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Passive Solar Design Captures the Sun's Energy

Passive solar design incorporates aperature, thermal mass, absorbers, control and distribution as five key elements. Orientation is important as well.

Good design incorporates aperature, thermal mass, absorbers, control and distribution as five key elements. Orientation is important as well.

Passive Solar Design Introduction

A sustainable heating strategy takes advantage of the natural transit of the sun across the sky to heat space within a house and shading techniques of building construction to cool the house.

Orientation

Essentially, the side of a home with the most windows is oriented towards the south with a sufficient amount of shading, such as overhanging eaves or insulating window blinds or shades.

Trees as Shade

Deciduous trees can be used to good effect. During the hot summers the shade provided by a leafy tree equals the air conditioning output of 10 window unit air conditioners. In the winters, when the leaves fall and the branches are bare, the sun can stream through to warm the home.

Thermal Mass

Sometimes masonry or tubes of water are included in the design to store the heat during the brightest sunshine and then release it gradually during cooler parts of the day or night. Concrete, stones or pavers are among the materials used to store heat.

Savings

A sun-heated home basically reconfigures the construction materials and layout of a home. This is different from an active system that installs panels, distribution and storage facilities in a home at an additional investment. The initial savings for passive system lies in the absence of increased up-front costs.

The University of Kentucky estimates that good window designs will produce between 40,000 and 50,000 BTUs of heat per heating season.

Five Main Elements of Passive Solar Housing Design

As the drawing in the top right shows, there are five elements necessary for any effective solar design.

Aperature - Placing the windows on the south will allow the winter's sunshine to enter the house and warm it.
Control - Overhanging eaves, curtains or other window treatments will keep out the summer sun and prevent overheating in that season.
Distribution - Thought must be given to how the sun's ultraviolet light enters the space to be stored, and then how the heat is released in infrared radiation. This is usually pretty simple; the simplicity being a major advantage of a passive design over an active system.
Absorber - There must be an appropriate surface to absorb the heat as it hits the desired area. Masonry or metal objects make the best absorbers because they conduct the heat well; fabrics or plastics are the worst because they are insulators that block the transfer of heat.
Thermal Mass - Thermal mass stores the solar heat for future use. Masonry, such as rocks, concrete blocks or even brickwork within the house, holds heat the best and releases it automatically when the house's temperature drops.

Passive Solar Design Concepts

Technical Descriptions of Basic Design

Energy Savers: Passive Solar Home Design
This site explains that proper orientation of the site is critical. But good insulation and air sealing are important; little or nothing is gained from building to heat with the sun if the heat simply leaks from around the windows or radiates from walls that do not have sufficient insulation.

SustainableSources.com: Passive Solar Design
Good ventilation is important to transfer the warm air to different parts of the living space of a solar home and to assist in cooling in the summer. This site provides descriptions and diagrams of basic strategies for accomplishing this.

Further, SustainableSources.com gives a run-down of the types of construction materials that are needed and suitable for naturally-heated building.

The site descibes how thermal mass, such as concrete floors or some other form of masonry, will "temper the heat" during hot, sunny days and store it for release in the cool evenings.

The eco-heating series of the Oil Drum, a site that covers peak oil
This series goes into the history and design principles of using the sun to heat a home. It provides a number of resources for determining the best oritation of a home, including a SolarPlot calculator referenced by a commenter. The overview also discusses how windows provide the aperture to collect the heat of the sun's rays.

The second part of the series discusses heat gain and heat loss, providing diagrams of effective windows to collect the sun's heat. The commentary provides resources that describe the effect of clouds, paints and other factors on the transfer of heat. The final part of the series discusses the thermal mass component of the design, describing how thermal mass stores and then redistribute's heat captured from the sun.

Passive Solar Design Primer