Last Updated Monday, July 24, 2000
compiled by Nick Sundt

Q, R


Quad.One quadrillion Btu. (1,000,000,000,000,000 Btu) (Source: US Department of Energy, 1999a).

Qualifying Facility. 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 and photovoltaic), and wind, or cogenerators who produce both heat and electricity using any type of fuel. PURPA requires utilities to purchase electricity from these power producers at a rate approved by a state utility regulatory agency under Federal guidelines. PURPA also requires utilities to sell electricity to these producers. Some states have developed their own programs for SPPs and utilities. (Source: US Department of Energy, 1999a).

Quaternary period. The latest period of geologic time, covering the most recent 2,000,000 years of the Earth's history. It is divided into two epochs: the Pleistocene - 2 million years ago to approximately 10,000 years ago - and the Holocene - the period from approximately 10,000 years ago to the present. The Quaternary period is the artificial division of time separating prehuman and human periods. It contains five ice ages and four interglacial ages, and temperature indicators seem to show sharp and abrupt changes by several degrees. (Source: Carbon Dioxide Information Analysis Center, 1990a).


R-value. A unit of thermal resistance used for comparing insulating values of different material. It is basically a measure of the effectiveness of insulation in stopping heat flow. The higher the R-value number, a material, the greater its insulating properties and the slower the heat flow through it. The specific value needed to insulate a home depends on climate, type of heating system and other factors. (Source: California Energy Commission, 1999a.)

Rad. A unit of measure of absorbed radiation. Acronym for radiation absorbed dose. One rad equals 100 ergs of radiation energy per gram of absorbing material. (Source: California Energy Commission, 1999a.)

Radiant barrier. Radiant barriers are thin sheets of highly reflective material, like aluminum, which reduce heat transfer from thermal radiation across the air space between the roof and the attic floor. Radiant barrier do nothing to prevent heat transfer by conduction or convection. An excellent website covering radiant barriers is the Department of Energy's Radiant Barrier Fact Sheet, produced by Oak Ridge National Laboratory (Source: Lawrence Berkeley Laboratory, 1999)

Radiant Ceiling Panels. Ceiling panels that contain electric resistance heating elements embedded within them to provide radiant heat to a room. (Source: US Department of Energy, 1999a).

Radiant Energy. Energy that transmits away from its source in all directions. (Source: US Department of Energy, 1999a).

Radiant Floor. A type of radiant heating system where the building floor contains channels or tubes through which hot fluids such as air or water are circulated. The whole floor is evenly heated. Thus, the room heats from the bottom up. Radiant floor heating eliminates the draft and dust problems associated with forced air heating systems. (Source: US Department of Energy, 1999a).

radiant flux density. The total flow of radiation received on a unit area of a given real or imaginary surface. Also called the irradiance. (Source: Carbon Dioxide Information Analysis Center, 1990a).

Radiant Heating System. A heating system where heat is supplied (radiated) into a room by means of heated surfaces, such as electric resistance elements, hot water (hydronic) radiators, etc. (Source: US Department of Energy, 1999a).

radiation. Energy emitted in the form of electromagnetic waves. Radiation has differing characteristics depending upon the wavelength. Because the radiation from the Sun is relatively energetic, it has a short wavelength (e.g., ultra-violet, visible, and near infrared) while energy re-radiated from the Earth’s surface and the atmosphere has a longer wavelength (e.g., infrared radiation) because the Earth is cooler than the Sun. See ultraviolet radiation, infrared radiation, solar radiation, longwave radiation, ter-restrial radiation.(Source: US Environmental Protection Agency, 1999a)

radiation balance. The difference between the absorbed solar radiation and the net infrared radiation. Experimental data show that radiation from the earth's natural surfaces is rather close to the radiation from a black body at the corresponding temperature; the ratio of the observed values of radiation to black body radiation is generally 0.90 - 1.0. (Source: Carbon Dioxide Information Analysis Center, 1990a).

radiative-convective models. Thermodynamic models that determine the equilibrium temperature distribution for an atmospheric column and the underlying surface, subject to prescribed solar radiation at the top of the atmosphere and prescribed atmospheric composition and surface albedo. Submodels for the transfer of solar and terrestrial radiation, the heat exchange between the earth's surface and atmosphere, the vertical redistribution of heat within the atmosphere, the atmospheric water vapor content and clouds are included in these one-dimensional models. Abbreviated as RCM. (Source: Carbon Dioxide Information Analysis Center, 1990a).

