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The Loop Equation Design Method has been proposed for sizing ventilation airflow components of natural and hybrid ventilation systems. While the approach has been demonstrated on a limited basis, the method has been automated in order to better evaluate its reliability under a more controlled, i.e., less error-prone, environment. LoopDA is a computer program developed by NIST that implements the Loop Equation Design Method of sizing the openings of naturally ventilated buildings. The tool, referred to as LoopDA for Loop Design and Analysis, is integrated with an existing multi-zone analysis tool CONTAM. LoopDA provides the designer of natural ventilation systems with an environment in which to perform and document the process of designing the opening sizes of natural ventilation systems and analyzing the system behavior under a variety of operating conditions. The accompanying manual describes the first version of the LoopDA program, provides an example of its application to the design of a naturally ventilated building and describes needs for future enhancements to the tool to increase its usefulness within the design community.

LoopDA 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. Screen Shots


airflow analysis, indoor air quality, multizone analysis, natural ventilation


The accompanying manual provides a test case as well as references to other applications of the Loop Equation Design Method. Validation of the underlying simulation engine (ContamX) is addressed by the tool CONTAM.

Expertise Required

Familiarity with CONTAM, buildings and natural ventilation systems.


More than 300 downloads world-wide.


Mechanical, environmental engineers; building designers; state and Federal agency staff; university faculty; researchers; private consultants.


The GUI is used to draw a schematic representation of a vertical building section including design opening locations and design pressure loops (i.e., the desired path of the natural ventilation airflow through the building section) and input interior design temperatures, ambient design temperature and wind speed, and design airflow rates.


Interactive dialogs displaying loop equation parameters including minimum opening sizes to aid in selecting natural ventilation opening sizes. Simulation results that can be used to verify performance of design. Results are very similar to those provided by CONTAM.

Computer Platform

PC-compatible computer with Pentium equivalent processor. Runs under Windows 95/98, NT/2000, and XP. A spreadsheet program is also recommended for viewing asymptotic plots of loop equations.

Programming Language



Graphic interface provides means to develop building sections, define pressure/flow loops and develop loop equations.


Lack of a diverse set of inverse flow component types, unrefined user interface features and need for consideration for design of mechanical components of a hybrid ventilation system. Requires interaction with third-party spreadsheet program.



National Institute of Standards and Technology


100 Bureau Drive, Stop 8633
Gaithersburg, Maryland 20899-8633
United States


+1 (301) 975-5860


+1 (301) 975-4409






Program and user manual are freely available at www.bfrl.nist.gov/IAQanalysis/LOOPDAdesc.htm.