Jan S. Strøm

Ammonia Emissions Affected by Airflow in a Model Pig House: Effects of Ventilation Rate, Floor Slat Opening, and Headspace Height in a Manure Storage Pit

Laboratory experiments were performed to study the influence of airflow on ammonia emissions from pig house slurry in a model growing/finishing pig house with slurry in the pit and a clean slatted floor with various opening areas, 100%, 33.3%, and 16.7%. The 100% opening area meant that the headspace was an integral part of the room air space, and this configuration was used as the reference treatment. The pig house model had two sidewall inlets and exhaust in the middle of the ceiling. The liquid slurry used was from a growing/finishing pig building and consisted of 1% to 2% dry matter, had pH of 8.05, and TAN (total ammonia nitrogen) of 2.38 g/L. Experiments in a model growing/finishing swine barn were conducted to determine the effects of room ventilation rate, slurry pit air exchange rates, slatted floor openings, and pit headspace on ammonia emissions. The results showed that ammonia emission rate increased as ventilation rate increased with a constant inlet opening. Increase in the slatted floor opening ratio increased the air exchange rate in the slurry pit, resulting in a higher ammonia emission rate. Different correlations between the ammonia emission rate and the air headspace height in the slurry pit caused by the type of flow in the boundary layer influenced the ammonia transport from the slurry surface to the ventilation air. A statistical model was developed to calculate the ammonia emission rate as a function of ventilation rate, slatted floor opening ratio, and slurry pit headspace (R2 = 0.93). It was found that the NH3 emission rate was more sensitive to the ventilation rate than to the slatted floor opening ratio and air headspace height in the pit. In addition, the NH3 emission rate was much more sensitive to variations in the ventilation rate at low ventilation rates than at high ventilation rates. Similar sensitivity responses were obtained for both slatted floor opening ratio and air headspace height.

PREDICTING NEAR–FLOOR AIR VELOCITIES FOR A SLOT–INLET VENTILATED BUILDING BY JET VELOCITY DECAY PRINCIPLES

Air velocities near the floor of slot–ventilated buildings are the result of interaction between the supply air jet and the geometry of the confined space. To predict air velocity, the effect of the inlet air jet momentum and the room geometry has to be included. Air movements in a 5 m wide × 3 m high × 8.5 m deep empty slot–ventilated room were studied for two different jet momentum situations under isothermal conditions. A negative–pressure ventilation system supplied air through a slot wall inlet with an adjustable flap. The inlet was installed beneath the ceiling. The exhaust air was taken out through a section of slatted floor along the inlet wall. Air velocity distribution in the room was recorded with a multi–channel measurement system. To study the center velocity decay of the incoming jet and the return airflow, the data used in this report are concentrated on the measurement points near the ceiling and the floor. The experiment showed that a given near–floor air velocity may be generated by choosing a proper supply jet momentum. Three–dimensional effects occurred in the symmetrical, empty room. Mean velocity prediction in the near–floor region was analyzed on the basis of supply jet momentum and room geometry. The prediction was accurate for the maximum near–floor air velocity that occurred near the end wall opposite the inlet. As the air returned along the floor towards the inlet wall, the measured velocity became consistently lower than the predicted value.

Model Estimation and Measurement of Ammonia Emission from Naturally Ventilated Dairy Cattle Buildings with Slatted Floor Designs

Abstract Laboratory experiments were carried out in a wind tunnel with a model of a slurry pit to investigate the characteristics of ammonia emission from dairy cattle buildings with slatted floor designs. Ammonia emission at different temperatures and air velocities over the floor surface above the slurry pit was measured with uniform feces spreading and urine sprinkling on the surface daily. The data were used to improve a model for estimation of ammonia emission from dairy cattle buildings. Estimates from the updated emission model were compared with measured data from five naturally ventilated dairy cattle buildings. The overall measured ammonia emission rates were in the range of 11–88 g per cow per day at air temperatures of 2.3–22.4 °C. Ammonia emission rates estimated by the model were in the range of 19–107 g per cow per day for the surveyed buildings. The average ammonia emission estimated by the model was 11% higher than the mean measured value. The results show that predicted emission patterns generally agree with the measured one, but the prediction has less variation. The model performance may be improved if the influence of animal activity and management strategy on ammonia emission could be estimated and more reliable data of air velocities of the buildings could be obtained.

Modeling Jet Drop Distances for Control of a Nonisothermal, Flap-adjusted Ventilation Jet

In order to find criteria which can be used to control the trajectory of the air jet into a ventilated airspace, modeling the drop distance using the Archimedes number is proposed. The term “jet drop distance”, defined as the horizontal distance from the inlet to the point where the jet reaches the occupational zone, is used to describe the status of the jet. Following an analysis of jet trajectory models for round inlet openings, jet drop distance models for a rectangular inlet with a bottom hinged flap are described. The models are functions of the inlet Archimedes number, the inlet opening hydraulic diameter and the inlet height above the floor.

AIR VELOCITY AND TEMPERATURE DISTRIBUTION IN A COVERED CREEP FOR PIGLETS

A covered creep is primarily used to protect temperature-sensitive piglets. Knowledge of the air motion and the temperature distribution in a covered creep space is important for the optimization of the creep configuration. Experiments were carried out to investigate the temperature distribution in a covered creep and the velocity generated in the front opening as a function of heat level, heat location, and front opening configuration. Heating panels on the floor simulated the heat produced by piglets. The inside dimensions of the experimental creep were 1 m wide, 0.6 m high, and 1.8 m long. It was made from 50 mm polystyrene foam panels for floor, walls, and ceiling. The front configuration was either open or restricted with a top plate and bottom board. The experiments showed that significant vertical temperature stratification took place in the creep. The degree of temperature stratification depended on heat level, heat location, and front opening configuration. The maximum temperature rise, defined as the temperature difference between the creep air and the surrounding room air, was in the range 4.1.C to 8.8.C for heat levels of 140 to 420 W with open front. Location of the heat resulted in local effects within the covered creep, but had only minor effects on the velocity and temperature profiles at the front opening. Different front opening configurations influenced the temperature rise. The maximum temperature rise recorded was in the range 9.6.C to 14.8.C for the restricted fronts, and thus considerably higher than with an open front. Measured air velocities at the front opening were generally not in excess of 0.2 m/s, except near the ceiling. Both theoretical estimation and measurements showed that the air velocities out of the upper part of the front opening were notably higher than the air entering into the creep near the floor level. The estimated height of the neutral axis was close to the measured results.