The past 10 years or so have brought significant changes in swine finishing facility design. Leading the way have been fully slotted, curtain-sided barns; tunnel-ventilated barns; double-wide, wean-to-finish units; large group size pens; pigs raised on solid bedded floors; hoop structures and a new generation of control systems.

This new generation of finishing facilities is now becoming middle-aged (from 5 to 15 years old) and it may be time for a checkup.

Producers may also be planning new facilities or remodeling existing ones, and wondering which production system or change performs best.

While every production system is unique, each also provides a set of environmental challenges that need to be addressed to obtain optimal performance.

Environmental Challenges

Providing the proper environment still can be a struggle despite new generation, computerized controllers designed to provide better temperature control. That's because the total ventilation and building system must be properly designed and managed to achieve the desired environmental conditions.

The optimum environment in a finishing system should enhance voluntary feed intake and minimize thermal and other environmental stresses that affect pig and worker health.

Voluntary feed intake is influenced by group size and composition, thermal environment (temperature, air speed and humidity), feeder spaces and space allocations per pig.

All of the diverse finishing production systems and climates challenge planners.

Thermal Environmental Factors

Maintaining temperatures within the pig's comfort zone and proper relative humidity (typically from 50 to 65%) are two primary functions of a ventilation system.

Effective environmental temperature is the temperature actually experienced by the pig.

When a total building system is analyzed, the way a pig loses heat needs to be considered to determine the effective environmental temperature. Pigs lose heat to the environment by conduction, convection and radiation, and by evaporation through their respiratory tracts.

Conduction is the transfer of heat from one surface to another and accounts for 10-15% of total animal heat loss. It can affect growth because of its relationship to animal comfort.

Dry concrete slats over a deep pit could contribute up to a 9°F-temperature deficiency when compared to ambient room temperature. A major advantage of bedded solid floors during cold weather is the effective temperature rise of 7-15°F, depending on the size and weight of the pig.

Convection is the transfer of heat from an object to the air around it. It makes up 35% of total animal heat loss. Convective heat loss is a positive during hot weather, but a potential detriment during cold and mild weather if air velocities are too high. Convective heat loss will create problems in wean-to-finish facilities without proper maintenance.

Table 1. Temperature Adjustments for Floor Level Air Speeds
Air speed Temperature Adjustment
< 25 fpm1 0°F
40 fpm -7°F
100 fpm -13°F
300 fpm -18°F
1Feet per minute


Ventilation Factors

Common terms used in ventilation are cfm, which stands for cubic feet per minute, and fpm, which refers to feet per minute.

For example, a 5,000 cfm fan would exhaust 5,000 cu. ft. of air per minute from the facility. Air velocity is defined by fpm or miles per hour (mph). An air speed of 88 ft. per minute would be equivalent to 1 mph.

During cold weather, air speeds at pig level should be kept to less than 30 fpm for small pigs. For larger pigs, air speed should be less than 40 fpm at floor level.

Floor-level air speed is a function of velocity at the air inlet, opposing air streams, distances to walls from the air inlets and drafts from unplanned openings.

As ventilation rates increase, there is typically an increase in the air speed at pig level. Fan set points should be adjusted far enough apart so animals are not chilled when higher ventilation rates are called for with rising room temperatures. High air speeds have a negative effect on average daily gain for small pigs. Table 1 shows the affect of air speed on effective environmental temperatures.

Radiation is the transfer of heat from an animal to a surrounding surface without direct contact. It normally accounts for 30% of total heat loss. Non-insulated surfaces such as exterior concrete walls and curtains are of concern in the northern climates, especially for small pigs in wean-to-finish facilities.

Evaporative heat loss is an advantage during hot weather. Since pigs don't sweat, they must dissipate heat in warm weather directly through the skin (conduction, convection and radiation) and through increased respiration rate (evaporation). A 300 fpm air speed past a pig (Table 1), typical for a tunnel-ventilated facility, will lower its skin temperature by 18°F. However, when air temperature starts to approach body surface temperature, the convective heat transfer from the skin is greatly reduced. When this occurs, air velocity needs to be supplemented with evaporative cooling to lower the air temperature. This can be accomplished with sprinklers or cool cells.

Table 2. Recommended Cold Weather Mechanical Ventilating Rates for Wean-to-Finish Animals
Production Stage Weight (lb.) Moisture Control* (cfm/head) Odor Control** (cfm/head) Add for Unvented Heaters (cfm/head)
Pre-nursery 9-30 1.0 3.5 0.5
Nursery 30-75 1.5 5.0 0.5
Grower 75-150 3.5 10 1.0
Finisher 150-260 5.0 18 1.0
*Typically used when designing ventilation for cold weather.
**Used only when odors are a concern. Airflow to control odors typically needs to be two to three times higher than ventilating for moisture control.


Table 3. Recommended Mechanical Ventilating Rates for Wean-To-Finish Animals Based on Weather Conditions
Production Stage Weight (lb.) Mild (cfm/head) Hot (cfm/head)
Pre-nursery 9-30 10 25
Nursery 30-75 15 35
Grower 75-150 24 75
Finisher 150-260 35 120


Ventilation Principles

The purpose of a ventilation system is to bring fresh, outside air into the building through planned openings, and thoroughly mix it with stale, inside air. In addition, good ventilation will pick up heat, moisture and air contaminants; lower temperature, humidity and contamination levels; and exhaust moist, contaminated air from the building.

