Heating and cooling uses more energy and drains more energy dollars than any other system in your home. Typically, 44% of your utility bill goes for heating and cooling. What’s more, heating and cooling systems in the United States together emit more than a half-billion tons of carbon dioxide into the atmosphere each year, adding to global warming. They also generate about 24% of the nation’s sulfur dioxide and 12% of the nitrogen oxides, the chief ingredients in acid rain.
Using solar energy and geothermal heat pumps can help heat and cool your home while drastically cutting your utility bills and helping the environment. Solar energy and geothermal heat pumps can also heat your water, and solar energy can help light your home. This chapter suggests ways for you to accomplish all these things.
The sun is the cleanest energy source for heating and lighting. Everyone uses solar energy to some extent: just opening your drapes during the day and turning off your lights is one way of using the abundant energy of the sun. Today, new technologies can help you use more solar energy in your home while creating a more comfortable living space.
The ancient Anasazi tribe of the American Southwest knew about solar energy, and they built their homes on south facing cliffs that would receive plenty of sunshine in the winter. The sun’s low arc across the southern sky heated their mud-and-sandstone homes effectively. In the summer, the sun’s higher arc in the sky allowed the cliff overhangs to shade their homes from the sun’s hot rays, keeping them cool.
Today, you can use this same wisdom to take advantage of solar energy for your home. South facing windows designed to let in the sun’s heat will help lower your energy bills, while overhangs above those windows can prevent the high summer sun from heating your home in the summer.
Ironically, one of the most important aspects of using solar energy in your home is assuring that you don’t let too much solar energy into your home during the summer. This is most critical on your south facing windows. Like the ancient Anasazi, you need to use overhangs to keep out the summer sun while letting in the winter sun.
In Hawaii, Guam, Puerto Rico, and southern Florida, you’ll want to keep out the sun’s heat year-round. You can use large overhangs, but the simpler approach would be to shade your south facing windows with shrubs or trees.
The opposite is true in Alaska, where you want no overhang or shading at all—you need all the solar heat you can get!
Alaska and other cold climates are also the only locations where you would want to leave your east and west facing windows unshaded. The summer sun, which actually rises in the northeast and sets in the northwest, blasts solar energy into the east and west sides of your home. This is especially noticeable near sunset, after your home has grown warm throughout the long summer day.
Once your windows are properly shaded, you’ll want to choose windows that will maximize your use of sunlight while minimizing energy leaks. The U. S. Department of Energy (DOE) and the Environmental Protection Agency (EPA) have developed an Energy Star® designation for products meeting certain energy performance criteria. The energy efficient performance of windows, doors, and skylights varies by climate zones. Look for new high efficiency Energy Star® windows that can let in the sun’s rays while insulating against the outside cold. In addition to the Energy Star® label, look for the label provided by the National Fenestration Rating Council (NFRC). The NFRC label includes the U factor—an indication of how well the window insulates—and the solar heat gain coefficient (SHGC), which indicates how well a window admits solar heat.
Of course, another aspect of sunlight is the light itself, which can supplement electric lighting while creating a brighter, more inviting living space. Because the sun’s visible light is actually a separate component of solar energy than the sun’s heat—which is actually non-visible infrared light—the two aspects of sunlight can be handled differently by windows. For instance, a window with a low SHGC—designed to reject the sun’s heat—can still allow in most of the sunlight. The recent innovation of “spectrally selective” coatings allow windows to reject heat without the dark tinting that was common on older heat-rejecting films.
Letting solar radiation into your home is only half the story of using solar energy; the other half is storing the solar energy for later use. It’s coldest at night, so the best use of solar energy is to absorb it with heat-retaining materials during the day, then allow those materials to keep the house warm at night. One choice is heavy tile flooring; anyone who has a tile floor knows how it can still feel warm hours after the sun has set. Brick and other masonry are also great materials; these can be used both in sun exposed floors and in walls.
Some designers have even incorporated water into walls to help store solar energy.
The idea of using heat-retaining materials has led to other solar energy innovations. For instance, Trombe walls actually incorporate heat storing materials, such as masonry, in south facing walls. A layer of glass or plastic glazing is mounted on the outside of this wall, leaving a small airspace between the glazing and the wall. This helps the wall absorb and retain heat. Trombe walls absorb the sun’s heat during the day, then radiate that heat from the inside of the wall into your home during the night.