CFD modeling of airflow, thermal environment, and ammonia concentration distribution in a commercial manure-belt layer house with mixed ventilation systems

Abstract

Ammonia (NH3) is a major gaseous pollutant in poultry houses and adversely affects production performance and the health of layers and workers. Knowledge of three-dimensional (3D) spatial distribution and seasonal variation of indoor environment inside layer houses is crucial to assess the risks and seek for optimization. This study developed a 3D Computational Fluid Dynamics (CFD) model and simulated the airflow, thermal environment, and NH3 concentration distributions inside a commercial manure-belt layer house retrofitted from a high-rise deep-pit layer house. With current ventilation, the average air temperatures in bird zone were 31.9 ± 2.2°C, 30.4 ± 2.5°C, and 29.1 ± 4.3°C; the average ammonia concentrations were 5.27±2.88, 3.37±0.94, and 7.13±2.02 ppm; and heat stress was found in 100%, 87.7%, and 62.9% cages in summer, fall, and winter, respectively. Higher temperatures and NH3 concentrations were observed in air stagnation zones, such as centers of circulating airflows and the spaces near the end walls. The layers stocked on the lower floor were exposed to 1.1–2.7 °C higher temperature and 22–43% higher NH3 level than those on the upper floor due to 33–94% larger local mean age of air (LMA) caused by a concrete middle floor. The locations of operating exhaust fans were found to significantly affect the indoor environmental conditions. Regarding NH3 exposure, the layers were safe in all seasons according to 25 ppm threshold concentration recommended by United Egg Producers. Workers were safe for a 15-min exposure but might be at potential risks in winter with an 8-hr exposure based on threshold of 35 ppm during any 15-min period and 25 ppm for 8-hr exposure suggested by NIOSH. These results can be used to establish operation guideline for retrofitted layer houses to enhance the health of birds and farmers and egg production performance.