Static pressure…


in a tunnel-ventilated house is basically an indicator of
how hard the exhaust fans are working.
High pressure - high work level



Tunnel Ventilation and Static
Pressure
high level of fan restriction
reduced air moving capacity…reduced cooling
Low pressure - low work level


minimum fan restriction
maximum air flow...maximum cooling
Michael Czarick
The University of Georgia
How does static pressure affect a our ability
to cool birds?
0.26
0.24
0.2
0.22
0.18
0.16
0.1
0.12
Cfm
0.08
0.06
0.04
0
Pressure
0.14
22,000
20,000
18,000
16,000
14,000
12,000
10,000
8,000
6,000
4,000
2,000
0
0.02
Cfm
Fan output Vs. Static pressure
Static Pressure
40’ X 500’ dropped ceiling house
Wind-chill effect at 85oF



0.15”
fan capacity=16,500 cfm
air velocity = 445 ft/min
22,000
20,000
18,000
16,000
14,000
12,000
10,000
8,000
6,000
4,000
2,000
0
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
0.22
0.2
0.18
0.16
0.14
0.12
0.1
0.08
0.06
0.04
0
0

0.05”
fan capacity=20,000 cfm
air velocity =540 ft/min
0.02

Cfm

Wind Chill (F)
(Ten fans, cross-sectional area = 370 ft2)
50 100 150 200 250 300 350 400 450 500 550 600
Air Velocity (ft/min)
Static Pressure
1
550 ft/min
350 ft/min
100.0°F
100
100.0°F
100
90
90
80.0
78.9
89.2
85.1
80
80
70.0°F
70.0°F
Static pressure can also affect air exchange
rates

Lower air exchange, greater temperature differential.
40’ X 500’ dropped ceiling house
(ten fans, cross-sectional area = 370 ft2)


Low pressure



0.05”
fan capacity=20,000 cfm
air velocity =540 ft/min
wind chill = 12oF
temp diff = 5oF





0.15”
fan capacity=16,500 cfm
air velocity = 445 ft/min
wind chill = 8oF
temp diff = 6oF

Possibly higher
High pressure
To optimize fan performance…
(air velocity and exchange)

We would like to keep static pressure as low as
practically possible.
What creates work/pressure for the tunnel
fans?

There are basically five areas in a poultry house that can
cause an increase in the static pressure the fans are
working against:
2

air speed at the inlet decreases
static pressure decreases
100

Static Pressure/Work
600
Increase the amount of opening
Air Velocity
0.07
0.06
0.05
0.04
0.03
0.02
0.01
0
550

air speed at the inlet increases
static pressure increases
500
Decrease the amount of opening


Relationship between tunnel inlet speed and
static pressure
static pressure (")

Amount of inlet opening
What is in the inlet opening (i.e., pads, light traps, nothing, etc.)
450
Relationship between tunnel inlet opening
and static pressure

400
5)

350
4)
Two factors that determine the amount of work required
to pull air into a house:
300
3)

250
2)
Tunnel inlet area
200
Tunnel inlet
Transition area
Area between inlet and exhaust (pipe)
Exhaust inlet – shutters/light traps
Exhaust outlet – wind or hoods
1)
150
Areas of work
air velocity
Example…40’ X 500’ house



Eight fans which move 25,000 cfm each
4’ X 50’ curtain opening on both sides of the house
How fast will the air enter the house?
40’ X 500’ house

Entrance velocity = cfm / opening area

Cfm =





Opening area
= 8 X 25,000 cfm
= 200,000
= 4’ X 50’ X 2 sides
= 400 ft2
Entrance velocity = 200,000 cfm / 400ft2
= 500 ft/min
3
600
550
500
450
400
350
300
100

0.07
0.06
0.05
0.04
0.03
0.02
0.01
0
250

Eight fans which move 25,000 cfm each
4’ X 50’ curtain opening on both sides of the house
How fast will the air enter the house?
How much work/pressure is required to pull the air into
the house?
200

150

Relationship between tunnel inlet speed and
static pressure
static pressure (")
Example…40’ X 500’ house
air velocity
40’ X 500’ house