The principals of the concept to determine cold, mild and hot weather ventilation rates are shown in Figure 1. Note the increased rates needed for odor control, as compared to moisture control, and the supplemental heat needed during cold weather.

The three most common ventilation systems are all-mechanical, mechanical/natural and all-natural.

There are two categories of mechanical ventilation:

  • Traditional, with ceiling air inlets and fans in the sidewall and pits; and

  • A three-season system (fall, winter and spring) with a traditional, mechanical system and tunnel ventilation during hot weather. Ventilation rates are spelled out in Tables 2 and 3.



Tunnel ventilation should provide 300 fpm of air movement. The fan capacity needed for tunnel ventilation can be determined by taking the room width times the height, times 300 fpm. A 41-ft.-wide barn with an 8-ft. ceiling would require about 100,000 cfm of fan capacity (41×8×300=98,400). A tunnel-ventilated facility should be designed with 50-60 cfm/pig of ventilation capacity (pit and wall fans and ceiling air inlets), so tunnel ventilation isn't needed until outdoor air temperatures reach 80°F. The additional conventional capacity will provide for more management flexibility and better air distribution when outdoor temperatures drop.

The mechanical/natural facilities have curtain sides and a flat ceiling. Operational problems can occur in the spring and fall or in transition between hot and cold seasons. This is especially true where curtains are opening too quickly because the inside temperatures are too warm.

Many curtain-sided barns with mechanical ventilation were designed for 25-30 cfm/pig. A 30 cfm rate should keep curtains from operating until outdoor temperatures reach 55°F with a room temperature of 68°F. Curtains in mechanically/naturally ventilated buildings should start to operate during the latter stages of mild weather conditions. A minimum 3-in. overlap should exist at the top to control cold air infiltration when fully closed.

Design Problems

One of the main problems with mechanically/naturally ventilated facilities is that finishing room temperatures exceed 70°F when outdoor temperatures are less than 50°F. Some reasons are: temperature set points may need adjusting, inadequate fan and/or air inlet capacity, air intake into the attic is undersized or being restricted, pit fans are connected to undersized transitions or the manure pit is full or fans/shutters are dirty.

Attempting to fine-tune indoor temperatures for this barn style is extremely difficult and often results in undesirable temperature fluctuations, drafts and air quality problems. The cross-sectional area adjacent to pit fans should be sized at a rate of 1,000 fpm. A 5,000 cfm pit fan would require an opening of 5 sq. ft. Dirty fans and shutters can reduce ventilation capacity up to 40%.

Fresh air intake into the attic space to “feed” interior ceiling air inlets should be sized by taking total ventilation (cfm) divided by 400 fpm. At 30 cfm/pig in a 1,000-head, curtain-sided barn, total fan capacity needs would be 30,000 cfm. Dividing 30,000 cfm by 400 equals an eave opening of 75 sq. ft. If the barn is 200 ft. long and the entire intake is placed on the south side, an opening of 4.5-5 in. is required the full length of the barn on the south side. Cover air intake openings with wire or plastic mesh no finer than ¾-in. to keep birds out.

Ridge vents are definitely needed when intake air is brought in through the eaves to help balance the pressure in the attic. There is always a negative pressure by the ridge, regardless of wind direction. Consult resources listed at the end of this article for the correct way to construct an adequate air intake.

If there are no eaves on your facility, consider bringing fresh air in from hooded openings on the gable ends of the barn.

Air Inlets

Enough air inlets should be installed for whole-room, fresh air distribution and the inlet capacity should match fan capacity. Air inlets should be adjusted so that exhaust air speeds are 700-1,000 fpm and room static pressure is 0.04-0.06 in. of water (Figure 2). A manometer, which measures static pressure (Figures 2 and 3), will help with room environment adjustments.

Controls

The controller should be functional and adaptable to your ventilation system, as well as flexible, understandable, reliable, accurate, serviceable and durable. Many producers have difficulty understanding and operating the controller.

Establish a written standard operating procedure (SOP) for facilities with your ventilation supplier and/or consultant before putting pigs in the barn. Modify as needed. This will help you to understand the controller operation and the total ventilation system.

Routinely check temperature settings and sensors, even with highly automated systems. This is especially true for humidity sensors. Also, a controller should not substitute for visual observations and good husbandry practices.

An important item to note about variable-speed fans and controllers is that the percentage shown on the controller as a minimum idle speed usually doesn't coincide with the amount of air being exhausted. There is usually no correlation between the input voltage to the fan and the actual cfm output. Certain controllers have a fan or motor curve function that allows for matching up with the variable speed fan in use. Having the proper fan curve should help smooth out this response, but it still needs checking.

Conclusion

Producers often ask which hog building system is best. The answer could be all or none of them. Hogs are extremely adaptable animals, and given the opportunity, will perform very well. Each building system and climate provides its own set of challenges.

For additional resource materials on swine facilities and ventilation systems, such as the Midwest Plan Service publication “Swine Wean-to-Finish Buildings” (AED-46), contact your local county Extension educator or Midwest Plan Service (http://mwpshq.org) at (800) 562-3616.

Ventilation Workshops

A series of ventilation workshops called “Managing Your Unseen Employee: The Ventilation System” are being planned in South Dakota, Nebraska, Iowa and Minnesota.

Workshops will take an in-depth look at the operation of a ventilation system in different seasons and its impact on pig performance. A working ventilation lab and other working models will be used to demonstrate these principles.

The workshops are currently being planned to start in December, sponsored by the Cooperative Extension Service and state pork producer councils.

For further details, contact state or local county Extension educators.