8.8 Duct Material Selection
319
• There will be less friction than in spiral ducts.
• They can only be used in forcing systems.
• They are very light.
• They can generally only be used for short lengths of ducting.
8.9 Determination of Duct Diameter
In principle, a duct with the largest possible diameter is always advisable, as this
reduces the pressure that the fan must supply in order to overcome friction losses.
This leads to the need for a less powerful fan and the lower pressure will, in turn,
reduce leaks. However, the duct diameter is ultimately limited by the height of the
mining machinery and the dimensions of the gallery where it will be situated. To
aid selection, many manufacturers collate data on different types of ducting and
their potential performance at different diameters using various airflow rates (e.g.
Table 8.4).
Table 8.4 Minimum duct diameters for different ventilation airflow rates and recommended
maximum velocities. Modified from de la Vergne (2008, p. 236)
Airflow rate Plastics or fibre
Metal
Inflatable
Spiral
Q
(m 3 s −1 )
D
(cm)
v
(m s −1 )
D
(cm)
v
(m s −1 )
D
(cm)
v
(m s −1 )
D
(cm)
v
(m s −1 )
2.4
38.1 21.1
40.6 18.5
43.2 16.4
50.8 11.8
4.7
53.3 21.1
55.9 19.2
58.4 17.5
71.1 11.8
7.1
66.0 20.8
68.6 19.2
73.7 16.6
86.4 12.1
9.4
76.2 20.6
78.7 19.3
83.8 17.0
101.6 11.6
18.9
109.2 20.2
111.8 19.3
119.4 16.9
142.2 11.9
23.6
121.9 20.2
124.5 19.4
132.1 17.2
157.5 12.1
35.4
149.9 20.1
154.9 18.8
162.6 17.0
198.1 11.5
47.2
172.7 20.1
177.8 19.0
188.0 17.0
228.6 11.5
8.10 Matching Duct Length and Fan Selection
The size of the fan is chosen bearing in mind that it will ultimately need to overcome
the losses that will occur in the duct as the gallery is excavated, thus it is necessary to
increase its length. In other words, the chosen fan must be capable of ventilating the
final length of the cul-de-sac. In the initial stages of excavation, therefore, it will be
oversized and its airflow rate must be regulated. Nowadays, this regulation tends to
be carried by means of a variable-frequency drive that acts to moderate the rotation
319
• There will be less friction than in spiral ducts.
• They can only be used in forcing systems.
• They are very light.
• They can generally only be used for short lengths of ducting.
8.9 Determination of Duct Diameter
In principle, a duct with the largest possible diameter is always advisable, as this
reduces the pressure that the fan must supply in order to overcome friction losses.
This leads to the need for a less powerful fan and the lower pressure will, in turn,
reduce leaks. However, the duct diameter is ultimately limited by the height of the
mining machinery and the dimensions of the gallery where it will be situated. To
aid selection, many manufacturers collate data on different types of ducting and
their potential performance at different diameters using various airflow rates (e.g.
Table 8.4).
Table 8.4 Minimum duct diameters for different ventilation airflow rates and recommended
maximum velocities. Modified from de la Vergne (2008, p. 236)
Airflow rate Plastics or fibre
Metal
Inflatable
Spiral
Q
(m 3 s −1 )
D
(cm)
v
(m s −1 )
D
(cm)
v
(m s −1 )
D
(cm)
v
(m s −1 )
D
(cm)
v
(m s −1 )
2.4
38.1 21.1
40.6 18.5
43.2 16.4
50.8 11.8
4.7
53.3 21.1
55.9 19.2
58.4 17.5
71.1 11.8
7.1
66.0 20.8
68.6 19.2
73.7 16.6
86.4 12.1
9.4
76.2 20.6
78.7 19.3
83.8 17.0
101.6 11.6
18.9
109.2 20.2
111.8 19.3
119.4 16.9
142.2 11.9
23.6
121.9 20.2
124.5 19.4
132.1 17.2
157.5 12.1
35.4
149.9 20.1
154.9 18.8
162.6 17.0
198.1 11.5
47.2
172.7 20.1
177.8 19.0
188.0 17.0
228.6 11.5
8.10 Matching Duct Length and Fan Selection
The size of the fan is chosen bearing in mind that it will ultimately need to overcome
the losses that will occur in the duct as the gallery is excavated, thus it is necessary to
increase its length. In other words, the chosen fan must be capable of ventilating the
final length of the cul-de-sac. In the initial stages of excavation, therefore, it will be
oversized and its airflow rate must be regulated. Nowadays, this regulation tends to
be carried by means of a variable-frequency drive that acts to moderate the rotation