Understanding microenvironments within tunnel-ventilated dairy cow freestall facilities: Examination using computational fluid dynamics and experimental validation

Abstract

The objective of this study was to determine the correlation between ventilation rates occurring in a barn designed to house dairy cows and the microenvironments that develop within the cow pens. To do this, a computational fluid dynamics model (CFD) of a tunnel-ventilated template barn was developed in accordance with the latest barn and ventilation design recommendations. For validation, the tunnel template model was benchmarked by comparing the outcome of a corresponding CFD model with microenvironment data collected experimentally in an actual tunnel-ventilated barn. The groups of cows inside the barn were modelled as an animal occupied zone through a porous-media with their presence characterised according to their animal densities: no-density (empty pen), low-density, and high-density. To distinguish between designs, the resting area with velocity magnitudes below 1 m s−1 was compared to the total resting area, and their ratio was defined as the “critical resting area.” Increasing the barn's ventilation rate produces diminishing returns; 40 air changes h−1 is the ventilation rate when airspeed can be augmented by local components, such as circulation fans placed over the stalls. Because approximately 20% of an average farmstead's electricity is used to power its ventilation system, this finding should present an opportunity to reduce energy costs associated with ventilation while still meeting the cows' physiological needs.