Passive Solar:


Passive solar design is one of the oldest and simplest uses of renewable energy. Passive design utilizes a building's structure to capture sunlight and store and distribute heat, thus providing free heat and light over the building's lifetime.

To date, builders have constructed more than 17,000 commercial buildings and 1 million residences in the United States that take advantage of passive solar design. In one study of 19 new and retrofitted passive-solar commercial buildings, the energy costs for the buildings were, on average, 51 percent less than the conventionally-designed buildings (Federal Energy Management Program (FEMP), May 1995). The International Energy Agency's Solar Heating and Cooling Program corroborated these findings. In climates ranging from the Mediterranean to the Arctic, the passive solar commercial buildings it studied from 1985 to 1991 used only 10-35 percent of the heat required in comparable buildings.

The specific applications for passive solar include solar heating, daylighting, natural ventilation, radiative and ground-coupled cooling, and peak load shifting with thermal mass. Solar heating is the most common passive solar application in structures under 10,000 feet, such as libraries, visitor centers, health care facilities and multi-family residences. Daylighting is the most common passive application in larger buildings. FEMPhas identified the four key components of passive-solar design:

1. Siting and orientation -- Building location that takes maximum advantage of sunlight and overall climate;

2. Windows -- Window location, size, design (e.g. properly-positioned overhangs to help block out the heat of the sun when desired), glazing material (transparent or translucent window glass which permits sunlight to enter, but doesn't allow heat to escape) and tight fitting double- or triple-paned windows;

3. Thermal mass -- Walls and floors that store heat from the sun and release it slowly at night; and

4. Building envelope -- Adequate insulation and low air leakage.

Besides saving energy, these design strategies can result in beautiful buildings that are pleasant places to live and work. Studies of commercial buildings document increased worker productivity as a benefit of passive solar design. Finally, passive designs can be implemented with little or no extra cost. A solar architect can often orient the building to create energy savings without even changing the design.

Because passive solar design incorporates both energy conservation and the use of renewable resources, it exemplifies complementary energy strategies with the brightest future.

Large Office Buildings Join the Daylighting Bandwagon

From coast to coast, many large buildings are using one type of passive solar design -- daylighting -- to cut energy costs, increase productivity and enhance workers' sense of well-being.

In daylit buildings, well-placed skylights, atria, windows and other types of glazing are used to light a room with natural sunlight, making electrical lighting less necessary. Devices that measure indoor light levels dim or turn off lights depending on the amount of available sunlight. Translucent baffles, light shelves or other means reduce glare by softly diffusing incoming sunlight so it is evenly and widely dispersed. The result is daylit spaces illuminated with light superior in quality to the best artificial lights. Even unassisted sunlight from overcast skies can supply light sufficiently bright to meet the lighting standards of the Illuminating Engineering Society.

Daylighting can save a significant amount of energy because artificial lighting typically consumes about 25 percent of a building's total energy. Artificial lighting also gives off substantial heat, elevating building temperatures and adding to cooling costs. But since daylight carries only 1/3 to 1/2 as much heat content as an equivalent electrical source of light, daylighting can also reduce air conditioning costs in the warmer months.

On the flip side, daylighting no longer brings uncontrollable heat gain. Recent developments in glass allow buildings to keep the heat-generating rays of the sun out, while letting the sun shine in. Properly-positioned overhangs and vertical glass also help block out the heat of the sun when it's not wanted. These two architectural tricks cut off the strongest rays of the sun when it is in its highest position in the sky without shielding the building from the benefits of the low sun in the winter.

Equally important is that daylit buildings boost the health and productivity of the people inside. For decades, studies have shown that workers exposed to daylight have fewer health complaints, are more resistant to fatigue and stress, and are more satisfied with their jobs than windowless workers.


In 1991, nonprofit Way Station, Inc. built a daylit mental health facility in Frederick, Maryland, an area that receives about 25 percent less sunshine than the national average. Daylighting was chosen primarily to improve the well-being of the facility's inhabitants. But despite the cloudy conditions, daylighting also enables the facility to use 75 percent less electrical lighting than comparable conventional facilities. Combined with energy-efficient lighting, the Way Station saved $30,428 on its 1992 electric bill compared to a similarly-sized facility.

Daylight enters the two-floor, 30,000-square foot facility through north- and south-facing windows, roof monitors and skylights. The windows utilize exterior and interior light shelves. A daylight tracking system comprised of moving reflective surfaces follows the path of the sun to reflect the best light through the skylight. The tracking system is powered by photovoltaic cells (see Photovoltaic Systems p. 6).

The added cost of incorporating energy efficiency and passive solar features into the Way Station's design is estimated at $170,000. Since about $35,428 of the facility's annual energy savings can be attributed to daylighting features, they will pay for themselves in no more than six years. According to Tena Meadows O'Rear, Director of the Way Station, the building design has had a profound and positive effect on patients suffering from Seasonal Affective Disorder (SAD), a depressive state triggered by a lack of natural light. Many have developed an enhanced sense of well-being and self-esteem at the daylit Way Station. Further, O'Rear attributes other positive developments to the building design, including:

* improved employee morale with staff volunteering to work more hours;
* greater competition for jobs offered at this location;
* reduced absenteeism; and
* a significant increase in the volunteer force

The example of Maryland's Way Station should inspire people who don't think they are in a sunny enough location for effective passive solar design, and encourage them to take advantage of the enormous health benefits of being in a sunny building.

