Glossary
G-H
Last Updated Monday, July 24, 2000
compiled by Nick Sundt


G, H



G

Gallium Arsenide - A compound used to make certain types of solar photovoltaic cells. (Source: US Department of Energy, 1999a).

gallon - A unit of volume. A U.S. gallon has 231 cubic inches or 3.785 liters. (Source: California Energy Commission, 1999a.)

gas - Gaseous fuel (usually natural gas) that is burned to produce heat energy. The word also is used, colloquially, to refer to gasoline. (Source: California Energy Commission, 1999a.)

Gas fill (window efficiency Terminology) - An inert gas such as argon is used instead of air between the window panes. Inert gases have a much better insulation value than air. (Source: Lawrence Berkeley Laboratory, 1999)

Gas Guzzler Tax - Originates from the 1978 Energy Tax Act (Public Law 95-618). A new car purchaser is required to pay the tax if the car purchased has a combined city/highway fuel economy rating that is below the standard for that year. For model years 1986 and later, the standard is 22.5 mpg. (Source: Center for Transportation Analysis, 1999a)

gas utility - any person engaged in, or authorized to engage in, distributing or transporting natural gas, including, but not limited to, any such person who is subject to the regulation of the Public Utilities Commission. (Source: California Energy Commission, 1999a.)

Gasification - The process in which a solid fuel is converted into a gas; also known as pyrolitic distillation or pyrolysis. Production of a clean fuel gas makes a wide variety of power options available. (Source: US Department of Energy, 1999a).

Gasifier - A device for converting a solid fuel to a gaseous fuel. (Source: US Department of Energy, 1999a).

Gasket/Seal - A seal used to prevent the leakage of fluids, and also maintain the pressure in an enclosure. (Source: US Department of Energy, 1999a).

Gasohol - A registered trademark of an agency of the state of Nebraska, for an automotive fuel containing a blend of 10 percent ethanol and 90 percent gasoline. (Source: US Department of Energy, 1999a).

Gasoline - A refined petroleum product suitable for use as a fuel in internal combustion engines. (Source: US Department of Energy, 1999a).

Gas Turbine - A type of turbine in which combusted, pressurized gas is directed against a series of blades connected to a shaft, which forces the shaft to turn to produce mechanical energy. (Source: US Department of Energy, 1999a).

Gauss - The unit of magnetic field intensity equal to 1 dyne per unit pole. (Source: US Department of Energy, 1999a).

general aviation - That portion of civil aviation, which encompasses all facets of aviation except air carriers. It includes any air taxis, commuter air carriers, and air travel clubs, which do not hold Certificates of Public Convenience and Necessity. See air carriers.(Source: US Environmental Protection Agency, 1999a)

General Circulation Model (GCM) - A global, three-dimensional computer model of the cli-mate system which can be used to simulate human-induced climate change. GCMs are highly complex and they represent the effects of such factors as reflective and absorptive properties of atmospheric water vapor, greenhouse gas concentrations, clouds, annual and daily solar heating, ocean temperatures and ice boundaries. The most recent GCMs include global representations of the atmosphere, oceans, and land surface.(Source: US Environmental Protection Agency, 1999a)

general lighting - Lighting designed to provide a substantially uniform level of illumination throughout an area, exclusive of any provision for special visual tasks or decorative effects. (Source: California Energy Commission, 1999a.)

generating station - A power plant. (Source: California Energy Commission, 1999a.)

generation company (Genco) - A regulated or non-regulated entity (depending upon the industry structure) that operates and maintains existing generating plants. The Genco may own the generation plants or interact with the short term market on behalf of plant owners. In the context of restructuring the market for electricity, Genco is sometimes used to describe a specialized "marketer" for the generating plants formerly owned by a vertically-integrated utility. (Source: California Energy Commission, 1999a.)

generation dispatch and control - Aggregating and dispatching (sending off to some location) generation from various generating facilities, providing backups and reliability services. Ancillary services include the provision of reactive power, frequency control, and load following. (Also see "Power Pool" and "Poolco" below.) (Source: California Energy Commission, 1999a.)

Generator - A device for converting mechanical energy to electrical energy. (Source: US Department of Energy, 1999a).

