EcoHearth: Come Home to the Earth

The sun is the source of 99.98% of all energy on Earth. Even the power in fossil fuels is just solar energy stored over the course of millions of years. Unfortunately, fossil fuels are costly to extract, cause global warming when released, and take the Earth eons to replace.

A better solution is to tap the energy in sunlight just as it reaches the Earth. Even without solar panels (which put a strain on our environment, though less so than fossil fuels), you can supply the lion’s share of your lighting and heating needs this way. Through thoughtful building design or retrofit, based on techniques known as daylighting and passive solar heating, it’s easy to save money and reduce your carbon footprint by leveraging the abundant, easily accessible and free solar energy flooding the planet daily.

Daylighting
Good daylighting creates beautiful, well-lit spaces while saving energy. At its most basic, daylighting is the practice of using natural light to illuminate building spaces rather than relying solely on electric lighting during the day. Daylighting reduces the need for electric lighting and connects people to the outdoors. The natural light it provides is easier on people’s eyes and improves worker productivity in offices—at a fraction of the cost of the most efficient electric lights.

Successful daylighting is part of an integrated design process from the outset, a combination of architecture and engineering. Climate and geographical region, as well as building type, use and orientation, are big factors in designing a successfully daylit building. Integrated from the start of construction, daylighting can be accomplished without increasing costs.

Daylighting design uses a variety of strategies, including:

• Carefully positioning and slanting windows
• Choosing a mix of window types depending on the building’s orientation
• Using clerestory windows
• Using reflective light shelves under windows
• Painting interior surfaces light colors to maximize reflection
• Incorporating skylights and light tubes

But daylighting is not just about saving energy. The quantity and quality of light affects health, safety, morale, comfort and productivity.

A study of daylighting in schools conducted by the Heschong-Mahone Group examined over 21,000 student records and found that test scores improved as much as 20% in math and 26% in reading for students with the maximum exposure to daylight in their classrooms. The study is the latest in a growing body of research linking academic achievement to natural lighting.  "There is clearly a statistically compelling connection between daylighting and student performance," stated Heschong.

"Smart school buildings mean smart kids," summed up David Nemtzow, President of the Alliance to Save Energy. "This study shows that schools that use natural lighting increase the rate of student learning, while cutting utility bills for school districts and taxpayers."

While many expect daylighting to increase a building’s cooling needs, in fact, properly designed daylighting emits far less heat into a building than conventional electric lighting. The cooling energy savings from daylighting were studied by the Energy Center of Wisconsin at a facility that specifically designed experiments involving commercial-building lighting and HVAC systems.

The research measured lighting and HVAC energy use in two sets of rooms. Different window configurations, glazing, lighting systems and automatic lighting controls were tested against a set of control rooms. The HVAC system remained the same for all tests.

The experiments found that lighting and HVAC operating cost savings for the daylit rooms are considerable, and represent a savings of more than 20% on operating costs of about $1.13 per square foot. The full findings are available in the report Energy Savings from Daylighting: A Controlled Experiment.

Passive Solar Heating
When most people think of solar energy, they think of photovoltaic (PV) cells perched on a building’s roof. But passive solar—unlike active solar systems—does not involve the use of mechanical and electrical devices, such as PV panels, pumps, fans or electrical controls to collect and move the solar heat. Instead, passive solar is the practice of designing a building to maximize the use of heat from the sun.

Passive solar design is highly energy efficient, reducing a building's energy demands for lighting, winter heating and summer cooling. Energy from the sun is free. Strictly passive designs capture it without additional investments in mechanical and electrical equipment.

Every passive solar building includes five distinct design elements:

• A collector - The large glass area through which sunlight enters the building. Passive buildings usually have large, south-facing windows.
• An absorber - A dark surface that absorbs solar heat. Materials that absorb and store the sun's energy as heat can be built into sunlit floors and walls.
• A thermal mass - Material that stores the absorbed heat, usually masonry(such as concrete, stone and brick) or a water tank. For example, the floors and walls store heat and slowly release it at night.
• A distribution method - Heat’s natural tendency is to move from warmer materials to cooler ones until there is no longer a temperature difference. In some buildings, passive distribution is augmented with fans, ducts and blowers to circulate the heat.
• A control mechanism - To regulate the amount of sunlight entering the building. This can be as simple as a roof overhang that allows more sunlight in during the winter and less in the summer.

Two common passive solar design features are sunspaces and Trombe walls. A sunspace (like a greenhouse) is built on the south side of a building in the northern hemisphere, as the southern side always receives the most sunlight. As sunlight passes through the windows, it heats the sunspace. Proper ventilation allows the heat to circulate into the building. A Trombe wall is a very thick, south-facing wall, painted black and made of a material that absorbs radiant energy. A pane of glass or plastic glazing, installed a few inches in front of the wall, helps hold in heat. The wall heats up slowly during the day and cools gradually during the night, radiating heat inside the building.

Of course, too much solar heating can be a problem in the summer, but there are many design features to keep passive solar buildings cool. For instance, overhangs can shade windows when the summer sun is high in the sky. Sunspaces can be closed off from the rest of the building, and buildings can be designed to use fresh-air ventilation in the summer.

Although passive solar seems counterintuitive to many architects and engineers, recent developments in software allow building professionals to calculate the window, wall, insulation and roof requirements; the best way to orient a building to maximize solar gain; and the complicated formulas to determine air movement.

Combining Daylighting and Passive Solar Heating
The Visitors Center at Zion National Park in Utah is a good example of making the most of passive solar and daylighting. Energy-efficient features save about $14,000 a year. Completed in 2000, the Center’s notable energy-saving measures include:

• Trombe walls: Most of the heat for the center comes from a Trombe wall.
• Daylighting: The primary source of light for the building is daylight from clerestory and other windows. When there is not enough sunlight, the building's energy-management computer adjusts electric light to provide just the right amount of additional light.
• Natural ventilation: The building was designed so that overhangs and the building's configuration block most of the windows from the summer sun. When the clerestory windows are open, cooler air naturally flows through the building, forcing the warmer air out. The energy-management computer automatically opens clerestory windows when the building is too warm.
• Cooling tower: When natural ventilation is not enough, water is circulated over pads at the top of a cooling tower. As the water evaporates, it cools the air. The cool air falls through the tower into the building.

For the foreseeable future, the sun will continue to shower the Earth with enormous amounts of free energy. It makes economic and environmental sense to use it to supplement your lighting and heating needs. Daylighting and passive solar heating will help you do just that. Whether designing from scratch or renovating an existing building, give them a try. Your wallet and the Earth will thank you.

Further recommended reading:
Daylighting: Natural Light in Architecture by Derek Phillips
The Passive Solar Energy Book by Edward Mazria

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