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Production and distribution of heat

Heat energy can be produced in various ways of which those using non-renewable sources have the highest environmental impact and those using renewable sources have a low or negligible impact. The various renewable heating methods are described in subsequent chapters.

Heating by combustion
The most common heating source is natural gas which is burned in a boiler. The heat is transferred to air, or more likely water, flowing through the heat exchanger. The heated water is distributed to for example the radiators, where heat is given off by conduction to the air and the heated air then circulates by convection around the room. The cooler water passes back to the boiler where it is reheated.

Similarly, oil, coal or wood, other types of gases or even biomass may be used in other types of boilers which will burn the fuel and heat the water in a similar way. The decision of which fuel to use will depend on its availability and cost. In terms of limiting climate change, it is important to consider the efficiency of combustion and resulting environmental pollution arising from the combustion process. The biggest pollutant is carbon dioxide which is the principal gas responsible for global warming whilst other pollutants which may be harmful include carbon monoxide and nitrous oxides. While wood and biomass are renewable energy sources, oil and gas have been created over millions of years and are being used up faster than they can be created.

Heating using electricity
Electricity is also used for heating homes. Then no chimney is required as the energy flows into the house by wire and is converted to heat through the resistance of an electrical element. A more efficient form of electrical heating is by a heat pump which concentrates the low grade heat energy available in the air, ground or water. Electricity is then only used to concentrate the heat not produce it.

Remember that electricity is only a carrier of energy and is produced somewhere else! Most often, the same fossil fuels mentioned above, are also used to generate electricity, a process which also results in environmental pollution; this time in a central location rather than distributed in individual homes.

Direct heating using the sun
This may be done by passive means such as conduction or convection (Trombe wall) or actively through solar thermal collectors. As air or water is heated directly, the only environmental impact is that of distributing the heat around the house.

Heat distribution
In our homes heat is most often distributed through radiators which are frequently located under the windows. The radiators are interconnected by small pipes which are sometimes visible and sometimes hidden in the walls and floors in which warm water is circulating. Other ways of heating include venting hot air through ducts and circulating water through pipes located beneath the floor.

The boiler itself may be a small box located somewhere in your house or flat. Alternatively it may be a larger boiler, located in your neighbourhood or in your apartment block, which allows heat to be distributed to all homes around you.



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