Glossary
C-D
Last Updated Monday, July 24, 2000
compiled by Nick Sundt

C, D

C

C3 plants - Plants (e.g., soybean, wheat, and cotton) whose carbon-fixation products have three carbon atoms per molecule. Compared with C4 plants, C3 plants show a greater increase in photosynthesis with a doubling of CO2 concentration and less decrease in stomatal conductance, which results in an increase in leaf-level water-use efficiency. (Source: Carbon Dioxide Information Analysis Center, 1990a).

C4 plants - Plants (e.g., maize and sorghum) whose carbon fixation products have four carbon atoms per molecule. Compared with C3 plants, C4 plants show little photosynthetic response to increased CO2 concentrations above 340 ppm but show a decrease in stomatal conductance, which results in an increase in photosynthetic water-use efficiency. (Source: Carbon Dioxide Information Analysis Center, 1990a).

call-back - A provision included in some power sale contracts that lets the supplier stop delivery when the power is needed to meet certain other obligations. (Source: California Energy Commission, 1999a.)

Calorie - The amount of heat required to raise the temperature of a unit of water, at or near the temperature of maximum density, one degree Celsius (or Centigrade [C]); expressed as a "small calorie" (the amount of heat required to raise the temperature of 1 gram of water one degree C), or as a "large calorie" or "kilogram calorie" (the amount of heat required to raise one kilogram [1,000 grams] of water one degree C); capitalization of the word calorie indicates a kilogram-calorie. (Source: US Department of Energy, 1999a).

Calorific Value - The heat liberated by the combustion of a unit quantity of a fuel under specific conditions; measured in calories. (Source: US Department of Energy, 1999a).

Candela - A unit of luminous intensity; the magnitude to the candela is such that the luminance of the total radiator, at the temperature of solidification of platinum, is 60 candelas per square centimeter. (Source: US Department of Energy, 1999a).

Candle Power - The illuminating power of a standard candle employed as a unit for determining the illuminating quality of an illuminant. (Source: US Department of Energy, 1999a).

canopy - The branches and leaves of woody plants that are formed some distance above the ground. (Source: Carbon Dioxide Information Analysis Center, 1990a).

Capability - The maximum load that a generating unit, power plant, or other electrical apparatus can carry under specified conditions for a given period of time, without exceeding its approved limits of temperature and stress. (Source: US Department of Energy, 1999a).

Capability Margin - The difference between net electrical system capability and system maximum load requirements (peak load); the margin of capability available to provide for scheduled maintenance, emergency outages, system operating requirements and unforeseen loads. (Source: US Department of Energy, 1999a).

Capacitor - An electrical device that adjusts the leading current of an applied alternating current to balance the lag of the circuit to provide a high power factor. (Source: US Department of Energy, 1999a).

Capacity (Condensing Unit) - The refrigerating effect in Btu/h produced by the difference in total enthalpy between a refrigerant liquid leaving the unit and the total enthalpy of the refrigerant vapor entering it. Generally measured in tons or Btu/h. (Source: US Department of Energy, 1999a).

Capacity (Effective, of a motor) - The maximum load that a motor is capable of supplying. (Source: US Department of Energy, 1999a).

Capacity (Heating, of a material) - The amount of heat energy needed to raise the temperature of a given mass of a substance by one degree Celsius. The heat required to raise the temperature of 1 kg of water by 1 degree Celsius is 4186 Joules. (Source: US Department of Energy, 1999a).

Capacity building - Building capacity involves developing the necessary individual and group perspectives, skills and organization to carry out activities. They include the knowledge, skills, technologies and institutions needed to conduct assessments, monitoring and evaluation, planning and implementation. (Source: Global Environment Facility, 2000a).

Capacity Factor - The ratio of the average load on (or power output of) a generating unit or system to the capacity rating of the unit or system over a specified period of time. (Source: US Department of Energy, 1999a).

Capital Costs - The amount of money needed to purchase equipment, buildings, tools, and other manufactured goods that can be used in production. (Source: US Department of Energy, 1999a).

Capital stock - Property, plant and equipment used in the production, processing and distribution of energy resources. (Source: US Energy Information Administration, 1999a).

captive customer - A customer who does not have realistic alternatives to buying power from the local utility, even if that customer had the legal right to buy from competitors. (Source: California Energy Commission, 1999a.)

carbon black - An amorphous form of carbon, produced commercially by thermal or oxidative decomposition of hydrocarbons and used principally in rubber goods, pigments, and print-er’s ink.(Source: US Environmental Protection Agency, 1999a)

carbon budget - The balance of the exchanges (incomes and losses) of carbon between the carbon reservoirs or between one specific loop (e.g., atmosphere - biosphere) of the carbon cycle. An examination of the carbon budget of a pool or reservoir can provide information about whether the pool or reservoir is functioning as a source or sink for CO2. (Source: Carbon Dioxide Information Analysis Center, 1990a).

carbon cycle - All parts (reservoirs) and fluxes of carbon; usually thought of as a series of the four main reservoirs of carbon interconnected by pathways of exchange. The four reservoirs, regions of the Earth in which carbon behaves in a systematic manner, are the atmosphere, terrestrial biosphere (usually includes fresh water systems), oceans, and sediments (includes fossil fuels). Each of these global reservoirs may be subdivided into smaller pools ranging in size from individual communities or ecosystems to the total of all living organisms (biota). Carbon exchanges from reservoir to reservoir by various chemical, physical, geological, and biological processes. (Source: Carbon Dioxide Information Analysis Center, 1990a).

carbon density - The amount of carbon per unit area for a given ecosystem or vegetation type, based on climatic conditions, topography, vegetative-cover type and amount, soils, and maturity of the vegetative stands. (Source: Carbon Dioxide Information Analysis Center, 1990a).

Carbon Dioxide - A colorless, odorless noncombustible gas with the formula CO2 that is present in the atmosphere. It is formed by the combustion of carbon and carbon compounds (such as fossil fuels and biomass), by respiration, which is a slow combustion in animals and plants, and by the gradual oxidation of organic matter in the soil. (Source: US Department of Energy, 1999a).

carbon dioxide fertilization - Enhancement of plant growth or of the net primary production by CO2 enrichment that could occur in natural or agricultural systems as a result of an increase in the atmospheric concentration of CO2. (Source: Carbon Dioxide Information Analysis Center, 1990a).

carbon equivalent (CE) - A metric measure used to compare the emissions of the different greenhouse gases based upon their global warming potential (GWP). Greenhouse gas emissions in the United States are most commonly expressed as "mil-lion metric tons of carbon equivalents" (MMTCE). Global warming potentials are used to convert greenhouse gases to carbon dioxide equivalents. See global warming potential, greenhouse gas.(Source: US Environmental Protection Agency, 1999a)

carbon flux - The rate of exchange of carbon between pools (reservoirs). (Source: Carbon Dioxide Information Analysis Center, 1990a).

carbon intensity - The relative amount of carbon emitted per unit of energy or fuels consumed.(Source: US Environmental Protection Agency, 1999a)

carbon isotope ratio - Ratio of carbon-12 to either of the other, less common, carbon isotopes, carbon-13 or carbon-14. (Source: Carbon Dioxide Information Analysis Center, 1990a).

Carbon Monoxide - A colorless, odorless but poisonous combustible gas with the formula CO. Carbon monoxide is produced in the incomplete combustion of carbon and carbon compounds such as fossil fuels (i.e. coal, petroleum) and their products (e.g. liquefied petroleum gas, gasoline), and biomass. (Source: US Department of Energy, 1999a).

