Bjarne Bjerg

Summary of best guidelines and validation of CFD modeling in livestock buildings to ensure prediction quality

Summarization of Best Practice Guidelines for CFD modeling.Address on the governing equations and numerical methods for CFD modeling.Procedures of reporting the work using the CFD as a tool.An example of validating CFD simulation in a full scale pig barn. Computational Fluid Dynamics (CFD) is increasingly used to study airflow around and in livestock buildings, to develop technologies to mitigate emissions and to predict the contaminant dispersion from livestock buildings. In this paper, an example of air flow distribution in a room with two full scale pig barns was simulated to show the procedures of validating a CFD simulation in livestock buildings. After summarizing the guideline and/or best practice for CFD modeling, the authors addressed the issues related to numerical methods and the governing equations, which were limited to RANS models. Although it is not necessary to maintain the same format of reporting the CFD modeling as presented in this paper, the authors would suggest including all the information related to the selection of turbulence models, difference schemes, convergence criteria, boundary conditions, geometry simplification, simulating domain etc. This information is particularly important for the readers to evaluate the quality of the CFD simulation results.

CFD Investigation of a Partly Pit Ventilation System as Method to Reduce Ammonia Emission from Pig Production Units

The objective of this work was to investigate the efficiency of a partly pit ventilation system with cleaning of the air exhausted from the pit. The analysis, including Computational Fluid Dynamics (CFD) methods, showed that evacuating and cleaning of 10% of the total ventilation capacity from a pit may reduce the ammonia emission of the system by 73%, and the ammonia concentration in the room was significantly reduced. In a similar production system without pit ventilation cleaning of 10% of the ventilation capacity reduced the ammonia emission by 41% compared to no cleaning. A drawback of the pit ventilation system is that it increases the ammonia release from the slurry surface by 26% and, consequently, may increase the operating cost of a cleaning system in order to remove this extra ammonia.

Reducing Odor Emission from Pig Production Buildings by Ventilation Control

Odor emissions from pig buildings have been the topic for many research projects. However, the fact that the odor emission is dependent on air as transportation medium is far less investigated. Therefore, more comprehensive investigations on the effects of odor release of airflow patterns and ventilation airflow rates are needed. The objective of this project was to study the feasibility of reducing ammonia and odor emission by choosing ventilation control strategies. At present, the ventilation capacity of a pig production building is based on an absolute maximum ventilation rate, which is determined according to the largest body weight of the animals during the production cycle. However, in modern batch production systems, the maximum ventilation rate is only required when the animals reach end weight and the outdoor temperature exceeds a certain level. In this study, a ventilation control strategy using a restricted maximum ventilation rate according to the pigs’ actual weight in the building was investigated. According to computer simulations, limiting the maximum ventilation rate to the actual body weight is feasible in practical application to reduce odor emission. That is in agreement with a primary investigation performed in field measurements by Danish Pig Production. In addition, the studies on the correlation between emission and airflow characteristics have shown that by choosing a proper ventilation control strategy, emission can be also reduced. The investigations were performed in scale model experiments and CFD (Computational Fluid Dynamics) simulations. Strategies such as constant inlet opening, constant inlet velocity, and constant inlet momentum were studied. The proposed control strategy suggests that the ventilation rates in a pig production building should be controlled to maintain a low inlet air momentum to reduce emission.

Assessment of modeling slatted floor as porous medium for prediction of ammonia emissions - Scaled pig barns

Effect of geometry scale on resistance coefficients of porous media modeling (POM).Comparison of POM and direct slatted floor model (SLM) in a scaled pig barn by CFD.Systematical validation of CFD simulation by air speed, concentration and emission. CFD has been increasingly applied in predictions of airflow and gaseous emissions in livestock buildings. In full scale pig barns, it is hardly applicable to model the slatted floor at actual size due to the quantity of small slots which leads to the extremely huge mesh number. This motivates the researchers to model the slatted floor as porous medium (POM). In this study, the effects of POM and slatted floor modeling (SLM) on air speed, concentration and emissions are investigated in a scaled pig barn (1:12.5). The results show that SLM generally provide better predictions of air speed than POM. POM can predict the air speed below the slatted floor appropriately while fails to predict the air speed at the point above the slatted floor comparing to the measurements. The prediction of ammonia emissions is comparable by using POM and SLM while both SLM and POM fail to predict the ammonia emissions for some cases comparing to the experimental measurements.

