William S. Monroe

“ The disadvantage of the automatic air valve is that when steam is turned on, the entire radiator will become heated. For this reason the author prefers the plain hand air valve on radiators in his own rooms, as the amount of the radiator heated can be very accurately regulated by means of them, especially when they are connected on a one-pipe system. The automatic air valve, however, takes the circulation in the radiator entirely out of the hands of persons who are not acquainted with their principles, and in the case of indirects is a necessity. ”

“ A brief study of the steam engine shows us that not much over 12 per cent. of the heat energy supplied to an engine is transformed into mechanical work, and by far the major part of the wasted heat escapes in the latent heat of the exhaust steam. This heat, though it has been thus far impossible to transform it into mechanical energy, is readily available for heating purposes; but a generation ago, when it was first proposed to use exhaust steam for heating, the problem involved the then serious question of back pressure on the engines. ”

“ From the earliest times in the latitudes of northern Europe and North America, some form of heating in cold weather has been a necessity for all buildings, whether caves or palaces, but even as late as the latter part of the nineteenth century such a thing as a uniform temperature in heated rooms in severe weather was never expected, while ventilation was invariably secured only by such means as would be accomplished by the circulation of air through doors and other openings. ”

“ The systems which may be employed for mechanical ventilation are numerous and varied, but they all embody the use of fans of one kind or another for forcing the air into the rooms, or exhausting it, or both, with proper provision for heating the incoming air in cold weather, and some one of the three heating systems is frequently, if not generally, employed in connection with a system of mechanical ventilation. ”

“ Baldwin's rule for pipe sizes.—In the early days of steam heating, pipe sizes were proportioned by various empirical rules, the usual basis of which was the principle of being sure to get the pipes large enough; and such rules are, to a large extent, blindly followed to-day. Mr. William J. Baldwin, in his earlier work on steam heating, gave a rule for proportioning steam pipes which is very convenient and has been very widely used. This rule states that in the sectional area of the pipe there should be allowed the area of a 1-inch pipe for every 100 square feet of radiator surface. ”

“ In laying out the floor plans for the heating system of a large office building it is a mistake to try to reduce the number of risers to a minimum. It is much better to put in risers enough so that a radiator can be placed under any window in the building without too long a connection from the riser, for in such buildings one can never know what changes in the arrangement of rooms or in the location of radiators may ultimately be desired. ”

“ If the steam circulation were uniform and continuous and the water of condensation kept separate from the steam supply, as in properly arranged two-pipe systems, the pipes might be very small; but it is necessary to allow for sudden opening of radiator valves, so as to take care of the momentary demand for steam which this causes, as well as the rush of water of condensation which accompanies it. For exhaust and low-pressure gravity systems, it may be laid down as a general rule that pipe sizes should be larger for the simple one-pipe system than for any other arrangement. ”

“ 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 heat conductivity of fluids, liquids and gases is very low, practically zero, but heat is transferred in them by convection. The particles in direct contact with the source of heat are heated above the temperature of the rest, and an increase in temperature of any liquid or gas invariably decreases its specific gravity and causes an upward current of the hot particles, which brings the colder particles in turn in contact with the hot body, thus maintaining a circulation which tends to raise the temperature of the entire mass. ”

“ 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. ”

“ The simplest method, and the one usually employed in exhaust-steam heating, consists in dividing the main exhaust pipe, which receives the exhaust steam from all engines and pumps about the steam plant, into two branches, one leading to the atmosphere, the other being connected to the heating system. On the pipe to the atmosphere is placed a back-pressure valve, the object of which is to automatically maintain a uniform pressure upon the exhaust and upon the heating system, so that the steam may flow into the heating system as fast as it condenses in the radiators. ”

“ But radiators are invariably built of clusters of pipes or surfaces, and as radiant heat travels only in straight lines and perpendicular to the surface of its source, a large proportion of the surface is wasted so far as radiant heat is concerned, due to what may be called the mutual interception of the rays. In the ordinary one-column cast-iron radiator, the proportion of surface from which no radiant heat takes place is nearly 20 per cent., in the two-column, 45 to 55 per cent. ”

“ Theoretically it would be possible to operate a simple gravity system below the atmospheric pressure if the whole system was perfectly air tight and the air was all boiled out of the water and forced out of the system in the first place. In such a case if the fires were put out and the system allowed to become cold, the condensation of steam would leave a perfect vacuum, and on starting up the fire, steam could be carried at any pressure below or above the atmospheric, according to the intensity of the fire. ”

“ This rule when applied to a boiler with a well-designed furnace, stack and setting should be very conservative. It is much better to estimate the steam consumption of the entire plant (see Chapter V., page 60 for steam consumption of radiation) and calculate the boiler requirements according to the rules of boiler design. The designs of the cast-iron heating boilers are innumerable and can only be selected by the careful judgment of the engineer. ”

