A material that retards the movement of water vapor through a building element (walls, ceilings) and prevents insulation and structural wood from becoming damp and metals from corroding. Often applied to insulation batts or separately in the form of treat ...

In reference to solar energy systems, the angle that a solar collector is positioned above horizontal.

A type of electrical current, the direction of which is reversed at regular intervals or cycles; in the U.S. the standard is 120 reversals or 60 cycles per second; typically abbreviated as AC.

Energy available as a result of motion that varies directly in proportion to an object's mass and the square of its velocity.

A measure of the heating requirements of a building expressed in Btu per degree-day.

The amount of heat energy that may be converted into useful energy from a fuel.

The angular position of the sun at solar noon with respect to the plane of the equator.

That portion of supply air that is drawn from outside, plus any recirculated air that has been treated to maintain a desired air quality.

A category of electric power producer established under the Public Utility Regulatory Policy Act (PURPA) of 1978, that includes small-power producers (SPP) who use renewable sources of energy such as biomass, geothermal, hydroelectricity, solar (thermal a ...

The transparent or opaque sphere in an electric light that the electric light transmits through.

The pressure corresponding to the outlet velocity of a fan; the kinetic energy per unit volume of flowing air.

A device used by energy auditors to pressurize a building to locate places of air leakage and energy loss.

An insulation product composed of loose fibers or fiber pellets that are blown into building cavities or attics using special pneumatic equipment.

Energy terms

The weight of a material per unit of volume compared to the weight of the same volume of water.

An air distribution outlet, typically located in the ceiling, which mixes conditioned air with room air.

An agency of the U.S. Dept. of Agriculture that makes loans to states and territories in the U.S. for rural electrification and the furnishing of electric energy to persons in rural areas who do not receive central station service. It also furnishes and i ...

In reference to solar energy systems, the angle at which direct sunlight strikes a surface; the angle between the direction of the sun and the perpindicular to the surface. Sunlight with an incident angle of 90 degrees tends to be absorbed, while lower an ...

A device used to simulate the angle of the sun for assessing shading potentials of building structures or landscape features.

A type of combustion heating appliance in which the combustion gases are vented to the outside, either with a fan (forced) or by natural convection.