HOT WEATHER VENTILATION

Bernard Green

It Starts With Your House

• For any ventilation system to work well, the condition of the house is the starting point

• This applies whether closed environment house, or open sided

For closed environment

• House must be well sealed

• House must be well insulated

• Pay particular attention to “thermal bridging”– This is often overlooked due to the extra cost involved

• Cannot afford to have radiant heat entering the house

• A ventilation system cannot ventilate radiant heat away

Roof “Insulation”

For open and closed environment houses

• Roof “insulation” is critical

• Poor roof insulation can result in RADIANT HEAT entering the house

• Cannot afford to have radiant heat enter the house

• A ventilation system CANNOT ventilate radiant heat away

• Pay particular attention to avoid structural “thermal bridging”– This is often overlooked due to the extra cost involved

Thermal Bridging

Outer roof sheet

Inner roof sheet

Structural steel

Insulation Insulation

Sun

Heat radiates into the house

The “Ideal” Roof

The IDEAL ROOF should take care of:

• Thermal bridging– Use an insulating material between the steel structure and the

internal ceiling

• Insulation material– Use an insulating material such as polyurethane, glass wool,

polystyrene, etc

– This will help keep the heat in during colder weather

• Radiant barrier– Usually a highly reflective, silver product used to deflect radiant heat

away from the house

– Correct installation of the radiant barrier is very important

House Tightness

For closed environment houses:

• Houses must be well sealed!!

• The tighter the house is sealed, the more control you have over how and where the air will enter the house

• In tunnel ventilation we want ALL the air to enter through the cooling pads or tunnel inlet

• Air leakage along the length of the house will result in:– Greater than normal temperature gradient from one end of the house

to the other

– Different air speed along the house

– Air speed increasing as you get closer to the fans

Tunnel Ventilation

• Probably the best management tool for hot weather

• For control of the birds effective temperature in hot weather– Effective temperature is how the bird feels when there is air

moving over it

• Takes place down length of house

• Exhaust fans at one end

• Long inlets in each side wall at opposite end

• Air is pulled down length of house

• Cooling effect of air movement (wind chill)

• Fans vary the air speed and effect

Typical Tunnel Ventilation House

Tunnel Ventilation Design

Before we can worry about how to ventilate houses in hot weather, we need to be sure that the houses are designed correctly

Steps to Tunnel Ventilation Design:

1. How much fan capacity do we need?

2. What will be the approximate operating pressure?

3. How many fans?

4. How much cooling pad area?

5. How much inlet area?

Have reliable performance data about the equipment you will be using!!

1. How Much Fan Capacity?

Fan Cap [m³/hr] = Speed [m/s] x CSA [m2] x 3600

• CSA = cross section area (effective area through which the air will flow)

• CSA = (W x H) + (½W x R)

• Area of nests/slats should be deducted from CSA

• 3600 = convert m/s to m/hr

W

H

R

2. Approximate Fan Operating Pressure

• The static pressure shows how hard the fans are working to bring the air into, and through the house

• The more the restrictions, the higher the fan pressure

• The higher the air speed, the higher the fan pressure

• The higher the pressure, the lower the fan performance

• The higher the pressure, the less energy efficient the fan

• So, we must be sure that everything “balances” in the design!

2. Approximate Fan Operating Pressure

∆P

∆P

∆P∆P

Fan Operating Pressure = ∆P + ∆P + ∆P + ∆P

∆P

∆P

The Effect Of Pressure On Fan Performance

0.75 kW1.1 kW

60

The Effect Of Pressure On Fan Performance

Pressure

Pa

0 12 25 31 37 50

Fan Cap

m³/hr

43 185 40 635 38 084 36 384 34 684 30 434

1 270mm fan with 0.75kW motor

Fan Design Pressure Guideline

The following is a design guideline for the fan operating pressure in tunnel ventilation:

• No cooling pad : 20Pa

• With 15cm cooling pad : 30Pa

• With 15cm cooling pad + nest boxes : 40Pa

• With 15cm cooling pad + light traps against the fan : 50 to 60Pa

Notes:

The above is only a guideline and is applicable up to air speeds of ±2,5m/s.

At higher air speeds the operating pressure can increase significantly.

It is dependent on the type of cooling pad being used.

It is dependent on the type of light trap being used.

