Animal Occupied Zone Research Articles

A numerical study on forced convective heat transfer of a chicken (model) in horizontal airflow

Under hot climatic conditions, heat stress of the animal is a general concern in livestock farming. To reduce the heat stress, an important approach is ensuring a suitable air speed in the animal occupied zone (AOZ) to increase convective heat removal for animals. Therefore, the relationship between convective heat transfer and air speed is essential to understand the effects of the airflow speed manipulation, and consequently, the optimal design and control of a ventilation system. In this study, computational fluid dynamics (CFD) was employed to study the convective heat transfer coefficient for a chicken. Simulated results were compared with the experimental data found in the literature. SST k–ω model was evaluated on a sphere model first by comparing it to a semi-experimental equation of the convective heat transfer coefficient. Good agreement was found and therefore this numerical method was adopted for further modelling with a more realistic geometric model of a chicken. Three different angles between the chicken trunk axis and airflow direction: 0°, 45°, and 90° were studied as well as various chicken weights of the model. The study results revealed that the angle at which the airflow struck the chicken model was not significant. By testing chicken models at different weights (bird mass of 0.2 kg, 0.9 kg, and 2 kg), larger specific surface (the ratio of surface area to the weight) led to a higher convective heat transfer coefficient. In addition, a correlation of the predicted convective heat transfer coefficients was found between a sphere and the chicken models used, indicating that a chicken can be simplified as spherical model in future studies.

Spatial variability of mixing ratios of ammonia and tracer gases in a naturally ventilated dairy cow barn

The use of the tracer gas ratio method to estimate emissions from naturally ventilated (NV) livestock barns excludes the need of monitoring ventilation rates. However, it requires accurate measurement of tracer release rate (Q T ) and a representative estimate of the mixing ratio between pollutant (P) and tracer (T) gases ( [ P ] / [ T ] ¯ ) . While the quality of Q T simply depends on using an accurate commercial mass flow controller, determination of a representative mixing ratio [ P ] / [ T ] ¯ is not trivial, since the NV livestock barn airspace presents complex movements that might be dependent on spatial vertical and cross horizontal dimensions. The goal was to assess the spatial variability of concentrations of the artificial tracer gas sulphur hexafluoride (SF 6 ), the metabolic carbon dioxide (CO 2 ) and the pollutant ammonia (NH 3 ), along with their mixing ratios ([NH 3 ]/[CO 2 ], [NH 3 ]/[SF 6 ], [CO 2 ]/[SF 6 ]), inside a NV dairy cow barn. The results indicated that the vertical variability of the calculated mixing ratios became more stable with increase in height, reaching approximately constant values above the animal occupied zone. Using both the metabolic CO 2 and the artificially injected SF 6 as tracer gases led to a homogeneous spread in behaviour of mixing ratios along V and HC directions. Finally, the possibility of finding a zone within the barn airspace where mixing ratios are considered to be representative for the whole barn, and the implications of applying artificial or metabolic tracers are discussed. • Using CO 2 or SF 6 as tracers gas led to homogeneous mixing ratios across the barn. • Best region to determine mixing ratios is above the animal occupied zone (AOZ). • Concentration data in the AOZ is highly uncertain and may not be representative. • Pollutant and tracer do not need to spread homogeneously for stable mixing ratios.

SPATIAL DISTRIBUTION OF AIR FLOW AND CO2 CONCENTRATION IN A NATURALLY VENTILATED DAIRY BUILDING

Air flow measurements as well as concentration measurements within a naturally ventilated dairy barn (NVD) were carried out during one summer season of 2012. Air flow measurements were performed using ultrasonic anemometers (UA), either as short duration (20 min duration) measurements with a higher spatial distribution (using up to 9 UAs at the same time) or as long period (roughly 2 weeks) measurements with a lower spatial resolution (3 to 5 UAs). Measurements were conducted at two heights, at 1.5 m within the animal occupied zone (AOZ) and at 2.6 m height above the AOZ for understanding the distribution of airflow within the building. The three wind components (u, v and w) were measured either as lateral profile or evenly distributed at the ground area of the building. The results showed that wind speeds measured at the height 2.6 m were generally smaller than wind speeds measured at the height 1.5 m. The analysis of the lateral profile showed that only the first third of the wind facing side seem to benefit from the approaching wind. The long term measurements (duration 2 weeks) showed a high variability in the data and a correlation analysis showed lower CO2 concentrations for higher wind speeds. However, the linear correlation was weak (p= -0.7), which implies that the relationship cannot be described simply by a linear correlation.

