Assessment of geometrical and seasonal effects on the natural ventilation of a pig barn using CFD simulations

Airflow in naturally ventilated barns usually presents high variability with time and it is rather difficult to estimate because of the presence and interaction of the animals. On the other hand, appropriate ventilation is an essential requirement to ensure animal welfare and efficient and sustainable production. In this regard, the computational fluid dynamic simulations represent a powerful and useful tool and, in this paper, CFD simulations are used to investigate and assess the geometrical and seasonal effects on the natural ventilation of an existing pig barn sited in the northern Italy and composed of six wings converging on a central body. First, the effects of the complex barn geometry on the ventilation parameters have been investigated by outdoor simulations with eight wind scenarios on a closed envelope building model. From these analyses, both the interaction among the different wings and the influence of the surrounding buildings, have been carefully evaluated and a dimensionless parameter, called ventilation rate ratio, has been proposed and applied to the case study barn to assess the effects of the building geometry on the ventilation efficiency. Then, starting from the statistical analysis of the free-field ventilation at the site, seven additional wind scenarios have been analysed on a different model of the barn, to evaluate the efficiency of indoor natural ventilation during summer and winter seasons, when the most extreme conditions for animal welfare take place. The ventilation resulted very different during the years from season to season, but also presented valuable differences in the same season, from wing to wing. The outcomes of the paper provide useful indications on the present conditions of the structure and they could be used as decision-making information for the management of the livestock building to identify the most favourable pens for the different finishing pig groups at different fattening stages but also for the planning of the most suitable ventilation retrofitting interventions.