Designing ‘greener’ pig barnsDesigning ‘greener’ pig barns
Advisory group rethinks typical finishing barn design options.
September 19, 2011
As feed costs continue to climb, pork producers are redoubling efforts to maximize pig growth and efficiency. In some cases, that means updating or reconfiguring grow-finish facilities to match breed-to-wean pig flows, while older, ill-matched facilities are being razed and replaced.
The question remains: “What does the ideal, 21st-century finishing barn look like?” That was the challenge placed before a team of a dozen pork industry professionals as part of a National Pork Board project.
“Ideally, swine buildings should be designed and built as an integrated system, not as separate components,” states Larry Jacobson, Extension agricultural engineer at the University of Minnesota, principle investigator of the project and chair of the advisory group.
“An integrated design should focus on providing the optimum conditions for maximum pig production efficiency while reducing energy and emissions and addressing worker health and safety and pig welfare issues. The building efficiencies should be integrated into the building design rather than by add-on technologies,” he states.
For the last three decades, many if not most swine confinement buildings were assembled by suppliers of the various components of the structure — ventilation, manure collection and storage, feed storage and delivery. Relatively inexpensive feed and fossil fuels, as well as limited concerns about emissions, led to popular barn designs such as tunnel-ventilated, deep-pit barns that typically increase energy use and air emissions, Jacobson points out.
Think tank’s task
Supported by the Minnesota Pork Board and the National Pork Board, the think tank group’s job description was to develop a smarter, greener housing design and management system that reduces energy use (fossil fuels and feed); limits the environmental impact of gases, particulates and manure produced; maintains good air quality for workers and pigs; ensures the welfare of the animals; and promotes consumer acceptance of pork.
The panel of advisers was challenged to rethink finishing barn designs for the northern tier states in the swine belt while reducing their environmental footprint. The group of researchers, Extension engineers and industry representatives met three times over a two-year period to brainstorm and prioritize building design criteria. They also received input from several researchers and industry representatives from northern Europe.
It was a tall order, Jacobson admits, but they summarized their recommendations in these eight areas:
Although fully slotted floors may be the preferred option, the committee noted that properly managed, partially slotted floors would have less emissions simply because there is less area to emit. And, partially slotted floors are viewed as more welfare friendly, they note.
The ratio of slots to solid flooring is open to debate, but the typical ratio is 2:1 solid vs. slots. A 24-ft.-long pen would therefore have 16 ft. of solid area and 8 ft. of slotted area, giving each pig 5.3 sq. ft. of solid floor space.
Pen size and stocking rate
Providing 8 sq. ft./market hog is common, so pen size is adjusted to the most preferred, most manageable group size. The number of pigs/pen is a matter of preference and available labor. Rates could be 16 to 100 pigs/pen, but the group agreed that 30 pigs/pen was most common and easiest to manage.
Size and shape of the building
Again, personal preference comes into play, but efficient pig flow from the farrowing site commonly dictates finishing building capacity with 1,200 or 2,400 head now most typical. Energy efficiency principles lean toward more square vs. long and narrow buildings, the group agreed. However, width is also dictated by the construction limitations (truss width, etc.) and building codes (i.e. snow load requirements). Building layout would be generally two rooms of 40 pens with a center walkway; therefore, the footprint would be 100 x 200 ft.
Feed and water
The advisory group agreed that wet-dry feeders or dry feeders with swinging nipples are acceptable options. They remind that nipple placement over the slotted area in partially slotted pens is important to establish good dunging habits.
Manure storage and handling
The impact of manure on the barn’s interior environment and the emissions expelled from it were key considerations for the advisory team. “From early on, the advisory team felt that to maintain air quality in the animal environment, some separation between the animal environment and the manure was important,” Jacobson says.
Long-term manure storage (six months or longer) under the barn contributes significantly to barn emissions and air quality. Safety risks during pump-out and, more recently, manure foaming and explosion hazards led the advisory group to recommend that future designs should focus on storing manure outside of the building. In doing so, the manure handling options with fully slotted or partially slotted floors would generally be flush systems or scraper systems.
“Flush systems typically produce more emissions and require manure treatment for flush water,” Jacobson explains. A modified pull-plug system with a V-shaped gutter tested in Denmark and Holland produced the least amount of emissions. Although gutter scrapers and belt conveyance systems were thought to require too much maintenance and might not gain favor with producers, the committee held that shallow gutters with manure scrapers may offer the best opportunity to improve barn air quality and reduce emissions.
“With a scraper system, manure is moved out of the barn at least twice a day, resulting in fewer anaerobically created gas emissions. Scraping removes all hazards related to intermittent high gas concentrations and subsequent hazards during agitation and pumping of deep pits, or when the plugs are pulled in shallow-gutter barns,” the committee reasons. They anticipate future barn designs will incorporate energy recovery systems, such as digesters, which need daily feeding of fresh manure for better digester performance.
Walls should be insulated to R-values of 15-20 and ceilings to R25-30. “If the attic is used as a tempering plenum, the underside of the roof should be insulated to R5-10,” he adds.
A control system would be based on the type of heating and cooling system, of course, but it should provide for micro-climate control. The goal is to minimize the number of controllers in the ventilation system, so set points can be managed more precisely. Heating, cooling and ventilation would be controlled using temperature, humidity and carbon dioxide, through a combination of ceiling and wall exhaust fans and ceiling inlets where air is drawn from the attic space that receives tempered air.
