Libfc r HANDBOOK FOR HEATING AND VENTILATING ENGINEERS BY JAMES D. HOFFMAN, M. E. PROFESSOR OF PRACTICAL MECHANICS AND DIRECTOR OF THE PRACTICAL MECHANICS LABORATORIES, PURDUE UNIVERSITY MEMBER AND PAST PRESIDENT A. S. H. & V. E. MEMBER A. S. M. E. ASSISTED BY BENEDICT F. RABER, B. S., M. E. PROFESSOR OF MECHANICAL ENGINEERING UNIVERSITY OF CALIFORNIA MEMBER A. S. M. E. FOURTH AND RESET *- * I ".""' McGRAW-HILL BOOK COMPANY 239 WEST 39TH STREET, NEW YORK 6 BOUVERIE STREET, LONDON, E. C. 1920 Engineering Library COPYRIGHT, 1910, 1913, 1920 BY JAMES D. HOFFMAN First Edition, 1910 Second Edition, 1913 Third Edition, 1917 Fourth Edition, 1920 PREFACE: TO FOURTH EDITION. Changes in the art of heating- and ventilating- buildings have been so pronounced in the last few years that it has been considered advisable to entirely reconstruct the Hand- book rather than to make additions to the old text. The book, therefore, has been rewritten and reset in every part. There have been added approximately 87 pages consisting of revisions, extended discussions of original text and new subject matter not before considered. Of this increase, Chap- ter I has 17 pages, including discussions on heat applications, combustion of fuels and analysis of flue gases; Chapters II, III, IV and V on air measurements, heat losses and furnace heating have 19 pages devoted largely to extensions; Chap- ters VI, VII, VIII and IX on hot water and steam heating have 28 pages, increasing the original text of this part by approximately 43 per cent. This includes descriptions of modified gravity systems, both steam and water, valves, fit- tings and piping connections; Chapters X, XI and Xll on mechanical warm air systems have 10 pages of extensions, and Chapter XIII has 4 pages of extensions to the calcula- tions of hot water and steam mains. The remainder of the book is in substance as it was with the addition of Sugges- tions to School Districts, 4 pages, Chapter XVIII, Suggested Pip- ing Connections for Vacuum System Details, 3 pages, Appendix 3, and several new tables on pipe sizes for hot water and steam service. Especial attention has been given to the simplification of every important subject by applications to practical prob- lems. These applications in most cases have been completely analyzed and their results compared with other parallel cases. No effort has been spared to have the entire subject matter complete and up to date and to present it in a way that will be at once simple and effective. This little book is as a growing child. We wish it to be very active and useful to the general public. To do this it must be versatile and resourceful, carrying no excess ma- terial and trained down to service condition. We ask the assistance of our friends and their suggestions in its behalf. LaFayette, Ind. J. D. H. 425899 EXTRACT FROM PREFACE TO FIRST EDITION. In the development of Heating- and Ventilating work, it is highly desirable that those engaged in the design and the installation of the apparatus be provided with a Handbook convenient for pocket use. Such a treatise should cover the entire field of heating and ventilation in a simplified form and should contain such tables as are commonly used in every day practice. This book aims to fulfill such a need and is intended to supplement other more specialized works. Be- cause of the scope of the work, its various phases could not be discussed exhaustively, but it is believed that the funda- mental principles are stated and applied in such a way as to be easily understood. It is suggestive rather than diges- tive. The principles presented are the same as those that have been stated many times before, but the arrangement of the work, the applications and the designs are all original. Many equations and rules are necessarily given; but it will be seen that, in most cases, they are developments from a few general equations, all of which can be readily under- stood and remembered. Practical points in constructive de- sign have also been considered. However, since the prin- ciples of heating 'and ventilation are founded upon funda- mental thermodynamic laws, it seems best to accentuate the theoretical side of the work in the belief that if this is well understood, practical points of experience will easily follow. All the standard works upon the subject have been freely consulted and used. In most cases where extracts are made, acknowledgment is given in the text. Because of these references throughout the book, we do not here repeat the names of their authors. We wish, however, to express our sincere appreciation of their valuable assistance. LaFayette, Ind. J. D. H. EXTRACT FROM PREFACE TO SECOND EDITION. A few corrections were made on the first edition and all the material has been revised and brought up to date. The work on air conditioning- has been amplified. The descrip- tions of hot water and steam heating have been improved by diagrams of the various piping systems. Two chapters have been added on refrigeration and many tatfles have been added in the Appendix. Many suggestions coming from men in practice have been included, thus enlarging upon the prac- tical side and the applications. Lincoln, Neb. J. D. H. CONTENTS CHAPTER I. (Heat and Combustion) Arts. Pages 1- 8 Introductory. Measurement of Heat and Temperatures 9- 16 9- 17 Discussion of Heat and Heat Applications 17- 34 CHAPTER II. (Air) 18- 23 Composition" of Air. Amount required per Person 35- 43 24- 27 Humidity 44- 51 28- 29 Convection of Air. Measurement of Air Velocities 52- 56 30- 34 Air used in Combustion. Chimneys. Cowls.. 