Good ventilation is indispensable in a poultry house (read more about this in our other blog: The relevance of a comfortable climate in poultry houses. With the help of mechanical ventilation and air inlets/outlets, it is possible to keep control over temperature, humidity, air speed and CO2 content in the poultry barn, while harmful substances are removed. Too little or too much ventilation results in less efficient growth of poultry, an unnecessarily high energy bill and an unhealthy barn climate for both humans and animals. But how do you keep control of fresh air supply for an optimal stable climate?
Closed- versus free-range houses
The easiest way to properly control the climate in a poultry house is to hermetically seal it from the outside world. Using fans, it is then possible to bring the exact right amount of fresh air into the house. Is there a need for more ventilation, for example because the temperature or CO2 content is too high? Then simply adjust the air inlets or outlets and turn on an extra fan, or make a controllable fan run faster. This way the weather outside the house has as little influence as possible on the climate inside of the house.
Lately, we see more and more farmers opting for free-range houses. At the desired moments, the pop-hole doors are opened so that the chickens can walk outside freely. This of course significantly improves the animal welfare of the poultry. However, it is important that the ventilation system is adjusted accordingly. In a regular negative pressure system, false air will irrevocably be drawn in through these openings, leading to an uncontrolled house climate.
Negative pressure vs equal pressure vs positive pressure
An even house climate requires fresh air to be well distributed over the house. This is achieved by strategically positioning the air inlets and outlets. Fans can be placed in the air inlets (positive pressure system), in the air outlets (negative pressure system) or both (equal pressure system).
Negative pressure system
Negative pressure systems are by far the most common in poultry houses. When using negative pressure ventilation, air is sucked out of the house with the help of exhaust fans. Because there is negative pressure relative to the air pressure outside, fresh air flows into the house through air intakes. By adjusting these air intakes to the amount of air that is extracted from the house, it is possible to control the incoming air flow. The position of the air inlets allows you to control the angle and the speed of the air that is entering the house. A negative pressure system is not suitable for use in free-range houses.
Equal pressure system
Equal pressure ventilation systems are becoming increasingly common in the poultry sector. Using an equal pressure system, both exhaust and intake fans are used, and the air pressure in the house is kept equal to the air pressure outside the house. The fans become slightly more economical because they do not have to build up any pressure, however, twice as many fans are required. The advantage of an equal air pressure is that the indoor climate is not disturbed when a door is opened somewhere. This makes equal pressure systems very suitable for free-range houses.
Positive pressure system
Poultry houses with a positive pressure ventilation system are rare in practice. In a house with positive pressure, fresh air is blown in with the help of fans and extracted in a controlled manner using air outlets. This increases the pressure in the house relative to the outside pressure. It will cause air to try to escape from every crack in the house. Insects, and therefore diseases, are less likely to enter the house. It is a principle that is also being used in hospitals and laboratories, for example. If a door is opened somewhere, air will flow out through this door. This makes a positive pressure system suitable for free-range houses. In practice, it is common to see free-range houses being equipped with both a negative and a positive pressure system.
Be sure to check out our other blogs if you would like to know more about the different ventilation systems or about common mistakes in poultry houses. Would you like to know which Multifan or EMI fans are suitable for poultry houses? Check out our poultry page.