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Read the title of the following text. What can this text deal with? Decide if the following statements are true or false. Read the text and check.
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a) There are two types of heating systems.
b) They differ in the way they circulate the warm air.
c) A direct system and indirect system both circulate the warm air.
d) A direct system circulates the warm air throughout the area being heated.
e) An indirect system circulates steam or hot water from convectors or radiators.
Central Heating Systems
There are two main kinds of central heating systems direct and indirect. They differ in the way they distribute heat. A direct system circulates the warm air throughout the area being heated. An indirect system circulates steam or hot water through pipes to convectors or radiators, which give off heat.
Warm-air heating. A warm-air heating system warms the air in a furnace and then forces it through a system of ducts (pipes) to each room. Another system of ducts carries cool air from the rooms back to the furnace. An electrically driven blower in the furnace moves the air through the ducts, and filters remove dust particles from the air.
Some private homes have warm-air systems. These systems can do more than just heat the air. With a humidifier, for example, a forced warm-air system adds moisture to the air and increases the humidity throughout the home. The ducts and blower can be used as part of a central air-conditioning unit.
Steam and hot-water heating systems. Steam or hot-water heating systems are used in many large buildings. These systems cost more than warm-air systems, but they have certain advantages over them. The pipes carrying steam or hot water are smaller than warm-air ducts and thus take up less space. Automatic valves can control the amount of hot water or steam flowing to convectors more easily than they can control warm air. Thus, it is easier to control the temperature in different rooms with these systems than with warm-air heating.
A steam heating system requires a boiler, and a hot-water heating system has a hot-water heater, also called a boiler. Fuel burning in the boiler produces heat for the system. The system also has a network of pipes and convectors. In steam heating, a condensate pump forces the condensed steam back to the boiler. In hot-water heating, a pump circulates the water through the system.
The convectors of a steam or hot-water system, often called radiators, give off most of their heat by convection and radiation. The amount of heat given off by radiation depends on the temperature of the converter and its surface area. With lower temperatures typical of hot-water heating, a greater part of the heat is delivered by convection and less by radiation. The amount of heat given off by a converter depends upon its shape and the amount of exposed metal surface. The more metal that is exposed, the more heat is given off.
One difficulty in heating with high temperature convectors is that the air near the ceiling becomes warmer than the air in other parts of the room. For example, the air at knee height may be 16°C, the air at breathing level may be 20°C, and the air at the ceiling may be 24°С. The air at floor level may be only 12°C. Such a low floor temperature is too cold for comfort. If an attempt is made to raise the temperature of the floor, the average room temperature increases and the upper parts of the room become uncomfortably warm.
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Radiant heating is a method of equalizing temperature within a room. A continuous loop of hot-water pipe or electric cable is installed in the ceiling or floor. Heat leaves the pipe or cable by radiation, which does not directly raise the temperature of the air within a room. Radiation affects only the objects it strikes, and so it produces more uniform heating than convection does. Radiant heat provides comfort at a lower room temperature than other heating systems.
Radiant heating may also be installed along the skirting boards of a room. One system uses a metal shield about 15 centimeters high to cover a hot-water pipe that runs close to the floor. Such a system distributes heat evenly. All radiant heating systems limit the temperature difference between the floor and the ceiling to only a few degrees.
Electric heating differs from other central systems because it requires no combustion of fuel in the building being heated. The fuel used to make electricity is burned at an electric power plant that may be far away. Nuclear plants produce electricity from nuclear energy.
Electric heat is produced by electric heating units. Such units produce heat by passing electricity through a material that resists the flow of current. This type of heating, called resistance heating, produces much radiant heat. Such heat warms the surface of the skin and clothing and makes people feel comfortable even in a cool room. Radiant electric heating uses a cable that produces heat from electricity. An electric heating unit can be placed in the ceiling, skirting boards, floor, or wall. The temperature can be controlled by thermostats in each room, or area.
COMPREHENSION CHECK
What parts of the text can you define? Do they correspond to the paragraphs? What are the titles to each part?
1) _______________
2) _______________
3) _______________
4) _______________
5) _______________
Reread the part of the text dealing with warm-air heating (WAH) and do the following tasks.
A. Answer the following questions and give examples.
1) Where does a warm-air heating system warm the air?
2) How does it transmit warm air to each room?
3) What is the function of filters?
4) What else can the system do except of heating the air?
5) Can WAH be used as a part of an air-conditioning unit?
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