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In cold and temperate climates, a large portion of human labor is devoted to procure and sustain such a degree of heat, as is necessary to a comfortable existence. The means of effecting this object, as far as the economy of fires and dwellinghouses is concerned, will be considered in the present chapter. To procure heat, to distribute it, to retain it, and to obviate its attendant inconveniences by ventilation, are the principal objects that present themselves in a survey of the subject.
PRODUCTION OF HEAT.
Fuel.--Heat is artificially obtained, for common purposes, by the combustion of fuel. Fuel may be usefully considered with regard to its compactness, or weight, its quantity of combustible matter, and its quantity of water.
Weight of Fuel.--In regard to the first consideration, if other things be equal, the more compact and heavy any fuel is, the more difficult it is to kindle, but the more permanent will it be found, when once on fire. Coal, for example, is a compact fuel, when compared with light, dry wood. Coal cannot so well be kindled by a small blaze, nor by a very small quantity of other combustible matter on fire, because its density renders it a rapid conductor, and it carries off the heat of the kindling substance, so as to extinguish it, before it is itself raised to the temperature necessary for its combustion. But, if the heat of other fuel be applied to it, in sufficient quantity, and long enough, to ignite it, it then produces a powerful fire, and a much more durable one, than lighter fuel. Light fuel, on the other hand, being a slow conductor of heat, kindles easily; and, from the admixture of atmospheric air in its pores and crevices, burns out rapidly, producing a comparatively short, though often a strong heat.
Combustible matter of Fuel.--The quantity of combustible matter of fuel is important, and if the weight and other circumstances be equal, it may be learnt from the ashes, or residuum, left after the combustion. For example,--good Newcastle coal contains a greater portion of combustible matter than some of the Virginia coals, and leaves behind a smaller amount of earthy and incombustible substance. The heating power, and consequent value, of different kinds of fuel, is affected by this circumstance, though by no means dependent on it. The fitness of fuel, for various purposes, is furthermore affected by the facility, with which it gives off a part of its combustible matter, in the form of vapor, or gas; which, being burnt in that state, produces flame.[A] For example, the bituminous coals abound in volatile matter, which, when ignited, supports a powerful blaze. On the other hand, the Lehigh, and other anthracite coals, are destitute of bitumen, and yield but little flame. It is from similar causes, that dry pine wood produces a powerful blaze, while its charcoal yields comparatively little. A blaze is of great service, where heat is required to be applied to an extensive surface, as in reverberating furnaces, ovens, glasshouses, &c. But, when an equable, condensed, or lasting, fire is wanted, the more solid fuels which blaze less, are to be preferred.
Water in Fuel.--The quantity of watery fluid contained in fuel, greatly affects the amount of heat it produces, much more, indeed, than is commonly admitted in practice. It is a well-known law of chemistry, that the evaporation of liquids, or their conversion into steam, consumes, and renders latent, a great amount of caloric. When green wood, or wet coal, are added to the fire, they abstract from it, by degrees, a sufficient part of its heat, to convert their own sap, or moisture, into steam, before they are capable of being burnt. And, as long as any considerable part of this fluid remains unevaporated, the combustion goes on slowly, the fire is dull, and the heat feeble. Green wood commonly contains a third, or more, of its weight of watery fluid; the quantity varying, according to the greater or less porosity of different trees. Nothing is further from true economy, than to burn green wood, or wet coal, on the supposition that, because they are more durable, they will, in the end, prove more cheap. It is true, their consumption is less rapid; but, to produce a given amount of heat, a far greater amount of fuel must be consumed. Wood that is dried under cover, is better than wood dried in the open air, being more free from decomposition.
[A] See Chapter IX., Art. Flame.
Not only the production of steam, but likewise the formation of different gases, which are evolved during combustion, affect the usefulness of fuel, according to their quantity and capacity for heat. It is difficult, however, to estimate with accuracy, the amount of their practical effect.
Charcoal.--Charcoal is prepared from wood, and coke in a similar manner from pitcoal, by raising those substances to a high temperature, sufficient to deprive them of their moisture and volatile matter. When intended for chemical uses, charcoal is made by exposing wood to heat, in iron cylinders, or other close vessels. It is also manufactured in kilns, built for the purpose. But, for the common purposes of fuel, it is made by a sort of smothered combustion, in which masses of wood, when set on fire, are covered with earth, so as nearly to exclude the atmospheric air. This exclusion of air prevents the wood from being consumed, while the red heat, which is kept up for some time, dissipates the moisture from its pores. Charcoal is generated in a small way, every night, in fires which are raked up; the brands, and half-burnt coals, are kept from consuming, by the partial exclusion of the air, while the light ashes, being a slow conductor of caloric, prevent them from cooling below a red heat. Charcoal, when newly made from the heavier kinds of wood, such as oak and walnut, is a powerful, and, for some purposes, an economical kind of fuel. Coke, a kind of fuel, used for certain purposes in England, and this country, is charred pitcoal. It produces a strong and steady heat, but does not blaze. Large quantities of coke are formed in the manufactories of coal gas. A kind of charcoal, said to be of superior quality, has been manufactured in France, from peat.
COMMUNICATION OF HEAT.
Radiated and conducted Heat.--Caloric, or heat, is communicated to apartments, by fires kept in them, in two ways. A part of it is radiated, the rest is conducted. The first portion passes through the air with great velocity, in diverging rays. The second penetrates slowly through the densest bodies, whether transparent, or opaque. In a fireplace, or open stove, the heat, which is felt by holding the hand before the fire, is radiated caloric. That which is felt by placing the band on the iron, or bricks, is conducted caloric. To enjoy the full effect of radiated caloric, we must be in presence, or sight, of the radiating object. To receive conducted heat, we must be in contact with the substance which imparts it. Since, however, we cannot remain in contact with the fire itself, we derive our conducted heat from the air, a fluid, which constantly touches, and envelopes our persons; and which, when heated, in itself becomes a source of warmth to us. The object of the various contrivances, known under the names of stoves and fireplaces, is to enable us to use fire with safety, and to obtain from it a due supply of radiated caloric, and heated air.