How fast will the air move down the house?
Velocity = Cfm / House cross-sectional area
40’ X 500’ house




House width = 40’
Side wall = 8’
Peak ceiling height = 10’
Fan capacity = 200,000 cfm
10’
8’
40’





40’ X 500’ house

Speed
= Cfm / (width X (peak + side wall)/2
= 200,000 / (40’ X (10’ + 8’)/2)
= 200,000 / (40’ X 9’)
= 200,000 / 360 ft2
= 555 ft/min
What would happen if we decrease the
tunnel inlet opening size to 3’?
The air will move down the house faster than it enters
because the house cross-sectional area is smaller than the
inlet area
500 ft/min
555 ft/min
500 ft/min
4
40’ X 500’ house
700
650
600
550
500
450
400
350
Entrance velocity = 200,000 cfm / 300ft2
= 667 ft/min
100

Cfm =
300

0.09
0.08
0.07
0.06
0.05
0.04
0.03
0.02
0.01
0
250

= 3’ X 50’ X 2 sides
= 300 ft2
= 8 X 25,000 cfm
= 200,000
200
Opening area

150


The level of work/pressure would increase
Entrance velocity = cfm / opening area
static pressure (")

air velocity
How fast would the air move down the
house?
40’ X 500’ house




House width = 40’
Side wall = 8’
Peak ceiling height = 10’
Fan capacity = 200,000 cfm
10’
8’
40’





Just because the air comes in faster doesn’t mean
the air will move down the house faster
Speed
= Cfm / (width X (peak + side wall)/2
= 200,000 / (40’ X (10’ + 8’)/2)
= 200,000 / (40’ X 9’)
= 200,000 / 360 ft2
= 555 ft/min
Tunnel inlet pressure

Evaporative cooling pads…how do fans affect
pressure/work?
5
Evaporative cooling pads and static
pressure

It is harder to pull air through a pad than through a clear
opening…
Evaporative cooling pads and static
pressure


Evaporative cooling pads and static
pressure.


It is harder to pull air through a pad than through a clear
opening…
How much harder depends on the construction of the
evaporative cooling pad

Thickness

Thicker pads…higher pressure
It is harder to pull air through a pad than through a clear
opening…
How much harder depends on the construction of the
evaporative cooling pad
Evaporative cooling pads and static
pressure.


It is harder to pull air through a pad than through a clear
opening…
How much harder depends on the construction of the
evaporative cooling pad


Thickness
Flute angles



It is harder to pull air through a pad than through a clear
opening…
How much harder depends on the construction of the
evaporative cooling pad



Thickness
Flute angles
Flute size

Smaller flutes = higher pressure
Relationship between tunnel inlet speed and
static pressure
0.2
Static Pressure (")
Evaporative cooling pads and static
pressure.
Steeper flutes…higher pressure
0.18
0.16
0.14
0.12
0.1
0.08
0.06
0.04
0.02
0
0
50
100
150
200
250
300
350
400
450
500
Velocity (ft/min)
no pad
6
Relationship between tunnel inlet speed and
static pressure
0.2
0.18
0.16
0.14
0.12
0.1
0.08
0.06
0.04
0.02
0
Static Pressure (")
Static Pressure (")
Relationship between tunnel inlet speed and
static pressure
0
50
100
150
200
250
300
350
400
450
0.2
0.18
0.16
0.14
0.12
0.1
0.08
0.06
0.04
0.02
0
500
0
50
Velocity (ft/min)
no pad
2"
Static Pressure (")


250
300
350
400
450
500
350
400
450
4"
2"
Thickness
Flute angles

200
300
It is harder to pull air through a pad than through a clear
opening…
How much harder depends on the construction of the
evaporative cooling pad

150
250
Evaporative cooling pads and static
pressure.

