The effect of external wind speed and direction on sampling point concentrations, air change rate and emissions from a naturally ventilated dairy building

Natural ventilation (NV) of buildings refers to the exchange of indoor air with outdoor air due to pressure differences caused by wind and/or buoyancy. Increased knowledge of the factors that affect NV and emissions from naturally ventilated dairy (NVD) buildings may lead to a better understanding of indoor air quality, an improvement of emission abatement technologies and a refinement of emission models. The influence of external wind speed and direction on point concentration, air change rate, ammonia (NH3) and methane (CH4) emissions was evaluated in an NVD building located in northern Germany. The measured data were classified according to four wind direction groups: 0°–10° (N), 85°–95° (E), 175°–185° (S), and 265°–275° (W), with consideration for similar wind frequencies and representation of each major side for further analyses and comparisons. The results showed that wind speed and wind direction had significant influence on air change per hour (ACH) (P < 0.05) both individually and when interacting. In contrast, only wind speed and interactions of external wind speed and direction significantly affected NH3 and CH4 emissions (P < 0.05). The surrounding obstacles, other climate parameters (temperature and relative humidity) and other emission sources should be taken into account when interpreting the effects of wind direction on ACH and emissions. Empirical models for ACH, NH3 and CH4 emissions were developed. Intensive experiments in the lab (e.g. scale model in boundary layer wind tunnel) and long-term measurement including all seasons at full scale are required to establish a good empirical model.

► Wind speed, wind direction and their interaction affected air change rate (ACH).
► ACH for wind from southerly direction was twice as high as that from east.
► Interaction of wind speed and direction influenced ammonia and methane emissions.
► The surrounding environment should be considered when interpreting ACH and emissions.