Natural Ventilation for Dairy Tie Stall Barns

Tie stall barns require a ventilation system that allows close control of air exchange and temperature to prevent the barn from reaching freezing temperatures.
Natural Ventilation for Dairy Tie Stall Barns - Articles

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Tie stall barns require a ventilation system that allows close control of air exchange and temperature to prevent the barn from reaching freezing temperatures. Good air distribution is especially critical because the cows are restrained and cannot move out of drafts or poorly ventilated areas.

When its 50 °F, a mature cow will breathe out four gallons of water per day in the form of water vapor and produce almost 1000 watts of heat. A typical portable electric heater produces 1200 to 1500 watts. The heat produced by that cow in 24 hours would equal the heat contained in about one gallon of propane. When animals are confined in tie stall barns a ventilation system is necessary to continuously exchange warm, humid inside air for drier, cooler outside air. (Typically, Holstein cows can maintain high levels of productivity between 20o and 76o Fahrenheit as long as relative humidity is not allowed to go too high.) Even the most basic ventilation systems should provide the following:

  • Air exchange. Ventilation systems can have either a mechanical driving force (fans) or natural driving force (winds and buoyancy). Sufficient air exchange can be accomplished by using either one or a combination of the two.
  • Control, or the ability to modify ventilation rates based on inside or outside conditions. Ventilation rates are changed by turning on and off fans or opening and closing curtains, dampers, windows or ventilation doors. Automatic control provides the most uniform conditions and response to changes in weather.
  • Flexibility. Ventilation systems should be flexible so they are able to meet the conditions needed during various seasons of the year. There are three distinct operating conditions:

    1. Continuous, low level air exchange, which is required even during sub-freezing conditions to remove moisture continuously produced by animals.
    2. Temperature control air exchange, which is necessary during cool and mild conditions to remove excess body heat from the barn, and
    3. Air velocity and high rates of air exchange, which are required during hot weather to help the cow remove large amounts of heat from her body and the immediate space around her.
  • Tight barn construction is also important to the performance of the ventilation system. When close temperature control is desired, the barn must be well-insulated to control heat loss and tightly constructed to minimize unplanned air exchange. Barns relying on natural air exchange must have sufficient and properly located openings to take advantage of breezes and thermal buoyancy (the "chimney effect").

Natural Ventilation Systems

Naturally ventilated tie stall barns use sidewall openings only or combinations of sidewall and ridge or stack openings. Figures 1-3 illustrate these systems and their requirements. For all systems the barn must be well constructed and insulated similarly to a mechanically ventilated barn. Openings require adjustment in response to wind and temperature changes. Automatic temperature-adjusting controllers will respond to changes even if no one is in the barn. Each sidewall and ridge or stack should be controlled separately.

Winds can affect one end of a long barn differently than the other end. In barns longer than 100 feet, divide long openings to allow one end to be adjusted independent from the other.

Figure 1. Completely insulated tie stall barn with automatically controlled continuous sidewall openings.

Characteristics

  • Continuous adjustable sidewall opening, 4 to 6 feet high.
  • Large doors or removable panels in end-wall for increased hot weather ventilation.
  • Manual adjustment for warm seasons
  • Thermostat-controlled automatic adjustment provides better conditions during changeable freezing weather.
  • Large doors or removable panels in endwall for increased hot weather ventilation.
  • Excellent air/vapor barrier between animal space and attic space.
  • Ventilate all enclosed attic spaces above animal areas (1 square inch of opening for each 1 square foot of ceiling area).

Figure 2. Completely insulated tie stall barn with automatically controlled ventilation ridge and sidewall openings (Source: Milne, R.J. Natural Ventilation of Tie Stall Dairy Barns.)

Characteristics

  • Ridge exhaust, 1 square foot per 100 square feet of floor area.
  • Continuous adjustable sidewall opening, 4 to 6 feet high.
  • Separate thermostat-controlled operation of ridge and sidewall.
  • Large doors or removable panels in end-wall for increased hot weather ventilation.
  • Excellent air/vapor barrier between animal space and attic space.
  • Ventilate all enclosed attic spaces above animal areas (1 square inch of opening for each 1 square foot of ceiling area).

Figure 3. Completely insulated tie stall barn with automatically controlled ventilation stacks and sidewall openings (Source: Milne, R.J. Natural Ventilation of Tie Stall Dairy Barns.)

Characteristics

  • Exhaust stacks, 1 square foot per 100 square feet of floor area.
  • Space stacks, 30 to 50 feet.
  • Continuous adjustable sidewall opening, 4 to 6 feet high.
  • Large doors or removable panels in end-wall for increased hot weather ventilation.
  • Separate thermostat-controlled operation of exhaust stacks and sidewalls.
  • Excellent air/vapor barrier between animal space and attic space.
  • Ventilate all enclosed attic spaces above animal areas (1 square inch of opening for each 1 square foot of ceiling area).