Generator Nameplate Capacity - The full-load continuous rating of a generator, prime mover, or other electric power production equipment under specific conditions as designated by the manufacturer. Installed generator nameplate rating is usually indicated on a nameplate physically attached to the generator. (Source: US Energy Information Administration, 1999b)

Geographic Information System (GIS) - Spatially derived information presented in map form to assist in planning and management of environmental resources. (Source: Global Environment Facility, 2000a).

geomorphology - The study of present-day landforms, including their classification, description, nature, origin, development, and relationships to underlying structures. Also the history of geologic changes as recorded by these surface features. The term is sometimes restricted to features produced only by erosion and deposition. (Source: Carbon Dioxide Information Analysis Center, 1990a).

Geopressurized Brines - These brines are hot (300 F to 400 F) (149 C to 204 C) pressurized waters that contain dissolved methane and lie at depths of 10,000 ft (3048 m) to more than 20,000 ft (6096 m) below the earth's surface. The best known geopressured reservoirs lie along the Texas and Louisiana Gulf Coast. At least three types of energy could be obtained: thermal energy from high-temperature fluids; hydraulic energy from the high pressure; and chemical energy from burning the dissolved methane gas. (Source: US Department of Energy, 1999a).

geosphere - The solid mass (lithosphere) of the Earth as distinct from the atmosphere and hydrosphere or all three of these layers combined. (Source: Carbon Dioxide Information Analysis Center, 1990a).

Geothermal Energy - Energy produced by the internal heat of the earth; geothermal heat sources include: hydrothermal convective systems; pressurized water reservoirs; hot dry rocks; manual gradients; and magma. Geothermal energy can be used directly for heating or to produce electric power. (Source: US Department of Energy, 1999a).

Geothermal Heat Pump - A type of heat pump that uses the ground, ground water, or ponds as a heat source and heat sink, rather than outside air. Ground or water temperatures are more constant and are warmer in winter and cooler in summer than air temperatures. Geothermal heat pumps operate more efficiently than "conventional" or "air source" heat pumps. (Source: US Department of Energy, 1999a).

Geothermal Power Station - An electricity generating facility that uses geothermal energy. (Source: US Department of Energy, 1999a).

Giga - One billion.

Gigawatt (GW) - A unit of power equal to 1 billion Watts; 1 million kilowatts, or 1,000 megawatts. (Source: US Department of Energy, 1999a).

Gigawatt-Hour (GWH) - One million kilowatt-hours of electric power. (Source: California Energy Commission, 1999a.)

glacial maximum - The position or time of the greatest advance of a glacier (e.g., the greatest equatorward advance of Pleistocene glaciation). (Source: Carbon Dioxide Information Analysis Center, 1990a).

glacial rebound - The isostatic adjustment of previously glaciated areas after glacial retreat (e.g., the uplift of Scandinavia after the most recent glaciation). (Source: Carbon Dioxide Information Analysis Center, 1990a).

glacier - A mass of land ice that is formed by the cumulative recrystallization of firn. A glacier flows slowly (at present or in the past) from an accumulation area to an ablation area. Some well-known glaciers are: the Zermatt, Stechelberg, Grindelwald, Trient, Les Diablerets, and Rhone in Switzerland; the Nigards, Gaupne, Fanarak, Lom, and Bover in Norway; the Wright, Taylor, and Wilson Piedmont glaciers in Antarctica; the Bossons glacier in France; the Emmons and Nisqually glaciers on Mt. Ranier, Washington; Grinnell glacier in Glacier National Park, Montana; the Dinwoody glacier in the Wind River Mountains and the Teton glacier in Teton National Park, both in Wyoming; and many glaciers in the Canadian Rockies. (Source: Carbon Dioxide Information Analysis Center, 1990a).

glacier flow (ice flow) - The slow downward or outward movement of ice in a glacier caused by gravity. (Source: Carbon Dioxide Information Analysis Center, 1990a).

Glare - The discomfort or interference with visual perception when viewing a bright object against a dark background. (Source: US Department of Energy, 1999a).

Glauber's Salt - A salt, sodium sulfate decahydrate, that melts at 90 degrees Fahrenheit; a component of eutectic salts that can be used for storing heat. (Source: US Department of Energy, 1999a).

Glazing - A term used for the transparent or translucent material in a window. This material (i.e. glass, plastic films, coated glass) is used for admitting solar energy and light through windows. (Source: US Department of Energy, 1999a).

