Abstract
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.
Highlights
Nowadays, no reference method exists for measuring air ventilation rates in naturally ventilated (NV) animal houses
A Non-Dispersive Infra-Red (NDIR) sensor technology was tested for monitoring of CO2 in a NV dairy cow barn
NDIR sensors were exposed to CO2 concentrations in the livestock barn together with Photo-Acoustic Spectroscope (PAS) analyzers and an OP-laser
Summary
No reference method exists for measuring air ventilation rates in naturally ventilated (NV) animal houses. The application of carbon dioxide (CO2) as a tracer gas for measuring ventilation and emission rates in livestock buildings involves CO2 metabolically produced by the animals and manure, which presents good mixing with most of the target pollutant gases found in livestock houses [13]. Representative sampling of the pollutant-tracer ratio is the most robust approach for quantifying emissions [1], and in case of inappropriate mixing spatial variability of this ratio should be included in the sampling strategy. One possible solution for this issue is by multi-point monitoring CO2 concentrations in a naturally ventilated livestock barn, and determination of spatial concentration profiles. Currently used measurement instruments to monitor CO2 concentrations are often expensive, or present limitations when used to sequentially measure points, resulting in complex, costly and labor intensive systems [17]
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