In common cases, radiant heat is more agreeable than conducted heat, when we wish to obtain a sudden warmth; since its degree may be increased at pleasure, by altering our proximity to the fire; the effect of the radiation being inversely proportionate to the square of the distance. But, as only one half of the recipient body can be warmed at a time, by radiation, no person, surrounded by a cold atmosphere, can be made uniformly warm, by the radiated heat of a fire. It is only when the surrounding atmospheric air has become warm, and a counter radiation is produced from other objects, that we obtain all the advantage which fire is capable of affording.
Fire in the open Air.--The simplest, and least effectual, mode by which heat can be obtained, is from a fire in the open air. The hunter, or backwoodsman, when he encamps for the night, builds a fire of logs, and lays down to sleep, with his feet extended towards it. In this situation, he can enjoy only a small portion of the radiated heat of the fire, this heat being thrown off equally in all other directions. Of the conducted heat, he obtains none; for the air which surrounds the fire, having nothing to confine it, ascends, by its diminished specific gravity, as fast as it is warmed, and its place is immediately supplied by strata of colder air from beneath. Hence, a current of cold air will take place, from the atmosphere, on all sides, towards the fire, so that the person who derives warmth from the fire, on one side, will on the other be exposed to additional cold. The first step towards remedying this inconvenience, is, to build up a barrier, or imperfect wall, on the outside of the place occupied by the tenant. This will intercept the current of cold air, and oblige it to approach the fire by other directions, at the same time that it will gradually become heated itself, and radiate back a portion of its warmth. The next improvement consists in extending the wall, so as completely to surround the fire, thus obliging the air to approach it from above, or from doors and avenues purposely left for its entrance. This is, in fact, the commencement of a dwellinghouse. A roof, with an aperture for the escape of the smoke, is a further improvement on the plan, and, lastly, the introduction of a chimney, at once renders the mansion convenient and tenantable.
Fireplaces.--Chimneys, from their usual situation in regard to rooms, and also for the sake of a more perfect draught, have an opening on one side of their base, to which we give the name of fireplace. The fireplace, in former times, was an oblong, or cubical, cavity, having its sides nearly at right angles with the back. In a cavity of this description, the greater part of the heat, generated by the fire, was totally lost to the apartment, nearly all the conducted heat being carried, with the air, up the chimney; while, of the radiated heat, but a small part could directly enter the room, viz., the part radiated from the front of the fire; the heat of the other sides being chiefly thrown into the hearth, back, and sides, or up the chimney. In the old fireplaces, the inconvenience was still further augmented, by increasing their dimensions to an enormous size, so that seats or benches could be placed on each side, on the inside of the jambs. The consequence was, that a prodigious current of air was constantly carried up the chimney, and the seats, on the inside of the fireplace, became the only comfortable ones in the room.
Admission of Cold Air.--It is obvious, that in apartments with open fireplaces, the air must be continually shifting, and that cold air must enter at the crevices of the doors and windows, to supply the place of that which maintains the combustion, or escapes up the chimney. In moderate weather, this change of air is an advantage, since it freshens and ventilates the room, the air of which would otherwise become close and impure. In moderate weather, also, the radiant heat is adequate to warm the walls of the room, which, in their turn, become sources of radiant heat, and likewise contribute to warm the air by their contact. But, in very cold weather, it is difficult to render a large apartment warm by means of a common open fireplace; for, in proportion to the briskness of the fire itself, will be the rapidity with which the cold air presses into the room, and a person near the hearth feels, perhaps, as much cold on one side of his body, as heat on the other.
Open Fires.--The cheerful sight of an open fire, to which habit and association have attached us, has created a strong, and almost general, preference for the open fireplace, over the close stove, and a desire, by remedying its defects, to make it more effectual and useful. Of various philosophers who have exercised their ingenuity on this subject, the two who appear to have labored with most success, are our countrymen, Dr. Franklin, and Count Rumford.
Franklin Stove.--Dr. Franklin, whose writings on the economy of fire contain the basis of many of the improvements which have since been introduced, invented an apparatus of cast-iron, to which he gave the name of the Pennsylvania Fireplace, but which is now often known by the name of Franklin Stove. This fireplace, when executed agreeably to the author's instructions, is one of the most effective and economical modes in which an open fire can be managed. By means of a narrow and circuitous smoke-flue, which is surrounded and intersected with air passages, a great part of the heat of the fire is retained in the room, and, at the same time, a current of fresh air, warmed by the fireplace, is introduced into the apartment. In Fig. 86, is seen a section of the Pennsylvania fireplace. A, is the place of the fuel and fire; BCD, the smoke flue, passing, first upward, then downward to the floor, and escaping by the chimney, D, next the wall, K. EH, is the air chamber, into which the air is admitted from without the house, through the passage, I. After being heated, it is discharged into the apartment by lateral openings at the top, G.[A]
Fireplaces which stand out into the room, and fireplaces with hollow backs, or pipes for hot air, are to be viewed, in most instances, as simplifications only, of Franklin's plan.
Rumford Fireplace.---Count Rumford's fireplace forms a pleasant and effectual mode of economizing the heat of an open fire; besides which, its cheapness and simplicity give it the advantage over more complicated plans, and have occasioned its very general introduction. The peculiarities of this fireplace consist, 1st, in an advanced back, which brings the fire nearer into the room, and, at the same time, by narrowing the throat of the chimney, diminishes the current of air which escapes through it; 2dly, in the oblique sides, or covings, of the fireplace, which are enabled, when heated, to radiate their warmth into the room. Count Rumford recommends that the angle, made by the sides with the back, should be one of one hundred and thirty-five degrees. He also advises that the color of the covings should be white, this color being best adapted for radiation.