Radiative Cooling. The process of cooling by which a heat absorbing media absorbs heat from one source and radiates the heat away. (Source: US Department of Energy, 1999a).

radiative forcing. A change in the balance between incoming solar radia-tion and outgoing infrared (i.e., thermal) radiation. Without any radiative forcing, solar radiation coming to the Earth would continue to be approximately equal to the infrared radiation emitted from the Earth. The addition of greenhouse gases to the atmosphere traps an increased fraction of the infrared radiation, reradiating it back toward the surface of the Earth and thereby cre-ates a warming influence.(Source: US Environmental Protection Agency, 1999a)

radiatively active gases. Gases that absorb incoming solar radiation or outgoing infrared radiation, thus affecting the vertical temperature profile of the atmosphere. Most frequently being cited as being radiatively active gases are water vapor, CO2, methane, nitrous oxide, chlorofluorocarbons, and ozone. (Source: Carbon Dioxide Information Analysis Center, 1990a).

radiosonde. A balloon-borne instrument for the simultaneous measurement and transmission of meteorological data up to a height of approximately 30,000 meters (100,000 feet). The height of each pressure level of the observation is computed from data received via radio signals. (Source: Carbon Dioxide Information Analysis Center, 1990a).

Radiator. A room heat delivery (or exchanger) component of a hydronic (hot water or steam) heating system; hot water or steam is delivered to it by natural convection or by a pump from a boiler. (Source: US Department of Energy, 1999a).

Radiator Vent. A device that releases pressure within a radiator when the pressure inside exceeds the operating limits of the vent. (Source: US Department of Energy, 1999a).

Radioactive Waste. Materials left over from making nuclear energy. Radioactive waste can living organisms if it is not stored safely. (Source: US Department of Energy, 1999a).

Radon. A naturally occurring radioactive gas found in the U.S. in nearly all types of soil, rock, and water. It can migrate into most buildings. Studies have linked high concentrations of radon to lung cancer. (Source: US Department of Energy, 1999a).

Rafter. A construction element used for ceiling support. (Source: US Department of Energy, 1999a).

Rammed Earth. A construction material made by compressing earth in a form; used traditionally in many areas of the world and widely throughout North Africa and the Middle East. (Source: US Department of Energy, 1999a).

rangeland. Land, mostly grasslands, whose plants can provide food (i.e., forage) for grazing or browsing animals. See feedlot.(Source: US Environmental Protection Agency, 1999a)

Rankine Cycle. The thermodynamic cycle that is an ideal standard for comparing performance of heat-engines, steam power plants, steam turbines, and heat pump systems that use a condensable vapor as the working fluid; efficiency is measured as work done divided by sensible heat supplied. (Source: US Department of Energy, 1999a).

Rate Base. The value of property upon which a utility is permitted to earn a specified rate of return as established by a regulatory authority. The rate base generally represents the value of property used by the utility in providing service and may be calculated by any one or a combination of the following accounting methods: fair value, prudent investment, reproduction cost, or original cost. Depending on which method is used, the rate base includes cash, working capital, materials and supplies, and deductions for accumulated provisions for depreciation, contributions in aid of construction, customer advances for construction, accumulated deferred income taxes, and accumulated deferred investment tax credits. (Source: US Energy Information Administration, 1999b)

Rated Life. The length of time that a product or appliance is expected to meet a certain level of performance under nominal operating conditions; in a luminaire, the period after which the lumen depreciation and lamp failure is at 70% of its initial value. (Source: US Department of Energy, 1999a).

Rate Schedule. A mechanism used by electric utilities to determine prices for electricity; typically defines rates according to amounts of power demanded/consumed during specific time periods. (Source: US Department of Energy, 1999a).

Rated Power. The power output of a device under specific or nominal operating conditions. (Source: US Department of Energy, 1999a).

Ratemaking Authority. A utility commission's legal authority to fix, modify, approve, or disapprove rates, as determined by the powers given the commission by a State or Federal legislature. (Source: US Energy Information Administration, 1999b)

Reactive Power. The electrical power that oscillates between the magnetic field of an inductor and the electrical field of a capacitor. Reactive power is never converted to non-electrical power. Calculated as the square root of the difference between the square of the kilovolt-amperes and the square of the kilowatts. Expressed as reactive volt-amperes. (Source: US Department of Energy, 1999a).

