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See also:VENTILATION (See also:Lat. ventilare, from ventus, See also:wind) , the See also:process and practice of keeping an enclosed See also:place supplied with proper See also:air for . breathing; and so, by See also:analogy, a See also:term used for exposing any subject to the winds of public See also:criticism. The air which we breathe consists chiefly of two gases, See also:oxygen and See also:nitrogen, with certain small proportions of other gases, such as carbonic See also:acid (See also:carbon dioxide), See also:ozone and See also:argon. Oxygen, which is the active and important constituent, and on which See also:life and See also:combustion depend, forms about one-fifth of the whole, while nitrogen, which is inert and acts as a diluent, forms nearly four-fifths. Of this mixture each adult See also:person breathes some 2600 gallons or 425 cub. ft. in twenty-four See also:hours. In air that has passed through the lungs the proportion of oxygen is reduced and that of carbon dioxide increased. Of the various impurities that are, found in the air of inhabited rooms, carbonic acid See also:gas forms the best See also:practical See also:index of the efficiency of the ventilation. The open air of See also:London and other large inland towns contains about four parts by See also:volume of the gas in 1o,00o of air. In the See also:country, and in towns near the See also:sea, two to three and a See also:half parts in lo,000 is a more usual proportion. Authorities on ventilation: usually take four parts in lo,000 as the See also:standard for pure air, and use the excess over that quantity in estimating the adequacy of the air See also:supply. But they differ as to the proportion to which the carbonic acid may be allowed Standard to rise under a See also:good See also:system of ventilation. It is of parity. generally admitted that the air in which See also:people dwell
and See also:sleep should not under any circumstances be allowed to contain more than ten parts in Io,000. This has been accepted as the permissible proportion by Carnelley, See also:Haldane and See also: The See also:rate at which an adult expires carbonic acid varies widely with his See also:condition of repose, being least in sleep, greater Rate of in waking See also:rest, and very much greater in violent See also:con- exercise. As a basis on which to calculate the air sswwdon necessary for proper ventilation we may take the of air. See also:production of carbonic acid by an adult as o•6 cub. • ft. per See also:hour. Hence he will produce per hour, in 6000 cub. ft. of air, a pollution amounting to one See also:part of carbonicacid in lo,000 of air. If the excess of carbonic acid were to be kept down to this figure (1 in ,o,000), it would be necessary to supply 6000 cub. ft. of fresh air per hour; if the permissible excess be two parts in ro,000 half this supply of fresh air will suffice; and so on. We therefore have the following relation between (x) the quantity of air supplied per person per hour, (2) the excess of carbonic acid which results, and (3) the See also:total quantity of carbonic acid See also:present, on the See also:assumption that the fresh air that is admitted contains four parts by volume in 10,000:- Air supplied per Carbonic Acid Adult per Hour. (Parts by Volume in 10,000). Cubic Feet. Excess due to Total Respiration. Quantity. moo 6 to 1200 5 9 'goo 4 8 2000 3 7 3000 .2 6 Some investigators have maintained that, in addition to an in-creased proportion of carbonic acid, air which has passed through the lungs contains a See also:special See also:poison. This view, however, is not accepted by others; J. S. Haldane and Lorrain See also: This proves in a striking' way the See also:advantage of systematic ventilation.
