- By Peter A. Gisolfi
- April 1st, 2009
To better understand the current rage for “green” buildings, it is important to refer to fundamental principles of sustainable design. Of these, the most basic ideas can be found in passive solar strategies that incorporate many traditions of indigenous architecture — a way of building that has evolved over a long period of time and has arrived at the right approach through trial and error from generation to generation. Passive solar design, when applied to schools, will result in better building performance, and will produce energy-cost savings.
Sustainability, when associated with building design and construction, refers to a set of values that relates to the natural environment. If a building is sustainable, it adapts itself to nature by doing two things — taking the greatest possible advantage of natural processes and natural materials, and imposing the least possible negative impact on the natural environment.
Passive solar design is a fundamental and less technical form of sustainability. It embraces a set of design principles that takes advantage of the sun by orienting buildings so that they are warmed in cooler seasons and protected from the heating effect of the sun in warm seasons. An essential ingredient is that the buildings be constructed of heavy materials that can absorb and temporarily store heat from the sun in cooler seasons. These heavy materials are referred to as high thermal mass.
Passive solar design is an ancient tradition in many societies, but has been significantly enhanced in modern times by the greenhouse effect of glass. Glass is transparent to shortwave solar radiation (admitting heat into a building), but is opaque to long-range radiation (preventing heat from being radiated easily out of a warmed building). Similarly, the so-called greenhouse gases, such as carbon dioxide, function in the atmosphere like glass — transparent to solar radiation but opaque to long wave radiation.
In most pre-industrial societies, people constructed buildings by using materials wisely and by using available solar energy effectively. For most places on earth, there are indigenous architectural traditions or techniques. Examples of these techniques are bountiful and usually the most sustainable.
It is instructive to examine three simple examples of indigenous architecture. The Forum Baths at Ostia Antica were constructed during the first century A.D. This structure is remarkable, with perfect orientation to the south, and with a direct connection to the protected south-facing exercise courtyard (the palestra). With sunshine and radiant heat, bathers could be comfortable in the middle of winter near Rome, even while exposed to the fresh air.
The Acoma Pueblo sits at 5,000 ft. above sea level near Taos, NM, and has been continuously occupied by the Acoma people for more than 1,000 years. These residential units are essentially south-facing, attached houses that step upward from the south side to the north, allowing winter sun penetration and providing much-needed summer shade.
The Jacobs House in Madison, WI, was designed by Frank Lloyd Wright in the 1950s to be a “passive hemicycle” (semicircular) house. Almost all of the glass is on the south, and the north exposure is protected by an earth berm. The building is filled with sunshine in the winter and shaded in the summer.
From these examples, we can see that over a period of 2,000 years similar strategies were developed by amazingly differently cultures. Some of the similarities are as follows.
Siting for Solar Benefit
- All of the buildings are masonry, with high thermal mass so that in the cool seasons, the sun can warm the masonry, which gradually will release heat to the inhabited spaces.
- The inhabited spaces face to the south and are flooded with sunshine in the winter, while being shaded in the summer.
- All three examples allow for simple cross ventilation.
- Only the Jacobs House uses glazing which, of course, results in a greater winter heating effect because south-facing glass at 42 degrees north latitude is advantageous for gathering energy from the sun in the winter.
Schools are considerably more complicated to design than houses. Perhaps they are more akin to a large Roman public building, such as the Forum Baths. In designing a site plan for a passive solar school in the northern hemisphere, it is advantageous to seek a south-to-southeast slope. That orientation exposes the building to winter sunshine, and the slight easterly shift warms the building earlier in the day in the winter; in the summer, a south-to-southeast orientation protects the building from the unwanted combination of solar radiation from the southwest and warm air in the afternoon.
Another important site planning factor to be considered is wind protection. Heat loss from a building is increased dramatically when the effects of cold air in the winter are exacerbated by winter winds. A building facing into the cold winter wind loses heat much more rapidly than a building exposed simply to cold still air. Hence, to determine the best possible site for a building, the designer must understand the direction of the prevailing winter winds. Other strategies can be employed to shield a building from winter wind exposure. These include protection by the natural topography, or by windbreaks made of plant material or earth berms, and by the use of fewer or smaller windows on the northern exposure. Most of a well-designed building’s heat loss is through its glazing.
School buildings often form the edges of outdoor protected spaces, such as courtyards and playgrounds. These spaces can be created to improve microclimates (the climate near the ground, influenced by topography, buildings, and planting.) The courtyard can be flooded with winter sunshine and protected from winter winds, thereby creating a warm outdoor environment even in cool seasons. On the other hand, that same courtyard can be shaded with deciduous trees in the spring, summer, and fall, and ventilated by seasonal breezes, which are more likely to come from the south in the warmer months.