57- 60 CHAPTER III. (Heat Losses) 35- 42 Heat Losses from Buildings 61- 73 43 Temperatures to be considered 73 44 Heat given off from Lights and Persons 74 45 Performance to Guarantee Heating Capacity 74- 75 CHAPTER IV. (Furnace Heating) 46- 47 Essentials of the Furnace System ." 76- 77 48- 61 Calculations in Furnace Design 77- 85 62 Application to a Ten Room Residence 86- 91 63 Determination of Best Outside Temperature 92- 94 64 Humidifying Furnace Air 95- 99 CHAPTER V. (Furnace Heating, Continued) 65- 66 Selecting, Locating and Setting the Furnace 100-105 67- 72 Air Ducts. Circulation of Air in Rooms 106-112 73 Fan Furnace Heating 113-114 74- 75 Hot Air Radiator Systems 115-117 76 Improving Sluggish Circulation 117 77 Suggestions for Operating Furnaces 118-119 CHAPTER VI. (Hot Water and Steam Heating) 78- 81 Comparison and Classification of Systems 120-125 82 Diagrams of Piping Systems 125-130 83- 85 Modified Gravity Systems 130-140 86 Standard Piping Connections 141-143 CHAPTER VII. (Hot Water and Steam Heating, Cont'd) Arts. Pages 87- 88 Heaters, Boilers and Accessories 144-150 89- 95 Classification and Efficiencies of Radiators.. ..150-157 96 Pipe and Fittings 157-163 97- 99 Expansion Tanks, Fire Coils and Corrosion. ...163-165 CHAPTER VIII. (Hot Water and Steam Heating, Cont'd) 100-104 Calculations for Boiler Size and Radiator Surface 166-177 105 Greenhouse Heating 177-180 106-107 Determination of Pipe Sizes 180-184 108-109 Pitch of Mains and Radiator Connections 184-185 110 General Application to Hot Water Design 185-191 111-112 Insulating Steam Pipes. Water Hammer 191-193 113 Feeding Return Water to Boiler 193-198 114 Hot Water Heating for Tanks and Pools 198 115 Suggestions for Operating Boilers 198-199 CHAPTER IX. (Mechanical Vacuum Heating) 116-117 General. Return line and Air line Systems Described 200-204 118 Vacuum Pumps and Regulation 205-208 119 Vacuum Specialties 208-212 CHAPTER X. (Mechanical Warm Air Heating) 120-124 General Discussion. Blowers and Fans. Heating Surfaces 213-223 125-128 Single and Double Duct Systems. Air Washing 223-233 CHAPTER XL (Mechanical Warm Air Heating, Cont'd) 129-133 Heat Loss. Air Required. Air Tempera- tures 234-237 134-135 Air Velocities. Area of Ducts 237-238 136-140 Heating Surface in Coils. Arrangement of Coils 238-247 141-143 Amount of Steam Used in the System 247-248 CHAPTER XII. (Mechanical Warm Air Heating, Cont'd) 144-148 Air Velocity and Pressure. Horse-Power in Moving Air 249-260 149-154 Fan Sizes and Drives. Speeds. Size of Engine. ' Piping Connections 260-266 155-156 General Application to Plenum System 267-274 CHAPTER XIII. (District Heating) Arts. Pages 157-161 General. Conduits. Expansion Joints. Anchors 275-289 162-164 Typical Design. Heat in Exhaust Steam 289-295 165-168 Hot Water Systems. General Discussion 296-298 169-171 Pressure and Velocity of Water in Mains 298-303 172-176 Radiation Heated by Exhaust Steam 304-306 177-182 Reheating Calculations 306-312 183-186 Circulating Pumps. Boiler Feed Pumps 313-318 187-191 Radiation Supplied by Boilers and Econ- omizers .* 319-323 192 Total Capacity of Boiler Plant 323-326 193-195 Cost of Heating from Central Station. Regulating the Heat Supply 326-332 196 Steam System. General Discussion 332-333 197-199 Pipe Sizes. Dripping the Mains 334-338 200 General Application of Steam System to District 338-340 CHAPTER XIV. (Temperature Control) 201-204 General. Johnson, Powers and National Systems 341-349 CHAPTER XV. (Electrical Heating) 205-207 Discussion and Calculations 350-352 CHAPTER XVI. (Refrigeration) 208-209 Discussion of Systems 353-354 210-211 Vacuum and Cold Air Systems 354-355 212-213 Compression and Absorption Systems 355-358 214 Condensers 359-361 215 Evaporators 361-363 216 Pipes, Valves and Fittings 363 217-218 Absorption System 364-367 219-220 Generators 368-369 221-225 Condensers, Absorbers, Exchangers and Pumps 369-371 226-227 Comparison of Systems 372 228 Methods of Maintaining Low Temperatures. .373-374 229 Influence of Dew Point 375-376 230-231 Pipe Line Refrigeration 376-377 CHAPTER XVII. (Refrigeration, Continued) Arts. Pages 232-234 Calculations 378-382 235 General Application 383-384 236-238 Method of Rating Capacity 384-385 239 Cost of Refrigeration 385-387 CHAPTER XVIII. (Specifications) Suggestions on Planning Specifications 388-394 Suggestions to School Districts 395-398 APPENDIX I. Tables 1-57 399-452 APPENDIX II. Tables 58-75 453-463 APPENDIX III. Test of House Heating Boilers and Data Required for Estimating Hot Water and Steam Boilers 465-467 Details of Vacuum Piping Systems 468-470 CHAPTER 1. HEAT ITS NATURE, GENERATION, USE, MEASUREMENT AND TRANSMISSION. 