Carbon output rate - The amount of carbon by weight per kilowatthour of electricity produced. (Source: US Energy Information Administration, 1999a).

carbon pool - The reservoir containing carbon as a principal element in the geochemical cycle. (Source: Carbon Dioxide Information Analysis Center, 1990a).

carbon sequestration - The uptake and storage of carbon. Trees and plants, for example, absorb carbon dioxide, release the oxygen and store the carbon. Fossil fuels were at one time biomass and continue to store the carbon until burned. See car-bon sinks.(Source: US Environmental Protection Agency, 1999a)

carbon sink - A pool (reservoir) that absorbs or takes up released carbon from another part of the carbon cycle. For example, if the net exchange between the biosphere and the atmosphere is toward the atmosphere, the biosphere is the source, and the atmosphere is the sink. (Source: Carbon Dioxide Information Analysis Center, 1990a).

carbon source - A pool (reservoir) that releases carbon to another part of the carbon cycle. (Source: Carbon Dioxide Information Analysis Center, 1990a).

carbon-based resources - The recoverable fossil fuel (coal, gas, crude oils, oil shale, and tar sands) and biomass that can be used in fuel production and consumption. (Source: Carbon Dioxide Information Analysis Center, 1990a).

carbon tetrachloride (CCl 4 ) - A compound consisting of one carbon atom and four chlorine atoms. Carbon tetrachloride was widely used as a raw material in many industrial uses, including the production of CFCs, and as a solvent. Solvent use ended when it was discovered to be carcinogenic. It is also used as a catalyst to deliver chlorine ions to certain processes. Its ozone depletion potential is 1.2. (Source: US Environmental Protection Agency, 1999b).

carcinogens - Potential cancer-causing agents in the environment. They include among others: industrial chemical compounds found in food additives, pesticides and fertilizers, drugs, toy, household cleaners, toiletries and paints. Naturally occurring ultraviolet solar radiation is also a carcinogen. (Source: California Energy Commission, 1999a.)

Carrying capacity - The amount of use an area can sustain—for recreation, for wildlife, etc., without deteriorating in its quality and become unsustainable. (Source: Global Environment Facility, 2000a).

Catalytic Converter - An air pollution control device that removes organic contaminants by oxidizing them into carbon dioxide and water through a chemical reaction using a catalysis, which is a substance that increases (or decreases) the rate of a chemical reaction without being changed itself; required in all automobiles sold in the United State, and used in some types of heating appliances. (Source: US Department of Energy, 1999a).

Cathedral Ceiling/Roof - A type of ceiling and roof assembly that has no attic. (Source: US Department of Energy, 1999a).

Cathode - The negative pole or electrode of an electrolytic cell, vacuum tube, etc., where electrons enter (current leaves) the system; the opposite of an anode. (Source: US Department of Energy, 1999a).

Cathode Disconnect Ballast - An electromagnetic ballast that disconnects a lamp's electrode heating circuit once is has started; often called "low frequency electronic" ballasts. (Source: US Department of Energy, 1999a).

Cathodic Protection - A method of preventing oxidation of the exposed metal in structures by imposing between the structure and the ground a small electrical voltage.(Source: US Department of Energy, 1999a).

Caulking - A material used to seal areas of potential air leakage into or out of a building envelope. (Source: US Department of Energy, 1999a).

Ceiling - The downward facing structural element that is directly opposite the floor. (Source: US Department of Energy, 1999a).

Ceiling Fan - A mechanical device used for air circulation and to provide cooling. (Source: US Department of Energy, 1999a).

Celsius - A temperature scale based on the freezing (0 degrees) and boiling (100 degrees) points of water. Abbreviated as C in second and subsequent references in text. Formerly known as Centigrade. To convert Celsius to Fahrenheit, multiply the number by 9, divide by 5, and add 32. For example:
10 degrees Celsius x 9 = 90; 90 / 5 = 18; 18 + 32 = 50 degrees Fahrenheit. (Source: California Energy Commission, 1999a.)

Cell - A component of a electrochemical battery. A 'primary' cell consists of two dissimilar elements, known as 'electrodes,' immersed in a liquid or paste known as the 'electrolyte.' A direct current of 1-1.5 volts will be produced by this cell. A 'secondary' cell or accumulator is a similar design but is made useful by passing a direct current of correct strength through it in a certain direction. Each of these cells will produce 2 volts; a 12 volt car battery contains six cells. (Source: US Department of Energy, 1999a).

Cellulose Insulation - Cellulose insulation is made from wastepaper, such as used newspaper and boxes. It is shredded into small particles, and chemicals providing resistance to fire and insects are added. Cellulose insulation is dusty and brown, with flat particles, on which you can frequently find legible print. (Source: Lawrence Berkeley Laboratory, 1999)

Cellulose Insulation - A type of insulation composed of waste newspaper, cardboard, or other forms of waste paper. (Source: US Department of Energy, 1999a).

Central Heating System - A system where heat is supplied to areas of a building from a single appliance through a network of ducts or pipes. (Source: US Department of Energy, 1999a).

Central Power Plant - A large power plant that generates power for distribution to multiple customers. (Source: US Department of Energy, 1999a).

CFCs - See chlorofluorocarbons.

Char - A byproduct of low-temperature carbonization of a solid fuel. (Source: US Department of Energy, 1999a).

Charcoal - A material formed from the incomplete combustion or destructive distillation (carbonization) of organic material in a kiln or retort, and having a high energy density, being nearly pure carbon. (If produced from coal, it is coke.) Used for cooking, the manufacture of gunpowder and steel (notably in Brazil), as an absorbent and decolorizing agent, and in sugar refining and solvent recovery. (Source: US Department of Energy, 1999a).

Chemical Energy - The energy liberated in a chemical reaction, as in the combustion of fuels. (Source: US Department of Energy, 1999a).

Chiller - A device for removing heat from a gas or liquid stream for air conditioning/cooling. (Source: US Department of Energy, 1999a).

Chimney - A masonry or metal stack that creates a draft to bring air to a fire and to carry the gaseous byproducts of combustion safely away. (Source: US Department of Energy, 1999a).

chlorofluorocarbons (CFC) - A compound consisting of chlorine, fluorine, and carbon. CFCs are very stable in the troposphere. They are broken down by strong ultraviolet light in the stratosphere and release chlorine atoms that then deplete the ozone layer. CFCs are commonly used as refrigerants, solvents, and foam blowing agents. The most common CFCs are CFC-11, CFC-12, CFC-113, CFC-114, and CFC-115. The ozone depletion potential (ODP) for each CFC is, respectively, 1, 1, 0.8, 1, and 0.6. A table of all ozone-depleting substances shows their ODPs, GWPs, and CAS numbers. CFCs are numbered according to a standard scheme. The National Oceanic and Atmospheric Administration provides more detailed information about CFCs on their web site (including graphs of their abundance in the atmosphere). (Source: US Environmental Protection Agency, 1999b).

chloroplast - An organelle in the cells of green plants. It contains chlorophyll and functions in photosynthesis and protein synthesis. (Source: Carbon Dioxide Information Analysis Center, 1990a).

Circuit - A device, or system of devices, that allows electrical current to flow through it and allows voltage to occur across positive and negative terminals. (Source: US Department of Energy, 1999a).

Circuit Breaker - A device used to interrupt or break an electrical circuit when an overload condition exists; usually installed in the positive circuit; used to protect electrical equipment. (Source: US Department of Energy, 1999a).

Circuit Lag - As time increases from zero at the terminals of an inductor, the voltage comes to a particular value on the sine function curve ahead of the current. The voltage reaches its negative peak exactly 90 degrees before the current reaches its negative peak thus the current lags behind by 90 degrees. (Source: US Department of Energy, 1999a).

Circulating Fluidized Bed - A type of furnace or reactor in which the emission of sulfur compounds is lowered by the addition of crushed limestone in the fluidized bed thus obviating the need for much of the expensive stack gas clean-up equipment. The particles are collected and recirculated, after passing through a conventional bed, and cooled by boiler internals. (Source: US Department of Energy, 1999a).

Clean Air Act (CAA) - Law amended by Congress in 1990. Title VI of the CAA directs EPA to protect the ozone layer through several regulatory and voluntary programs. Sections within Title VI cover production of ozone-depleting substances (ODS), the recycling and handling of ODS, the evaluation of substitutes, and efforts to educate the public. (Source: US Environmental Protection Agency, 1999b).

Clean Development Mechanism (CDM) - The Kyoto Protocol of the UN Framework enabled industrialized countries to finance emissions-avoiding projects in developing countries and receive credit for doing so. (Source: UN Climate Change Secretariat, 1999a)

clean fuel vehicle - A term frequently incorrectly used interchangeably with "alternative fuel vehicle." Generally, refers to vehicles that use low-emission, clean-burning fuels. Public Resources Code Section 25326 defines clean fuels, for purposes of the section only, as fuels designated by ARB for use in LEVs, ULEVs or ZEVs and include, but are not limited to, electricity, ethanol, hydrogen, liquefied petroleum gas, methanol, natural gas, and reformulated gasoline. (Source: California Energy Commission, 1999a.)

clear cutting - A forest-management technique that involves harvesting all the trees in one area at one time, which may result in increased soil erosion by wind and water as well as loss of fertility in the soil that remains. Overgrazing and poor farming practices may also produce similar results as clear cutting a forest. (Source: Carbon Dioxide Information Analysis Center, 1990a).

