Steam heating

“ In this country it is well within the memory of most men in active life when even our largest factories and office buildings were heated by means of open fires and stoves, but the development from a primitive life to a congested and complex civilization has been phenomenally rapid, especially in the last quarter century, and the greatest advances in steam heating, as well as in most practical sciences, have been made in that period. ”

“ When both exhaust and live steam are used for heating, many engineers prefer to use independent lines of pipe for each, rather than run the risk of interference and waste caused by admitting exhaust and live steam into the same system at the same time. Nevertheless, the advantages gained by being able to increase the heating power of a system in extremely cold weather by utilizing the entire radiating surface for high pressure steam, are so great that it is probably better so to arrange the system of pipes and connections that this can be done. ”

“ It is certainly the most scientific method of steam-heating, and heat can be made to travel a greater distance by its aid than by any other means. The heat of the pipes is great, but can be easily regulated. The system is economical in fuel, but needs skilled attendance to keep the appliances and fittings in order. The steam is introduced into the pipes at about the pressure of the atmosphere, and is sucked through the system by means of a vacuum pump, which at the same operation frees the pipes from air and from condensation water. ”

“ Air is heavier than steam of the same pressure, but in a heating system the air will always find its way to the dead end, or point where there is no circulation. If a straight, vertical pipe, closed at the top, be connected to a source of steam supply, any air in the system will accumulate at its top. If steam is turned on an ordinary two-column steam radiator which is full of air and has a tight air valve, after some moments the first few loops will become filled with steam and perfectly hot, the remaining loops being full of air and cold. ”

“ They say it’s more convenient for a small house because you don’t have to keep up such a big fire all the time.”
“That’s so; in steam heating there has to be fire enough to make steam, anyway, doesn’t there?”
“And when the steam in the pipes cools it turns to water and dribbles away, but in the hot water system there will be some heat in the outside of your radiator as long as the water inside has any warmth at all.”
“How does the expense compare?” inquired James who was always interested in the financial side of all questions.
“The hot water system is said to be cheaper,” replied Dorothy. ”

“ In many mills and factories which use condensing engines, and in which, consequently, exhaust steam is not readily available for heating, steam for this purpose is taken direct from the boilers through a reducing pressure valve and used in the heating system at a pressure of 5 to 20 pounds per square inch. ”

“ Vacuum systems.—As a refinement of exhaust-steam heating there has been developed within the last decade what is known as vacuum systems of steam heating, the object of these being to exhaust the air from the system by artificial means so that circulation may be effected at atmospheric pressures with absolutely no back pressure on the exhaust pipes from the engines. ”

“ To regulate the heat it is necessary either to instal a number of small radiators or to divide the radiators into sections, each section controlled by distinct valves; steam may then be admitted to all the sections of the radiator or to any less number of sections as desired. In a hot-water system the heat is given off at a lower temperature and is consequently more agreeable than that yielded by a steam-heating apparatus. The joint most commonly used for hot-water pipes is termed the “rust” joint, which is cheap to make, but unfortunately is inefficient. ”

“ A safety valve (Fig. 36) is attached to steam-heating systems instead of an expansion tank. This keeps the pressure of the steam in the boiler from becoming too great, and thereby prevents an explosion. The pressure gage (B, Fig. 35) must be set, and, when set, should only be changed by a person understanding it. Build and manage the fire for a steam boiler the same as [70] for any stove or furnace. Keep water in the boiler at 212 degrees Fahrenheit, so steam may form, for without it, the radiators will not be heated. Small valves are attached to most steam radiators. ”

“ But since the time of Tredgold, heating by steam has increased in extent and popularity year after year, especially since the increase in size of buildings began to be very rapid, and its economy of operation and incidental advantages of convenience and simplicity have become more and more apparent, until at the present day, in some form or another, it is used almost universally in all installations requiring distribution of heat over any considerable area. ”

“ The question of practical efficiency is, therefore, more strictly speaking, only one of effectiveness of surface. That is, of two radiators under exactly the same conditions of temperature and surroundings, that one which has such an arrangement of its surfaces as to give out the most heat per square foot is the most effective, usually called the most efficient. In all tests of radiators, the heat given off is measured by connecting them so that the steam which condenses can be accurately weighed, its pressure, quality and temperature being determined at the same time. ”

“ The quantity, gives the number of heat units necessary to raise cubic feet of air 1 degree in temperature. Prof. Carpenter states that the radiating surfact should be equal to in which is the required temperature of the room, the outside temperature, the temperature of the steam in the radiator, and is a coefficient of heat transmission from a radiator which varies from 1.7 for low-pressure steam heating to 1.9 for steam pressure of 40 pounds and 2.4 for steam pressure of 100 pounds. ”

“ In a vast manufactory of steel cars, of steel structural forms, steam has to be conveyed long distances from the boilers. Here, as in similar huge establishments, or in the heating of towns and cities from central stations, it is desirable to lose as little heat as possible by the way, for undue waste means enormous inroads upon profits. There are other reasons for wishing to keep heat within a steam pipe; much damage may be done to fruit, flour and other merchandise unduly warmed. ”

“ It occasionally happens that a conservatory attached to a dwelling is heated by the same steam apparatus employed to heat the latter, but we believe that a person who should advocate, at the present day, the general adoption of steam as a means of heating horticultural structures, would be regarded as belonging to a generation which has now passed away.
Steam travels through pipes with great rapidity, and parting with its heat rapidly, it becomes quickly condensed, unless the boiler is of large capacity and capable of furnishing a full supply. ”

