Simulation of site-specific irrigation control strategies with sparse input data

Crop and irrigation water use efficiencies may be improved by managing irrigation application timing and volumes using physical and agronomic principles. However, the crop water requirement may be spatially variable due to different soil properties and genetic variations in the crop across the field. Adaptive control strategies can be used to locally control water applications in response to in-field temporal and spatial variability with the aim of maximising both crop development and water use efficiency. A simulation framework ‘VARIwise’ has been created to aid the development, evaluation and management of spatially and temporally varied adaptive irrigation control strategies (McCarthy et al., 2010). VARIwise enables alternative control strategies to be simulated with different crop and environmental conditions and at a range of spatial resolutions. An iterative learning controller and model predictive controller have been implemented in VARIwise to improve the irrigation of cotton. The iterative learning control strategy involves using the soil moisture response to the previous irrigation volume to adjust the applied irrigation volume applied at the next irrigation event. For field implementation this controller has low data requirements as only soil moisture data is required after each irrigation event. In contrast, a model predictive controller has high data requirements as measured soil and plant data are required at a high spatial resolution in a field implementation. Model predictive control involves using a calibrated model to determine the irrigation application and/or timing which results in the highest predicted yield or water use efficiency. The implementation of these strategies is described and a case study is presented to demonstrate the operation of the strategies with various levels of data availability. It is concluded that in situations of sparse data, the iterative learning controller performs significantly better than a model predictive controller

Air pollution and livestock production

The air in a livestock farming environment contains high concentrations of dust particles and gaseous pollutants. The total inhalable dust can enter the nose and mouth during normal breathing and the thoracic dust can reach into the lungs. However, it is the respirable dust particles that can penetrate further into the gas-exchange region, making it the most hazardous dust component. Prolonged exposure to high concentrations of dust particles can lead to respiratory health issues for both livestock and farming staff. Ammonia, an example of a gaseous pollutant, is derived from the decomposition of nitrous compounds. Increased exposure to ammonia may also have an effect on the health of humans and livestock. There are a number of technologies available to ensure exposure to these pollutants is minimised. Through proactive means, (the optimal design and management of livestock buildings) air quality can be improved to reduce the likelihood of risks associated with sub-optimal air quality. Once air problems have taken hold, other reduction methods need to be applied utilising a more reactive approach. A key requirement for the control of concentration and exposure of airborne pollutants to an acceptable level is to be able to conduct real-time measurements of these pollutants. This paper provides a review of airborne pollution including methods to both measure and control the concentration of pollutants in livestock buildings

Opening Size Effects on Airflow Pattern and Airflow Rate of a Naturally Ventilated Dairy Building-A CFD Study

Airflow inside naturally ventilated dairy (NVD) buildings is highly variable and difficult to understand due to the lack of precious measuring techniques with the existing methods. Computational fluid dynamics (CFD) was applied to investigate the effect of different seasonal opening combinations of an NVD building on airflow patterns and airflow rate inside the NVD building as an alternative to full scale and scale model experiments. ANSYS 2019R2 was used for creating model geometry, meshing, and simulation. Eight ventilation opening combinations and 10 different reference air velocities were used for the series of simulation. The data measured in a large boundary layer wind tunnel using a 1:100 scale model of the NVD building was used for CFD model validation. The results show that CFD using standardk-epsilon turbulence model was capable of simulating airflow in and outside of the NVD building. Airflow patterns were different for different opening scenarios at the same external wind speed, which may affect cow comfort and gaseous emissions. Guiding inlet air by controlling openings may ensure animal comfort and minimize emissions. Non-isothermal and transient simulations of NVD buildings should be carried out for better understanding of airflow patterns

Opening Size E ects on Airflow Pattern and Airflow Rate of a Naturally Ventilated Dairy Building : A CFD Study

Airflow inside naturally ventilated dairy (NVD) buildings is highly variable and difficult to understand due to the lack of precious measuring techniques with the existing methods. Computational fluid dynamics (CFD) was applied to investigate the effect of different seasonal opening combinations of an NVD building on airflow patterns and airflow rate inside the NVD building as an alternative to full scale and scale model experiments. ANSYS 2019R2 was used for creating model geometry, meshing, and simulation. Eight ventilation opening combinations and 10 different reference air velocities were used for the series of simulation. The data measured in a large boundary layer wind tunnel using a 1:100 scale model of the NVD building was used for CFD model validation. The results show that CFD using standard k-ε turbulence model was capable of simulating airflow in and outside of the NVD building. Airflow patterns were different for different opening scenarios at the same external wind speed, which may affect cow comfort and gaseous emissions. Guiding inlet air by controlling openings may ensure animal comfort and minimize emissions. Non-isothermal and transient simulations of NVD buildings should be carried out for better understanding of airflow patterns

Comparison of CO2- and SF6- based tracer gas methods for the estimation of ventilation rates in a naturally ventilated dairy barn

Livestock production is a source of numerous environmental problems caused by pollutant gas emissions. In naturally ventilated buildings, estimating air flow rate is complicated due to changing climatic conditions and the difficulties in identifying inlets and outlets. To date no undisputed reference measurement method has been identified. The objective of this paper was to compare CO2- and SF6-based tracer gas methods for the estimation of ventilation rates (VRCO2 vs. VRSF6 ) in naturally ventilated dairy barns both under conventional and very open ventilation situations with different spatial sampling strategies. Measurements were carried out in a commercial dairy barn, equipped with an injection system for the controlled release of SF6, and measurement points for the monitoring of SF6 and CO2 concentrations to consider both horizontal and vertical variability. Methods were compared by analysing daily mean VRCO2=VRSF6 ratios. Using the average gas concentration over the barn length led to more accurate ventilation rates than using one single point in the middle of the barn. For conventional ventilation situations, measurements in the ridge seem to be more representative of the barn average than in the middle axis. For more open situations, both VRCO2 and VRSF6 were increased, VRCO2=VRSF6 ratios being also more variable. Generally, both methods for the estimation of ventilation rates gave similar results, being 10-12% lower with the CO2 mass balance method compared to SF6 based measurements. The difference might be attributed to potential bias in both methods