3. Number Of Fans Required

• Number of Fans = CFC ÷ FC

Where:

• CFC = Calculated Fan Capacity [m³/hr]

• FC = Fan Capacity [m³/hr] at the design operating pressure– This information must come from a reliable source!

• If answer is a fraction, then round UP to the nearest fan

• Example : Answer = 9,2 fans → use 10 fans

4. Cooling Pad Area

Pad Area [m²] = Fan Cap[m³/hr] ÷ 1,78[m/s] ÷ 3600

• Fan Cap = total real operating fan capacity• 1,78 - 2,0m/s = design air speed thru 15cm pad (45x15)• 1,27m/s = design air speed thru 10cm pad• 3600 = conversion from m³/hr to m³/s

• Install equally on either side (at end of the house)• Ensure pad is installed in correct orientation• Preferable to install on doghouse• Allows pressure control after pad

Different Pad TypesExample A

66

756

16

Different Pad TypesExample B

45 x 45 Pad

150mm thick

±50Pa

Cooling Pad Orientation

Dog House

Cooling Pad

Rack and Pinion Inlet

5. Inlet Area

Inlet Area [m²] = Fan Cap[m³/hr] ÷ 2,5[m/s] ÷ 3600

• Fan Cap = maximum real operating fan capacity• 2,0 – 2,5m/s = design air speed thru tunnel inlet• 3600 = conversion from m³/hr to m³/s

• The inlet area must be the total, UNRESTRICTED open area• Ensure inlet door seals VERY well

– This is extremely important for Winter

House Design Notes

The above is a basic guideline to house design

Design values in the guideline may change due to:

• Design air speed

• Cooling pad type

• House width

• House obstructions (nests, baffles, heaters, fences)

• Light trap type (if applicable)

• Always try to have accurate, reliable data about the equipment you are using

• If in doubt, be conservative!

Tunnel Ventilation Design Example

Required Fan Capacity

• CSA = (W x H) + (½W x R) = (15 x 2,4) + (½ x 15 x 1,0)

• CSA = 43,5m²

• Fan Cap. [m³/hr] = 2,5 [m/s] x 43,5 [m2] x 3600

= 391 500m³/hr

15m

2,4m

1,0m

Example – Number of Fans

Pressure

Pa

0 12 25 31 37 50

Fan Cap

m³/hr

43 185 40 635 38 084 36 384 34 684 30 434

Assume using 15cm cooling pad, then fan operating pressure ±30Pa

Fan capacity is 36 384m³/hr

Number of fans = 391 500 ÷ 36 384 = 10,8 fans

Use 11 fans = 36 384 x 11 = 400 224m³/hr

• If I use fan capacity = 43 185m³/hr (0Pa)

• Number of fans = 391 500 ÷ 43 185 = 9 fans

• But the real capacity is 36 384m³/hr (at 30Pa)

• Then the air speed will be:

• Air speed = (actual fan capacity) ÷ (CSA x 3600)

= (9 x 36 384) ÷ (43,5 x 3600) = 2,1m/s

Example – Cooling Pad Area

• Total operating fan capacity = 400 224m³/hr

• Pad area = 400 224 ÷ 1,78 ÷ 3600 = 62,5m²

• This is the total area for 15cm pad (45 x 15 flute angle)

• Install 32m² per side

Example – Tunnel Inlet Area

• Total operating fan capacity = 400 224m³/hr

• Inlet area = 400 224 ÷ 2 ÷ 3600 = 56m²

• This is the total unrestricted area

• Install ±28m² per side (minimum)

Air Deflectors

Air Deflectors

Air Deflectors

• For houses that do not have enough fan capacity

• Air Deflectors increase the air speed through the house

• They do this by reducing the Cross Section Area that the air travels through

Installation:

• 10-12m apart

• Not less than ±2,2m above the shavings

• Installing them too low can increase the fan negative pressure significantly.