100
200
no pad
0.2
0.18
0.16
0.14
0.12
0.1
0.08
0.06
0.04
0.02
0
50
150
Velocity (ft/min)
Relationship between tunnel inlet speed and
static pressure
0
100
Steeper flutes…higher pressure
500
Velocity (ft/min)
4"
2"
6"
What would static pressure if we added
pads to the previous example?
500 ft/min
500 ft/min
Relationship between tunnel inlet speed and
static pressure
Static Pressure (")
no pad
0.24
0.22
0.2
0.18
0.16
0.14
0.12
0.1
0.08
0.06
0.04
0.02
0
0
50
100 150 200 250 300 350 400 450 500 550
Velocity (ft/min)
no pad
4"
2"
6"
7
Fan output Vs. Static pressure
No pad
22,000
20,000
18,000
16,000
14,000
12,000
10,000
8,000
6,000
4,000
2,000
0
6”
2”
0.26
0.24
0.2
0.22
0.18
0.16
0.14
0.1
0.12
0.08
0.06
0.04
0
4”
0.02
Cfm
How would this affect fan performance?
Static Pressure
To keep static pressure from becoming
excessive...
We have to increase pad area….pull air through the pads
slower…which will lower pressure/work
Entrance pad pressure example:
(40’ X 500’ – 200,000 ft3/min)


As a general rule we do not want the pressure required
to pull air through the pads to exceed 0.06” (maximum).
Relationship between tunnel inlet speed and
static pressure
How fast can the air be drawn through the 6” pads so the
pad static pressure/work does not exceed 0.06”?
Static Pressure (")

What is an excessive pressure?
0.1
0.09
0.08
0.07
0.06
0.05
0.04
0.03
0.02
0.01
0
0
50
100
150
200
250
300
350
400
450
500
Velocity (ft/min)
6"
8
How much 6” pad do we need?
40’ X 500’ house

Pad area
How much 6” pad do we need?
40’ X 500’ house
= cfm / velocity
= 200,000 ft3/min / 375 ft/min
= 533 ft2








But keep in mind that pad pressure will
increase over time
= cfm / velocity
= 200,000 ft3/min / 375 ft/min
= 533 ft2
Pad system height
= 5’
Pad system length
= 533 ft2 / (2 sides X 5’)
= 53 ft
Tunnel inlet pressure

As pads become dirty pressure/work increases
What if we wanted to lower the initial
pressure to 0.05”
Static pressure – dirty vs. clean
Pressure
Pad area
0.12
0.11
0.1
0.09
0.08
0.07
0.06
0.05
0.04
0.03
0.02
0.01
0

How much pad area would we need to install?
dirty
new
100
150
200
250
300
350
Air speed through pad (ft/min)
400
450
9
Static Pressure (")
Relationship between tunnel inlet speed and
static pressure
How much 6” pad do we need?
40’ X 500’ house

0.1
0.09
0.08
0.07
0.06
0.05
0.04
0.03
0.02
0.01
0





0
50
100
150
200
250
300
350
400
450
Pad area
= cfm / velocity
= 200,000 ft3/min / 350 ft/min
= 570 ft2
Pad system height
= 5’
Pad system length
= 570 ft2 / (2 sides X 5’)
= 57 ft
500
Velocity (ft/min)
6"
Pressure
Adding pad does not reduce the importance
of keeping pads clean
0.12
0.11
0.1
0.09
0.08
0.07
0.06
0.05
0.04
0.03
0.02
0.01
0
1)
2)
dirty
new
100
150
200
250
300
350
Air speed through pad (ft/min)
400

Anytime you increase the speed of the
air…work/pressure is required.
Air turning and tumbling can also add to pressure
350 ft/min
555 ft/min
Tunnel inlet
Transition area
0.05”
450
Transition pressure

Areas of work
Transition pressure as a function of average
house air speed
Air speed
(ft/min)
400
Pressure
0.02”
500
0.03”
600
0.045”
700
0.06”
800
0.08”
350 ft/min
10
Areas of work
1)
2)
Tunnel inlet
Transition area
It is very important to realize that
pressure/work is additive in a tunnel house

Pressure

0.05”
0.05”
0.03”
Tunnel inlet pressure can be affected by
other factors as well…


= pad pressure + transition pressure
= 0.05” + 0.03”
Tunnel curtain/doors can cause an increase in
work/pressure if they are smaller than the pad area
Pressure/restriction tends to be minimal if the opening is
80% of the pad area (0.01” or less)
0.03”
So a tunnel door, depending on size/construction
can add to the total pressure