Air velocity measurements using ultrasonic anemometers in the animal zone of a naturally ventilated dairy barn

Air velocity measurements were collected from one horizontal plane across the entire animal occupied zone (AOZ) floor area of a dairy barn. Data recorded from the undisturbed approaching airflow (25° deviation from normal to the sidewall of the building) and an approach flow disturbed by obstacles (surrounding buildings) in front of the barn (at an incident angle of 20° from normal to the building facade) were analysed. The 96.2 m long, 34.2 m wide and 10.7 m high (ridge) building had open sidewalls, wind protecting nets and large openings in both gable walls. The barn, with a loose housing system with freestalls, accommodated 364 dairy cows. The outside temperatures were between 10 and 20 °C, and the outside wind speeds were between 0.7 and 3.9 m s −1 . The air speed in the AOZ varied from 0.2 to 1.4 m s −1 . Differences between single areas inside the barn were large and led to different climatic conditions for different animal groups. The undisturbed approaching airflow (at an incident angle of 25° from normal) resulted in a heterogeneous airflow pattern inside the barn with no defined outlet. This airflow pattern was probably influenced by the surrounding buildings on the leeward. In contrast, the disturbed approaching airflow (with obstacles at the windward side) resulted in a homogeneous flow pattern with a lower airflow. A linear model showed that only the interaction between the outside wind speed and the outside wind direction significantly influenced the inside air velocity. Long term measurements at or above the AOZ are needed to complement existing data. ► Air velocity measurements were made at 36 locations in a naturally ventilated barn. ► Interaction between wind speed and direction had significant effect on inside flow. ► Different areas had different wind speeds leading to different climatic conditions. ► Undisturbed approaching flow (normal to sidewall) gave heterogeneous flows in the barn. ► Disturbed approaching flow (with windward obstacles) gave homogeneous flow pattern.

Evaluation of methods for determining air exchange rate in a naturally ventilated dairy cattle building with large openings using computational fluid dynamics (CFD)

Naturally ventilated dairy cattle buildings are a major source of ammonia and greenhouse gas emissions. Accurate estimation in gas emissions constitutes the first step towards reducing the negative impact of emissions on the local environment. The greatest uncertainty in the emission estimation from a naturally ventilated livestock building with large openings is the determination of the air exchange rate (AER) and the choice of the gas sampling positions for representative outlet gas concentration. To reduce the uncertainties in the emission estimation, the performances of three techniques – integrating volume flow rates (VFR), tracer gas decay (TGD) and constant tracer gas (CTG) for determination of ventilation rates were assessed in this paper by Computational fluid dynamics (CFD). In the developed CFD model, the animal occupied zone (AOZ) was treated as porous media and the resistance coefficient of porous zone was derived by pressure drops across AOZ using a sub-CFD model. The results showed that AERs predicted by VFR and TGD were in good agreement with each other within a large range of wind speeds. The large difference in AER estimation using CTG and VFR indicates that the mean CO2 concentration of the entire room may not represent the concentration at the air exit. It may be not suitable to calculate AER using mean concentration of internal sampling positions. When wind became stronger, the accuracy of CTG decreased. The gas sampling positions should be close to the openings or even in the openings; the gas sampling positions should be located adjacent to the openings or even in the openings. To reduce the uncertain introduced by wind direction, all the openings especially of different azimuths should possess sampling tubes. The maximum gas concentrations in the different openings could be the optimum value to represent the concentration in the exit air.

