## 1 Introduction  
Air exchange in livestock buildings is very essential for creating a comfortable environment with satisfactory indoor air quality. ventilation air is also a medium of transporting pollutants (i.e., gas, odor, and dust) from livestock buildings [1] which adversely affect animals, workers, neighbors, and the environment [2]. It is essential to have suitable tools to understand airflow characteristics and predict ventilation performance in buildings for regulating the indoor air parameters and controlling emissions. The natural ventilation system with large side wall openings and a roof opening is commonly used in dairy cow barns of temperate climate regions [3]. Hence, atmospheric influences under continuously changing conditions [4] (such as outdoor temperature, wind speed and wind direction, as well as its turbulence properties) influences the emission from naturally ventilated dairy (NVD) barns directly. Milk production and milk quality are badly affected by stale air. However, animal activity changes in response to heat stress [5] and insufficient fresh air [6]. The design and performance of the ventilation system, including ventilation openings strategies, maintain desired environmental conditions in intensive livestock production systems. Ventilation in an NVD building is the result of pressure differences created by either temperature differences (thermal buoyancy), wind on the building or combinations of the two. As a consequence, the indoor environmental parameters (temperature, gases, and humidity) are governed by airflow patterns. The essential link between the outdoor environment and the buildings microclimate is formed by the airflow patterns including air velocities and turbulence intensity; thus, an understanding of the principles of air motion is necessary in order to provide optimum air flow, air exchange rate (AER), and the proper airflow distribution patterns to meet the needs of the livestock and environment. The major problem of natural ventilation is the lack of precise, continuous, and online measuring and control techniques for ventilation rate [7]. Ventilation rates and the emission streams from naturally ventilated buildings have been measured and calculated, respectively by applying different measuring techniques (e.g., heat balance [8], CO\({}_{2}\) balance [9], moisture balance [10], hot wire anemometer [11], tracer gas [12], etc.). Depending on the different methods and techniques, imperfect mixing of tracer gases and lack of representative sampling errors give errors up to 100% [7; 13]. Recently, wind tunnel investigations using 1:40 scale models of a naturally ventilated dairy building were conducted for better understanding of opening effects on indoor airflow pattern and on the discharge coefficient, which is an important parameter in the airflow rate determination when using the orifice equation method [14; 15]. However, wind tunnel experiments are expensive, labor intensive, and technically difficult, because extensive information on airflow characteristics in the space is needed and the number of points that can be measured is limited [13]. Thus, a model would be very helpful for predicting the airflow rates and airflow characteristics by using parameters easily measured or obtained from the available literature. For understanding airflow characteristics of NVD buildings, numerical simulation using computational fluid dynamics (CFD) could ideally complement full scale and scale model experiments [16; 17]. [PERSON] and [PERSON] [18] investigated the flow around cows using CFD to investigate the heat and mass transfer phenomena coupled fur model to calculate sensible and latent heat losses from the skin surface of an actual cow in a forced ventilated enclosure of simple geometry. The total heat loss from an animal is highly dependent on both the animals' position and orientation to the flow field.