Global Commons - The natural resources and vital life-support services, such as the earth’s climate system, ozone layer, and oceans and seas, that belong to all humankind rather than to any one country or private enterprise

Global Environment Facility (GEF) - The multi-billion-dollar GEF was established by the World Bank, the UN Development Programme, and the UN Environment Programme in 1990. It operates the UN Climate Convention's "financial mechanism" on an interim basis and funds developing country projects that have global climate change benefits. (Source: UN Climate Change Secretariat, 1999a)

Global Insolation (or Solar Radiation) - The total diffuse and direct insolation on a horizontal surface, averaged over a specified period of time. (Source: US Department of Energy, 1999a).

Global Warming - A popular term used to describe the increase in average global temperatures due to the greenhouse effect. (Source: US Department of Energy, 1999a).

Global Warming Potential (GWP) - The index used to translate the level of emissions of various gases into a common measure in order to compare the relative radiative forcing of different gases without directly calculating the changes in atmospheric concentrations. GWPs are calculated as the ratio of the radiative forcing that would result from the emissions of one kilogram of a greenhouse gas to that from the emission of one kilogram of carbon dioxide over a period of time (usually 100 years). Gases involved in complex atmospheric chemical processes have not been assigned GWPs. The GWP of CO2 is defined to be 1.0 . CFC-12 has a GWP of 8,500, while CFC-11 has a GWP of 5,000. Various HCFCs and HFCs have GWPs ranging from 93 to 12,100. Water, a substitute in numerous end-uses, has a GWP of 0. A table of all ozone-depleting substances shows their ODPs, GWPs, and CAS numbers, and another table shows the GWPs for many non-ozone-depleting substances. (Source: US Environmental Protection Agency, 1999a and 1999b)

Governor - A device used to regulate motor speed, or, in a wind energy conversion system, to control the rotational speed of the rotor. (Source: US Department of Energy, 1999a).

grassland - Terrestrial ecosystem (biome) found in regions where moderate annual average precipitation (25 to 76 cen-timeters or 10 to 30 inches) is enough to support the growth of grass and small plants but not enough to sup-port large stands of trees.(Source: US Environmental Protection Agency, 1999a)

Grain Alcohol - Ethanol. (Source: US Department of Energy, 1999a).

Green Pricing - In the case of renewable electricity, green pricing represents a market solution to the various problems associated with regulatory valuation of the nonmarket benefits of renewables. Green pricing programs allow electricity customers to express their willingness to pay for renewable energy development through direct payments on their monthly utility bills. (Source: US Energy Information Administration, 1997a.)

greenhouse effect - A popular term used to describe the roles of water vapor, carbon dioxide, and other trace gases in keeping the Earth's surface warmer than it would be otherwise. These " radiatively active" gases are relatively transparent to incoming shortwave radiation, but are relatively opaque to outgoing longwave radiation. The latter radiation, which would otherwise escape to space, is trapped by these gases within the lower levels of the atmosphere. The subsequent re-radiation of some of the energy back to the surface maintains surface temperatures higher than they would be if the gases were absent. There is concern that increasing concentrations of greenhouse gases, including carbon dioxide, methane, and anthropogenic chlorofluorocarbons, may enhance the greenhouse effect and cause global warming. (Source: Carbon Dioxide Information Analysis Center, 1990a).

greenhouse gases (GHG) - Those gases, such as water vapor, carbon dioxide, tropospheric ozone, nitrous oxide, and methane, that are transparent to solar radiation but opaque to longwave radiation. Their action is similar to that of glass in a greenhouse. Also see greenhouse effect and trace gas. (Source: Carbon Dioxide Information Analysis Center, 1990a).

Greenland Ice Sheet - See ice sheet. (Source: Carbon Dioxide Information Analysis Center, 1990a).

Greenwood - Freshly cut, unseasoned, wood. (Source: US Department of Energy, 1999a).

Green Power - A popular term for energy produced from renewable energy resources. (Source: US Department of Energy, 1999a).

Green Pricing and Marketing - To price and sell green power/electricity higher than that produced from fossil or nuclear power plants, supposedly because some buyers are willing to pay a premium for green power. (Source: US Department of Energy, 1999a).

Greywater - Waste water from a household source other than a toilet. This water can be used for landscape irrigation depending upon the source of the greywater. (Source: US Department of Energy, 1999a).

