An Integrated Approach to Passive Solar Design By MARkUS BERgER “Now in houses with a south aspect, the sun’s rays penetrate into the porticos in winter, but in the summer, the path of the sun is right over our heads and above the roof, so that there is shade. If then this is the best arrangement, we should build the south side loftier to get the winter sun and the north side lower to keep out the winter winds. To put it shortly, the house in which the owner can find a pleasant retreat at all seasons and can store his belongings safely is presumably at once the pleasantest and the most beautiful.” ritten almost 2,500 years ago, Socrates’ descrip- tion of the “megaron House” above reflects one of the earliest consciously designed solar homes. By opening up towards the sun, minimizing the building’s surface, zoning for solar gain (with buffer zones towards the north), shading selectively, and utilizing the building’s mass, the sun’s energy could become an important element in the economy and context of designing a building. Since then, our technological mastery over nature has transformed how we build. instead of working with nature’s resources, we have come to rely on external energy sources (nonrenewable energy) to perform the role of heating and cooling the places we inhabit. However, the time has come for us to relearn valuable design lessons from our predecessors, from Socrates’ description of the megaron House to rock-sheltered buildings of the Pueblo indians in North America and natural cooling systems in the indian subcontinent and iran, and relearn the ways in which we can work with nature instead of against it. We can go a step further. Our modern study of biology has revealed to us how insects, animals, and plants in nature have perfected their designs for survival This Austrian passive solar house was built on an altitude of 2,400 feet in one of Austria’s coldest areas. The house needs additional heating only on three to four days a year. and coexistence through billions of years of evolution. We can now learn from nature itself the very design principles that can allow us to build and live with nature. This must shape how we approach passive solar design. Some of these useful design principles from nature include the following: • design should be integrated instead of a combination of added-on con- structions. • design should focus on optimizing the whole, instead of maximizing single elements. FA L L 2 0 0 7 I N O R T H E A S T S U N I 7 Passive solar homes in the Northeast has to be part of a whole, so that a passive solar building is the result of a total design approach. Context The specific context of a building itself, a study of the environmental context should also include aspects like closeness to school, work, public facili- ties, and transportation so that the very way we live in the passive solar buildings we design will make the lowest possible negative impact on the environment. Design The first step of any design requires drafting a client’s building needs and translating them into an assessment of energy requirements and goals for energy • design should make fine adjustments to specificity of contexts. • design should be energy efficient. • design should use direct and indirect forms of solar energy. • design should be multi-functional, instead of mono-functional. • design should focus on total recycling of resources instead of waste and garbage production. Thus, passive solar design is not simply about adding on new technologies for renewable energy, but about develop- ing an integrated and well-coordinated design approach that can optimize both the natural context and all relevant tech- nology and to create a building that re- cycles maximum energy sources to result in minimum energy consumption. The context, design, construction, and use of technology must, therefore, come together for a well-planned passive solar building. With an understanding of nature's design rules, each of the above 8 I N O R T H E A S T S U N I FA L L 2 0 0 7 matters a lot. An analysis of the local topography and its orientation to the sun is important, for it influences the expo- sure to low-altitude winter sun for passive solar heating and shelter from heat loss “We can now learn from nature itself the very design principles that can allow us to build and live with nature.” provided by nearby trees, adjacent build- ings, or surrounding hills and mountains. in addition, a study of the environmental context should include an analysis of the local climatic conditions, including tem- peratures per season, humidity, altitude, and wind direction and velocity. While this article focuses on building design efficiency. By making the energy needs of a building integral to the design, one allows for a series of decisions about the geometric forms of the building, locations of primary and buffer rooms, etc. to be made in an integrated manner. For instance, the lesser the exterior surface, the lesser the loss of energy. Therefore, the volume/surface ratio— the relationship of the volume of the building to the exposed outer skin sur- face of the building—is an extremely important consideration in designing the shape and structure of the building in its specific context. Optimized energy- conscious building forms take local con- ditions into consideration. Here, indige- nous buildings are good examples of designs adapted to local conditions for minimum energy consumption, and buildings lowered into the ground in windy locations are an old intelligent design solution. The study of forms and shapes in nature can be another source of Eleven Commandments of Passive Solar Design By Joel N. Gordes 1. All sustainability is local. Just because a building is reported to work great in Austin or Chattanooga, don’t think it will perform the same in the Northeast. 