Real Price. The unit price of a good or service estimated from some base year in order to provide a consistent means of comparison. (Source: US Department of Energy, 1999a).

real-time pricing. The instantaneous pricing of electricity based on the cost of the electricity available for use at the time the electricity is demanded by the customer. (Source: California Energy Commission, 1999a.)

recharge. The process by which water is added to a reservoir or zone of saturation, often by runoff or percolation from the soil surface. (Source: Carbon Dioxide Information Analysis Center, 1990a).

Recirculation Systems. A type of solar heating system that circulate warm water from storage through the collectors and exposed piping whenever freezing conditions occur; obviously a not very efficient system when operating in this mode. (Source: US Department of Energy, 1999a).

Receiver. The component of a central receiver solar thermal system where reflected solar energy is absorbed and converted to thermal energy. (Source: US Department of Energy, 1999a).

Recirculated Air. Air that is returned from a heated or cooled space, reconditioned and/or cleaned, and returned to the space. (Source: US Department of Energy, 1999a).

recool. The sensible cooling of air that has been previously heated by HVAC systems serving the same building. (Source: California Energy Commission, 1999a.)

recovered energy. Reused heat or energy that otherwise would be lost. For example, a combined cycle power plant recaptures some of its own waste heat and reuses it to make extra electric power. (Source: California Energy Commission, 1999a.)

recovery efficiency. (Thermal efficiency) In a water heater, a measure of the percentage of heat from the combustion of gas which is transferred to the water as measured under specified test conditions. (Source: California Energy Commission, 1999a.)

Rectifier. An electrical device for converting alternating current to direct current. The chamber in a cooling device where water is separated from the working fluid (for example ammonia). (Source: US Department of Energy, 1999a).

Recuperator. A heat exchanger in which heat is recovered from the products of combustion. (Source: US Department of Energy, 1999a).

Recurrent Costs. Costs that are repetitive and occur when an organization produces similar goods or services on a continuing basis. (Source: US Department of Energy, 1999a).

Recycling. The process of converting materials that are no longer useful as designed or intended into a new product. (Source: US Department of Energy, 1999a).

Reflectance. The amount (percent) of light that is reflected by a surface relative to the amount that strikes it. (Source: US Department of Energy, 1999a).

Reflective Coatings. Materials with various qualities that are applied to glass windows before installation. These coatings reduce radiant heat transfer through the window and also reflects outside heat and a portion of the incoming solar energy, thus reducing heat gain. The most common type has a sputtered coating on the inside of a window unit. The other type is a durable "hard-coat" glass with a coating, baked into the glass surface. (Source: US Department of Energy, 1999a).

Reflective Window Films. A material applied to window panes that controls heat gain and loss, reduces glare, minimizes fabric fading, and provides privacy. These films are retrofitted on existing windows. (Source: US Department of Energy, 1999a).

Reflective Glass. A window glass that has been coated with a reflective film and is useful in controlling solar heat gain during the summer. (Source: US Department of Energy, 1999a).

Reflective Insulation (see also radiant barrier). An aluminum foil fabricated insulator with backings applied to provide a series of closed air spaces with highly reflective surfaces. (Source: US Department of Energy, 1999a).

relative sea level. The height of the boundary between sea and air as measured in relationship to a fixed reference point on land. (Source: Carbon Dioxide Information Analysis Center, 1990a).

reflectivity. The ratio of the energy carried by a wave that is reflected from a surface to the energy of a wave incident on the surface. (Source: Carbon Dioxide Information Analysis Center, 1990a).

Reflector Lamps. A type of incandescent lamp with an interior coating of aluminum that reflects light to the front of the bulb. They are designed to spread light over specific areas. (Source: US Department of Energy, 1999a).

reforestation. Replanting of forests on lands that have recently been harvested.(Source: US Environmental Protection Agency, 1999a)

reformulated gasoline (RFG). A cleaner-burning gasoline that has had its compositions and/or characteristics altered to reduce vehicular emissions of pollutants. (Source: California Energy Commission, 1999a.)

Refraction. The change in direction of a ray of light when it passes through one media to another with differing optical densities. (Source: US Department of Energy, 1999a).

