;ERIES. I * ot 1 ION T H TH LLIAM G. SNOW, S.B., tv iOCIE*n BCH S NOLAN, A.M., M.- , RRICAX 1 : -.--iJTS, SOB NEW YORK: B. VAN NOSTRAND COMPANY, 23 -M i w . i> 27 WARREN STREETS. 1906. THE VAN NOSTRAND SCIENCE SERIES. 16nio. Boards. Price 50 Coats Each. Amply Illustrated when the Subject Demands. No. *. CHIMNEYS FOR FURNACES AND STEAM-BOIL- ERS. By R. Armstrong, C.E. 3d American ed. Revised and partly rewritten, with an Appendix on Theory of Chimney Draught, by F. E. Idell, M.E. No. 2. STEAM-BOILER EXPLOSIONS. By ZeraL Colburn. New edition, revised by Prof. R. H. Thurston. iNo. 3. PRACTICAL DESIGNING OF RETAINING- WALLS, Fourth edition. By Prof. W. Cain. No. 4, PROPORTIONS OF PINS USED IN BRIDGES?* By Chas. E. Bender, C.E. 2d edition, with appendix. Mb. ft, VBNTILAT: ON OF BUILDINGS. By W. F. Butler. Second ecition, re-edited and enlarged by Jamea L. Greenleaf, C. E. No. C.-ON THE DESIGNING AND CONSTRUCTION OF STORAGE RESERVOIRS. By Arthur Jacob, A. B. Second edition, revised, with additions by E. Sherman Gould. No. 7. SURCHARGED AND DIFFERENT FORMS OF RE- TAINING-WALLS. By James S. Tate, C.E. No. a A TREATISE ON THE COMPOUND ENGINE. By John Turobull, jun. Second edition, revised by Prof. S. W. Robinson. No. 9. A TREATISE ON FUEL. By Arthur V. Abbott, C.E. Founded on the original treatise of C. Will- iam Siemens, D.C.L. No. H). COMPOUND ENGINES. Translated from the French of A. Mallet. Second edition, revised, with results of American Practice by Richard H. Buel, C.E. No. II. THEORY OF ARCHES. By Prof. W. Allan. No. 12.-THEORY OF VOUSSOIR ARCHES. By Prof. W. ? Cain. Second edition, revised and enlarged. No. 18. OASES MET WITH IN COAL-MINES. By J. J. Atkinson. Third edition, revised and enlarged by Edward H. Williams, jun. NO, Mr-FRICTION OF AIR IN MINES. By J. J. Atkinson. Second American edition. No. J&43KEW ARCHES. By Prof. E. W. Hyde, C.E. Illustr. No. 16. A GRAPHIC METHOD FOR SOLVING CERTAIN QUESTIONS IN ARITHMETIC OR ALGEBRA. By Prof. G. L. Vose. Ma. ir.-JWATER AND WATER-SUPPLY. By Prof. W. H. Cortield of the University College, London. Second American edition. NO. 18. SEWERAGE AND SEWAGE PURIFICATION. By M. N. Baker, Associate Editor " Engineering News." THE VAN NOSTEAND SCIENCE 8ERIS8. No. 19. STRENGTH OF BEAMS UNDER TRANSVERSE LOADS. By Prof. W. Allan, author of "Theory of Arches." Second edition, revised. No. SO. BRIDGE AND TUNNEL CENTRES. By John B. McMaster, C.E. Second edition. Ho. Sl.-SAFETY VALVES. Second Edition. By Richard H. Buel, C.E. Wo. 22. HIGH MASONRY DAMS. By E. Sherman Gould, M. Am. Soc. C. E. No. 23. THE FATIGUE OF METALS UNDER REPEATED STRAINS. With various Tables of Results and Experiments. From the German of Prof. Ludwig Spangenburgh, with a Preface by S. H. Shreve, No. 24. A PRACTICAL TREATISE ON THE TEETH OF WHEELS. By Prof. S. W. Robinson. Second edition, revised. No. 25 ON THE THEORY AND (' A I.( TLATION OF CON- TINUOUS BRIDGES. By R. M. Wilcox, Ph. D. No. 26. PRACTICAL TREATISE ON THE PROPERTIES OF CONTINUOUS BRIDGES. By Charles Bender, C.E. No. 27. ON BOILER INCRUSTATION AND CORROSION. By F. J. Rowan. New Ed. Rev. by F. E. Idell. No. 28.-TRAK3MISSION OF POWER BY WIRE ROPES. Second edition. By Albert W. Stahl, U.S.N. No. 29. STEAM INJECTORS. Translated from the French of M. Leon Pochet. No. 30. TERRESTRIAL MAGNETISM AND THE MAG- NETISM OF IRON VESSELS. By Prof, Fair- man Rogers. No. 31. THE SANITARY CONDITION OF DWELLING- , HOUSES IN TOWN AND COUNTRY. By j George E. Waring, jun. No. 32.-CABLE-MAKING FOR SUSPENSION BRIDGES, By W. Hildebrand, C.E. No. 33.-MECHANICS OF VENTILATION. By George W. Rafter, C.E. New and Revised Edition. No. 34. -FOUNDATIONS. By Prof. Jules Gaudard, C.E. Second edition. Translated from the French. No. 35. THE ANEROID BAROMETER : ITS CONSTRUC TION AND USE. Compiled by George W Plympton. Eighth edition. No. 36. MATTER AND MOTION. By J. Clerk Maxwell, - M.A. Second American edition. No. 37.-GEOGRAPHICAL SURVEYING ; ITS USES, METHODS, AND RESULTS. By Frank De Yeaux Carpenter, C.E. No. 38. MAXIMUM STRESSES IN FRAMED BRIDGES. By Prof. William Cain, A.M., C.E. New and revised edition. VAN VOSTRAm SC1SNCOB SSKOHk No. . A HANDBOOK OP THE ELECTRO-MAGNETIC TELEGRAPH. By A. E. Loring. No. 40. TRANSMISSION OF POWER BY COMPRESSED AIR. By Robert Zahner, M.E. Second edition. Ko. 41. STRENGTH OF MATERIALS. By William Kent, C. E., Assoc. Editor, Engineering News. Second Ed. No. 42. THEORY OF STEEL-CONCRETE ARCHES, AND OF VAULTED STRUCTURES. By Prof. William Cain. Ha 48. WAVE AND VORTEX MOTION. By Dr. Thonwi Craig, of Johns Hopkins University. No. 44. TURBINE WHEELS. By Prof. W. P. Trowbridge, Columbia College. Second edition. Revised. No. 46. THERMODYNAMICS. By Prof. H. T. Eddy, Uni- versity of Cincinnati. No. 4. ICE-MAKING MACHINES. From the French of M. Le Doux. Revised by Prof. Denton. No. 47.-LINKAGES ; THE DIFFERENT FORMS AND USES OF ARTICULATED LINKS. By J. D. C. de Roos. No. 48.-THEORY OF SOLID AND BRACED ARCHES By William Cain, C.E. No. 49. ON THE MOTION OF A SOLID IN A FLUID. By Thomas Craig, Ph.D. No. 50.-DWELLING-HOUSES: THEIR SANITARY CON- STRUCTION AND ARRANGEMENTS. By Prof. W. H. Corfield. No, 51. THE TELESCOPE: ITS CONSTRUCTION, ETC. By Thomas Nolan. No. 53. IMAGINARY QUANTITIES. Translated trom th French of M. Argand. By Prof. Hardy. No. 53.-INDUCTION COILS: HOW MADE AND HOW USED. Fifth edition. No. 54. KINEMATICS OF MACHINERY. By Prof. Ken- nedy. With an introduction by Prof. R. H. Thurston. No. 55. SEWER GASES : THEIR NATURE AND ORIGIN. By A. de Varona. 2d ed., revised and enlarged. No. 56. THE ACTUAL LATERAL PRESSURE OF EARTH- WORK. By Benjamin Baker, M. Inst. C.E. !