CFD simulation of airflows and ammonia emissions in a pig compartment with underfloor air distribution system: Model validation at different ventilation rates

Abstract Pig buildings with underfloor air distribution (UFAD) system provide the animal area with efficient cooling and better air quality compared ceiling air inlets. This is because the air inlets near the floor and the exhaust opening at the ceiling allow the excess heat and the old air to be displaced from the animal area to the upper part of the building. Typical inlet types of UFAD systems in Flanders (Belgium) are the slatted floor units placed in service alley. The main drawback in pig buildings with UFAD systems is that during winter, cold draughts often occur in the animal area, and due to the air displacement ventilation process, there is a risk of NH3 transport from the slurry pit. The effect of NH3 emissions is important as it leads to acidification and eutrophication. Modelling airflows and NH3 emissions using Computational Fluid Dynamics (CFD) can promote the development of techniques for mitigating NH3 emissions, improving indoor air quality and animal thermal comfort. A steady-state CFD model was therefore developed to predict the indoor airflow and NH3 distribution in a pig compartment with a UFAD system. An advanced NH3 emission modelling approach was implemented in the CFD model to simulate NH3 generation in the slurry pit and pen floor. In order to validate the CFD model, two experiments were performed. The first experiment was conducted in a compartment with mock-up pigs at different ventilation rates to validate the modelled air velocity and temperature fields. The second experiment was conducted in a compartment occupied by real pigs to validate the modelled airflow patterns, temperature, CO2 and NH3 concentrations. Overall, there was a good agreement between the simulated and measured results. The field experiment and CFD model results confirmed that NH3 was transported from the slurry pit to the compartment. The air exchange rate of the slurry pit in the CFD model increased from 10.4 to 26.1 h−1 as the ventilation rate was increased from 11 to 92 m3 h−1 pig−1 due to the air displacement in the slurry pit.