Double Fireplace.--For parlors, and common apartments, no contrivance appears so pleasant and effectual, as the double fireplace, which has, of late years, been extensively introduced in this city and vicinity. It is a modification of Franklin's plan, and is made from any common fireplace, by inserting within it another fireplace, made of soapstone, leaving an empty space, of about an inch in depth, between the two, so that, when finished, the back and sides may be hollow. This hollow space does not communicate with the fire, but has two openings, one at bottom, communicating with the external atmosphere by a perforation in the wall, or by a tin pipe laid in the floor; the other, opening into the apartment, at a point higher than the fireplace, and commonly at the side of the chimney. In this fireplace, an open fire, of wood or coal, may be used with the full advantage, ever obtained, of its radiant heat. A large part of the conducted heat is also saved, since the air, which enters from without, becomes heated in the hollow space, and ascends by it, in consequence of its diminished specific gravity, entering the room in a strong warm current. This air serves the purpose of ventilation; it supersedes the entrance of cold air through the crevices and keyholes, and is also a preventive against smoking. The circumstances to be attended to, in the construction, are as follows: 1. The openings for the air should be large, in common cases from four to seven inches in diameter, since it is better to introduce a large quantity of air, moderately warmed, than a small quantity made very hot. More heat will, in this case, be conducted from the stone, and the unpleasant effects of burnt air will be avoided. 2. The openings into the room should be made, when practicable, at least a foot higher than the top of the fireplace; for, when they are on a level with it, or lower, the warm air is liable to be drawn up the chimney, and the main object defeated. But, if the opening is above the fireplace, then the warm air will ascend, and be diffused through the upper parts of the room, till the whole is gradually warmed. 3. The cold air should be taken from without the house, and not from an entry or cellar; because changing the air of those places, in Winter, is apt to reduce them to a freezing temperature. The external opening should be guarded with a wire net, to exclude leaves and light substances; and the internal, should be commanded by a shutter, to regulate the heat. For safety, it is best, though not always
necessary, that the hot air passage should not be in contact with the wood work of the house. 4. Good soapstone is the best material for these fireplaces, and, with careful use, will last many years. See Soapstone. For wood fires, the stone should be an inch and a half thick, and for coal fires, two or three inches.
[A] Most of the articles, now sold as Franklin stoves, are very different from the original Pennsylvania fireplace. If any defect existed in the plan of the inventor, it was in the small quantity of air admitted through a circuitous and obstructed channel, and in the bad character of the material, cast-iron being liable to warp and crack, if exposed to great heat and cold on opposite sides.
The first person who suggested the introduction of heated air, through hollow passages, appears to have been M. Gauger, in a work, entitled, La Mechanique de Feu, published in 1709.
In Fig. 87, is a section of a double fireplace. A, is the place of the fire; H, the soapstone back; B, the throat; C, the chimney; E, the external opening; DGG, the hollow, or passage, for heated air; M, a pipe for conveying the hot air to N, a lateral opening into the room; P, the mantel-piece. A soapstone fireplace may be rendered very effectual, by causing it to project a little into the room, and by adding an air box to the top, as seen in Figs. 88 and 89. In the section, Fig. 88, A, is the fire; BB, the smoke passage; C c c, the air passage; D, a box for heated air, covering the fireplace, and communicating with the hollow back c c, by a side passage, at the dotted lines; E, a side opening for discharging the hot air into the room; G, the mantel-piece. In fireplaces of cheap construction, a simple, hollow back, made by one slab of soapstone, with openings, as have been described, will contribute much to increase the warmth of the room.
Coal Grate.--When coals are used for fuel, it is necessary, on account of their small size, to confine them together with a grate. As they contain more combustible matter, in the same space, than wood, and produce a greater degree of heat, a much smaller fireplace answers for them. A very small throat, also, in the chimney, is sufficient to carry off the smoke from a common coal grate. With this exception, it has the same characteristics as a common fireplace.
Anthracite Grate.--Grates for burning anthracite, require more perpendicular height than others, and should be of such a proportionate depth, as will keep the coal together, and not offer too great a surface to the atmosphere. In extremely cold weather, it is observed, that the front surface of anthracite grows black, and burns feebly, in an open grate, while it does not in a furnace or stove. In this case, the cold air conducts off the heat of the surface faster than the combustion renews it; and, if the amount of surface be too great, in proportion, for that of the solid contents, the fire will go out. Anthracite grates are usually provided with a very narrow throat, to carry off the gases, which result from the combustion; there being no visible smoke. The throat, however, should always be large enough to transmit the smoke of any other fuel; for otherwise, a part of the carbonic acid which is formed, will escape into the room, and contaminate the atmosphere, in the same way as burning charcoal. See chapter II. article Anthracite.
Burns's Grate.--Mr. Burns, of Glasgow, has made an alteration in the coal grate, by introducing the external air through an opening immediately under the grate. This air supplies the fuel with oxygen, and furnishes most of the current which passes up the chimney. The air of the room, of course, remains comparatively stationary, and is sooner heated. This plan, when combined with the double fireplace, already mentioned, is a powerful mode of obtaining heat. A movable stone screen may be placed in front of the ash pit, to prevent the ashes from being blown into the room. The external opening which admits the air, should not be near any wood work, as sometimes the current is reversed by winds, and sparks and smoke are driven out at the opening.