( 57. INCANDESCENT ELECTRIC LIGHTING. A Practical Description of the Edison System. By L. H. Latimer, to which is added the Design and Operation of Incandescent Stations. By C. J. Field, and the Maximum Efficiency of Incandes- cent Lamps, by John W. Howell. Mb. 58. THE VENTILATION OF COAL-MINES. By W. Fairley, M.E., F.S.S., and Geo. J. Andr6. Mo. 80. RAILROAD ECONOMICS ; OR, NOTES, WITH COMMEOT8. By S. W. Robinson. C.E. VENTILATION OF BUILDINGS WILLIAM G. SNOW, S.B., MEMBER AMER THOMAS NOLAN, A.M., M.S., FELLOW AMERICAN INSTITUTE OF ARCHITECTS, ASSISTANT PROFESSOR OF ARCHITECTURE, UNIVERSITY OF PENNSYLVANIA. NEW YORK: D. VAN NOSTRAND COMPANY, 23 MURRAY AND 27 WARREN STREETS. 1906. COPYRIGHT, 1906, BY D. VAN NOSTRAND COMPANY. PREFACE. IT has been the desire of the authors to condense into a small compass in the following pages a statement of the gen- eral principles of ventilation and of their application to different kinds of buildings. No claim to originality is made except for the form in which the subject is pre- sented, and due credit is intended to be given for any extracts or quotations from the works of others. The authors of* this little book believe that while there are excellent comprehensive treatises and manuals on both the science and the art of warming and ventilating buildings for those who wish to investigate either ex- haustively, there is room also for a primer in the subject for those who wish to be told simply and briefly what is to-day considered the best practice. 140219 The subject matter, in about the form here presented, has formed the basis of one part of a series of lectures by the authors in the Department of Architect- ure of the University of Pennsylvania, the details of that phase of the subject which relates to the mechanics of venti- lation having been purposely omitted, as they are discussed in another volume of this series. It is hoped that the book may prove useful, not only as a popular presentation of the subject for the general public, but also as a suggestive outline in architect- ural, engineering and other schools in connection with, or as supplementary to courses of lectures which are introduc- tory to the whole subject of the ventila- tion of buildings. THE AUTHORS. PHILADELPHIA, January, 1906. CONTENTS. I. GENERAL PRINCIPLES OF VENTI- LATION. 1. Importance of Ventilation . . . 7 2. Composition and Impurities of the At- mosphere 10 3. Removal of Dust . . . .14 4. Testing the Quality of the Air . . 14 5. Proportion of Carbonic- Acid Gas . 18 6. Amount of Air-supply Necessary . 20 7. Draughtlness 24 8. Compulsory Ventilation . . .25 9. Space per Occupant of Rooms . . 28 10. Cost of Ventilation .... 31 11. Humidity ...... 35 12. Cooling the Air 37 13. Testing Systems of Ventilation . . 40 14. Ventilation and Acoustics . . 42 II DIFFERENT SYSTEMS OF VENTI- LATION. 1. Systems of Ventilation . . .44 2. Fans and Blowers . . . .52 3. Plenum and Exhaust or Vacuum Sys- tems of Ventilation Compared . 54 4. Aspirating Coils versus Exhaust Fans . 56 5. Downward Ventilation . . .58 6. Upward Ventilation . . . .63 HI. VENTILATION OF DIFFERENT KINDS OF BUILDINGS. 1. Residences . 66 2. School Buildings 68 3. Churches 71 4. Halls and Court-rooms . , .74 5. Theaters .... .75 6. Hospitals and Asylums . . .76 7. Office Buildings 79 8. Department Stores . . . .81 9. Manufacturing Buildings . . .83 VENTILATION OF BUILDINGS. I. GENERAL PRINCIPLES OF VENTILATION. 1. IMPORTANCE OF VENTILATION. UNDER modern conditions, and with buildings having a tight construction and a relatively small accidental in-leak- age of air, the question of providing a sufficient supply of air becomes an im-r portant one, especially in the case of rooms which are crowded or occupied continuously for many hours. As Billings observes:* "It requires the observation of the effects on the health and life of a number of men ex- posed to such air for a series of months or years, to demonstrate the slow but * Billings, J. S., "Ventilating and Heating," 1893, Chap. VII., page 180. 8 certain production of throat and lung troubles, the loss of energy and vitality, and the shortening of life which are thus produced. These observations have been made on soldiers occupying ill-ventilated barracks and operatives working in close workrooms, and comparison of these re- sults has shown that where in any room occupied by human beings there is a defi- nite, unpleasant animal or musty odor, perceived by a person whose sense of smell is of the usual acuteness and who enters from the fresh outer air, the con- tinued breathing of the air producing such odor will be injurious to health." In certain buildings, where the results of changing from poor to good ventila- tion have been carefully observed, a marked improvement in the general health of the occupants has been mani- fest. For example, the records of the United States Pension Bureau state that " just prior to its occupancy of the pres- ent thoroughly-ventilated structure, the department was housed in numerous 9 small and poorly-ventilated buildings, under which conditions the sickness of employes entailed an aggregate annual loss of time amounting to 18,736 days. In the new building the loss immediately dropped to only 10,114 days, a reduction of over 45 per cent. When we consider the conditions of yearly salary under which most of these clerks are paid, the financial return from improved ventila- tion is emphatically evident." Professor S. H. Woodbridge, of the -Massachusetts Institute of Technology, in documents relating to ventilation sta- tistics, states that carefully collected data show that the death-rates have been re- duced by the introduction of efficient ventilating systems in children's hospi- tals from 50 to 5 per cent., in