Commonly Used Terms

	mission how to... interactive case study map glossary links help about gdc / blog	The following terms can be found throughout the site. Click on any links to get a better idea of what that term is referring to. Absorptance: the ratio of the radiation absorbed by a surface and the total energy falling on that surface measured as a percentage. Adobe: a sun-dried, unburned brick of clay (earth) and straw used in construction. Within the United States, adobe is used primarily in the Southwest. Caulking: making an airtight seal by filling in cracks around windows and doors. Clerestory: a window that is placed vertically (or near vertical) in a wall above one's line of vision to provide natural light into a building. Climate: the meteorological conditions including temperature, precipitation, humidity, and wind that characteristically prevail in a particular region. (Climate is not synonymous with weather.) Conduction: the process by which heat energy is transferred through materials (solids, liquids, or gases) by molecular excitation of adjacent molecules. Convection: the transfer of heat between a moving fluid medium (liquid or gas) and a surface, or the transfer of heat within a fluid by movements within the fluid. Evaporative cooling: the process of using the evaporation of water to cool a space or surface. Glare: an abundance of daylight that may cause problems with vision due to the angle of the light; the contrast between bright windows and dark walls, reflections of the sun's image or other lighting and vision-related factors. Glazing: a covering of transparent or translucent material (glass or plastic) used for admitting light. Infiltration: the uncontrolled movement of outdoor air into the interior of a building through cracks around windows and doors or in walls, roofs, and floors. This may work by cold air leaking in during the winter, or the reverse in the summer. Insulation: materials or systems used to prevent loss or gain of heat, usually employing very small dead air spaces to limit conduction and/or convection. Photovoltaic array: a collection of panels or modules which convert solar energy into direct current electricity using photovoltaic technology. Radiation: the direct transport of energy through space by means of electromagnetic waves. Solar radiation is electromagnetic radiation emitted by the sun. Reflectance: the ratio or percentage of the amount of light reflected by a surface to the amount incident. The remainder that is not reflected is either absorbed by the material or transmitted through it. Good light reflectors are not necessarily good heat reflectors. Relative humidity: the ratio of the amount of water vapor in the atmosphere at a given temperature to the maximum amount of water vapor that could be held. Solar heat gain: occurs most often as "direct" solar heat gain when sunlight is transmitted through a window and collected by a space as heat. Solar gain can be stored in materials, enhanced with reflectors, or generally manipulated in order to contribute heat to a space and lessen the burden on mechanical heating systems. Stack ventilation/"chimney effect": the tendency of air or gas to rise when heated, owing to its lower density compared with that of surrounding air or gas. This principle is used to help cool a space by allowing hot or warm air to escape through upper level windows. Thermal Mass: the amount of potential heat storage capacity available in a given assembly or system. An adobe wall is an example of thermal mass. Transmissivity: the ability of a material to transmit solar energy. U-value (aka "coefficient of heat transfer"): the number of Btu's that flow through one square foot of roof, wall, or floor, in one hour, when there is a 1° difference in temperature between the inside and outside air, under steady state conditions. The U-value is the reciprocal of the resistance or R-factor. Vapor barrier: a component of construction which is impervious to the flow of moisture and air and is used to prevent condensation in walls and other locations of insulation. All definitions are taken or derived from The Passive Solar Energy Book, Expanded Professional Edition, by Edward Mazria.
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