Modelling air change rate of naturally ventilated dairy buildings using response surface methodology and numerical simulation

Abstract

The air change rate (ACR) of naturally ventilated dairy buildings (NVDBs) plays an important part in the design and control of the ventilation system, as well as in the estimation of the gaseous emission rate. The objectives of this research were to model the ACR based on a quantitative investigation of the relationship between the ACR and its potential influencing factors, including the opening ratio (r), the building length to width ratio (α), the wind speed (U), and the wind direction (θ). The investigations were performed using the response surface methodology integrated with the Box-Behnken design and Computational Fluid Dynamics (CFD) simulations. Three response surface models of the ACR of NVDBs were established for three opening ratio ranges of 5%–42.5%, 42.5%–80%, and 5%–80%, respectively. It was found that the selection of the opening ratio range had almost no effect on the developed response surface models. The results showed that the ACR of NVDBs was not influenced by α, but was significantly affected by r, U, θ, and interaction effects between every two of the three factors. The highest ACR was 6.7 s−1, 6.0 s−1, and 4.0 s−1 when θ, U, and r was at their respective medium value while the rest parameters were at the highest values, indicating that the r played an important role in the value of ACR. It was concluded that in the prediction of the ACR of a building, the influences of both individual and interactional effects of θ, U, and r should be considered.