CFM 50
CFM50 is the airflow needed to create a change in building pressure of 50 Pascals.
Combustion Appliance Zone


The component of an electric motor composed of solid bars (of usually copper or aluminum) arranged in a circle and connected to continuous rings at each end. This cage fits inside the stator in an induction motor in channels between laminations, thin flat discs of steel in a ring configuration.


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.

Calorific Value

The heat liberated by the combustion of a unit quantity of a fuel under specific conditions; measured in calories.


The luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency 540 × 1012 hertz and that has a radiant intensity in that direction of 1/683 watt per steradian.

Candle Power

The illuminating power of a standard candle employed as a unit for determining the illuminating quality of an illuminant.


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.

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.


A measure of the electrical charge of a capacitor consisting of two plates separated by an insulating material.


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.


The load that a power generation unit or other electrical apparatus or heating unit is rated by the manufacture to be able to meet or supply.

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.

Capacity (Effective, of a motor)

The maximum load that a motor is capable of supplying.

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.

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.

Capital Costs

The amount of money needed to purchase equipment, buildings, tools, and other manufactured goods that can be used in production.

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.

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.

Carbon Zinc Cell Battery

A cell produces electric energy by the galvanic oxidation of carbon; commonly used in household appliances.

Carnot Cycle

An ideal heat engine (conceived by Sadi Carnot) in which the sequence of operations forming the working cycle consists of isothermal expansion, adiabatic expansion, isothermal compression, and adiabatic compression back to its initial state.

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.

Cathedral Ceiling/Roof

A type of ceiling and roof assembly that has no attic.


The negative pole or electrode of an electrolytic cell, vacuum tube, etc., where electrons enter (current leaves) the system; the opposite of an anode.

Cathode Disconnect Ballast

An electromagnetic ballast that disconnects a lamp’s electrode heating circuit once is has started; often called “low frequency electronic” ballasts.

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.


A material used to seal areas of potential air leakage into or out of a building envelope.


The downward facing structural element that is directly opposite the floor.

Ceiling Fan

A mechanical device used for air circulation and to provide cooling.


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.


An enzyme complex, produced by fungi and bacteria, capable of decomposing cellulose into small fragments, primarily glucose.


The fundamental constituent of all vegetative tissue; the most abundant material in the world.

Cellulose Insulation

A type of insulation composed of waste newspaper, cardboard, or other forms of waste paper.

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.

Central Power Plant

A large power plant that generates power for distribution to multiple customers.

Central Receiver Solar Power Plants

Also known as “power towers,” these use fields of two-axis tracking mirrors known as heliostats. Each heliostat is individually positioned by a computer control system to reflect the sun’s rays to a tower-mounted thermal receiver. The effect of many heliostats reflecting to a common point creates the combined energy of thousands of suns, which produces high-temperature thermal energy. In the receiver, molten nitrate salts absorb the heat energy. The hot salt is then used to boil water to steam, which is sent to a conventional steam turbine-generator to produce electricity.

Cetane Number

A measure of a fuel’s (liquid) ease of self-ignition.


A byproduct of low-temperature carbonization of a solid fuel.


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.

Charge Carrier

A free and mobile conduction electron or hole in a semiconductor.

Charge Controller

An electronic device that regulates the electrical charge stored in batteries so that unsafe, overcharge conditions for the batteries are avoided.

Chemical Energy

The energy liberated in a chemical reaction, as in the combustion of fuels.

Chemical Vapor Deposition (CVD)

A method of depositing thin semiconductor films used to make certain types of solar photovoltaic devices. With this method, a substrate is exposed to one or more vaporized compounds, one or more of which contain desirable constituents. A chemical reaction is initiated, at or near the substrate surface, to produce the desired material that will condense on the substrate.


A device for removing heat from a gas or liquid stream for air conditioning/cooling.


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.

Chimney Effect

The tendency of heated air or gas to rise in a duct or other vertical passage, such as in a chimney, small enclosure, or building, due to its lower density compared to the surrounding air or gas.

Chlorofluorocarbon (CFC)

A family of chemicals composed primarily of carbon, hydrogen, chlorine, and fluorine whose principal applications are as refrigerants and industrial cleansers and whose principal drawback is the tendency to destroy the Earth’s protective ozone layer.


A device, or system of devices, that allows electrical current to flow through it and allows voltage to occur across positive and negative terminals.

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.

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.

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.

