This system does not use any fans for moving air, but depends on the natural draught in the building. The sidewalls are usually open and can be controlled with curtains or other material, whilst the ridge is open and can sometimes also be controlled. Hot air rises and leaves the building through the open ridge. Fresh, cooler air enters through the sidewalls. When there is no wind and temperatures are high, results can be very poor.
This system uses fans and the air is forced through the building. The most common type is roof ventilation.
Fans are placed in airshafts in the ridge of the roof to suck the air out of the stable. Air inlets are placed in both sidewalls.
For cross ventilation the fans are placed onone side of the long wall of the building ,whilst the air enters through adjustable inlet flaps in the other sidewall. The fans have diameters of 122 or 90cm and depending on type displace 16,000-45,000 m³ of air per hour. These fans can be installed in groups, but also divided across the full length of the building. They are controlled in stages, where in turn one or two fans start running at full speed. For minimum ventilation a time function can be set or a variable speed can be used.
This ventilation system is to a large degree similar to cross ventilation. The fans are the same, but are now placed in the front wall. Both sidewalls are provided with adjustable inlet flaps. In principle, the system works the same as for cross ventilation.
This system is similar to length ventilation, only for tunnel ventilation special air inlets are used, that are placed opposite the fans at the other end of the building. This creates a so-called tunnel effect, as a result of which the air speed inside the building can be 2.0-2.5 m/sec. This has a positive influence on the wind-chill factor for the animals. On hot summer days, the wind-chill factor can thus be 6-8 degrees lower. For tunnel ventilation, all other inlets are closed.
When a tunnel ventilation system is in place, it is relatively easy to add a cooling system. For this purpose so-called pads are used. Water is pumped across these pads and fans draw air through them. The resulting airflow makes the water evaporate and cools down the hot air. This cooler air is then drawn through the building. Depending on outside temperatures and humidity, the temperature can be lowered by 10-15 degrees.The pads are mounted inside a housing and placed in front of the tunnel inlets on the outside of the stable. An even better solution is to provide a small extension that simplifies maintenance and catches any water loss. Excess water is received and recirculated by a water pump.