Grid - A common term referring to an electricity transmission and distribution system. (Source: US Department of Energy, 1999a).

Gross Calorific Value - The heat produced by combusting a specific quantity and volume of fuel in an oxygen-bomb colorimeter under specific conditions. (Source: US Department of Energy, 1999a).

Gross Generation - The total amount of electricity produced by a power plant. (Source: US Department of Energy, 1999a).

Gross National Product (GNP) - The total market value of the goods and services produced by a nation before deduction or depreciation charges and other allowance for capital consumption and is widely used as a measure of economic activity.

Ground - A device used to protect the user of any electrical system or appliance from shock. (Source: US Department of Energy, 1999a).

ground cover - Plants occurring naturally or planted to prevent soil from eroding and nutrient loss. Examples of ground cover include mosses, annuals and perennials, small shrubs in forests, grasses, and agricultural crops. Primary succession in which communities are established in newly formed habitats is often longer and slower than secondary succession in which communities are re-established in areas where they were destroyed. Plants covering the ground may vary at different stages of succession. (Source: Carbon Dioxide Information Analysis Center, 1990a).

Ground Reflection - Solar radiation reflected from the ground onto a solar collector. (Source: US Department of Energy, 1999a).

Ground-Source Heat Pump - (see geothermal systems) (Source: US Department of Energy, 1999a).

grounding line - The boundary between the area where an ice shelf or a glacier is floating on water and where it is in contact with the shore or underlying earth (grounded). (Source: Carbon Dioxide Information Analysis Center, 1990a).

groundwater - The supply of fresh water found beneath the surface of the Earth (usually in aquifers) that often supplies wells and springs. (Source: Carbon Dioxide Information Analysis Center, 1990a).

Group of Eight(G-8) - The eight industrialized countries—the United States, Canada, Japan, the United Kingdom, France, Germany, Italy, and Russia. (Source: Global Environment Facility, 2000a).

Group of 77 and China - The G-77 was founded in 1967 under the auspices of the United Nations Conference for Trade and Development (UNCTAD). It seeks to harmonize the negotiating positions of its 132 developing-country members. (Source: UN Climate Change Secretariat, 1999a)

gyres - Major circular flow patterns in the oceans. The wind-driven eastward- and westward-flowing equatorial currents are blocked by the continents and rotate slowly in a clockwise direction in the North Atlantic and Pacific Oceans and in a counter-clockwise direction in the South Atlantic, South Pacific, and Indian Oceans. (Source: Carbon Dioxide Information Analysis Center, 1990a).


H

Habitat - The place where a population(e.g. human, animal, plant, micro-organism) lives and its surroundings, both living and non-living. (Source: Global Environment Facility, 2000a).

halocarbons - Chemicals consisting of carbon, sometimes hydrogen, and either chlorine, fluorine, bromine or iodine.(Source: US Environmental Protection Agency, 1999a)

halocline - In the oceans, a well-defined vertical gradient of salinity. (Source: Carbon Dioxide Information Analysis Center, 1990a).

halons - a compound consisting of bromine, fluorine, and carbon. The halons are used as fire extinguishing agents, both in built-in systems and in handheld portable fire extinguishers. Halon production in the U.S. ended on 12/31/93 because they contribute to ozone depletion. They cause ozone depletion because they contain bromine. Bromine is many times more effective at destroying ozone than chlorine. At the time the current U.S. tax code was adopted, the ozone depletion potentials of halon 1301 and halon 1211 were observed to be 10 and 3, respectively. These values are used for tax calculations. Recent scientific studies, however, indicate that the ODPs are at least 13 and 4, respectively. Note: technically, all compounds containing carbon and fluorine and/or chlorine are halons, but in the context of the Clean Air Act, "halon" means a fire extinguishing agent as described above. A table of class I substances shows their ODPs, GWPs, and CAS numbers. Halons are numbered according to a standard scheme. The National Oceanic and Atmospheric Administration provides more detailed information about HCFCs on their web site. (Source: US Environmental Protection Agency, 1999b).

Head - A unit of pressure for a fluid, commonly used in water pumping and hydro power to express height a pump must lift water, or the distance water falls. Total head accounts for friction head losses, etc. (Source: US Department of Energy, 1999a).