Clean Power Generator

A company or other organizational unit that produces electricity from sources that are thought to be environmentally cleaner than traditional sources. Clean, or green, power is usually defined as power from renewable energy that comes from wind, solar, biomass energy, etc. There are various definitions of clean resources. Some definitions include power produced from waste-to-energy and wood-fired plants that may still produce significant air emissions. Some states have defined certain local resources as clean that other states would not consider clean. For example, the state of Texas has defined power from efficient natural gas-fired power plants as clean. Some northwest states include power from large hydropower projects as clean although these projects damage fish populations. Various states have disclosure and labeling requirement for generation source and air emissions that assist customers in comparing electricity characteristics other than price. This allows customers to decide for themselves what they consider to be “clean.” The federal government is also exploring this issue.

Cleavage of Lateral Epitaxial Films for Transfer (CLEFT)

A process for making inexpensive Gallium Arsenide (GaAs) photovoltaic cells in which a thin film of GaAs is grown atop a thick, single-crystal GaAs (or other suitable material) substrate and then is cleaved from the substrate and incorporated into a cell, allowing the substrate to be reused to grow more thin-film GaAs.


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.


The prevailing or average weather conditions of a geographic region.

Climate Change

A term used to describe short and long-term affects on the Earth’s climate as a result of human activities such as fossil fuel combustion and vegetation clearing and burning.

Close Coupled

An energy system in which the fuel production equipment is in close proximity, or connected to, the fuel using equipment.

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.

Closed-Loop Geothermal Heat Pump Systems

Closed-loop (also known as “indirect”) systems circulate a solution of water and antifreeze through a series of sealed loops of piping. Once the heat has been transferred into or out of the solution, the solution is recirculated. The loops can be installed in the ground horizontally or vertically, or they can be placed in a body of water, such as a pond. See horizontal ground loopvertical ground loopslinky ground loop, and surface water loop for more information on the different types of closed-loop geothermal heat pump systems.

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.


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.

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).

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.

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.

Coincidence Factor

The ratio of the coincident, maximum demand or two or more loads to the sum of their noncoincident maximum demand for a given period; the reciprocal of the diversity factor, and is always less than or equal to one.

Coincident Demand

The demand of a consumer of electricity at the time of a power supplier’s peak system demand.


The use of two or more different fuels (e.g. wood and coal) simultaneously in the same combustion chamber of a power plant.


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.


A class of energy producer that produces both heat and electricity from a single fuel.


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.

Cold Night Sky

The low effective temperature of the sky on a clear night.


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).

Collector Efficiency

The ratio of solar radiation captured and transferred to the collector (heat transfer) fluid.

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.

Collector Tilt

The angle that a solar collector is positioned from horizontal.

Color Rendering or Rendition

A measure of the ability of a light source to show colors, based on a color rendering index.

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.

Color Temperature

A measure of the quality of a light source by expressing the color appearance correlated with a black body.

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.


The process of burning; the oxidation of a material by applying heat, which unites oxygen with a material or fuel.

Combustion Air

Air that provides the necessary oxygen for complete, clean combustion and maximum heating value.

Combustion Chamber

Any wholly or partially enclosed space in which combustion takes place.

Combustion Gases

The gaseous byproducts of the combustion of a fuel.

Combustion Power Plant

A power plant that generates power by combusting a fuel.

Combustion Turbine

A turbine that generates power from the combustion of a fuel.

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.

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.

Comfort Zone

A frequently used room or area that is maintained at a more comfortable level than the rest of the house; also known as a “warm room.”


The process by which a power plant, apparatus, or building is approved for operation based on observed or measured operation that meets design specifications.

Compact Fluorescent

A smaller version of standard fluorescent lamps which can directly replace standard incandescent lights. These lights consist of a gas filled tube, and a magnetic or electronic ballast.

Complete Mix Digester

A type of anaerobic digester that has a mechanical mixing system and where temperature and volume are controlled to maximize the anaerobic digestion process for biological waste treatment, methane production, and odor control.


The process of degrading organic material (biomass) by microorganisms in aerobic conditions.

Composting Toilet

A self-contained toilet that use the process of aerobic decomposition (composting) to break down feces into humus and odorless gases.

Compound Paraboloid Collector

A form of solar concentrating collector that does not track the sun.

Compressed Air Storage

The storage of compressed air in a container for use to operate a prime mover for electricity generation.

Compressed Natural Gas (CNG)

Natural gas (methane) that has been compressed to a higher pressure gaseous state by a compressor; used in CNG vehicles.

Compression Chiller

A cooling device that uses mechanical energy to produce chilled water.


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.

Concentrating (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. Concentrating collectors for home or small business solar water heating applications are usually parabolic troughs that concentrate the sun’s energy on an absorber tube (called a receiver), which contains a heat-transfer fluid.


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.


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.


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.

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.

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.

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.

Conditioned Space

The interior space of a building that is heated or cooled.


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.

Conduction Band

An energy band in a semiconductor in which electrons can move freely in a solid, producing a net transport of charge.

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.