surgical wards of general hospitals from 44 to 13 per cent., in army hospitals from 23 to 6 per cent. , and in prisons from 80 to 8 per cent. Even among horses a reduction has been made from 19 to 1.5 per cent, in army stables, while during an epidemic 10 the rate has been reduced fully 80 per cent, by improved methods of ventila- tion. 2. COMPOSITION AND IMPURITIES OF THE ATMOSPHERE. Atmospheric air is a mixture composed of about 79 parts of nitrogen and 21 parts of oxygen by volume, and in 10,000 volumes there are from 3 to 5 volumes of carbonic-acid gas. The relative purity of the atmosphere is generally expressed by the number of parts by volume of carbonic-acid gas, expressed by the symbol C0 2 , contained in 10,000 parts or volumes of air. The proportion of this gas contained in the atmosphere may be easily deter- mined by several methods, and it affords a fairly good index of the relative num- ber of micro-organisms present. It is the latter which cause the discomfort and danger to persons who remain for long periods in an atmosphere containing a large proportion of C0 a . 11 * " It is very improbable that a minute quantity of organic matter contained in the air expired from human lungs has any deleterious influence upon men wha inhale it in ordinary rooms. In ordinary quiet respiration no bacteria are con- tained in the expired air. In the act of coughing or sneezing such organisms may be thrown out. . . . Air is contaminated by minute particles of dust. . . . Ex- periments in hospital wards showed that in this dust there were micro-organisms- including some of the bacteria which produce inflammation and suppuration, and it is probable that these were the- only really dangerous elements in this air. "The experiments made on animals compelled to breathe air vitiated by pro- ducts of respiration make it improbable- that there is any peculiarly volatile poisonous matter in the air expired by healthy men and animals other than C0 2 . * 4t Expired Air and Problems of Ventilation," Apple* ton's Popular Science Monthly, Feb., 1896. Drs. Billings,, Mitchell, and Bergey. 12 ". . . Tuberculosis and pneumonia are most prevalent among persons living and working in unventilated rooms. These diseases are caused by specific bacteria which for the most part gain access to the air-passages by adhering to particles of dust which are inhaled, and it is prob- able that the greater liability to those diseases of persons living in crowded and unventilated rooms is to a large extent due to the special liability of such rooms to become infected with the germs of those diseases. * ' The discomfort produced by crowded, ill-ventilated rooms is not due to the ex- cess of C0 2 nor to bacteria, nor in most cases to dusts of any kind. The two great causes of such discomfort though not the only ones are excessive temper- ature and unpleasant odors. The cause of the unpleasant musty odor ... is Tinknown. It may be due in part to vol- atile products of decomposition contained in the expired air of persons having de- cayed teeth, foul mouths, or certain dis- 13 orders of the digestive apparatus; and in part to volatile fatty acids given off with or produced from the excretions of the skin. ". . . The problem of securing comfort and health in inhabited rooms requires the consideration of the best methods of preventing or disposing of dusts of various kinds, of properly regulating temperature and moisture, and of pre- venting the entrance of poisonous gases, such as CO, derived from heating and lighting apparatus, rather than a con- sideration of simply a dilution of air to a certain standard or proportion of C0 2 present." It will be noted that the opinion ex- pressed in the last paragraph is quite at variance with the opinions favoring the commonly accepted method of maintain- ing a certain standard of purity, based upon the amount of C0 2 present, by ad- mitting a sufficient volume of fresh air to dilute the foul air to any desired degree. 14 3. KEMOVAL OF DUST. To secure the removal of dust, cheese- cloth stretched on frames is commonly used, but to be effective it is necessary that the area be large, otherwise the cloth will soon become clogged with dust and the flow of air impeded. It is well so to proportion the screen that the ve- locity of the air through the cloth does not exceed 60 feet per minute. Sometimes the air is washed, by caus- ing it to pass through a coke-filter over which water trickles; and in other cases the air is brought in contact with fine sprays of water from specially designed nozzles. 4. TESTING THE QUALITY OF THE AIR. Several methods have been employed to determine directly the number of mi- cro-organisms present in air. *" The first is known as Hesse's method, *Sir Henry E. Roscoe, "A Lecture on Ventilation of Schools," 1889. 15 in which a solid medium is used for the nutrition of the micro-organisms. The principle of this method consists in drawing a known volume of air through a long, wide tube, the inside of which is coated with Koch's nutrient gelatine peptone. As the air passes through the tube the micro-organisms settle on the jelly, and in the course of a few days de- velop into colonies, which become visible to the naked eye and can be counted. The second method is that proposed by Carnelly, the air being aspirated through a sterilized conical flask also containing solid sterilized jelly. The micro-organ- isms fall on the surface of the sterilized jelly, and in a few days the separate col- onies due to each special organism make their appearance, and can be counted. In the third method, that of Percy Frankland, the air is drawn through a glass tube containing two sterilized plugs of glass wool, which are afterward trans- ferred to a flask containing sterilized gelatine." 