In project four I researched the passive building systems of the Pantheon. I chose to research the Pantheon because it is in my opinion the oldest and most successful example of designing with passive systems. The Pantheon’s design supports passive ventilation, natural light, thermal mass, and water drainage. The oculus, lime-pozzolana concrete building material, and marble floor are the main passive design elements. The careful use of building materials and varying levels of porosity connect the Pantheon and allow it to mediate its relationship to external systems.
In my CAD class I designed a 3-D model of the Pantheon which I used to develop a series of sectional diagrams illustrating the passive ventilation via convection through the oculus, and natural lights absorption into the building walls via radiation and thermal mass.
The Pantheon in Rome was initially built by Marcus Agrippa, the son-in-law of Roman Emperor Augustus. The word “Pantheon” is Greek and it means “to honor all gods”, therefore making the Pantheon a temple to honor all gods. Agrippa built the temple around 27 B.C. and it was rebuilt in 123 A.D. by the Emperor Hadrian.
Reconstruction maintained the original design of the foundation ring, cylindrical walls, and dome. In addition, the orientation and configuration are the same because old Roman Religion required that temples be rebuilt to their original design and tradition required that the main entrance face north, and thus the whole building was oriented on a north-south axis.
The Pantheon’s passive ventilation system is the result of the open oculus. Air interacts with the oculus in two ways, convection and the venturi effect, to produce airflow in to the portico entrance and out of the oculus. Convection is the movement of molecules in fluids, typically following the rule that hotter molecules rise and cooler molecules fall. The oculus creates a vacuum as air rises by natural convection and the portico entrance is the inlet for cool air at the bottom of the building creating an upward-moving air current.
The venturi effect is caused by airflow over the oculus. The dome shape forces air passing over the oculus to increase in velocity. The increase in velocity results in a decrease in pressure. Near the portico, the air is slower resulting in an increase in air pressure. The difference in air pressure creates airflow from high to low pressure, from the portico to the oculus.
The second passive system I researched was the Pantheon’s use of thermal mass to cool the interior space. Thermal mass refers to materials that have the ability to store thermal energy for extended periods of time. Some examples of thermal mass include concrete, rock, earth, cement, brick, water and ceramic tile. The Pantheon’s structure is mainly made out of lime-pozzolana concrete. During the day, the non-insulated concrete absorbs daytime heat, reducing the amount of heat that reaches the interior space, and resulting in a cooler interior air temperature. The thermal energy absorbed by the concrete is negated due to the airflow of the passive ventilation system and the lack of insulation on interior or exterior.
It is important to note that the thermal massing system of the Pantheon cools the building during the hot summer months, but is less effective at heating the building during the winter months because of the open oculus. The extreme conditions of winter and summer must be considered when determining the possible effectiveness of the passive systems. Rome, Italy is in a middle climate, therefore receiving both weather extremes instead of only one, such an equatorial climate that is always warm or a polar climate that is always cold.
If insulation was integrated onto the exterior and the Pantheon’s oculus was closed, inhibiting the passive ventilation system, then the thermal massing system would both passively cool and heat the interior space. The thermal energy absorbed during the daytime and stored in the thermal mass would then be released during the night time counteracting the atmospheric cooling and resulting in a more constant the air temperature. This alternate condition is depicted by this graph and my diagrammatic representation.
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Moore, D., P.E. (1995). The Pantheon. Retrieved November 1, 2011, from
Kosny, J., Petrie, T., Gawin, D., Childs, P., Desjarlais, A., & Christian, J. (2001, August 13). Thermal Mass - Energy Savings Potential in . Retrieved from Oak Ridge National Labs website: http://www.ornl.gov/sci/roofs+walls/research/detailed_papers/thermal/ index.html Kwok, A., Grondzik, W., & Grondzik, W. T. (n.d.). The Green Studio Handbook: Environmental Strategies for Schematic Design (2nd ed.). (Original work published 2007) Retrieved from http://www.amazon.com/Green- Studio-Handbook-Second-Environmental/dp/0080890520#reader_0080890520