The cost of energy derived from fossil fuels has gone up and down over the past 40 years. While many social and economic factors affect the design and size of homes, the cost of heating, cooling, and operating them with gas, fuel oil, and electricity are expected to continually rise.
At the same time, we have become increasingly aware of how extracting and utilizing these fuels negatively affects the environment. Home design can respond to these trends in two ways: by conserving energy and by using natural forces whenever possible to provide light, heat, and cooling.
Home heating with the sun
The sun is a constant source of heat and light; unfortunately, though the energy is free for the taking, capturing it costs money as does storing it for when we need it. The energy crises of the 1970s spawned many technologies for using the sun’s energy for heating, cooling, lighting, and electricity. Some of these fell by the wayside in the intervening years because they were either too costly or too complicated. Spikes in energy costs in recent years have combined with greater environmental awareness to bring solar technologies once again into the building mainstream.
Active solar heating systems use rooftop collectors to trap solar heat into a liquid medium or air that circulates the heated liquid into the house via heat exchangers and fans. Because of the unattractive appearance of solar collectors on roofs and the cost, complexity, and high-maintenance requirements of active systems, their appeal has been limited and mainly confined to southern locations, where they can provide most of the heat needed as well as heat water for swimming pools in the warm season. In other areas, the passive approach has proven more popular.
Of the numerous devices invented to turn sunshine into useful home heat, the most cost-effective approaches to date have also been the simplest. They use the house itself to collect, distribute, and store solar heat rather than depending on complicated systems of panels, pumps, distribution lines, and controls.
The ideal passive solar house has a well-insulated envelope and compact footprint, with the longest side facing as close to due south as possible. Most passive solar houses in North America collect the sun’s heat directly or indirectly, through a sunspace.
Windows are necessary in any case. They can also help heat the house if located on the south side, where they receive the greatest solar exposure. The simplest way to get heat from the sun into a house is through the windows. But the windows have to face the sun, which means southward for houses in the Northern Hemisphere. Solar rays penetrate the glass and strike an opaque surface, which then radiates the energy as heat to the space. If the surface is a dark-colored dense material, such as brick, stone, tile, or colored concrete, some of the heat is trapped or stored in the material and slowly released—ideal for the times when the sun isn’t shining. Windows for passive solar heating should be energy efficient and preferably coated with low-E coating. Roof overhangs or other shading devices should be part of the design to protect against overheating in times of the year when solar heat isn’t wanted. Windows used for direct gain need protection against heat during times of the year when warmth is not needed. Inside controls such as blinds and drapes control light but don’t keep out heat because it has already penetrated the glass. Awnings or roof overhangs mounted outside work better. The following formula is a rule of thumb for sizing an overhanging awning or roof eave: Horizontal Overhang Projection = Vertical Distance x Overhang Factor.
For example, if you want to find the overhang length for a south-facing kitchen window in Salt Lake City, you first determine that Salt Lake City is at North Latitude 40˚. The sill height above the floor is 42 inches. If the eave height is 9 feet above the floor, you will have a vertical distance of 108 minus 42 inches, or 66 inches, to enter in the formula. The required overhang length will thus be 66 x 0.29 = 19 inches. This rule of thumb is generally good for areas that can benefit from some solar heat. For climatic zones that always need cooling, such as south Florida, the overhangs should block as much of the sun as possible year-round.
The sun’s heat can also be collected indirectly through an adjoining room, sunspace, or solarium. This approach has the advantage of greater control of heat flow than direct gain. Because the space can be isolated from the main living area at night, it won’t draw heat from the house on cold winter nights (although it may be desirable to either allow some heat from the house or provide an auxiliary heater on the coldest nights to keep plants from freezing). Sunspaces can serve functional needs as well as providing solar heat. When properly designed, they can make a welcoming entry-mud room and place to grow plants. As with direct gain systems, sunspace design must provide means for shading during warm seasons.