1C As these methods are rather too refined for ordinary work, the carbonic-acid test has become the recognized one, owing to the ease with which it can be made, and to the fact that the results show closely enough for practical purposes the quality of the atmosphere. One of the best methods of making this test is to take six clean, dry bottles, with tight stoppers, having a capacity of respectively 100, 200, 250, 300, 350, and 400 cubic centimeters; a glass tube having a capacity of exactly 15 cubic centimeters to a given mark; and a bottle of perfectly clear, fresh lime- water, as the apparatus required. The bottles are to be filled with the air to be examined by means of a bellows or a hand- ball syringe. To the smallest bottle 15 cubic centimeters of the lime-water are to be added, the cork put in, and the bottleVell shaken. If turbidity appears, the amount of carbonic acid will be at least 16 parts in 10,000. If no turbidity appears, the bottle of 200 cubic centi- 17 meters is to be treated in the same man- ner ; turbidity in this will indicate 12 parts in 10,000. In similar manner, tur- bidity in the 250 cubic centimeter bottle will indicate at least 10 parts in 10,000 ; in the 300, 8 parts; in the 350, 7 parts; and in the 400, less than 6 parts. . The ability to conduct more accurate analy- ses can be acquired only by special study and a knowledge of chemical properties and methods of investigation. Other apparatus and tests are em- ployed which are more convenient than the preceding, and give fairly close re- sults. In the air tests designed by Dr. Fitz of Harvard University, a measured vol- ume of a colored solution known as phe- nolph thalein is placed in a tube. This tube, of telescopic pattern, when elongated brings a known volume of air in contact with the liquid. The thumb is placed over the end of the tube, which is then shaken. If the color in the liquid does not disappear, 18 the telescopic portion is pushed down to release the air, and again drawn ont in order to bring a fresh volume in contact with the liquid. This operation is re- peated until the color in the liquid dis- appears. The tube is graduated, the marks in- dicating cubic centimetres, and a table accompanies the apparatus showing the number of parts of C0 2 in the air cor- responding to various volumes, required to cause the disappearance of color in the liquid. Dr. Fitz considers air containing 14 parts of C0 2 in 10,000 very bad; 9 parts, bad; 7 parts, fair, and 5 parts, good. Another convenient test, giving ap- proximately correct results, is that made by the use of what is known as " Wol- pert's apparatus." 5. PROPORTION OF CARBONIC-ACID GAS. I An average adult at rest exhales about 480 cu. in. of air per minute. Woodbriclge puts it at 15 cu. ft. per hour. Of this, 19 about four per cent, is C0 2 , which, though heavier than the surrounding air when at the same temperature, tends to rise be- cause of the higher temperature gained by passing through the lungs. In addition to the exhalation from the lungs, there is given off from the body considerable vapor, which must be absorbed by the surrounding air. One function of ventilation is to so dilute the air of occupied rooms that the proportion of C0 2 is kept within certain limits. Ventilation may be considered good when the number of parts of C0 2 in a room does not exceed from 6 to 7 parts in 10,000. With 8 parts, the air appears close to one entering froni out-of-doors. When the C0 2 exceeds 10 parts in 10,000, the quality of the air is noticeably bad, and produces a feeling of weariness in a person breathing it for some time. Con- tinuous breathing of musty air, that is, air noticeably close-smelling to a person entering from out-of-doors, reduces the 20 vitality of persons breathing it, and ren- ders them more susceptible to disease. 6. AMOUKT OF AIR-SUPPLY NECES- SARY. The volume of fresh air that must be supplied to keep the air in the room at a certain degree of purity may be readily computed. For example : What volume of air must be supplied to an occupied room to prevent the C0 2 from exceeding 7 parts in 10,000? Taking as a basis the commonly accepted figures of 0.6 cu. ft. as the amount of C0 2 given off per person per hour, and 4 parts in 10,000 as the proportion of C0 2 in the outside air; if the fresh air admitted absorbs 3 parts to reach the standard of 7 parts as explained above, 3 cu. ft. of C0 2 is taken up, which is equal to that given off by 3-^0.6=5 persons. That is, 10,000 cu. ft, of air must be admitted per hour to 5 persons, or 2000 cu. ft. per hour per person in order that the number of parts of C0 a in 10,000 shall not exceed 7. 21 By similar computations, 6000 en. ft per hour per person will be found neces- sary to dilute the air to 5 parts of C0 2 in 10,000 parts, 3000 cu. ft. to dilute it to 6 parts, 1000 cu. ft. for 7.33 parts, 1500 cu. ft. for 8 parts, and so on. Where gas-lights are used, an addi- tional supply of air must be provided, since the vitiation of air caused by each jet is as great as that caused by five or six men. The air-supply commonly accepted as sufficient for different classes of build- ings is shown by the following table : Class of building. Cu. ft. per hour per occupant. Cu . ft. per min. per occupant. Hospitals 4000-6000 66-100 Court-rooms 2000 33 Legislative halls.. Theaters 2000 1500-1800 33 25-30 HalJs 1000-1200 17-20 Churches 1000-1200 17-20 Schools 1800-2400 30-40 22 * "The quantities of air which should be furnished by ventilating means can- not be safely based solely on the number of those to occupy the rooms to be pro- vided for. . . . The smaller the per capita space, the less the per capita air- supply must necessarily be made. On the other hand, the larger the per capita space, the greater the per capita supply required to maintain the agreeable if not the wholesome quality of the air. The most active and dangerous impurity in the air of occupied enclosures is the mat- ter of organic nature, called effluvia, thrown off by the body through its pores. That matter rapidly changes in charac- ter, passing through a fermenting and decomposing to a putrescent condition. The longer it is retained within a room, the worse its odor becomes and the more morbific its condition. The aims of ventilation should be, as far as practica- ble, to limit atmospheric impurities to *Prof. S. H. Woodbridge in Conn. School Document Ho. 13, 1898. 