In the ventilation of buildings four See also:main points have to be considered: (1) the See also:area of See also:floor to be provided for each person; (2) the cubic capacity of the See also:room required Ventna for each occupant; (3) the See also:allowance to be made See also:Lion of for the vitiation of the air by gas or oil burners; banding'. and () the quantity of fresh air which must be brought in and of vitiated air that must be extracted for each individual. The first will depend upon the See also:objects to which the room is devoted, ; whether ' a See also: To preserve the lowest standard of purity tolerated by sanitarians, ventilation must go on at the rate per person of moo cub. ft. per hour, and 3000 cub. ft. per hour are required to preserve the higher standard on which some authorities insist. E. A. See also:Parkes advised a supply of 2000 cub. ft. of air per hour for persons in See also:health and 3000 or 4000 cub. ft. for sick persons. In the case of a public assembly See also: In a shaft 20 ft. high, See also:vertical and smooth inside, with a difference in temperature of 20°, the velocity will be about 21 ft. per second, or 9000 ft. per hour; that is, it will carry off 9000 cub. ft. of air per hour for every square foot of its sectional area. To convey 48,000 cub. ft., it must have a sectional area of 52 sq. ft. A See also:general See also:idea of the floor area, cubic space and fresh air supply per inmate allowed by See also:law or by See also:custom in certain cases is given in the table below: Class of See also:Building. Floor Area Cubic Cubic Feet of in Feet Capacity in Fresh Air .per Person. Feet per supplied and Person.' Foul Air extracted per Person. Schools . 9to10 200 I,Boo See also:Barracks 70 720 I ,800 Prisons . . 90 800 ',Soo See also:Concert halls and 9 I08 2,000 theatres . Billiard and See also:smoke- 2,000 rooms . . Hospitals . 120 1,44o 2,000 to 3,000 Public See also:libraries 20 2,400 2,500 See also:Turkish See also:baths. 70 800 5,000 Workshops . I20 I,440 Cowsheds, per cow 90 I, See also:I00 5,000 10,000 Stables; per See also:horse . I20 r,600 12,000 ' In calculating the cubic capacity per person the height should not be measured beyond 12 ft. above the floor. The supply of fresh air indicated in the table should not be regarded as entirely satisfactory, for the standard of purity suggested is See also:low, and ought to be exceeded, but it might deter many from moving in the matter if a proper and higher standard were to be laid down at first. One of the most important points is the proper warming of the fresh air introduced into buildings, for unless that be done, when a See also:cold See also:day occurs all the ventilating arrangements will probably be closed. The fact should not be lost sight of that the air in a room may on the one hand be quite cold and yet very foul, and on the other, warm and yet perfectly fresh. To avoid See also:draught the air should enter through a large number of small orifices, so that the currents may be thoroughly diffused. This is done by gratings. The See also:friction of their bars, however, seriously diminishes their capacity for passing air, and carefulexperiments show conclusively that very ample grating area is required to deliver large volumes. The same remark applies to extracting-flues. Owing to the small size and the roughness of the See also:surface the velocity of the upward current is small, and the quantity of air that passes out is often much less than is requisite. Means of Ventilation.—In See also:order that the atmosphere of a room should be changed by means of air currents, thereby securing proper ventilation, three things are necessary; (I) an inlet or inlets for the fresh air, (2) an outlet or outlets for the vitiated air, and (3) a See also:motive force to produce and maintain the current. In systems which are distinguished by the general name of mechanical or artificial ventilation special provision is made for See also:driving the air, by fans, or by furnaces, or by other contrivances to be described more fully below. In what is called natural ventilation no special appliance is used to give motive force, but the forces are made use of which are supplied by (I) the wind, (a) the elevated temperature of the room's atmosphere, and (3) the draught of fires used for See also:heating. Natural Ventilation.—The See also:chief agent in domestic ventilation is the See also:chimney; when a See also:bright See also:fire is burning in an open See also:grate, it rarely happens that any other outlet for foul air from a room need be provided. The See also:column of hot air and burnt gases in the chimney is less heavy, because of its high temperature, than an equal column of air outside; the pressure at the See also:base is therefore less than the pressure at the same level outside. This supplies a motive force compelling air to enter at the bottom through the grate and through the opening over the grate, and causing a current to ascend. The motive force which the chimney supplies has not only to do See also:work on the column of air within the chimney, Chimney in setting it in See also:motion and in ove.!.oming frictional re- draught. sistance to its flow: it has also to set the air entering the room in motion and to overcome frictional resistance at the inlets. From want of proper inlets air has to be dragged in at a high velocity and against much resistance, under the doors, between the window sashes and through many other chinks and crevices. Under these conditions the air enters in small streams or narrow sheets, See also:ill-distributed and moving so fast as to See also:form disagreeable See also:draughts, the pressure in the room is kept so low that an opened See also:door or window, lets in a See also:deluge of cold air, and the current up the