2. Use moderation in all things. Two people living a 12,000-square-foot passive solar home is not an example of sustainability and is wasteful of the energy embodied in the materials. 3-6. Any basic home design can be a passive solar home if care is taken with the following: Insulation. In New England, and at current and foreseeable energy prices, ceiling insulation should be a mini- mum of R-45, walls at R-20 or, pref- erably, closer to R-30, and be sure to insulate the floors (heat can go down) to R-19. Orientation. Ideally, the majority of the glazing should be within 20 degrees of true south. Trees grow, and as they do so over a twenty-year period, they can destroy the value of a passive solar home’s ability to function. In addition, too often the basic home design is flawed by other portions of the home shading the south- facing windows. Fenestration. Placement of windows and doors should consider moderating non- south glazing, with south glazing being seven to 15 percent of the floor area. Beyond seven percent, consider the need for additional thermal mass to pre-vent overheating. With unshaded west-facing glass, having a low solar heat gain factor should be strongly consid-ered. 7. Be mindful of diminishing returns that usually kick in on some of the factors described above. At some point, each additional inch of insulation, square foot of glass, or inch thickness of thermal mass gains. It can also stress and break the glass seals if not properly supported. 9. Too often, extremely long overhangs are incorporated, and in most cases they shade expensive glass during the winter when maximum aperture should be exposed. 10. West glass may be great for a view, but it can be the main reason for requiring mechanical air conditioning due to afternoon heat gains. West overhangs can be expensive and/or largely ineffective. 11. Think “replicability” and resale value. Passive homes that look uncon- ventional, ungainly, or ugly are not what people want to replicate. To beat climate change and energy security issues that face us, more conventional designs will win converts and probably have a higher resale value. is less effective than the one that came Air Sealing. Too often this is an area that is skimped upon. For best results, use a full wall, 6-mil polyethylene vapor barrier and doors and windows with good weather stripping. Building a vestibule or airlock entry also keeps the cold air leakage down. If you get below one air change per hour, con- sider an air-to-air heat exchanger for healthy levels. before it. A better rule is “some is good, more is better, enough is best.” Learn to find the point of “enoughness.” 8. Some designers believe glass is best at a 60-degree-angle slant, but this pre- cludes easy, aesthetic, and inexpensive shading for summer cooling strategies while not appreciably increasing winter Joel N. Gordes is an independent energy consultant and president of Environ- mental Energy Solutions. inspiration, as they have energy efficiency inherent in their design. Today, with the help of 3d software, it is possible to analyze, test, and calculate the develop- ment of the right form for a minimum surface-to-volume ratio with a maximum solar gain, maximum daylighting, and minimum heat loss. Passive solar gains are achieved sig- nificantly through window areas, where glass qualities and storage masses are important factors in a well-working building. different types of systems for solar gains have been developed and can be categorized as direct and indirect gain systems, isolated and combined gain systems, and passive cooling systems. direct gain systems work with non- diffusing and diffusing light entry, which is directed to an insulated storage mass, and form the simplest principle of a passive solar design for directly heating a room. indirect gain systems, like the mass trombe wall and the water trombe wall, work with controlled heat transfer from a mass heat storage system to rooms. insulated gain systems, like an attached sunspace and thermosyphon system, transport heat from one room to another. Combined heating and cooling systems, like roof ponds or underground buildings, store the heat or the cooling energy in the water of the roof pond or the earth surrounding the building. As cooling is approximately three times as expensive as heating, passive or “free” cooling has to be integrated into the total design approach, particularly in contexts where summer heat is an issue. Here we can again learn from a number of ancient systems, like evaporative cooling, desic- cant cooling (where humidity is reduced FA L L 2 0 0 7 I N O R T H E A S T S U N I 9 through porous materials), cooling ponds, and induced ventilation systems (like solar chimneys). in