How the Sun Heats a Home Interior
Conduction is the transfer of heat energy through solid matter from particle to particle. Heat is conducted through a solid material much the same way electricity is. Conduction is slowed by insulation.
Heat always moves from warm areas to cooler areas according to a physical property called the Thermal Gradient.
Convection is the transfer of heat energy through a gas or liquid by movement of currents. The heat moves with the fluid. When warm air comes out of a register, it rises. This action is called thermal buoyancy. As it cools, it falls. This movement of air is called convection current. Convection can be interrupted by a physical barrier.
Fluids carrying heat always move from areas of high pressure toward areas of low pressure according to a physical property called the Pressure Gradient.
*Radiation *is electromagnetic waves which directly transport heat energy through space. Sunlight is radiated through space to our planet without the aid of fluids or solids. Through radiation, the sun transfers heat through 93 million miles of empty space!
How Heat Moves from the Sun to the Home Interior
Depending on the roof color, a large part of the sunlight radiated to earth is absorbed by a roof as heat, which moves downward through the roof covering material into the sheathing and rafters through conduction, since these are solid materials. As the solid parts of the roof become warmer, they warm the air next to their surfaces, which is then carried to other parts of the attic by convection currents.
As they warm, the roof covering and framing materials also begin to radiate heat to the ceiling framing members and insulation between the ceiling joists. Ceiling joists absorb this heat and conduction helps spread it throughout the length and width of each joist.
As radiation hits the insulation and is absorbed by the fibers on the upward-facing surface, the fibers begin to warm. As they warm, they pass the heat they contain to the microscopic air pockets nearest to them. Through conduction and convection, heat moves slowly downward through the insulation.
As heat from the roof increases, this process happens more quickly until the ceiling has warmed enough to begin to radiate heat into the home interior where it’s absorbed by objects, including people. Heat is distributed through these solid objects by conduction, and they in turn warm the air around their surfaces. This warm air is spread through the home by convection currents, natural air movement, fans and blowers.