23 the location of their origin, and to re- duce the quantity and the time of reten- tion of such impurities within an inclo- sure to a minimum. In proportion as the per capita space of an inclosure is greater, the quantity of such matter con- tained in it is larger, the time of its re- tention longer, and its character more offensive and harmful. It follows, there- fore, that the more sparsely occupied rooms of a building are those to which the largest per capita supply should be furnished. "Considering only the permanent ef- fects upon health, an individual air-sup- ply of 1000 cu. ft. per hour furnished to a crowded audience-hall having but 100 cu. ft. of space per capita, may be re- garded as giving as good ventilation as a 3000 cu. ft. per capita supply of air per hour furnished to a school-room having a 300 cu. ft. per capita space." 7. DKAUGHTINESS. The frequency with which the air in a room may be changed depends upon the possibility of introducing it without caus- ing draughts. With wall registers overhead, it is difficult to change the air oftener than every five or six minutes. Even then, great care must be taken to thoroughly distribute the supply. This is done in many cases by means of ' 'cliff users " at- tached to the registers. These devices are made of vertical strips of metal, which are set at different angles and thus cause the air discharged through the reg- ister to spread out over a larger area. In regard to draughtiness, it may be said that experiment has shown that a velocity of air of 1^ ft. per second is not perceptible to the senses, and a velocity of 3 ft. per second causes no discomfort. Accordingly, in seating spaces, care must be taken to prevent air-currents from exceeding the higher velocity stated. 25 In school-buildings and halls, into which the air may be introduced at a tempera- ture above that of the room and -at a point considerably above the heads of the occu- pants, no uncomfortable draughts need be felt. The air will pass across the ceiling until the exposed walls and win- dows are reached, when it will become chilled, descend to the floor and be drawn through the seating space to the vent openings located near the floor. The greatest difficulty in preventing draughts occurs in the case of a supply of air from above, which must be brought in at a temperature below that of the room, as in the case of a crowded hall having little or no exposure. In such cases the air must be brought in through numerous openings of relatively small size. 8. COMPULSORY VENTILATION. Massachusetts was the pioneer in the matter of compulsory ventilation. In that State the Department of Inspection of Factories, Workshops, and Public 26 Buildings demands that the following re- quirements be guaranteed in the specifi- cations accompanying plans submitted to the Department for approval : 1. The apparatus must, with proper management, heat all the rooms, inclu- ding the corridors, to 70 F. in any weather. 2. With the rooms at 70 F. and a dif- ference of not less than 40 between tho temperature of the outside air and that of the air entering the room at the warm- air inlet, the apparatus must supply at least 30 cu. ft. of air per minute for each scholar accommodated in the rooms. 3. Such supply of air must so circu- late in the rooms that no uncomforta- ble draught will be felt, and that the difference in temperature between any two points on the breathing plane in the occupied portion of a room will not ex- ceed 3. 4. Vitiated air in amount equal to the .supply from the inlets must be removed through the vent outlets. 5. The sanitary appliances must be so ventilated that no odors therefrom will be perceived in any portion of the building. The laws of Pennsylvania require that schoolhouses shall have in each class- room at least 15 sq. ft. of floor space and not less than 200 cu. ft. of air space per pupil, and shall provide for an approved system of heating and ventila- tion by means of which each class-room shall be supplied with fresh air at the rate of not less than 30 cu. ft. per minute for each pupil, and warmed to maintain an average temperature of 70 F. during the coldest weather. The New York State requirements are practically .the same, and provide in ad- dition that the facilities for exhausting the foul or vitiated air shall be posi- tive and independent of atmospheric changes. 