Maintenance

• Proper maintenance is a critical part of ventilating any poultry house during hot weather

• Fans– Pulley’s

– Belts

– Shutters must open freely

• Cooling pads– Clean

– Unrestricted

• Light traps– In good condition

– Clean from dust

Monitoring Tunnel Ventilation Performance

• Measuring pressure at the fans is a good way to monitor the “condition” of the house and equipment

• When the house is new, or pads replaced and fan maintenance done, operate full tunnel ventilation and measure static pressure near the fans

• If pressure starts to reduce over time, could be from:– Fan condition (pulley’s, belts, shutters, motor)

– House not as air tight as before

• If pressure starts to increase over time, could be from:– Pads becoming blocked

Wind Chill

• Probably the most important factor in Tunnel Ventilation

• Cooling effect from air movement on the birds

• Depends on: bird age, dry bulb temperature, air speed, RH, stocking density

• Remember - Controller probe/sensor, dry bulb thermometer cannot measure wind chill

• In tunnel ventilation the bird feels a different temperature to what the thermometer shows

• Various wind chill charts available– They should only be seen as a guideline

• How many fans should I use? Watch the birds!

• Always base the final decision on bird comfort

Windchill Example

0.5 1.0 1.5 2.0 2.5 3.0

Air Velocity (m/s)

8.0

5.5

3.5

1.0

9.0

6.5

4.5

2.0

Win

d C

hill

(°C

)

Managing Windchill Effect

• Windchill has a different effect depending on bird age

• So, we need to manage fan differential settings different for different ages

• When birds are young – greater differential between fans– “Differential” – the temperature increase before the next fan operates

– A greater differential means that the house temperature will increase more before the next fan switches ON

– We don’t want too many fans running too early

• As birds get older – less differential between fans– We want the fans to activate quicker

Managing Windchill Effect

Below is an estimation of the wind chill effect at different ages(This is more specific to broilers)

Age [Days] Windchill [°C/ms-1]1 8,07 7,014 6,021 4,528 3,035 2,5

Example :According to the above : 28 day old bird ; 2,5m/s air speedCooling effect = 3,0°C/ms-1 x 2,5m/s = 7,5°C

The figures above are only an estimation used by a specific equipment company. This was not achieved through any form of scientific research. Always watch bird behaviour.

1,25 m/s air speed

2,5 m/s air speed

Air speed is important

House design and set up must be correct

Relative Humidity (RH)

• Comparison of amount of water in the air at a certain temperature, relative to maximum potential amount at same temperature

• As temperature increases, RH decreases

• As temperature decreases, RH increases

• When RH is low, evaporative cooling works well

• When RH is high, evaporative cooling doesn’t work well

• Amount of cooling depends on RH level

Cooling Potential

ΔT = Maximum cooling possible

Cooling pad is ±75% efficient, soActual cooling = 0,75 x ΔTThis will be the temperature right at the pad

Dry Bulb Wet Bulb

Birds and Evaporative Cooling

When a bird is heat stressed, it loses heat by:1. Convection, conduction, radiation (air movement)2. Evaporative cooling – panting• Effectiveness of birds panting depends on house RH• If RH low effective• If RH high ineffective (can lead to mortality)

Rule of Thumb (guideline):• If house RH > 70%*, switch cooling OFF• Temperature will increase, RH will decrease

CANNOT operate cooling on temperature alone!MUST operate on combination of Temp and RH

* Recent research indicates that higher RH percentage can be tolerated provided that there is good air speed through the house

Operating Pad Cooling

• The purpose of a cooling pad is NOT to reduce the house temperature

• The purpose is to MAINTAIN a temperature• Use fan capacity (air speed and wind chill) to try keep

the birds comfortable• The number of fans required at any time should be

based on the activity of the birds and NOT on actual house temperature

• During tunnel ventilation the actual house temperature should ALWAYS be higher than the required set point

Operating Pad Cooling

• When all the fans are operating and the birds are showing signs of being too warm, then introduce cooling

• Cooling pumps should not run continuously at first• They should cycle ON and OFF to control how much

water goes onto the pad• This way you are able to control the temperature

more accurately• Operating the pumps ONLY on temperature will result

in large temperature fluctuations (4-8°C)• Most modern control systems function this way

Operating Pad Cooling

For more effective bird cooling:• Using more fan capacity (wind speed) along with

controlled pad cooling creates more cooling effect than using fewer fans and more water cooling

Transitional Ventilation

• Can be seen as a 3rd ventilation system

• Involves extra sidewall inlets

• Uses minimum and some tunnel ventilation fans together

• Air introduced through sidewall inlets

• Allows high air volume without TV effect

• Provides transition from CV to TV

• Used when more than CV is required, but too “early” to go to TV

• DO NOT switch to TV too early!

• You can stress the birds with too much air movement even if the temperature is high

Minimum Ventilation

Transitional Ventilation

Tunnel Ventilation

Thank You