Clerestory - A window located high in a wall near the eaves that allows daylight into a building interior, and may be used for ventilation and solar heat gain. (Source: US Department of Energy, 1999a).

climate - The statistical collection and representation of the weather conditions for a specified area during a specified time interval, usually decades, together with a description of the state of the external system or boundary conditions. The properties that characterize the climate are thermal (temperatures of the surface air, water, land, and ice), kinetic (wind and ocean currents, together with associated vertical motions and the motions of air masses, aqueous humidity, cloudiness and cloud water content, groundwater, lake lands, and water content of snow on land and sea ice), and static (pressure and density of the atmosphere and ocean, composition of the dry air, salinity of the oceans, and the geometric boundaries and physical constants of the system). These properties are interconnected by the various physical processes such as precipitation, evaporation, infrared radiation, convection, advection, and turbulence. (Source: Carbon Dioxide Information Analysis Center, 1990a).

climate change - The long-term fluctuations in temperature, precipitation, wind, and all other aspects of the Earth's climate. External processes, such as solar-irradiance variations, variations of the Earth's orbital parameters (eccentricity, precession, and inclination), lithosphere motions, and volcanic activity, are factors in climate variation. Internal variations of the climate system also produce fluctuations of sufficient magnitude and variability to explain observed climate change through the feedback processes interrelating the components of the climate system. (Source: Carbon Dioxide Information Analysis Center, 1990a).

climate feedback - An atmospheric, oceanic, terrestrial, or other process that is activated by direct climate change induced by changes in radiative forcing. Climate feedbacks may increase (positive feedback) or diminish (negative feed-back) the magnitude of the direct climate change. (Source: US Environmental Protection Agency, 1999a)

climate lag - The delay that occurs in climate change as a result of some factor that changes very slowly. For example, the effects of releasing more carbon dioxide into the atmos-phere may not be known for some time because a large fraction is dissolved in the ocean and only released to the atmosphere many years later. (Source: US Environmental Protection Agency, 1999a)

climate sensitivity - The magnitude of a climatic response to a perturbing influence. In mathematical modeling of the climate, the difference between simulations as a function of change in a given parameter. (Source: Carbon Dioxide Information Analysis Center, 1990a).

climate signal - A statistically significant difference between the control and disturbed (see climate sensitivity) simulations of a climate model. (Source: Carbon Dioxide Information Analysis Center, 1990a).

climate system - The five physical components (atmosphere, hydrosphere, cryosphere, lithosphere, and biosphere) that are responsible for the climate and its variations. (Source: Carbon Dioxide Information Analysis Center, 1990a).

climate variation - The change in one or more climatic variables over a specified time. (Source: Carbon Dioxide Information Analysis Center, 1990a).

climate zone - A geographical area is the state that has particular weather patterns. These zones are used to determine the type of building standards that are required by law. (Source: California Energy Commission, 1999a.)

climatic analog - A past climate situation in which changes similar to the present occurred. Used in making climatic projections. (Source: Carbon Dioxide Information Analysis Center, 1990a).

climatic anomaly - The deviation of a particular climatic variable from the mean or normal over a specified time. (Source: Carbon Dioxide Information Analysis Center, 1990a).

climatic optimum - The period in history from about 5000 to about 2500 B.C. during which surface air temperatures were warmer than at present in nearly all regions of the world. In the Arctic region, the temperature rose many degrees C, and in temperate regions, the increase was 1.0 degree - 1.7 degrees C. In this period, glaciers and ice sheets receded greatly, and the melt-water raised mean sea level by about 3 meters. (Source: Carbon Dioxide Information Analysis Center, 1990a).

Close Coupled - An energy system in which the fuel production equipment is in close proximity, or connected to, the fuel using equipment. (Source: US Department of Energy, 1999a).

Closed Cycle - A system in which a working fluid is used over and over without introduction of new fluid, as in a hydronic heating system or mechanical refrigeration system. (Source: US Department of Energy, 1999a).

Closed-Loop - A type of heating system in which the heat transfer fluid circulates from the heating component to a heat exchanger that is immersed in a heat storage media, passing its heat to the storage media without physically contacting it. (Source: US Department of Energy, 1999a).

Closed Loop Biomass - As defined by the Comprehensive National Energy Act of 1992 (or the Energy Policy Act; EPAct): any organic matter from a plant which is planted for the exclusive purpose of being used to produce energy." This does not include wood or agricultural wastes or standing timber. (Source: US Department of Energy, 1999a).

cloud - A visible mass of condensed water vapor particles or ice suspended above the Earth's surface. Clouds may be classified on their visible appearance, height, or form. (Source: Carbon Dioxide Information Analysis Center, 1990a).

cloud albedo - Reflectivity that varies from less than 10% to more than 90% of the insolation and depends on drop sizes, liquid water content, water vapor content, thickness of the cloud, and the sun's zenith angle. The smaller the drops and the greater the liquid water content, the greater the cloud albedo, if all other factors are the same. (Source: Carbon Dioxide Information Analysis Center, 1990a).

cloud feedback - The coupling between cloudiness and surface air temperature in which a change in surface temperature could lead to a change in clouds, which could then amplify or diminish the initial temperature perturbation. For example, an increase in surface air temperature could increase the evaporation; this in turn might increase the extent of cloud cover. Increased cloud cover would reduce the solar radiation reaching the Earth's surface, thereby lowering the surface temperature. This is an example of negative feedback and does not include the effects of longwave radiation or the advection in the oceans and the atmosphere, which must also be considered in the overall relationship of the climate system. (Source: Carbon Dioxide Information Analysis Center, 1990a).

clunkers - Also known as gross-polluting or super- emitting vehicles, i.e., vehicles that emit far in excess of the emission standards by which the vehicle was certified when it was new. (Source: California Energy Commission, 1999a.)

co-control benefit - The additional benefit derived from an environmental policy that is designed to control one type of pollution, while reducing the emissions of other pollutants as well. For example, a policy to reduce carbon dioxide emissions might reduce the combustion of coal, but when coal combustion is reduced, so too are the emissions of particu-lates and sulfur dioxide. The benefits associated with reduc-tions in emissions of particulates and sulfur dioxide are the co-control benefits of carbon dioxide reductions. (Source: US Environmental Protection Agency, 1999a)

coal - A black or brownish black solid, combustible substance formed by the partial decomposition of vegetable matter without access to air. The rank of coal, which includes anthracite, bituminous coal, subbituminous coal, and lig-nite, is based on fixed carbon, volatile matter, and heating value. Coal rank indicates the progressive alteration, or coalification, from lignite to anthracite. See anthracite, bituminous coal, subbituminous coal, lignite. (Source: US Environmental Protection Agency, 1999a)

coal conversion - Changing coal into synthetic gas or liquid fuels. See GASIFICATION. (Source: California Energy Commission, 1999a.)

coal seam - A mass of coal, occurring naturally at a particular location, that can be commercially mined. (Source: California Energy Commission, 1999a.)

coal slurry pipeline - A pipe system that transports pulverized coal suspended in water. (Source: California Energy Commission, 1999a.)

coalbed methane - Methane that is produced from coalbeds in the same manner as natural gas produced from other strata. Methane is the principal component of natural gas.(Source: US Environmental Protection Agency, 1999a)

coastal zone - Lands and waters adjacent to the coast that exert an influence on the uses of the sea and its ecology or whose uses and ecology are affected by the sea. (Source: Carbon Dioxide Information Analysis Center, 1990a).

Codes - Legal documents that regulate construction to protect the health, safety, and welfare of people. Codes establish minimum standards but do not guarantee efficiency or quality. (Source: US Department of Energy, 1999a).

Coefficient of Heat Transmission (U-Value) - A value that describes the ability of a material to conduct heat. The number of Btu that flow through 1 square foot of material, in one hour. It is the reciprocal of the R-Value (U-Value = 1/R-Value). (Source: US Department of Energy, 1999a).

Coefficient of Performance (COP) - A ratio of the work or useful energy output of a system versus the amount of work or energy inputted into the system as determined by using the same energy equivalents for energy in and out. Is used as a measure of the steady state performance or energy efficiency of heating, cooling, and refrigeration appliances. The COP is equal to the Energy Efficiency Ratio (EER) divided by 3.412. The higher the COP, the more efficient the device. (Source: US Department of Energy, 1999a).

