Norbert M. Lechner, Professor and Architect Auburn University

College of Architecture, Design, and Construction 119 Dudley Hall

Auburn, AL 36849-5315 USA

Tel 334-844-5378 Fax 334-844-5386

lechnnm@auburn. edu

Since buildings use more than a third of all energy, and since most of that energy is for heating, cooling and lighting, and since the sun has a great impact on each of these energy uses, solar responsive architecture is a key factor in addressing global warming, energy depletion and pollution. The problem is not what to do, but why aren’t we doing it. Some people assume that solar responsive design is too expensive, others believe it is too complicated, and still others believe it is not ready yet but will be in the future. How then can we convince the great majority of people that solar responsive design makes sense right now?

I have found that a conceptually clear heliodon, such as the one I developed, can be both very convincing and impelling. The Sun Emulator heliodon is so conceptually clear that within two minutes even young children understand solar geometry as related to buildings. After all, it is not only building professionals but also clients, and future clients (children today) that need to be convinced of the benefits and appropriateness of solar responsive design.

Experience has shown that the Sun Emulator can clearly and quickly convince people of the great benefits and importance of such things as street orientation, building orientation, window placement, shading devices, clerestories (instead of skylights), and tree placement. The Sun Emulator makes clear that many of these beneficial strategies have no cost associated with them, and that we are missing out on many opportunities because of lack of knowledge and conviction.

The benefits of solar responsive design depend on the proper use of solar geometry which can be quite complicated when expressed mathematically or graphically, but is easily understood with physical models used on a conceptually clear heliodon. The Sun Emulator is such a conceptually clear heliodon because the ground plane always remains horizontal, the lights move across the model just like the sun moves across a building, and because the solar window is clearly and continuously simulated. There are no other heliodons that are as conceptually clear as the one I have developed, and because the Sun Emulator is so engaging, it is easy to teach solar geometry to any audience.

As a result of 25 years of experience with the use of heliodons, the author
recommends that all schools of architecture or building, science museums, energy resource centers, and some professional offices obtain a conceptually clear heliodon such as the Sun Emulator in order to inform not only the professionals but also the general public.

1. Heliodons:

Many different heliodons exist and almost all utilize one light to simulate the sun. Since the three variables of latitude, time of year, and time of day determine sun angles, a heliodon must be adjustable for all three factors. Only a few heliodons exist where the model is fixed and the light moves along three axes to adjust for all variables. In most heliodons, however, the model is rotated about one, two, or three axes instead of only moving the light. The disadvantage of these types of heliodons is that they do not match our real world experience and therefore such heliodons are not “conceptually clear.” They are neither very convincing to the uninitiated nor do they effectively teach the basic pattern of solar geometry as related to a building.

More than twenty years ago, the author built a heliodon with about 130 lights to simulate the sun every hour of the 21st day of all twelve months (Fig. 1). Electrical switches control for the variables of time of day and year. The model table was still tilted for the latitude adjustment. Although "conceptual clarity” was greatly improved, there are a number of problems with tilting the model. With too much of a tilt, some of the conceptual clarity was lost, some lights moved below the horizon, and, of course, the model had to be carefully glued together and fastened to the table to keep it from sliding. Recognizing the weakness of a tilting table, the author developed over the last ten years a heliodon where the model of the building and remains stationary on the table, while the light moves to simulate the sun’s travels across the sky (Fig. 2). Although Copernicus would be upset, this situation fits perfectly with out daily real-world experience, and thus it allows us to form a mental model of the solar geometry that can be used for the design of buildings. While some heliodons accomplish this same goal with the use of only one light to simulate the sun, it turns out better to use seven lights to simulate the sun at different times of the year.

The Sun Emulator simulates our real-world experience by keeping the building model Stationary and horizontal while the lights move to simulate the sun’s apparent motion across the sky.