A term for energy; such as, steam, hot water, or chilled water; which is produced at a central location and then transmitted to various specific sites in a given area (district) for uses; such as, space heating and cooling, or domestic hot water heating.

Such a system can substitute for furnaces, air conditioners, etc. within the district's individual buildings.

1. The heating of a material by the heat energy from an electric arc, which has a very high temperature and very high concentration of heat energy.
2. The heating of matter by an electric arc.

The material may be solid, liquid, or gaseous and when the heating is direct, the material to be heated is one electrode; but for indirect heating, the heat is transferred from the arc by conduction, convection, or radiation.

Any method or process in which electric energy becomes heat energy by resisting the free flow of electric current; such as, radiant heating.

1. A fuse that is ignited by a self-contained electronic element; for example, a proximity fuse or an electronically triggered device designed to detonate an explosive charge in a missile, etc., at a predetermined distance from the target.
2. A fuse; such as, the radio proximity fuse, set off by an electronic device incorporated within it.

A fuse that detonates a warhead when the target is within some specified region near the fuse.

Radio, radar, photoelectric, or other devices may be used as activating elements.

1. Heating which is generated by a radio-frequency power source, that produces a radio-frequency current.
2. Heating with radio-frequency current that is produced by an electron-tube oscillator or an equivalent radio-frequency power source.
3. A method of heating a material by inducing a high-frequency current into it or having the material act as the dielectric (having little or no ability to conduct electricity) between two plates charged with a high-frequency current.

Heating resulting from absorption of gamma-ray energy by a material.

1. Energy in the form of natural heat flowing outward from within the plant Earth and contained in rocks, water, brines, or steam: Geothermal heat is produced mainly by the decay of naturally occurring radioactive isotopes of thorium, potassium, and uranium in the Earth's core.

Geothermal energy is produced by tapping the Earth's internal heat. At present, the only available technologies to do this are those that extract heat from hydrothermal convection systems, where water or steam transfer the heat from the deeper part of the Earth to the areas where the energy can be tapped.

The amount of pollutants found in geothermal vary from area to area but may contain arsenic, boron, selenium, lead, cadmium, and fluorides. They also may contain hydrogen sulphide, mercury, ammonia, radon, carbon dioxide, and methane.

Getting the Earth's Heat

Geothermal power plants, which tap hot subterranean water or steam, are high on the lists of at least thirty states in the U.S. which are requiring utility companies to generate some portion of their electricity from such renewable sources.

Most utilities have not pursued geothermal energy primarily because up-front costs, including exploratory drilling, can be expensive since geothermal taps deep reservoirs, not groundwater, which collects much closer to the surface.

An extensive study recently released by the Massachusetts Institute of Technology has shown that the heat available under ground is surprisingly plentiful nationwide.

More information about special Geothermal Energy sources.

The number of British thermal units (BTU, btu) produced by the combustion at constant pressure of one cubic foot of a fuel, under standard conditions of temperature and pressure.

A British thermal unit is a widely used unit of measure, generically defined as the average amount of energy required to produce a change in temperature of one degree Fahrenheit (F) in one pound of pure liquid water; often specified as occurring at standard atmospheric pressure and a specified temperature increase; equivalent to about 1055 joules or 252 calories.