Coefficient of Utilization (CU) - A term used for lighting appliances; the ratio of lumens received on a flat surface to the light output, in lumens, from a lamp; used to evaluate the effectiveness of luminaries in delivering light. (Source: US Department of Energy, 1999a).

Coincident Demand - The demand of a consumer of electricity at the time of a power supplier's peak system demand. (Source: US Department of Energy, 1999a).

Cofiring - The use of two or more different fuels (e.g. wood and coal) simultaneously in the same combustion chamber of a power plant. (Source: US Department of Energy, 1999a).

Cogeneration - The generation of electricity or shaft power by an energy conversion system and the concurrent use of rejected thermal energy from the conversion system as an auxiliary energy source. (Source: US Department of Energy, 1999a).

Cogenerator - A class of energy producer that produces both heat and electricity from a single fuel. (Source: US Department of Energy, 1999a).

Coil - As a component of a heating or cooling appliance, rows of tubing or pipe with fins attached through which a heat transfer fluid is circulated and to deliver heat or cooling energy to a building. (Source: US Department of Energy, 1999a).

Cold Night Sky - The low effective temperature of the sky on a clear night. (Source: US Department of Energy, 1999a).

Collector - The component of a solar energy heating system that collects solar radiation, and that contains components to absorb solar radiation and transfer the heat to a heat transfer fluid (air or liquid). (Source: US Department of Energy, 1999a).

Collector Efficiency - The ratio of solar radiation captured and transfered to the collector (heat transfer) fluid. (Source: US Department of Energy, 1999a).

Collector Fluid - The fluid, liquid (water or water/antifreeze solution) or air, used to absorb solar energy and transfer it for direct use, indirect heating of interior air or domestic water, and/or to a heat storage medium. (Source: US Department of Energy, 1999a).

Collector Tilt - The angle that a solar collector is positioned from horizontal. (Source: US Department of Energy, 1999a).

Color Rendering or Rendition - A measure of the ability of a light source to show colors, based on a color rendering index. (Source: US Department of Energy, 1999a).

Color Rendition (Rendering) Index (CRI) - A measure of light quality. The maximum CRI value of 100 is given to natural daylight and incandescent lighting. The closer a lamp's CRI rating is to 100, the better its ability to show true colors to the human eye. (Source: US Department of Energy, 1999a).

Color Temperature or CCT (lighting terminology) - The CCT refers to the color objects emit when heated to a certain temperature on the absolute temperature scale (Kelvin). The lower numbers correspond to reddish color and the higher to blue-white color. For color similar to incandescent lighting look for CCTs around 2700. (Source: Lawrence Berkeley Laboratory, 1999)

Column Ozone - ozone between the Earth's surface and outer space. Ozone levels can be described in several ways. One of the most common measures is how much ozone is in a vertical column of air. The dobson unit is a measure of column ozone. Other measures include partial pressure, number density, and concentration of ozone, and can represent either column ozone or the amount of ozone at a particular altitude. (Source: US Environmental Protection Agency, 1999b).

Combined-Cycle Power Plant - A power plant that uses two thermodynamic cycles to achieve higher overall system efficiency; e.g.: the heat from a gas-fired combustion turbine is used to generate steam for heating or to operate a steam turbine to generate additional electricity. (Source: US Department of Energy, 1999a).

Combined Cycle Unit - An electric generating unit that consists of one or more combustion turbines and one or more boilers with a portion of the required energy input to the boiler(s) provided by the exhaust gas of the combustion turbine(s). (Source: US Energy Information Administration, 1999b)

combined hydronic space/water heating - A system in which both space heating and domestic water heating are provided by the same water heater(s). (Source: California Energy Commission, 1999a.)

Combustion - The process of burning; the oxidation of a material by applying heat, which unites oxygen with a material or fuel. (Source: US Department of Energy, 1999a).

Combustion Air - Air that provides the necessary oxygen for complete, clean combustion and maximum heating value. (Source: US Department of Energy, 1999a).

Combustion Chamber - Any wholly or partially enclosed space in which combustion takes place. (Source: US Department of Energy, 1999a).

Combustion Gases - The gaseous byproducts of the combustion of a fuel. (Source: US Department of Energy, 1999a).

Combustion Power Plant - A power plant that generates power by combusting a fuel. (Source: US Department of Energy, 1999a).

Combustion Turbine - A turbine that generates power from the combustion of a fuel. (Source: US Department of Energy, 1999a).

comfort conditioning - The process of treating air to simultaneously control its temperature, humidity, cleanliness, and distribution to meet the comfort requirements of the occupants of the conditioned space. (Source: California Energy Commission, 1999a.)

comfort zone - The range of temperatures over which the majority of persons feel comfortable (neither too hot nor too cold). (Source: California Energy Commission, 1999a.)

Commercial Building - A building with more than 50 percent of its floor space used for commercial activities, which include stores, offices, schools, churches, libraries, museums, health care facilities, warehouses, and government buildings except those on military bases. (Source: US Department of Energy, 1999a).

Commercial Sector - Consists of businesses that are not engaged in transportation or manufacturing or other types of industrial activities. Standard Industrial Classification (SIC) codes for commercial establishments are 50 through 87, 89, and 91 through 97. (Source: US Department of Energy, 1999a).

Commissioning - The process by which a power plant, apparatus, or building is approved for operation based on observed or measured operation that meets design specifications. (Source: US Department of Energy, 1999a).

Compact Fluorescent Lamps - These fluorescent lamps are small, and are designed to fit in regular lamp sockets. They do require a special fixture. The electronic ballast-based fluorescents are more efficient, and produce better light than the older magnetic ballast models. (Source: Lawrence Berkeley Laboratory, 1999)

competitive transmission charge - A non-bypassable charge that customers pay to a utility for the recovery of its stranded costs. (Source: California Energy Commission, 1999a.)

commercialization - Programs or activities that increase the value or decrease the cost of integrating new products or services into the electricity sector. (See "Sustained Orderly Development.") (Source: California Energy Commission, 1999a.)

composting - The natural biological decomposition of organic material in the presence of air to form a humus-like material. (Source: Carbon Dioxide Information Analysis Center, 1990a).

Composting Toilet - A self-contained toilet that use the process of aerobic decomposition (composting) to break down feces into humus and odorless gases. (Source: US Department of Energy, 1999a).

Compound Paraboloid Collector - A form of solar concentrating collector that does not track the sun. (Source: US Department of Energy, 1999a).

Compressed Natural Gas (CNG) - Natural gas (methane) that has been compressed to a higher pressure gaseous state by a compressor; used in CNG vehicles. (Source: US Department of Energy, 1999a).

Compression Chiller - A cooling device that uses mechanical energy to produce chilled water. (Source: US Department of Energy, 1999a).

Compressor - A device used to compress air for mechanical or electrical power production, and in air conditioners, heat pumps, and refrigerators to pressurize the refrigerant and enabling it to flow through the system. (Source: US Department of Energy, 1999a).

Concentrator (Solar) Collector - A solar collector that uses reflective surfaces to concentrate sunlight onto a small area, where it is absorbed and converted to heat or, in the case of solar photovoltaic (PV) devices, into electricity. Concentrators can increase the power flux of sunlight hundreds of times. The principal types of concentrating collectors include: compound parabolic, parabolic trough, fixed reflector moving receiver, fixed receiver moving reflector, Fresnel lense, and central receiver. A PV concentrating module uses optical elements (Fresnel lense) to increase the amount of sunlight incident onto a PV cell. Concentrating PV modules/arrays must track the sun and use only the direct sunlight because the diffuse portion cannot be focused onto the PV cells. (Source: US Department of Energy, 1999a).

Condensate - The liquid resulting when water vapor contacts a cool surface; also the liquid resulting when a vaporized working fluid (such as a refrigerant) is cooled or depressurized. (Source: US Department of Energy, 1999a).

Condensation - The process by which water in air changes from a vapor to a liquid due to a change in temperature or pressure; occurs when water vapor reaches its dew point (condensation point); also used to express the existence of liquid water on a surface. (Source: US Department of Energy, 1999a).

Condensation (window efficiency terminology) - Condensation is the buildup of water droplets on a cold window pane. This can occur on the inside of single pane windows, and in between the panes of multiple pane windows. Condensation on single pane windows can damage windowsill and wall surfaces if extensive. Condensation between the panes of multiple pane windows indicates a problem with the seal between the panes. (Source: Lawrence Berkeley Laboratory, 1999)

Condenser - The device in an air conditioner or heat pump in which the refrigerant condenses from a gas to a liquid when it is depressurized or cooled. (Source: US Department of Energy, 1999a).

