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H–Coal Process: A means of making coal cleaner so it will produce less ash and less sulfur emissions.

HSPF: See Heating Seasonal Performance Factor.

Heat Balance: The outdoor temperature at which a building's internal heat gain (from people, lights and machines) is equal to the heat loss through windows, roof and walls.

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.

Heat Content: The total amount of heat released when a fuel is burned.

Heat Engine: An engine that converts heat to mechanical energy.

Heat Gain: An increase in the amount of heat contained in a space, resulting from direct solar radiation, heat flow through walls, windows, and other building surfaces and the heat given off by people, lights, equipment and other sources.

Heat Loss: A decrease in the amount of heat contained in a space, resulting from heat flow through walls, windows, roof and other building surfaces and from exfiltration of warm air.

Heat Pump: An air–conditioning unit which is capable of heating by refrigeration, transferring heat from one (often cooler) medium to another (often warmer) medium, and which may or may not include a capability for cooling. This reverse–cycle air conditioner usually provides cooling in summer and heating in winter.

Heat Rate: A number that tells how efficient a fuel–burning power plant is. The heat rate equals the Btu content of the fuel input divided by the kilowatt–hours of power output.

Heat Transfer: Flow of heat energy induced by a temperature difference. Heat flow through a building envelope typically flows from a heated, or hot area to a cooled, or cold area.

Heating Degree Day (HDD): A measure of how cold a location is over a period of time relative to a base temperature, most commonly specified as 65 degrees Fahrenheit. The measure is computed for each day by subtracting the average of the day's high and low temperatures from the base temperature (65 degrees), with negative values set equal to zero. Each day's heating degree days are summed to create a heating degree–day measure for a specified reference period. Heating degree days are used in energy analysis as an indicator of space heating energy requirements or use.

Heating Load: The rate at which heat must be added to a space in order to maintain the desired temperature within the space.

Heating Oil: A distillate fuel oil used in atomizing–type burners for domestic heating or for moderate capacity commercial and industrial burner units.

Heating Seasonal Performance Factor (HSPF): A representation of the total heating output of a central air–conditioning heat pump in Btus during its normal usage period for heating, divided by the total electrical energy input in watt–hours during the same period.

Heating Value: The amount of heat produced by the complete combustion of a given amount of fuel.

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

Heavy Oil: The fuel oils remaining after the lighter oils have been distilled off during the refining process. Except for start–up and flame stabilization, virtually all petroleum used in steam–electric power plants is heavy oil.

Heavy Water: A type of hydrogen atom that may be used as fuel for fusion power plants. Also called Deuterium, it is found in abundance in the seas.

Heliochemical: Using solar radiation to cause chemical reactions.

Heliothermal: A process that uses the sun's rays to produce heat.

Henry Hub Spot Prices: Nebraska is a part of the East Region (see map) which is a major natural gas consumer, particularly in the residential and commercial sectors. The industrial sector, which includes agriculture, is also a major consumer in this state. Most of the gas is supplied from the Producing Region with a fair amount imported from Canada. The Henry Hub in southern Louisiana is a major market center with interconnections for many of the pipelines that transport U.S.-produced gas to the East Region. Furthermore, the Henry Hub is the preferred reference point for prices for most of the domestic gas destined for the East. Therefore, market conditions and developments in the East Region and price movements and trends at the Henry Hub are usually highly correlated.

Hertz: A unit of electromagnetic wave frequency that is equal to one cycle per second. Hertz is named after Henrich R. Hertz.

High Sulfur Coal: Coal whose weight is more than one percent sulfur.

Horsepower (HP): A unit for measuring the rate of doing work. One horsepower equals about three–fourths of a kilowatt (745.7 watts).

Hot Dry Rock: A geothermal resource created when impermeable, subsurface rock structures, typically granite rock 15,000 feet or more below the earth's surface, are heated by geothermal energy. The resource is being investigated as a source of energy production.

Hybrid Vehicle: Usually a hybrid electric vehicle, a vehicle that employs a combustion engine system together with an electric propulsion system. Hybrid technologies expand the usable range of electric vehicles beyond what an all–electric–vehicle can achieve with batteries only.

Hydroelectric Power: Electricity produced by falling water that turns a turbine generator. Also referred to as Hydro.

Hydronic Heating: A system that heats a space using hot water which may be circulated through a convection or fan coil system or through a radiant baseboard or floor system.

Hydrothermal Systems: Underground reservoirs that produce either dry steam or a mixture of steam and water.

Hygas: A process that uses water to help produce pipeline–quality gas from coal.