Development of a reference method for ventilation rate measurements in a naturally ventilated test facility

Gases produced in animal houses, such as NH3 and CO2, are not only harmful to the animals and farmers, but can also have negative effects on the environment. An optimum has to be found between maintaining a suitable indoor climate and preventing excessive emissions. For indoor climate control and especially emission measurements a reliable estimate of the airflow rate is essential. However, for naturally ventilated animal houses, no generally accepted reference technique exists to measure the airflow rate. Most existing techniques fail to account for the heterogeneous airflow patterns caused by the constantly changing external conditions of wind speed and direction. A new measuring method was developed through a stepwise approach starting from steady state measurements in wind tunnels up to measurements in a real size naturally ventilated test facility. This method, based on the automated traverse movement of a 3D ultrasonic anemometer across a rectangular vent, delivered detailed velocity profiles from which the airflow rate could be calculated. It was proven that the method accounts for both the temporal and spatial variability of the velocity profiles which are characteristic of naturally ventilated openings. The relative measurement error between the total building inflow and outflow rates remained within the range of ±20%. Due to the extensiveness of the experiments under a large range of wind incidence angles and speeds, a unique reference testing platform was created. The in depth knowledge of the velocity profiles and the associated in- and outflow rates through each vent, create possibilities for the development, the calibration and the validation of new and existing airflow rate measurement techniques for natural ventilation

Airflow Characteristics Downwind a Naturally Ventilated Pig Building with a Roofed Outdoor Exercise Yard and Implications on Pollutant Distribution

The application of naturally ventilated pig buildings (NVPBs) with outdoor exercise yards is on the rise mainly due to animal welfare considerations, while the issue of emissions from the buildings to the surrounding environment is important. Since air pollutants are mainly transported by airflow, the knowledge on the airflow characteristics downwind the building is required. The objective of this research was to investigate airflow properties downwind of a NVPB with a roofed outdoor exercise yard for roof slopes of 5°, 15°, and 25°. Air velocities downwind a 1:50 scaled NVPB model were measured using a Laser Doppler Anemometer in a large boundary layer wind tunnel. A region with reduced mean air velocities was found along the downwind side of the building with a distance up to 0.5 m (i.e., 3.8 times building height), in which the emission concentration might be high. Additional air pollutant treatment technologies applied in this region might contribute to emission mitigation effectively. Furthermore, a wake zone with air recirculation was observed in this area. A smaller roof slope (i.e., 5° slope) resulted in a higher and shorter wake zone and thus a shorter air pollutant dispersion distance

Effects of variability of local winds on cross ventilation for a simplified building within a full-scale asymmetric array: overview of the Silsoe field campaign

The large body of natural ventilation research, rarely addresses the effects of the urban area on ventilation rates. A novel contribution to this gap is made by the REFRESH cube campaign (RCC). During 9 months of observations, the Silsoe cube was both isolated and surrounded by a limited asymmetrical staggered array. A wide range of variables were measured continuously, including: local, reference and internal flow, stability, background meteorological conditions, internal temperature, and ventilation rates (pressure difference techniques for cross ventilated cases). This paper tests the impact of the array on the relation between local and reference wind speeds as modified by wind direction and on cross ventilation rates. The presence of the array causes a 50% to 90% reduction in normalised ventilation rate when the reference wind direction is normal to the cube. The decrease in natural ventilation varies with wind direction with large amounts of scatter for both setups. The relation between local and reference wind speeds for the array case had two characteristic responses, not explained by reference wind (speed or direction) nor sensitive to averaging period, turbulence intensity or temperature differences. Given the singular response of the CIBSE approach, it is unable to capture these conditions

강제환기식 육계사의 환기량 산정 방안 연구

학위논문 (석사)-- 서울대학교 대학원 : 농업생명과학대학 생태조경·지역시스템공학부, 2018. 2. 이인복.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.Chapter 1. Introduction 1 Chapter 2. Literature Review 4 2.1. Evaluating method for ventilation rate of livestock houses 4 2.2. Evaluation of ventilation rate according to static pressure difference 6 Chapter 3. Materials and Methods 9 3.1. Experimental broiler house 9 3.1.1. Ire broiler farm 9 3.1.2. Daeseon broiler farm 12 3.2. Fan performance curve 14 3.2. Orifice equation 16 3.3. Experimental instruments 18 3.4. Computational Fluid Dynamics (CFD) 19 3.5. Research method 20 3.5.1. Measurement of ventilation rate of Ire broiler house in winter condition 20 3.5.2. Measurement of ventilation characteristics in Daeseon broiler farm 21 3.5.3. Ventilation rate formula according to operating condition 26 3.5.4. CFD model design and validation 27 Chapter 4. Results and Discussion 31 4.1. Ventilation rate measurement in Ire broiler farm 31 4.2. Airflow measurement in Daeseon broiler farm 32 4.2.1. Measurement of environmental factors and ventilation characteristic 32 4.2.2. Evaluation of in-situ fan performance curve 34 4.2.3. Airflow decrease by windbreak 37 4.2.4. Evaluation of discharge coefficient of slot opening 39 4.3. Validation of CFD simulation model 43 4.4. CFD simulation result 48 4.4.1. Static pressure distribution 48 4.4.2. In-situ fan performance curve according to length of broiler house 51 4.5. Ventilation rate formula according to the operating condition 52 Chapter 5. Conclusion 57Maste