1. AMBIGAINE: a tool to aid the drilling of air
circulation ducts in feeding rooms
P. Robin1, G. Amand2 , M. Pertusa2
1INRA, 2ITAVI - France
2. Lille - 22 to 24 February 2017
Livestock housing: let's build the future 2
Summary
• Reminders about the problem of air circulation
• Reminders about the phenomena associated with
blowing air through a duct
– Fan-blown air
– Air exit through the holes in the duct
– Impact on the choice of drilling
• Presentation of the tool to help calculate duct
perforations
6. Blowing air through a duct
– Static and dynamic pressure in the duct
Static pressure
Dynamic pressure
Static pressure
Dynamic pressure
At start of duct
At end of duct
• Two types of pressure are exerted:
static pressure is exerted against the walls
swelling the duct
dynamic pressure propels the air in the
duct and decreases when speed decreases
• Total pressure decreases as you move away
from the fan (“load loss” due to friction of the
air against the walls)
• Dynamic pressure turns into static pressure
with reduction of flow
7. Blowing air through a duct
– Fan-blown air (example FANCOM 3463 17,000 m3/h)
• Static pressure
increases with
frequency
• Flow too
• Flow decreases
if static
pressure
increases
8. Blowing air through a duct
– Air rotation in the duct
• The rotation of the fan causes the air in the duct
to rotate
If the holes are drilled symmetrically, the
air reaches a different location depending
on the side of the duct
To get the same ventilation on both sides
of the duct, drilling must be asymmetrical
• The effect of rotation decreases with air speed
it becomes negligible at a certain distance
from the fan
(effect of flow straightener?)
9. Blowing air through a duct
– Blow cone
• On leaving the duct, the blown air pushes the air
outside the duct
the speed at the centre decreases with
distance from the hole
the cone diameter increases with distance
from the hole
the length increases with the diameter of the
hole
• At end of duct the cone leaves perpendicularly to
the duct wall
• At the start of the duct, the cone is DIVERTED
forwards by the dynamic pressure and to the side
by rotation => increased distance between duct
and housing
10. Blowing air through a duct
– Consequences on the drilling plan
• Diameter of holes greater at start of duct as:
Longer duct-duck distance
Lower static pressure
• Offset holes maximum at start of duct =>
compensation of deviation due to:
• air rotation
• fan exit speed
Static pressure
Dynamic pressure
11. Blowing air through a duct
– Consequences on the drilling plan
• Distribution of the air in the housing varies
according to frequency:
different flow and static pressure induce a
different cone angle for the same hole
different static pressure induces a different
speed cone
• For a given frequency, flow decreases and
pressure in the duct increases when the
number of holes and their diameter decrease
=> flow and pressure depend on the drilling
plan