Natural Ventilation of Commercial Dairy Cow Houses: Simulating the Effect of Roof Shape Using CFD

In livestock buildings the ventilation rate influences both the pollutant emission rates and animal¿s welfare. In the present study a 3D simulation model was used to simulate 7 commercial dairy cow houses with different roof types and side ventilators. The simulations have been carried out considering different wind speeds (1, 4 and 8 m/s), different wind directions (0, 45 and 90°) and different outside air temperatures (0, 10 and 20°C). The resistance of the cows to the air flow was calculated by simulating a virtual wind tunnel with cows. The ventilation rate was calculated by simulating the experimental tracer gas method (constant injection of a virtual gas having the same physical properties with air). The results show that both ventilation rate and uniformity of indoor climate were influenced by the roof shape. For the same dairy cow house type the ventilation rate was influenced by the wind speed, wind direction and air temperature differences. At low wind speeds the ventilation rate depends on both wind direction and air temperature differences; while at high wind speeds the most important factor seems to be the wind direction. For all the cases the ventilation rate at the cow level is different than the ventilation rate calculated for the overall house. These differences are varying even for the same house type, showing that the knowledge of overall ventilation rate does not provide enough information about the environmental conditions at cow level