 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
|
|
|
|
|
|
|
|
||||||||||
|
|
|
|||||||||||||||
|
|
||||||||||||||||
|
|
|
|
||||||||||||||
|
Free Resources | Land Use | Articles |
|||||||||||||||||||||
|
|
Energy and the Human Environment: Toward Better Neighborhood Design Cont… Space Heating and Cooling: The House Although the homes in Village Homes use a large variety of solar systems, they all share a few concepts and details of design and construction which make them exceptionally energy-efficient. These general energy conservation features include 1) good insulation, 2) extensive use of south facing glass with overhangs, 3) the incorporation of high mass material and 4) window placement for cross ventilation. Some of these are specifically designed to fit the Davis climate, but most of them are applicable almost anywhere. The climate in Davis is known as a Mediterranean climate. This describes a fairly temperate climate with strong marine influence. The summer days are hot (reaching 100 degrees regularly), but as the hot air rises over the Sacramento Valley, it draws in the cool air form the Pacific Ocean and nighttime lows are comfortably cool, averaging about 56 degrees over the summer. The Pacific also moderates the winter extremes, and freezing temperatures are a fairly rare occurrence. Careful insulation is one of the first steps in reducing energy demand in a house. Walls and roofs are almost always insulated now, but thicker insulation is often desirable. Many of the houses in the Village Homes have used two-by-six walls instead of two-by-four walls so that more insulation can be put between inner and outer walls to increase their resistance to heat flow. Roof insulation is typically R30, compared to R19 in standard houses nearby. Insulating the other exposed areas of a house is also important and often not done. For example, the edge of the floor slab is often not insulated and as a result the slab provides a path for unwanted heat loss in the winter and heat gain in the summer. It is inexpensive and easy to add insulation to the edge of the slab during construction, and all of the builders in Village Homes do so as a standard practice. Windows are another area where energy conservation must be considered. Although the primary concern is usually radiation gain from sunshine, windows are also an important factor in conductive heat loss in the winter and unwanted heat gain in the summer. A single pane window, for example, has an R value of only 0.9 or only 1/20 that of the typical wall used in Village Homes. The use of thermal pane windows increases the R value to 1.8 which is better, although still not very good. As a result, many of the houses in Village Homes further improve their windows by providing thermal shutters or drapes. These come in many types with widely different costs and vary from R values of only two to three to an impressive nineteen. Another facet of energy conserving design is the choice of exterior color for the walls and roof, and the choice of roofing and siding material. Unwanted heat gain can be greatly reduced by using light colored walls, and most housed in Village Homes use white or off-white for this reason. The choice of roof color and materials also affects also affects heat gain. The houses in Village Homes use tile and shakes because they have proven to have the best thermal performance in tests carried out near Davis. Shakes and concrete tile remained the coolest of the six roofing materials tested. Light colored tile and shakes remained 40 degrees below light colored metal roofing or composition roofing on clear sunny summer day. The final energy conservation measure involves tightening up the house, or weatherproofing it. This involves carefully sealing the many areas where unwanted cold or hot air can enter the house. This is important because in a well-insulated house, infiltration losses may almost equal conductive losses. The construction of the house must be done with an eye to reducing infiltration. The sills are set in mastic to reduce leakage under the walls. Caulking is done around doors and windows where cracks are left between the rough frame and the finished window or door frame. After all these insulation features and considerations have been included in design, it is time to turn to another design consideration, using the heat of the sun to warm the house. To use solar energy effectively means taking advantage of the position of the sun. In summer, the sun is high in the sky and traverses an arc of 240 degrees from east to west. In winter, the sun is low and traverses an arc from east to west of only 120 degrees. The proper orientation of the houses in Village Homes maximizes heat gain in the winter while minimizing unwanted heat gain in the summer. A house that is longer east - west and shorter north - south with most windows on the south and a modest overhang on the south will receive full sun during the winter, yet be fully shaded during the summer. The homes in Village Homes all have very few windows on the east and west sides where summer heat gain is the worst. The south side, in contrast, has many windows with overhangs or arbors to shade them in the summer. Arbors covered with deciduous vines are used often because they provide shade when it is most needed, the summer and fall. If springtime weather is cool, the leafing is delayed allowing the house to stay warm, while a warm fall will keep leaves on the vines, providing needed shade. Passive solar homes are designed to store the sun's heat through the incorporation of high mass materials. The massive adobe walls of the old missions are a classic example of this principle. The adobe absorbs and stores heat and cool to bring the temperature extremes within the comfort zone. Other materials with the ability to store heat include water, concrete, stone, brick and tile. We have incorporated these materials in a variety of ways within the houses of Village Homes. Water is stored in water tanks camouflaged as walls, barrels or culvert pipes sealed at both ends. A passive solar home not only stays warm in the winter, but is cool in the summer. South winds come from the ocean in Davis in the evening providing cool breezes cool nighttime temperatures. Homes are designed to ventilate well and the cool breezes cool down the thermal mass of the house. During the day, the house is kept tightly closed. The well insulated walls and ceilings keep the coolness inside. All windows are designed either with overhangs or shade screens to prevent the sun from providing unwanted solar heating. Most residents do not even have an air conditioner, saving seven percent on their overall family energy use. Five percent of the energy used by a typical Davis family is devoted to water heating, yet solar water heating can provide up to eighty percent of those energy needs. Solar water heating makes sense. It provides lower cost hot water, increases one's feeling of self sufficiency, and helps conserve needed high grade energy for more important uses. As Amory Lovins has said, "Heating water with electricity is like cutting butter with a chainsaw." The solar water heating systems are installed along with reasonable water conservation measures. These include such inexpensive and readily available equipment as constrictors on the shower and water faucet, pressure reducers, aerators, better pipe insulation, and others. Strict application of all possible conservation measures can reduce hot water consumption to ten percent of existing use. |
|||||||||||||||||||||
| | |
||||||||||||||||||||||