Refrigerant. The compound (working fluid) used in air conditioners, heat pumps, and refrigerators to transfer heat into or out of an interior space. This fluid boils at a very low temperature enabling it to evaporate and absorb heat. (Source: US Department of Energy, 1999a).

Refrigeration. The process of the absorption of heat from one location and its transfer to another for rejection or recuperation. (Source: US Department of Energy, 1999a).

Refrigeration Capacity. A measure of the effective cooling capacity of a refrigerator, expressed in Btu per hour or in tons, where one (1) ton of capacity is equal to the heat required to melt 2,000 pounds of ice in 24 hours or 12,000 Btu per hour. (Source: US Department of Energy, 1999a).

Refrigeration Cycle. The complete cycle of stages (evaporation and condensation) of refrigeration or of the refrigerant. (Source: US Department of Energy, 1999a).

Refuse-Derived Fuel (RDF). A solid fuel produced by shredding municipal solid waste (MSW). Noncombustible materials such as glass and metals are generally removed prior to making RDF. The residual material is sold as-is or compressed into pellets, bricks, or logs. RDF processing facilities are typically located near a source of MSW, while the RDF combustion facility can be located elsewhere. Existing RDF facilities process between 100 and 3,000 tons per day. (Source: US Department of Energy, 1999a).

Regenerative Cooling. A type of cooling system that uses a charging and discharging cycle with a thermal or latent heat storage subsystem. (Source: US Department of Energy, 1999a).

Regenerative Heating. The process of using heat that is rejected in one part of a cycle for another function or in another part of the cycle. (Source: US Department of Energy, 1999a).

reheat. The heating of air that has been previously cooled either by mechanical refrigeration or economizer cooling systems. (Source: California Energy Commission, 1999a.)

Relamping. The replacement of a non-functional or ineffective lamp with a new, more efficient lamp. (Source: US Department of Energy, 1999a).

Relative Humidity. A measure of the percent of moisture actually in the air compared with what would be in it if it were fully saturated at that temperature. When the air is fully saturated, its relative humidity is 100 percent. (Source: US Department of Energy, 1999a).

Reliability. This is the concept of how long a device or process can operate properly without needing maintenance or replacement. (Source: US Department of Energy, 1999a).

Renewable Energy. Energy derived from resources that are regenerative or for all practical purposes can not be depleted. Types of renewable energy resources include moving water (hydro, tidal and wave power), thermal gradients in ocean water, biomass, geothermal energy, solar energy, and wind energy. Municipal solid waste (MSW) is also considered to be a renewable energy resource. (Source: US Department of Energy, 1999a).

reserve. The extra generating capability that an electric utility needs, above and beyond the highest demand level it is required to supply to meet its users' needs. (Source: California Energy Commission, 1999a.)

reserve generating capacity. The amount of power that can be produced at a given point in time by generating units that are kept available in case of special need. This capacity may be used when unusually high power demand occurs, or when other generating units are off-line for maintenance, repair or refueling. (Source: California Energy Commission, 1999a.)

reserve margin. The differences between the dependable capacity of a utility's system and the anticipated peak load for a specified period. (Source: California Energy Commission, 1999a.)

reservoir. Any natural or artificial holding area used to store, regulate, or control a substance. (Source: Carbon Dioxide Information Analysis Center, 1990a).

residence time. Average time spent in a reservoir by an individual atom or molecule. Also, this term is used to define the age of a molecule when it leaves the reservoir. With respect to greenhouse gases, residence time usually refers to how long a particular molecule remains in the atmosphere. See lifetime.(Source: US Environmental Protection Agency, 1999a)

Residential Sector. All private residences, whether occupied or vacant, owned or rented, including single- family homes, multifamily housing units, and mobile homes. Secondary homes, such as summer homes, are also included. Institutional housing, such as school dormitories, hospitals, and military barracks, generally are not included in the residential sector; they are included in the commercial sector.

Resistance. The inherent characteristic of a material to inhibit the transfer of energy. In electrical conductors, electrical resistance results in the generation of heat. Electrical resistance is measured in Ohms. The heat transfer resistance properties of insulation products are quantified as the R-value. (Source: US Department of Energy, 1999a).

Resistance Heating. A type of heating system that provides heat from the resistance of an electrical current flowing through a conductor. (Source: US Department of Energy, 1999a).

