RAMMED EARTH AND EARTH SHELTERING: THERMAL MASS IN THE HOT DRY DESERT, TWO CASE STUDIES.

 

Current building practices of residential construction lack simple methods of using passive solar techniques. Does passive solar really work, and how can it be applied in a hot arid environment? These two case studies will show how earth material can provide a cooling effect without additional mechanical systems. The building prototypes chosen are a rammed earth house, and an earth sheltered concrete block house. These two houses will be example of how the materials operate once in construction form and support that passive solar does really provide a cooling effect.

In this study, there are many issues addressed including:

    • Using local building materials reduces the environmental degradation of current residential practices.
    • How does thermal mass perform without mechanical aid in a hot arid desert?
    • What are the benefits of using thermal mass beyond the obvious cooling effect?
    • How does testing Mean Radiant Temperatures support the cooling effect of thermal mass, and how these variables apply to the "Comfort Program" PMV model.

Using local building materials reduces the impact of the embodied energy that is required in constructing a house. Materials that are derived from the desert earth can both reduce pollution and support environmental sustainability in the life cycle costs..

The case studies were tested over a period of time without mechanical support, to find out how the materials operated as a built construction material. The structures observed are similar in design size therefor reducing the variables between the prototypes. Mean radiant temperatures were collected as well as surface temperatures of the walls, ceilings, floors, and windows by 15 thermocouples set to collect data every half hour for 7 days straight. Humidity and outdoor temperatures were utilized along with the collected temperatures by the Pmv comfort model, which analyzed the existing structures.

The comfort model chosen is based upon P.O. Fangers comfort model, which takes very basic parameters such as ambient temperatures, humidity, surface temperatures, clo values, stress activity level, and combine these into a quantifiable equation that can show a person’s comfort level. If the comfort level is the same for a rammed earth house as compared to a wood-frame insulated house, then the deciding factors should be the embodied energy, and the environmental degradation of the operation of each. If simple local materials such as earth can be used to construct a house, and the materials allow the house to cool naturally without mechanical aid, then the house requires minimal assistance and promotes minimal utility pollution from power plants.

This study will show how two local building materials in Phoenix, Arizona operate as thermal mass. It will also show how this mass provides cooling effects that enhance comfort levels for the inhabitants. Obtaining comfort is the primary goal in design, therefore the hypothesis of this study shows that if comfort can be achieved naturally, without additional means of mechanical devices, the idea of sustainability is supported, and promotes a more local building construction practice.

 

Author—Candace Gossen, Solar 7.83 Consultants, 2323 SE Tamarack, Portland, Oregon 97214. 503-236-0915/ 503-238-6607 fax, email Solar783@aol.com.

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The research of this paper is currently being documented, please stay tuned.