The material through which electricity is transmitted, such as an electrical wire, or transmission or distribution line.


A tubular material used to encase and protect one or more electrical conductors.

Congressional (Energy) Committees:

House Subcommittee on Energy and Environment — This committee has legislative jurisdiction and general and special oversight and investigative authority on all matters relating to energy and environmental research and development and demonstration.House Water and Power Committee — This committee has oversight over the generation and marketing of electric power from federal water projects by federally charted or Federal RPM authorities, measures and matters concerning water resources planning, compacts relating to use and apportionment of interstate waters, water rights or power movement programs, measures and matters pertaining to irrigation and reclamation projects and other water resources development programs.

Senate Committee on Energy and Natural Resources — This committee has jurisdiction on: coal production, distribution and utilization; energy policy; energy research, conservation, and development; hydroelectric power; irrigation; mineral conservation; nonmilitary development of nuclear energy; solar energy systems; and over territorial possessions, including trusteeships of the United States.
Senate Subcommittee on Energy Research, Development, Production and Regulation — This committee has jurisdiction on the oversight and legislative responsibilities for: coal, nuclear, and non-nuclear energy commercialization projects; DOE National Laboratories; global climate change; new technologies research and development; commercialization of new technologies including, solar energy systems; Federal energy conservation programs; energy information; and power provider policy.
Connection Charge
An amount paid by a customer for being connected to an electricity supplier’s transmission and distribution system.


To reduce or avoid the consumption of a resource or commodity.

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.)

Constant Dollars

The value or purchasing power of a dollar in a specified year carried forward or backward.

Constant-Speed Wind Turbines

Wind turbines that operate at a constant rotor revolutions per minute (RPM) and are optimized for energy capture at a given rotor diameter at a particular speed in the wind power curve.

Consumption Charge

The part of a power provider’s charge based on actual energy consumed by the customer; the product of the kilowatt-hour rate and the total kilowatt-hours consumed.

Contact Resistance

The resistance between metallic contacts and the semiconductor.

Continuous Fermentation

A steady-state fermentation process.


The difference between the brightness of an object compared to that of its immediate background.


The transfer of heat by means of air currents.

Conventional Fuel

The fossil fuels: coal, oil, and natural gas.

Conventional Heat Pump

This type of heat pump is known as an air-to air system.

Conventional Power

Power generation from sources such as petroleum, natural gas, or coal. In some cases, large-scale hydropower and nuclear power generation are considered conventional sources.

Conversion Efficiency

The amount of energy produced as a percentage of the amount of energy consumed.


A device for transforming the quality and quantity of electrical energy; also an inverter.

Cooling Capacity

The quantity of heat that a cooling appliance is capable of removing from a room in one hour.

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.

Cooling Load

That amount of cooling energy to be supplied (or heat and humidity removed) based on the sensible and latent loads.

Cooling Pond

A body of water used to cool the water that is circulated in an electric power plant.

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.


The potentially useful byproducts of ethanol fermentation process.

Cord (of Wood)

A stack of wood 4 feet by 4 feet by 8 feet.


A unit for the quantity of electricity transported in 1 second by a current of 1 ampere.

Counterflow Heat Exchanger

A heat exchanger in which two fluids flow in opposite directions for transfer heat energy from one to the other.


Restrictions on the use of a property.


The unoccupied, and usually unfinished and unconditioned space between the floor, foundation walls, and the slab or ground of a building.


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.

Critical Compression Pressure

The highest possible pressure in a fuel-air mixture before spontaneous ignition occurs.

Crystalline Silicon Photovoltaic Cell

A type of photovoltaic cell made from a single crystal or a polycrystalline slice of silicon. Crystalline silicon cells can be joined together to form a module (or panel).

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.

Cube Law

In reference to wind energy, for any given instant, the power available in the wind is proportional to the cube of the wind velocity; when wind speed doubles, the power availability increases eight times.

Current (Electrical)

The flow of electrical energy (electricity) in a conductor, measured in amperes.

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.

Customer Charge

An amount to be paid for energy periodically by a customer without regard to demand or energy consumption.

Customer Class

Categories of energy consumers, as defined by consumption or demand levels, patterns, and conditions, and generally included residential, commercial, industrial, agricultural.


The lowest wind speed at which a wind turbine begins producing usable power.


The highest wind speed at which a wind turbine stops producing power.


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.

Cycling Losses

The loss of heat as the water circulates through a water heater tank and inlet and outlet pipes.

Cyclone Burner

A furnace/combustion chamber in which finely ground fuel is blown in spirals in the combustion chamber to maximize combustion efficiency.

Czochralski Process

A method of growing large size, high quality semiconductor crystal by slowly lifting a seed crystal from a molten bath of the material under careful cooling conditions.