Condenser Coil - The device in an air conditioner or heat pump through which the refrigerant is circulated and releases heat to the surroundings when a fan blows outside air over the coils. This will return the hot vapor that entered the coil into a hot liquid upon exiting the coil. (Source: US Department of Energy, 1999a).

Condensing Furnace - A type of heating appliance that extracts so much of the available heat content from a combusted fuel that the moisture in the combustion gases condenses before it leaves the furnace. Also this furnace circulates a liquid to cool the furnace's heat exchanger. The heated liquid may either circulate through a liquid-to-air heat exchanger to warm room air, or it may circulate through a coil inside a separate indirect-fired water heater. (Source: US Department of Energy, 1999a).

Condensing Unit - The component of a central air conditioner that is designed to remove heat absorbed by the refrigerant and transfer it outside the conditioned space. (Source: US Department of Energy, 1999a).

conditioned floor area - The floor area of enclosed conditioned spaces on all floors measured from the interior surfaces of exterior partitions for nonresidential buildings and from the exterior surfaces of exterior partitions for residential buildings. (Source: California Energy Commission, 1999a.)

Conduction - The transfer of heat through a material by the transfer of kinetic energy from particle to particle; the flow of heat between two materials of different temperatures that are in direct physical contact. (Source: US Department of Energy, 1999a).

Conductivity (Thermal) - This is a positive constant, k, that is a property of a substance and is used in the calculation of heat transfer rates for materials. It is the amount of heat that flows through a specified area and thickness of a material over a specified period of time when there is a temperature difference of one degree between the surfaces of the material. (Source: US Department of Energy, 1999a).

Conductor - The material through which electricity is transmitted, such as an electrical wire, or transmission or distribution line. (Source: US Department of Energy, 1999a).

Conduit - A tubular material used to encase and protect one or more electrical conductors. (Source: US Department of Energy, 1999a).

Conference of Parties (COP) - The supreme body of the United Nations Framework Convention on Climate Change (UNFCCC). It comprises more than 170 nations that have ratified the Convention. Its first session was held in Berlin, Germany, in 1995, and it is expected to continue meeting on a yearly basis. The COP’s role is to promote and review the implementation of the Convention. It will periodically review existing com-mitments in light of the Convention’s objective, new sci-entific findings, and the effectiveness of national climate change programs. See United Nations Framework Convention on Climate Change.(Source: US Environmental Protection Agency, 1999a)

congestion - A condition that occurs when insufficient transfer capacity is available to implement all of the preferred schedules simultaneously. (Source: California Energy Commission, 1999a.)

conifer - See coniferous trees.(Source: US Environmental Protection Agency, 1999a)

coniferous trees - Cone-bearing trees, mostly evergreens, that have needle-shaped or scale-like leaves. They produce wood known commercially as softwood. See deciduous trees.(Source: US Environmental Protection Agency, 1999a)

Connected Load - The sum of the ratings of the electricity consuming apparatus connected to a generating system. (Source: US Department of Energy, 1999a).

Connection Charge - An amount paid by a customer for being connected to an electricity supplier's transmission and distribution system. (Source: US Department of Energy, 1999a).

Conservation - To reduce or avoid the consumption of a resource or commodity. (Source: US Department of Energy, 1999a).

Conservation Cost Adjustment - A means of billing electric power consumers to pay for the costs of demand side management/energy conservation measures and programs. (See also Benefits Charge.) (Source: US Department of Energy, 1999a).

Constant dollars - A series of figures is expressed in constant dollars when the effect of change in the purchasing power of the dollar has been removed. Usually the data are expressed in terms of dollars of a selected year or the average of a set of years. (Source: Center for Transportation Analysis, 1999a)

Consumer Price Index (CPI) - An index issued by the U.S. Department of Labor, Bureau of Labor Statistics. The CPI is designed to measure changes in the prices of goods and services bought by wage earners and clerical workers in urban areas. It represents the cost of a typical consumption bundle at current prices as a ratio to its cost at a base year. (Source: Center for Transportation Analysis, 1999a)

Consumption Charge - The part of an energy utility's charge based on actual energy consumed by the customer; the product of the kilowatt-hour rate and the total kilowatt-hours consumed. (Source: US Department of Energy, 1999a).

Contact Resistance - The resistance between metallic contacts and the semiconductor. (Source: US Department of Energy, 1999a).

continental crust - The layer of the Earth that lies under continents and the continental shelves. It ranges in thickness from 35 to 60 km. Its upper layer has a density of 2.7 g/cm3 and is composed of rocks that are rich in silica and alumina. (Source: Carbon Dioxide Information Analysis Center, 1990a).

continental plate - A thick continental crust. (Source: Carbon Dioxide Information Analysis Center, 1990a).

continental shelves - Those parts of the continent that are covered by water. They are several to more than 322 km wide and about 122 m deep. At the edges of the shelves, the continental slopes drop rapidly from 100 to 200 m to 3000 to 3700 m. (Source: Carbon Dioxide Information Analysis Center, 1990a).

continental slopes - See continental shelves.

Contrast - The difference between the brightness of an object compared to that of its immediate background. (Source: US Department of Energy, 1999a).

convection - The transfer of heat by means of air currents.(Source: US Department of Energy, 1999a).

convection - Atmospheric or oceanic motions that are predominately vertical and that result in vertical transport and mixing of atmospheric or oceanic properties. Because the most striking meteorological features result if atmospheric convective motion occurs in conjunction with the rising current of air (i.e., updrafts), convection is sometimes used to imply only upward vertical motion. (Source: Carbon Dioxide Information Analysis Center, 1990a).

Conventions - The conventions, or treaties, are international environmental and related agreements that governments have ratified to achieve goals related to sustainable development. The Convention on Biological Diversity(CBD) and the Framework Convention on Climate Change(FCCC) have both adopted the GEF as their financial mechanism, and provide guidelines on policy, strategy, program priorities, and eligibility. The GEF has a complementary relationship with the Montreal Protocol on Substances that Deplete the Ozone Layer, and is a principal funding source for international and regional ocean and freshwater protection agreements. (Source: Global Environment Facility, 2000a).

Convention on Biological Diversity (CBD) - Signed by governments at the Rio Conference in 1992, the Convention is a legally binding agreement committing 169 governments to take action to stem the worldwide loss of biological diversity. It seeks to conserve biodiversity, provide for sustainable use, and give fair and equitable sharing of benefits from genetic resources. The GEF is the interim funding mechanism for the Convention and responds to the guidance of its COP. (Source: Global Environment Facility, 2000a).

Conventional Fuel - The fossil fuels: coal, oil, and natural gas. (Source: US Department of Energy, 1999a).

conventional gas - Natural gas occurring in nature, as opposed to synthetic gas. (Source: California Energy Commission, 1999a.)

Conventional Heat Pump - This type of heat pump is known as an air-to air system. (Source: US Department of Energy, 1999a).

Conversion Efficiency - The amount of energy produced as a percentage of the amount of energy consumed. (Source: US Department of Energy, 1999a).

Conversion Factor - A number that translates units of one system into corresponding values of another system. Conversion factors can be used to translate physical units of measure for various fuels into Btu equivalents. (Source: US Energy Information Administration, 2000a)

Converter - A device for transforming the quality and quantity of electrical energy; also an inverter. (Source: US Department of Energy, 1999a).

Cooling Capacity - The quantity of heat that a cooling appliance is capable of removing from a room in one hour. (Source: US Department of Energy, 1999a).

Cooling Degree Day - A value used to estimate interior air cooling requirements (load) calculated as the number of degrees per day (over a specified period) that the daily average temperature is above 65 degrees Fahrenheit (or some other, specified base temperature). The daily average temperature is the mean of the maximum and minimum temperatures recorded for a specific location for a 24 hour period. (Source: US Department of Energy, 1999a).

Cooling Load - That amount of cooling energy to be supplied (or heat and humidity removed) based on the sensible and latent loads. (Source: US Department of Energy, 1999a).

Cooling Pond - A body of water used to cool the water that is circulated in an electric power plant. (Source: US Department of Energy, 1999a).

Cooling Tower - A structure used to cool power plant water; water is pumped to the top of the tubular tower and sprayed out into the center, and is cooled by evaporation as it falls, and then is either recycled within the plant or is discharged. (Source: US Department of Energy, 1999a).

co-op. - This is the commonly used term for a rural electric cooperative. Rural electric cooperatives generate and purchase wholesale power, arrange for the transmission of that power, and then distribute the power to serve the demand of rural customers. Co-ops typically become involved in ancillary services such as energy conservation, load management and other demand-side management programs in order to serve their customers at least cost. (Source: California Energy Commission, 1999a.)

