A Comparison of Three Balance Methods for Calculating Ventilation Rates in Livestock Buildings

Ammonia emissions from two mechanically ventilated UK livestock buildings

A Survey of Ventilation Rates in Livestock Buildings in Northern Europe

Natural ventilation systems are commonly used in livestock buildings, where the natural ventilation is a more energy efficient approach to provide effective ventilation. The foremost predicament of natural ventilation is the lack of precise, continuous and direct measuring techniques for ventilation rates, which is critical for monitoring gaseous emissions in livestock buildings for controlling the indoor air quality. Several ventilation rate measurement methods have been reported in the literature. However, these methods have some limitations and errors. The objectives of this study are to investigate the different tracer gas techniques (TGTs) especially using a radioactive tracer gas, to elucidate the applied methodology and instrumentation required and to investigate the methods of data analysis with results using radioactive TGT. The paper presents the technique of radioactive tracer gas preparation in the isotopes laboratory, tools used, the release methods, and locations, and calculations. This study has initiated a development of a radioactive TGT for an accurate determination of ventilation rates in naturally ventilated animal buildings. The radioactive TGT can be applied to other larger naturally ventilated buildings, such as warehouses, aircraft hangers and depositories, as well as to smaller rooms such as offices, class rooms and store.

Determination of Minimum Ventilation Rate in Pig Houses with Natural Ventilation based on Carbon Dioxide Balance

Reliable estimation of the ventilation rate (VR) in intensive livestock buildings is necessary for studying building environmental control strategies and predicting indoor air quality and air emissions. As direct air exchange measurements are time-consuming and expensive, it is environmentally inefficient to measure livestock building VR continuously in practice. Hence, indirect VR estimation methods have been widely used in modelling environmental control and air emissions, and also to measure airflow in the field. The accuracy of indirect measurement methods needs to be evaluated by comparing with direct measurements. In this study, the direct and indirect methods of determining hourly and daily mean VRs were applied to a mechanically-ventilated dairy free stall barn monitored by the 24-month National Air Emissions Monitoring Study. The direct method was used to continuously monitor fan rotational speeds, and differential static pressures, coupled with periodic in-situ fan performance assessments, to calculate the VR. The indirect method consisted of estimating the VR using CO2 concentration measurements and the CO2 mass balance method. The average daily and hourly means (mean±SD) of directly measured barn ventilation rates for two years were (246±73) m3/s and (245±77) m3/s, respectively. The average daily and hourly means (mean±SD) of barn ventilation rates estimated by the CO2 mass balance method were (287±93.4) m3/s and (287±118) m3/s, respectively. Correlation analyses showed a strong correlation between the indirect CO2 mass balance method and direct measurement methods (r=0.93 for daily means and r=0.85 for hourly means). Keywords: dynamic ventilation rate, modern dairy, free stall barn, carbon dioxide, mass balance, dairy cow, direct and indirect determination, comparison DOI: 10.25165/j.ijabe.20201306.5767 Citation: Zou B, Heber A J, Shi Z X, Du S H, Jin Y, Lim T T. Comparison of direct and indirect determinations of dynamic ventilation rate in a modern dairy free stall barn. Int J Agric & Biol Eng, 2020; 13(6): 41–46.

Ventilation rates in mechanically-ventilated commercial poultry buildings in Southern Europe: Measurement system development and uncertainty analysis

95/04255 A study of ventilation and carbon dioxide in an office building

Knowledge of ventilation rates in dairy buildings is essential for determining indoorair quality and for estimating green house gases and particle emissions. Two new methods for estimating ventilation rates are introduced for situations where air velocities atventilation inlets and outlets are tedious or impossible to measure. The first method is applicable to buildings whose ventilation can be stopped or closed totally. The second method is useful in naturally ventilated buildings with large openings and high ventilation rates where spatial gas concentrations are heterogeneously distributed. In addition, traditional heat balance, moisture balance, carbon dioxide balance and direct airflow measurements for ventilation estimation are used. Confirmation experiments were performed to evaluate the different methods. Good agreement was found between heat, moisture and carbon dioxide balances. Direct velocity measurement for ventilation rate estimation was found to be impractical for naturally ventilated buildings. The two introduced methods were found to be simple and adaptable for estimating ventilation rates in dairy buildings.

