Printed directions for the use of the Sun Emulator are extremely brief and almost unnecessary because this heliodon is a model of our everyday reality. First, the model to be tested is placed at the center of the round table, its south orientation aligned with that of the heliodon. Then the cradle holding the seven rings is adjusted for the correct latitude by means of a single locking knob. Next, a twelve position rotary switch is used to choose the sunbath for the 21st day of any desired month. To simulate the daily motion, the appropriate ring is rotated by hand from sunrise to sunset. Other rings are then rotated to investigate solar access and shading patterns at other times of year. To

see what happens through the year at a particular time of day, the lights of all the rings are aligned and the rotating switch is turned to simulate the annual travel of the sun up and down the sky.

2. Applications

Although the Sun Emulator was developed primarily for architecture students, it is appropriate for a much wider audience, as will be discussed below. For architecture, landscape architecture, planning, and interior design students a heliodon has three separate applications: (1) the initial learning of concepts and principles, (2) the design process, and (3) presentation. As was described above, the Sun Emulator is an unsurpassed teaching tool. As a design tool, it can be used to actually assemble a design as, for example, when the length of an overhang is determined on the model by a trial and error method. Or the heliodon can be used as an analysis tool where a design, developed away from the device, is tested for its performance. In my own classes, I have students test models of designs they developed previously in studio. After the analysis establishes what works and what doesn’t, the students redesign their projects to be more solar responsive. Next, fast and dirty study (not presentation) models are built of an important window and shading system and these are then tested on the heliodon to determine what weaknesses remain for further redesign. A popular application among the students is for presentation purposes. They use the heliodon to photograph their models to document their designs’ solar responsiveness for juries and portfolios.

Homebuilders are another major user group. Most homebuilders are in fact designers. They often decide which building design will be used, what its orientation will be, where it will be located on a lot, what trees will be left standing or where trees will be planted, etc. Each of these decisions would benefit greatly from the understanding of solar responsive design principles. Developers are even more in need of this knowledge because street orientation has major consequences, since it will usually determine orientation of the buildings which are almost always aligned with the street rather than the sun. One of the most successful developments in the second half of the twentieth century, Village Homes in Davis, California, was designed by means of physical models tested for solar responsiveness.

Government officials also need to understand the benefits and practicality of solar responsive planning and design. Laws, planning regulations, and building codes generally do not encourage solar design because their writers were not convince of the benefits and the feasibility of solar designs. I have direct experience with a government official who after seeing the heliodon demonstration developed an interest in the potential of solar responsive regulations.

If homeowners and architectural clients are not interested in solar responsive design, then there is little incentive for building professionals to provide such designs. Thus, it is imperative that all who finance or control the design of buildings should be knowledgeable about the potential benefits of working with the sun, and ironically, many of these benefits come from strategies that cost little or are free.

In effect almost everyone should understand and thus believe the financial and environmental benefits of solar responsive design. This widely held understanding, I believe, is best accomplished by means of a "conceptually clear” heliodon. If the hands-

on science museums for children had heliodons, children would understand early on and in a lasting manner the logic of designing with the sun. Schools too could use heliodons in their earth science or physics courses. If children routinely learned about these principles, we would have future generations that would demand the benefits of solar responsive design because they would know that they are real, achievable, and economically wise.

3. Limitations

The Sun Emulator is an excellent heliodon for teaching and designing where high precision is not vital, which is the case for most building design. For example, the precise knowledge of the shading from a tree is meaningless since trees grow. Also weather is too variable to establish precise dates when sun or shade must be available.

Although the sun angles for the point at the center of the heliodon table are very precise, as one moves away from that point, in all three axes, error accumulates. Thus, small models are best and some larger models can be moved around so that the part of the model being analyzed is placed over the center of the table.

The highest precision in model testing is possible with sundials mounted on models tested outdoors, the only place where parallel light rays are readily available. Although such model testing is extremely precise, it is inconvenient, awkward, and conceptually unclear. It is awkward because you can’t test models outdoors at night, in the rain, or on cloudy days, and it is frustrating and uncomfortable under partially cloudy, windy, hot and cold conditions. Testing models outdoors requires the model to be tilted to account for all three variables of sun angles: latitude, time of year, and time of day. As described earlier these problems are both practical and conceptual in nature. Non-horizontal models must be well glued and prevented from sliding. They are also not easily analyzed since we find it hard to relate to buildings that are not horizontal. Consequently, I recommend outdoor analysis with sundials only after a design is ready for presentation purposes, or for fine tuning when high precision is required.

Although a larger heliodon could handle larger models, the Sun Emulator was sized so that it can still pass through a standard door, be completely fabricated at the factory, shipped fully assembled, and take up very little space when stored (less than 2 square meters) (Fig. 3). After unpacking or storage, it is only necessary to plug the heliodon into an electrical outlet and to rotate the model table from vertical to horizontal.

Although some other heliodons are more precise for larger models than the Sun Emulator, its "conceptual clarity” ease of use, and other advantages described above, more than compensate for its limited precision.