For More Info: Tena Meadows O'Rear, Director, Way Station, PO Box 3826, Frederick, MD 21705; (301) 662-0099; Fax: (301) 694-9932; Gregory Franta, Architect, ENSAR (Environmentally Sustainable Architecture), 2305 Broadway, Boulder, CO 80304; (303) 449-5226; Fax: (303) 449-5276.


In 1983, Lockheed Missiles & Space Company built a daylit office building in Sunnyvale, California, just outside of San Francisco. (Now Lockheed Martin Missiles & Space). This five-level building with a 3,000-employee capacity immediately proved that substantial net savings from daylighting are not limited to smaller buildings. Based on the US Department of Energy's computer simulation estimates, informally confirmed by Lawrence Berkeley Labs, daylighting features saved Lockheed nearly $500,000 in energy costs in the building's first year over comparable California buildings built the same year. At the same time, the abundance of sunlight has increased the productivity of Lockheed Martin's employees. Company officials estimate that in the building's first year, heightened productivity saved the company $2 million.

Daylight illuminates Building 157 softly and evenly. This is the result of multiple daylight entry points, as well as design features that allow sunshine to permeate the office space. Daylight enters through glass running from ceiling to floor along the length of the office area on the north and south sides of the building, and through the top of a large atrium occupants call the "litetrium." Outside of the north- and south-side glazing, exterior light shelves reflect daylight upward through the windows where it is bounced off of interior light shelves into the office space. A slightly sloped ceiling helps the light penetrate deeply into the work areas. Photocell sensors are attached to the interior light shelves to dim or illuminate auxiliary fluorescent lamps as necessary so that light levels are always between 30 and 35 footcandles.

To minimize unwanted heat gain and glaring direct sunlight, the designers left out any east or west-facing windows. They also designed the exterior light shelves to act as overhangs for the windows below, shielding the building from the strongest summer rays of the sun. The top row of windows are shielded by an extra two-foot overhang. Employees can operate internal, horizontal blinds to block the sun's low-angled rays as needed in the winter.

By reducing lighting and cooling costs, daylighting features contributed to almost all of Lockheed Martin's overall $500,000 first-year energy savings. Since the added construction cost was $2 million, Lockheed earned a 25 percent rate of return on its investment. Not accounting for inflation or fluctuations in the cost of energy, Lockheed began earning net savings after four years from the reduced energy consumption alone.

An equally positive benefit of daylighting is the improved productivity and morale of the employees who work there. From the start, it was estimated that building occupants were absent from work 15 percent less than when they worked in previous buildings. An informal survey of employees by the Dept. of Energy and the Rocky Mountain Institute found that workers were uniformly enthusiastic about their office environment. The estimated $2 million savings due to greater productivity alone paid for the cost of adding daylighting features after just one year.

For More Info: Bob Burgess, Public Relations, Lockheed Missiles and Space Company, PO Box 3504, Dept. 2401/ Bldg. 101, Sunnyvale, CA 94088-3504; (408) 742-7442; Fax: (408) 743-2239.

Passive Solar Resources

Designing Low Energy Buildings Workshop, Federal Energy Management Program (FEMP) and Passive Solar Industries Council (PSIC). This workshop is for federal designers, contract A&Es, policy makers, building programmers, and contract and procurement specialists interested in using energy efficiency and renewable energy strategies to balance the heating, cooling and lighting requirements of a building. The workshop teaches participants how to incorporate daylighting, cooling load avoidance strategies, natural ventilation and passive heating techniques into office buildings, visitor centers, courthouses, and other facilities. Attendees also learn how to ensure contractors maximize their use of renewable energy technologies. The workshop is $300 for government officials; $350 for non-government officials. For More Info: Terry Doyle, PSIC, 1511 K Street, NW, Washington, DC 20005; (202) 628-7400, Ext. 204; Fax: (202) 393-5043; E-mail:; Web:

Energy Design Handbook, Donald Watson. This comprehensive handbook describes multiple passive solar design techniques for buildings. The handbook costs $45. For More Info: Blaine Collison at PSIC; (202) 628-7400, ext. 201; (see other PSIC contact information above).

Designing Low Energy Buildings: Guidelines and Energy 10 Software, PSIC and the National Renewable Energy Lab (NREL). Building on the passive solar concepts outlined in Watson's guidebook (described above), this software package helps architects create optimal passive solar designs for customized use. The user inputs a range of variables that affect passive solar energy performance and the software simulates the impact different strategies will have on the building's energy use. The customized simulations factor in local utility rates, occupancy and use schedules, the HVACsystem and the control system. The package costs $50 for students and $250 for professionals. For More Info: PSIC (see above).

Daylighting: Performance and Design, Gregg Ander. This comprehensive book guides the reader step-by-step through the process of incorporating natural light into architectural design. The book is available for $59.95 For More Info: (800) 842-3636, dept. Z 3820.

Sun Angle, Chrisopher Gronbeck. This is a free software program built into the Center for Renewable Energy and Sustainable Technology's World Wide Web site. It calculates the optimum positions and lengths of window overhangs for maximizing solar heat gain in the winter and minimizing heat in the summer. Without having to download the program, the user inputs the height of a window, the "real time" hours and months the user is seeking these solar gain effects, and the geographic latitude of the user's location. The Web page instantly displays the ideal position and length for the overhang. For More Info: Web: http://solstice.