Heat - A form of thermal energy resulting from combustion, chemical reaction, friction, or movement of electricity. As a thermodynamic condition, heat, at a constant pressure, is equal to internal or intrinsic energy plus pressure times volume. (Source: US Department of Energy, 1999a).

Heat Absorbing Window Glass - A type of window glass that contains special tints that cause the window to absorb as much as 45% of incoming solar energy, to reduce heat gain in an interior space. Part of the absorbed heat will continue to be passed through the window by conduction and reradiation. (Source: US Department of Energy, 1999a).

Heat Balance - Energy output from a system that equals energy input. (Source: US Department of Energy, 1999a).

heat capacity - The amount of heat necessary to raise the temperature of a given mass one degree. Heat capacity may be calculated by multiplying the mass by the specific heat. (Source: California Energy Commission, 1999a.)

Heat Content - The amount of heat in a quantity of matter at a specific temperature and pressure. (Source: US Department of Energy, 1999a).

Heat Engine - A device that produces mechanical energy directly from two heat reservoirs of different temperatures. A machine that converts thermal energy to mechanical energy, such as a steam engine or turbine. (Source: US Department of Energy, 1999a).

Heat Exchanger - A device used to transfer heat from a fluid (liquid or gas) to another fluid where the two fluids are physically separated. (Source: US Department of Energy, 1999a).

heat flux (thermal flux) - The amount of heat that is transferred across a surface of unit area in a unit of time. (Source: Carbon Dioxide Information Analysis Center, 1990a).

Heat Gain - The amount of heat introduced to a space from all heat producing sources, such as building occupants, lights, appliances, and from the environment, mainly solar energy. (Source: US Department of Energy, 1999a).

heat index - An index that combines air temperature and humidity to give an apparent temperature (eg. how hot it "feels"). Here is a heat index formula originally from Weatherwise magazine. It gives valid results above 70 deg. F.
(-42.379+2.04901523*t+10.14333127*r-.22475541*t*r-(6.83783e-3)*t^2-(5.48 1717e-2)*r^2+(1.22874e-3)*t^2*r+(8.5282e-4)*t*r^2-(1.99e-6)*t^2*r^2)
t = temp deg f and r = % rel hum
See Heat Index Chart (Source: National Weather Service, 1999a.)

heat island effect - A dome of elevated temperatures over an urban area caused by the heat absorbed by structures and pavement. (Source: Carbon Dioxide Information Analysis Center, 1990a).

Heat Loss - The heat that flows from the building interior, through the building envelope to the outside environment. (Source: US Department of Energy, 1999a).

Heat Pipe - A device that transfers heat by the continuous evaporation and condensation of an internal fluid. (Source: US Department of Energy, 1999a).

Heat Pump - A heat pump is basically an air conditioner with a reversible valve that allows it to operate in reverse, removing heat from your house and shunting it outdoors in the summer, and removing heat from outdoor air and shunting it into your house in the winter. Because heat pumps do not actually create heat—they just move it from one place to another—heat pumps are more efficient than other forms of heating. (Source: Lawrence Berkeley Laboratory, 1999)

Heat Pump Water Heaters - A water heater that uses electricity to move heat from one place to another instead of generating heat directly. (Source: US Department of Energy, 1999a).

Heat Rate - The ratio of fuel energy input as heat per unit of net work output; a measure of a power plant thermal efficiency, generally expressed as Btu per net kilowatt-hour. (Source: US Department of Energy, 1999a).

Heat Recovery Ventilator - A device that captures the heat from the exhaust air from a building and transfers it to the supply/fresh fresh air entering the building to preheat the air and increase overall heating efficiency. (Source: US Department of Energy, 1999a).

Heat Register - The grilled opening into a room by which the amount of warm air from a furnace can be directed or controlled; may include a damper. (Source: US Department of Energy, 1999a).

Heat Sink - A structure or media that absorbs heat. (Source: US Department of Energy, 1999a).

Heat Source - A structure or media from which heat can be absorbed or extracted. (Source: US Department of Energy, 1999a).

Heat Storage - A device or media that absorbs heat for storage for later use. (Source: US Department of Energy, 1999a).

Heat Storage Capacity - The amount of heat that a material can absorb and store. (Source: US Department of Energy, 1999a).

Heat Transfer - The flow of heat from one area to another by conduction, convection, and/or radiation. Heat flows naturally from a warmer to a cooler material or space. (Source: US Department of Energy, 1999a).

