Here is some more insight into using SketchUp for Building Performance Simulation

These hands-on tutorials will help you, step-by-step, test drive a new set of 3D modeling and energy analysis tools: Open Studio, SketchUp and EnergyPlus. After viewing the videos, you may earn four hours of HSW Credit by taking a quiz on the peer learning site.

Downloadable Programs
Google Sketchup
Google Earth

Hands-on Tutorials (Streaming Video)
Google SketchUp for Energy Analysis Using EnergyPlus
Google SketchUp, Part 1
Google SketchUp, Part 2
EnergyPlus, Part 1
EnergyPlus, Part 2

Session Handouts
Google SketchUp

Find out more at AIA/ Practicing Architecture