order to control solar gains as well as sun shading, it is essential to control the sunlight by adjusting the beam of light at its different radiation intensities throughout the year. This can be done with adjustable systems or with calculat- ed and simulated fixed elements. Active power production elements like photo- voltaic elements, solar collectors, and wind turbines make the most sense when integrated into this total design approach. Construction The most important aspects of construc- tion in a passive solar building are ther- mal mass and insulation. For highly com- fortable living, the thermal mass and insulation have to be well calculated, controlled, and targeted. When considering the interior environment of a building, it is impor- tant to have sufficient thermal mass to store the solar energy absorbed by the construction. Thermal mass has a direct effect on the energy required for heating. massive clay brick walls, concrete walls, or stone walls can store solar heat gains and radiate the energy out when it is needed, whereas lightweight construc- tions cannot exploit this energy or only small parts of it. The process of storing and distributing solar radiation involves several steps. The incoming energy is either absorbed or reflected. The sunlight is absorbed in the material in the form of heat. it is important to have storage materials with low thermal resistances and high heat capacities to induce the heat to remain within the storage. insulation plays a crucial role in a passive solar home. Exterior surfaces, like walls, roofs, and exposed floors, have to in heat loss. Other aspects of building physics that require attention in low- energy buildings include vapor diffu- sion, wind tightness, building dampness, and an attention to building connections. Technical building equipment and usage For low-energy or passive-energy houses, ventilation plays a significant part of the total heat loss. in several countries, state- of-the-art mechanical ventilation systems incorporating heat recovery are now com- mon. These ventilation systems, com- bined with smart operation of the equip- ment, reduce the heating energy require- ments dramatically. Based on the calcu- lations of heating and cooling energy requirements, as well as ventilation requirements, one can assign the right “Because energy-conscious buildings are not only ecological, but also de- pendable, healthy, and timeless, they should be the only design option for all new buildings.” systems like heat pumps, ventilation systems with heat recovery, solar water heating, groundwater cooling, and so on. Our lifestyles have a very significant effect on overall thermal efficiency of any building. research has shown that care- less actions and routines can triple the energy required to heat a building. Exces- sive ventilation, such as windows open all day even in winter, can negate the Mistakes to avoid The four elements listed above provide an overview of the parameters and pos- sibilities that need to be considered in order to plan a project well. But it is also important to underline certain mistakes in the planning of a passive solar design. The surface-to-volume ratio of a building is crucial, so projections such as bay and dormer windows should be kept to a minimum. The dangerous times of over- heating are the two ends of the heating season when the building still requires heating but outdoor temperatures are moderate and solar energy becomes stronger. Overheating is controlled through ventilation and through the thermal mass used for heat storage. Poor insulation, inadequate sun shading, poor ventilation, and a wrong glass-to-mass ratio are the biggest mistakes to avoid. The best design for new buildings A passive solar building can consume up to 90 percent less energy than a compa- rable building of the same size. in addi- tion, passive solar buildings have a higher degree of comfort and are less costly to maintain. Because energy-conscious buildings are not only ecological, but also dependable, healthy, and timeless, they should be the only design option for all new buildings. Furthermore, while this approach to design works best and most efficiently for new buildings, existing buildings can also be redesigned to adopt and integrate the principles of passive solar, resulting in substantial energy savings. We need a thoughtful and creative approach to our built environment so that we can better use an energy source that is available almost daily—for our own well being and for the planet’s. be intelligently insulated (from 8 to 18 benefits otherwise associated with energy inches, depending on the construction), and attention also has to be given to glass openings (including triple glazing), as well as all construction elements that pene- trate the main insulation, and which could act as thermal bridges, resulting efficiency measures described here. it is therefore important that we are aware and educated about energy efficiency, for with this awareness we can maintain a high indoor air quality without com- promising energy efficiency. Markus Berger, IO Design Inc., teaches passive solar design at the Rhode Island School of Design. See www.designinsideout.net. Contact m.berger@risd.edu. FA L L 2 0 0 7 I N O R T H E A S T S U N I 11