“ With vacuum systems which have a vacuum only on the air-valve connection, such as the Paul system, it is impracticable to reduce much the sizes of the steam pipes below those given in Table II, as the only feature of this system is that it keeps pipe and radiators perfectly free from air, and does not greatly affect the flow of steam and water of condensation. ”

“ In the gravity system the water stands in the return pipes and risers at practically the same level as that in the boiler, though in the remote parts of the system it rises above the boiler level by a height equivalent to the pressure required to effect the circulation through the system. For this reason gravity systems should be designed for free circulation, with pipes of ample size, the difference of pressure required between the steam mains and the most extreme point of the returns never exceeding a pound or two per square inch. ”

“ 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. ”

“ In practice, a given radiator in a given setting, and with given temperatures of steam and outside air, condition of wind being constant, will deliver a definite amount of air heated to a definite degree and the velocity and final temperature adjust themselves until there is an equality between the temperature head acquired and the velocity head plus the head necessary to overcome the resistance. ”

“ Where boilers of the kinds used for steam power are employed in simple heating plants of large size of which there are to-day but few—there is an old—rule for proportioning the size, to the effect that there must be 1 square foot of boiler surface to 10 square feet of radiating surface. ”

“ Furthermore, experience shows that in order to ensure reliability it is necessary to have a separate flue for almost every room and to locate the radiators, directly beneath the vertical flue, so that in buildings of any size, especially those more than one or two stories in height, the arrangement of radiators in the basement becomes difficult, and the system of air flues, which are necessarily large, is complex and expensive in space and also in construction. ”

“ But forests were in time reduced, cities grew, and buildings were made larger and with a much larger number of rooms; and people were forced to find more economical ways of heating than by laboriously carrying expensive fuel to separate fires in each individual room. Stoves were built to get more uniform combustion and save some of the heat lost up the flue, and gradually various forms of distributing heat through many rooms from one central fire were developed to economize labor. ”

“ It may be stated in general that brick buildings are much tighter than wooden; and fireproof buildings which have wooden flooring laid on some kind of a concrete filling are much tighter than the ordinary brick buildings. It is perhaps a valuable thing that the walls of buildings are not less porous than they are, for in far too many cases there is no ventilation in winter, except what is obtained in this way. ”

“ The chief points to be considered are efficiency of heating surface and capacity of grate in proportion to surface, strength of parts, tightness of joints, ease of cleaning and effectiveness of circulation—there should be no "dead ends" where the water is not kept in circulation by the heat of the fire. ”

“ Flue radiators, such as shown in Figures 12 and 13, are sometimes spoken of as veiled-surface radiators. Most low radiators of considerable width in proportion to the height are of the flue type. The radiator that has been used for direct radiation much more widely than any other is the two-column plain-surface radiator, such as is shown in Figure 10, but the numerous other forms are being more and more extensively introduced.
Most radiators for steam heating have all the loops connected by only one steam passage through the bottom, but some are also connected at the top as well. ”

“ One of the greatest sources of fuel waste is found in uncovered mains in basements of buildings where heat is noth- ing but an inconvenience, and in order to dispel it in moderate weather windows are opened, which greatly increase the wasteful condensation. A good pipe covering will save from 65 to 80 per cent, of the heat which would ordinarily be wasted from the pipes. Coverings of which 85 per cent, is carbonate of magnesia, certain molded forms of pure asbestos fiber, and molded forms of mineral wool are the best kinds of protection for steam pipes to reduce condensation. ”

“ 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. ”

“ 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. ”

“ Consequently an air valve is almost a necessity on every radiator, and those which are now almost universally used are automatic; that is, they close as soon as the hot steam comes in contact with them, and open if air accumulates and they become cold. ”

“ Having selected the system of heating to be employed according to the needs of the building in hand, and having proportioned the radiator surface according to the requirements of the various rooms, it then remains to lay out the system of piping and arrange the various details of construction. ”

“ Exhaust steam heating.—The greater economy in high-pressure steam for engines, however, gradually increased the boiler pressure used for steam power, and with this increase in pressure it became difficult to heat a building directly from the same boiler that supplied steam to the engines, as steam heating at high pressure was found unsatisfactory for many reasons, principally on account of the very high temperature of the radiators and the liability to leaks and the increased danger from water-hammer. ”

“ With these the heating is accomplished entirely by convection, while with direct radiators the radiant heat rarely amounts to 40 per cent., generally not over 30, and often in practice considerably less. For a radiator in any particular location the radiant heat is constant for the same conditions of temperature of the radiator and surrounding objects, and is independent of currents of air. ”

“ Heated air, heated water and steam were all in turn experimented with as a means of distributing heat, and systems employing them have been rapidly and scientifically evolved to meet various requirements, and are to this day very widely used. ”