Passive Solar Explained

Passive Solar: The Future and Past of Architecture

Introduction to Passive Solar

Everyday, enormous amounts of energy from the sun reach the earth in the form of light and heat. People feel this energy everyday and have used it as a source of heating for a long time, but it is no longer the primary method for heating buildings. Passive solar technologies can capture the heat (or deflect it) and utilize the light. Passive solar relies on clever building design rather than elaborate mechanical devices like photovoltaic systems, and is usually cost effective. Passive solar buildings collect the energy from the warmth of the sun and release it as needed to keep the home comfortable. Passive solar buildings embrace the idea of sustainability, that development meets the needs of the present without compromising the needs of future generations. While photovoltaic solar power can be expensive because of the cost of installing solar panels, passive solar systems can be included in the design of the building and have little effect on the cost of building. Buildings that are designed to utilize the sun’s energy through their materials and layout should be the primary design of future architects because they drastically reduces environmental impact and create comfortable, natural, living environments with little or no additional cost. Passive solar design elements include placement of windows for light and energy, thermal mass, and shading techniques.

History of Passive Solar

The power of the sun has been known throughout human existence. The Greeks and Romans developed one of its first uses in architecture between the first and fourth century A.D. Greek bathhouses used large south facing openings to let the sun’s rays warm the baths. The Greek philosopher Socrates once wrote “In houses that look toward the south, the sun penetrates the portico in winter”(Southface). The Romans improved upon the Greek design by incorporating glass and a semi-translucent rock called mica into the openings to form windows that could allow the sun’s rays into the building and keep the heat from escaping. In the sixth century A.D., the Roman Empire added “sun rights” to its zoning codes because so many houses utilized sun rooms, a room of the house that was heated by the sun’s rays. Native Americans also used the sun’s energy. The Anasazi, who lived in current day New Mexico and Arizona, built adobe and sandstone homes into south facing cliff walls so that the winter sun would heat the rock, which would stay warm throughout the night. The basic understanding of the sun’s warming capabilities was used for centuries. However, in more recent years (starting with the mid 1800’s) the sun’s ability to provide heat has been overshadowed by the invention and refinement of photovoltaic technologies. During World War II, Americans looked for alternatives to fossil energy and were again intrigued by the power of the sun. Homes were retrofitted with roof-mounted solar water heaters, which utilized the suns rays to heat much of the water used in the home. In the early 1950’s, architect Frank Bridges designed the world’s first commercial office building to use solar water heating and passive design techniques. One of the biggest credits to the ingenuity and success of the building’s design is that it has been continuously operational since the time it was built. In recent years, there has again been an increased interest in the power of the sun. One of the most notable buildings of the 1990’s is 4 Times Square, which incorporated more energy efficient techniques than any other commercial skyscraper, including the ability to keep the temperature of the building within a comfort zone relying solely on passive technologies.

Passive Solar vs. Active Solar

Active solar technologies, such as photovoltaic solar panels, currently get more attention in the news than passive solar because they generate electricity. Unfortunately the cost of solar panels is not yet cheap enough to compete with the cost of fossil fuels and not cheap enough to be implemented in most conventional home design. Passive solar design, however, is easy to implement because it is completely dependent on the materials used and the layout of the structure. Passive systems have very few moving parts and are far more likely to last the lifetime of the building without need of repair. The cost of building a passive solar home is comparable to that of a regular home, and saves operating costs over the long run because there are no added energy costs from poor design. Passive solar homes cut down on the need for electricity or fossil fuels to heat, light, and cool the home because the temperature of the home can be kept consistent throughout the year. Although the initial cost of a passive solar home might be slightly more than a conventional design because of the current expense of thermal mass materials over that of wood framed homes, the house will earn back its initial cost because of electrical and heating savings. The first passive solar house built in Iowa cost $6000 more than a house conventional home because of the additional “$2000… for extra glazing and $4000 for the extra cost of concrete.” But records indicate that the home itself (which costs the owners about $585 more a year in mortgage) is still cheaper than conventional homes in the area. According to Ron Judkoff, director of the Buildings and Thermal Systems Center at the National Renewable Energy Lab, “passive-solar features increase the cost of building a new home by anywhere from nothing to about 3 percent”(Chiras). There should not be a contest between passive and active solar technologies as they are both effective alternatives to fossil fuels and centralized electrical sources, but passive solar designs should be incorporated into all new homes because they add very little additional up-front cost, while saving energy and energy related operating costs.

