Model-based control of natural ventilation in dairy buildings Xiong Shen a,b , Guoqiang Zhang a,⇑ , Wentao Wu a , Bjarne Bjerg c a Department of Engineering, Faculty of Sciences and Technology, University of Aarhus, Blichers Allé 20, 8830 Tjele, Denmark b School of Environmental Science and Engineering, Tianjin University, Tianjin 300072, China c Department of Large Animal Sciences, University of Copenhagen, Grønnegardsvej 2, 1870 Frederiksberg C, Denmark article info Article history: Received 30 October 2012 Received in revised form 7 February 2013 Accepted 16 February 2013 Keywords: Model-based control Natural ventilation Air exchange rate Computational Fluid Dynamics (CFDs) Response Surface Methodology (RSM) abstract Without automatic control, the ventilation rate in naturally ventilated dairy buildings is often signifi- cantly higher than the required to provide good conditions for the animal in windy conditions, and this over ventilation will result in increased ammonia emission. Therefore, automatic control of the ventila- tion via adjustment of the ventilation openings in relation to the weather conditions can be used to reduce the ammonia emission. In this context, the model-based control method can be used and a pre- dictive model can estimate the wind driven ventilation rate of a naturally ventilated dairy building as a function of the outdoor wind conditions and sizes of sidewall openings. In the present study, the Response Surface Methodology (RSM) was applied to develop the predictive model. Three dimensional numerical simulations for a real dairy building were conducted to estimate the ventilation rate under dif- ferent wind and opening conditions. The model was formulated by the results of thirty cases of CFD sim- ulation, which were planned by the experimental design method: optimal design. Results showed that sizes of two sidewall openings significantly influenced the ventilation rate of the building. Based on the developed RSM model, the most desirable level of opening sizes can be determined for control of the ventilation air exchange rate in prevailing wind conditions. Ó 2013 Elsevier B.V. All rights reserved. 1. Introduction Natural ventilation is commonly preferred for dairy farms. Dairy buildings are often designed with sufficiently large wall openings so as to ensure the required air change at calm wind con- ditions. In windy weather, the ventilation rate can be several times higher than required for providing good air conditions for the ani- mal. This over-ventilation may result in more ammonia emissions from the buildings, leading to negative impacts on both the local and global environment (FAO, 2006). Those emissions from the livestock building can affect the ecosystem by causing water eutro- phication and soil acidification (Ngwabie et al., 2009). Previous researches have shown that the ventilation rate was highly correlated with the emission rate of ammonia in mechani- cally ventilated livestock buildings. Through laboratory scale mod- el experiments, higher ventilation rate will lead to higher ammonia emission rate (Saha et al., 2011; Ye et al., 2008; Zhang et al., 2008a, 2008b). Similar finding has been reported by the field experiment in several mechanically ventilated livestock buildings (Aarnink et al., 1995; Fabbri et al., 2007; Saha et al., 2010) and naturally ven- tilated buildings (Demmers et al., 2001; Zhang et al., 2005; Wu et al., 2012a, 2012b). To reduce the ammonia emission from live- stock buildings, the ventilation rate should be maintained at a level not higher than what is necessary to ensure the desired conditions for the animal welfare and production. The ventilation rate is often controlled according to the indoor air temperature (Boaventura Cunha et al., 1997) and CO 2 concen- tration (Chao and Hu, 2004) in mechanical and natural ventilation systems. Thermal control with feedback sensors has been applied in some NVLB equipped with adjustable openings to avoid high in- door air velocities at cool and windy weather conditions (Hoff, 2004; Strøm and Morsing, 1984). In many dairy farms the openings size can be controlled by sidewall curtains response to the indoor climate relative to the desired set-point room temperature (Duncan et al., 1975; Samer et al., 2012). When the indoor temper- ature is higher than the set-point, the curtains will move down and leave a larger opening size so as to attract more ventilation rate from outside. In contrast, when the indoor temperature is lower, the curtain will move up to reduce the opening size to decrease the ventilation rate. In this context, when the indoor temperature is commonly higher than the set-point in summer conditions, all the openings will open maximally. CO 2 based ventilation strategy is often applied to maintain the indoor air quality in mechanical ventilation systems by control of the minimum ventilation so that indoor CO 2 , not exceed the desired concentration level (Lu et al., 2011). However, the thermal and CO 2 control method may face diffi- culty in choosing the representative position for sensors since the indoor air is hardly perfect mixed and involves high spatial 0168-1699/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.compag.2013.02.007 ⇑ Corresponding author. E-mail address: Guoqiang.Zhang@agrsci.dk (G. Zhang). Computers and Electronics in Agriculture 94 (2013) 47–57 Contents lists available at SciVerse ScienceDirect Computers and Electronics in Agriculture journal homepage: www.elsevier.com/locate/compag