chimney is much reduced. If the See also:attempt is made to stop draughts by applying See also:sand-bags and listing to the crevices at which air streams in, matters only become worse in other respects; the true remedy of course lies in providing proper inlets. The See also:discharge of air by an ordinary open fire and chimney varies widely, depending on the rate of combustion, the height and See also:section and form of the chimney, and the freedom with which air is entering the room. About Io,000 cub. ft. per hour is probably a See also:fair average, about enough to keep the air fresh for half a dozen persons. Even when no fire is burning the chimney plays an important part in ventilation; the air within an inhabited room being generally warmer than the air outside, it is only necessary that an up-current should be started in order that the chimney should maintain it, and it will usually be found that a current is, in fact, passing up. When a room is occupied for any considerable length of time by more than about half a dozen persons, the chimney outlet should be supplemented by others, which usually take the form Other of gratings in the See also:ceiling or cornices in communication outlets. with flues leading to the open air. These openings should be protected from down-draught by light flap valves of oiled See also:silk or See also:sheet See also:mica. With regard to inlets, a first care must be to avoid such currents of cold air as will give the disagreeable and dangerous sensation of draught. At ordinary temperatures a current of See also:outer air Inlets. to which the See also:body is exposed will be See also:felt as a draught if its velocity exceeds 3, or even 2 ft. per second. The current entering a room may, however, be allowed to move with a See also:speed much greater than this without causing discomfort, provided its direction keeps it from striking directly on the persons of the inmates. To secure this, it should enter, not horizontally nor through gratings on the floor, but vertically through openings high enough to carry the entering stream into the upper atmosphere of the room, where it will mix as completely as possible with warm air before its presence can be felt. A favourite form of inlet is the Sheringham (fig. 1). When opened it forms a See also:wedge-shaped See also:projection into the room, and admits air in an upward stream through the open See also:top. It should be placed at a height of 5 or 6 ft. above the level of the floor. Other inlets are FIG. I.—Sheringham Air Inlet. made by using hollow perforated blocks of earthenware, called air-bricks, built into the See also:wall; these are often shaped on the inner See also:side like an inverted louvre-See also:board or venetian See also:blind, with slots that slope so as to give an upward inclination to the entering stream. In another and most valuable form of ventilator, the See also:Tobin See also:tube, the fresh air enters vertically upwards. The usual arrangement Tobin of Tobin tube (shown in front See also:elevation and section in tube. fig. 2) is a short vertical shaft of See also:metal See also:plate or See also:wood which leads up the wall from the floor level to a height of 5 or 6 ft. Its lower end communicates with the outer air through an air-grating in the wall; from its upper end, which is freely open, the current of fresh air rises in a smooth stream. Various forms of section may be given to the tube: if placed in a corner it will be triangular or segmental; against a See also:flat wall a shallow rectangular form is most usual, or it may be placed in a channel so as to be flush with the See also:face of the wall; a lining of wood forming a dado may even be made to serve as a Tobin tube by setting it out a little way from the wall. The tube is often furnished with a regulating See also:valve, and contrivances may be added for cleansing the entering air. A See also:muslin or See also:canvas bag hung in the tube, or a See also:screen be used to See also:filter out dust; the same See also:object is served in some degree by forcing the air, as it enters the tube at the bottom, to pass in See also:close contact with the surface of See also:water in a See also:tray, by means of a deflecting plate. These complications have a See also:double See also:drawback: they require frequent See also:attention to keep them in order, and by put'ang resistance in the way of the stream they are See also:apt to reduce the efficiency of the ventilation.' The air entering by a Tobin tube may be warmed by a coil of hot pipes within the tube or by a small gas-See also:stove (provided, of course, with a flue to discharge outside the pro- ducts of combustion), or the tube may draw its supply, not directly from the outer atmosphere, Tobin Tube. always be about the level of a See also:man's See also:head, but the tube need not extend down to the floor: all that is essential is that it should have sufficient length to let the air issue in a smooth vertical current without eddies (fig. 3). These inlets are at once so See also:simple and effective that no hesitation need be felt in introducing them freely in the rooms of dwelling-houses. When no special provision is made for them in the walls, the advantage of a current entering vertically may still be in some degree secured by help of certain makeshift contrivances. One of these, suggested by Dr Hinkes See also:Bird, is to open one See also:sash of the window a few inches and fill up the opening by a board; air then enters in a zigzag course through the space between the See also:meeting rails of the sashes. Still another See also:plan is to have a light See also:frame of wood or metal or See also:glass made to See also:fit in front of the lower sash when the window is opened, forming virtually a Tobin tube in front of the window.
