One of the most cost-effective ways to reduce energy use without driving up construction costs is to use passive solar design principles. Reducing heat loss is one of these principles. Together energy efficiency and passive solar design can dramatically reduce heating and cooling costs while enhancing comfort.

Unfortunately, there is no magic bullet for designing an energy-efficient building. You need to consider dozens of variables from site orientation to construction techniques to material selection. If ever there was a job intended for a computer, it's figuring out the energy performance of a building design and then comparing it to other options. A design package from the Passive Solar Industries Council (now called the Sustainable Buildings Industries Council) combines a manual of time-tested passive solar building strategies with the brand-new Energy-10 computer software.

Energy-10 combines a solid energy modeling ability with an easy-to-use interface. Getting started is a snap. You only need to enter four pieces of information: the floor area, the building's use, the number of stories and the type of HVAC system. The program creates two buildings, a reference case and your preferred design. The program makes assumptions about all the other building components, which you refine as the design progresses. You compare your design to the reference building without the energy saving options.

The program evaluates 16 energy-saving strategies, including passive solar heating, daylighting, lighting, insulation, solar water heating, glazing, HVAC controls and thermal mass. The building's computerized description is automatically modified to incorporate strategies you choose. You view the results in a series of charts and graphs. Energy-10 ranks the options based on your priorities, which might be minimum energy use or minimum payback time.

As the design evolves, you can enter specific design details that were assumed in the early stages. All along the way you can quickly assess the energy impact of these refinements. The program runs an hour-by-hour energy simulation that takes about two minutes to complete. Energy-10 easily handles residential and small commercial buildings up to 10,000 sq. ft.

The programs requires a 486 DX2 processor or better, 8MB of RAM (16 strongly recommended), at least 9MB of hard disk space and Windows 3.1, Windows NT, Windows 95 or OS/2. The price is $250.

Energy-10 can be purchased through the Sustainable Buildings Industies Council.