Natural Lighting and Heating

One of the most common uses of passive solar heating, south-facing windows, is also used in homes that are not specially designed for energy efficiency. In conventional homes, windows are responsible for about 25% of all heat lost from the home; even though double-pane windows are more expensive, they will save up to 15% on heating and make the home more comfortable both in temperature and noise. Multi-pane windows help the homes efficiency in both heating and cooling. Double-pane windows insulate the home almost twice as well as single-pane and more expensive double-panes have gases trapped between the glass to slow heat transfer through the window. This insulation helps to keep the sun’s heat inside the home during the winter and, if other techniques are used, out during the summer. Newer windows have an “e” rating: low e windows have a coating inside the double pane window that both help to keep heat inside the home for colder climates, or reflect the heat out of the home and still allow light to enter. Low e windows cost 10 to 15% more than normal double pane windows, but the heating or cooling savings add up quickly. “Superwindows” are the most efficient window. According to Lawrence Berkeley National Laboratory (a part of UC Berkeley which researches for the U.S. Dept. of Energy) it “performs better than an insulated wall in winter, since the sunlight that it admits is greater than its heat loss over a 24 hour period.” The windows have two or more layers of film between their panes that make them similar to quadruple-pane windows and they reduce the amount of ultraviolet rays that enter the home and damage interiors. Solar orientation plays a huge role in all forms of passive solar, but in the case of effectiveness of windows, it is a vital component. South-facing walls get the most sun year round and are the most effective use the sun’s light and heat. Southern walls should have at least “7 to 12 percent glass” according to a recent article by Mother Earth News. The other walls, however, should have less than 4% glass in order to keep unwanted heat gain and loss to a minimum.

Thermal Mass

Window quality and placement plays an important role in all homes. Thermal mass is another key element to the functionality of passive solar heating. Thermal mass, normally a floor or a wall, is a term for a material that can capture the sun’s heat cast through windows (usually south-facing) and store it to be released later into the home. Commonly brick, concrete, or tile are used either in flooring or interior walls. The percentage of thermal mass inside south-facing rooms needs to be greater than the area of the windows for that room and should be at least four inches thick but not thicker than six inches. Even a thicker drywall can increase the thermal capacity of regular walls in a home. Thermal mass is most common in direct gain systems, which utilize the living space as the solar energy collector. “South facing glass admits solar energy into the house where it strikes directly… thermal mass materials… [Utilizing] 60 to 75% of the suns energy striking the windows”(Greenbuilder). During the day the thermal mass absorbs the heat to reduce the temperature in the home and when the sun is no longer heating the home, the heat slowly releases into the home from the thermal mass. To be most effective, all thermal masses, including floors, should be left as bare as possible (without carpeting or paint) to best allow transmission of the sun’s heat. Another use for thermal mass is in an indirect gain system where the thermal mass is not a part of the living area. Trombe walls are located just inside south facing windows and use vents at the top and bottom of the surface to use natural convection to transmit heat through the home. Because the Trombe wall is constructed inside the house, it is not a source of heat loss on overcast days and requires little maintenance. Also, since thermal mass is basically any heat storing material, it is relatively the easiest passive solar system to design into a home and it can be added to already existing buildings.

Shading for Natural Cooling

Overhangs on south facing windows are an easy way to reduce unwanted heat gains in the summer and allow full sun in the winter to heat the home. Overhangs are designed so that winter sunrays, which are at a lower angle, can enter the home, but summer rays, which are higher, hit the overhang or the wall beneath the window and are unable to enter the home. Unlike interior shades, which block light and still allow heat into the building, exterior-shading techniques can block heat and allow light. Another way to shade the home is through proper landscaping. Placing trees or vines in front of southern windows can create a microclimate around the home and shade unwanted sun. Mature trees “reduce the average temperature in suburban areas by about three degrees,” according to Mother Earth News. Deciduous trees (those that loose their leaves during the winter), are perfect for blocking unwanted heat gains during summer months, but should be carefully placed so that bare branches don’t block the sun’s warmth in winter. For example, maple trees are effective passive solar landscape additions because they grow relatively rapidly and do not produce as much debris as other alternatives such as pines or aspen. Well-placed trees can deflect winter winds and allow warmth into the home, while deflecting summer heat and allowing wind to cool the home. Another less common landscape element is the use of arbors or lattice and vines. Vines can be grown relatively close to windows and block a fair amount of heat in summer while allowing diffused light to enter the home. In winter, the vines can be trimmed to allow heat and light into the home. Grapevines are a productive option to solar shading, as during summer they shade the home and ripen quicker because of the homes radiant heat; in winter the vines are bare and allow maximum heat and light into the home.