1. Introductory: In all localities where the atmosphere drops in temperature much below 60 Fahrenheit, there is created a demand for the artificial heating of buildings. As the buildings have grown in size and complexity of con- struction, so also this demand has grown in extent and pre- ciseness, with the general result that out of the open fire place and iron stove there has developed a science growing richer each day from inventive genius and manufacturing technique the science of the heating and ventilating of buildings. The purpose of this handbook shall be to out- line the fundamental principles and practical applications of this science in its various branches. To the average heating engineer it may be that the exact nature of heat itself is of much less moment than its generation and transmission, but these facts should be im- pressed, that heat is one form of molecular energy, that it cannot be created except by conversion from some other form, and that it is infallibly obedient to certain physical laws and principles which should be understood and used by every engineer. In generating heat for heating purposes the almost uni- versal method is combustion. The union of the combustible content of such substances as coal, wood or peat with the oxygen of the air is always attended by a liberation of heat derived from the chemical action of the combination; and this heat is carried by some common carrier, such as air, water or steam, to the building or room to be heated where it is given off by the natural cooling process. In some in- stances this heat is converted into electrical energy which is carried by wire to the place of use and given off as heat through a set of resistance coils. This method is not much favored as yet because of its inefficiency and the resulting expense, an objection which does not hold in the case of water power installations where the combustion of fuel is entirely eliminated. 10 IDEATING A'ND VENTILATION *J. **eni -'^emiK'.-jituro: The meaning of the word heat should not be confused with that of the word temperature. Although closely related they are far from being inter- changeable. In a given mass of any substance, except when passing through a change of state, the universal law is that the addition of heat raises the temperature and the subtraction of heat lowers the temperature of the sub- stance. Heat is the cause and temperature is one of the effects. In the measurement of heat the most commonly accepted unit in practical engineering work is the British thermal unit, abbreviated B. t. u. This may be denned as that amount of heat which ivill raise the temperature of one pound 'of pure water one degree Fahrenheit (See definition for specific heat, Art. 8). This unit value, the B. t. u., measures the quantity of heat, while the temperature measures the inten- sity or degree of heat. In equal masses of the same sub- stance the two are proportional. The Fahrenheit scale is the more commonly used temperature scale, especially in steam engineering. The unit of this scale is derived by dividing the distance on the thermometer between the freezing point and the boiling point of water into 180 spaces called de- grees, the freezing point being marked 32 and the boiling point 212. All temperatures in this book, unless otherwise stated, will be taken according to the Fahrenheit scale and all quantities of heat expressed in British thermal units. A second unit of quantity of heat considerably used in scientific research is the calorie, abbreviated cal., and defined as that amount of heat which will raise one kilogram of pure water from 17 to 18 centigrade. The centigrade scale is a second temperature scale, the unit of which is derived by dividing the distance on the thermometer between the freezing point and the boiling point of water into 100 de- grees, the freezing point being marked and the boiling point 100. It is often found desirable to change the expression for temperature or for quantity of heat from one system of terms to that of the other. For this purpose the follow- ing equations will be found useful: 9 5 F = C + 32 and C = (F 32) (1) 5 9 where F = Fahrenheit degrees and C = centigrade degrees. From these equations it may be seen that the two scales MEASUREMENT OF TEMPERATURE 11 coincide at but one point, -- 40. For conversion of the quantity units the following 1 may be used: \ British thermal unit = 0.252 calorie. 1 calorie = 3.968 British thermal units. These are for the absolute conversion of a certain quantity of heat from one system to the other. If, however, the effect of this heat is considered upon a given weight of substance and the weight also is expressed in the respective systems, the following values hold: 1 calorie per kilogram 1.8 British thermal units per pound. 