RP-1404 developed analysis methodologies by which the time period for field monitoring of energy use in buildings can be reduced to less than a whole year while satisfying preset accuracy levels of annual energy performance verification. The seminar presents the methodology of investigating the capabilities and the limits of hybrid inverse models developed from the shortest monitoring periods possible for a reliable and accurate long-term energy performance prediction in large commercial buildings. Such methodologies would be of great benefit to high performance buildings, and to Energy Service Companies who need a more cost-effective and acceptable alternative to year-long monitoring.