There are some research projects aimed to develop or improve methodologies for validation of building simulation software:

BESTEST - Building Energy Simulation TEST

IEA Task 22 - Building Energy Analysis Tools : Analyzing Solar And Low-Energy Buildings

IEA Task 34 - Testing and Validation of Building Energy Simulation Tools

ANSI/ASHRAE Standard 140-2004 - Standard Method of Test for the Evaluation of Building Energy Analysis Computer Programs

ASHRAE Research Project 1052 - Development of an Analytical Verification Test Suite for Whole Building Energy Simulation Programs – Building Fabric

ASHRAE Research Project 865 - Development Of Accuracy Tests For Mechanical System Simulations