Passive Solar Design

Passive solar - a term referring to those technologies that can be employed to convert natural sunlight into usable heat, to cause air-movement for ventilation or cooling, or to store the heat for future use, without the use of electrical or mechanical equipment.

A "passive" solar house provides cooling and heating to keep the home comfortable without the use of mechanical equipment. This style of construction results in homes that respond to the environment.

For passive heating and cooling, the plan of the house, careful site selection and planning, construction materials, building features and other aspects of the home are designed to collect, store and distribute the sun's heat in winter; and to block the sun's rays in summer. Passive solar houses can be built in any architectural style and in any part of the country.

The following techniques use passive solar strategies to provide heat:

Direct Gain is radiant heat resulting from sunlight admitted directly to the living spaces through south-facing windows, which warms the interior surfaces (walls, furniture, floors, etc.). For direct gain, the south-facing window area must be sized for the climate, the type of window used and the amount of thermal mass in the home.

Indirect Gain In a design that employs indirect gain, an attached sunspace or Trombe wall collects heat from the sun before transferring it to other spaces within the home. The air heated in a sunspace circulates naturally or with the aid of fans to other rooms.

Thermal Mass is any material in the home that absorbs and stores heat. Concrete, brick, tile and other masonry materials are the most common choices for thermal mass in a passive solar home, but let's not forget logs. These materials absorb and release heat slowly and are easily and inexpensively integrated into the house design. They are most effective when dark colored and located in direct sunlight. The addition of thermal mass allows saved solar energy to heat the house at night or on cloudy days. The combination increases the performance and energy-saving characteristics of the home, generally for only a modest cost increase.

The following techniques use passive solar strategies to provide cooling:

Passive solar cooling can reduce or even eliminate the need for air conditioning in homes. At its simplest, passive cooling includes overhangs for south-facing windows, few windows on the west, shade trees, thermal mass and cross ventilation. Some of the same strategies that help to heat a home in the winter also cool it in the summer. For example, with a well-designed overhang, the south-facing windows that admit the low-angled rays of the winter sun are shaded from the high-angled summer sun. Thermal mass, which stores heat in the winter to release in the evening, works in reverse in the summer. The mass cools down in the evening and retains that coolness the next day, moderating the effects of high daytime temperatures.

Passive solar space cooling is used in warm climates around the world. Although it is not common in Canada, the potential for its use is large. Key concepts are:

locate windows in the upper floor of the building so that this space is solar-heated during the warm season
open the windows when building cooling is needed
allow fresh, cooler air to enter the building through the bottom floor; this air may pass through a duct in the ground so that it is further cooled
close other windows in the building so that only cooler air from the lower level enters the building

The heated air in the top of the building is naturally drawn outside and replaced with cooler air in the lower portion of the house. Essentially this is a "chimney" effect in the building.

Passive solar design utilizes energy efficiency

Energy efficiency minimizes the need for heating, cooling and electricity, solar or otherwise. Designers of solar homes use insulation levels that are higher than those found in typical construction and energy efficiency appliances and lighting.

Windows are up to twice as resistant to heat loss as those used in conventional construction. Air infiltration is also reduced by carefully sealing and caulking around window and door openings and under sill plates.

Daylighting

In designing a building it is important to consider the optimal use of daylight. The term "daylighting" refers to using the overall light of the surrounding sky to illuminate building spaces, not just direct sunlight. In large commercial buildings, daylighting can significantly reduce energy consumption and provide a more comfortable working environment. Correct daylighting design will not only reduce costs related to electrical lighting but will also reduce the need for air-conditioning in rooms heated by light bulbs or ballasts.

A good daylighting system will consider the following elements: the orientation and space planning of the spaces to be lit; the location, form and dimensions of the opening through which the daylight will pass; the location of internal surfaces which may be able to reflect the daylight and the location of movable or permanent objects which provide protection from excessive light or glare.

Adapted from "Consumer Guide to Solar Energy," K. Sheinkopf and S. Sklar, Bonus Books, Inc. and "Buildings for a Sustainable America Case Studies," Burke Miller Thayer, American Solar Energy Society.