This is the second in a series of four papers that describe a 3-year EU-funded research project into the application of passive downdraught evaporative cooling (PDEC) to non-domestic buildings. The paper describes the use of computational fluid dynamics (CFD) for modelling PDEC. It describes the modelling techniques used and application to investigate the performance of a hypothetical office building in Seville. From the CFD analysis it is concluded that: (i) CFD is invaluable for analysing the ventilation performance of PDEC buildings, (ii) wind buffering and appropriate aperture sizes are essential to maintain well-regulated flows, and (iii) a top-down ventilation strategy performs equally well in upflowing mode, e.g. during night venting.