Modelling of ammonia emissions from naturally ventilated livestock buildings. Part 1: ammonia release modelling

Gaseous emissions from livestock buildings are a major environmental concern worldwide and an increasing number of countries have now introduced legislation that aims to reduce the emission of pollutants like ammonia. This paper is the first of a series of three reviews focussing on the utilisation of different modelling techniques to estimate ammonia emissions from naturally ventilated livestock buildings. Well-designed naturally ventilated buildings can provide occupants with good indoor air quality as well as energy consumption below levels for mechanically ventilated systems. But the time-dependence and the large fluctuations of air movement through the ventilation openings provide significant challenges for both modelling and measuring ammonia emission from naturally ventilated livestock buildings.This paper considers 12 studies published within the last 32 years that have included process-level models using mechanistic approaches for estimating ammonia release from different surfaces in cattle, pig and poultry buildings. Several models are available for predicting the release of ammonia from urine puddles on floors and from manure pits under pig and cattle buildings. Five models have been validated against measurements in mechanically or naturally ventilated livestock buildings with animals. One model predicted ammonia release from broiler litter, but it was based on laboratory measurements only. No mechanistic models were identified predicting ammonia release from mixtures of urine, faecal and bedding material on floor surfaces in pig and cattle buildings.Air velocity above the release surfaces was an important parameter in all the models. The models that were validated against full scale emission measurements used empirically determined relationships to estimate air velocity. CFD (Computational Fluid Dynamics) methods can provide a significant opportunity to model spatially and temporal distributed environmental conditions around ammonia release surfaces in livestock buildings. However, the full potential of integration of CFD with process level models of ammonia release cannot currently be realised because of the lack of good validation data and of the processing capacity needed to handle the complex computational needs of 3D CFD models