Green/Sustainable Design, Part III

[Sharabella Fini]

I realized it’s time for another blog on Green and Sustainable Design. I thought for this part I go over some basics on “Passive Solar Design.

Passive Solar Design refers to design and material choices which use or avoid the sun’s heat to promote thermal comfort and energy conservation and/or reduce the need for mechanical heating, cooling, and ventilation systems. It is the traditional method used throughout the world to increase comfort.

Optimum design features and material choices depend on the conditions to be mitigated in the area in which building is located. A measure which works well in one place may not work well in another. For example, sunrooms and skylights are effective means of heating in cold climates, but they are likely to result in overheating in Central Texas. Central Texas has fairly consistent cooling breezes from the Gulf of Mexico, but if a building site is on the west side of the hill, it will be cut off from this breeze. It should be easy to provide all heating needed in Central Texas with Passive Solar means, care must be taken to avoid overheating.

Whether for passive heating or cooling in Central Texas, some design features should be utilized; I will briefly cover a few.

Two primary elements are required: south facing glass and thermal mass to absorb, store, and distribute. (Thermal Mass examples: Walls and Floors)

There are three approaches to passive systems-direct gain, indirect gain, and isolated gain.

The direct gain is the applicable method in Central Texas. The goal is to capture the sun’s heat within the building and release that heat during periods when the sun is not shining. In this system the actual living space is a solar collector, heat absorber and distribution system. South facing glass admits solar energy into the house where it strikes thermal mass materials such as masonry floors and walls. The direct gain utilizes 60-75 percent of the sun’s energy striking the windows.

Direct Gain system rules of thumb for Central Texas:

-Conduct a heat load analysis of the house

-Do not exceed 6 inches of thickness in thermal mass materials

-Do not cover thermal mass floors with wall to wall carpeting. Keep floors as bare as functionally and aesthetically possible.

-Use a medium dark color for masonry floors and use light colors for low-mass walls. Thermal mass walls may be nay color

-For every square foot of south glass, use 150 pound of masonry.

-Fill the cavities of concrete block used for thermal storage with concrete.

-It’s better to have thermal mass spread throughout the living space rather than concentrated in one place.

-The surface area of mass exposed to direct sunlight should be 9 times the area of windows.

I think this a good stopping point before it gets too detailed. Hope this has helped or be help to you at some point.

Until next time,

[Sharabella Fini]

Thanks Rachel...so glad you like it.

[Rachel Butler]

wow- very informative post. Sustainable design is so very crucial. Your post really makes me want to build!