The Loop equation Design/Analysis software allows you to determine the size of natural ventilation openings necessary to provide airflow rates that satisfy design objectives based on minimum ventilation and cooling load requirements. The method employed is based largely upon the Loop Equation Design Method that provides for sizing of openings to utilize driving wind and stack pressures to achieve design airflow rates. This version implements a simple thermal design calculation to assist in determining design temperatures and airflow rates. A streamlined graphical interface assists the designer in performing the needed steps of developing the natural ventilation system design including: establishing the global geometry and topology of zones and interconnecting flow paths, establishing design conditions, setting up and solving the representative loop equations based on the “design” form of the airflow components, and analyzing operation under a variety of conditions. LoopDA 3.0 is an update to version 1.0 of the natural ventilation design tool developed by the National Institute of Standards and Technology in 2003.