A comparison of three balance methods for calculating ventilation rates in livestock buildings

Three methods for the calculation of the ventilation rate in Northern European livestock buildings were compared on the basis of the balances of animal heat, moisture and carbon dioxide for fattening pigs, dairy cattle and laying hens. The analyses were made on data sets from a collaborative project using literature values for the rates of production of heat, moisture and carbon dioxide. For heat and moisture production, it was found that the balance equations could be improved by including a correction for evaporation of water from fresh food, faeces and urine in livestock buildings, and by adjustment of the equations for partitioning total heat into sensible and latent heat for pigs and poultry. The correction, which is valid for climatic regions and production schemes that exist in Northern Europe, was calculated for each building in such a way that the heat and moisture balances gave the same ventilation rate. The three methods gave reliable results on a 24 h basis, except when there were small hourly differences between indoor and outdoor temperature (less than 2°C), absolute humidity (less than 0.5 × 10-3 kg of water/m3) and carbon dioxide concentration (less than 200 p.p.m.). On a 24 h basis the correlation coefficient (r2) between the ventilation rate based on carbon dioxide and on heat and moisture was 0.67 (p < 0.01) for fattening pigs and 0.90 (p < 0.001) for laying hens and dairy cows. For periods shorter than 24 h, a correction was needed for diurnal changes in animal heat, moisture and carbon dioxide production to achieve good agreement between calculated and measured ventilation rates.