Emissions of Ammonia, Hydrogen Sulfide, and Odor before, during, and after Slurry Removal from a Deep-Pit Swine Finisher

It is a common practice in the midwestern United States to raise swine in buildings with under-floor slurry storage systems designed to store manure for up to one year. These so-called “deep-pit” systems are a concentrated source for the emissions of ammonia (NH3), hydrogen sulfide (H2S), and odors. As part of a larger six-state research effort (U.S. Department of Agriculture-Initiative for Future Agriculture and Food Systems Project, “Aerial Pollutant Emissions from Confined Animal Buildings”), real-time NH3 and H2S with incremental odor emission data were collected for two annual slurry removal events. For this study, two 1000-head deep-pit swine finishing facilities in central Iowa were monitored with one-year storage of slurry maintained in a 2.4 m-deep concrete pit (or holding tank) below the animal-occupied zone. Results show that the H2S emission, measured during four independent slurry removal events over two years, increased by an average of 61.9 times relative to the before-removal H2S emission levels. This increase persisted during the agitation process of the slurry that on average occurred over an 8-hr time period. At the conclusion of slurry agitation, the H2S emission decreased by an average of 10.4 times the before-removal emission level. NH3 emission during agitation increased by an average of 4.6 times the before-removal emission level and increased by an average of 1.5 times the before-removal emission level after slurry removal was completed. Odor emission increased by a factor of 3.4 times the before-removal odor emission level and decreased after the slurry-removal event by a factor of 5.6 times the before-removal emission level. The results indicate that maintaining an adequate barn ventilation rate regardless of animal comfort demand is essential to keeping gas levels inside the barn below hazardous levels.

CLIMATE CONTROL BASED ON TEMPERATURE MEASUREMENT IN THE ANIMAL-OCCUPIED ZONE OF A PIG ROOM WITH GROUND CHANNEL VENTILATION

It is known that there can be a significant temperature difference between the position of the climate controllersensor (room temperature) and the animal-occupied zone (AOZ) in a pig room. This study explores the advantages of usingAOZ temperature in climate control. The objectives were: (1) to evaluate a current climate control system in a practical roomwith ground channel ventilation for weaned piglets by comparing AOZ and room temperature, and (2) to determineadvantages of control of the heating system based on AOZ temperature by a model-based predictive (MBP) controller.Comparison of AOZ and room temperature showed that during the first 10 days of the two experimental batches, AOZtemperature was lower and showed greater fluctuations than room temperature, most likely due to the switching of the heatingsystem (on/off). Animals close to the sensor could disturb the AOZ measurement. This was not the case during colder nights,when animals moved away from the sensor and the measured AOZ temperature was a good indicator of the air temperaturearound the animals. The data for those periods were suitable for use in this climate control study, but when applying the systemin practice the disturbing effect needs to be prevented by better protection of the AOZ sensor. For the second objective, thecourse of the AOZ temperature was modeled based on data for five nights when the heating switched on and off several times(goodness of fit Rt 2 = 0.77). One of the models was integrated in a simulated MBP controller that uses the model to predictfuture AOZ temperature; the controller switches the heating system on before the AOZ gets too cold and off before it gets toowarm. The simulated AOZ temperature was more stable during an 11 h cold period; the standard deviation was reduced from0.44C to 0.18C.

MEASUREMENT OF AIR VELOCITY IN ANIMAL OCCUPIED ZONES USING AN ULTRASONIC ANEMOMETER

The air velocity in the animal occupied zone (AOZ) of a pig facility influences the thermal comfort of pigs andis affected by the ventilation system in the building. Little is known about the relationship between the air velocity in the AOZand the ventilation system design. This article describes the development and a practical test of an air velocity measuringsystem in the AOZ using ultrasonic anemometers.<br><br>The anemometers were protected by a wire protection cage, which resulted in a lower air velocity measurement that wascorrected by a linear correction factor of 0.83. A suitable aggregation interval for timeaveraged air velocity measurementsin occupied pens was 300 s. The effect of animal activity on the measured air velocity was minimal and therefore neglected,but the location of the anemometer in a pen was deemed important. A representative location was above the resting placeof the animals over the solid floor. The presence of an anemometer in a pen resulted in some minor changes in the lyingbehavior of the animals.<br><br>In the experimental doorventilated room with weaned piglets there was a clear (0.04 m/s) and significant difference inaverage air velocity between pens 3 and 9 (P < 0.001). The maximum air velocity of 0.15 m/s advised was exceeded in 21%of the time a pen in the back of the room. In a pen closer to the door, air velocities appeared to be too high less than 2% ofthe time.<br><br>The measuring system described in this article can be combined with air quality and temperature measurements in the AOZfor determination of the performance of ventilation systems and comparison of ventilation systems.

