CCRES Home Design Basics

CROATIAN CENTER of RENEWABLE ENERGY SOURCES

CCRES Home Design Basics

Passive solar design can make a home more comfortable in every season. The winter sun can warm a home´s interior, while simple shading and thermal mass strategies can prevent summer overheating.

The home designs on the following pages balance four primary building elements orientation, windows, overhangs, and thermal mass—to optimize use of the sun´s energy. While these elements are found in most conventional homes, the designs included here put the right amount in the right places for maximal efficiency and performance. Most of them also provide ample south-facing roof space to accommodate the addition of solar hot water collectors and solar-electric arrays—part of a whole-house plan for energy efficiency and independence.

Whether you´re having a builder construct your own home from these plans or building for a client, consider these best design bets.More info at: http://solarserdar.blogspot.com

Site Right

In the winter, the sun rises in the southeast, is low in the south sky at midday, and sets in the southwest in the middle latitudes in North America. In the summer, the sun rises in the northeast, is high in the south sky at midday, and sets in the northwest.

In all areas except the southern tip of Florida, choose a home site that receives full southern sun in winter and is unobstructed by trees, other buildings, or hillsides. Besides your own observations about shading during the seasons, site analysis tools can provide a quick, accurate assessment of your proposed building site. You can also use a compass to help find true north and south, but keep in mind that a compass points to magnetic north, which can vary by as much as 25 degrees from true north. This difference is called magnetic declination.

To maximize winter sun and summer shade, orient the home´s south face to within 10 degrees of true south. Even though orienting the house 30 degrees from true south reduces winter solar gain by only 13 percent, the cooling penalty can be greater. Homes facing from 30 to 45 degrees east or west of south may need longer overhangs. This is especially true if the home´s orientation favors the west, because overhangs quickly become much less effective as the hot western sun, low in the sky, strikes the house. In most locations, a slight orientation to the east is desirable to increase winter morning sun and decrease summer afternoon sun.More info at: http://solarserdar.blogspot.com

Proper Window Placement

Heat from the sun entering south-facing windows and doors with glass can provide between 20 and 80 percent of the heat required to keep a house warm in winter. The highest percentages are possible in homes in mild climates and those that are well insulated.

South-facing glass should be at least 5 percent and usually no greater than 12 percent of the conditioned square footage of the house. (For example, a 1,000-square-foot house would have between 50 and 120 square feet of south-facing glazing.) Ideally this should apply separately to each floor of the house. Include only the glazing square footage—do not include window or door frames. For instance, a 30- by 60-inch window (12.5 square feet) might only have 10 square feet of glazing.

Homes with south glass area between 5 and 7 percent are commonly referred to as sun-tempered, and are appropriate for very hot climates such as the southernmost areas of the United States (as a rule, below 35 degrees north latitude, although there are many exceptions based on local climate conditions). If south glass exceeds 7 percent of the floor area, install materials with high thermal mass inside the house, such as concrete or masonry, to moderate interior temperature swings.

Place just enough windows on the north, east, and west walls to balance interior light levels, capture any views, create an attractive house, and allow for natural cooling. But be sparing, because windows placed in these orientations are energy drains in cold months and, in the summer, eastern and western windows let in unwanted hot morning or afternoon sun, unless they are shaded. For balanced lighting and ventilation, place windows on opposite or at least two sides of each room. Limit the use of skylights, which admit too much sun in the summer and are difficult to shade. Instead, install sun tubes (also known as tubular skylights) in interior rooms without windows, which let in some light, but less heat.

Window manufacturers often use "solar" to describe glazing, but usually this is an indication that the glass blocks the sun (has a low solar heat gain coefficient; SHGC) and can be very misleading. For passive solar space heating, south-facing windows should have a high SHGC (at least 0.52) to maximize the amount of the sun´s heat that passes through the glass. A window with a SHGC of 0.33 lets in only 33 percent of the sun´s heat energy. If you can´t find high SHGC windows, a reasonable option is to install clear (uncoated) double-paned glass and use insulated blinds or shutters at night to minimize heat loss. Alternatively, triple-paned clear glass will let in a large amount of sun while limiting heat loss. Some building codes stipulate a maximum SHGC of 0.4, but then allow you to average all of the SHGCs so that windows with higher SHGCs can be used on the home´s south face.More info at: http://solarserdar.blogspot.com

Seek Summertime Shade

Overhangs, awnings, and porches can shade windows in certain seasons and prevent the home from overheating. For cold climates, design overhangs for a long season of full sun striking the south glass. Overhangs should fully shade south-facing windows during the summer months, and allow full sun on windows during the wintertime. For hot climates, design overhangs for a long season of full shade on the south glass. It is fairly simple to achieve full shade on June 21, the summer solstice, when the sun is high. Shading in August becomes more difficult, since increasing the overhang depth will also shade the window in April, when more solar gain may be desirable for heating. This is where a slight easterly rotation of the house can help.

South window overhangs should be sized for the height of the windows, wall height, and the construction detail of where the roof meets the wall. West and east windows require much longer overhangs, and these windows are best shaded by other methods, such as porches or trees.