Coproducts - The potentially useful byproducts of ethanol fermentation process. (Source: US Department of Energy, 1999a).

Cord (of Wood) - A stack of wood 4 feet by 4 feet by 8 feet. (Source: US Department of Energy, 1999a).

Corporate Average Fuel Economy (CAFE) standards - CAFE standards were originally established by Congress for new automobiles, and later for light trucks, in Title V of the Motor Vehicle Information and Cost Savings Act (15 U.S.C. 1901, et seq.) with subsequent amendments. Under CAFE, automobile manufacturers are required by law to produce vehicle fleets with a composite sales-weighted fuel economy which cannot be lower than the CAFE standards in a given year, or for every vehicle which does not meet the standard, a fine of $5.00 is paid for every one-tenth of a mpg below the standard. (Source: Center for Transportation Analysis, 1999a)

Cost-effective - Actions or activities that reduce or save expenses and hence are effective in cutting costs. Achieving the best possible results though the least amount of expenditure; for example, the greatest possible reduction of carbon dioxide emissions at the lowest cost. (Source: Global Environment Facility, 2000a).

Cost sharing - Distributing the costs of projects, programs and activities between two or more sources so as to reduce the financial burden on any one of them. (Source: Global Environment Facility, 2000a).

Cost recovery - Achieving ways to regain the costs of or expenditures on an activity. (Source: Global Environment Facility, 2000a).

Coulomb - A unit for the quantity of electricity transported in 1 second by a current of 1 ampere. (Source: US Department of Energy, 1999a).

Counterflow Heat Exchanger - A heat exchanger in which two fluids flow in opposite directions for transfer heat energy from one to the other. (Source: US Department of Energy, 1999a).

Covenants - Restrictions on the use of a property. (Source: US Department of Energy, 1999a).

Crawlspace - The unoccupied, and usually unfinished and unconditioned space between the floor, foundation walls, and the slab or ground of a building.(Source: US Department of Energy, 1999a).

Creosote - A liquid byproduct of wood combustion (or distillation) that condenses on the internal surfaces of vents and chimneys, which if not removed regularly, can corrode the surfaces and fuel a chimney fire. (Source: US Department of Energy, 1999a).

crop residue - Organic residue remaining after the harvesting and pro-cessing of a crop.(Source: US Environmental Protection Agency, 1999a)

crop rotation - Planting the same field or areas of fields with different crops from year to year >.to reduce depletion of soil nutri-ents. Plants such as corn, tobacco, or cotton, which remove large amounts of nitrogen from the soil, are plant-ed one year. The next year legumes such as soybeans, which add nitrogen to the soil, are planted.(Source: US Environmental Protection Agency, 1999a)

crop water-use efficiency - Deposits, which includes the continental ice sheets, mountain glaciers, sea ice, surface snow cover, and lake and river ice. Changes in snow cover on the land surfaces are by and large seasonal and closely tied to the mechanics of atmospheric circulation. The glaciers and ice sheets are closely related to the global hydrologic cycle and to variations of sea level and change in volume and extent over periods ranging from hundreds to millions of years. (Source: Carbon Dioxide Information Analysis Center, 1990a).

cryosphere - One of the Earth's spheres of irregular form existing in the zone of interaction of the atmosphere, hydrosphere and lithosphere, distinguished by negative or zero temperature and the presence of water in the solid or super-cooled state. The term refers collectively to the portions of the Earth where water is in solid form. It includes snow cover, floating ice, glaciers, ice caps, ice sheets, seasonally frozen ground and perennially frozen ground (permafrost). (Source: NSIDC, Arctic Climatology and Meteorology)

Cubic Foot (of Natural Gas) - A unit of volume equal to 1 cubic foot at a pressure base of 14.73 pounds standard per square inch absolute and a temperature base of 60 degrees Fahrenheit. (Source: US Department of Energy, 1999a).

Current (Electrical) - The flow of electrical energy (electricity) in a conductor, measured in amperes. (Source: US Department of Energy, 1999a).

Current Dollars - The value or purchasing power of a dollar that has not been reduced to a common basis of constant purchasing power, but instead reflects anticipated future inflation; when used in computations the assumed inflation rate must be stated. (Source: US Department of Energy, 1999a).

Customer Charge - An amount to be paid for energy periodically by a customer without regard to demand or energy consumption. (Source: US Department of Energy, 1999a).

Customer Class - Categories of energy consumers, as defined by consumption or demand levels, patterns, and conditions, and generally included residential, commercial, industrial, agricultural. (Source: US Department of Energy, 1999a).

Cycle - In alternating current, the current goes from zero potential or voltage to a maximum in one direction, back to zero, and then to a maximum potential or voltage in the other direction. The number of complete cycles per second determines the current frequency; in the U.S. the standard for alternating current is 60 cycles. (Source: US Department of Energy, 1999a).

Cycling Losses - The loss of heat as the water circulates through a water heater tank and inlet and outlet pipes. (Source: US Department of Energy, 1999a).

Cyclone Burner - A furnace/combustion chamber in which finely ground fuel is blown in spirals in the combustion chamber to maximize combustion efficiency. (Source: US Department of Energy, 1999a).


D

Dam - A structure for impeding and controlling the flow of water in a water course, and which increases the water elevation to create the hydraulic head. The reservoir creates, in effect, stored energy. (Source: US Department of Energy, 1999a).

Damper - A movable plate used to control air flow; in a wood stove or fireplace, used to control the amount and direction of air going to the fire. (Source: US Department of Energy, 1999a).

Darrius (Wind) Machine - A type of vertical-axis wind machine that has long, thin blades in the shape of loops connected to the top and bottom of the axle; often called an "eggbeater windmill." (Source: US Department of Energy, 1999a).

Daylighting - The use of direct, diffuse, or reflected sunlight to provide supplemental lighting for building interiors. (Source: US Department of Energy, 1999a).

daylighting control - A control system that varies the light output of an electric lighting system in response to variations in available daylight. (Source: California Energy Commission, 1999a.)

De-energize(d) - To disconnect a transmission and/or distribution line; a power line that is not carrying a current; to open a circuit. (Source: US Department of Energy, 1999a).

Decentralized (Energy) System - Energy systems supply individual, or small-groups, of energy loads. (Source: US Department of Energy, 1999a).

deciduous trees - Trees such as oaks and maples that lose their leaves dur-ing part of the year. See coniferous trees.(Source: US Environmental Protection Agency, 1999a)

Declination - The angular position of the sun at solar noon with respect to the plane of the equator. (Source: US Department of Energy, 1999a).

Declining Block Rate - An electricity supplier rate structure in which the per unit price of electricity decreases as the amount of energy increases. Normally only available to very large consumers. (Source: US Department of Energy, 1999a).

Decommissioning - The process of removing a power plant, apparatus, equipment, building, or facility from operation. (Source: US Department of Energy, 1999a).

decomposers - Heterotrophic organisms that break down wastes and dead protoplasm and use some of the products and release others for use by consumer and producer organisms. Nutrients processed by decomposers are comprised of low energy molecules. (Source: Carbon Dioxide Information Analysis Center, 1990a).

decomposition - The breakdown of matter by bacteria and fungi. It changes the chemical makeup and physical appearance of materials. (Source: Carbon Dioxide Information Analysis Center, 1990a).

Deep Discharge - Discharging a battery to 20 percent or less of its full charge capacity. (Source: US Department of Energy, 1999a).

deep water - That part of the ocean below the main thermocline. (Source: Carbon Dioxide Information Analysis Center, 1990a).

deforestation - The removal of forest stands by cutting and/or burning to provide land for agricultural purposes, residential or industrial building sites, roads, etc. or by harvesting the trees for building materials or fuel. Oxidation of organic matter releases CO2 to the atmosphere, and regional and global climate impacts may result. (Source: Carbon Dioxide Information Analysis Center, 1990a).

Degree Day - A unit for measuring the extent that the outdoor daily average temperature (the mean of the maximum and minimum daily dry-bulb temperatures) falls below (in the case of heating, see Heating Degree Day), or falls above (in the case of cooling, see Cooling Degree Day) an assumed base temperature, normally taken as 65 degrees Fahrenheit, unless otherwise stated. One degree day is counted for each degree below (for heating) or above (in the case of cooling) the base, for each calendar day on which the temperature goes below or above the base. (Source: US Department of Energy, 1999a).

