18. Read the following text and speak on the main energy sources for heating systems. Render the text in Russian. Text c. Energy Sources for Heating Systems.

Most home heating systems obtain their heat by burning coal, gas, or oil. When any of these fuels is burned with a deficiency of combustion air or with an improperly adjusted burner, it can produce carbon monoxide. It is a deadly gas that is unsafe to breathe in any concentrations greater than 1 part in 10,000 parts of air. For this reason, one should recognize the importance of properly venting the gaseous products of combustion to the outside of the house, particularly in the case of a small, tightly constructed house.

Coal. The use of coal as a home heating fuel has diminished steadily in recent years because of its cost, its fuel and ash handling difficulties, and its limitation on designing for completely automatic operation. Where still in use, coal is fed to a furnace or boiler by hand or by a mechanical stoker. The stoker fire must be started by hand, but the rate of coal feed can be regulated by a thermostat in the heated space.

Gas. Natural gas (methane) is the most widely used home heating fuel. This gas is collected from large gas pockets in the earth and piped underground at high pressure to cities where it is used. In the home the gas is reduced to low pressure and burned in gas burners. Gas burners should be equipped with adequate safety controls because natural gas is a highly flammable fuel.

Liquefied petroleum gas (propane or butane) is often used where the home is not near a gas main. This gas is liquefied under moderate pressure, delivered to the home in special tank trucks, and stored in a large pressure container. When released from the pressure container for home use, the fluid returns to its gaseous state. A liquefied petroleum gas (LPG) heating system operates with the same convenience and cleanliness as a natural gas system.

Oil. Fuel oil, which is available in various grades, is delivered to home storage tanks by tank truck. Oil burners are available in many designs, with each burner designed to use a particular grade of fuel oil. Generally, oil burners are more complex than gas burners since they must vaporize the oil before it can be burned. As a general rule, fuel oil does not burn as cleanly or as efficiently as gas, and it requires somewhat more service attention. However, its flammable characteristics are somewhat less dangerous than those of gas because it is a low–volatile fuel.

Electricity. Electricity is a high–grade energy source that can be used for heating by sending current through resistance elements located, for instance, in conventional warm–air furnaces or hot–water boilers, or directly in baseboard units. In areas where economic factors justify its use, the electricity is supplied to homes under special all–electric rate schedules. Electricity has the advantages of convenience, cleanliness, low maintenance, and easy control, and it does not have the dangers associated with fuel burning.

Notes:

deficiency – отсутствие чего–л., нехватка, дефицит

diminish – сокращать, уменьшать

equip – снабжать; оборудовать

LPG – сжиженный нефтяной газ

low–volatile – с малым выходом летучих компонентов

baseboard unit – плинтусные устройства, приборы

rate schedule – таблица тарифов на электроэнергию