Overview of Ventilation Techniques

Brian J. Holmes, PhD

Professor & Extension Specialist, Emeritus

Department of Biological Systems Engineering

University of Wisconsin - Madison

Q. What is ventilation?

A. Air Exchange Between Inside

and Outside

- Removes Contaminated Air

- Introduces Clean Air

Types Of Ventilation Systems

Mechanical Ventilation – Fans

cause the air exchange

Natural Ventilation – Forces of

nature cause the air exchange

Natural ventilation uses the

forces of nature to cause the

air exchange -

Wind is the primary force

Natural Ventilation - Winter

Air

In

Wind

Air

Out

Air Out

Eave Opening

Natural Ventilation - Summer

Air

Out

Wind

Air

In

Air Out

N Effect of Prevailing Summer Wind

Wind Direction

Orientation #1 Orientation #2

N Effect of Prevailing Summer Wind

Wind Direction

Orientation #1 Orientation #2

N Effect of Prevailing Summer Wind

Wind Direction

Orientation #1 Orientation #2

Barns Provide Shade

From Solar Radiation

Shade

Zone

N Effect of Solar Gain

Morning Sun Noon Sun Afternoon Sun

Orientation #1 Orientation #2

Natural Ventilation

Doesn’t Work When:

•Site has obstructions

•Structure can’t meet design criteria

•Site doesn’t allow for correct

orientation

•Wind doesn’t blow enough

•Interior air blockages

Silos Obstruct Natural

Ventilation In Summer

Summer

Wind

Corn Field

Trees

Hill

Summer

Wind

Ventilation Rate vs Wind Speed

0

500

1000

1500

2000

2500

3000

3500

4000

0 1 2 3 4 5 6 7 8 9 10 11

Wind Speed (MPH) @ 45o Angle

Ven

tila

tio

n R

ate

(C

FM

/Co

w)

.

4-Row, 10 ft Wall Open 4-Row, 12 ft Wall Open

6-Row, 10 ft Wall Open 6-Row, 12 ft Wall Open

Standard

Recommended Summer

Ventilation Rate

12 ft Wall Open

Natural Ventilation Supplements Heat Stress Relief :

- Circulation Fans

High Speed Low Volume

Low Speed High Volume

- Sprinkling Cows

- Evaporative Misters/Foggers

Supplemental Circulating Fans in

the Feed Line and Freestall Areas

Side View

High Speed Low Volume (HSLV)

Fans in Freestall Barn

Cooling Fans for Close-up Cows

Fans in

Holding

Area

High Volume

Low Speed

(HVLS) Fans

HVLS Fan Layout

3 0 ' 0 " 6 0 ' 0 " 6 0 ' 0 " 6 0 ' 0 " 3 0 ' 0 "

HVL S F a n

Al l e y

Al l e y

F re e s ta l l s

F e e d L a n e

F a n Sp a c i n g

49' 6"

49' 6"

99' 0"

A lley

Freestalls

H V LS Fan

60' 0" 30' 0"

Fan S pacing

60' 0"

Freestalls

W ater

Feed Lane

A lley

30' 0"

36

' 0

"2

6'

0"

62

' 0

"

4 and 6 Row Barns

(Over Feed Lane)

3 Row Barn

(Over Freestalls)

Spacing @ 60’ o.c. Height @ 16-18’ from Floor

Sprinklers

Sprinklers

Nozzle

Conclusion:

Air Velocity & Sprinkling

give best heat stress control

Fans and Foggers in Freestall

Barn

Natural Ventilation Supplements Air Distribution:

- Circulation Fans

- Positive Pressure Tubes/Ducts

Reasons for Positive Pressure Tubes in Naturally Ventilated Barns:

Design Criteria for building not met Wind not blowing Wind blocked by other structures or features Operator refuses to open eave inlets Interior feature causes dead air zones Stocking rate is excessive Calves entering are sick or have been exposed to pathogens

Positive Pressure Duct

8 Fan

Aim Holes at

Floor

Barn End Wall Outside

Air

Fan Intake

Size Fan for Winter Minimum Ventilation Rate

Perforations

Fan Unit

Compliments UW School

of Veterinary Medicine

Individual Calf Pens

Positive Pressure

Tube

Compliments UW School

of Veterinary Medicine

12 ft

X X

16 ft

8 ft 4 ft 4 ft

Feeder Room

Positive Pressure Tube in Group Pen

10 ft 10 ft 11 ft

47 ft

37 o

Not to Scale

Feeder Room

Positive

Pressure Ducts

Feed Zone

Resting Zone

Access

Mechanical Ventilation Types

- Negative Pressure

- Positive Pressure

- Neutral Pressure

- Mechanical/Natural Combinations

Mechanical Ventilation Requirements

- Fans

- Inlets/Outlets

- Controls (Manual, Temperature,

Pressure, Humidity, Software)

Negative Pressure - Fans Exhaust Air

Air enters through inlets

Uniform Air Distribution

Slot inlets

Area inlets

Recirculation ducts

Wind Tunnel

Cross Ventilation

TO 19 Ft.

Negative Pressure w Single Slot Inlet

Slot Inlet (Wall Hung Baffle)

FAN 3 FAN 1

19 FT

SLOT INLET

FAN 2

Negative Pressure – Single Slot Inlet Less Than 19 Feet Wide

<

19 - 38 Ft.

