Glossary

Below is a glossary of terms you might encounter in discussions of energy-conscious design. These terms are defined in Sun, Wind & Light: Architectural Design Strategies by GZ Brown (New York: John Wiley & Sons, 1985) (ISBN: 0-471-895067).

Attached sunspace
A room that doubles as a solar collector; also called an attached greenhouse or a solarium. The term "attached" also implies a space that shares one common wall with the associated building.

Conductance
A measure of the rate of heat flow between two surfaces, measured in BTUs per hour per degrees Fahrenheit per square foot of material that separates the two surfaces.

Direct gain
The transmission of sunlight directly into the space to be heated, where it is converted to heat by absorption into the interior surfaces.

Direct radiation
The component of solar radiation that comes directly from the sun without being diffused or reflected.

Glare
A very bright light or a high contrast of light making it uncomfortable or difficult to see.

Glazing
Transparent or translucent materials, usually glass or plastic, used to cover an opening without impeding the admission of heat and light.

Heat gain
The gross amount of heat that is introduced into a space, whether from incoming radiation or from internal sources such as occupants, lights, and equipment.

Indirect gain
The transfer of solar heat into the space to be heated from a collector that is coupled to the space by an uninsulated, conductive, or convective medium, e.g., thermal storage walls and roof ponds.

Insulation
Low-mass material with high thermal resistance used to slow the transfer of heat by conduction.

Internal heat gain
Heat generated inside the building by sources other than the space-heating equipment, usually by appliances, lights, and people.

R-value
A measure of the thermal resistance of a building element; the reciprocal of the U-value. See also thermal resistance.

Solar aperture
That portion of the solar wall covered by glazing. The orientation of the opening should be within 30 degrees of south to be considered a solar aperture.

Solar radiation
Radiation emitted by the sun, including infrared radiation, ultraviolet radiation, and visible light.

Thermal radiation
Energy transfer in the form of electromagnetic waves from a body by virtue of its temperature, including infrared radiation, ultraviolet radiation, and visible light.

Thermal resistance
A measure of the insulation value or resistance to heat conduction of building elements or materials; specifically, the reciprocal of the thermal conductance. Also called R-value.

Thermal storage mass
High-density building elements, such as masonry or water in containers, designed to absorb solar heat during the day for release later when heat is needed.

Trombe wall
Masonry thermal storage wall placed between the solar aperture and the heated space. Heat is transferred into the space by conduction through the masonry (and by natural convection if vents are provided). Trombe is the last name of the Frenchman who first used this system, in 1966.

U-value
A measure of heat flow: the number of BTUs that flow through one square foot of building skin in one hour, when there is a one-degree difference in temperature between the inside and outside air, under steady-state conditions. The U-value is the reciprocal of the resistance or R-value.