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

Measuring gas emissions from livestock buildings: A review on uncertainty analysis and error sources

Measuring gaseous and particulate emissions from livestock houses has been the subject of intensive research over the past two decades. Currently, there is general agreement regarding appropriate methods to measure emissions from mechanically ventilated buildings. However, measuring emissions from naturally ventilated buildings remains an elusive target primarily because there is no reference method for measuring building ventilation rate. Ventilation rates and thus building emissions estimates for naturally ventilated buildings are likely to contain greater errors compared with those from mechanically ventilated buildings. This work reviews the origin and magnitude of errors associated with emissions from naturally ventilated buildings as compared to those typically found in mechanical ventilation. Firstly, some general concepts of error analysis are detailed. Then, typical errors found in the literature for each measurement technique are reviewed, and potential sources of relevant systematic and random errors are identified. The emission standard uncertainty in mechanical ventilation is at best 10% or more of the measured value, whereas in natural ventilation it may be considerably higher and there may also be significant unquantifiable biases. A reference method is necessary to obtain accurate emissions estimates, and for naturally ventilated structures this suggests the need for a new means of ventilation measurement. The results obtained from the analysis of information in this review will be helpful to establish research priorities, and to optimize research efforts in terms of quality of emission measurements. (C) 2012 IAgrE. Published by Elsevier Ltd. All rights reserved.Calvet Sanz, S.; Gates, RS.; Zhang, G.; Estellés, F.; Ogink, NWM.; Pedersen, S.; Berckmans, D. (2013). Measuring gas emissions from livestock buildings: A review on uncertainty analysis and error sources. Biosystems Engineering. 116:221-231. doi:10.1016/j.biosystemseng.2012.11.004S22123111

Tracer gas techniques for airflow characterization in double skin facades

Monitoring airflow rates and fluid dynamics phenomena in the ventilated cavity is a challenging aspect of the experimental assessment of the performance of double-skin facades (DSF). There are various methods to characterize the fluid-dynamics behavior of DSF, but each of these has its advantages and drawbacks. This paper presents the airflow characterization in the cavity of a double-skin façade installed in a full-scale outdoor facility through various methods, and, more specifically, it compares two tracer gas methods with the velocity traverse method. In the paper, we highlight how different characterization results can be explained by considering the features of each method, and how these differences are linked to velocity ranges and airflows in the cavity. By discussing (i) the challenges of these methods and their applicability, (ii) the requirements in terms of experimental set-up and (iii) the limitations linked to instrumentation, we aim to enhance the discussion on experimental methods for advanced building envelope characterization and contribute to a more grounded understanding of the suitability of tracer gas methods for in-field characterization of airflows in facades

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

Development and evaluation of methods for the measurement of airborne emissions form animal houses

Airborne emissions from livestock production are nowadays one of the major concerns of this activity. For this reason, the reduction of these emissions is a requirement in many countries. The development of abatement techniques for the reduction of emissions needs for accurate knowledge about their magnitude. Emission measurement techniques arise then as a key issue. The development of measurement techniques considering not only the accuracy of the results but also the optimization of resources is needed. In this sense, in this thesis a tool and three options for the rationalization on the use of resources when measuring airborne emissions are investigated. The tool is the uncertainty analysis and the three options are: downscaling measurements, indirect measurement of airflow rates and reduction of sampling rates. In this thesis, theoretical and practical studies were conducted to determine the suitability of these techniques to obtain reliable data from more rational measurements on airborne emissions. Firstly, an uncertainty model was developed in order to assess the trustworthiness of the results when determining N2 and N2O emissions from a biological scrubber using a combined N-balance in air and water. This model was later partially validated throughout an experimental work in a chemical scrubber. The uncertainty model and the experimental work agreed in the key results of both studies, finding that N-balances were not successful for the proposed aims. Secondly, a flux chamber for the measurement of gas emissions from rabbits was designed and built. A measuring protocol for gas emissions from both animals and their manure was also developed. This chamber was later used to determine the CO2 emission rate from fattening rabbits during the whole fattening cycle. Using this CO2 emission rate from fattening rabbits, the carbon dioxide balance was tested as an option to determine the ventilation rate from fattening rabbit houses. The results of these balances were compared with direct measurements of ventilation rates finding no statistical differences. Finally, the effect of reducing sampling when measuring ammonia emissions from livestock facilities was evaluated. Emissions calculated using semi-continuous measurements of NH3 concentrations and airflow rates were compared with emissions calculated on 24-hour average values for these parameters. The error committed with these low time-resolution measurements resulted to be low in comparison with other error sources committed when measuring emissions from livestock facilities. The main conclusion of this work is that there are available techniques that allow optimizing the use of resources of measurement processes, by keeping the accuracy of the results.Estellés Barber, F. (2010). Development and evaluation of methods for the measurement of airborne emissions form animal houses [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/9036Palanci

