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Tunnel
Ventilation Barns |
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| Open endwall
on a tunnel-ventilated freestall barn. The goal is to provide approximately
1 sq. ft. of endwall opening per 400 cfm of in-place fan capacity.
This goal is generally met by fully opening the endwall as shown.
Notice that there are no major obstructions to block airflow at cow
level. (Note, this barn was not in the tunnel ventilation mode when
this image was taken.) |
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| Endwall opposite
of the inlet. A large number of high capacity fans are used to draw
air through the barn. Total fan capacity is determined by meeting
the greatest of two criteria: 1) ensuring an average air velocity
of 400 to 600 fpm in the tunnel barn, and 2) providing an air exchange
(ventilation) rate 1,000 cfm per cow. Fans should be position ed as
low as possible on the endwall to help keep airflow at cow level.
The lowest fans should be on the primary (first) stage of ventilation
if a stage ventilation control is used. |
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| Many times insufficient
endwall space exists in order to mount all tunnel ventilation fans.
Fans can be also located on the sidewall as shown here, although research
as found that as much as 25 percent reduction of fan capacity is lost
with fans mounted on the sidewall. Why? Because moving air has both
mass and velocity, and therefore momentum. The momentum of the air
moving longitudinally down the barn will tend to carry it past the
sidewall fans. If fans are mounted on the sidewall, it is best to
stack fans in vertical columns rather than position them in horizontal
rows as is shown in this picture. |
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| An alternate
way to mount fans is to build the endwall at an angle with respect
to the sidewall as shown here. Field research has shown that fans
mounted in this fashion function well with little loss in efficiency.
Notice a panel fan is positioned in the gable endwall to tunnel ventilate
the attic space. |
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| This is a floor
plan for the barn shown above. Notice that additional length is added
to the barn in order to mount fans in this fashion. This 3-row freestall
barn has one less overhead door than is conventionally used for this
barn configuration. Also notice that fans are positioned to enhance
airflow in the animal zone of the barn. |
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| This is an inside
image of the tunnel-ventilated 3-row barn described above. Notice
that the barn has a flat ceiling with a continuous moisture barrier.
A ceiling is used to reduce the overall required fan capacity for
the barn by reducing the building's cross sectional area perpendicular
to the direction of airflow. A ceiling also helps keep meaningful
airflow at cow level when the barn is tunnel-ventilated (summer),
but limits natural air exchange during natural ventilation times (fall,
winter, and spring). |
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| Vertical baffles
are sometimes positioned in a barn to help keep airflow at cow level.
Baffles in this picture are placed approximately 40 feet apart and
are made from curtain sidewall material. Baffles are not as effective
as a ceiling in tunnel-ventilated barns but are more friendly during
non-tunnel (natural) ventilation periods. |
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