UNCERTAINTY ANALYSIS OF USING CO2 PRODUCTION MODELS BY COWS TO DETERMINE VENTILATION RATE IN NATURALLY VENTILATED BUILDINGS

To provide accurate estimation of gas emission from livestock production facilities relays on the precision of the measurement of the ventilation flow and gas the concentration. However, it is difficult to make reliable direct measurements of the airflow exchange in naturally ventilated open type livestock buildings. Using tracer is one of the approaches to determine the ventilation flow rates. Application of an artificial tracer gas is complex, expensive, and may involve technical difficulties to make its distribution uniformly in the buildings. A feasible approach that has been applied by several published researches is using the CO2 produced by livestock as tracer gas to estimate the ventilation airflow in open buildings. This paper reviewed the CO2 production model and the field measurements of five dairy cattle buildings to estimate the feasibility of applying CO2 production model to determine the ventilation airflow rates in naturally ventilated livestock buildings. The method of using CO2 production model was compared with that of using an artificial tracer gas. The feasibility of estimating the ventilation rates based on the differences of the carbon dioxide concentration in and out of the building, and carbon dioxide production of the animals were addressed. Uncertainty of determination of ventilation rates based on CO2 production model was analyzed. The most important questions on measurement positions and animal carbon dioxide production models were raised and discussed. The conclusion is that for open buildings, the methods based on animal CO2 production as tracer gas achieve the similar accuracy as other methods using tracer gas.