As an example of the systematic ventilation of dwelling-rooms
on a large See also:scale, the following particulars may be quoted of arrange-
ments ments that have been successfully used in See also:English
In barracks. One or more outlet-shafts of wood fitted with
mints
barracks. flap valves to prevent down-draught are carried from the
highest part of the room, discharging some feet above the roof under a louvre. The number and size of these shafts are such as to give about 12 sq. in. of sectional area per head, and the chimney gives about 6 sq. in. more per head. About half the air enters cold through air-bricks or Sheringham valves at a height of about 9 ft. from the floor, and the other half is warmed by passing through flues behind the grate. The inlets taken together give an area of about 11 sq. in. per head. A fairly See also:regular circulation of some I200 cub. ft. per head per hour is found to take place, and the proportion of carbonic acid ranges from 7 to 10 parts in 1o,000.
' When the air is not filtered, and when it has been warmed before entering, the vertical direction of the stream is readily traced by dust, which is deposited on the wall in a nearly upright column, spreading slightly See also:fan-See also:wise as it rises. With cold air the See also:deposit of dust is comparatively slight. The difference is due to the fact, noticed and explained by Mr See also: If the air is to be ~' warmed before it enters, the supply may be See also:drawn from a chamber warmed by hot-water or See also:steam pipes or by a Stove, and the temperature of the room may be regulated by allowing part of the air to come from a hot chamber and part from outside, the two currents mixing in the shaft from which the inlets to the room draw their supply. Outlets usually consist of gratings or See also:plain openings at or near the ceiling, preferably at a considerable distance from points vertically above the inlet tubes. One of the chief difficulties in natural ventilation is to guard them against down-draught through the action of the wind. Numberless forms of See also:cowl have been devised with this object, with the further intention of turning the wind to useful See also:account by making it assist the up-current of foul air. Some of these exhaust cowls are of the revolving class, made to various designs and dimensions and put in rotation by Exhaust the force of the wind. Revolving cowls are liable to fail cowls. by sticking, and, generally speaking, fixed cowls are to be preferred. They are designed in many forms, of which See also:Buchan's may be cited as a good example. Fig. 4 shows this ventilator in See also:horizontal section: as is the vertical exhaust flue through which the foul air rises; near the top this expands into a polygonal chamber, bbbb, with vertical sides, consisting partly of perforated sheet-metal plates; outside of these are fixed vertical curved See also:guide-plates, c,c,c,c; the wind, blowing between these and the polygonal chamber, sucks air from the centre through the perforated sides. The efficient working of an exhaust cowl, however, depends almost entirely upon the favourable conditions of the wind? The two things that supply motive force in automatic or natural ventilation by a'Imo) means of exhaust cowls and similar FIG. 4.—Sectional Plan of appliances—the difference of See also:tempera- Buchan's Exhaust Cowl. See also:ture between inner and outer air, and the wind—are so variable that even the best arrangements of. inlets and outlets give a somewhat uncertain result. As an example, it is evident that on a hot day with little See also:movement in the air this mode of ventilation would be practically ineffectual. Under other conditions these automatic air-extractors not infrequently become inlets, thus See also:reversing the whole system and pouring cold air on the heads of the inmates of the apartment or hall. To secure a strictly See also:uniform delivery of air, unaffected by changes of See also:season or of weather, it is necessary that the influence of these irregular motive forces be as far as possible minimized, and recourse must consequently be had to some mechanical force as a means of driving the air and securing adequate ventilation of the building. Artificial Ventilation.