Using computational fluid dynamics to develop positive-pressure precision ventilation systems for large-scale dairy houses

Abstract

Heat stress has become a significant challenge to the US dairy industry because climate change has produced longer and hotter summers and because most dairies are milking higher-yielding breeds. These cows require more feed and thus generate more internal heat, which diminishes their ability to cope with hot and humid microenvironmental conditions. Consequently, they suffer significantly more of the kinds of welfare issues that can lead to substantial economic loss. The risk of heat stress is also increasing because, as dairy herds become larger, more and more cows are being housed together in mechanically-ventilated facilities. Providing a consistent supply of adequately cool fresh air to each cow throughout a large-scale barn has thus become much more challenging. This study evaluates a proposed cooling system called positive-pressure precision ventilation (PPPV), which, if effective, could precisely deliver fresh air jets to every animal in the stall and other target areas inside a dairy barn at desired speeds using innovative, positive-pressure technology. To assess the effectiveness of the proposed system, a computational model of a prototype was developed. Subsequently, a corresponding true-to-scale physical prototype was used to validate the model's predictions and substantiate our claim that the PPPV system can deliver an evenly distributed flow of cooled air at a specified velocity and targeted at levels equivalent to both standing and reclining cows. The proposed PPPV system could require fewer fans than currently existing mechanically ventilated systems and thus would require less electrical power and operate more economically.