Degree Hour - The product of 1 hour, and usually the number of degrees Fahrenheit the hourly mean temperature is above a base point (usually 65 degrees Fahrenheit); used in roughly estimating or measuring the cooling load in cases where processes heat, heat from building occupants, and humidity are relatively unimportant compared to the dry-bulb temperature. (Source: US Department of Energy, 1999a).

Dehumidifier - A device that cools air by removing moisture from it. (Source: US Department of Energy, 1999a).

delta - A difference in temperature. Often used in the context of the difference between the design indoor temperature and the outdoor temperature. (Source: California Energy Commission, 1999a.)

Demand - The rate at which electricity is delivered to or by a system, part of a system, or piece of equipment expressed in kilowatts, kilovoltamperes, or other suitable unit, at a given instant or averaged over a specified period of time. (Source: US Department of Energy, 1999a).

Demand Charge - A charge for the maximum rate at which energy is used during peak hours of a billing period. That part of a utility service charged for on the basis of the possible demand as distinguished from the energy actually consumed. (Source: US Department of Energy, 1999a).

Demand(ed) Factor - The ratio of the maximum demand on an electricity generating and distribution system to the total connected load on the system; usually expressed as a percentage. (Source: US Department of Energy, 1999a).

Demand Power - see Peak Power (Source: US Department of Energy, 1999a).

Demand-Side Management (DSM) - The process of managing the consumption of energy, generally to optimize available and planned generation resources. (Source: US Department of Energy, 1999a).

Demand (Tankless) Water Heater - A type of water heater that has no storage tank thus eliminating storage tank standby losses. Cold water travels through a pipe into the unit, and either a gas burner or an electric element heats the water only when needed. (Source: US Department of Energy, 1999a).

demonstration - The application and integration of a new product or service into an existing or new system. Most commonly, demonstration involves the construction and operation of a new electric technology interconnected with the electric utility system to demonstrate how it interacts with the system. This includes the impacts the technology may have on the system and the impacts that the larger utility system might have on the functioning of the technology. (Source: California Energy Commission, 1999a.)

dendrochronology - The dating of past events and variations in the environment and the climate by studying the annual growth rings of trees. The approximate age of a temperate forest tree can be determined by counting the annual growth rings in the lower part of the trunk. The width of these annual rings is indicative of the climatic conditions during the period of growth; wide annual rings signify favorable growing conditions, absence of diseases and pests, and favorable climatic conditions, while narrow rings indicate unfavorable growing conditions or climate. (Source: Carbon Dioxide Information Analysis Center, 1990a).

dendroclimatology - The use of tree growth rings as proxy climate indicators. Tree rings record responses to a wider range of climatic variables over a larger part of the Earth than any other type of annually dated proxy record. (Source: Carbon Dioxide Information Analysis Center, 1990a).

density - The mass of a unit volume of a substance. (Source: California Energy Commission, 1999a.)

Dependable Capacity - The load-carrying ability of an electric power plant during a specific time interval and period when related to the characteristics of the load to be/being supplied; determined by capability, operating power factor, and the portion of the load the station is to supply. (Source: US Department of Energy, 1999a).

Derating - The production of energy by a system or appliance at a level less than its design or nominal capacity. (Source: US Department of Energy, 1999a).

Deregulation - The process of changing regulatory policies and laws to increase competition among suppliers of commodities and service. The process of deregulating the electric power industry was initiated by the Energy Policy Act of 1992. (See also Restructuring) (Source: US Department of Energy, 1999a).

derivatives - A specialized security or contract that has no intrinsic overall value, but whose value is based on an underlying security or factor as an index. A generic term that, in the energy field, may include options, futures, forwards, etc. (Source: California Energy Commission, 1999a.)

desertification - The progressive destruction or degradation of vegetative cover especially in arid or semiarid regions bordering existing deserts. Overgrazing of rangelands, large-scale cutting of forests and woodlands, drought, and burning of extensive areas all serve to destroy or degrade the land cover. The climatic impacts of this destruction include increased albedo leading to decreased precipitation, which in turn leads to less vegetative cover; increased atmospheric dust loading could lead to decreased monsoon rainfall and greater wind erosion and/or atmospheric pollution. (Source: Carbon Dioxide Information Analysis Center, 1990a).

Desiccant - A material used to desiccate (dry) or dehumidify air. (Source: US Department of Energy, 1999a).

Desiccant Cooling - To condition/cool air by dessication. (Source: US Department of Energy, 1999a).

Desiccation - The process of removing moisture; involves evaporation. (Source: US Department of Energy, 1999a).

Design Cooling Load - The amount of conditioned air to be supplied by a cooling system; usually the maximum amount to be delivered based on a specified number of cooling degree days or design temperature. (Source: US Department of Energy, 1999a).

Design Heating Load - The amount of heated air, or heating capacity, to be supplied by a heating system; usually the maximum amount to be delivered based on a specified number of heating degree days or design outside temperature. (Source: US Department of Energy, 1999a).

Design Life - Period of time a system or appliance (or component of) is expected to function at its nominal or design capacity without major repair. (Source: US Department of Energy, 1999a).

Design Temperature - The temperature that a system is designed to maintain (inside) or operate against (outside) under the most extreme conditions. (Source: US Department of Energy, 1999a).

Design Voltage - The nominal voltage for which a conductor or electrical appliance is designed; the reference voltage for identification and not necessarily the precise voltage at which it operates. (Source: US Department of Energy, 1999a).

Desuperheater - An energy saving device in a heat pump that, during the cooling cycle, recycles some of the waste heat from the house to heat domestic water. (Source: US Department of Energy, 1999a).

Dewpoint - The temperature to which air must be cooled, at constant pressure and water vapor content, in order for saturation or condensation to occur; the temperature at which the saturation pressure is the same as the existing vapor pressure; also called saturation point. (Source: US Department of Energy, 1999a).

diesel oil - Fuel for diesel engines obtained from the distillation of petroleum. It is composed chiefly of aliphatic hydrocarbons. Its volatility is similar to that of gas oil. Its efficiency is measured by cetane number. (Source: California Energy Commission, 1999a.)

Differential Thermostat - A type of automatic thermostat (used on solar heating systems) that responds to temperature differences (between collectors and the storage components) so as to regulate the functioning of appliances (to switch transfer fluid pumps on and off). (Source: US Department of Energy, 1999a).

Diffuse Solar Radiation - Sunlight scattered by atmospheric particles and gases so that it arrives at the earth's surface from all directions and can not be focused. (Source: US Department of Energy, 1999a).

Diffusion - The movement of individual molecules through a material; permeation of water vapor through a material. (Source: US Department of Energy, 1999a).

Digester (Anaerobic) - A device in which organic material is biochemically decomposed (digested) by anaerobic bacteria to treat the material and/or to produce biogas. (Source: US Department of Energy, 1999a).

Dimmer - A light control device that allows light levels to be manually adjusted. A dimmer can save energy by reducing the amount of power delivered to the light while consuming very little themselves. (Source: US Department of Energy, 1999a).

Dioxins - A classification of chlorine-containing compounds that are considered extremely toxic carcinogenic agents. Toxic effects include anorexia, hepatotoxicity, chloracne, vascular lesions, and gastric ulcers. Dioxins are byproducts in the manufacture of some chemicals. Causes of dioxin production in combustion begin with chlorine compounds in fuel, inadequate supply of combustion air, too low refractory temperatures, and improper mixing of fuel and air. (Source: US Energy Information Administration, 1997a.)

Dip Tube - A tube inside a domestic water heater that distributes the cold water from the cold water supply line into the lower area of the water heater where heating occurs. (Source: US Department of Energy, 1999a).

Diode - An electronic device that allows current to flow in one direction only. (Source: US Department of Energy, 1999a).

Direct Access - The ability of an electric power consumer to purchase electricity from a supplier of their choice without being physically inhibited by the owner of the electric distribution and transmission system to which the consumer is connected to. (See also Open Access.) (Source: US Department of Energy, 1999a).

Direct Beam Radiation - Solar radiation that arrives in a straight line from the sun. (Source: US Department of Energy, 1999a).