Ventilation rate (VR) is one of the two key elements for quantifying aerial emissions from animal production facilities. Direct, continuous measurement of building VR can be challenging and impractical under certain circumstances, e.g., naturally ventilated animal housing or a large number of ventilation fans in the building. This study examined the suitability of estimating VR of broiler houses with built-up litter (mixture of manure and bedding), when supplemental heating was not in use, through either carbon dioxide (CO 2 ) balance or the relationship of VR to CO 2 concentration difference between exhaust and inlet air. The reference VR was based on direct measurement by continuously monitoring operation of the in-situ calibrated exhaust fans. The comparative analysis of the direct method vs. each indirect method was conducted for a measurement integration time (MIT) of 10, 30, 60, or 120 min. The analyses revealed that MIT of 30 min or greater resulted in non-significant differences in VR between the indirect and direct methods. The broiler building VR (m 3 s -1 ) may be related to the exhaust-inlet CO 2 concentration difference (ΔCO 2 , ppm) as VR (±3.0) = 4456 (±41) ΔCO 2 -0.786 (±0.019) at 30 min MIT. The VR may also be determined by the CO 2 balance method (including litter CO 2 generation) with a correction factor of 0.97 at MIT of 30 to 120 min. If litter CO 2 generation is omitted from the total building CO 2 production, the actual VR may be estimated by applying a correction factor of 1.077 to the bird respiration CO 2 balance VR. Hence, the CO 2 balance or concentration difference method offers a viable alternative or supplemental check for quantifying building VR under certain conditions where direct, continuous VR measurement is not feasible.

Animal housing is a major source of gaseous emissions, such as ammonia (NH3), methane (CH4), nitrous oxide (N2O), and carbon dioxide (CO2). Ammonia is an atmospheric pollutant and responsible for eutrophication and soil acidification, while CO2, CH4, and N2O are greenhouse gases (GHG) that contribute to global warming. The quantification of gaseous emissions from livestock buildings with natural ventilation systems is a particularly difficult task and is associated with uncertainties that are largely unknown. One key issue is to measure the ventilation rate and then to quantify the gaseous emissions. Therefore, in this study, the ventilation rate was determined by three different methods simultaneously. Field experiments were carried out to study the ventilation rate in a naturally ventilated dairy barn located in northern Germany during the summer seasons from 2006 to 2010. The air exchange rates (AER) as well as the ventilation rates were determined by the decay of the radioactive tracer krypton-85, the carbon dioxide (CO2) balance, which was used as the reference method in this study, and the combined effects of wind pressure and temperature difference forces (WT method). Subsequently, the results were compared with each other by carrying out Pearson correlation analysis and developing a regression model. During each field experiment, continuous measurements of gas concentrations (NH3, CO2, CH4, and N2O) inside and outside the building and 85Kr tracer gas experiments were carried out. Meanwhile, the temperature was measured and recorded inside and outside the barn. Furthermore, the wind velocity was measured. Although the WT method showed minor overestimation by about 1.11 (p < 0.05) times the reference method, it is not reliable because it showed no linear correlation (0.05; p = 0.88) with the reference method. This was due to large fluctuations in the wind velocity (direction and speed), which negatively affected the WT method, which is basically dependent on wind velocity. In contrast, the 85Kr tracer gas technique showed a good linear correlation (0.82; p < 0.05) with the reference method, which accentuates that the 85Kr tracer gas technique is a promising method. However, this technique overestimated the air exchange rate by about 2.05 (p < 0.05) times the reference method. Therefore, the 85Kr tracer gas technique should be further developed to produce values consistent with those estimated by the reference method. The emissions factors, subject to the reference method, were 32, 157.7, 13736, and 7.9 kg year-1 AU-1 for NH3, CH4, CO2, and N2O, respectively.

