Begin At The Beginning - Understanding Heat

To understand how a passive solar designed home works, it's important to understand the basics of heat. Heat does not stay still, it moves, spreading out from hotter things to cooler ones until both are the same temperature. You probably think you don't know anything about collecting solar energy (heat); however, you've most likely already experienced its basic effect.

If you've ever left your car in the sun with the windows rolled up, you returned to a car that was warmer inside than was the air outside (not to mention the hot seat!) In this case, sunlight passes through the car's windows to heat the interior like the dashboard and seats. They, in turn, pass their heat to the trapped air in the car. This trapped air becomes warmer and warmer because there is no way for it to escape.

You've just experienced what a passive-design home does - collect, store and distribute heat. This natural movement of heat occurs in three different ways - radiation, conduction and convection - and a passive solar home uses all three.

Radiation - When you stand in the sunshine, the sunlight feels warm because you are taking in heat energy from the sun. This heat travels through space to earth in invisible, straight lines called heat radiation.

This radiant heat is what you feel when you stand next to a fireplace or stove - one side of you is warmed, while the other remains cool. A passive designed home collects this heat directly as sunlight coming through windows warming interior objects, then radiates the heat into the interior air.

Conduction - When heat moves through materials that are in direct contact with each other, that's conduction. A pan, warmed by the stove beneath it, conducts heat to the soup inside it, to the sides and handle of the pan itself, and to the air immediately surrounding it.

Convection - How can a heater on one side of a room, heat the entire room? Convection. The heater warms up the air just around it. As this heated air rises, cold air sinks down to take its place. This cold air is then warmed by the heater and as it become heated, rises. Soon, air is moving around the room, carrying heat energy with it, until the temperature of the entire room is higher.