Pressure

= pad + door + transition pressure
= 0.06” + 0.01” + 0.03”
0.01”
0.06”
0.03”
Tunnel inlet pressure can also be affected
by other factors such as hoods and shades
Anything that causes the air speed to increase or the
air to turn will increase pressure
11
Tunnel doors, hoods, screens are not always
a problem


If designed properly they will minimally increase the
pressure if any (0.01” or less)
If the opening size is similar to the pad size the increase
in pressure will be minimal.
Shade structures can add to the total
pressure

Pressure

= pad + door + shade + transition pressure
= 0.06” + 0.01” + 0.01” + 0.03”
0.01”
0.01”
0.06”
0.03”
Areas of work
1)
2)
3)
Area between inlet and exhaust
Tunnel inlet
Transition area
Area between inlet and exhaust (pipe)
Pressure gain for air flowing down the
typical tunnel ventilated broiler house
Air speed
(ft/min)
Pressure
gain per 100’


Typically minimal 0.01” to 0.03”
Function of house length, air speed, and “pipe
smoothness”
40’ X 500’ house with 50’ of evaporative
cooling pad


300
0.002”

400
0.0035”

500
0.006”
600
0.008”
Average air speed = 555 ft/min
Pipe pressure
= length/100 X pipe pressure factor
= 450 / 100 X 0.007
= 0.03”
12
Pressure is additive

Pressure
Air deflectors?
= pad + transition + pipe
= 0.05” + 0.03” + 0.03

0.05”
0.03”
0.03”
0.05”
Air deflectors

Increase static pressure…




approximately 0.005” - 0.01”
depends on deflector geometry
depends on deflector spacing
This pressure increase is per deflector!


Cages?
10 deflectors = 10 X 0.005” =.05”
Pressure increase is generally manageable if deflectors are
not excessively restrictive

9’ height
Static pressure increase per 100’ of travel in
broiler and caged layer houses
In caged layer houses pipe pressure is
typically 0.10” or more
0.040
Commercial layer house
0.030
0.025
0.020
0.015
Broiler house
0.010
0.005
600
550
500
Average air speed (ft/min)
450
400
350
300
250
200
150
100
0
0.000
50
Static pressure rise
0.035
13
Broiler breeder house with nests?
Static pressure increase per 100’ of travel
0.040
Commercial layer houses
Static pressure rise
0.035
0.030
0.025
0.020
0.015
Breeder house
0.010
Broiler houses
X
0.005
600
550
500
Average air speed (ft/min)
450
400
350
300
250
200
150
100
0
Pipe pressure in a broiler breeder house is
typically between 0.04” and 0.08”
50
0.000
In a broiler breeder house the pipe pressure
can be a substantial portion of the total

Pressure


= pad + transition + pipe
= 0.05” + 0.03” + 0.08”
=
0.05”
0.03”
0.08”
0.05”
Areas of work
1)
2)
3)
4)
Tunnel inlet
Transition area
Area between inlet and exhaust (pipe)
Exhaust inlet – shutters/light traps
Typically “zero” because it is taken into
account in fan tests.

Fan tests are conducted with the fan shutter in place so
its “pressure” is already factored in when it comes to fan
performance.
14
But, dirty shutters can increase the
pressure that a fan is working against




Pressure is additive
Fan shutters can collect up to 1/4 of pound of dust a day
depends heavily on the type of cooling system

Pressure

Which increases the static pressure the fans are working
against.
A dirty shutter can increase the pressure the fans are
working against by 0.05” points or more thereby
decreasing the air moving capacity of the fan.
= pad + trans. + pipe + dirty shutter
= 0.05” + 0.03” + 0.03” + 0.05”
0.05”
0.05”
0.03”
0.03”
0.05”
Areas of work
1)
2)
3)
4)
5)
Wind pressure
Tunnel inlet
Transition area
Area between inlet and exhaust (pipe)
Exhaust inlet – shutters/light traps
Exhaust outlet – wind or hoods

Wind pressure (in)
Pressure vs. Wind Speed
Wind can increase the pressure fans are working against.
Pressure is additive

