Ultimate Analysis — A procedure for determining the primary elements in a substance (carbon, hydrogen, oxygen, nitrogen, sulfur, and ash).
Ultraviolet — Electromagnetic radiation in the wavelength range of 4 to 400 nanometers.
Unglazed Solar Collector — A solar thermal collector that has an absorber that does not have a glazed covering. Solar swimming pool heater systems usually use unglazed collectors because they circulate relatively large volumes of water through the collector and capture nearly 80 percent of the solar energy available.
Underground Home — A house built into the ground or slope of a hill, or which has most or all exterior surfaces covered with earth.
Unitary Air Conditioner — An air conditioner consisting of one or more assemblies that move, clean, cool, and dehumidify air.
Unvented Heater — A combustion heating appliance that vents the combustion by-products directly into the heated space. The latest models have oxygen-sensors that shut off the unit when the oxygen level in the room falls below a safe level.
Useful Heat — Heat stored above room temperature (in a solar heating system).
Utility — A regulated entity which exhibits the characteristics of a natural monopoly (also referred to as a power provider). For the purposes of electric industry restructuring, "utility" refers to the regulated, vertically-integrated electric company. "Transmission utility" refers to the regulated owner/operator of the transmission system only. "Distribution utility" refers to the regulated owner/operator of the distribution system which serves retail customers.
U-Value (see Coefficient of Heat Transmission) — The reciprocal of R-Value. The lower the number, the greater the heat transfer resistance (insulating) characteristics of the material.
Vacuum Evaporation — The deposition of thin films of semiconductor material by the evaporation of elemental sources in a vacuum.
Valence Band — The highest energy band in a semiconductor that can be filled with electrons.
Vapor Retarder — 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 treated papers, plastic sheets, and metallic foils.
Variable-Speed Wind Turbines — Turbines in which the rotor speed increases and decreases with changing wind speed, producing electricity with a variable frequency.
Vent — A component of a heating or ventilation appliance used to conduct fresh air into, or waste air or combustion gases out of, an appliance or interior space.
Vent Damper — A device mounted in the vent connector that closes the vent when the heating unit is not firing. This traps heat inside the heating system and house rather than letting it draft up and out the vent system.
Vented Heater — 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.
Ventilation — The process of moving air (changing) into and out of an interior space either by natural or mechanically induced (forced) means.
Ventilation Air — That portion of supply air that is drawn from outside, plus any recirculated air that has been treated to maintain a desired air quality.
Vent Pipe — A tube in which combustion gases from a combustion appliance are vented out of the appliance to the outdoors.
Vertical-Axis Wind Turbine (VAWT) — A type of wind turbine in which the axis of rotation is perpendicular to the wind stream and the ground.
Vertical Ground Loop — In this type of closed-loop geothermal heat pump installation, the fluid-filled plastic heat exchanger pipes are laid out in a plane perpendicular to the ground surface. For a vertical system, holes (approximately four inches in diameter) are drilled about 20 feet apart and 100 to 400 feet deep. Into these holes go two pipes that are connected at the bottom with a U-bend to form a loop. The vertical loops are connected with horizontal pipe (i.e., manifold), placed in trenches, and connected to the heat pump in the building. Large commercial buildings and schools often use vertical systems because the land area required for horizontal ground loops would be prohibitive. Vertical loops are also used where the soil is too shallow for trenching, or for existing buildings, as they minimize the disturbance to landscaping. Also see closed-loop geothermal heat pump systems.
Visible Light Transmittance — The amount of visible light that passes through the glazing material of a window, expressed as a percentage.
Visible Radiation — The visible portion of the electromagnetic spectrum with wavelengths from 0.4 to 0.76 microns
Volt — A unit of electrical force equal to that amount of electromotive force that will cause a steady current of one ampere to flow through a resistance of one ohm.
Voltage — The amount of electromotive force, measured in volts, that exists between two points.
Volt-Ampere — A unit of electrical measurement equal to the product of a volt and an ampere.
Zoning — The combining of rooms in a structure according to similar heating and cooling patterns. Zoning requires using more than one thermostat to control heating, cooling, and ventilation equipment.
Air Conditioning Units