A predictive model of equivalent temperature index for dairy cattle (ETIC)

Thermal stress imposed on cows adversely affects health and productivity. Various thermal indices exist in the literature that can be used to assess the level of heat stress on cattle by linking environmental conditions with physiological responses. However, many of these indices either do not incorporate all of the environmental variables or may consider only the main effects of the independent variables without considering the interaction effects. The objective of this study was to develop a thermal index for dairy cattle, referred to as Equivalent Temperature Index for Cattle (ETIC), which incorporates air temperature, relative humidity, air velocity and solar radiation and their interactions. Environmental and physiological data from two studies were pooled together to develop and validate the proposed index. The index (ETIC) expressed in terms of temperature units is derived from equivalent air temperature of relative humidity, air velocity and solar radiation. ETIC heat-stress level thresholds were defined according to the thresholds for temperature-humidity index (THI). The results indicate that the ETIC model predicts the measured physiological responses very well. The coefficient of correlation, R2, for skin temperature, core-body temperature, and respiration rate were 0.79, 0.40, and 0.49, respectively. The ETIC prediction of skin temperatures, core-body temperatures, and respiration rates were better compared to that of three recently developed thermal indices (adjusted THI, heat load index, and comprehensive climate index). The proposed index could be a useful tool to assess thermal environments to ensure animal comfort.

A review and quantitative assessment of cattle-related thermal indices

Many thermal indices have been developed to assess the levels of heat stress imposed on cattle during hot weather. In this paper, the 16 cattle-related thermal indices are critically reviewed. The primary emphasis is to evaluate each indexs coherence to the typical heat transfer characteristics of a cow. Other perspectives including incorporated environmental parameters in the equation(s), experimental data, correlated physiological responses, heat-stress thresholds, scope of application, specific cattle breed involved, and experiment location(s) are also well categorised and discussed. The coherence evaluation indicates that the main effects of environmental parameters on heat stress have been properly reflected, while some interactions between the parameters have been treated differently. Given the variety of the equations used to define the 16 indices and the wide range of information used to develop each index, we conclude that each thermal index is distinct to an extent that it should be selected and employed carefully.

Design-oriented modelling on cooling performance of the earth-air heat exchanger for livestock housing

Abstract Access to inexpensive cooling sources is a precondition for developing cost-effective methods to mitigate heat stress among farm animal under hot climate conditions. The earth-air heat exchanger (EAHE) is a promising energy-effective technique that can be used to reduce the cooling load of a livestock building in hot days. Several studies have been carried out to assess the feasibility of EAHE for tempering air in livestock buildings. However, no mathematical model serving for EAHE design for livestock buildings has been developed, in which the EAHE system is often operated continuously to keep animals comfortable and productive. This work firstly deduced a regression model for predicting the air temperature difference between an EAHE tube inlet and outlet (ΔTi-o) using response surface methodology (RSM) based on the data obtained from validated steady-state numerical simulations. Four key design and operation factors (tube diameter, tube length, air velocity, and the temperature difference between inlet air and the undisturbed soil) were incorporated into the model. Based on the regression model, a mathematical model for predicting the cooling capacity (CC) of an EAHE tube was obtained. Parametric analysis was conducted to reveal the effects of the four factors on both the ΔTi-o and the CC. The models on cooling performance allow the designers to optimize the EAHE configuration for cooling livestock buildings.