0.5
0.45
0.4
0.35
0.3
0.25
0.2
0.15
0.1
0.05
0
Pressure

= pad + door + trans. + pipe + wind
= 0.05” + 0.03” + 0.03” + 0.10”
0.10”
0.05”
0.03”
0
5
10
15
Wind speed (mph)
20
25
0.03”
30
0.05”
15
Reducing the effect of the wind on exhaust
fans
Reducing the effect of the wind on exhaust
fans
Other external pressures
Other external pressures

Screens
Dust/odor control devices

Fan hoods
If we assume no wind and clean shutters…




Pressure
= pad + trans. + pipe
= 0.05” + 0.03” + 0.03”
= 0.11”
This is the total pressure the fans are working against
0.05”
0.03”
0.03”
0.05”
16
Pad static pressure does not increase
linearly…
800
750
700
650
600
550
500
450
400
350
300
250
200
150
100
0
0.24
0.22
0.2
0.18
0.16
0.14
0.12
0.1
0.08
0.06
0.04
0.02
0
50
Static pressure
What happens to static pressure as we
increase our air velocity in our houses?
Air speed through pad
Transition static pressure does not increase
linearly…
Pipe static pressure does not increase
linearly…
0.090
0.014
800
750
700
650
600
550
500
450
400
350
300
250
200
0
800
750
700
650
600
550
500
450
400
350
300
250
200
0.24
0.22
0.2
0.18
0.16
0.14
0.12
0.1
0.08
0.06
0.04
0.02
0
0
More simply put, if you double the velocity of a fluid, the
pressure/work required to move the fluid increases four
fold
Static pressure
Law of physics discovered by Daniel Bernoulli in the early
1700’s
Tunnel velocity (ft/min)
For instance double the speed of the air
through a pad the pressure increases 4 X
Pressure increases with the square of velocity


800
750
700
650
Tunnel velocity (ft/min)
600
550
500
450
400
350
300
250
200
150
0.000
100
0.002
0.000
0
0.010
Relationship between air speed and static
pressure

0.004
150
0.020
0.006
100
0.030
0.008
150
0.040
0.010
100
0.050
50
0.060
0.012
50
Static pressure increase
0.070
50
Static pressure increase
0.080
Air speed through pad
17
Double the air speed in a house the
transition static pressure increases 4 X
Double the air speed down the house the
pipe pressure increases 4 X
0.090
0.014
800
750
700
650
600
550
500
450
400
350
Tunnel velocity (ft/min)
Lets look at an example…
500’ house with 400 ft/min
But the transition pressure and pipe pressures can not be
reduced.
Transition pressure as a function of average
house air speed
Pad pressure
0.05”
Air speed
(ft/min)
0.1
0.09
0.08
0.07
0.06
0.05
0.04
0.03
0.02
0.01
0
Air speed through pad
500
450
400
350
300
250
200
150
100
50
100
0
Static pressure

0
800
750
700
650
Tunnel velocity (ft/min)
600
550
500
450
400
350
300
250
200
150
0.000
100
0.002
0.000
0
0.010
Now pad static pressure isn’t necessarily a problem
because we can keep adding more to keep the
pressure down.

0.004
300
0.020
0.006
250
0.030
0.008
200
0.040
150
0.050
0.010
100
0.060
0.012
50
Static pressure increase
0.070
50
Static pressure increase
0.080
Pressure
gain
0.00”
200
0.01”
300
0.013”
400
0.02”
500
0.03”
600
0.045”
700
0.06”
800
0.08”
18
300
0.002”
400
0.0035”
500
0.006”
600
0.008”
700
0.012”
800
0.016”
Total pressure




Pad pressure
Transition pressure
Pipe pressure
Total
= 0.05”
= 0.02”
= 0.015
= 0.085”
Pad pressure stays the same because we
can simply add more pad…
0.05”
500
450
400
0.1
0.09
0.08
0.07
0.06
0.05
0.04
0.03
0.02
0.01
0
350

