Accuracy assessment of methane emissions measurement systems tailored to mechanically ventilated livestock buildings.

Tremblay, F., Massé, D.I., and Bluteau, C.V. (2014). "Accuracy assessment of methane emissions measurement systems tailored to mechanically ventilated livestock buildings.", Canadian Biosystems Engineering, 56(1), pp. 7.1-7.10. doi : 10.7451/CBE.2014.56.6.1  Access to full text

Abstract

The objective of this study was to design and develop reliable, robust, and accurate tools for measuring the methane emissions produced by commercial dairy herds without interfering with producer practices or affecting herd performance. The approach that was developed uses mechanically ventilated barns. A mass balance is established for the building enclosure by quantifying the mass flow rates of methane at the barn’s air inlets and outlets. The difference between the mass flow rate of methane at the outlets and inlets is attributed to the production of enteric methane emissions of the dairy herd inside the barn. The system is fully automated and performs continuous monitoring 24 h a day and 365 d a year. The system can carry out 3 to 10 methane mass balances per hour depending on the number of fans operating in the building. Different approaches were used to quantify the air flow rates in the two commercial barns: fan performance curves developed in situ at farm A and anemometers developed into our lab and deployed at farm B. The accuracy of each measurement system was validated by releasing known masses of methane into the respective building that were then quantified by the system. The means of the ratios of the methane mass measured by the system to the known mass of methane released into barns A and B were 99.4 and 101.4% for the two systems, with standard deviation of 16 and 9% respectively. In the two barns, the methane emissions were measured between fall 2004 and winter 2007. The two herds produced mean methane emissions equivalent to 24.5 and 24.7 L/kg milk produced. The mean methane production of the herds reported on the basis of the milk fat produced by the animals was 612 L/kg milk fat for Farm A and 688 L/kg milk fat for Farm B.

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