Carbon dioxide production from a fattening pig building with partial pit ventilation system

In previous studies, increased ventilation rates and reduced indoor carbon dioxide concentrations have been associated with improvements in health at work and increased performance in work-related tasks. Very few studies have assessed whether ventilation rates influence performance of real work. This paper describes part one of a two-part analysis from a productivity study performed in a call center operated by a health maintenance organization. Outside air ventilation rates were manipulated, indoor air temperatures, humidities, and carbon dioxide concentrations were monitored, and worker performance data for advice nurses, with 30-minute resolution, were analyzed via multivariate linear regression to look for an association of performance with building ventilation rate, or with indoor carbon dioxide concentration (which is related to ventilation rate per worker). Results suggest that the effect of ventilation rate on worker performance in this call center was very small (probably less than 1%) or nil, over most of the range of ventilation rate experienced during the study (roughly 12 L s{sup -1} to 48 L s{sup -1} per person). However, there is some evidence suggesting performance improvements of 2% or more when the ventilation rate per person is very high, as indicated by indoor CO{sub 2} concentrations exceeding outdoor concentrations by less than 75 ppm.

Abstract. In considering hen housing systems, up-to-date heat and moisture production data are essential to producing properly designed and managed ventilation and supplemental heating systems. The aviary system is one housing type under consideration by egg producers. The aviary system has a much lower bird stocking density and thus more freedom of movement for the birds compared to conventional cage housing. This study was conducted to obtain baseline heat and moisture production values for Hy-Line Brown hens in such houses in the Midwestern U.S. House-level thermal environment, gaseous concentrations, and bird production performance of two commercially operated 50,000-hen aviary houses were continually monitored over a 19-month period. The two houses used similar management practices and Hy-Line Brown hens with a 20-week difference in age. Data were collected for a complete flock (17 to 83 weeks, no molt) in each house. Total heat production (THP) of the hens, house-level latent heat production (LHP) or moisture production (MP), house-level sensible heat production (SHP), and respiratory quotient (RQ) were determined from the monitored variables using indirect calorimetry and mass/energy balance, respectively. Variations in THP, LHP/MP, SHP, and RQ within the day were delineated. Results of the study showed mean (±SE) THP, house-level LHP, house-level SHP, and RQ values of 5.94(±0.09) W kg -1 , 1.83(±0.03) W kg -1 , 4.11(±0.08) W kg -1 , and 0.94(±0.01), respectively, for the aviary housing system. The new data will improve the design and operation of building ventilation, supplemental heating, and ultimately production efficiency of aviary housing systems. The THP and RQ data will also be useful to indirect determination of building ventilation rate using the carbon dioxide (CO 2 ) balance method.

The Development of Robust Methods for Measuring Concentrations and Emission Rates of Gaseous and Particulate Air Pollutants in Livestock Buildings

Dust mass concentrations, temperatures, and carbon dioxide concentrations were mapped in a modern, 1048-pen swine gestation barn in winter, spring, and summer. In each season, two technicians measured respirable mass concentrations with an aerosol photometer and temperatures and carbon dioxide concentrations with an indoor air quality monitor at 60 positions in the barn. Stationary photometers were also deployed to measure mass concentrations during mapping at five fixed locations. In winter when building ventilation rates were low (center-barn mean air velocity=0.34 m s(-1), 68 fpm) to conserve heat within the barn, mass and carbon dioxide concentrations were highest (mass geometric mean, GM=0.50 mg m(-3); CO2 GM=2060 ppm) and fairly uniform over space (mass geometric standard deviation, GSD=1.48; CO2 GSD=1.24). Concentrations were lowest in summer (mass GM=0.13 mg m(-3); CO2 GM=610 ppm) when ventilation rates were high (center-barn mean air velocity=0.99 m s(-1), 196 fpm) to provide cooling. Spatial gradients were greatest in spring (mass GSD=2.11; CO2 GSD=1.50) with low concentrations observed near the building intake, increasing to higher concentrations at the building exhaust. Mass concentrations obtained in mapping were generally consistent with those obtained from stationary monitors. A moderately strong linear relationship (R2=0.60) was observed between the log of photometer-measured mass concentration and the log of carbon dioxide concentration, suggesting that carbon dioxide may be an inexpensive alternative to assessing air quality in a swine barn. These results indicate that ventilation can effectively reduce contaminant levels in addition to controlling temperature.