Study on ventilation rate estimation of mechanically ventilated broiler house

Abstract

The percentage share of the livestock industry output value of Korean agriculture has been steadily increasing since the 1990s. Among them, the chicken production has been increasing as consumption per capita. Broiler houses had been increased their scale and breeding density in order to meet the chicken consumption. However, dense breeding density causes accumulation of heat, moisture, and contaminants inside the broiler house. The improper environment in broiler house leads to a decline in productivity. Various problems can occur because of the failure of environmental control, such as dehydration due to the high temperature and low humidity, and proliferation of pathogenic microorganisms due to excessive humidity, and weakening of broiler's immunity due to the accumulation of pollutants. Mechanically ventilation system and automatic control system were being introduced into broiler houses, to improve production efficiency through precise environmental control. Mechanically ventilated broiler house has an advantage in terms of controlling ventilation, which is the main environmental control mechanism in livestock houses. Heat, moisture, and pollutants generated inside the broiler house are discharged through ventilation. In order to discharge appropriate amount of substance, accurate evaluation of the ventilation rate is required. The ventilation control in mechanically ventilated broiler house is based on maximum airflow of exhaust fans currently. However, the actual airflow of the fan is reduced as the inlet area of facility decreases and thus static pressure difference between inside and outside of the facility increases. In consideration of this phenomena, evaluating method of ventilation rate was proposed using a fan performance curve, which is the ventilation characteristic of the exhaust fan and orifice equation, ventilation characteristic of the inlet. The in-situ fan performance curve and the discharge coefficient, which is the coefficient of orifice equation have to be evaluated in order to estimate the exact amount of ventilation rate in the broiler house. In this study, ventilation rate was evaluated according to the operating conditions of the ventilating facility, in two mechanically ventilated broiler houses. Reduction of ventilation rate to set value was measured in the Ire broiler farm located in Buyeo, Chungcheongnam-do. The airflow of sidewall fans was measured according to the operating fans, under slot opening condition of winter. As a result, average airflow through target sidewall fan decreased as the number of operating fans increase. Measured ventilation rate when all three sidewall fans were operated was 77.0% of the set ventilation rate. The slot opening, inlet of target broiler house was 25% open during the experiment. It was analyzed that the static pressure difference due to the narrow slot opening area reduced ventilation rate by acting as a load on the exhaust fans. Experiment for evaluating ventilation characteristic was conducted in mechanically ventilated broiler house located in Gimje, Jeollabuk-do. The ventilation rate of tunnel fan and the static pressure difference between inside and outside of target broiler house were measured according to the ventilation operating condition, a number of operating fans and slot opening area. Computational fluid dynamics model of target broiler house was designed to overcome the limitation of the field experiment. As a result of regression analysis of the airflow for model validation, a significant difference between measured and simulated airflow was not observed (p-value = 0.239). The measured ventilation rate and static pressure difference were analyzed to calculate the ventilation characteristic of target broiler house: in-situ fan performance curve and the discharge coefficient. The static pressure difference of in-situ fan performance curve was average 33.7 Pa low than design fan performance curve provided by the manufacturer. Computational fluid dynamics results showed low static pressure difference of in-situ fan performance curve was due to the distribution of static pressure. The static pressure difference between inlet and outlet of exhaust fans was relatively high according to the design fan performance curve. On the other hand, in most of the remaining space including the measurement position of the experiment, constant and low static pressure difference was formed. Computational fluid dynamics models of broiler houses with different lengths were additionally designed. A significant difference between simulated fan performance curve by broiler house length was not calculated (p-value = 0.189). Therefore, the in-situ fan performance curve was analyzed to be a unique characteristic of the target exhaust fan. The discharge coefficients were calculated 0.344 to 0.743 according to the slot opening area. The measured discharge coefficients were 5.29%–114.3% of widely used discharge coefficient of the vent (0.65). For the general application of the discharge coefficient, regression analysis was conducted. The linear relationship between the discharge coefficient and slot opening area was derived (R² = 0.851). Ventilation rate formula was derived from in-situ fan performance curve and orifice equation. It is expected that the ventilation rate can be calculated by a number of operating fans and slot opening area through the estimation formula proposed in this study, instead of field measurement using expensive equipment.