300
Now let’s increase the air speed to 600
ft/min
0.001”
250
0.0035” X 450/100 = 0.015”
0
200
200

Pressure
gain per 100’
100
150
Pipe pressure
Air speed
(ft/min)
50

Pipe pressure
= 0.05”
= 0.02”
= 0.07”
0

Pad pressure
Transition pressure
Total
Static pressure

100
Total pressure?
Air speed through pad
19
Transition pressure increases…
Air speed
(ft/min)
Pressure
gain
100
0.00”
200
0.01”
300
0.013”
400
0.02”
500
0.03”
600
0.045”
700
0.06”
800
0.08”



Pipe pressure increases…
Air speed
(ft/min)



Pad pressure
Transition pressure
Pipe pressure
Total
Pad pressure
Transition pressure
Total
= 0.05”
= 0.045”
= 0.095”
Pipe pressure
Pressure
gain per 100’
100
0
200
0.001”
300
0.002”
400
0.0035”
500
0.006”
600
0.008”
700
0.012”
800
0.016”
Total pressure

Total pressure?

0.006” X 450/100 = 0.027”
800 ft/min?
= 0.05”
= 0.045”
= 0.027”
= 0.122”
20
Pad pressure stays the same…
Transition pressure increases…
0.05”
Air speed
(ft/min)
0.1
0.09
0.08
0.07
0.06
0.05
0.04
0.03
0.02
0.01
0
500
450
400
350
300
250
200
150
100
50
100
0
Static pressure

Air speed through pad
Total pressure?



Pad pressure
Transition pressure
Total
Pipe pressure

0.016” X 450/100 = 0.072”
Pressure
gain
0.00”
200
0.01”
300
0.013”
400
0.02”
500
0.03”
600
0.045”
700
0.06”
800
0.08”
Pipe pressure increases…
= 0.05”
= 0.08”
= 0.13”
Air speed
(ft/min)
Pressure
gain per 100’
100
0
200
0.001”
300
0.002”
400
0.0035”
500
0.006”
600
0.008”
700
0.012”
800
0.016”
Total pressure




Pad pressure
Transition pressure
Pipe pressure
Total
= 0.05”
= 0.08”
= 0.072”
= 0.202”
21
Tunnel speed vs. Total static pressure
0.25


0.2
Static pressure
Example of what happens when we don’t
take pressure into account

0.15


0.1

50’ X 560’ X 9.25’ broiler house
We want an air velocity of 800 ft/min
How much fan capacity (cfm) do we need to install?
Cfm = air velocity X house cross-sectional area
= 800 ft/min X (9.25’ X 49’)
= 362,600 cfm
0.05
0
600
Air velocity
800
Traditionally we sized our fans at 0.10”







Choretime – 52” high capacity
0.05”
= 29,100 cfm
0.10”
= 27,300 cfm
0.15”
= 25,000 cfm
0.20”
= 22,700 cfm
0.25”
= 20,200 cfm
0.30”
= 17,000 cfm
How much pad area?









Pad area
= total cfm @ 0.05” / 350
= 378,300 / 350
= 1,080 square feet
Pad length = Pad area / Pad height
= 1,080 / 4.7’
= 230 linear feet
Or
= 115 feet per side
Let’s put in 120’ feet per side to be safe
How many fans?



# of Fans = Total cfm/fan cfm
= 362,600 / 27,300
= 13 fans
Air speed vs. number of fan operating
850
Average air speed (ft/min)
400
750
650
550
450
350
250
150
3
4
5
6
7
8
9 10 11
Number of fans operating
12
13
22
Measured static pressure along length of the
house with all fans operating
Measured static pressure along length
of the house with all fans operating
low
high
Static pressure increased from pad to inlet
40” tunnel door opening on 5’ tall pad
0.18
0.16
Static pressure
0.14
0.12
0.1
0.08
0.06
0.04
0.02
0
pad
door
1/4
house
260'
20'
behind
3/4
20' from
house end fans
Static pressure increased from pad to inlet
0.18

0.16

0.14
Static pressure
Traditionally we sized our fans at 0.10” but the
pressure is significantly higher in high air speed
tunnel houses

