Passive Airflow Study

Students from Dartmouth’s Thayer School of Engineering worked with Build Health International (BHI) on their senior capstone project, to create a design guide of alternative ventilation strategies for resource strained areas. Currently, exhaust fans are being used to reach the12 air changes an hour (ACH) required by the CDC to ventilate isolation rooms. When the exhaust fans break down, it is not only difficult and expensive to repair them, but it puts hospital staff and visitors at risk. The team was tasked with creating a ventilation system that reduced electrical demand and addressed the health, safety, and welfare of staff and visitors. Since passive elements alone couldn’t sufficiently ventilate isolation rooms, software models were used to measure how ceiling fans move air within structures, and to determine which construction factors allow the ceiling fan to exhaust air most effectively. Both natural and mechanical ventilation studies were reflected in a full architectural model of an isolation ward that used sustainable principles to optimize mechanical airflow and maximize natural ventilation while also minimizing costs. The design guide provides information not only on how to minimize costs, but to maximize patient comfort, and reliably prevent the spread of airborne diseases.




    Dartmouth Thayer School of Engineering


    Fond des Blancs, Haïti


    March 2018

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    Dartmouth Thayer School of Engineering: Fiona Bowen, Michelle Dundek, Kyran McKinney-Crudden, David Morrison, Jorge Siwady-Kattan, Celeste Vazquez

    Faculty Advisor: Jack Wilson

    Advisor: BHI (Abby & Rob)

Project Success Factors

Sustainable Approach

Natural ventilation from wind and temperature differentials is an inexpensive and easily maintainable alternative to exhaust fans. In Haiti’s climate, natural elements are not enough to consistently achieve the minimum 12 ACH necessary to prevent the spread of airborne disease. However, natural ventilation can provide some cooling effects and can act as a backup for mechanical systems. The design guide contains recommendations on optimizing the building layout for passive airflow by including a central courtyard, sloped ceilings, roof overhangs, and outdoor corridors.


Every exhaust fan replaced with a ceiling fan will save facilities $1,300 USD in initial costs and $200 USD annually in electricity and maintenance costs. These fans also provide a cooling effect, are easier to notice if they break, and are simple to fix or replace.

Software Modeling

Computational Fluid Dynamics (CFD) software can model how ceiling fans move air within structures. In a validation test, the results of a CFD simulation were within 35% of experimental data in a room roughly the size of an isolation room with a ceiling fan, showing that CFD is a valid tool for estimating ACH from ceiling fans in isolation rooms if an appropriate factor of safety is included. Forty-eight isolation room designs were simulated in a Design of Experiment (DOE) to determine which construction factors allow the ceiling fan to exhaust air most effectively.

UN Sustainable Development Goals

GOAL 3 – Good Health & Well Being
GOAL 9 – Industry, Innovation & Infrastructure