—Buildings may be mechanically ventilated on the vacuum system, the plenum system, or on a system combining the best points of both. In nearly every case of the application to See also:modern buildings of mechanical means of ventilation the combined system in one form or another is adopted. In the vacuum system the motive force is applied at the outlets; the vitiated air is drawn from the rooms, and the pressure of the atmosphere in them is slightly less than the pressure outside. Upon the foul air being withdrawn fresh air finds its way in by means of conveniently placed inlets. In the plenum the motive force is applied at the inlets; fresh air is forced in and drives the vitiated air before it until it escapes at the outlets provided. The pressure within the room is greater than outside. The plenum method has distinct advantages: it makes the air See also:escape instead of coming in as a cold draught at every crevice and casual opening to the outer air; it avoids See also:drawing foul air from sewers and See also:basement; and with it, more easily than with the other, one may guard against the disturbing influence of wind. In the plenum method the air is driven by fans; in the vacuum method suction is produced by fans or by heating the column of air in a See also:long vertical shaft through which the discharge takes place. Water jets and steam jets have also been employed to impel or See also:extract the air. Whatever system of ventilation is adopted, it is most important that windows capable of being widely opened should also be provided to aerate at frequent intervals the whole building, either as a whole or in sections, and they should be so arranged that no corner can be See also:left stagnant or unswept by the purifying current. The See also:Victoria Hospital at See also:Glasgow and the Royal General Hospital at See also:Birmingham are, however, ventilated on the plenum system without the aid of open windows, with what are said to be satisfactory results. In the case of hospitals, it is evident that aeration by means of open windows could not in Great See also:Britain be effected except on warm and sunny 2 For an account of tests of various forms of ventilating cowls, see S. S. Hellyer, The Plumber and Sanitary Houses. Ventilation by window and door. days, but in the case of concert halls, theatres and similar buildings, it is possible (and most essential) thoroughly to aerate the building between each occupation. The extraction of foul air should in most cases be effected at the top of a room or building, so as to utilize the natural tendency of Bxtrac- warm air to rise; but at Birmingham and elsewhere the Hon ac outlets are near the floor, the fresh air being brought in vitiated half-way up the walls and directed towards the ceiling. air . The air inlets should be Tobin tubes or similar devices, placed some 4 or 5 ft. above the floor, and so arranged that the air should be passed in contact with radiators or pipes to warm it before entering. In the case of a building for one of the See also:American legislatures, the warmed fresh air is allowed to enter on the level in front of the See also:desk of each member, so that he secures a proper volume of fresh air for his own use before it is breathed by his See also:neighbour. The introduction of rapidly revolving, but silent, fans, driven by See also:electricity, is a great advance which places within the reach of the Fans. engineer or architect the means for solving the problem of ventilation of buildings, and has been to a large extent responsible for the rapid progress of the See also:art of ventilation. The fan and motor combined extend the advantages of See also:positive mechanical ventilation to all who have See also:access to electric current, with the further benefit that the extreme simplicity of the electric driving of the fans greatly facilitates the See also:control and See also:distribution of ventilating effect. The moderate See also:power required by these fans for a given See also:duty has contributed greatly to their extended use. They should deliver into a chamber of considerable size, so that the velocity of the air may become reduced before it passes into the distributing flues. The question of silence in See also:running, in such places as houses of See also:parliament, law courts, churches and chapels, is of See also:paramount importance, and no fan should be accepted until it is proved by actual working to be noiseless. In some instances revolving pumps of the See also:Root's blower type are used (see BELLOW s AND BLOWING See also:MACHINES). At the See also:Dundee See also:College a See also:battery of five of these blowers, each discharging over 150,000 cub. ft. of air per hour, is driven easily by a gas See also:engine of two horse-power. The air is passed through two filters of coarsely See also:woven fabrics which serve to remove all particles of impurity. The rooms are heated by having coils of See also:Perkins's high-pressure hot-water pipes (see HEATING) in the main distributing flues. The inlets are flat upright tubes extending up the side walls to a height of nearly 6 ft., and open at the top. Outlets are generally provided in the end walls, one See also:group near the ceiling, another a few feet from the foot. They are fitted with doors which allow one or other to be closed; the high-level outlets are used in warm weather, when the fresh air that