The tracer gas ratio method, using CO2 as natural tracer, has been suggested as a pragmatic option to measure emissions from naturally ventilated (NV) barns without the need to directly estimate the ventilation rate. The aim of this research was to assess the performance of a low-cost Non-Dispersive Infra-Red (NDIR) sensor for intensive spatial field monitoring of CO2 concentrations in a NV dairy cow house. This was achieved by comparing NDIR sensors with two commonly applied methods, a Photo-Acoustic Spectroscope (PAS) Gas Monitor and an Open-Path laser (OP-laser). First, calibrations for the NDIR sensors were obtained in the laboratory. Then, the NDIR sensors were placed in a dairy cow barn for comparison with the PAS and OP-laser methods. The main conclusions were: (a) in order to represent the overall barn CO2 concentration of the dairy cow barn, the number of NDIR sensors to be accounted for average concentration calculation was dependent on barn length and on barn area occupation; and (b) the NDIR CO2 sensors are suitable for multi-point monitoring of CO2 concentrations in NV livestock barns, being a feasible alternative for the PAS and the OP-laser methods to monitor single-point or averaged spatial CO2 concentrations in livestock barns.

Air flow rate CO 2 mass balance Tracer gasLivestock 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 CO 2 -and SF 6 -based tracer gas methods for the estimation of ventilation rates (VR CO2 vs. VR SF6 ) 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 SF 6 , and measurement points for the monitoring of SF 6 and CO 2 concentrations to consider both horizontal and vertical variability. Methods were compared by analysing daily mean VR CO2 =VR SF6 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 VR CO2 and VR SF6 were increased, VR CO2 =VR SF6 ratios being also more variable. Generally, both methods for the estimation of ventilation rates gave similar results, being 10e12% lower with the CO 2 mass balance method compared to SF 6 based measurements. The difference might be attributed to potential bias in both methods.

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