This paper outlines the complexity of the building energy modelling problem and describes the ESP program and, in particular, its air flow modelling capabilities. The issue of "technology transfer" is highlighted and mention made of the recently established RIASEnergy Design Advisory Service, a Government-funded technology transfer initiative to provide Scottish building designers with subsidised access to advanced energy simulation technology. Three "case studies" from EDAS work are presented, outlining some of thepractical applications of the ESP program.