During the late summer and early fall months, it may be necessary to close blinds or curtains, and pay more attention to passive cooling strategies like opening windows when the temperature drops below 70°F, and closing up the house in the morning, before the day begins to warm. Likewise, in late spring, there may be a few cool days where more heat is desired than is entering the partially shaded south windows. Conserving the heat that does enter by using insulated curtains on the windows can be highly effective.More info at: http://solarserdar.blogspot.com

Make It Massive

Materials with high thermal mass, such as brick, stone, ceramic tile, and concrete, absorb direct solar gain in the winter and indirect heat during the summer. Although it is best to locate thermal mass in the path of direct sunlight, other mass in contact with the material that receives direct solar gain can serve the same function. Including thermal mass is especially important for homes with glass above 7 percent of the home´s square footage. Locate the mass as close to south-facing windows as possible. For each square foot of glass above 7 percent, add:

• 5.5 sq. ft. of mass in floors that receive direct sunlight
• 8.3 sq. ft. of mass in walls and ceilings in the same room
• 40 sq. ft. of mass in floors that don´t receive direct solar gain

Strive for a minimum of 2 inches (and a maximum of 4 inches) of thermal mass. Less than 2 inches does not store sufficient heat and more than 4 inches (unless it is an 8-inch wall with both sides exposed) can absorb so much heat that it will be too slowly released. The maximum amount of floor mass area that should be used is 1.5 times the south-facing window area, since the sun cannot hit large areas all at once.

For cost effectiveness, use concrete, concrete masonry, and earthen plasters as thermal mass. Slab-on-grade construction, where a concrete floor is poured over insulation, can economically combine the foundation with a heat-absorbing floor. ICF (insulating concrete form) foundations, which sandwich concrete between expanded polystyrene foam panels, are very compatible with cold-climate slabs, even when the upper part of the house is framed with studs. ICFs are an excellent option for the main house walls also. Studies have shown that their combination of mass and insulation helps temper interior temperature swings, even though the foam somewhat isolates the concrete (mass) from the living areas.

Interior heat-absorbing walls, made of concrete block, stone, or brick, can also serve to absorb solar heat. Masonry walls are commonly incorporated into fireplace or wood heater surrounds. With the creative use of decorative concrete block, or coverings (veneers) of stone, brick, stucco, plaster, or tile, heat-storing walls can become effective passive heating elements, as well as beautiful accent walls and focal points in a home.More info at: http://solarserdar.blogspot.com




Daylighting

Daylighting is the art and science of using natural light to illuminate indoor spaces. It saves energy, and can make living and working areas more attractive and comfortable. Daylighting in homes is typically accomplished using windows, translucent doors, skylights, light pipes (tubular skylights), and clerestories. A well-designed daylit home on a sunny lot can get by without any electric lighting between dawn and dusk.

Daylight is sunlight that is direct or reflected. Sunshine provides us with vitamin D, and also combats seasonal affective disorder, or winter depression. Natural light doesn´t change the character of colors the way artificial lights can and, with its subtly changing intensity, daylight is much more interesting. It can make us feel more connected to nature and supports our natural biological rhythms, which contribute to restful sleep.

Using sunlight in your home can decrease heating and cooling loads through passive solar design techniques, as well as eliminate most lighting needs during the day. Its use has been proven, in commercial settings and schools, to decrease absenteeism and increase productivity and test scores. Also, people who work in naturally lit buildings report a sense of well-being.

Designing a daylit home can be very simple. In most regions, provide a long south wall of windows and locate the main living spaces along the south side to take advantage of direct solar gain in the wintertime. In the summer, adequately deep, fixed overhangs will block heat gain but still allow indirect light to enter the windows.

First, arrange rooms based on your preferences. Morning people tend to like their bedrooms located in the southeast corner of a home. Kitchen and breakfast rooms may compete for that corner. Night folks usually don´t mind a bedroom on the west; by the time they retire, the room will have cooled off. Artists, especially painters, usually locate their studios on a home´s north side to take advantage of the uniformity of northern light.

Next, select your daylighting strategies. Start with windows for almost every room. Consider light, heat gain, ventilation, views, aesthetics, and emergency exits when making your choices of window sizes and types. Add a clerestory for overhead, private light, increased ventilation, and desirable heat gain. A small operable skylight with a flared light well can provide sky-gazing opportunities and overhead light, with privacy and increased ventilation. Light pipes are a great choice for naturally lighting small interior spaces and dark corners.

Daylight is extremely variable in intensity and duration, changing throughout the day and year. These characteristics can make it challenging to deliver consistent lighting. Light sensors can control artificial light sources, on dimmers, to maintain minimum light levels.

Glare is a potential problem for many systems. Controlling reflected sun by using light shelves (interior "overhangs") or wide windowsills is effective, and using sheer fabrics to filter incoming light can also help.

Living with natural light helps us feel less isolated from nature, and being indoors seems more like a temporary condition, rather than a permanent sentence. With thoughtful daylighting design incorporated into your home, you´ll find that from dawn to dusk, the best things in light are free.More info at: http://solarserdar.blogspot.com

CROATIAN CENTER of RENEWABLE ENERGY SOURCES (CCRES)