DEVELOPMENT OF CO2 BALANCE FOR ESTIMATION OF VENTILATION RATE IN NATURALLY CROSS-VENTILATED DAIRY BARNS

摘要

The determination of ventilation rates through naturally ventilated livestock barns is complicated and shows large uncertainties. One key issue is to develop further the measurement methods. Experiments were performed to study air exchange rates (AER) occurring in a naturally ventilated dairy barn during spring seasons. The ventilation rates (VR) were determined simultaneously by three different methods: the combined effects of wind pressure and temperature difference forces (WT method), the exact CO2 balance (CO2-ex), and the CO2 balance for a one-hour interval (CO2-h). During each experiment, CO2 concentrations and air temperatures were continuously measured and recorded inside and outside the barn. Furthermore, the wind velocity (speed and direction) was recorded by a weather station. The CO2 concentration measurements required to implement the CO2-ex were conducted at the same time interval as the measurements of wind velocity and temperature required to implement the WT method. However, the CO2 concentration measurements required to implement the CO2-h were conducted at a wider time interval, and the measurements for the WT method fell in the middle of this time interval. The results showed that the CO2-h produced reliable results (p < 0.05; R-2 = 0.856) in relation to the VR values derived from the independent variables outdoor temperature, indoor temperature, and wind velocity (speed and direction). Therefore, the hourly CO2 balance is more accurate than the exact CO2 balance