CONTAMINANT AND HEAT REMOVAL EFFECTIVENESS OF THREE VENTILATION SYSTEMS IN NURSERY ROOMS FOR PIGS

In this research, three ventilation systems (ground channel, porous ceiling, and door ventilation) were tested on their performance in supplying fresh air to the animal occupied zone (AOZ), each in a room for 70 weaned piglets. Measurements of the CO2 concentration and temperature of the inlet air, at one point in the AOZ, and in the outlet air were recorded every 36 minutes for three successive batches. Less frequent measurements were done on the CO2 concentration in two other points in the AOZ. System effectiveness was expressed as the contaminant removal effectiveness (CRE) for CO2 and the heat removal effectiveness (HRE): CRE or HRE equals 1 when the CO2 concentration or temperature in the AOZ equals that of the outlet air. Values lower than 1 reflect higher CO2 concentrations or temperatures within the AOZ; values higher than 1 the reverse. In all rooms, the value of CRE or HRE varied in time by varying the ventilation rate. CRE was highest in the room with ground channel ventilation, varying with measurement location. CRE was 1.39 on average and HRE was 1.13 on average in the middle of the pen. CRE was higher closer to the air inlet and lower further to the back of the pen, closer to the outlet, because air renewal was based on displacement of old air by fresh air. In the room with door ventilation, CRE was 1.20 and HRE was 0.95 at a point in the second half of the room in the back of a pen. Air passed over the operator walkway to the back of the room, and back over the pens, resulting in a decreased CRE in the pens closer to the door that acted as an air inlet. In the room with a porous ceiling, CRE values were lower. At one sampling point, CRE was 1.01 and HRE was 0.94. In the lying area of the animals in the back of the room, CRE values were lower than at a sampling point in the front of the room. In the lying area, the heat production of the animals resulted in an upward airflow, which lowered the CRE.

VARIABLE RATE HEATER CONTROL FOR LIVESTOCK SPACE HEATING

An unvented liquid propanegas (LP) space heater, often used in animal housing, was modified to provideautomated variable heat output. As manufactured, the heater had manuallyadjusted output settings between 14.7 and29.3 kW (50,000 and 100,000 Btu/h). The heater was modified by adding a stepper motor and speed reducer to the manualproportioning valve to provide continuous and automated heater output adjustment between 14.7 and 29.3 kW.<br><br>Experiments were conducted to compare animal occupied zone (AOZ) velocities, AOZ temperatures, and fuel consumptionusing on/off and automated variable control modes. These experiments were conducted using inside set point and ambientair temperature differences of 14 and 28
C (25 and 50
F). All experiments were conducted in the Air Dispersion Laboratoryat Iowa State University.<br><br>Adding automated variable control reduced the AOZ temperature fluctuations from 5.3
C (on/off) to 1.1
C (9.5 to 2.0
F).In the AOZ, the standard deviation across the entire test room was reduced from 1.4
C (on/off) to 0.3
C (2.6 to 0.5
F). TheAOZ airspeed fluctuations were reduced from 10 cm/s (on/off) to 2 cm/s (20 to 4 ft/min). No differences were found in fuelconsumption. Results indicate a need for heaters capable of continuous adjustment to even lower energy output levels.

A GENERAL PURPOSE LABORATORY FOR EVALUATING LIVESTOCK VENTILATION SYSTEMS

A facility developed at Iowa State University was designed to test and provide research for full-scale livestockhousing ventilation systems. A test chamber representing a 24-ft (7.3 m) section of a 42-ft-wide (12.8 m) swine finishing ornursery barn can be outfitted with a complete ventilation system. Operating characteristics of the ventilation system aremonitored. These characteristics include ventilation rate, airspeed, and temperature in the animal-occupied zone, air jetprofiles generated by the inlets, energy consumption of the ventilation system, and response characteristics of the controlsystem. The chamber contains no animals. Sensible heat production is simulated with cone resistance heaters. Equipmentin production barns such as feeders, waterers, gates, and flooring are included. The test chamber is also equipped with apit area for conducting pit-ventilation studies. The test chamber, housed within the Air Dispersion Laboratory, is currentlyin use to investigate pit-ventilation effectiveness, heater control logic, ventilation system performance from manufacturedsystems, and to verify current recommendations of ventilation performance standards for livestock ventilation systems(Proposed ASAE Standard X567).

