A COMPARISON OF 3 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 balance s of animal heat, moisture and carbon dioxide for fattening pigs, dair y cattle and laying hens. The analyses were made on data sets from a c ollaborative project using literature values for the rates of producti on of heat, moisture and carbon dioxide. For heat and moisture product ion, it was found that the balance equations could be improved by incl uding a correction for evaporation of water from fresh food, faeces an d urine in livestock buildings, and by adjustment of the equations for partitioning total heat into sensible and latent heat for pigs and po ultry. The correction, which is valid for climatic regions and product ion schemes that exist in Northern Europe, was calculated for each bui lding 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 ba sis, except when there were small hourly differences between indoor an d outdoor temperature (less than 2 degrees C), absolute humidity (less than 0.5 x 10(-3) kg of water/m(3)) and carbon dioxide concentration (less than 200 p.p.m.). On a 24 h basis the correlation coefficient (r (2)) 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 < 0.00 1) for laying hens and dairy cows. For periods shorter than 24 h, a co rrection was needed for diurnal changes in animal heat, moisture and c arbon dioxide production to achieve good agreement between calculated and measured ventilation rates. (C) 1998 Silsoe Research Institute.