Backdrafting - The flow of air down a flue/chimney and into a house caused by low indoor air pressure that can occur when using several fans or fireplaces and/or if the house is very tight.
Backup Energy System - A reserve appliance; for example, a standby generator for a home or commercial building.
Bacteria - Single-celled organisms, free-living or parasitic, that break down the wastes and bodies of dead organisms, making their components available for reuse by other organisms.
Baffle - A device, such as a steel plate, used to check, retard, or divert a flow of a material.
Bagasse - The fibrous material remaining after the extraction of juice from sugarcane; often burned by sugar mills as a source of energy.
Baghouse - An air pollution control device used to filter particulates from waste combustion gases; a chamber containing a bag filter.
Balance of System - In a solar energy system, refers to all components other than the collector. In terms of costs, it includes design costs, land, site preparation, system installation, support structures, power conditioning, operation and maintenance costs, indirect storage, and related costs.
Balance Point - An outdoor temperature, usually 20 to 45 degrees Fahrenheit, at which a heatpump's output equals the heating demand. Below the balance point, supplementary heat is needed.
Baling - A means of reducing the volume of a material by compaction into a bale.
Ballast - A device used to control the voltage in a fluorescent lamp.
Ballast Efficacy Factor - The measure of the efficiency of fluorescent lamp ballasts. It is the relative light output divided by the power input.
Ballast Factor - The ratio of light output of a fluorescent lamp operated on a ballast to the light output of a lamp operated on a standard or reference ballast.
Band Gap - In a semiconductor, the energy difference between the highest valence band and the lowest conduction band.
Band Gap Energy - The amount of energy (in electron volts) required to free an outer shell electron from its orbit about the nucleus to a free state, and thus promote it from the valence to the conduction level.
Barrel (petroleum) - 42 U.S. gallons (306 pounds of oil, or 5.78 million Btu).
Basal Metabolism - The amount of heat given off by a person at rest in a comfortable environment; approximately 50 Btu per hour (Btu/h).
Baseboard Radiator - A type of radiant heating system where the radiator is located along an exterior wall where the wall meets the floor.
Baseload Capacity - The power output of a power plant that can be continuously produced.
Baseload Demand - The minimum demand experienced by a power plant.
Baseload Power Plant - A power plant that is normally operated to generate a base load, and that usually operates at a constant load; examples include coal fired and nuclear fueled power plants.
Basement - The conditioned or unconditioned space below the main living area or primary floor of a building.
Base Power - Power generated by a utility unit that operates at a very high capacity factor.
Batch Process - A process for carrying out a reaction in which the reactants are fed in discrete and successive charges.
Batt/Blanket - A flexible roll or strip of insulating material in widths suited to standard spacings of building structural members (studs and joists). They are made from glass or rock wool fibers. Blankets are continuous rolls. Batts are pre-cut to four or eight foot lengths.
Battery - An energy storage device composed of one or more electrolyte cells.
Battery Energy Storage - Energy storage using electrochemical batteries. The three main applications for battery energy storage systems include spinning reserve at generating stations, load leveling at substations, and peak shaving on the customer side of the meter.
Beadwall (TM) - A form of movable insulation that uses tiny polystyrene beads blown into the space between two window panes.
Beam Radiation - Solar radiation that is not scattered by dust or water droplets.
Bearing Wall - A wall that carries ceiling rafters or roof trusses.
Benefits Charge -The addition of a per unit tax on sales of electricity, with the revenue generated used for or to encourage investments in energy efficiency measures and/or renewable energy projects.
Bimetal - Two metals of different coefficients of expansion welded together so that the piece will bend in one direction when heated, and in the other when cooled, and can be used to open or close electrical circuits, as in thermostats.
Binary Cycle - Combination of two power plant turbine cycles utilizing two different working fluids for power production. The waste heat from the first turbine cycle provides the heat energy for the operation of the second turbine, thus providing higher overall system efficiencies.
Binary Cycle Geothermal Plants - Binary cycle systems can be used with liquids at temperatures less than 350 F (177 C). In these systems, the hot geothermal liquid vaporizes a secondary working fluid, which then drives a turbine.
Bin Method - A method of predicting heating and/or cooling loads using instantaneous load calculation at different outdoor dry-bulb temperatures, and multiplying the result by the number of hours of occurrence of each temperature.
Biochemical Oxygen Demand - The weight of oxygen taken up mainly as a result of the oxidation of the constituents of a sample of water by biological action; expressed as the number of parts per million of oxygen taken up by the sample from water originally saturated with air, usually over a period of five days at 20 degrees centigrade. A standard means of estimating the degree of contamination of water.
Bioconversion - The conversion of one form of energy into another by the action of plants or microorganisms. The conversion of biomass to ethanol, methanol, or methane.
Bioenergy - The conversion of the complex carbohydrates in organic material into energy.
Biogas - A combustible gas created by anaerobic decomposition of organic material, composed primarily of methane, carbon dioxide, and hydrogen sulfide.
Biogasification or biomethanization - The process of decomposing biomass with anaerobic bacteria to produce biogas.