Building a Fire.--In building and maintaining an open fire, whether of wood or coal, certain circumstances deserve attention, in the common fireplaces. It is advantageous, to make the perpendicular height of the fuel as great, as is consistent with safety. A stratum of coals, or ignited wood, will radiate more heat into the lower part of the room, if placed vertically, than if laid horizontally Fuel, for economy, should be so subdivided, as to be easy of ignition, and so placed, as to give free access for the air to its different surfaces. In this way, the smoke is more likely to be burnt. To secure the greatest effect of radiation, the combustion should be kept, as much as possible, to the front surface. In kindling a fire, the live coals should be kept together, and placed near the bottom. A blower, added to a common grate, converts it, for the time being, into a wind furnace.
Furnaces.--The object of the furnaces, used by artists and manufacturers, is the reverse of that intended to be produced by stoves and fireplaces; furnaces being required to produce an intense heat, and to confine it to a limited space. Hence, furnaces and their chimneys are surrounded with non-conductors, that they may expend as little of their heat as possible, on the air and surrounding objects. They are commonly made of fire-proof bricks, and, when small, are enclosed in iron. Their most simple form is that of an upright, hollow cylinder, with a grate at bottom. Air, or wind, furnaces, have their combustion supported by a draught of air, which ascends rapidly, because it is strongly heated and rarefied. Blast furnaces have the air driven through their fuel with bellows. Reverberating furnaces are provided with a concave covering, which reverberates, or throws back the flame, upon the substances to be heated or melted. There are some cases, in which furnaces are used for warming dwellinghouses, particularly when fuel is used which requires strong ignition, such as the anthracites.
Stoves.--Stoves differ from fireplaces, by enclosing the fire, so as to exclude it from sight, the heat being given out through the material of which the stove is composed. The common Holland stove, of which we have an almost infinite variety of modifications, is an iron box, of an oblong square form, intended to stand in the middle of a room. The air is admitted to the fire through a small opening in the door, and the smoke passes off through a narrow funnel. The advantages of this stove, are--1. That, being insulated, and detached from the walls of the room, a greater part of the heat, produced by the combustion, is saved. The radiated heat being thrown into the walls of the stove, they become hot, and, in their turn, radiate heat on all sides to the room. The conducted heat is also received by successive portions of the air of the room, which pass in contact with the stove. 2. The air being made, as in furnaces, to pass through the fuel, a very small supply is sufficient to keep up the combustion, so that little need be taken out of the room. 3. The smoke, being confined by the cavity of the stove, cannot easily escape into the room, and may be made to pass off by a small funnel, which, if sufficiently thin and circuitous, may cause the smoke to part with a great portion of its heat, before it leaves the apartment. These circumstances render the Holland stove one of the most powerful means we can employ, for keeping up a regular and effectual heat, with a small expense of fuel.
The disadvantages of these stoves are, that houses containing them are never well ventilated, but that the same air remains stagnant in a room, for a great length of time. Hence, it necessarily becomes impure, by the breath of persons who remain in it, and by the burning of dust, and other substances, which settle on the heated iron of the stove. A dryness of the air is also produced, which is oppressive to most persons, so that it often becomes necessary to place an open vessel of water on the stove, the evaporation of which may supply moisture to the atmosphere. Where rooms are kept very warm by stoves, it is found advantageous, even, to cause the water to boil, in order to insure a sufficient supply of vapor. Stoves are very useful in large rooms, which are frequented occasionally, but not inhabited constantly; as halls, churches, &c. But, for common rooms, which are occupied at all times, they are objectionable, for the reasons which have been stated.
Russian Stove.--In cold countries, where it is desirable to obtain a comfortable warmth, even at the sacrifice of other conveniences, various modifications of the common stoves have been introduced, to render them more powerful, and their heat more effectual. The Swedish and Russian stoves are small furnaces, with a very circuitous smoke-flue. In principle, they resemble a common stove, with a funnel bent round and round, until it has performed a great number of turns, or revolutions, before it enters the chimney. It differs, however, in being wholly enclosed in a large box of stone, or brick work, which is intersected with air pipes. In operation, it communicates heat more slowly, being longer in becoming hot, and also slower in becoming cold, than the common stove. Russian stoves are usually provided with a damper, or valve, at top, which is used to close the funnel, or passage, when the smoke has ceased to ascend. Its operation, however, is highly pernicious; since burning coals, when they have ceased to smoke, always give out carbonic acid in large quantities, which, if it does not escape up the chimney, must deteriorate the air of the apartment, and render it unsafe.
Cockle.--The name of cockle is given to an upper part of a stove, or furnace, resembling an inverted vessel. A large cockle saves much heat, since its extensive surface conveys the heat from the flame and smoke, and communicates it to the atmosphere. In some stoves, the cockle is filled with a checker-work of bricks, among which the smoke and flame circulate. After becoming once heated, these bricks are slow in cooling, and continue to yield warmth to the apartment, like the Russian stoves, for some time after the fire is extinguished.
Thermometer Stove.--Dr. Arnott's thermometer stove is a contrivance, for keeping up a uniform temperature, by an apparatus which regulates its own combustion, increasing or diminishing the draught, as the temperature falls or rises. It consists of an interior stove, or fire-pot, for burning anthracite coal, lined with fire-brick, and provided with the usual appendages of a door, grate, ash-pit, and pipe, or smoke-flue. Outside of this fire-pot, is placed a much larger box of sheet iron, in which the smoke, or rather the hot gas, from the anthracite, is made to circulate, by means of internal screens or partitions, until it is at length discharged into the chimney, thus keeping the surface of the outer box equally heated, in all parts. But the peculiar characteristic of this stove consists in a self-regulating door, or valve, which admits the air to support the combustion, and which shuts, when the heat increases, and opens when it diminishes, so that the quantity of air admitted shall be such as to sustain always a uniform temperature. This air regulator is constructed on the principle, that all bodies expand by heat, and it may be contrived in a variety of ways. Bars, compounded of metals, having a different expansibility, have been made, to open and shut valves, as the heat and expansion increase or diminish. Out of many contrivances, Dr. Arnott appears to prefer some form of an inverted syphon, containing mercury, with a column of air inclosed in one of its legs. When the air expands or contracts, it moves the column of mercury, carrying with it a float, which raises or depresses the valve commanding the door.
