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

Modelling and reducing gas emissions from naturally ventilated livestock buildings

Livestock buildings are identified to be a major source of ammonia emissions. About 30% of the total ammonia emission within livestock sectors is from naturally ventilated dairy cattle buildings. The main objectives of this study are to predict emissions from naturally ventilated dairy cattle buildings and to establish a systematic approach to curtail the emissions.Gas concentrations were measured inside two dairy cattle buildings in mid-Jutland, Denmark. CO2 balance method was thus applied to estimate ventilation and emission rates. Computational fluid dynamics (CFD) was used to find the optimum gas sampling positions for outlet CO2 concentration. The gas sampling positions should be located adjacent to the openings or even in the openings. The NH3 emission rates varied from 32 to77 g HPU-1 d-1 in building 1 and varied from 18 to30 g HPU-1 d-1 in building 2.Scale model experiment showed that partial pit ventilation was able to remove a large portion of polluted gases under the slatted floor. In the full scale simulations, a pit exhaust with a capacity of 37.3 m3 h-1 HPU-1 may reduce ammonia emission only by 3.16% compared with the case without pit ventilation. When the external wind was decreased to 1.4 m s-1 and the sidewall opening area were reduced to half, such a pit ventilation capacity can reduce ammonia emission by 85.2%. The utilization of pit ventilation system must be integrated with the control of the natural ventilation rates of the building

The impact of atmospheric boundary layer, opening configuration and presence of animals on the ventilation of a cattle barn

Naturally ventilated livestock buildings (NVLB) represent one of the most significant sources of ammonia emissions. However, even the dispersion of passive gas in an NVLB is still not well understood. In this paper, we present a detailed investigation of passive pollutant dispersion in a model of a cattle barn using the wind tunnel experiment method. We simulated the pollution of the barn by a ground-level planar source. We used the time-resolved particle image velocimetry (TR-PIV) and the fast flame ionisation detector (FFID) to study the flow and dispersion processes at high spatial and temporal resolution. We employed the Proper Orthogonal Decomposition (POD) and Oscillating Patterns Decomposition (OPD) methods to detect the coherent structures of the flow. The results show that the type of atmospheric boundary layer (ABL) and sidewall opening height have a significant impact on the pollutant dispersion in the barn, while the presence of animals and doors openings are insignificant under conditions of winds perpendicular to the sidewall openings. We found that the dynamic coherent structures, developed by the Kelvin-Helmholtz instability, contribute to the pollutant transport in the barn. We demonstrate that in any of the studied cases the pollutant was not well mixed within the barn and that a significant underestimation (up to by a factor 3) of the barn ventilation might be obtained using, e.g. tracer gas method. © 2020 The Author

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

Optimization Design on Ventilation Openings of Super Large Circular Coal Storage Dome

In order to reduce the pollution of the atmospheric environment, the super large coal storage warehouse has gradually become the main coal storage mode of power plants and other enterprises. However, due to the enclosed structural form, volatile coal dust and coal seam volatile combustible gas concentration is too high, which resulting in increased risk of ignition detonation. Therefore, this paper based on ventilation engineering theory and combined with CFD which focus on natural ventilation used in large diameter (D = 100 m) circular coal storage dome. The impact of opening modes, opening positions and opening size of super large circular coal storage dome on ventilated characteristics were also studied. The designed method of ventilated openings for super large circular coal storage dome is further proposed

Investigation of natural ventilation performance of large space circular coal storage dome

Large space circular coal storage dome (LSCCSD) offers an environmental and dependable alternative to open stockpiles, and it has been consequently widely applied in China. However, due to the lack of scientific guidelines, its natural ventilation performance is lower than expected. Natural ventilation potential strongly depends on the roof geometry and opening mode, which have not yet been investigated for LSCCSD. This paper presents a detailed evaluation of the impact of dome geometry (rise span ratio), opening height, and opening modes on the ventilation performance of LSCCSD. The evaluation is based on computational fluid dynamics (CFD) methods and is validated by available wind tunnel testing. We employed three evaluation indicators, which are wind pressure coefficient, effective ventilation rate, and wind speed ratio. The results demonstrate that the rise span ratio has a significant effect on the wind pressure difference and the effective ventilation rate increases by approximately 9%–42% with a single-annular opening. When double-annular openings are set in a strong positive pressure zone, the effective ventilation rate increases by 100% and the average wind speed ratio increases by 50%. When it is compared with single one with similar opening height, the effective ventilation rate increases by 25%. The optimum natural ventilation performance for LSCCSD is achieved at a rise span ratio of 0.37. In addition, the lateral middle opening is kept higher than the ridge top of the coal pile. The proposed evaluation approach and design parameters provided instructive information in the building design and ventilation control for LSCCSDs

The impact of ventilation type on the heat load of dairy cows

Received: January 31st, 2021 ; Accepted: March 27th, 2021 ; Published: November 26th, 2021 ; Correspondence: [email protected] load in cattle causes deterioration of health and reduced production of milk. Therefore, it is necessary to protect cows by appropriate passive and active means and monitor the air quality in barns. Based on several indicators of environmental quality, is possible to make a more comprehensive assessment of the microclimate and more precise conclusions. This study, was monitoring the values of air temperature, relative humidity, and air velocity in two barns with the same volume and layout with floor dimensions of 26.6 m × 62.1 m. In barn 1, roof ridge of which had underwent only partial reconstruction, there were installed fourteen basket fans with a total fan performance Q(1)fans = 218,400 m3 h -1 . In barn 2, there were twelve panel fans with a total fan performance Q(2)fans = 289,320 m3 h -1 . The resulting THI, HLI and ETIC values were compared in relation to each other and in relation to the recommended values. Despite the operating ventilation technology and enlargement of wall openings, the above-limit values of climatic characteristics were observed in both barns during tropical days. There were no differences between the barns (p ˃ 0.05), in barn 1: THI(1) = 83.10 ± 0.51; HLI(1) = 85.62 ± 1.42; ETIC(1) = 27.24 ± 0.31, and in barn 2: THI(2) = 83.12 ± 0.34; HLI(2) = 85.77 ± 1.50; ETIC(2) = 27.29 ± 0.28, however, there were found significant differences in values of temperature indices obtained in the detailed measurements at points arranged perpendicularly, as well as parallelly, to the direction of air velocity in the animal zone (p < 0.05)