we’re only pulling that air across a maximum of 16 cows, and it’s parallel to the cow’s body.”
With head-to-head stalls, baffles were also placed between the front of two rows of stalls, resulting in an increase in air speed in the stall space.
“So now in the stall space where the cow’s laying, air speed is five to six mph; in the alley, it may only be two to three mph. In a conventional tunnel where the cows are laying, it may be two to three mph and in the alleys it may be five to six mph,” says Harner.
Benefits of the LPCV
The benefits of the LPCV are many:
- In the winter the building is 20 to 30 degrees warmer. As far as manure management, that means alleyways aren’t freezing —except possibly the ones near the inlet side of the building where cold air enters.
- The cows have a more consistent environment year round. “Wind speed is never more than about two miles an hour in the winter and yet, in the summertime, in the stall area where the cow’s resting, it can be five to six miles an hour,” says Harner. “In the summertime, we’re using an evaporative cooling system so we’re dropping the air temperature anywhere from 10 to 20 degrees or more, depending on location in the United States.”
- Reducing the heat and cold stress significantly decreases income over feed cost. Reports have shown that when temperatures exceed the 70 to 80°F range, cows begin to pant, sweat and eat less. One study, by J. F. Smith, J. P. Harner, and B. J. Bradford of Kansas State University, and M. Overton of the University of Georgia, states that when this happens, it increases the cows’ energy costs, “resulting in up to 35 percent more feed necessary for maintenance. When dry matter intake decreases during heat stress, milk production also decreases. A dairy cow in a 100°F environment decreases productivity by 50 percent or more, relative to thermoneutral conditions.”
- LPCV barns can improve pregnancy rates and reduce abortions because they reduce the impact of heat stress on reproductive performance.
- Improving a cow’s environment greatly reduces the impact of heat stress on present and future milk production.
- Odor is extremely low in these LPCV barns. Measurements were taken from the first building and in a study produced by R.E. Sheffield and a team of scientists, it was stated that:
- Gaseous emissions were found to be dominated by nitrogen-based compounds. Hydrogen sulfide was not detected inside the barn using an open-path ultraviolet spectrometer at R2 ≥ 0.75 of library prediction. Indoor ammonia concentrations were found to be considerably less than those reported in naturally ventilated freestall barns during previous studies. Lastly, emission rates from the 800-cow barn were lower than 100 lb/day CERCLA/EPCRA reporting limits, but would likely be exceeded if more than 1100 cows were housed together.
Harner says there is some added costs involved in running a LPCV barn — specifically, the electrical costs will be higher on a cow-per-day basis.
“When comparing costs, we have to make sure we compare equivalent barns,” he says. “If we’re talking about a natural barn with no heat abatement, that’s the cheapest. But if you put the fans in a naturally ventilated barn, fan horsepower is pretty much a wash. However, you will have fan costs October to May that you might not have in a natural barn.
“The big utility or electrical cost difference is the lighting, because inside we have basically 100 percent artificial lighting,” he adds.
Farmers give it the thumbs up
The added electrical costs are obviously worth it. Dairy producers, once they caught wind of the project, wanted to see the first LPCV up close.
“Rick and his colleagues were gracious enough to allow literally hundreds of people to go through those first two buildings the first couple of years,” says Harner. “Now, I think we have six or seven of the barns in different states — North Dakota, South Dakota, Minnesota, Iowa, Wisconsin, New York, and Texas. Producers in other states have also inquired about the potential of LPCV housing.”
When asked if a farmer can retrofit his barn to work like this, Harner wasn’t sure. “There aren’t any retrofitted barns right now, that may be something in the future. We’ve got some people looking at it. And I’ve had a lot of requests and sent lots of information out, but nobody has called back and said, ‘I’ve done it’ yet.”
No design is perfect and there is some concern about the need for artificial lighting in LPCV barns.
“Employees are in pretty much the same artificial lighting that you would find in a grocery or departmental store type of atmosphere,” says Harner. And it’s something they are looking into.
For now, there is always room for improvement and Harner and Smith, along with allied industry partners, are continuing to fine-tune the ventilation system.
“Right now, we’re focusing on winter ventilation, including optimum inlet location and air exchanges per hour,” says Harner. “We’re also working with managers of these facilities to help them understand how the static pressure is influenced by open inlet area and the number of fans operating.”
To get more information on the LPCV barns, log onto http://www.asi.ksu.edu/DesktopDefault.aspx?tabid=1264. There you will find at least a dozen reports about the LPCV freestall facilities, from air quality to design considerations.