The air regulator appears useful in remedying the evil, to which small anthracite stoves are liable, of burning out the coal too rapidly, and overheating the room at some times, while they are deficient in heat at others. Some objection would seem to exist against the employment of mercury in the regulator, on account of, the deleterious fumes which may arise from that metal, when heated. But no practical inconvenience appears to have been noticed in Dr. Arnott's work. In regard to its heating power, it may be doubted whether this stove is adequate to counteract the cold of an American Winter, in the Northern States.
Carrying Heat.--Besides the methods, already mentioned, by which rooms are warmed by the radiation and communication of heat, from fires kept in the rooms themselves; another method has been used, in various buildings, by which fires, burning in one room, or part of the building, may warm other rooms, at a distance. This is done by communicating the heat to some movable vehicle, which afterwards carries it to different parts of the building, and expends it where it is wanted. The vehicles employed for this purpose are currents of air, water, and steam.
Heating by Air Flues.--Such is the tendency of heated, or rarefied, air to ascend, that buildings may be effectually warmed by air flues, communicating with stoves in the cellar, or any part of the building below that to be warmed. A large suite of apartments may be sufficiently heated, in this way, by a single stove. The stove, for this purpose, should be large, and of a kind best adapted to communicate heat. It should be entirely enclosed in a detached brick chamber, the wall of which should be double, that it may be a better non-conductor, and prevent waste of the heat. The space between the brick chamber and stove, should not exceed an inch. In the apparatus of the Derbyshire and Wakefield Infirmaries, which has been imitated in this country, the whole of the air is repeatedly conducted, by numerous pipes, within half an inch of the stove and its cockle. For the supply of fuel, the same door which opens into the chamber, should open also into the stove, that there may never be any communication with the air of the cellar. A current of external air should be brought down by a separate passage, and delivered under the stove. A part of this air is admitted, to supply the combustion; the rest passes upward, in the cavity between the hot stove and the wall of the brick chamber, and, after becoming thoroughly heated, is conducted through passages in which its levity causes it to ascend, and be delivered into any apartment of the house. Different branches being established from the main pipe, and commanded by valves or shutters, the hot air can be distributed at pleasure, to any one or more rooms at a time. This plan is very useful in large buildings, such as manufactories, hospitals, &c, on account of the facility with which the same stove may be made to warm the whole, or any part of them. The advantage of a long, vertical, draught, enables us to establish a more forcible current of warm air. The rooms, while they are heated, are also tolerably ventilated; for the air, which is continually brought in by the warm pipes, displaces that which was previously in the room, which blows out at the crevices and keyholes, instead of blowing in, as it does in rooms with common fireplaces. Nevertheless, the warmth obtained from heated air alone, has some disadvantages, when compared with radiant heat, as is stated in the general remarks, at the end of this chapter.
Heating by Water.--Rooms may be warmed by causing a current of hot water to circulate through them, in tubes of various forms, giving out its heat as it proceeds. If we suppose a tight tube, of a circular form, to be filled with water, and placed upright, it may represent the simplest form of this apparatus. If a fire be applied to one side of this tube, the water in that side will become gradually heated, and, being thus rendered specifically lighter than the rest of the water, it will ascend, causing the water of the opposite side to descend, until it comes, in its turn, to be heated by the fire. Thus a continued current will be kept up, and heat given out from the most distant parts of the tube. By varying the application of this principle, hot water has been made to warm manufactories, dwellinghouses, and conservatories. But, when much heat is required, the apparatus becomes large and expensive; and, if negligently attended in Winter, the water is liable to freeze, and burst the tubes.
Another mode has been introduced by Mr. Perkins, of heating by water under a high pressure. In this mode, the water is confined in strong iron tubes, not exceeding an inch or two in diameter, and variously convoluted, so as to afford the requisite amount of surface, for giving off the heat. The water is raised to a higher temperature than the boiling point, the strength of the tubes counteracting its explosive tendency. It thus gives off more heat than water, at temperatures below this point; but its use requires caution.
Heating by Steam.--Steam is found to be a useful medium for communicating heat to large buildings. It has the advantage, that it conveys heat in any direction, horizontally, upward, or downward, and to the most remote apartments of the largest buildings. In greenhouses, it has been made to yield a sufficient supply of heat, at the distance of eight hundred feet from the boiler in which it is produced. When steam of low pressure is employed, the heat never exceeds two hundred and twelve degrees, Fahrenheit, so that the air, in contact with the apparatus, is never contaminated by the burning of dust.
In constructions for heating by steam, a strong boiler is made use of, provided with a safety-valve, and the other appendages common to the boilers of steam-engines. From this boiler, a steam-pipe is carried in any required direction, and distributes branches to the different apartments which are to be warmed. Whenever the Water in the boiler is heated to the point of ebullition, steam passes into the pipes, and drives out the atmospheric air through valves, provided for the purpose. As long as the surface of the pipes remains of a less heat than two hundred and twelve degrees, a part of the steam continually condenses, and is immediately succeeded by fresh steam from the boiler. In the act of condensing, it gives out its latent heat to the material of which the pipe is made, and this material, in turn, imparts it to the air of the room. In this manner, the steam will continue to be condensed, and to give out heat, as long as the air of the room is at any point, below two hundred and twelve degrees. By the condensation, a quantity of water is constantly formed, which, for economy of heat, is returned by a separate pipe, while it is yet warm, to the boiler. Inverted syphons, containing water, are used, to prevent the air and steam from communicating. If the steam pipes are made of thin, or weak materials, it is necessary to provide them with safety valves, opening inward; otherwise, they would be crushed, by the pressure of the atmosphere, when the fire is extinguished.