Heat Transfer Fluid - A gas or liquid used to move heat energy from one place to another; a refrigerant. (Source: US Department of Energy, 1999a).

Heat Transmission Coefficient - Any coefficient used to calculate heat transmission by conduction, convection, or radiation through materials or structures. (Source: US Department of Energy, 1999a).

Heating Capacity (Also specific heat) - The quantity of heat necessary to raise the temperature of a specific mass of a substance by one degree. (Source: US Department of Energy, 1999a).

Heating Degree Day(s) (HDD) - The number of degrees per day that the daily average temperature (the mean of the maximum and minimum recorded temperatures) is below a base temperature, usually 65 degrees Fahrenheit, unless otherwise specified; used to determine indoor space heating requirements and heating system sizing. Total HDD is the cumulative total for the year/heating season. The higher the HDD for a location, the colder the daily average temperature(s). (Source: US Department of Energy, 1999a).

Heating Fuels - Any gaseous, liquid, or solid fuel used for indoor space heating. (Source: US Department of Energy, 1999a).

Heating Fuel Units - Standardized weights or volumes for heating fuels. (Source: US Department of Energy, 1999a).

Heating Load - The rate of heat flow required to maintain a specific indoor temperature; usually measured in Btu per hour. (Source: US Department of Energy, 1999a).

Heating Season - The coldest months of the year; months where average daily temperatures fall below 65 degrees Fahrenheit creating demand for indoor space heating. (Source: US Department of Energy, 1999a).

Heating Seasonal Performance Factor (HSPF) - An efficiency rating for heat pumps. It is a measure of the average number of Btu of heat delivered for every Watt-hour of electricity used by the heat pump over the heating season. It takes into account variations due to weather conditions over a season. HSPF is comparable to knowing how many miles per gallon of gasoline your car got, averaged over the entire year. (Source: Lawrence Berkeley Laboratory, 1999)

Heating Value - The amount of heat produced from the complete combustion of a unit of fuel. The higher (or gross) heating value is that when all products of combustion are cooled to the pre-combustion temperature, water vapor formed during combustion is condensed, and necessary corrections have been made. Lower (or net) heating value is obtained by subtracting from the gross heating value the latent heat of vaporization of the water vapor formed by the combustion of the hydrogen in the fuel. (Source: US Department of Energy, 1999a).

Heating, Ventilation, and Air-Conditioning (HVAC) System - All the components of the appliance used to condition interior air of a building. (Source: US Department of Energy, 1999a).

Heliochemical Process - The utilization of solar energy through photosynthesis. (Source: US Department of Energy, 1999a).

Heliodon - A device used to simulate the angle of the sun for assessing shading potentials of building structures or landscape features. (Source: US Department of Energy, 1999a).

Heliostat - A device that tracks the movement of the sun; used to orient solar concentrating systems. (Source: US Department of Energy, 1999a).

Heliothermal - Any process that uses solar radiation to produce useful heat. (Source: US Department of Energy, 1999a).

Heliothermic - Site planning that accounts for natural solar heating and cooling processes and their relationship to building shape, orientation, and siting. (Source: US Department of Energy, 1999a).

Heliothermometer - An instrument for measuring solar radiation. (Source: US Department of Energy, 1999a).

Heliotropic - Any device (or plant) that follows the sun's apparent movement across the sky. (Source: US Department of Energy, 1999a).

herbivore - An animal that feeds on plants. (Source: Carbon Dioxide Information Analysis Center, 1990a).

Hertz - A measure of the number of cycles or wavelengths of electrical energy per second; U.S. electricity supply has a standard frequency of 60 hertz. (Source: US Department of Energy, 1999a).

heterotroph - An organism (most bacteria, fungi, and animals) that breaks down and uses organic matter. This organism cannot manufacture its own high-energy compounds from low-energy inorganic raw materials. Bacteria and fungi depend mainly on absorption as their mode of feeding, while animals may be herbivores (eat green plants and obtain high-energy compounds directly from the organisms that first made them), carnivores (eat the animals that ate the plants), or omnivores (eat both animal and plant material). (Source: Carbon Dioxide Information Analysis Center, 1990a).

