Analysis of ventilation and cooling effects of installing axial fans in wet curtain cooling dairy cattle barn

High temperature and humidity often occur in summer, since one type of dairy cattle barn, the low profile cross ventilated (LPCV) was introduced into North China. This study aims to evaluate the effect of axial flow fan applied in various sizes of LPCV dairy cattle barns, thereby improving the living environment of cattle. A field pre-test was carried out to verify the experimental simulation of air flow field. Low-pressure axial flow fans with large flow were installed at the leeward side of deflectors in two LPCV dairy cattle barns with different sizes. One axial flow fan was equipped with 6 deflectors, the blade diameter of 1 830 mm, the rated power of 2 237.1 W, and the maximum air volume of 86 000 m3/h. The results showed that the working efficiency of axial flow fans depended mainly on the installation position and the span of the cowshed. In the cowshed with a small span, the nonuniformity coefficient of wind speed was less than 0.20. In the cowshed with a large span, the higher working efficiency was achieved in the fans that were installed near the end of the wet curtain, although the nonuniform coefficient was larger with relatively low uniformity of jet field. In cowshed 1, the wind speed of the fan jet decreased by 25.3%, from plane A (3.0 m away from the pole) to plane C (6.0 m away from the pole). In cowshed 2, the wind speed of the fan jet at row 2 to 3 and row 6 to 7 decreased by 31.5% and 24.8%, respectively. An evaluation was obtained on the environmental conditions and physiological indexes of dairy cows after the installation of axial flow fans. In cowshed 1, the wind speed through the wet curtain was (2.17±0.20) m/s, increasing by 45.6%, while the wind speed at the stalls was (1.95±0.85) m/s, increasing by 10.8%, where the intake rate of air increased by 418 339.09 m3/h. In the cowshed, the average temperature was (27.7±1.9)℃, and the average relative humidity was (75.9 ± 6.6)%, decreasing by 9.2%CO2. The average respiratory rate and skin temperature of cows decreased significantly (P<0.05). In cowshed 2, the wind speed through the wet curtain was (1.96 ± 0.20) m/s, while the average wind speed at the horizontal fence was (1.62±0.91) m/s, and the air intake rate was 1 008 568.80 m3/h, meeting the needs of ventilation and cooling in summer. In the cowshed, the average temperature was (27.7±1.8)℃, and the average relative humidity was (74.6±5.8)%. There was no significant difference in the average temperature, the average relative humidity, the respiratory rate, and skin temperature of dairy cows in cowshed 1 with axial flow fan (P>0.05). Furthermore, the daily average equivalent temperature index for cattle (ETIC) values for the group no axial flow fan 1 (NAFF1), axial flow fan 1 (AFF1), and axial flow fan 2 (AFF2) were 24.64±2.09 ℃, 22.71±1.55 ℃ and 22.03±1.39 ℃, respectively. The temperature-humidity index (THI) value in the barns showed a downward trend from the end of the wet curtain to the fan end, after the installation of axial flow fans. The THI value in the treatment group of AFF1 and AFF2 decreased by 0.03 and 0.02 per meter along the airflow direction, opposite to that before installing the fan. The installation of an axial flow fan can significantly improve the barn environment for the better living of dairy cows.