In calculating the effect of this method, it has been ascertained, that, under favorable circumstances, one cubic foot of boiler will heat about two thousand cubic feet of space, in a cotton-mill, where the required temperature is from seventy to eighty degrees of Fahrenheit.[A] And, if we allow twenty-five cubic feet of a boiler for one horse's power, in a steam-engine supplied by it, it will follow, that such a boiler is adequate to warm fifty thousand cubic feet of space, for every horse's power. It is said, also, that every square foot of surface, in a steam-pipe, will warm two hundred cubic feet of space. These calculations, however, do not apply to buildings unfavorably arranged, nor to very cold weather. The pipes, employed to distribute the steam, should be made of materials which cool most rapidly. Iron, of which the surface is tarnished with rust, is found to exceed tinned iron, in the rapidity of cooling, in the proportion of about eighteen to ten.[A] Room must be allowed for the expansion of the pipes, which, in cast-iron, may be taken at a tenth of an inch for every ten feet in length. In cotton and calico manufactories, steam is found very advantageous in drying cloths quickly, and well.
[A] Buchanan, on Heat and Fuel, p. 160.
In comparing the effect of steam heat, with that of smoke-flues, different representations have been made by writers on the subject. Mr. Tredgold observes, that "he must be a novice in the science of heat, who cannot produce nearly the same effect by the one as by the other, all other circumstances being the same." The steam-apparatus, however, requires more careful management, and does not admit of neglect. Although easily kept in order, by a skilful attendant, yet it cannot, in common cases, be intrusted to ordinary or careless persons.
RETENTION OF HEAT.
Causes of Loss.--However advantageously heat may be produced and distributed, it will fail in producing its desired effect, unless suitable provision is made for retaining it, where it is wanted. Heat constantly tends to an equilibrium; and, unless this tendency be retarded, dwellinghouses and their apartments will cool, as fast as they are warmed. The chief causes which operate to cool apartments, are--1. The escape of the warm air upward, through crevices, apertures, and chimneys. 2. The power of conducting and of radiating heat, which all substances possess, in a greater or less degree, and by which the internal heat of houses is gradually conveyed to the external atmosphere. To obviate the first of these causes, apartments should be made as tight as possible; and to prevent the second, at least in part, their walls should be made thick, and of materials which are slow conductors of heat.
[A] Tredgold, p. 58.
Crevices.--As crevices in rooms commonly occur from the shrinking of their materials, care should be taken to employ, in building, wood which is thoroughly seasoned, and which is known to be permanent in its dimensions. Of the kinds of wood employed for doors and windows, mahogany is the most permanent, and next to this, is cherry-tree, and pine. Oak, and some other hard woods, are very liable to shrink, and crack.
Chimneys.--Chimneys occasion less expenditure of warm air from rooms, than their size would lead us to expect, because they open at the bottom, or near the floor. If, therefore, the room be tight, and the chimney cold,. the warm air, while at rest, will be retained in the upper portion of the room, or that which is above the fireplace, as effectually as in a gasometer. But if a chimney is heated, and a current thus established through it, it may then drain off the air of the apartment; and hence the foundation for the common belief, that a room becomes colder in the night, for having had a fire in the day. The warm air may be retained, if the throat of the fireplace be closed with a damper.
Entries and Skylights.--Entries, as they are commonly constructed, extending from the bottom of a house, to the top, have a bad influence on the retention of heat. The evil is increased, when they are surmounted with a skylight, the panes of which are arranged like tiles, and not air tight. Such entries are difficult to warm, and serve to drain off the warm air of apartments, whenever the communicating doors are left open; and to transmit it to the roof.[A] To prevent this effect, entries should be commanded with doors in different stories; and skylights should be made sufficiently erect, to have their sashes complete, or else a tight, horizontal window should be added, underneath the skylight.
Windows.--The heat conducted off by the external atmosphere, passes, most readily, through the windows, since the walls of houses, especially when thick, are slow in conducting caloric, while a pane of glass interposes but a slight barrier against its escape. On this account, the unnecessary multiplication of windows should be avoided. In cold climates, a great advantage is obtained from using double windows in winter, which, by confining between them a stratum of air, interpose a powerful non-conductor between the room and the atmosphere. To secure the full benefit of the double window, it should be made sufficiently tight, so that the included stratum of air may not easily change; otherwise, the expected benefit will not be obtained. It should not, however, be hermetically tight, for, in that case, the glass may become opaque in Winter, by the condensation of moisture.
[A] The opposite currents, in an open door, by which cold air enters at bottom, and warm air escapes at top, may be made obvious, in the familiar experiment of holding a lighted candle at the bottom and top of the door. In one case, the flame will point into the room, and in the other, out of it.
Objects.--If the only object of human habitations were to procure heat, it would be best obtained by keeping the air in a state of stagnation, and employing those means to create warmth, which are attended with the least circulation, or change. But, since the air of inhabited rooms would become, in time, unfit for respiration, it is necessary that it should be removed, as fast as deteriorated, and be replaced by fresh air from abroad.
Modes.--Rooms which are heated with stoves, are never well ventilated. Those heated by common fireplaces, are ventilated, at the expense of losing much of their warmth by the admission of cold air. Those heated by the double fireplace, [p. 310,] are sufficiently ventilated, with air at an agreeable temperature. Rooms heated by steam, or by hot water, are not at all ventilated, unless it be by additional arrangements. Those warmed by hot-air flues are apparently well ventilated; yet, in hospitals, and crowded buildings, it is sometimes necessary to add fire-places, or other openings, for discharging the air.
