Basic Elements of Passive Solar Design

passive solar

There are many ways to incorporate passive solar into your home design.

The sun has been utilized as a heat source in the architectural design of buildings for thousands of years.  Passive solar technology is, by definition, a means of utilizing sunlight as an energy source without the aid of mechanical systems.  Passive solar design (also called climatic design) employs the walls, windows, and floors of a building to collect, store, and distribute solar energy in the form of heat during winter.  The same system will reject solar heat during the summertime.

A “passive solar home” is designed with a specific purpose in mind of taking advantage of the local climate to heat and cool the home.  Techniques for passive solar design are easier to apply when a new home is being designed.  But existing homes can passively collect and store heat by being retrofitted.

There are five basic elements of passive solar design, those being aperture, absorber, thermal mass, distribution, and control; more details follow.  For passive solar design to truly be successful, all of these separate elements must work in tandem.

Aperture or Collector

The apertures, the collectors of heat, are large windows through which the sunlight enters a building.  Ideally, the apertures face within 30 degrees of true south.  Apertures should not be shaded by trees or other structures from 9 a.m. to 3 p.m. daily during cold months.

Absorber

The absorber is a surface that is hard and darkened; it serves as a storage element.  This surface is placed in the direct path of sunlight and could be a floor, masonry wall, or water container.  When sunlight hits an absorber, it is absorbed as heat.

Thermal mass

Thermal mass is the component in passive solar design which stores the sun’s heat.  The absorber and thermal mass typically form the same floor or wall.  The absorber is the part of the surface that’s exposed and the thermal mass is behind the absorber.

Some of the materials which are typically used for thermal mass include:

passive solar

Stone floors and tall windows are often used in passive solar to maximize the power of the sun.

1.     Water, which has the highest volumetric heat capacity among the materials commonly used.

2.     Various forms of masonry, such as clay bricks and concrete.  Concrete made with stones is more effective than concrete made with other insulating aggregates such as perlite or ash.

3.     Mud, earth, and sod.  The heat capacity of dirt depends on several factors, such as moisture content, density, temperature, particle shape, and composition.  Rammed earth is composed of appropriate proportions of sand, gravel, and clay and is highly compressed into a frame or mold that’s externally supported.

4.     Natural stones and rocks.

5.     Logs.

Distribution

Distribution is the method by which the solar heat circulates from the points of collection and storage to other areas of the home.  With strictly passive solar design, distribution is achieved through conduction, convection, and radiation.

•       Conduction is the way heat travels from molecule to molecule through materials.

•       Convection is how heat circulates through gases and liquids.

•       Radiation is when heat moves from warmer to cooler objects.

Control

Roof overhangs are the typical element of control in passive solar design.  They are used to shade the aperture during summertime.  Other devices are low-emissivity blinds and awnings.

In addition to the five basic elements of passive solar design, other significant factors include:

•       The type of glazing on a window.

•       Window location.

•       Insulation.

•       Air sealing.

People found ways to stay cool in summer and warm in winter long before there was such a thing as central heating and air conditioning, and it was primarily through the use of passive solar design.

It only makes sense that with the continued advancement of solar technology, it’s feasible to get back to more natural means of climate control.

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