Resource Recovery. The process of converting municipal solid waste to energy and/or recovering materials for recycling. (Source: US Department of Energy, 1999a).

respiration. A biochemical process by which living organisms take up oxygen from the environment and consume organic matter, releasing both carbon dioxide and heat. In plants, the organic matter in photosynthate produced during daylight hours. (Source: Carbon Dioxide Information Analysis Center, 1990a).

Restructuring. The process of changing the structure of the electric power industry from one of guaranteed monopoly over service territories, as established by the Public Utility Holding Company Act of 1935, to one of open competition between power suppliers for customers in any area. (Source: US Department of Energy, 1999a).

Retrofit. The process of modifying a building's structure. (Source: US Department of Energy, 1999a).

Return Air. Air that is returned to a heating or cooling appliance from a heated or cooled space. (Source: US Department of Energy, 1999a).

Return Duct. The central heating or cooling system contains a fan that gets its air supply through these ducts, which ideally should be installed in every room of the house. The air from a room will move towards the lower pressure of the return duct. (Source: US Department of Energy, 1999a).

Retail Wheeling. A term for the process of transmitting electricity over transmission lines not owned by the supplier of the electricity to a retail customer of the supplier. With retail wheeling, an electricity consumer can secure their own supply of electricity from a broker or directly from the generating source. The power is then wheeled at a fixed rate, or at a regulated "non-discriminatory" rate set by a utility commission. (Source: US Department of Energy, 1999a).

Reversing Valve. A component of a heat pump that reverses the refrigerant's direction of flow, allowing the heat pump to switch from cooling to heating or heating to cooling. (Source: US Department of Energy, 1999a).

R-Factor. See R-Value. (Source: US Department of Energy, 1999a).

Ribbon (Photovoltaic) Cells. A type of solar photovoltaic device made in a continuous process of pulling material from a molten bath of photovoltaic material, such as silicon, to form a thin sheet of material. (Source: US Department of Energy, 1999a).

Rigid Insulation Board. An insulation product made of a fibrous material or plastic foams, pressed or extruded into board-like forms. It provides thermal and acoustical insulation strength with low weight, and coverage with few heat loss paths. (Source: US Department of Energy, 1999a).

Rock Bin. A container that holds rock used as the thermal mass to store solar energy in a solar heating system. (Source: US Department of Energy, 1999a).

Rockwool Insulation. Dirty grey, although the color can range through green and brown as well. Rockwool looks like old wool with dark flecks, and you can often find what looks like sand or small pebbles underneath the insulation. Rockwool is spun, like fiberglass, from the slag from refining metals. The debris that settles underneath the insulation is remnants of the slag, and condensed droplets of metal. (Source: Lawrence Berkeley Laboratory, 1999)

Roof. A building element that provides protection against the sun, wind, and precipitation. (Source: US Department of Energy, 1999a).

Roof Pond. A solar energy collection device consisting of containers of water located on a roof that absorb solar energy during the day so that the heat can be used at night or that cools a building by evaporation at night. (Source: US Department of Energy, 1999a).

Roof Ventilator. A stationary or rotating vent used to ventilate attics or cathedral ceilings; usually made of galvanized steel, or polypropylene. (Source: US Department of Energy, 1999a).

Rotor. An electric generator consists of an armature and a field structure. The armature carries the wire loop, coil, or other windings in which the voltage is induced, whereas the field structure produces the magnetic field. In small generators, the armature is usually the rotating component (rotor) surrounded by the stationary field structure (stator). In large generators in commercial electric power plants the situation is reversed. In a wind energy conversion device, the blades and rotating components. (Source: US Department of Energy, 1999a).

runoff. That part of precipitation, snowmelt, or irrigation water that flows from the land to streams or other surface waters. (Source: Carbon Dioxide Information Analysis Center, 1990a).

R-Value. R-value is a measurement of heat resistance. It is the inverse of the U-value, so the higher the R-value the better the insulation resists heat transfer. Many factors can affect the R-value of insulation, including the type of insulation, and the age of the insulation. To determine the R-value of the insulation in your house, first determine the type of insulation present, whether that insulation is new, and measure the depth of the insulation in inches. Look your insulation up on the table below, and multiply the R-value per inch by the number of inches present in your house. (Source: Lawrence Berkeley Laboratory, 1999)