When the decision to acquire new fans has been made, the next question is often: How many fans do I need to achieve the desired result. While this depends heavily on the application, some general assumptions can be made for the use in dairy barns. The ideal number of fans partly depend on a set of installation choices, which you can read more about in our other blog “Where to mount fans in dairy barns”. In this article we mention a few other factors that influence the amount of fans you will need.
Air speed and air volume
A commonly used fact in ventilation is that every kilogram of cattle needs around one cubic meter of fresh air per hour. Depending on the age and the amount of cows, you can then calculate how much air needs to be refreshed every hour using exhaust fans. However, when circulating air, it is more important that a specific air speed can be reached and maintained. Cows experience a cooling effect when the air speed is above 2 meters per second. An additional advantage is that air above that speed also significantly reduces gadflies. Above an air speed of 2.5 meters per second, also other types of flies are kept away.
Area of effect and efficiency
When we look beyond all other influences and purely look at the fans themselves, we see that our 130 cm basket fan can provide an air speed of 2 meters per second across a reach of around 15 meters. By mounting another fan after 15 meters, the moving air is sucked in again and blown through to another potential fan. This does not only improve the area of effect of the fan but also increases its efficiency.
For a demonstration of the calculation mentioned above, have a look at our white paper covering the installation of fans in dairy barns, speed controllers and other related topics that will help you create an optimal barn climate.