28 9. SPACE PER OCCUPANT OF BOOMS. The space provided per occupant is obviously an important matter, and, as noted, is one of the provisions in the laws governing the ventilation of schools. The larger cities guard, the welfare of tenement-house dwellers by demanding certain capacities, heights, and window areas of rooms. Thus in Philadelphia it is required that "Every habitable room in every such tenement-house shall be of such dimen- sions as to contain at least 700 cu. ft. of air. Every habitable room in every such tenement-house shall be in every part not less than eight feet in height from floor to ceiling; . . . the to- tal window space for one room shall not be less than twelve square feet." The Boston Building Laws require that " Every room in every tenement or lodging house hereafter built, and in every building hereafter altered to be 29 used as such, shall 1 not be less than eight feet in height in the clear in every story, except that in the attic it may be less than eight feet high for one half the area of the room. Every such room shall have one or more windows on an open air-space with an area at least one tenth as great as that of the room. The top of at least one window on such air- space in each room shall be at least seven feet six inches from the floor, and the upper sash of the same window shall be movable." The New York City requirements are as follows: The height of rooms must be not less than eight feet, and the total area of window or windows in every room communicating with the external air shall be at least one tenth of the su- perficial area of such room; and the top of one, at least, of such windows shall not be less than seven feet six inches above the floor, and the upper half, at least, shall be made so as to open the full width. 30 Every habitable room of a smaller area than one hundred superficial feet, if it does not communicate directly with the external air, and is without an open fire- place, must be provided with special means of ventilation, by a separate air- shaft extending to the roof, or otherwise, as the board of health may prescribe. In all tenement-houses hereafter con- structed, and buildings hereafter con- verted to the purposes of a tenement- house, each room must have a separate window opening to the outer air. Each water-closet room must have a window opening to the outer air, and such water-closet in closure, if provided with a ventilating flue or duct, may have the window opening on any court or shaft containing at least twenty-five square feet in area. Certain minimum requirements abroad are stated in the following schedule : 31 |.S Kind of building. |l| Authority. 5 a General school- rooms (minimum allowed) 130 London School Board. Graded schools (mini- mum allowed) 117 u it n Dundee board school, average 152 Common lodging-house (sleeping-rooms) 300 Local Govt. Board. British army barracks (minimum) 600 Army Regulations. Prisons, seldom under 750-800 Parkes' u Hygiene." Non-textile workrooms 250 Factory Act. Army horses (minimum) 1GOO Army Regulations. " " (in infirmary) 1900 " In this country the per capita space in churches is generally 300 cu. ft., or more. Schools have about 200 cu. ft. and ordi- nary halls frequently have only 100 cu. ft., or even less. 10. COST OF VENTILATION. The relatively great cost of ventilation is due not only to a loss of heat accom- panying the escape of air through the 32 yent-flues greater than would be the case if they were not provided, but it is also due to the fact that in the case of mechanical ventilation, a considerable part of the expense is chargeable to the operation of the fans, driven by engines or motors. The relative cost of steam and gas en- gines, electric and water motors, depends upon a variety of conditions, such as the steam-pressure, quality of gas, voltage, and water-pressure. In a general way, however, for apparatus of 10 horse-power or less, the gas-engine costs much more than any of the others. The steam- engine and the electric motor do not differ greatly in first cost, and the water- motor, in comparison with the others, is very inexpensive. As to the running expense, gas-engine makers claim a consumption of from 15 to 17 cu. ft. of gas per effective horse- power. With small gas-engines under ordinary working conditions, the con- sumption is likely to be double this 33 amount, or more, costing with dollar gas four or five cents per horse-power per hour. It is not uncommon for small low- pressure steam-engines to take from 50 to 75 Ibs., or even as much as 100 Ibs. of steam per horse-power, equivalent to from 7 to 14 or more Ibs. of coal per horse-power per hour, and costing from 1J to 3^ cents per horse-power per hour. If the exhaust steam is utilized, however, it matters not how much steam the engine consumes, since the exhaust steam is practically as good for heating purposes as live steam. A common meter-rate for electric mo- tors is equivalent to about 10 cents per horse-power per hour, which, with the discount based upon a sliding scale, ac- cording to the power usefl, is not far from 8 cents per horse-power per hour for a motor of moderate size. Power developed by water-motors at ordinary city rates varies, according to the pressure, from 30 to 40 cents per 34 horse-power per hour, a prohibitive rate. Of course, the higher the pressure the less the consumption of water, and the lower the cost. From the preceding, it may be said that to develop each horse-power per hour would cost roughly, exclusive of attendance, 5 cents with gas, 3 cents with steam when the exhaust is not util- ized, 10 cents with electricity, and 40 cents with water, these figures being based upon small machines under ordi- nary working conditions. Of these machines, the electric and. water motors are the least noisy, and also require the least attention. With the gas- engine very careful treatment is neces- sary to muffle the exhaust. The steam- engine, if of heavy pattern, low speed, and in proper adjustment, will run practically without noise; but the pulsations of the exhaust should be diminished, by allow- ing the steam to escape into a receiver or equalizing-chamber