Direct Current - A type of electricity transmission and distribution by which electricity flows in one direction through the conductor; usually relatively low voltage and high current; typically abbreviated as dc. (Source: US Department of Energy, 1999a).

direct energy conversion - Production of electricity from an energy source without transferring the energy to a working fluid or steam. For example, photovoltaic cells transform light directly into electricity. Direct conversion systems have no moving parts and usually produce direct current. (Source: California Energy Commission, 1999a.)

direct expansion.(refrigeration) - Any system that, in operation between an environment where heat is absorbed (heat source), and an environment into which unwanted heat is directed (heat sink) at two different temperatures, is able to absorb heat from the heat source at the lower temperature and reject heat to the heat sink at the higher temperature. The cooling effect is obtained directly from a fluid called a refrigerant that absorbs heat at a low temperature and pressure, and transfers heat at a higher temperature and higher pressure. (Source: California Energy Commission, 1999a.)

Direct-Gain - The process by which sunlight directly enters a building through the windows and is absorbed and stored in massive floors or walls. (Source: US Department of Energy, 1999a).

direct radiation - Radiation that has traveled a straight path from the sun, as opposed to diffuse radiation. (Source: California Energy Commission, 1999a.)

direct solar gain - Solar energy collected from the sun (as heat) in a building through windows, walls, skylights, etc. (Source: California Energy Commission, 1999a.)

Direct Vent Heater - A type of combustion heating system in which combustion air is drawn directly from outside and the products of combustion are vented directly outside. These features are beneficial in tight, energy-efficient homes because they will not depressurize a home and cause air infiltration, and backdrafting of other combustion appliances. (Source: US Department of Energy, 1999a).

Direct Water Heater - A type of water heater in which heated water is stored within the tank. Hot water is released from the top of the tank when a hot water faucet is turned. This water is replaced with cold water that flows into the tank and down to just above the bottom plate under which are the burners. (Source: US Department of Energy, 1999a).

Discounting - A method of financial and economic analysis used to determine present and future values of investments or expenses. (Source: US Department of Energy, 1999a).

Discount Rate - The interest rate at which the Federal Reserve System stands ready to lend reserves to commercial banks. The rate is proposed by the 12 Federal Reserve banks and determined with the approval of the Board of Governors. (Source: US Department of Energy, 1999a).

Dispatching - To schedule and control the generation and delivery of electric power. (Source: US Department of Energy, 1999a).

Dispatchability - The ability to dispatch power. (Source: US Department of Energy, 1999a).

Displacement Power - A source of power (electricity) that can displace power from another source so that source's power can be transmitted to more distant loads. (Source: US Department of Energy, 1999a).

District Heat - Steam or hot water from an outside source used as an energy source in a building. The steam or hot water is produced in a central plant and is piped into the building. District heat may be purchased from a utility or provided by a physical plant in a separate building that is part of the same facility (for example, a hospital complex or university). (Source: US Energy Information Administration, 2000a)

Distributed Generation - A popular term for localized or on-site power generation. (Source: US Department of Energy, 1999a).

Distribution - The process of distributing electricity; usually defines that portion of an electrical utility's power lines between a utility's power pole and transformer and a customer's point of connection/meter. (Source: US Department of Energy, 1999a).

Distribution Feeder - (see Feeder) (Source: US Department of Energy, 1999a).

Distribution Line - One or more circuits of a distribution system on the same line or poles or supporting structures' usually operating at a lower voltage relative to the transmission line. (Source: US Department of Energy, 1999a).

Distribution System - That portion of an electricity supply system used to deliver electricity from points on the transmission system to consumers. (Source: US Department of Energy, 1999a).

District Heating - A heating system in which steam or hot water for space heating or hot water is piped from a central boiler plant or electric power/heating plant to a cluster of buildings. (Source: US Department of Energy, 1999a).

divestiture - The stripping off of one utility function from the others by selling (spinning-off) or in some other way changing the ownership of the assets related to that function. Most commonly associated with spinning-off generation assets so they are no longer owned by the shareholders that own the transmission and distribution assets. (See also "Disaggregation.") (Source: California Energy Commission, 1999a.)

Dobson Unit (DU) - a measurement of column ozone levels. If 100 DU of ozone were brought to the Earth's surface, it would form a layer 1 millimeter thick. In the tropics, ozone levels are typically between 250 and 300 DU year-round. In temperate regions, seasonal variations can produce large swings in ozone levels. For instance, measurements in Leningrad have recorded ozone levels as high as 475 DU and as low as 300 DU. These variations occur even in the absence of ozone depletion, but they are well understood. Ozone depletion refers to reductions in ozone below normal levels after accounting for seasonal cycles and other natural effects. For a graphical explanation, see NASA's TOMS site. (Source: US Environmental Protection Agency, 1999b).

Domestic Hot Water - Water heated for residential washing, bathing, etc. (Source: US Department of Energy, 1999a).

dose - The amount of ionizing radiation energy absorbed per unit mass of irradiated material at a specific location, such as a part of a human body. (Source: California Energy Commission, 1999a.)

Double-Pane or Glazed Window - A type of window having two layers (panes or glazing) of glass separated by an air space. Each layer of glass and surrounding air space reradiates and traps some of the heat that passes through thereby increasing the windows resistance to heat loss (R-value). (Source: US Department of Energy, 1999a).

Double Wall Heat Exchanger - A heat exchanger in a solar water heating system that has two distinct walls between the heat transfer fluid and the domestic water, to ensure that there is no mixing of the two. (Source: US Department of Energy, 1999a).

downwelling - The process of accumulation and sinking of warm surface waters along a coastline. A change of air flow of the atmosphere can result in the sinking or downwelling of warm surface water. The resulting reduced nutrient supply near the surface affects the ocean productivity and meteorological conditions of the coastal regions in the downwelling area. (Source: Carbon Dioxide Information Analysis Center, 1990a).

Draft - A column of burning combustion gases that are so hot and strong that the heat is lost up the chimney before it can be transferred to the house. A draft brings air to the fire to help keep it burning. (Source: US Department of Energy, 1999a).

Draft Diverter - A door-like device located at the mouth of a fireplace chimney flue for controlling the direction and flow of the draft in the fireplace as well as the amount of oxygen that the fire receives. (Source: US Department of Energy, 1999a).

Draft Hood - A device built into or installed above a combustion appliance to assure the escape of combustion byproducts, to prevent backdrafting of the appliance, or to neutralize the effects of the stack action of the chimney or vent on the operation of the appliance. (Source: US Department of Energy, 1999a).

Drainback (Solar) Systems - A closed-loop solar heating system in which the heat transfer fluid in the collector loop drains into a tank or reservoir whenever the booster pump stops to protect the collector loop from freezing. (Source: US Department of Energy, 1999a).

Draindown (Solar) Systems - An open-loop solar heating system in which the heat transfer fluid from the collector loop and the piping drain into a drain whenever freezing conditions occur. (Source: US Department of Energy, 1999a).

Dry Bulb Temperature - The temperature of the air as measured by a standard thermometer. (Source: US Department of Energy, 1999a).

Dry Steam Geothermal Plants - Conventional turbine generators are used with the dry steam resources. The steam is used directly, eliminating the need for boilers and boiler fuel that characterizes other steam-power-generating technologies. This technology is limited because dry-steam hydrothermal resources are extremely rare. The Geysers, in California, is the nation's only dry steam field. (Source: US Department of Energy, 1999a).

Dual Duct System - An air conditioning system that has two ducts, one is heated and the other is cooled, so that air of the correct temperature is provided by mixing varying amounts of air from each duct. (Source: US Department of Energy, 1999a).

Dual Fuel (or Flex Fuel) Vehicle - A vehicle with an engine capable of operating on two different types of fuels. (Source: US Department of Energy, 1999a).

Duct(s) - The round or rectangular tube(s), generally constructed of sheet metal, fiberglass board, or a flexible plastic-and-wire composite, located within a wall, floor, and ceiling that distributes heated or cooled air in buildings. (Source: US Department of Energy, 1999a).

Duct Fan - An axial flow fan mounted in a section of duct to move conditioned air. (Source: US Department of Energy, 1999a).

Duty Cycle - The duration and periodicity of the operation of a device. (Source: US Department of Energy, 1999a).

Dynamo - A machine for converting mechanical energy into electrical energy by magneto-electric induction; may be used as a motor. (Source: US Department of Energy, 1999a).

Dynamometer - An apparatus for measuring force or power, especially the power developed by a motor. (Source: US Department of Energy, 1999a).

Dyne - The absolute centimeter-gram-second unit of force; that force that will impart to a free mass of one gram an acceleration of one centimeter per second per second. (Source: US Department of Energy, 1999a).