0.12

0.1

0.08

0.06

0.04
Choretime – 52” high capacity
0.05”
= 29,100 cfm
0.10”
= 27,300 cfm
0.15”
= 25,000 cfm
0.20”
= 22,700 cfm
0.25”
= 20,200 cfm
0.30”
= 17,000 cfm
0.02
0
pad
door
1/4
house
260'
20'
behind
3/4
20' from
house end fans
23,850 cfm
23
Air speed is what you should expect once the actual
operating static pressure is taken into account



23,850 X 13 = 310,050
310,050 / (9.5 X 49)
666
General design static pressure at various
tunnel air speeds:







General design static pressure at various
tunnel air speeds:





400 ft/min = 0.09”
500 ft/min = 0.10”
600 ft/min = 0.13”
700 ft/min = 0.16”
800 ft/min = 0.18”
This is for smooth walled houses, without tunnel
doors, and clean pads
Realistically you would probably need one to two
points of pressure to determine the true operating
pressure.
High air speeds = High static pressure
400 ft/min = 0.09” - 0.11”
500 ft/min = 0.10” - 0.12”
600 ft/min = 0.13” - 0.15”
700 ft/min = 0.16” - 0.18”
800 ft/min = 0.18” - 0.20”
And there really isn’t much you
can’t do about it
Adding pad will do little good
0.24
0.22
0.2
0.18
0.16
0.14
0.12
0.1
0.08
0.06
0.04
0.02
0
800
750
700
650
600
550
500
450
400
350
300
250
200
150
100
0
To decrease static pressure by one point
Pad area needs to be increased 15%
50
Static pressure
Can’t we just add more pad to limit static
pressure?
Air speed through pad
24
and besides the longer the pad the larger
the “dead spot” becomes…
Static pressure
0.18
0.16
Static pressure
0.14
0.12
0.1
0.08
0.06
0.04
0.02
0
pad
total inlet
1/4
house
260'
20'
behind
3/4
20' from
house end fans
40’ X 500’ house with 600 ft/min air speed
Air speed (ft/min)
What would happen if we removed pads
from a house?
650
600
550
500
450
400
350
300
250
200
With pad
4
Air speed (ft/min)
40’ X 500’ house with 600 ft/min air speed
650
600
550
500
450
400
350
300
250
200

Pressure decreased
0.12” to 0.09”
4
5
6
7 8 9 10 11 12
Number of fans
6
7
8
9 10
Number of fans
11
12
Do some of our houses have too much pad
area?

With pad
without pad
5



Originally….400 cfm per
square foot of 6” pad,
Then we increased it to
375 cfm/ft2,
Then to 350 cfm/ft2,
Now some people are
using 325 cfm/ft2
As a result pad area per
cfm has increased 15
percent or more.
25
Add to this the fact that traditionally we based our
pad area on what the fans move at 0.05”


0.18
0.16
safety margin
But today many of our fans are operating at a pressure of
between 0.15” and 0.20” but we are still sizing our pads
at the fans air moving capacity of 0.05”


Static pressure
Size fans at 0.10” and size pads at 0.05”
more safety margin
As a result pad area per cfm have increased another 10%
or more
0.14
Static pressure

0.12
0.1
0.08
0.06
0.04
0.02
0
pad
Is this really of benefit?

66’ X 600’ house (805 ft/min)







21, 52” fans
124’ X 6’ of pad on each side wall
2 X 12’ X 6’ of pad on the end of the house.
1/4
house
260'
20'
behind
3/4
20' from
house end fans
66’ X 600’ house – 805 ft/min