Insulation

Naturally ventilated tie stall barns should be insulated to the same levels as mechanically ventilated barns. This is important to conserve heat and minimize condensation on wall and ceiling surfaces. Typical recommendations for Pennsylvania are R = 9 - 19 for sidewalls and R = 12 - 30 for ceiling. Colder regions should use higher values. Using a moisture resistant insulation will minimize damage from any moisture that may migrate from the animal space into the insulation.

Controlling Moisture Movement

Livestock barns that are kept above freezing require careful steps to protect insulation and unheated attic spaces from the moist air in the animal space. Steps to achieve this goal include moisture resistant insulation, properly installed air/vapor barriers and ventilation of unheated areas especially attic spaces. It is difficult to install and maintain satisfactory sealed joints between panels of rigid board insulation with a vapor barrier facing. An excellent air/vapor barrier such as a continuous 6 mil plastic film is recommended

Attic spaces above warm animal spaces should be ventilated by providing 1 square inch of opening for each square foot of ceiling area. The openings should be divided equally between the high point (ridge and upper end wall) and low point (eaves and lower end walls) to provide for intake and exhaust of air.

Figure 4. Warm moist barn air can easily flow into enclosed attic spaces. Proper design and careful construction will minimize this problem.

Barns with only sidewall ventilation are a particular challenge. These barns exhaust warm moist air along both sidewalls. On still days this plume of warm moist air may flow into attic ventilation openings along the eaves (Figure 4). Large quantities of warm moist air diverted into attic spaces will condense or freeze on cold roof surfaces and subsequently cause damage to insulation and building components. To minimize this problem, provide as much attic ventilation opening space on end walls and at the ridge as practical. Eaves should be built with solid soffits. Slots for attic ventilation should be placed along vertical fascias. All cracks and crevices at insulation joints, light fixtures, poles or other penetrations through the insulation and vapor/air barrier must be tightly sealed. Even small openings and cracks can allow large amounts of warm moist air to flow into the cold attic by convection.

Barns with ridge or stack outlets also require good air/vapor barriers. However, because warm moist air is likely to exit from the stack or ridge during still conditions there is less chance it will be diverted into the attic space. At times when stacks or ridges are providing little draw it is still possible for air to flow by convection through cracks into the attic.

Sidewall Closures

Continuous, easily adjusted sidewall openings are necessary for satisfactory ventilation. Curtains, panels, or gangs of windows that allow adjustment of large sections from one point are recommended. Insulated curtains, panels or windows will minimize condensation and heat loss. However, insulated curtains or panels do not allow light to enter the barn. The alternative of using single ply translucent curtains results in extra heat loss and condensation on the curtains during cold weather. Water running off of curtains can damage building components and cause wet feed mangers.

Ridge and Stack Openings

Continuous open ridges, sections of open ridges, or intermittent stacks can easily be installed in new single story barns. Stacks are easier to install in two story barns and existing single story barns being converted to natural ventilation. Open ridges should not be used with king post type trusses. Portions of trusses or roof rafters exposed within the open ridge area should be protected by painting or sealing with good quality paint or exterior urethane sealer. Continuous ridge openings can remove moist air from the entire length of the barn. However, they are more difficult to control when low ventilation rates are required. Also, wind may result in air flowing in portions of the ridge and flowing out at other locations. Proper attic ventilation is more difficult with continuous ridge openings because the ridge opening interferes with attic exhaust openings. A system that spaces adjustable ridge outlets from the stable along half the roof length and attic vents between them accomplished both requirements. Chimneys or stacks with adjustable dampers are the easier to control when very small exhaust openings are desired. The sidewalls of chimneys or ridges must be insulated all the way to the exhaust opening to prevent condensation of warm moist air. Chimney caps or ridge covers must be high enough to allow free air flow beneath them. The total open area beneath the cap should be larger than the ridge or stack area. The undersides of chimney covers or ridge caps should be insulated to prevent condensation and dripping.

Figure 5. Adjustable ridge openings spaced along barn length provide better air flow control. Attic vents are placed between ridge openings.

Summary

A properly designed and operated natural ventilation system will provide healthful conditions for dairy cattle in tie stall barns. Regular adjustment of ventilation openings is necessary to account for changes in wind speed, wind direction, and temperatures. Automatic adjustment using thermostats and power operators is best. Regular observation is necessary if automatic control is not possible. Barns with stacks or ridges seem to be more tolerant of less control than barns with only sidewall openings. It is important to have sufficient air exchanges to keep the barn air dry and fresh.

Prepared by Robert E. Graves, Professor emeritus, Agricultural Engineering

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