Simulating the effect of forces pit ventilation on ammonia emission from naturally ventilated cow houses with CFD

Atmospheric NH3, mainly originates from agricultural sources, can cause serious environmental problems related to eutrophication and soil acidification. Emissions from dairy houses are 15% of total agricultural NH3 emissions. Due to open buildings, existing abatement options are limited. Pit air separation was identified as a potentially efficacious option. In this study a model simulation of a commercial dairy cow building with slatted floor is presented. The model was solved for 12 cases, differing wind speed, direction and both air and manure temperature. For each case three solutions were obtained, which correspond a) to a building where a forced pit ventilation system is applied at capacity of 250 and 500 m-3 h-1 cow-1 and b) to a building without forced pit ventilation system. The results show that due to forced pit ventilation system, at 250 and 500 m-3 h-1 cow-1, the ventilation rate was increased 3.1% and 6.2% respectively. The contribution of the pit ventilation system to the total ammonia released from the pit during winter, ranged from 31-35%, 16-19% and 11-8%, for wind speed of 1.0, 4.0 and 8.0 m s-1 respectively. Correspondingly, during summer, the contribution of the system ranged from 44-48%, 20-21% and 12-9%. Although obvious benefits arise from a forced pit ventilation system, the main mass flow of ammonia from the pit still emitted through the building ventilation openings, especially at high wind speeds.