before passing to the exhaust-pipe leading to the roof. 35 11. HUMIDITY. The humidity or moisture in the at- mosphere is commonly expressed in terms of relative humidity; that is, complete saturation, or the "dew-point," corre- sponds to a relative humidity of 100. A fair average humidity, in what is consid- ered fine weather, in northern latitudes, is about 70. In certain sections of the country it is often much lower, and in others much higher; and in heated rooms it frequently falls to one third of the above. Whether or not these low humidities work injury to persons ex- posed* to them, is a question in regard to which the opinions of investigators differ. To whatever extent it may affect the health, it is a pretty generally accepted fact that air which is too dry in heated rooms causes sensations which are not as agreeable to a healthy person as air con- taining a greater amount of moisture. Since evaporation cools the air, and the rate is more rapid when it is dry than 36 when it is moist, it follows that to secure the same degree of comfort the tempera- ture must be kept at a higher point when the humidity is low than when it is high. To increase the relative humidity ar- tificially, evaporating pans or fine sprays of water are employed. The former in their simplest forms are the little pans with which most furnaces are equipped, but which, in fact, have little effect upon the large volume of air passing through the heater. The capacity of air to ab- sorb moisture increases rapidly with a rise in temperature. For example, air at 70 F. will absorb approximately eight times as much moisture as air at *15 F. Hence if the air at the latter temperature had a relative humidity of 70, it is quite evident that a large amount of water would have to be evaporated to give the same relative humidity to the air in the rooms. To evaporate a pound of water, 1000 heat-units, in round numbers, are required; and since only from 8000 to .9000 heat-units can be utilized per pound 37 of coal burned, it is readily seen that to increase, to any extent, the relative humidity of air supplied to a building, an amount of coal must be burned to evaporate the water far in excess of what, at first thought, would be considered necessary. The cost of artificially rais- ing the relative humidity in rooms to that corresponding to June weather is not the only drawback, experimenters having found that with a relative humid- ity in rooms of much over 30, and an outside temperature of F., the windows become thickly coated with frost, due to the condensation of moisture on them. 12. COOLIKG THE AlR. For cooling air on a small scale, ice may be conveniently employed. Each pound in melting absorbs about 142 heat- units; and since 1 heat-unit absorbed from the atmosphere will lower the tem- perature of approximately 55 cu. ft. of air 1 F., it is a simple matter to com- pute how much ice must be melted to 38 cool a given volume of air a certain num- ber of degrees. Chilling the air reduces its capacity for absorbing moisture, and increases its relative humidity. An excess of humidity causes dis- comfort, and hence air-supply systems are sometimes arranged to pass the air over trays of chloride of calcium, which has a strong affinity for moisture, and to thus dry the air, after passing it over the ice and before allowing it to enter the rooms. For large plants a refrigerating ma- chine should be used, with brine at a very low temperature circulating through coils, over which the air is forced or drawn by fans. * Professor Woodbridge states that *' either of two methods may be fol- lowed for making the treated [chilled] air salubrious and agreeable. The whole quantity of air cooled may be * Report on Heating and Ventilation of the Senate Wing, U. S. Capitol, Washington, Dec. 14, 1895. 39 brought down to so low a temperature as to precipitate the necessary moisture for drying it, and then warmed again by artificial heating to the temperature and dryness essential to comfort; or a part only of the air may be so sharply chilled as to remove the weight of moisture nec- essary to insure dry ness, and this chilled and dried air may then be passed on and mixed with the untreated part, resulting in the drying and cooling of the entire volume of air." The capacity of refrigerating machines is commonly expressed in " tons of ice- melting capacity in 24 hours/' one ton refrigerating effect being equivalent to 284,000 heat-units. One ton of coal should produce at least 13 tons of refrig- eration, based upon ice-melting capacity; and one ton of refrigeration should be produced by the expenditure of not over 1.2 engine horse-power. 40 13. TESTING SYSTEMS OF VENTILATION. In addition to testing the quality of the air, as previously explained, it is often necessary to determine the volume of air entering or leaving a room. For this purpose an anemometer, or air- meter, is used, by means of which the velocity at the register may be deter- mined. Knowing this, and knowing the area through which the air must pass, the volume is readily determined. Air-pressures may be determined by means of the ordinary U tube, one end being connected with the duct or flue, and the other with the atmosphere, the difference in pressure being indicated by the difference in level of the water in the two legs of the tube. This reading of pressure differences in inches of water may be readily transformed into pressure in ounces by multiplying by .578 this factor being the equivalent, in ounces, of the pressure due to a head of one inch of water. 