Architects Achieve LEED Certification in Sustainable Buildings

This article was contributed by Francisco José Lara Garachana of Simulaciones y Proyectos, SL.

FLOW-3D simulates the airflow to help obtain LEED certification
FLOW-3D simulates the airflow to help obtain LEED certification.

LEED (Leadership in Energy and Environmental Design) is a voluntary certification system that provides third-party verification of green buildings. Participation in the voluntary LEED process demonstrates leadership, innovation, environmental stewardship and social responsibility. LEED provides building owners and operators the tools they need to immediately impact their building’s performance and bottom line, while providing healthy indoor spaces for a building’s occupants.

FLOW-3D has helped to earn the credit “IEQ- Credit 2 – Increased Ventilation” in an office building in Bogotá (Colombia). In order to receive this credit, it has to be proved that the outdoor air exceeds by 30%, the ASHRAE standards rates. In this building, the outdoor air is provided by the effects of thermal buoyancy caused by a temperature difference generated by 2 glassed chimneys on the roof heated up by solar radiation. This has to be achieved under zero wind conditions.

HVAC model for increased ventilation
The model has been easily created using Google SketchUp® and exported directly to FLOW-3D in STL format. The STL model was imported as STL baffles in FLOW-3D.

Initial conditions of temperature in spaces and thermal loads (or losses) were obtained from an external energy simulation software. This software considers solar radiation, thermal inertia, insulation, internal loads, insulation, glass and all other parameters that define the thermal behavior of a building. The thermal loads are included in FLOW-3D giving the final temperature distribution when the CFD simulation is done.

Final temperature distribution
Left: Airflow streamlines inside the building. Right: Temperature distribution inside the building

In the figure on the left, the 2 thermal chimneys provoke the outdoor air ingress even at zero wind conditions. Ventilation efficiency, air changes per hour, local turbulences, residence time of air are some of the variables that can be inspected in the design process. In the figure on the right, FLOW-3D gives the temperature distribution inside the building so that a thermal comfort assessment can be done in the design process. The grill sizes can be adjusted to obtain desired comfort temperatures in all spaces.

Outdoor air temperature and atmospheric pressure were set up in the boundary conditions (intake and outflow air grills). FLOW-3D did the rest obtaining the detailed air movement inside the building. The simulation was carried out until energy steady-state conditions were achieved.

The building architecture and grill dimensions had to be adjusted to obtain the correct distribution of air inside the building as well as adequate comfort temperatures. After this iteration process, the model was validated and LEED credit conditions were achieved.