Correct ventilation is a key aspect of bird comfort, welfare and productivity. Careful monitoring of bird behaviour will ensure that ventilation is correct for the flock as it progresses through its life.
Ventilation is a management tool which allows a grower to control bird comfort and air quality to optimise performance, bird health and welfare. The ventilation requirements of a bird changes as it grows, and with climatic conditions; ranging from providing a minimum amount of fresh air in cold weather or during brooding to creating high air speed to keep birds comfortable during hot and/or humid conditions.
Minimum ventilation is used whenever the house temperature is below the set point temperature. The focus is to supply enough heat to keep the birds comfortable, and enough ventilation to maintain acceptable air quality. The house must be equipped with adequate, well distributed, heating capacity to cope with the coldest ambient temperature, while still ventilating to maintain air quality.
During minimum ventilation, air enters the house through sidewall inlets. The aim is to direct the cold incoming air up to the peak of the roof where warm air accumulates (Figure 1). Inlet management is a key part of minimum ventilation. Inlets operate based on negative pressure, and in order to achieve the required pressure, the house must be well-sealed and air tight.
Inlet management involves finding the best combination of;
The inlets in use should be evenly distributed along the length of the house. Inlet air flow should be checked regularly using a smoke test or the ‘cassette tape’ method. This should be done when the house is at set point temperature, and it is cold outside.
Figure 1 – Correct air flow.
The cassette tape method involves hanging light weight strips of plastic (±10-15cm long) every 1-1.5m in front of a minimum ventilation inlet, with the last strip being in the peak of the roof. When the fans run, every strip should move, but with the movement getting less the closer the strip is to the apex of the roof. Air quality in the house is controlled by careful management of the cycle timer fans.
Transitional ventilation begins when the house temperature goes above the set point (within 1-2˚C). The emphasis changes from maintaining temperature and air quality, to ventilating to remove heat. Fans run continuously and large volumes of fresh air are brought in from outside. The inlets still operate on the basis of negative pressure and the incoming air should be directed upward and away from the birds. As before, operating pressure should be routinely checked, and confirmed.
Due to the large volume of continuous air flow during transitional ventilation, there will be some air movement and wind chill effect on the birds. As such, pay little attention to thermometer and sensor readings and base ventilation decisions on bird behaviour.
The primary function of tunnel ventilation is to remove excess heat and RH, and create wind chill on the birds. Tunnel ventilation should only be used when it is clear that transitional ventilation can no longer maintain bird comfort.
During tunnel ventilation air is drawn along the length of the house creating air flow over the birds, creating a wind chill or cooling effect. The wind-chill effect alters the temperature the bird feels compared to the thermometer temperature. The number of fans running should therefore be based on bird behaviour, and not thermometer temperature. For broilers, the use of migration fences will help maintain a uniform bird and heat distribution within the house.
When all tunnel fans are operating and the birds are still showing signs of being hot, introduce evaporative cooling. The cooling system should not reduce internal house temperature but maintain it at the level as when it started.
Ideally, during maximum tunnel ventilation the temperature difference along the length of the house should not be more than 2.8°C. A well-sealed, well insulated house will improve the performance of your tunnel ventilation system. Maintenance of fans and cooling system is a key part of tunnel ventilation.