Heating and cooling
At the outset, the advisory group says it is important to differentiate between “make-up air heating systems” and “radiate heating of surfaces.” For pig comfort, they suggested it was more effective to provide zone heating where floor surfaces were heated vs. heating a whole room or building. This approach addresses the common problem of overheating buildings in the winter, which not only wastes fuel, but stresses the pigs and likely reduces performance.
Jacobson cites a paper by John E. Baker, DVM, Warrick Veterinary Clinic, Chandler, IN, on the factors impacting effective environmental temperatures for pigs (http://www.aasv.org/shap/issues/v12n3/v12n3ptip.html).
In general, high air velocities (drafts) and cold surfaces significantly reduce effective temperature. The producer response is to bump up the heat, which subsequently increases fuel requirements. Recognizing the complexity of quantifying maximum pig performance, Jacobson says the temperature range most commonly used is 65-70°F. Beginning and ending pig weight, group size, pig space allocation and genotype can affect the temperature considered to be “ideal.”
It is difficult to maintain optimum conditions with popular sprinkling or fogging systems and evaporative cooling pads during the warm summer months, the group agrees. As an alternative, they proposed floor cooling with evaporative cooling pads or mechanical cooling with floor cooling. Since only a limited amount of body heat can be removed through the floor, other air cooling systems, such as geothermal or ground source heat pumps in combination with floor cooling, should be considered. Floor cooling is needed in either case to ensure proper dunging habits of the pigs on partially slotted floors. When it is hot, the solid floor must be cooler than the slotted floor surface to prevent dunging on the solid floor, they remind. They recommended PEX tubing, made from cross-linked, high-density, polyethylene polymer, in the solid floors.
Although the cooling capabilities are significant, it is unlikely floor cooling would have a significant impact on pig performance — just dunging habits, Jacobson explains. Therefore, an evaporative cooling pad system or a geothermal cooling system would be needed to further reduce ambient air temperatures.
“Ceiling exhaust fans with variable-frequency-drive electric motors are recommended for all minimum ventilation fans in the geothermal system because they are likely to resist wind pressures better than wall fans,” Jacobson explains. However, additional wall fans would be needed to provide higher air exchange rates for warm weather ventilation and/or the evaporative cooling pad option. “As a result of this cooling, maximum ventilation rates in the barn would be reduced by one-third (to 80 cfm/pig) for the evaporative system and by two-thirds (to 40 cfm/pig) for the geothermal system,” he notes.
Both cooling systems would use the attic as a plenum to distribute cool air through ceiling inlets positioned over the rows of pens. Inlets are directional to allow for air distribution over the slats or on the solid portion of the floor to help control dunging habits in the partially slotted barns. Fans and inlet controls would be synchronized and controlled by multiple temperature sensors in the barn to help ensure uniform conditions.
“It was understood that the cost of an improved building design would likely be greater than standard construction and would have to be significantly offset by improved pig performance,” Jacobson acknowledges. “Building design features, such as outside manure storage, floor cooling and geothermal cooling that can reduce emissions and provide cleaner air and greater barn environmental control adds to facility cost when compared to current swine finishing designs.
“One possible method of cost recovery is improved pig performance. Increased average daily gain, improved feed conversion, lower death loss and lower pig health costs can cover all or some of the added costs. Research data on the effects of level and uniformity of temperature and ventilation air speed can be used to estimate improved pig performance for the building design alternatives suggested in this report,” he says.
“However, confidently estimating this improvement is challenging, since most available research was collected under constant conditions (such as temperature). Obviously, conventional facilities currently in use have environments (temperature, ventilation air speed, humidity, etc.) that vary during the day and season. The effect of short-term stress from less than ideal conditions and potential compensatory gain complicate estimation of performance differences in comparisons to more constant ideal conditions.”
Green Barn Payback
“The building design concepts proposed are expected to save energy in the winter due to better insulation and environmental control. However, when warm room temperature exceeds the thermal neutral zone and reduces pig feed intake, the proposed barn cooling designs would have the largest economic benefit,” Jacobson says.
“Building construction costs per pig space are expected from 1.3 to 2 times higher than typical construction for these design changes. These costs are offset by a 3-7% increase in average daily gain and 5-10% decrease in feed consumption per pound of meat produced,” he continues.
“Other benefits include better pig health and worker environment. Using these assumptions, a standard economic projection has estimated a 6- to 13-year payback over the baseline building (2,400-head deep pit, double-sided, tunnel-ventilated barn). These economic projections would improve significantly with additional gains in animal performance.
Performance gains are anticipated, but there is currently no supporting research data to confidently predict the magnitude of these performance improvements on an annual basis in commercial scale operations. Construction and monitoring of these design concepts is a critical next step in moving to more sustainable pig production systems,” he concludes.
Joining Jacobson in the advisory group were: David Schmidt, Robert Koehler, Bill Lazarus and Mark Whitney, University of Minnesota; Steve Pohl and Richard Nicolai, South Dakota State University; Jay Harmon and Steven Hoff, Iowa State University; Rick Stowell and Crystal Powers, University of Nebraska; Mike Brumm, Brumm Swine Consultancy, North Mankato, MN; and Tom Stuthman, Automated Production Systems, Assumption, Ill.
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