66’ X 600’ house – 805 ft/min
total inlet
21, 52” fans (27,700 cfm @ 0.05”)
27,700 X 21 = 581,700 cfm
581,700/350 = 1,662 square feet
1,662 / 6’ = 271 total linear feet
271’ / 2 = 136’ feet per side of house
Average air velocity
810
800
790
780
770
760
750
740
730
720
710
all the pad
front pads covered
26
0.03”
0.24
0.22
0.2
0.18
0.16
0.14
0.12
0.1
0.08
0.06
0.04
0.02
0
0
50
100
150
200
250
300
350
400
450
500
550
600
650
700
750
800
0.14”
Pressure vs. Air speed
Static pressure
Pressure at pads – 124’ X 6’ on side wall
Air speed through pad
60’ X 600’ House with tunnel doors
(sides and ends doors opened)
60’ X 600’ House with tunnel doors
(front doors closed)
Air speed 18” above floor
Fans
46’
323
259
363
363
259
323
46'
Air speed 18” above floor
14’
287
207
61
61
208
287
14'
1'
14'
26'
33’
45’
58’
What if we removed 14’ from the pads on
the side wall?
46’
349
240
304
304
240
349
46'
Fans
14’
329
250
68
68
250
329
14'
1'
14'
26'
33’
45’
58’
Average air velocity
810
800
790
780
770
760
750
740
730
720
710
all the pad
front pads covered
14' of side wall
pads covered
27
What if we removed 24’ from the pads on
the side wall?
Average air velocity
810
800
790
780
770
760
750
740
730
720
710
all the pad
Reducing pad area reduces the dead spot
14' of side
wall pads
covered
24' of side
wall pads
covered
But the extra pad will help us when it gets
dirty…right?

How does the size of our tunnel doors affect
pressure and air speed?
front pads
covered
To some extent but….
50’ X 500’ – 600 ft/min
92’ of 5’ tall pad with a 5’ tall tunnel door
28
Average air velocity vs. Tunnel door opening
30
36
42
48
54
Tunnel Door opening (top to top)
pressure at pad
pressure at tunnel inlet
pressure at 1/4 house
pressure at fan end
60
0.15
0.14
0.13
0.12
0.11
0.10
30
35
40
45
50
55
Tunnel door opening (top to top)
60
66’ X 600’ – 600 ft/min
Fan performance vs. Pressure
110’ of 6’ tall pad
0.22
0.2
0.21
0.19
0.18
0.17
0.16
0.15
0.14
0.13
0.12
0.1
27,000
26,000
25,000
24,000
23,000
22,000
21,000
20,000
19,000
18,000
0.11
Fan cfm
0.16
700
680
660
640
620
600
580
560
540
520
500
Static pressure
0.16
0.14
0.12
0.10
0.08
0.06
0.04
0.02
0.00
Average air speed (ft/min)
Static pressure (“)
Static pressure as a function of door
opening
Static pressure
605
0.16
600
0.15
0.14
595
0.13
590
0.12
585
0.11
580
Static pressure (")
Air velocity vs. Tunnel door opening
Average air speed (ft/min)
5’ tunnel door on a 6’ tall pad
0.10
34 36 38 40 42 44 46 48 50 52 54 56 58
Tunnel opening (top to top)
29
46’ X 565’ – 700 ft/min
110’ of 5’ tall pad
5’ tunnel door on a 5’ pad
46’ X 565’
Upgrading to higher air velocities can be difficult
because older fans may not work well under high
static pressures…
Air speed (ft/min)
706
704
702
700
698
696
694
50’ X 500’
11 old 48” slant wall fans
1 new 50” fan
2 old 36” fans
Static Pressure
0.19
0.18
0.17
0.16
0.15
0.14
0.13
0.12
0.11
0.10
708
34 36 38 40 42 44 46 48 50 52 54 56 58 60
Tunnel Opening
Cfm
Late 1980’s 48” slant wall fan
17,000
16,000
15,000
14,000
13,000
12,000
11,000
10,000
9,000
8,000
Average velocity = 350 ft/min
In the end…


The existing fan capacity @ 0.15”
Additional fan capacity required
= 145,000 cfm
= 120,000 cfm
0.030.040.050.060.070.080.090.100.110.120.130.140.15
Total Static Pressure
30
48” fan performance results from other
farms (+10 years old)
Farm 1, 48” slant wall fan performance
21,000
19,000
17,000
15,000
13,000
11,000
0.00
0.05
0.10
0.15
0.20
Farm 2, 48” cone fan performance
Farm 3, 48” slant wall fan performance
21,000
21,000
19,000
19,000
17,000
17,000
15,000
15,000
13,000
13,000
11,000
11,000
0.00
0.05
0.10
0.15
0.20
0.00
0.05
0.10
0.15
0.20
Farm 4, 48” slant wall fan performance
21,000
19,000
17,000
15,000
13,000
11,000
0.00
0.05
0.10
0.15
0.20
31