Ventilators.--The principal gases, which it is the object of ventilation to remove, are carbonic acid, and nitrogen; these being produced in excess, by the process of respiration, by the combustion of lamps, and by fires with an imperfect draught. The specific gravity of carbonic acid is greater than that of common air. That of nitrogen is somewhat less. These gases, when evolved, are at a higher temperature than the surrounding air, and are mixed with steam; therefore, while rarefied by heat, they ascend to the top of the apartment. On this account the ventilators intended to discharge them, are made to consist of openings, commanded by shutters, at the upper part of the room. In rooms which are liable to be crowded with people, these ventilators have a good effect, especially in warm weather, and the larger they are, the greater is the advantage derived from them. In cold weather, however, they have the disadvantage, that they discharge the pure heated air, in common with the noxious vapors, and thus defeat our efforts to obtain warmth. In common dwellinghouses, no more ventilation is necessary, than can be obtained from doors, open fireplaces, and windows, which open at top, as well as at bottom.
An ingenious and effectual mode of ventilation has been introduced in the House of Commons in London, by Professor Reid. The fresh air, before entering the house, is warmed, by passing between flat tubes of iron, filled with hot water. From a place of these, in a vault below, it spreads under the floor, and enters the room from a vast number of small openings in the floor. It then passes upward, carrying with it the impure gases of the room, and escapes, through openings made for the purpose in the ceiling. From these, it is collected, and carried downward, in a suitable flue, till it arrives under the grate, where it is used to feed the fire. A regular and agreeable change of air is thus kept up, sufficient, it is said, to render imperceptible in a few minutes, the vapor of ether, or of fired gunpowder. Some inconvenience has been experienced from the raising of dust, introduced on the feet of the occupants; but this, as Dr. Arnott suggests, might be remedied, by making the air enter a little above the floor, or carpet.
Dr. Ure recommends the ventilation of crowded rooms by mechanical means. A fan ventilator, made to revolve by a steam-engine, produces an effect thirty-eight times greater, than can be obtained by the consumption of the same fuel, in the ordinary mode of chimney ventilation.
Culverts.--In the Derbyshire Infirmary, an ingenious mode of ventilation is adopted, by means of an empty culvert, or subterranean passage; one end of which opens into the building, while the other end is provided with a turncap, presenting its open mouth to the wind. The air, in passing this culvert, partakes of the temperature of the earth, and is thus warmed in Winter, and cooled in Summer. The effect, however, is obviously of a limited kind, since the continual transmission of air must bring the surface of the culvert to a temperature, approaching that of the surface of the ground.
Smoky Rooms.--Under the head of ventilation, may be placed the art of remedying smoky apartments. Smoke is a heterogeneous vapor, composed of the gases which result from combustion, together with a quantity of opaque matter, which escapes from the fuel without being burnt. Smoke is specifically heavier than the atmosphere, and always descends, after it is cooled, as may be seen by observing the current of smoke from a chimney, in a cold morning. At the time, however, of its disengagement from the fire, it is rarefied by heat, and will always ascend through a chimney properly constructed, if it is not prevented by some opposing influence. The causes which produce smoky apartments are, principally, the following.
Damp Chimneys.--When a fire is first made in a chimney, which has not been used for many months, it is apt to smoke. This is, because the chimney is cold, and the column of air which it contains is not lighter than the surrounding atmosphere. The difficulty of remedying this evil is greater, if the bricks have absorbed much moisture, or the chimney be new; as; in this case, the chimney will not be well heated, till the moisture is evaporated. To expedite the drying and heating of the chimney, a window should be kept open on the side against which the wind blows, and the communication with the rest of the house, at the same time, closed. This will mechanically assist the smoke and hot air, in ascending the chimney.
Large Fireplaces.--If a fireplace be made too high, it will be liable to smoke; for, since the throat of the chimney takes in air from all directions, if the fire be too remote from this point, its smoke will be less likely to find its proper way. On the other hand, the lower the mantel-piece is brought, the nearer will the fireplace approach to the character of a wind furnace. In like manner, if the throat of the fireplace be too large, the air of the room, as well as that of the fire, will pass freely up the chimney, and thus the whole included air being colder, its current will be more sluggish. The advanced back of the Rumford fireplace, by contracting the throat, remedies this difficulty; and, at the same time, presents a mechanical obstacle against sudden counter currents.
Close Rooms.--Closeness of a room is a cause of its being smoky. If the walls, doors, and windows, are air tight, or nearly so, the outer air cannot enter, to take the place of that which passes up the chimney. The current of heated air and smoke will, therefore, be interrupted, and expand into the room. In most rooms, it happens, that the crevices, occasioned by the shrinking of the wood, or by the want of exactness in finishing, admit air enough, and more than enough, to supply the chimney. In new apartments, however, where all the joinings have been made with great accuracy, it has been found necessary to make perforations in the walls, to admit air sufficient to keep up a current. These should always be made behind the back of the fireplace, when possible, for reasons already explained.
Contiguous Doors.--The doors of a room, if placed very near a fireplace, or on the same side of the room with it, are apt to occasion a smoke, as often as they are opened. The gust of air, which enters at an open door, so situated, blows across the chimney. A part of it ascends the flue, while the rest extends into the room, carrying with it a part of the smoke.
Short Chimneys.--The longer a chimney is, the more perfect is its draught, since the upward tendency is proportionate to the difference of weight, between the column of air included in the chimney, and a similar column of external air. Short chimneys, or flues, are liable to smoke, from the heated passage not being long enough to establish a strong current. The fireplaces in upper stories are more apt to smoke, than those in the lower apartments. In low houses, outhouses, &c., the chimney should always be carried to the greatest practicable height. Two flues, in the same chimney, or stack, should not communicate at any point, short of the top.
Opposite Fireplaces.--When two chimneys exist in different parts of the same room, or in rooms which communicate by doors, it is difficult to kindle a fire in one, while the other is burning, especially if the room be tight; because, in this case, the fire, which is first established, feeds itself by a current brought down the vacant chimney. After both fires are kindled, it is necessary to keep up a certain equilibrium between them, otherwise, the stronger will overpower the latter, and draw down its smoke into the room. If doors or windows be opened, the evil is obviated. If the fires are in different rooms, the communicating doors between them should be shut.