Biomass - any organic matter which is available on a renewable basis, including agricultural crops and agricultural wastes and residues, wood and wood wastes and residues, animal wastes, municipal wastes, and aquatic plants.
Biomass Energy - Energy produced by the conversion of biomass directly to heat or to a liquid or gas that can be converted to energy.
Biomass Fuel - Biomass converted directly to energy or converted to liquid or gaseous fuels such as ethanol, methanol, methane, and hydrogen.
Biomass Gasification - The conversion of biomass into a gas, by biogasification (see above) or thermal gasification, in which hydrogen is produced from high-temperature gasifying and low-temperature pyrolysis of biomass.
Biophotolysis - The action of light on a biological system that results in the dissociation of a substrate, usually water, to produce hydrogen.
Blackbody - An ideal substance that absorbs all radiation falling on it, and reflecting nothing.
Blower - The device in an air conditioner that distributes the filtered air from the return duct over the cooling coil/heat exchanger. This circulated air is cooled/heated and then sent through the supply duct, past dampers, and through supply diffusers to the living/working space.
Blower Door - A device used by energy auditors to pressurize a building to locate places of air leakage and energy loss.
Blown In Insulation (see also Loose Fill) - An insulation product composed of loose fibers or fiber pellets that are blown into building cavities or attics using special pneumatic equipment.
Boiler - A vessel or tank where heat produced from the combustion of fuels such as natural gas, fuel oil, or coal is used to generate hot water or steam for applications ranging from building space heating to electric power production or industrial process heat.
Boiler Feedwater - The water that is forced into a boiler to take the place of that which is evaporated in the generation of steam.
Boiler Horsepower - A unit of rate of water evaporation equal to the evaporation per hour of 34.5 pounds of water at a temperature of 212 degrees Fahrenheit into steam at 212 degrees F.
Boiler Pressure - The pressure of the steam or water in a boiler as measured; usually expressed in pounds per square inch gauge (psig).
Boiler Rating - The heating capacity of a steam boiler; expressed in Btu per hour (Btu/h), or horsepower, or pounds of steam per hour.
Bone (Oven) Dry - In reference to solid biomass fuels, such as wood, having zero moisture content.
Bone Dry Unit - A quantity of (solid) biomass fuel equal to 2,400 pounds bone dry.
Booster Pump - A pump for circulating the heat transfer fluid in a hydronic heating system.
Boot - In heating and cooling system distribution ductwork, the transformation pieces connecting horizontal round leaders to vertical rectangular stacks.
Boron - The chemical element commonly used as the dopant in solar photovoltaic device or cell material.
Bottled Gas - A generic term for liquefied and pressurized gas, ordinarily butane, propane, or a mixture of the two, contained in a cylinder for domestic use.
Bottoming-cycle - A means to increase the thermal efficiency of a steam electric generating system by converting some waste heat from the condenser into electricity. The heat engine in a bottoming cycle would be a condensing turbine similar in principle to a steam turbine but operating with a different working fluid at a much lower temperature and pressure.
Brayton Cycle - A thermodynamic cycle using constant pressure, heat addition and rejection, representing the idealized behavior of the working fluid in a gas turbine type heat engine.
Brine - Water saturated or strongly impregnated with salt.
British Thermal Unit (Btu) - The amount of heat required to raise the temperature of one pound of water one degree Fahrenheit; equal to 252 calories.
Building Energy Ratio - The space-conditioning load of a building.
Building Envelope - The structural elements (walls, roof, floor, foundation) of a building that encloses conditioned space; the building shell.
Building Heat-Loss Factor - A measure of the heating requirements of a building expressed in Btu per degree-day.
Building Orientation - The relationship of a building to true south, as specified by the direction of its longest axis.
Building Overall Energy Loss Coefficient-Area Product - The factor, when multiplied by the monthly degree-days, that yields the monthly space heating load.
Building Overall Heat Loss Rate - The overall rate of heat loss from a building by means of transmission plus infiltration, expressed in Btu per hour, per degree temperature difference between the inside and outside.
Bulb - The transparent or opaque sphere in an electric light that the electric light transmits through.
Bulb Turbine - A type of hydroturbine in which the entire generator is mounted inside the water passageway as an integral unit with the turbine. These installations can offer significant reductions in the size of the powerhouse.
Bulk Density - The weight of a material per unit of volume compared to the weight of the same volume of water.
Burner Capacity - The maximum heat output (in Btu per hour) released by a burner with a stable flame and satisfactory combustion.
Burning Point - The temperature at which a material ignites.
Bus (electrical) - An electrical conductor that serves as a common connection for two or more electrical circuits; may be in the form of rigid bars or stranded conductors or cables.
Busbar - The power conduit of an electric power plant; the starting point of the electric transmission system.
Busbar Cost - The cost of producing electricity up to the point of the powerplant busbar.
Bypass - An alternative path. In a heating duct or pipe, an alternative path for the flow of the heat transfer fluid from one point to another, as determined by the opening or closing of control valves both in the primary line and the bypass line.
Last Modified : 5/3/2021