Conduction, Convection, Radiation in Green Homes

Please Note: This page explains green building for a climate zone comparable to North Texas or Central Texas, such as the climate of Waco or Dallas-Fort Worth, Texas. It is important to hire a green builder who is an expert in energy-efficient building in your climate zone.

Heat transfer is an important aspect of green building. There are three types of heat transfer:

1. Conduction
2. Convection
3. Radiation

Conduction is the transfer of heat througha material. Heat is transferred directly in and through the substance.Conduction heat loss or gain results from the transfer of heat directly throughthe materials of the building envelope. If the outside temperature is greaterthan the inside temperature, there is heat gain from outside the building.

Heat is primarily lost or gained through our windows, walls and roofs. We speak of building materials as being poor or good conductors of heat. Two objects must be touching for this transfer to occur.

Conduction is an important transfer (in order of importance) through:

1. Solid objects
2. Liquids
3. Gases

Convection is the transfer of heat from particle to particle. It is the transfer of heat by the movement of fluids suchas air or water. For example, the heated air around a stove will tend to rise to the ceiling. We all know hot air rises and cool air sinks. That is natural convection. Forced convection refers to the use of fans or pumps to move fluid/air and the heat contained in it. We generally have forced-air furnaces inour homes.

Convection transfers heat (in order of importance)

1. Between fluids and solids
2. Within fluids.

Radiation is energy transmitted directly through space. Although it does not require matter in transmission, it does require a line of sight connection between the objects. All objects radiate energy or heat, which heats all cooler objects around it.Solar radiation passes through space to heat (and light) objects that it strikes. A person in a room with cold windows will radiate heat to the windows and that person will feel cool even if the air in the room is warm. If the window is covered, the sight connection is broken and that person will no longer feel cool.

The greenhouse effect is experienced firsthand by entering a closed car that has been sitting in the sun. Solar radiation is primarily in the range of visible light, and readily passes through transparent objects, like the car window, then is absorbed by the objects inside and converted to heat. Much of the inside build-up of heat from the sunshine isdue to the protection of the enclosure. It provides against heat loss by convective air movement.

Phase change happens at constant temperatures with the movement of energy or latent heat. For example,evaporation absorbs energy and condensation releases energy.

Note: This page is for the climate zone that includes North Central Texas or the DFW area such as Plano, Keller, or Dallas-Fort Worth Texas. Regardless of your climate zone, the first priority for green building or energy-efficient remodeling is to hire an energy consultant and a green builder who understand and use up-to-date green building practices for your area.

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