comes in is comparatively cool; the low-level ones are used in cold weather, when the fresh air, having been heated before it enters, would tend to rise and pass out too directly if the outlets near the ceiling were open. The outlet shafts communicate with a louvred See also:tower or turrets on the roof. Each room receives a volume of air equal to its cubic capacity in about 12 minutes, so that the atmosphere is completely changed five times in an hour. The inlets are proportioned to do this without allowing the velocity with which air enters to exceed 6 ft. per second. The water-spray ventilator is a mechanical ventilator using a See also:jet Water- of water to impel the air. A nozzle at the top of a circular aair-shaft delivers a conical sheet of water, which impinges spray on the sides of the shaft a little way below and carries vend- down with it a considerable stream of air. This ventilator lame. is used either to force air into rooms or to draw it out; in the former case a small stove is often added to See also:heat the supply. In the See also:early days of mechanical ventilation extraction by a hot-air shaft was a more common mode of ventilating hospitals and other t;xtrac- public buildings than now. The heat was applied by a Hon by See also:furnace or stove at the bottom of the shaft, or by coils hot-air of hot-water or steam pipes. In the lecture See also:theatre of the shalt. See also:Paris See also:Conservatoire See also:des Arts A. J. See also:Morin employed this means of extraction, and arranged that the fresh air should enter through the ceiling and the foul air be drawn off through the floor from under the seats; this reversal of the natural direction of the current is of course only possible when a sufficient See also:external motive force is applied. In theatres and similar buildings clusters of gas jets or sunlight burners, fixed at the ceiling level at the base of a metal shaft which is connected with the open air, serve as effective ventilating agents by extracting the foul air which collects in the upper part of the hall. To ensure the See also:admission of the desired amount of air into a room, and to arrive at the proper allowance of inlets and outlets, it is The necessary to ascertain the direction and velocity of the measure- movement of the air through them. The quantity of air See also:meat passing through a given opening is found by multiplying of air. the area of the opening expressed in square feet by the velocity of the current of air stated in lineal feet per minute, the product being the number of cubic feet passing per minute. Where the air is admitted through gratings only the clear area should be calculated, the amount of solid material being deducted from the See also:gross superficies of the grating. The velocity of the air current may be determined by means of an See also:anemometer (q.v.). We may conclude with a short See also:summary of the methods adopted of ventilating a number of typical buildings of various classes of different countries. The Smallpox Hospital at See also:Bradford consists of two wards, 75 ft. by 15 ft., placed back to back, with a space of about 3 ft. between them enclosed by walls forming a foul-air chamber of the same length as the wards, and reaching to the ceiling. At this level are outlets for the vitiated air—one over each See also:bed. A furnace at the base of a tall shaft withdraws through these outlets the air which passes through the furnace on its way to the outer air. The windows are tightly closed and fresh air enters from a chamber below through gratings in the floor at the foot of each bed. The New See also:York General Hospital was stated in 1875 to contain 163 beds. In the wards there is one window to each bed, each See also:pier between the windows containing a foul-air extracting flue running from the base of the building and connected in the roof with large trunks leading to an exhaust fan. The heating is by steam coils placed in the basement in such a way that by a valve the cool fresh air can be sent either through or around the heating coil. The warmed fresh air is conveyed through an air-tight See also:iron See also:pipe fitted in each extracting shaft and is admitted to the wards through slits in the window-sills forming a jet directed upward on the principle of Tobin tubes. The outlet openings for the foul air are placed one beneath each bed, with extra outlets for occasional use at the top and base of the external walls. The placing of the fresh-air supply pipes in an inaccessible position inside the foul air ducts cannot be approved for hospital ventilation, as it is quite possible that in time, through the decay of the pipe See also:joints or of the pipes themselves, communication may be established between the fresh and foul air, thus entirely upsetting the system of ventilation.