Neighboring Eminences.--The vicinity of elevated objects, such as hills, precipices, or very high buildings, is productive of smoky rooms to houses in their neighborhood. When the wind blows in a direction from the elevated object to the house, it falls down, in an oblique direction, upon the roof; a part of it enters the chimney, and beats down the smoke, by overpowering its current. On the other hand, when the wind sets towards the hill, or elevated object, its passage becomes obstructed, and it presses in every direction to escape; and while its upper portions pass off by the top of the opposing body, the lower portions press downward, through any passages which may afford them an escape. Chimneys, in houses thus situated, should be carried up to a great height, so as, if possible, to overtop the eminence, their sides being secured by iron braces.
Turncap, &c.--In many instances, a turncap, which is a curved tube, regulated by a weathercock, so as always to turn its mouth in a direction from the wind, will prevent smoking, in the case last stated. The turncap offers, also, a security against the influence of strong winds, which, in common cases, and in houses most favorably situated, often invert the course of the smoke, by the strong pressure they exert on the tops of chimneys, and by impinging against their inner side. In like manner, the pots, which are frusta of cones, or pyramids, placed on the tops of chimneys, assist the escape of smoke, by causing the wind to glance upward from their sides.
Contiguous Flues.--When two chimneys are contiguous to each other, or in the same stack, one is frequently liable to smoke, when the other contains a fire, from a variety of circumstances. Not only the effect of high winds, but also any circumstance, which tends to produce an inverted current, may bring down the smoke from one chimney into the apartment which contains the other. To prevent this evil, the fireplaces should be furnished with dampers, which can be closed, when the flue is not in use.
Burning of Smoke.--This subject has excited great attention, owing to the nuisance produced by smoke, in large cities and manufacturing towns, chiefly where coal is burnt. In an economical view, it deserves attention, since it renders the same fuel more effective. Several methods of getting rid of smoke have been proposed, and executed with some success. The first mode is, to cause the smoke to pass through a portion of fuel which is perfectly ignited, and does not smoke, and which, if accurately managed, burns it up. This has been effected by an inverted draught, in a syphon chimney, and also by a revolving grate, which places the ignited fuel between the fresh fuel and the chimney. In a method of burning smoke, lately introduced by Messrs. Chanter and Gray, the form of the furnace, and position of the bars of the grate, are so arranged, that the fuel is regularly advanced, by gravitation, upon the inclined bars, without the aid of machinery, so that the inflammable gases are first set free, and being more charged with heat and oxygen, they are perfectly burnt, in passing over the fire. Another mode is, to mix a current of fresh air with the smoke, by tubes, or otherwise, which causes it to burn, upon passing in contact with a clear fire. A third method, which has been adopted for disposing of smoke, consists in building chimneys of an extraordinary height, so that most of the smoke may be deposited in soot, upon their sides. It has also been proposed to build circuitous chimneys, in one part of which the smoke should pursue a descending course; and that, in this part, a shower of water should be kept up, to precipitate the denser particles of the smoke. The expense of this method will probably prevent its use, unless, in some cases, to get rid of dangerous metallic fumes, in manufactories.
General Remarks.--Whatever be the methods adopted for the artificial warming of houses, two general considerations appear essential to the health and comfort of those who reside in them. These are, 1st, to maintain the purity of the atmosphere, and, 2dly, to keep in it an agreeable temperature. The first requires, that the air should be duly shifted by ventilation. The second requires, that a state of things should exist, in which the occupants should not be sensible of excess of heat, or cold. It is not, however, necessary for this purpose, that the atmosphere itself should always be heated to a temperate warmth. On the contrary, the faculties of healthy persons are more active in lower temperatures, and respiration is more satisfactory, because the volume of air inspired affords more oxygen. Generally, it is better to obtain heat, as far as practicable, from radiation and clothing, rather than from a hot atmosphere. An open fire, which sends off its rays of heat on one side, while they are reflected back from the opposite walls, will keep persons comfortable in a room, the air of which is ten or more degrees below the point which would be necessary, if the room were only warmed by a current of hot air, brought from a distant fire, the radiation of which is not available to the persons who require its benefit. It is probable, also, that a warmer clothing, than that commonly worn within doors, would be useful, in enabling persons to remain, with impunity and advantage, in moderately low temperatures. People, who are properly clothed and covered, ride with pleasure in cool weather, and sleep with health and comfort in cold chambers. On the other hand, a very warm atmosphere, whether produced artificially in Winter, or naturally in Summer, is always relaxing and debilitating, even under the lightest clothing. In hospitals, and sick chambers, it is found very difficult to render the warmth agreeable, at the same time, to those who are in bed, and to those who are sitting up, on account of their difference of covering. The practice, which has of late been gaining ground in this country, of keeping entries, and the sleeping chambers communicating with them, raised in Winter to a Summer heat, by means of stoves and cellar furnaces, cannot be regarded as otherwise than injurious. It produces the relaxing effect of warm weather, and rentiers the body tender, and more susceptible of the influence of cold, whenever it is exposed to the outer air.
WORKS OF REFERENCE,--FRANKLIN'S Works;--RUMFORD'S Works;--TREKGOLD, on Warming and Ventilating Buildings, 8vo, 1824; BUCHANAN, on the Economy of Fuel, and Management of Heat, 8vo. 1810; SYLVESTER'S Philosophy of Domestic Economy, and Account of the Derbyshire Infirmary, 4to.;--Account of the Wakefield Asylum, fol.;--FLOOD, on Warming Buildings by Hot Water, 8vo. 1837;--ARNOTT, on Warming and Ventilating 1838;--BBANDE'S Quarterly Journal, Nos. 22, 24, 27, 37, &c.
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