School buildings are part of an overall community. They are not isolated on prototypical southeast slopes. With that in mind, it is instructive to look at the urban center plan of Ostia Antica. The Forum Baths are part of an urban complex, which is inflected to allow for an ideal orientation for the Baths. Such a strategy might be adopted for siting a school building in a built-up setting.
Interior Space Planning
Establishing an intelligent school floor plan that relates to solar orientation is another challenge. The layout of a school building is usually determined by pedagogy, adjacency preferences, and the constraints of budget. To minimize construction costs, most classroom buildings are arranged as double-loaded corridors. This arrangement leads to a building where south-facing classrooms are across the corridor from north-facing classrooms, and where east-facing classrooms are across the corridor from west-facing classrooms. Neither of these arrangements is ideal. If we go back to the example of Jacobs House or the Forum Baths, we see that major living and recreation spaces are located to face south.
Even so, south-facing classrooms present a particular challenge: if the classroom glazing faces south, to collect heat from the sun, it is likely that the occupants will pull down the shades to stop the glare — thus defeating the original purpose of the orientation. Nevertheless, it is possible to design schools that benefit from the sun by constructing buildings with single-loaded corridors that are oriented to face south. This results in classrooms facing north, which provides good light for teaching and for computer use. No one is bothered by the glare of sunshine in the corridors; moreover, the corridors can be constructed of materials that absorb solar heat. In warmer seasons, leaving the corridor windows and the classroom doors and windows open promotes natural cross ventilation. The natural ventilation of the classrooms can be further enhanced with ceiling fans or exhaust fans.
Of course, school buildings do not consist only of classrooms. These other spaces and their arrangement within the building need to be considered carefully. Cafeterias can be pleasant with direct exposure to solar radiation and simple cross ventilation; libraries are more akin to classrooms; gymnasiums require daylight but not direct sunlight; and auditoriums are often dark but might take advantage of reflected daylight. All of these spaces are accessed by corridors and lobbies that can be flooded with sunshine, providing heat in cooler seasons.
Sun Penetration and Airflow
Buildings are designed in three dimensions. Plans represent only the two horizontal dimensions. Elevations and sections include the vertical dimensions. Section drawings are particularly important for understanding sun penetration and how air will move through constructed spaces. In the northern hemisphere, the sun is high in the sky in the summer and low in the sky in the winter. Because of this, it is possible that the same window might admit sunshine in the winter when the sun is low, but not admit sun in the summer when the sun is high. This can be accomplished with a roof overhang or by a horizontal sunscreen placed above the window opening. Similarly, the paths of air movement can be understood in section drawings. Consider the convection effect, by which warm, less dense air expands and rises, and the denser cool air falls. If a room is ventilated by a double-hung window and the window is open at the bottom and at the top, cooler air would tend to enter the space through the bottom sash, and warmer air would escape through the upper sash. This is a simple convection current.
When window openings are located to take advantage of prevailing breezes, the patterns of cross ventilation can be enhanced by the convection effect. In the example of cross ventilation from a south-facing corridor to a north-facing classroom, air entering through the lower part of the corridor windows and exiting through the upper portion of the classroom windows would move at increased velocity because of the convection effect. The convection effect is directly proportional to the height between the lower and upper openings. In multistory buildings or in high spaces, convection can be used creatively and advantageously to provide natural ventilation and cooling.
Applying Passive Solar Strategies
Clearly, there are common themes for designing with climate that carry over from indigenous traditions and passive solar strategies to school designs:
- locate a site with the right orientation, south to southeast;
- design a floor plan to allow for effective sun penetration in the winter;
- construct the building with high thermal mass materials that can be warmed by the sun during the cool seasons;
- incorporate sun shading devices and/or plant trees to keep the building in shade in the warm seasons; and
- adopt methods to allow for and enhance natural cross ventilation.
At the same time, we are always challenged to discover methods that integrate school buildings with physical patterns of the community. I particularly like the example of the Forum Baths at Ostia because a larger, more public building was constructed to admit the needed winter sunshine into a series of public rooms.
“Intrinsic sustainability” is a term I use frequently. This refers to those aspects of sustainable practice that are most closely associated with the design of the building itself. Thus, the layout and orientation of a building and the choice of materials for that building might be intrinsic to the building design, whereas a particular heating control device, which adds to the energy efficiency of the building, is not intrinsic to the design solution.
Ideally, architectural forms should be derived from the manner in which the building relates to the site and to other natural factors. Intrinsic sustainability is the essential first step to designing sustainable schools because intrinsic sustainability employs the most basic, time-tested strategies that have been used by societies for millennia. It is essential to look at passive solar design ideas at the beginning of the design process, and separately from the LEED criteria. When we are overwhelmed with the checklists and the data of the green building certification process, it is easy to ignore these intrinsic factors.
Peter Gisolfi is senior partner of Peter Gisolfi Associates, in Hastings-On-Hudson, NY, and chairman of the School of Architecture, Urban Planning, and Landscape Architecture at the City College of New York.