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

Greenhouse gas and ammonia emissions from dairy barns

Livestock farming is blamed to bear the bulk of certain gaseous emissions from agriculture such as ammonia (NH3) and methane (CH4). Emission measurement in naturally ventilated buildings in general, but the determination of the air exchange rate in particular, is very complex. Consequently, there is a lack of knowledge regarding gaseous emissions from modern, naturally ventilated dairy cattle buildings. The objectives of the thesis comprise the development and the utilization of measuring and modelling methods in order to determine NH3 and CH4 emissions from dairy barns. The first study focused on the development of a robust method for the long-term measurement of CH4 and NH3 emissions from a naturally ventilated dairy barn. A rough but solid model for the calculation of the ventilation rate by means of wind parameters was developed. At zero wind speed, the ventilation level in the building was over 870 m3 h-1 LU-1 and each m s-1 increase in wind speed increased the ventilation rate by 1,500 m3 h-1 LU-1. The second study presents results of a one-year measurement campaign in a tripartite, naturally cross ventilated dairy barn allowing for an accurate comparison of the two housing systems slatted floor and solid floor including emissions from barn and storage. Emissions from slatted floor including storage with low intensity of slurry homogenization led to lowest NH3 and CH4 emissions (324.9 ± 123.6 g CH4 LU-1 and 29.8 ± 13.1 g NH3 LU-1 d-1 as annual average, respectively). The effect of slurry homogenization beneath the slatted floor was affecting the level of both CH4 and NH3 emissions in a similar way (+17 and +29% higher emissions due to higher intensity of manure homogenization). Furthermore, in the third chapter emission modelling and measuring science was brought together and discussed in an interdisciplinary study. Therefore, the greenhouse gas calculation module of the dairy farm-level model DAIRYDYN was validated by long-term measurement data. The comparison of indicator-modelled CH4 emissions with online measurements offered relatively moderate deviations in case of very detailed indicator schemes (between -6.4 and 10.5%) compared with findings from literature. As a whole, the thesis contributes to the development and improvement of measuring methods for gaseous emissions from naturally ventilated dairy barns offering links for further research activities in this field. The thesis provides emission factors for different housing systems and manure management practices for dairy cows.Klimagas- und Ammoniakemissionen aus Milchviehställen Die landwirtschaftliche Nutztierhaltung ist für einen Großteil der gasförmigen Emissionen des Agrarsektors, wie Methan (CH4) und Ammoniak (NH3), verantwortlich. Die Messung dieser umwelt- oder klimaschädlichen Gase und insbesondere die Bestimmung des Luftwechsels von frei belüfteten, modernen Tierställen ist jedoch sehr komplex und die Datengrundlage daher gering. Ziel dieser Arbeit war die Entwicklung und Anwendung von Messmethoden und Modellen zur Bestimmung von gasförmigen Emissionen aus Milchviehställen. Die erste Studie beschreibt die Entwicklung einer robusten Messmethodik für die Bestimmung der CH4 und NH3 Emissionen aus einem frei belüfteten Milchviehstall. Dazu wurde anhand von Windparametern ein Luftwechselmodell für das Stallgebäude entwickelt. Bei Windstille wurde ein Luftvolumenstrom von mehr als 870 m3 h-1 LU-1 ermittelt, wobei ein Anstieg der Windgeschwindigkeit um 1 m s-1 eine Erhöhung des Luftvolumenstroms von etwa 1.500 m3 h-1 LU-1 zur Folge hatte. Die zweite Studie umfasst Ergebnisse einer einjährigen Messreihe in einem frei belüfteten, dreigeteilten Milchviehstall und ermöglichte einen Vergleich der zwei Haltungsvarianten „Spaltenboden“ und „planbefestigte Laufflächen“ unter Einbeziehung der Emissionen aus dem Flüssigmistlager. Das Stallabteil mit Spaltenboden wies bei geringer Intensität des Flüssigmist-Homogenisierens im Jahresmittel die geringsten NH3 und CH4 Emissionen auf (324,9 ± 123,6 g CH4 GV-1 d-1 und 29,8 ± 13,1 g NH3 GV-1 d-1). Das intensive Homogenisieren des Flüssigmistes unter dem Spaltenboden führte im Jahresmittel sowohl bei CH4 als auch bei NH3 zu signifikant höheren Emissionsraten im Vergleich zum weniger intensiven Homogenisieren (+17% bei CH4 und +29% bei NH3). Darüber hinaus wurden in der dritten Studie Erkenntnisse aus Emissionsmessung und -modellierung in einer interdisziplinären Arbeit zusammengeführt. Das Klimagas-Berechnungsmodul des einzelbetrieblichen Simulationsmodells DAIRYDYN wurde anhand von Ergebnissen aus Langzeit Messungen validiert. Bei Einbeziehung sehr detaillierter Produktionsparameter in das Modell wurden im Vergleich zur Literatur relativ geringe Abweichungen (-6,4 bis 10,5%) zu den Messergebnissen festgestellt. Die vorliegende Arbeit leistet somit einen Beitrag zur Entwicklung und Verbesserung der Messmethoden für gasförmige Emissionen aus frei belüfteten Milchviehställen und zeigt weiteren Forschungsbedarf in diesem Themengebiet auf. Darüber hinaus liefert die Arbeit Emissionsfaktoren für verschiedene Haltungsverfahren bzw. Entmistungsvarianten für Milchkühe bei unterschiedlichem Flüssigmistmanagement