Higher Heating Value (HHV) - The maximum heating value of a fuel sample, which includes the calorific value of the fuel (bone dry) and the latent heat of vaporization of the water in the fuel. (See moisture content and net (lower) heating value, below.) (Source: US Department of Energy, 1999a).

High-Intensity Discharge Lamp - A lamp that consists of a sealed arc tube inside a glass envelope, or outer jacket. The inner arc tube is filled with elements that emit light when ionized by electric current. A ballast is required to provide the proper starting voltage and to regulate current during operation. (Source: US Department of Energy, 1999a).

High-Pressure Sodium Lamp - A type of High-Intensity Discharge (HID) lamp that uses sodium under high pressure as the primary light-producing element. These high efficiency lights produce a golden white color and are used for interior industrial applications, such as in warehouses and manufacturing, and for security, street, and area lighting. (Source: US Department of Energy, 1999a).

histosol - Wet organic soils, such as peats and mucks. (Source: US Environmental Protection Agency, 1999a)

Holocene. The most recent epoch of the Quaternary period, covering approximately the last 10,000 years. (Source: Carbon Dioxide Information Analysis Center, 1990a).

Home Energy Rating Systems (HERS) - A nationally recognized energy rating program that gives builders, mortgage lenders, secondary lending markets, homeowners, sellers, and buyers a precise evaluation of energy losing deficiencies in homes. Builders can use this system to gauge the energy quality in their home and also to have a star rating on their home to compare to other similarly built homes. (Source: US Department of Energy, 1999a).

Horizontal-Axis Wind Turbines - Turbines in which the axis of the rotor's rotation is parallel to the wind stream and the ground. (Source: US Department of Energy, 1999a).

Horsepower (hp) - A unit of rate of operation. Electrical hp: a measure of time rate of mechanical energy output; usually applied to electric motors as the maximum output; 1 electrical hp is equal to 0.746 kilowatts or 2,545 Btu per hour. Shaft hp: a measure of the actual mechanical energy per unit time delivered to a turning shaft; 1 shaft Hp is equal to 1 electrical Hp or 550 foot pounds per second. Boiler Hp: a measure to the maximum rate to heat output of a steam generator; 1 boiler Hp is equal to 33,480 Btu per hour steam output. (Source: US Department of Energy, 1999a).

Horsepower Hour (hph) - One horsepower provided over one hour; equal to 0.745 kilowatt-hour or 2,545 Btu. (Source: US Department of Energy, 1999a).

hot (colloquial) - The word is sometimes used to describe electric utility lines that are carrying electric currently. It also is used to refer to anything that is highly radioactive. (Source: California Energy Commission, 1999a.)

Hot Air Furnace - A heating unit where heat is distributed by means of convection or fans. (Source: US Department of Energy, 1999a).

Hot Dry Rock - A geothermal energy resource that consists of high temperature rocks above 300 F (150 C) that may be fractured and have little or no water. To extract the heat, the rock must first be fractured, then water is injected into the rock and pumped out to extract the heat. In the western United States, as much as 95,000 square miles (246,050 square km) have hot dry rock potential. (Source: US Department of Energy, 1999a).

Hot Water Heating Systems - (see hydronic) (Source: US Department of Energy, 1999a).

Humidifier - A device used to maintain a specified humidity in a conditioned space. (Source: US Department of Energy, 1999a).

Humidity - A measure of the moisture content of air; may be expressed as absolute, mixing ratio, saturation deficit, relative, or specific. (Source: US Department of Energy, 1999a).

humus - Decomposed organic material. (Source: Carbon Dioxide Information Analysis Center, 1990a).

HVAC (Heating Ventilation and Air Conditioning) - A system that provides heating, ventilation and/or cooling within or associated with a building. (Source: California Energy Commission, 1999a.)

hybrid vehicle - Usually a hybrid EV, a vehicle that employs a combustion engine system together with an electric propulsion system. Hybrid technologies expand the usable range of EVs beyond what an all-electric-vehicle can achieve with batteries only. (Source: California Energy Commission, 1999a.)