41 The humidity of the air may be ascer- tained by a hygrometer, an instrument provided with two standard thermome- ters one, the dry bulb, showing the temperature of the air, the other, the wet bulb, the temperature due to evap- oration. When the air is saturated no evaporation takes place and the ther- mometers read the same. The dryer the air, the more rapid the evaporation of water from the wet bulb, and the lower the temperature of that thermometer, in comparison with that of the dry bulb. The greater the temperature difference, the lower the relative humidity. A table is provided with these instru- ments, showing the relative humidity corresponding to various temperature differences. For determining temperatures in ordi- nary ventilating work, good standard thermometers are all that are necessary. 42 14. VENTILATION AND ACOUSTICS. * " The arguments sometimes urged against the upward ventilation of audi- toriums because of the alleged inter- ference of such ventilation with their acoustic properties are for the most part fallacious and groundless. Sound-waves are disturbed by traveling through air of unequal density. When air lacks homo- geneity, because of decided inequalities of temperature or moisture, the travel of sound is affected in somewhat the same manner as is that of light when it passes through heated air rising from a stove or other heat source. Heated air rising in mass and in column form from a floor register through the cooler air of a room, or cold air falling in reversed fashion from a ceiling opening through the warmer air of a room, presents an obsta- cle to the even movement of sound- * Prof. S. H. Woodbridge in Report on Heating and Ventilating, House of Representatives, 1899. 43 waves. When, however, the movement is diffused and the air temperature is approximately even throughout the whole mass, that slow movement, whether up- ward or downward, has no appreciable effect on sound-travel. " 44 II. DIFFERENT SYSTEMS OF VEN- TILATION. 1. SYSTEMS OF VENTILATION. THE fireplace is the simplest example of exhaust ventilation, and the furnace the simplest means for securing a supply of warm fresh air. With other systems the heat of the fire is first transferred to a medium, wa- ter or steam, which in turn warms the air passing to the rooms. In the furnace system the air is heated by direct contact with cast-iron or steel- plate surfaces, cold air being brought into the space between the body of the furnace and the casing by a box or duct connected with the outdoor air. Of course if cellar air is used, the fresh- air supply feature is, to a very great ex- tent, lost, the supply depending upon the tightness of basement walls and win- 45 dows against the in-leakage of fresh air. The indifference of the dwellers in houses heated by furnaces, in many parts of the country, to the importance of hav- ing a cold-air box for a fresh-air supply, is simply astounding, and can be ex- plained only by assuming a widespread ignorance of the bad effects on health from the long-continued breathing of cellar air. The indirect steam or hot-water sys- tem works on the same general principle as the furnace, and it possesses several ad- vantages and has a wider range of appli- cation. Buildings which would require several furnaces are easily heated by a single boiler, the benches of indirect radiators being placed near the base of the flues, thus avoiding the relatively long pipes common in furnace heating. With the latter, the longer the pipes the more sluggish the flow of air and the greater the chance of failure in heating rooms on the exposed sides during strong winds. 46 Direct-indirect, as its name A mplies, is a compromise between direct heating with radiators in the rooms, and indi- rect heating with radiators suspended from the basement ceiling and incased in galvanized iron or wood, and with cold-air and warm-air ducts connected with the spaces below and above these radiators. This direct-indirect system is a great improvement in point of ventilation over the direct system, but falls far short of the indirect system in positive results. The greatest difficulty with the direct- indirect method is experienced in mild weather, when a constant supply of fresh air equivalent to that required in cold weather cannot be admitted without over- heating the room, since it must pass up over the radiating surface. If the steam is shut off, the air enters at the outdoor temperature, which may be too cold for comfort in the room. With this method of heating, the rooms on the windward side of a build- 47 ing are excessively ventilated, while those on the lee side receive a less gener- ous supply of fresh air on account of the tendency to a vacuum condition existing on that side. Ordinary indirect systems, commonly called "gravity" systems, depend solely on the difference in the temperatures of the air in the flues and the air outside, to cause the desired velocity. This differ- ence varies with changes in the weather, and consequently the flow of air is not constant, becoming more sluggish as the- weather grows milder. Winds also seri- ously affect its flow. To overcome these- faults the "blower" or "fan" system is used. In the oft-quoted words of the lato Eobert Briggs, " If air is wanted in any particular place, at any particular time,, it must be put there, not allowed to go. . . . Xo other method than that of impelling air by direct means, with a fan, is equally independent of accident- ally natural conditions, equally efficient 48 for a desired result, or equally controlla- ble to suit the demands of those who are ventilated." The "fan "system is more expensive than others, both in first cost and in run- ning expense, but the results are far su- perior to those attainable by any other method. In manufacturing buildings the