Light from the sun, called daylighting by architects and engineers, is most always welcome in kitchens and baths for the free light it provides and, even more, for the cheerful way it enlivens a room. Any plants used to enhance the space thrive better in natural light as well. Sunlight can enter a space from a skylight or window in any wall, but the direction the window faces affects the amount of heat and light it will admit. High-performance windows contain improvements that make the control of heat and light that streams through much easier than the single- and double-glazed windows of the past. But even efficient windows will perform better with respect to their contribution to the home’s lighting if the following guidelines are observed.
South-facing windows Windows on the southern walls receive the most total light year round. The light is direct when the sky is clear and thus glare is a problem. Overhangs, awnings, or other shading devices designed for the latitude, as described previously, can protect against unwanted heat during warm seasons.
North-facing windows Windows situated in the north walls only receive direct sunlight during early mornings and late afternoons in North America. At all other times the light is diffuse, with no glare. While they are not cursed with glare and unwanted heat, north-facing windows are always a heat-loss liability in the winter, so their total areas should be minimized in energy-conserving homes and the windows themselves be energy efficient.
East-facing windows The early-morning sunlight from windows facing eastward is especially welcome in kitchens, dining areas, and baths. Except in very warm climates, east-facing windows probably do not need shade protection except to possibly minimize glare.
West-facing windows The afternoon light that streams in through west-facing windows also admits heat, which doesn’t help much in winter when it is needed because of the shorter days and angle of the sun. In summer it can add a great amount of unwanted heat. Shade trees of proper size and location provide the best control. In their absence use vertical blinds or shutters, preferably mounted outside for warm season control of heat and glare.
Energy design by the climate
North America contains several climatic zones. A successful home design makes the best use of the features of its location. The next sections describe the characteristics of each region and some energy-conserving design strategies. These guidelines are not intended to replace but rather to supplement any requirements of state or local energy codes that may be enforced in an area.
Northern U.S/Southern Canada Summers are short and mostly pleasant in the band that stretches across the northern portion of the U.S. and Canada. Autumns can be spectacular. The downside is the cold, long winters that dominate the climate and are the major focus of energy-efficient design. Homes in this zone need a well-insulated envelope to keep heat loss to a minimum, with roofs insulated to a minimum of R-38, walls and foundations to R-19, and floors above crawl spaces to R-19. Trees and other natural features should be used to protect winter winds. The envelope should be well-sealed against infiltration. Choose the most efficient windows (R-3 or better) and make generous use of south-facing windows to collect winter sun.
Mountain West Dryness and abundant sunshine mark the climate of the western states that lie between the Sierra Nevadas and Great Plains. Numerous mountains, valleys, and canyons create a variety of microclimates. Winters can be cold and stormy with cold winds barreling down out of the northwest. In spring, winds often blast down out of canyons. The good news—outside of the dryness—is the winters in this region are tempered by plentiful sunshine. Summers in the mountains are cool enough to require some heating throughout the year. Low-lying areas can be hot but the low humidity and cool nights makes them bearable.
Start with a tight, well-insulated envelope. Insulate roofs and ceilings to a minimum R-38, and walls, foundations, and floors above crawl spaces to R-19. Locations in the higher mountains or those prone to winter winds coming down out of the mountains should receive higher insulation levels. Orient the main windows southward to capitalize on solar heating. Massive interior materials such as tile-on-concrete floors and masonry walls can help both comfort and save energy by absorbing solar heat during the day and releasing it during the night. Protect windows with overhangs or plants against the strong summer sun and minimize glass on the west-facing side, if possible. Divert or screen winter winds by landscaping but allow breezes to cool the interior in summer. Ponds near exterior walls can help cool the building by cooling air before it enters.
North Pacific Coast The rain, fog, and steady Pacific breezes of the coastal zone west of the Cascades make for cool and gray conditions much of the year. Even so, this climate is one of the easiest to design for. Despite the lack of sunshine, solar heating is worth the effort because so little heat is needed. South-facing windows can transmit solar heat to massive floors, which will absorb and store the energy. Window placement should defend against the cold, wet winds that plague this region. Insulate roofs and ceilings to R-38, and walls, foundations, and floors above crawl space to R-19.