Negative Pressure w Double Slot Inlet

Perimeter = (2 x L) + (2 x W)

Adjustable Four Sided Area Inlet

Negative Pressure with Recirculation

Recirculation Duct Inlet

Figure 7-X. Wind tunnel barn

Exhaust Fans

Height

Wind Tunnel

Exhaust Fans

Tunnel Ventilation

• Air Exchange

• Air Velocity

Wind Tunnel Fans

Wind Tunnel Inlet - Closed

8

8

8 8

8

8

8

8

8

8

8

8 8

Waterers

Fans Waterers

Tunnel Ventilation without Inlet Restrictions

and Vault Open – Empty Barn

Plan View

Side View

8

8

8 8

8

8

8

8

8

8

8

8 8

Waterers

Fans Waterers

Tunnel Ventilation without Inlet Restrictions

Baffles Installed - Empty Barn

Baffles

Plan View

Side View

When does tunnel ventilation have

fewer fans than natural ventilation

with circulating fans?

Fans Needed vs Barn Capacity

0

10

20

30

40

50

60

70

80

90

100

110

120

130

140

150

160

0 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400

Barn Capacity (Cows)

Nu

mb

er

Fa

ns

Ne

ed

ed

.

6-Row Tunnel Fans Needed 4-Row Tunnel Fans Needed

6-Row Circ. Fans Needed 4-Row Circ. Fans Needed

1000 CFM/Cow

Controls

52 Fans

Natural Ventilation w

Circulating Fans

Tunnel Ventilation

Figure 7-Y. Cross ventilated barn

Exhaust Fans

Height

Cross Ventilation

420'

84 - 51" fans located along west side

Baffle

184 Freestalls per Pen (46" stall width)

20' Cross Alley (2 - 8' Water Troughs)

NORTH

Entrance Doors

Evaporative Pad

To

Milk

Pa

rlor

Bottom of Baffle 8' above alley floor (6'4" opening)

200 Cows

200 Cows

200 Cows

200 Cows

200 Feedspaces

210'

Baffle

Basic Layout of Cross Ventilated Low Profile Freestall Building

Source: Joe Harner, K-State

Evaporative Pads

84 – 51” Fans along West Side

Low Flow Fans

Cross Ventilation Fans

Evaporative Pads

Evaporative Pads

5 ft

5 ft

Baffle

6.5 ft

Cross Section Air Flow Path at Baffle Roof

Baffle

Baffle

Feed Alley Freestall Freestall

Video of the Barn Being Smoked?

YES

Advantages of Cross-Ventilated Barns w Cooling Pads*

• Better control of cow environment

• Shorter pull distance than tunnel ventilation

• Excellent air quality

• Greater air exchange rate vs tunnel

• Minimal barn air temp. variation vs other barns

• Air past cows at high velocity

• No or limited sprinkling

• Option for short or long day lighting

• Elimination of direct solar heat gain-shade

• Elimination of sunlight on cow behavior

* From Jim Barmore-Five-Star Dairy Consulting

& John Smith K-State

Advantages of Cross-Ventilated Barns w Cooling Pads*

• Minimal flies and birds in barn

• Shorter walk distance to parlor vs Natural Ventilation

• Small footprint for barn siting & site preparation

• Minimal concern for barn orientation (N-S vs E-W)

• Air flow is parallel to cow body-better cooling

• Cows do not block air flow from other cows as

much as in tunnel ventilation & high speed fans

* From Jim Barmore-Five-Star Dairy Consulting

& John Smith K-State

Disadvantages of Cross-Ventilated Barns w Cooling Pads*

• Fans run 24/7/365

• Back-up generator required

• Pressure drops high

• Most experience is w 8-row barns

• Shut down cooling pads in evening to “dry”

• Greater potential for airborne disease transmission??

• Fan maintenance is critical

• Parlor and breezeway must be integrated with

negative pressure ventilation

* From Jim Barmore-Five-Star Dairy Consulting

& John Smith K-State

Positive Pressure:

- Fans Force Air Into Building

- Air Exits through Outlets

Positive Pressure:

- Fan Into Duct (Cold, Cool, Warm, or

Hot Seasons)

- Fans Through Wall (Warm, Hot

Season)

Wind Tunnel

Cross Ventilation

Positive Pressure – Duct Only

Barn 40 - 50 Feet Wide

Positive Pressure Ventilation System – Plan View

8 Step 1

Step 2

8

8

Step 3 Step 4

Outlet

Mow

Floor

Duct

Positive Pressure Fans Forcing

Air Into Duct Through Mow Wall

Wall

8

8 Louver

Duct Transition Winter Fan

Spring & Fall Fan

Adjustable

Slot Inlet

Milking

Parlor

Holding Area

8 8 8 8

8 8 8 8

Positive Pressure Wind Tunnel

Fans Blow In Outlet

8

Fans Blow In

Fans Blow In

Circulating Fans

Neutral Pressure:

Fan Force Air into Building and

Fans Exhaust Air from Building

- Fan Into Duct (Cold, Cool Seasons)

- Fans Through Wall (Warm, Hot

Season)

- Fans Exhaust through Walls, Floor or Roof

Neutral Pressure Ventilation System – Plan View

8 Step 1

Step 2

8

8

Step 3 Step 4

8

Step 3 Step 4

8

Step 1

Step 2 8

Positive Pressure for Winter, Spring/Fall

Natural / Mechanical Combination:

- Natural Ventilation (Cold, Cool, Warm Seasons)

- Mechanical Ventilation (Hot Season)

Example:

Natural & Wind Tunnel

QUESTIONS?

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