1 British thermal unit per pound = 0.555 calorie per kilogram. For conversion tables see Marks' Mechanical Engineers' Handbook or Kent's Mechanical Engineers' Pocket-Book. 3. Instruments Used in Measuring Temperature: In- struments intended to indicate degree or intensity of heat, i. e., the temperature of substances, are designed upon many different principles. Of these the following represent the important general classifications: EXPANSION OF A LIQUID WITH INCREASE IN TEMPERATURE. The ordinary mercury, alcohol or ether-in-glass thermometers be- long to this great class. Mercury thermometers should not be used to register temperatures near the top of the scale for fear of rupturing the glass. To overcojne this difficulty some thermometers are made with a mercury-well at the upper end of the mercury column. The objection to be offered to this form is the difficulty of completely emptying the upper well after it has been partially or wholly filled with mercury. The ordinary mercury-in-glass thermometer, either with or without the upper mercury-well, should not be used on temperatures above 600 F. because of the fact that mercury boils at 680 F. Mercury-in-glass or mercury- in-quartz thermometers have been used up to 1300 F. by compressing into the space above the mercury some neutral gas, as nitrogen or carbon dioxide. This type, however, is open to the objection of high breakage costs. Due to the fact that mercury freezes at 38 F. it cannot be used for low temperature thermometers. These are usually made with alcohol as the liquid, since alcohol freezes at 170 F. EXPANSION OF A SOLID WITH INCREASE IN TEMPERATURE. In- struments built upon this principle are commonly called ex- pansion pyrometers. Fig. 1, a, shows such a pyrometer. Inside HEATING AND VENTILATION the stem of the instrument is a metallic expansion element, the movement of the free end of which operates the hand on the dial. Such an instrument may be used up to the lowest temperature of the softening- point of the metals in the stem. Ordinarily, errors of 2 to 5 per cent, may be expected in the temperature reading. Fig. 1. FUSION OF CONES OF REFRACTORY MATERIALS. This principle is exceedingly simple in application as shown in Fig. 1, 6. Several of a series of cones, varying in mineral compositions and hence in melting points, are exposed to the temperature MEASUREMENT OP TEMPERATURE 13 to be measured and this temperature is indicated by that cone of the series which just melts or softens sufficiently to lose its shape. With the cones is furnished a table of tem- peratures for comparison. From the illustration, the tem- perature indicated is evidently that corresponding to cone number 08, which from the Seger cone table is 1814 F. Seger cones for such measurements may be obtained to indi- cate temperatures from 1094 F. to 2800 F. by increments varying- from 25 to 55 degrees. TRANSFER OF A HIGH TEMPERATURE BODY AND ITS HEAT TO A KNOWN QUANTITY OF WATER. This is the principle embodied in all pyrometers of the calorimetric type, one of which is shown in Fig. 1, c. A thoroughly insulated vessel contains a known quantity of water, a thermometer and a stirring device. A ball of platinum, copper or iron of known weight and specific heat is exposed to the temperature to be measured, by means of the handle shown in the figure or by a small crucible. When the ball has reached its upper temperature, it is quickly transferred to the water of the insulated vessel and the rise of temperature of the water is noted from the thermometer. Upon the suppositions that all the heat In the ball is transferred to the water and that the ball and the water finally reach the same temperature, the assump- tion may be made that the heat gained by the water equals that lost by the ball, hence the product of the weight, tem- perature rise and specific heat of the water, divided by the product of the weight and specific heat of the ball gives the drop in temperature through which the ball has passed. From this the upper temperature reached by the ball may be obtained by adding to the temperature drop, the final temperature of the water and the ball. Let s = specific heat of the ball, T upper temperature of ball, m = weight of the ball, t and t' respectively = beginning and ending tem- peratures of the water, and w = weight of the water. Remembering that the specific heat of water is 1, we have w (*' t) = am (T f ) whence (2) w (t' t) T = + f sm The objections to this method of temperature measurement are its slowness due to the necessary computations and manipulations, and the fact that considerable error may be introduced during the transference of the ball from the heated space to the calorimeter. When this method is used 14 HEATING AND VENTILATION for very high temperatures the ball is made of porcelain or fire clay. CHANGE OF RESISTANCE OF AN ELECTRIC CONDUCTOR, OR CHANGE OF VOLTAGE OF AN ELECTRIC THERMO-COUPLE. Instruments built upon either of these two electrical principles are extremely delicate but give very accurate results, it being- possible to determine temperatures