Three-dimensional Airflow in a Livestock Test Room with Two-dimensional Boundary Conditions

This work is part of a project to develop numerical simulation methods for predicting the effect of animals and pen partitions on the airflow in the animal-occupied zone. As a reference case for this, it was desired to create a steady two-dimensional flow near the floor in an empty test room (8·5 m long, 3 m high and 5 m wide). A plane wall jet is usually expected to generate a two-dimensional airflow and therefore the test room was equipped with a slot inlet beneath the ceiling on one entire wall of the room. A slot outlet was placed in the floor near the inlet wall. Numerical simulation and measurements of air velocity and airflow direction revealed that the flow was highly three-dimensional. The three-dimensional effects were analysed in a number of additional numerical simulations and it was found that the relation between room width and room height had a crucial influence on the development of the three-dimensional effects of the airflow. The three-dimensional effects were small unless the room width to height ratio was larger than one, and in rooms with width to height ratios larger than about three, simulations showed a number of similar airflow patterns repeated transversely to the main flow direction.

Isothermal Airflow Characteristics in the Animal-occupied Zone of a Slot-ventilated Swine Facility

Airspeed and turbulence measurements were collected in a full-scale swine grower facility. Data were collected in three horizontal planes at eight axial locations from the inlet sidewall. Three inlet slot heights (20, 40, and 60 mm) and two fan stages resulted in six ventilating conditions investigated. The resulting 2 3 8 factorial experiment showed that fan stage, inlet height, and axial position from the inlet significantly affected (p < 0.01) airspeed variations in the animal-occupied zone (AOZ). Correlations between the AOZ and a convenient measuring plane (MP) were sought. AOZ airspeed was highly correlated with MP airspeed (rxy = 0.91). AOZ turbulent intensity (rxy = 0.51) and turbulent kinetic energy (rxy = 0.75) were moderately correlated with MP airspeed. AOZ turbulence levels were not correlated with MP turbulence levels. A procedure, consistent with the system characteristic technique, is proposed for predicting axial variations in AOZ airspeed. The technique can be used to assess AOZ airspeed levels relative to penning layout and ventilating conditions.

Simulated and Measured Effect of Rectangular Obstructions on Carbon Dioxide Gas Dispersion in a Scaled Swine Building

Gas dispersion from shallow manure storage pits was experimentally measured and mathematically modeled in a 1:6-scale ventilation chamber. The chamber represents a geometrically scaled model of a production swine grower facility. Gas injection was simulated from shallow pits using carbon dioxide (CO2). The results indicate significant differences in gas concentration between the animal-occupied zone (AOZ) and human-occupied zones (HOZ), especially at ventilation rates representative of mild weather conditions. AOZ CO2 concentrations were 12 times higher than HOZ during minimum ventilation conditions and six times higher during mild weather ventilation conditions. Large variations in normalized CO2 concentration were found as a function of both vertical location from the floor and horizontal location from the inlet, especially at vertical locations representative of the AOZ. Rectangular obstructions, physically representing the overall size of 60 kg pigs, did significantly (p 0.05) affect gas dispersion at low ventilation rates, implying that airflow patterns near the AOZ were significantly affected by the presence of rectangular obstructions at high ventilation rates. The mathematical model provided excellent prediction of the measured results. Vertical profiles were closely predicted with large gradients near the floor, in agreement with the measured results.

A Simplified Turbulence Model for Describing Airflow in Ceiling Slot-ventilated Enclosures

A numerical model was developed to predict flow occurring with opposing plane-wall ceiling jets representative of slot-ventilated livestock facilities. This model, termed the BETA model, was evaluated by comparing predicted axial and animal occupied zone (AOZ) velocity distributions with a low Reynold’s Number turbulence model (LBLR) and a laminar model (LAM). In addition, the BETA model results were compared with experimental results from a laboratory-scale test chamber. For opposing plane-wall ceiling jets, the predominant gradient in turbulent viscosity was predicted to occur in the vertical direction. An effective viscosity was defined as a function of the inlet Reynold’s Number (ReH) and normalized vertical height from the floor. The effective viscosity was used to selectively augment the laminar viscosity in the Navier-Stoke’s equation. Predicted comparisons between BETA and the LBLR models showed negligible differences for ventilating conditions between ReH of 35,032 and 11,752. Comparison with experimentally measured axial velocity decay indicated that the BETA model reproduced ceiling jet development as well as the LBLR model.