The ventilation and environmental control parameters of two broiler houses were measured and monitored in California at one site of the National Air Emissions Monitoring Study. This article presents the ventilation measurement results from 15 November 2007 to 13 September 2009, which covered 12 broiler production cycles. The duration of each cycle was about 45 d for raising new chicks to 2.7 kg market-size birds. The two broiler houses had identical structural designs and ventilation, feeding, and litter management practices. Each house contained about 21,000 broilers in each production cycle and was mechanically ventilated with eleven fans, including one 91 cm fan and ten 122 cm fans. All the fans, heaters, and evaporative cooling systems were automatically operated to control the house temperature from 32 degrees C at the beginning to 18 degrees C at the end of each production cycle. The environmental parameters that were monitored included temperature, relative humidity, and static pressure inside the houses, and ambient temperature, relative humidity, wind speed and direction, and solar radiation outside the houses. The operational status and rotational speed of all ventilation fans were continuously monitored. The ventilation rate of each house was estimated by calculating the airflow rate through all the fans based on the static pressure difference in the building, fan performance, and operation status. The production cycle average daily mean ventilation rate was correlated with the cycle average daily mean ambient temperature. The ventilation rate for any day within a cycle was influenced primarily by bird age and ambient temperature. The daily ventilation rate ranged from 0.14 to 11.5 m(3) h(-1) bird(-1), and the average rate was 2.8 m(3) h(-1) bird(-1). The minimum and maximum ventilation rates occurred in January and July-August, respectively. Average ventilation volume per broiler during a growth cycle was 2981 m(3). Ventilation rate was successfully correlated with chicken age and ambient temperature. Average fan usage was 21% and ranged from 13% to 61% of total time for this ventilation management scheme.
