20. Read the texts a and b and make notes under the following headings. Then use your notes and the illustrations to talk on the topics

1. Types of Boilers.

2. Split Air Conditioning.

SECTION II. SUPPLEMENTARY READING MATERIAL

Unit I hvac systems. Heating

Text 1.

Heating

The desire for warmth and comfort may well have motivated man's first use of a fire. The earliest evidence shows that man used wood and charcoal in open fires to produce warmth, as well as to prepare food, in his cave or shelter. Such simple open fires were used as late as the 19th century by American Indians, who built fires in their huts and tepees, which had openings to allow the smoke to escape. A different method was devised by 300 b. c. by Europeans who built crude fireplaces with connecting chimneys; with this arrangement, combustion efficiency and room ventilation were much improved. By the first century b. c, the Romans had developed the hypocaust, which provided a better way to heat a room. The hypocaust was a basement with a low arched–vault furnace made of brick or stone. The hot air from the furnace passed through tile flues in the walls of the room above the furnace, heating the room. After the fall of Rome, the hypocaust went into disuse.

In America during colonial days the fireplace was the heart of the house. The chimney often was a massive structure built of field stones, adobe, or bricks. Some chimneys had several fireplace openings at different levels for the various rooms in the house.

In many regions the fireplace and chimney arrangement for heating rooms remained in use for thousands of years. It still is used in some areas.

Stoves. Records and artifacts show that clay stoves were used in Europe during Roman times. The early Chinese used stoves to heat bricks, which were then used to heat beds in other rooms of the house. In the American colonies, Benjamin Franklin invented the iron Franklin stove in 1743; it gained a reputation of high efficiency.

The use of stoves provided a new way to heat rooms. The fire was contained in a combustion chamber usually made of ceramic or iron sections. It heated the stove wall, which in turn heated the room, mainly by convection of the room air over the hot surface. Previously, the fireplace provided only the radiant heat of the fire, and most of the heating value of the fuel was lost in the hot combustion gases passing up the chimney. Space–heating stoves were first designed to burn wood or charcoal but were later adapted to burn coal or oil as these fuels became available.

Central Heating. As technology advanced, individual room stoves were superseded by central heating for the entire building. In this arrangement a furnace or a boiler is located in a basement or some other isolated area, and steam, hot water, or hot air is transported to the rooms of the buildings by pipes or ducts. As a result of the heating unit being in an isolated location, there was a great improvement in comfort, convenience, and cleanliness in the home.

The steam boiler was developed for the steam engine in England during the 18th century, but engineers soon learned to adapt it for central steam heating systems. For instance, central steam heating was installed in the Parliament building in England during that period. Steam heating systems are particularly suitable for l% 3TA serving large public buildings because large quantities of heat can be carried long distances by small pipes.

In the 20th century the adaptation of circulating fans and pumps to heating systems made possible the forced air and hot–water systems now in widespread use in central–heating systems for homes and other buildings Fuels. Improvements in systems for handling and burning fuels also were important developments. Coal was the predominant fuel for many years, but its use drastically declined in favor of gas and oil. Modern heating systems, whether installed in the largest skyscraper or the smallest house, normally provide draft–free and even–temperature heat, quiet and clean operation, and automatic performance at a reasonable cost with a minimum of service. These systems are often combined with summer air cooling and other air conditioning functions.

Text 2.