Characterization of ventilation and thermal environment in a horse trailer during transport
Ventilation and thermal environmental parameters were measured simultaneously in ten locations in a slant load, four-horse trailer. Vehicle speed, vent configuration, location in the trailer, and presence of animals were used as treatment levels in a factorial design. Increases in vehicle speed increased ventilation and decreased temperature differences in the trailer. Ventilation increased and temperature differences decreased as open vent and window area increased. The presence of horses in the trailer reduced ventilation by 33% and increased temperature differences. Ventilation effectiveness was uniform (CV ≤ 20%), thus the airspace in the trailer can be characterized as well-mixed. Horses experienced heat stress conditions inside the trailer for a majority of the 45 observations in this study. The maximum ventilation rate measured was 0.83 and 1.21 min−1 with and without horses, respectively. With horses in the trailer, the maximum ventilation was 60% of that recommended for stables in warm weather (1.38 min−1 ), illustrating the need for trailer design changes to improve ventilation.
A sensible heat balance model was developed to relate trailer air temperature and ventilation rate. The model was used to determine the ventilation rate required to maintain an air temperature difference of 3°C. Measured air exchange rates were found to be less than 15% of those predicted by the model.
A series of wind tunnel tests were conducted to better visualize airflow behavior within and around a scale model of the horse trailer. Two-dimensional Digital Particle Image Velocimetry (DPIV) was used to measure the velocity field inside a 1:10.5 scale model of the trailer, at various representative planes. DPIV experiments recreated the general characteristics of the flow in the prototype trailer, although maximum Reynolds number for the experiments was limited (2 · 106). Flow at the windows was observed to be unsteady, and inlet flow tended to occur over the trailing section of the window. The presence of scale model horses reduced flow velocity through the windows of the model. Ventilation rates predicted by velocity integration were generally poor, most likely from three-dimensional movement of the flow and air being drawn in through the seeding inlet.