“ On these grounds it is not so economical, so far as the consumption of fuel is concerned, to use steam instead of water, either water heated to a high temperature under pressure, or to heat air for warming purposes, because the gases from the fire employed to produce the higher degree of heat will pass off at a high temperature, and the heat they contain be wasted. On the other hand, the capital outlay required, where highly-heated pipes are used, is smaller than with hot-water pipes, because a smaller heating surface, and therefore smaller pipes, will suffice when the temperature is high ”

“ But if it be attempted to run much below atmospheric pressure the slightest leak anywhere in the system will rapidly break the vacuum and allow air to accumulate. It is, however, impossible to make a system theoretically air tight, and steam invariably contains some air from the feed water, as water will absorb several times its own volume. Air in the radiators and piping is, therefore, an evil that cannot be avoided, and it rapidly accumulates in the radiators or ends of pipes where the flow of steam is slowest. ”

“ The practice of heating by low pressure steam will save in labor, coal and construction one-fifth of the expense by old methods, and nearly all the large green-house establishments in this country, whether private or commercial, have been for some years furnished with the best apparatus. But when visiting London, Edinburgh and Paris in 1885, I neither saw nor heard of a single case where steam had been used for green-house heating. ”

“ For special purposes in connection with machinery various heating devices are required, of which steam and gas are those most universally used. Steam tubes or coils may be carried through any fixed or movable part of a machine. Steam-heated surfaces, such as tables, pans, chambers, &c., steam-jacketed cylinders, and similar contrivances, are much used. Gas jets from perforated tubes, which may be shaped to any required position, are also convenient for dry heat and higher temperatures than can be obtained from steam. ”

“ But as soon as they are a second time cooled down below 212° a further portion of steam will condense, and a further quantity of latent heat will pass into the state of heat of temperature, and so on until the whole quantity of latent heat has been abstracted and the whole of the steam condensed, in which state it will possess just as much heating power as a similar bulk of water at the like temperature ”

“ By cutting off the steam, however, at one third of the stroke, a heating surface of 13-1/2 square feet will give a threefold power, and it will usually be the most judicious course to carry the expansion as far as possible, and then to add the proportion of heating surface necessary to make good the deficiency still found to exist. ”

“ But it is impracticable to have all the radiators of a system turned on at one time, and the difficulty with such a system is made evident the minute steam is turned into a cold radiator. When the steam comes in contact with a perfectly cold radiator a large amount is condensed at once in heating the cold iron, and as soon as the pressure becomes adjusted this bulk of water flows out of the radiator connection at one time and drops down the vertical pipe. ”

“ Thus in a return flue boiler the heated gases become cooled often to such an extent before they pass out at the smokestack that they do not help the generation of steam. Yet a heat just below 357 degrees would turn water into steam under 149 lbs. pressure. Though it has work in it, the heat is lost.
Another practical point as to economy in large heating surface is that it costs money to make, and is cumbersome to move about. It may cost more to move a traction engine with large boiler from place to place than the saving in fuel would amount to. ”

“ The water level in the return pipes and return risers will stand at a higher level than in the heater or boiler in the case of Figures 1 to 4, by a distance representing the difference in pressure required to force the steam through the system, just as in the ordinary gravity system. As a matter of fact, also, it is found that in the system shown in Figure 7 the pump operates much more smoothly and uniformly if the system is made a gravity system by connecting a small equalizing steam pipe between the main steam supply of the heating system and the top of the receiving tank and governor. ”

“ As heating systems are now designed, one which requires a pressure of 5 pounds to ensure a good circulation is defective in design, and 2 pounds is more than ought to be required in most cases. A back pressure of this amount on an engine running at 50 pounds mean effective pressure would increase the coal consumption but a fraction of 1 per cent., while taking the heating power that is available in the exhaust steam directly from the boiler would increase the coal consumption over 60 per cent. ”

“ In producing mechanical motion at a power-house, the engines waste at least ninety per cent. of the applied heat. To this heavy tax must be added the expenses of distribution, administration and maintenance. Until, therefore, the electrician reaches a mode of creating his current from heat without the enormous losses of present practice, we cannot look to him for a system of general heating. A word has already been said in this book about methods of district heating by steam. ”

“ If this is used to evaporate water, and the steam therefrom [42] drives an engine, less than 4200 heat units are actually utilized, the remaining 9800 heat units being lost in the transformation from the fuel to power.
The value of considering and providing for condensation, compression, superheating, re-heating, compounding, and radiation, and to properly arrange the clearance spaces, the steam jackets, the valve adjustments, the sizes of the ports and passages, and the governor, all form parts of the knowledge which must be gained and utilized. ”

“ The remaining one-third of the heating surface should be exposed in the halls and some in the other parts of the house, to heat by direct radiation, but under no [49] circumstances should a room or office be occupied heated exclusively by direct radiation from exposed steam pipes. It is one of the worst, most unhealthy, killing systems in existence.
Steam furnaces require the evaporation of an additional amount of moisture as well as any other system of heating. ”

“ The patent includes also a number of applications of superheated steam.
In later years the system of circulating water in closed pipes of small diameter, heated up to two thousand pounds per square inch of steam pressure, was applied to the heating of bakers' ovens. This has been extensively adopted: it possesses the advantage that the heat may be easily regulated. ”