Figure 1. Windbreak wall

Figure 2. Odour dispersion plume from a windbreak wall (bottom image)

Windbreak walls have been used as a solution to controlling and reducing odour and dust from tunnel ventilated chicken sheds. They have been promoted as one of a few cost-effective ways to improve odour dispersion and to reduce odour impacts.

But do they really work and are they really a potential solution to one of the biggest issues facing the poultry industry – reducing odour impacts?

To answer this question the RIRDC commissioned the Queensland Department of Agriculture, Fisheries and Forestry (QDAFF) to investigate windbreak walls and how effective they are in terms of reducing odour and dust impacts on surrounding neighbours.

What Are Windbreak Walls?

Windbreak walls are simply barriers placed several metres from outlet ventilation fans. They can be constructed from a variety of materials including vegetation screens, tarpaulins, MDPE, hay bales, corrugated iron or wood.

Their purpose is to enhance the dispersion of smelly air upwards into wind resulting in dilution and dispersion of the odour, and hopefully less complaints from neighbours (Figures 1 and 2).

Are Windbreak Walls Effective in Reducing Odour?

Windbreak walls were introduced in 2000 as a way to improve dispersion of odours from tunnel ventilated livestock buildings. Reported windbreak wall performance was based on theory and a few smoke observations. Even at this early stage, it was identified that dispersal of odour by windbreak walls was unreliable and would probably decrease in calm, stable weather.

The aims of the study by QDAFF were to:

1. Identify the value of windbreak walls for improving dispersion of exhaust air from tunnel ventilated sheds;
2. Evaluate the use of windbreak walls as an odour reduction strategy for meat chicken sheds.

How Was the Study Conducted?

The research team used a combination of tracer gas measurements, smoke observations and sophisticated computer modelling to test the effectiveness of windbreak walls. They conducted their tests on sheds with walls and nearby sheds without walls to see if they could find differences in the way air travelled and behaved.

After using the tracer gas method, they discovered that this was not providing them with good information. However the smoke observations and computer modelling proved to be far more effective and these methods were then used to conduct their tests.

Note: Short stacks are upward facing funnels or pipes placed over the ventilation fans and are designed to direct the ventilated air upwards promoting dispersion and dilution of odour coming from the sheds. See figure 3.

Figure 3. Example of short stacks placed over ventilation fans on broiler sheds.

What Did They Find?

In short, they found that windbreak walls are generally not effective in reducing downwind odour from tunnel ventilated sheds.

Their tests showed that odour dispersion depended on conditions such as atmospheric stability, horizontal wind speed, the number of active fans and air temperature. Some of their tests showed that under some conditions, windbreak walls actually increased downwind odour.

They found that some reduction in odour may be achieved close to the windbreak walls, within 150 metres, but that this very much depended on weather conditions. They also performed testing of short stacks but found that these did not perform much better than windbreaks.

Overall, after conducting tests under a range of weather conditions, the research found that neither windbreak walls nor short stacks were reliable in reducing odour from tunnel ventilated chicken meat sheds.

Do Windbreak Walls Have Any Benefits?

For farmers who have installed windbreak walls to control odour, this report is obviously not good news. However the research team did note that windbreak walls could have some benefits unrelated to odour control.

The benefits may include:

• blocking sunlight from entering the shed through open fan shutters
• altering dust deposition close to the exhaust fans
• reducing fan noise
• maintaining fan performance when strong opposing winds prevail.

These benefits may be sufficient to justify installation of windbreak walls at some poultry farms.

For a copy of the full research report, as well as many other useful publications and resources, go to the RIRDC web site [click here].

Adapted from ‘Control of Odour and Dust from Chicken Sheds, Evaluation of Windbreak Walls’ by Mark Dunlop and Geordie Galvin, RIRDC, 2013.

September 2014