Central Pacific Coast Hot, dry summers and abundant sunshine mark the Mediterranean climate of California’s Central Valley, which stretches from Oregon to Los Angeles. Winters are moderately rainy and colder in the north than south. Variations in elevation and proximity to the mountains and sea create numerous microclimates.
We can learn much from the ranch houses, missions, and adobes indigenous to this region. Long and low, with the long sides oriented toward the winter sun, their overhangs block summertime solar heat. Floors and interior walls are often masonry, which absorbs heat during the day to release it during the cooler night. Patios and courtyards offer outdoor living during the abundant periods of mild weather. Operable windows on upper and lower levels allow cooling breezes inside at night. If fences contain outdoor living spaces, they are held away from these windows so as not to block the ventilation. Insulate roofs and ceilings to R-30, and walls and foundations to R-19.
Southwest Desert Vacationers and retirees flock to the desert climate of Southern Arizona, California, and Arizona for the warm, dry climate that prevails for most of the year. But many leave in summer when things get really hot. The searing temperatures of a summer day are often followed by a chilly night. Wide temperature swings combine with more sunshine than anywhere else in the U.S. to make this region the best location for solar heating. Massive construction materials should be used for floors and walls to store solar heat and balance the diurnal temperature extremes. Trees and man-made shading devices can help cool buildings by blocking the sun, while water near the building can cool nearby air through evaporation. Recommended levels of insulation provide levels of R-30 in roofs and ceilings, R-19 in walls, and R-11 in foundations.
Central Heartland The region stretching westward from the Mid-Atlantic coast to the plains of Texas and northward from the Gulf states to Great Lakes has a relatively temperate climate with four distinct seasons. Summers are hot and humid. Winters are mild along the Atlantic coast and colder farther inland. Rainfall, also heaviest along the Atlantic slope, prevails throughout the region. The ever-present winds sometimes become tornadoes or hurricanes in summer and fall. Climate-responsive design in this region starts with walls insulated to R-19, roofs to R-38, and foundations and floors above crawl space to R-19. Windows should be placed to catch winter sun and cooling breezes in warm periods, but shield them from the summer sun and hurricane winds.
Gulf South For most of the year, heat and humidity dominate the coastal areas that lie on the Gulf of Mexico. Heavy rains and hurricane-force winds also plague the region. On the upside, very mild winters make the heating season short—even non-existent—in Southern Florida. Sunlight is a liability in this region for most of the year, so windows should be placed for light, view, and ventilation, rather than capturing solar heat. Provide them with roof overhangs or awnings to block unwanted heat and protect from both high winds and heavy rains. Exterior shutters that completely close over the windows are a good option here. Climate control is easier with an array of many smaller windows than a few large ones. Insulate roofs and ceilings to R-30, walls to R-19, and foundations to R-19 except in southern Florida, where R-19 suffices. Floors need no insulation.
Today’s well-designed homes not only guard against the natural forces that create unlivable conditions but also make use of natural energies to heat, cool, and light the interiors. Solar energy can be put to good use actively with mechanical equipment to convert it to usable heat, or passively by relying on the design of the building itself to heat it directly.
The sun can also lessen the building’s dependence on electricity through openings in the envelope designed to admit sunlight but block unwanted solar heat with the use of natural features and artificial shading devices. North America contains several climatic zones, each with its particular features. Understanding these features and how best to counter regional liabilities while exploiting their assets is the key to successful energy design. PR
This article is excerpted from the NKBA Professional Resource Library volume: Kitchen & Bath Residential Construction and Systems, Second Edition by Jerry Germer. Copyright: 2014 National Kitchen & Bath Association; published by John Wiley & Sons, Inc. This material is reproduced with the permission of John Wiley & Sons, Inc.