Performance of Tunnel Ventilation for Freestall Dairy Facilities as Compared to Natural Ventilation with Supplemental Cooling Fans

Abstract

Three pairs of naturally ventilated and tunnel-ventilated dairy barns were monitored during the summer of 2000 to compare the thermal environments developed by the two warm-season ventilation systems. Supplemental cooling fans were used within each of the naturally ventilated barns to direct airflow onto the cows. Ambient air temperatures during midsummer were cooler than normal in both New York and Ohio, but both states had near-normal cooling seasons. Both ventilation systems performed well during these temperate summer conditions with indoor thermal conditions closely tracking those outdoors. Tunnel ventilation provided only a slight advantage during the heat of the day in terms of moderating dry-bulb air temperature and THI. Each of the tunnel-ventilated barns provided a slightly cooler interior environment than its naturally ventilated counterpart when outdoor conditions were potentially stressful (THI greater than 70). The average advantages in terms of reduced differentials between indoor and outdoor environments were -0.4 C and -0.3 for air temperature and THI, respectively, for the tunnel-ventilated barns. Average air speeds within the cow spaces of the barn pairs were equal – no difference existed for the two summertime ventilation systems. Considerable spatial variation in air speed existed with both systems - at least a spread of 1 m/s in all barns. There was also no difference in temporal variation of airspeed in the cow spaces of the barns – both ventilation systems produced fluctuating airspeeds at cow level in one or more barn quadrants. Therefore, microclimate control should be an area of emphasis with both ventilation systems. Risk management approaches should be used to evaluate these systems on a regional basis using historical weather data. Improved designs are needed for tunnel ventilation to enable systems to maintain desired air velocities throughout the cow space and to better accommodate large barns..