Feasibility of Passive Solar Building

An essential feature of passive solar buildings is that they use common building materials, most of which are commonly available wherever a building is to be built. Trombe walls are made from concrete or brick, the shade can be created using common trees or well design overhangs, and the windows are the higher quality products carried by hardware stores around the country. The only thing different about how passive solar buildings are built is that their site is researched before design begins to best capitalize on orientation, insulation, and mass. This initial research makes passive solar buildings the least intrusive on their site because they are built into the natural surroundings. Passive solar systems are well suited for use with other environmentally friendly construction techniques, such as PISE, or Pneumatically Impacted Stabilized Earth, which takes the earth dug out of the site for the foundation and uses it in the walls of the house. These walls are thicker than normal walls and therefore increase the homes thermal mass and isolative properties. Also, passive solar pairs well with luxury, such as hydronic flooring (heating the floor using hot water running through pipes), because the same materials are used in both designs for heat storage properties. The main purpose of the design of passive solar homes is to keep the occupants comfortable throughout the year with little or no peripherals such as heaters or air conditioning. The homes can be designed to minimize the need for electric lighting as well, allowing most of the home to be lit be sunlight throughout the year. Because simple passive solar homes rely less on mechanical operations, they are easier to maintain and are a sustainable building technique.

Government Subsidies

One of the reasons active solar solutions, like photovoltaic panels, have been popular in recent years is because the government offers incentives of up to 30% off the cost of the system. Unfortunately passive solar systems have no way of giving power back to the electrical grid and it is difficult to calculate how much energy is saved when compared to active solar systems with meters. The government currently does not offer any direct subsidies or tax breaks for passive solar construction, but this should not be a deterrent to its use. With little additional cost to new home construction, several passive solar techniques can be implemented that will save the resident hundreds of dollars per year in electricity and gas bills by reducing the need for heating, cooling, and lighting. The savings for passive solar systems compare to that of active solar systems even without the government credits. Any new building in California, however, that passes the difficult LEED (Leadership in Energy and Environmental Design) certification, and is therefore embodying the principles of “sustainable site development, water savings, energy efficiency, materials selection, and indoor environmental quality”(LEED). Another option is to use both active and passive systems. A house with photovoltaic panels and solar water heaters could incorporate passive solar techniques and be completely self-supporting. A self supporting house would get government subsidies for its active systems and save enough energy through passive solar systems that it could sell power back to the electrical company, saving and making even more money than either a strictly passive or active solar home. Hopefully, future government regulations will recognize the benefits of passive solar technologies as a viable alternative to completely artificially controlled interior systems.

Conclusion

Passive solar systems are a cost affective style of building that saves on normal costs, while keeping the living environments comfortable for the occupants, and utilizes environmentally conducive construction. The use of the natural resources, sun and shade, and common building materials makes passive solar a feasible approach to all future construction projects. All style of building are capable of incorporating some portion of passive solar design through site orientation, increased thermal mass, selective materials, or simply low e windows. Most passive solar systems are designed specifically for their own particular site so as to best utilize the environment around the home. This does not mean that passive designs are not acceptable for large-scale projects or suburbs; passive techniques can be used with any home and can even be part of the renovation process. To use passive designs in suburbs, orientation is the most important factor; the majority of a building must be facing south with common use areas, such as kitchens, on the southern wall. If the majority of the buildings are along the same axis, their designs can be very similar to regular suburbs are today. The future of home design should incorporate passive solar into all of its designs because it has little effect on the overall look of the home, but improves interior feeling and saves energy and money. The government should require all new buildings to be rated by the LEED system designed by the US Green Building Council. California legislation requires all new government buildings to achieve at least silver rating on the LEED system, so requiring all new buildings to be certified (obtaining half credit on the rating system) seems a reasonable goal for future legislation. Even if the government only required the buildings to be tested, with or without eventual certification, it would allow for government subsidies and encourage green building techniques. A step towards the future of architecture is the incorporation of passive design in new buildings, to increase natural occupant comfort, save energy, and enhance the sustainability of new construction.

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