It is a common practice to use longitudinal ventilation to cool the chickens in the hot summer season. For high-density intensive laying hen farming, the wind speed in the general chicken house should be at least 3m/s or more. The wind speed should be greater than 4m/s in order to obtain a better "air cooling effect".
"Air cooling effect" mainly refers to reducing the body temperature of chickens through wind speed
"According to a study by the University of Georgia, the wind speed increases from 0m/s to 2.54m/s. The chicken's body temperature will drop by more than 6°C"
In order to obtain greater wind speed, our usual practice is to make the chicken house as a suspended ceiling, reduce the height of the chicken house, or install windshields or windshields at regular intervals along the triangular roof from the top of the chicken house to reduce the The cross-sectional area of the house to increase the wind speed in the house.
Why do this, mainly because the wind speed is closely related to the cross-sectional area of the chicken house;
Calculation of wind speed of longitudinally ventilated chicken house: wind speed = ventilation volume / cross-sectional area of chicken house
It is clear from the calculation formula that to increase the wind speed of the house, either increase the ventilation volume of the house, that is, increase the number of anti-negative pressure fans, or reduce the cross-sectional area of the house.
Adding fans means increasing costs, increasing power consumption, and increasing maintenance costs, which will increase operating costs for enterprises in the long run;
Then increasing the wind speed should be considered in terms of reducing the cross-sectional area of the chicken house. Let's understand the changes of the chicken house before and after adding the windshield through specific calculations.
For example: the chicken house is 12m wide and 100m long, the side wall height of the chicken house is 2.4m, the middle (highest) of the chicken house is 4.8m, and 10 50-inch fans are installed in the chicken house, and the ventilation volume of each fan is 31000m³ at -50 Pa. /h;
=31000/3600×10/【12×（4.8＋2.4）/2】=86.1/43.2=1.99m/s
Then the wind speed of the chicken house should be
Wind speed = ventilation volume / cross-sectional area
=31000/3600×10/[12×(4.8+2.4)/2]=86.1/43.2=1.99m/s
=31000/3600×10/【12×（3.6+2.4）/2】=86.1/36=2.39m/s
If we install a suspended ceiling or a windscreen in the chicken house, so that the height of the top of the chicken house or the lower edge of the vertical curtain from the ground is 3.6m, and the height on both sides of the chicken house remains unchanged, then the wind speed is
=31000/3600×10/[12×(3.6+2.4)/2]=86.1/36=2.39m/s
Therefore, when the number of fans remains the same, by reducing the cross-sectional area of the house, the wind speed can be increased by 0.4m/s on the original basis, that is, the efficiency is increased by 20%, and the air cooling effect caused by the change of wind speed is also different. The temperature difference corresponding to the air cooling effect is about 2 °C. In the case of extreme high temperature, the temperature difference of 2 °C is enough to cause serious damage to the chickens.
We have learned the benefits of using windshields in tunnel-ventilated chicken houses, so is the larger the windshield in the chicken house, the better? Does the windshield have a negative effect on ventilation?
一、Negative effects of windshield on longitudinal ventilation
In actual production, it is more common to install the windshield at a lower level, hoping to obtain a higher wind speed. However, this incorrect use method will cause some negative effects:
1.1 It will cause uneven wind speed in the chicken house
If the windshield is installed too low, the wind speed under the windshield will be very high, but the wind speed oil between the windshields is too low. In this way, the difference between the lowest and the highest wind speed may reach between 1~3m/s, and the air cooling effect of this uneven wind speed on the chickens is also very uneven.
1.2 Increased house static pressure
Because in negative pressure ventilation, each windshield will increase a certain static pressure value, especially when the windshield is installed too low, the increase in static pressure is obvious, as shown in the figure, The higher the static pressure of the chicken house, the greater the negative pressure, and the greater the negative pressure, the easier it is for the air to enter from the air leakage of the chicken house (without cooling through the wet curtain), which affects the longitudinal ventilation effect.
1.3 Reduce fan efficiency
In fact, this is also caused by the increase in static pressure in the chicken house. The higher static pressure increases the exhaust resistance, which directly reduces the working efficiency of the fan, and the efficiency will be reduced by 30% or more, and the load Larger fans are more prone to failure
1.4 Reduce air flow in the house
The increase of static pressure, the increase of air flow resistance, and the decrease of fan efficiency reduce the circulation and exchange of air in the house, thereby reducing the amount of cooling air entering the house from the air inlet through the wet curtain, and the cooling effect of the wet curtain is reduced. This is also not what we want to see.
Due to the above factors, the temperature difference in the chicken house is relatively large, which makes the actual feeling of the chicken group also quite different.
二、Precautions for installation and use of windshield
The installation of windshields in the chicken house during longitudinal ventilation in summer does have a positive effect on improving the wind speed and cooling effect in the chicken house, but if it is used improperly, it will also cause some negative effects. Therefore, the following must be paid attention to during installation and use. several aspects:
2.1 For example, the height of the side wall of the chicken house is 2.4 meters, and the height of the lower edge of the windshield from the ground should not be less than 2.7m. If the windshield is installed too high, the effect of increasing the wind speed will not be obvious. If the installation is too low, it will affect the chickens. ventilation in the house.
2.2 The distance between the windshields should not exceed 12m. If the distance between the windshields is too large, the effect of increasing the wind speed will not be obvious.
2.3 The windshield has a significant effect on increasing the wind speed in the chicken house, but it should not be used as the main means to increase the wind speed. The wind speed increased by installing the windshield should be controlled at about 0.5m/s. Any expectation of obtaining higher wind speed from it may be will have the opposite effect.
The calculation method of the height of the windshield of the longitudinal ventilation chicken house:
The distance of the curtain from the ground = [ventilation volume / (wind speed × width)] × height - minimum high speed
For example: the chicken house is 12m wide and 100m long, the side wall height of the chicken house is 2.4m, the middle (highest) of the chicken house is 4.8m, and 10 50-inch fans are installed in the chicken house, and the ventilation volume of each fan is 31000m³ at -50 Pa. /h;
We increased the wind speed to 2.5m/s by adding a windshield
The height of the windshield = [(31000/3600×10)/(2.5×12)]×2-2.4m≈3.4m, that is, when installing the windshield, the height of the lower edge from the ground is about 3.4m.
In general, the installation of windscreens in the house during longitudinal ventilation has a positive effect on increasing the wind speed and reducing the temperature of the house, but we must clearly recognize that the wrong use of the windscreen will also cause adverse consequences, so , For those chicken houses whose height is not high and the wind speed is sufficient, there is no need to install the windshield; for the completed chicken house, it is advisable to increase the wind speed without increasing the fan. However, it is necessary to grasp the instructions of the windshield to ensure that the ventilation volume and wind speed of the chicken house are uniform and unaffected.
