Validation of ventilation rate measurement methods and the ammonia emission from naturally ventilated dairy and beef buildings in the United Kingdom

Measurements of ammonia emission, especially from cattle buildings, are needed to assess the environmental impact of ammonia. There are no data available for cattle buildings in the United Kingdom because most buildings are naturally ventilated and methods for long-term measurement of emission from naturally ventilated buildings have not been developed. Two measurement methods, based on either the release of a tracer gas or on the pressure difference across ventilation openings, were validated in a full-scale cross-section of a naturally ventilated livestock building against a known release rate of a gaseous pollutant at high and low wind speeds. A good correlation between the measured and the actual release rates was found for the tracer gas method with an average recovery rate of 108%. The method based on pressure difference failed to estimate the ventilation rate correctly when only measured pressure coefficients were used, because the measurements of mass flow rates in and out through all openings of the building failed to balance. The traditional approach, based on measured values for the external pressure coefficients and an estimate of the internal coefficient balanced the flow through the building by definition, but failed to estimate the actual emission rate correctly. Current knowledge of the discharge coefficient for the opening designs of the building is insufficient for the pressure difference method to be used to estimate the ventilation rate. Using the tracer method, measurements were carried out between February and May 1996 in a straw-based beef house and a slurry-based dairy cow house with cubicles and scraped passage ways. The buildings were space bearded and had a covered ridge. The ammonia emission was estimated to be 3.5 and 8.9 kg NH3 per livestock unit per year for the beef and dairy buildings, respectively. (C) 2001 Silsoe Research Institute.