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

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. (C) 2019 IAgrE. Published by Elsevier Ltd. All rights reserved.