Assignment 4 – The Pantheon’s Passive Systems

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.

By Christopher Chu

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.

By Christopher Chu

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.

By Christopher Chu

By Christopher Chu

 

Bibliography

Hein, M (n.d.). Historical Timeline of Concrete. Retrieved November 1, 2011, from

https://fp.aubrun.edu/heinmic/ConcreteHistory/Pages/PantheonStructure.htm

Moore, D., P.E. (1995). The Pantheon. Retrieved November 1, 2011, from

http://romanconcrete.com/docs/chapt01/chapt01.htm

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 

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6 Responses to Assignment 4 – The Pantheon’s Passive Systems

  1. D says:

    I like that you used an ancient building to show some of the most fundamental “sustainable” design choices. I feel like a lot of people immediately conclude that sustainable design is only achievable through extravagant technological advancements. I think, moving forward, it would be interesting to utilize the passive ventilation system you spoke about in great detail. While the Pantheon uses a single oculus at the uppermost part of the building, you could make an escape route for the hot air in your design. Maybe your design includes many of these oculus forms, or just one, as seen here. Using the Venturi effect to passively heat, cool and ventilate your children’s art museum, at least in some places, could be really interesting. Also, I know the oculus was placed in an appropriate place so that points in the building, such as the front entry, would be illuminated on specific religious holidays, or at certain times of the day. Dealing with a building that holds art, your window placements should be focused on directing light in a certain way to a specific place. Since not all art can receive direct light, you could do studies on where the light hits your interior galleries, or how you can diffuse the light, so that it merely illuminates your gallery spaces.

  2. Similar to D, I found it extremely interesting that the Pantheon utilizes such sustainable systems. Usually one thinks of the Pantheon as being designed artistically and sculpturally, and not for natural, efficient systems. Because it is such a big, heavy structure, one does not generally associate it with ventilation, air flow, and light. I like that you analytically considered various aspects of the building’s design that could have been improved, such as how the building is not warmed in the winter months. I also think it is good that you proposed a solution to this problem, and showed how the thermal massing system could be improved.

  3. Randy Hume says:

    Great stuff. Many homes older than 100 years have an open central area (stairway) and a way to vent the top floor outside, such as an Italianate cupola.

    I have been interested in venturi effect in a slightly different approach. Most of us have had the unfortunate experience of being in a glassed in stair well in a parking garage and know how warm it can get. Would it be possible to purposely create a solar chimney open to the outside at the top and bottom to create a rising air flow? Then, use narrower features at each floor level to draw warm ceiling air out of each floor of the building into the chimney and out of the building? On one hand, it is hard for me to imagine passively rising air to have enough velocity to create much venturi effect. But, perhaps having extreme differences in cross section of the chimney would compensate for low flow.

    I would be interested in hearing if anyone is familiar with inexpensive modeling software to simulate these kinds of situations.

  4. Good work. May I use a couple of your images in my ppt? (I will add your name to acknowledge and site reference). Maybe you would like to check out Colt International on http://www.coltgroup.com?

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