The ventilation system is a key tool in achieving the genetic potential of broiler flocks and multi-function systems are proving increasingly popular, such as those with a tunnel ventilation mode to help overcome the effects of excess temperatures.
A ventilation system should enable performance from birds throughout the year, regardless of the season. It should be capable of maintaining in-house temperature and air quality, as well as minimising heating costs in the winter and heat stress in the summer.
The thermoneutral zone of a broiler bird changes through its life cycle and in attempting to maintain the birds within that relatively narrow temperature band in which optimum performance is achieved, various ventilation modes may be necessary.
A starting point in getting the best out of a ventilation system is ensuring that the system has been properly designed, equipped, and installed to best suit the objective and ambient conditions. A ventilation system that has not been properly designed and implemented will make the task of the grower more difficult and can compromise performance.
Common to all stages of any ventilation system is the house and probably the most important criteria in any successful ventilation system is an airtight house. The more airtight the house is, the more control there is over the ventilation system, how effectively it operates, how it is used, and the less impact the ambient conditions will have on internal conditions.
Along with air tightness, is the need for a suitably insulated building. The more the influence of ambient conditions can be reduced within the house, the better the internal environment can be maintained.
Getting chicks off to a good start is the key to a successful flock. The brooding period is characterised by maintaining air quality and temperature, minimising temperature fluctuations and eliminating draughts on the chicks.
Fans operate on a cycle timer and good air inlet management is essential in maintaining acceptable house conditions. Inlets should open equally, be evenly distributed and be set at the correct negative pressure to ensure that they direct air away from the birds into the peak of the roof. This enables incoming air to mix with the warm air in the house before reaching the birds (Figure 1).
Houses must not only be equipped with adequate heating capacity, but the heat must suitably spread to provide adequate, uniform temperature throughout the entire brooding area.
As the house temperature rises above the target set point, the focus switches from heating the house and providing minimum ventilation, to removing heat from the house in order to keep the birds comfortable. The importance of this stage of ventilation is sometimes under estimated because ambient and house conditions are warming up and at times the focus switches too quickly to trying to keep the birds cool.
Bear in mind that even in warm weather, the birds can become chilled (stressed) if exposed to excessive air movement prematurely. Thus, the transitional stage, before going to the hot weather ventilation system, is a stage where large volumes of air are required, but still without creating air movement on the birds.
In tunnel-ventilated houses this would mean using some tunnel fans along with the minimum ventilation fans, introducing air through the sidewall inlets, keeping the tunnel inlet closed (Figure 2). The sidewall inlet capacity must match the fan capacity with the inlets set at the correct negative pressure, directing air to the peak of the roof, just as during minimum ventilation.
While tunnel ventilation may be the most effective means of keeping birds cool in warm weather, misuse of the system can be very damaging to the birds. The combination of air temperature, relative humidity, air speed and bird age create varying degrees of cooling effect (wind chill) on the birds (Figure 3). Wind chill cannot be measured with dry bulb thermometers or by conventional controller probes.
So, when using tunnel ventilation, the decision on how many fans should be running at any specific time should be based on what the thousands of “thermometers” living in the house are telling you rather than the reading on a single dry bulb thermometer or controller display.
Where tunnel ventilation is being retrofitted to existing houses, ensure that the design is correct, allowing for the correct number of fans to create the desired air speed, with the fans selected at what will be the actual operating pressure. If used, the area of cooling pad must match the operating fan capacity. The pads should be installed on a dog-house. Pay specific attention to the tunnel inlet closing system to be used.
Whether this be curtains, tunnel inlet doors, or any other system, ensure that when this inlet is closed it forms an airtight seal. The tunnel inlet is a long inlet, and if it does not seal effectively, cold air leakage can have a negative effect on a significant area of the house when trying to operate negative pressure minimum ventilation.
When conditions become so warm that wind chill can no longer keep the birds comfortable, then evaporative cooling (spray or pad cooling) should be introduced.
Using and managing any form of evaporative cooling requires an awareness and understanding of relative humidity and how this affects the birds own internal (evaporative) cooling system (panting).
Relative humidity should be measured in any house where evaporative cooling is being used. A general guideline is to switch cooling systems off when the relative humidity inside the house exceeds 70-80%.
* Bernard Green is an independent consultant at Green Environmental Services and he is a consultant to Aviagen