Abstract
The direct measurement of emissions from naturally ventilated dairy barns is challenging due to their large openings and the turbulent and unsteady airflow at the inlets and outlets. The aim of this study was to quantify the impacts of the number and positions of sensors on the estimation of volume flow rate and emissions. High resolution measurements of a naturally ventilated scaled building model in an atmospheric boundary layer wind tunnel were done. Tracer gas was released inside the model and measured at the outlet area, using a fast flame ionization detector (FFID). Additionally, the normal velocity on the area was measured using laser Doppler anemometry (LDA). In total, for a matrix of 65 × 4 sensor positions, the mean normal velocities and the mean concentrations were measured and used to calculate the volume flow rate and the emissions. This dataset was used as a reference to assess the accuracy while systematically reducing the number of sensors and varying the positions of them. The results showed systematic errors in the emission estimation up to +97%, when measurements of concentration and velocity were done at one constant height. This error could be lowered under 5%, when the concentrations were measured as a vertical composite sample.
Highlights
Agriculture is a main contributor to the European ammonia and greenhouse gas (GHG)emissions—around 11% for ammonia [1] and 37% for GHG can be related to the livestock management of cattle [2]
If the carbon dioxide (CO2 ) produced by the animals is used as tracer gas, which is the most common approach, additional error sources can occur in the estimation of the CO2 source term, which directly biases the estimation of the air exchange rates [7]
Under the simplifications made of a naturally ventilated dairy barns (NVDBs) under constant, isothermal cross-flow with constantly fully-opened sidewalls, the following conclusions can be drawn for the direct measurement of the volume flow rates and emissions: 1
Summary
Agriculture is a main contributor to the European ammonia and greenhouse gas (GHG)emissions—around 11% for ammonia [1] and 37% for GHG can be related to the livestock management of cattle [2]. Dairy cows are mainly housed in naturally ventilated dairy barns (NVDBs) with large openings, connected directly to the ambient, turbulent weather conditions This makes the measurements of volume flow rate and gaseous emissions from these buildings challenging. If the carbon dioxide (CO2 ) produced by the animals is used as tracer gas, which is the most common approach, additional error sources can occur in the estimation of the CO2 source term, which directly biases the estimation of the air exchange rates [7] These additional error sources can be related to animal parameters, such as weight, activity, productivity and pregnancy, and additional CO2 sources, such as manure [6]
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