Hybrid Renewable Energy System - A renewable energy system that includes two different types of renewable energy technologies that produce the same type of energy; for e.g., a wind turbine and a solar photovoltaic array combined to meet a power demand. (Source: US Department of Energy, 1999a).

hydrocarbons - Substances containing only hydrogen and carbon. Fossil fuels are made up of hydrocarbons. Some hydrocarbon compounds are major air pollutants.(Source: US Environmental Protection Agency, 1999a)

Hydrobromofluorocarbon (HBFC) - a compound consisting of hydrogen, bromine, fluorine, and carbon. Although they were not originally regulated under the Clean Air Act, subsequent regulation added HBFCs to the list of class I substances. A table of class I substances shows their ODPs, GWPs, and CAS numbers. (Source: US Environmental Protection Agency, 1999b).

hydrochlorofluorocarbons (HCFCs) - a compound consisting of hydrogen, chlorine, fluorine, and carbon. The HCFCs are one class of chemicals being used to replace the CFCs. They contain chlorine and thus deplete stratospheric ozone, but to a much lesser extent than CFCs. HCFCs have ozone depletion potentials (ODPs) ranging from 0.01 to 0.1. Production of HCFCs with the highest ODPs will be phased out first, followed by other HCFCs. A table of ozone-depleting substances shows their ODPs, GWPs, and CAS numbers. HCFCs are numbered according to a standard scheme. The National Oceanic and Atmospheric Administration provides more detailed information about HCFCs on their web site. (Source: US Environmental Protection Agency, 1999b).

Hydroelectric Power Plant - A power plant that produces electricity by the force of water falling through a hydro turbine that spins a generator. (Source: US Department of Energy, 1999a).

hydrofluorocarbons (hfcs) - a compound consisting of hydrogen, fluorine, and carbon. The HFCs are a class of replacements for CFCs. Because they do not contain chlorine or bromine, they do not deplete the ozone layer. All HFCs have an ozone depletion potential of 0. Some HFCs have high GWPs. HFCs are numbered according to a standard scheme. The National Oceanic and Atmospheric Administration provides more detailed information about HFCs on their web site. (Source: US Environmental Protection Agency, 1999b).

Hydrogen - A chemical element that can be used as a fuel since it has a very high energy content. (Source: US Department of Energy, 1999a).

hydrologic budget - A quantitative accounting of all water volumes and their changes with time for a basin or area. (Source: Carbon Dioxide Information Analysis Center, 1990a).

hydrologic cycle - The process of evaporation, vertical and horizontal transport of vapor, condensation, precipitation, and the flow of water from continents to oceans. It is a major factor in determining climate through its influence on surface vegetation, the clouds, snow and ice, and soil moisture. The hydrologic cycle is responsible for 25 to 30 percent of the mid-latitudes' heat transport from the equatorial to polar regions. (Source: Carbon Dioxide Information Analysis Center, 1990a).

hydrology - The science dealing with the properties, distribution, and circulation of water. (Source: Carbon Dioxide Information Analysis Center, 1990a).

Hydronic Heating Systems - A type of heating system where water is heated in a boiler and either moves by natural convection or is pumped to heat exchangers or radiators in rooms; radiant floor systems have a grid of tubing laid out in the floor for distributing heat. The temperature in each room is controlled by regulating the flow of hot water through the radiators or tubing. (Source: US Department of Energy, 1999a).

hydropower - Electrical energy produced by falling or flowing water. See hydroelectric power plant.(Source: US Environmental Protection Agency, 1999a)

hydrosphere - The aqueous envelope of the Earth, including the oceans, freshwater lakes, rivers, saline lakes and inland seas, soil moisture and vadose water, groundwater, and atmospheric vapor. (Source: Carbon Dioxide Information Analysis Center, 1990a).

Hydrothermal fluids - These fluids can be either water or steam trapped in fractured or porous rocks; they are found from several hundred feet to several miles below the Earth's surface. The temperatures vary from about 90 F to 680 F (32 C to 360 C) but roughly 2/3 range in temperature from 150 F to 250 F (65.5 C to 121.1 C). The latter are the easiest to access and, therefore, the only forms being used commercially. (Source: US Department of Energy, 1999a).

hypsithermal period - The period about 4000 to 8000 years ago when the Earth was apparently several degrees warmer than it is now. More rainfall occurred in most of the subtropical desert regions and less in the central midwest United States and Scandinavia. It is also called the altithermal period and can serve as a past climatic analog for predicting the regional pattern of climate change should the Earth's mean surface temperature increase because of an increase in atmospheric carbon dioxide concentration. (Source: Carbon Dioxide Information Analysis Center, 1990a).