加装大风量风机对夏季湿帘降温奶牛舍的防暑降温效果分析

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

低屋面横向通风(Low Profile Cross Ventilated,LPCV)牛舍在华北地区应用,引发高温高湿问题。为解决此问题,该研究选择石家庄某奶牛场的2栋不同尺寸的LPCV牛舍,加装数量不同的轴流风机。结果表明:轴流风机的工作效率受牛舍跨度以及其安装位置的影响,30m跨度牛舍运行更稳定,风速不均匀系数小于0.20;在74m跨度牛舍,南侧湿帘端的风机工作效率更高。舍内环境与奶牛生理指标评价表明:30m跨度舍加装轴流风机后,过帘风速为2.17±0.20 m/s,提升45.6%,舍内卧栏处风速为1.95±0.85 m/s、提升10.8%,进风量增加418339.09 m3/h,舍内平均温度为27.7±1.9℃,相对湿度下降9.2%、平均值为(75.9±6.6)%。74 m跨度舍过帘风速为1.96±0.20 m/s,卧栏处平均风速为1.62±0.91 m/s,进风量为1008568.80 m3/h,平均温度为27.7±1.8℃,舍内平均相对湿度为(74.6±5.8)%;二栋牛舍内平均温度、相对湿度、奶牛呼吸频率与皮肤温度在加装轴流风机后无显著性差异(P>0.05)。综上,加装轴流风机可以显著改善舍内环境,并创造有利于奶牛生存的环境。

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 1830 mm,the rated power of 2237.1 W,and the maximum air volume of 86000 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 418339.09 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 1008568.80 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.