The See also:City Hospital of See also:Hamburg, containing 130 beds, was opened in 1890. The buildings are one See also:storey high and are heated on the See also:ancient See also:Roman See also:hypocaust principle. Beneath the entire floor run longitudinally a number of See also:brick and See also:concrete flues about 30 in. square, covered on the top with See also:marble tiles, forming the floor of the wards. In these flues are placed the steam heating pipes. Warmed .fresh air is admitted through large radiators in the centre of the wards, the vitiated air escaping through openings in the See also:ridge of the roof. Mr H. See also:Percy See also: In the Houses of Parliament at See also:Westminster} which were designed and built for the public business in 1836, considerable attention is devoted to the question of the See also:purification of the air, but the arrangements are lamentably antiquated and ineffectual in their working. The supply of fresh air is drawn by fans from the See also:terrace at the See also:river front, and, after being warmed and moistened or cooled by water-spray or blocks of See also:ice, as the temperature may require, passes through exceedingly tortuous and restricted air passages to the various See also:chambers, where it is admitted through large gratings in the floor, which are covered by, porous See also:matting to prevent draughts. The outlets for the vitiated air are in the ceilings of the apartments, and from these the air has to be dragged down to the base of the ventilating shaft in the Victoria tower, where an up-current is maintained by a large furnace. The French Chamber of Deputies, according to a See also:report made by M. Frelat in 1891, is much overcrowded, the allowance of floor space for each member being only 3o square centimetres. The apparatus is powerful enough to See also:change the air every six minutes, but to avoid draughts it can only be worked slowly. Fresh air is driven down by a fan through openings in the ceiling, and vitiated air removed at the floor, giving a downward system of ventilation. For the ventilation of the new Sessions See also:House at the corner of Newgate See also:Street and Old See also:Bailey, London, opened in 1907, an elaborate system on the plenum downward principle was installed: The fresh air, drawn in at the basement by powerful fans, passed in turn through purifying screens, on which water was constantly playing, and over steam-heated coils, before entering the distributing trunks; into these sufficient cold air also was admitted to reduce it to the required temperature. See also:Branch ducts conveyed this warmed fresh air to the points of inlet just below the ceiling. The outlets for the vitiated air were placed near the floor level, an electric fan drawing it up and discharging it at the roof. It was claimed that 600 tons of filtered and warmed or cooled fresh air were passed through the building every hour. In the Capitol at See also:Washington in .See also:America the upward system is installed. Fresh air, warmed by coils in the basement, is delivered by means of fans through openings in the floors of the various chambers and galleries, and the extractors are placed in the ceilings. This foul air passes out of the building through louvre ventilators placed on the roof ridge. Some of the vitiated atmosphere, however—that from the corridors and galleries—is drawn by means of a fan to the basement and blown up a lofty shaft. The See also:Grand See also:Opera House in See also:Vienna is ventilated on a most elaborate and See also:complete system, the arrangements there giving excellent results. The See also:scheme for heating and ventilating this building was designed by D. Bohm. The building See also:measures 397 ft. by 299 ft., and the theatre will hold about 2700 persons. Ventilation is effected by two fans, the lower for propulsion, the upper for extraction. The latter is aided also by the heat produced by the great See also:pendant which has ninety burners. The heating is effected by steam, and the air enters the hall at a temperature of from 63° to 65° F., the points of entrance being at the floor and the risers of the seating. Each See also:gallery and compartment of the theatre, including the See also:stage, has a See also:separate See also:installation of heating apparatus and supply duct so that any one portion may be warmed and ventilated independently of the rest. The velocity of the incoming air is between 1 and 2 ft. per second. The driving fan in the basement sends air into the building at the rate of 1059 cub. ft. per head per hour by means of electricity. The temperature in different parts of the house can be observed in a central control See also:office, and here also are the levers which control the valves regulating the air supply, both hot and cold. During a performance the See also:superintendent of heating and ventilation is on duty in this office and secures to each part of the building its proper supply of fresh air at a proper temperature. For the ventilation of mines see See also:MINING, and for that of railway tunnels see See also:TUNNEL. (J. Additional information and CommentsThere are no comments yet for this article.
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