In selecting a heating plant for residences there must be considered the size, the type of building, the climate and the first cost of operation.

FROM THE HISTORY OF DAM CONSTRUCTION (2.800)

Dams have a history just as long as such branches of civil engineering as bridge building, road construction and the laying down of canals. Not only do dams represent some of the most impressive achievements of engineers over the centuries but their vital role in supplying water to towns and cities, irrigating dry lands, providing a sources of [power and controlling floods is more than sufficient to rank dam building among the most essential aspects of man’s attempts to harness, control and improve his environment.

In antiquity dams were built as an essential part of the need to practice irrigation on which the production of food was based. It was not until the Roman came on the scene trhat the size of dams was increased and new uses were found, such as the application of dams to problems of flood control and protection. The most important contribution, however, was the reservoir dam which, to a large extent, was a result of the Roman’s concern with the water supply to cities and towns. That they were able to build so many big dams, many of which have lasted for a very long time and survived, despite eighteen centuries of use and neglect, was also a result of their evolving better methods of construction based on better materials, especially hydraulic mortar and concrete. Moreover, proper attention was paid to hydraulic problems to ensure that the water could not percolate through the dams and that when it overflowed them, spillways were provided.

The Industrial Revolution contributed much to the further development of water resources not only for water supply purposes but also for water wheels, and, later, in the 19-th century, for their logical successor- water turbines. In their mode of operation, particularly that of reaction turbines, it was a fundamentally new idea closely linked with an improved understanding of hydrodynamics. The development of electric generators refers to the major scientific discoveries in the early part of the century, and one feature of electric power was of supreme significance, namely, that it is only form of energy in a ready-to-use state which can be transmitted over long distances.

One of the greatest advantages of a water-power station is that it utilizes an energy carrier which renews itself constantly and does not exhaust energy resources. This makes its maintenance costs relatively low.

With the discovery of a generator three separate seemingly diverse branches of engineering, those concerning dams, water turbines and electric generators, came together to found a new branch of power generation utilizing hydropower resources. All the three elements have undergone changes in the height, volume and efficiency.

Model analysis, a technique for stimulating the complex behaviour of a structure, a dam, for instance, promotes a reliable forecast in designing new schemes and in the transformation and modernization of the old ones to increase their efficiencies.

WATER-POWER DEVELOPMENT —INTEGRAL PART OF CIVIL ENGINEERING (3.000)

With the growth of towns and their industries, with the increase of population and the improvement of living con­ditions the demand for water rises rendering the work of water power engineers ever more important.

There are so many uses for river water that it seems natural it is always made to serve more than one purpose. A large reservoir formed by the dam may be used for flood control, for improving industrial and domestic water supply for nearby areas, for irrigation and navigation, for recreation and sport. To accomplish such miscellaneous tasks a hydro-power development built on the river should comprise besides the dam such structures as a power station, navigation locks, spillway facilities, and canals and tunnels for discharging floods, and other ancillary structures of minor importance.

In harnessing a river to make it serve the man a dam as an impervious barrier should be placed in its way, which impounds water and raises the level of the river thus creating the head necessary for power generation. Since dams are to withstand various stresses, much thought should be given to the problems of increasing their strength, watertightness, stability and safety. It becomes аll the more important now­adays as the heights of dams have steadily been increased and this fact calls for a drastic improvement of the methods of design and a deeper knowledge of the foundation character and the prop­erties of the materials used.

Well executed, the dam is of great benefit to the community but if it is not, a dam failure is, perhaps, the most serious man-made catastrophe likely to occur in the peace time. The disasters that took place showed that the mechanism of a dam failure is very complex, that a whole series of effects occur in quick succession. The determination of the true state of stress in a dam undertaken so far now requires a more elaborate treatment as people have come to realize that the best of theories is useless if the materials used do not comply with the assumptions made about their properties.

Modern industrial growth should not be threatened for want of electric energy and this calls for providing better use of resources of various sorts to attain maximum techni­cal and financial efficiency.

Thus the idea of a pumped-storage station using small riv­ers or basins appeared. The principle of its operation demands storing water in an upper basin and then directing it into a lower basin where from the water is pumped back into the upper basin to repeat the cycle. The scheme demands a special kind of machinery—a reversible pump-turbine type. The station of this kind readily covers peak energy periods and is most efficient when combined with some other type of power plant.

In some countries for lack of any more economically exploitable water power development the new power demand will be covered by nuclear stations.

Nuclear, conventional thermal and hydropower plants' are complementary, but not mutually exclusive. The problem of high load factor and peak load demands is to be solved by coupling nuclear stations, providing base load energy, with hydropower plants dealing with the peaks. Before arriving at a decision in favour of any of the ways of power generation, the full technical as well as financial aspects (capital investments and fuel costs) should be thoroughly examined.

SYSTEMS OF HEATING (1.400)

Heating. In order to maintain standard room temperature, the heating apparatus must supply heat to replace the lost through the walls, floors, and ceilings, and, in addition, the heat necessary to warm the cold fresh air used for ventilation. Heat is lost by conduction through cracks around doors, windows, etc.

Systems of heating. Leaving stoves and fireplaces out of consideration, the systems ordinarily employed for heating may be classified as follows:

a) hot air

b) steam

c) hot water

Hot air systems. In a hot air system, heated air from the furnace is introduced through leaders, stacks, and registers into the room. This air is at a higher temperature than the room, and, in flowing across the ceilings and down by the walls, heat is abstracted until it is eventually cooled to the desired room temperature. Fresh warm air from the furnace then forces the air that has been cooled to room temperature out of the room through cracks, fireplaces, etc. A heat balance may therefore be written as follows: the heat given up by the entering air equals the heat lost by conduction.

The force which causes hot air to flow from furnace to room results from the difference in densities of the cold air outside and the warm air inside the furnace and pipes.

Advantages. A hot air system is cheap to install, has a low cost of maintenance, and is not hard to manage, its operating cost is little, if any, greater that of hot water or steam system of equal capacity.

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