up to 2000 F. with a variation of but one or two degrees. For practical work electric pyrom- eters are more commonly of the thermo-couple type (See Fig. 1, (1). To the right is shown a porcelain tube enclosing a thermo-couple of two dissimilar metals. If this tube is subjected to the temperature to be measured, the potential generated by the couple upon heating is proportional to the temperature. Hence, if connected to a voltmeter as shown at the left, the voltage generated may be indicated, or as is usual, the temperature may be read directly since the scale of the voltmeter may be graduated in degrees instead of in volts. This type of pyrometer is extensively used. From each of a large number of testing points, thermo- couple wires may be brought to a central point, where by means of a switch the temperature at any couple may be instantly observed by throwing its current into a common voltmeter or temperature indicator. Other types of temperature measuring instruments are designed upon the principle of the optical pyrometer, and the gas and air thermometers, but these are not used to as large an extent in practice as are the five above mentioned. 4. Absolute Temperature: In experiments that have been carried on with pure gases with the use of air ther- mometers, it has been found that gases expand or contract 1 1 approximately of their volumes at 32 F. ( of their 492 460 volumes at zero F.) per degree change in temperature, or 1 of their volumes at zero C. From the same line of 273 reasoning, by cooling a gas to 460 F. or 273 C, it would cease to exist. This theoretical point is called the absolute zero of temperature. All 'gases change to liquids or solids before this point is reached, however, and hence do not obey the law of contraction of gases at very low temperatures. The fact that air at constant pressure changes its volume almost exactly in proportion to the abso- lute temperature, T, (460 + t, where t is temperature Fahr- MECHANICAL EQUIVALENT OF HEAT 15 enheit) gives a starting- point to be used as a basis for all air volume-temperature calculations. For instance, if a volume of 20000 cubic feet of air at is heated to 70 with constant pressure, its volume after heating- will be greater in the same proportion as its absolute temperature x 530 is greater; that is, = ; x = 23000 cubic feet, or 20000 460 an increase of 15 per cent. 5. Gage and Absolute Pressures: Gage pressure is the total pressure per square inch in a container minus the pressure of one atmosphere. Thus 65 pounds gage pressure means that the container is carrying 65 pounds pressure per square inch of surface above the pressure of the atmosphere. Atmospheric pressure at sea level, 14.696 commonly written 14.7, is used on all but the most exact calculations. This pressure becomes less as the elevation rises above sea level. As a general statement it may be said that atmospheric pressure reduces l / 2 pound for each 1,000 feet above sea level (See Table 8, Appendix). The total pressure exerted within the container is therefore 65 + 14.696 = 79.696 at sea level. This total pressure is known as the absolute pressure and when stated in pounds per square foot of area is called specific pressure. 0, Mechanical Equivalent of Heat: By experiment it has been determined that if the heat energy represented by one B. t. u. be changed into mechanical energy without loss, it would accomplish 778 foot pounds of work. Similarly, one calorie is equivalent to 428 kilogrammeters of work. 7. Latent Heat, Total Heat, Etc.: Not all the heat applied to a body produces change in temperature. Under certain conditions the heat applied produces internal or molecular changes and is called latent heat. Thus in a nor- mal atmosphere if heat is applied to ice at the freezing point, no rise of temperature is noted until all the ice is melted; and again, heat applied to water at the boiling point does not raise its temperature until all the water is changed to steam. The first is called latent heat of fusion, which for ice is 144 B. t. u. per pound; the latter is called latent heat of vaporization, which for water is 970.4 (Marks and Davis) B. t. u. per pound. For most calculations the approximate value 970 may be used. Consult books on ther- modynamics for further discussion of latent heat as com- posed of internal and external work equivalents. Sensible heat 16 HEATING AND VENTILATION is that heat whose addition or subtraction can be detected by a thermometer. As applied to the standard steam tables, this is equal to the total heat above 32 minus the latent heat of vaporization. Heat of the liquid, as applied to the standard steam tables, is that quantity of heat added to a pound of water at 32 to bring it to the temperature of the boiling point at any given pressure. At atmospheric pres- sure this is 180 B. t. u. Total heat is that quantity of heat represented by the sum of the latent heat of vaporization and the heat of the liquid. In the evaporation of water at atmospheric pressure this is 970.4 + (212 32) = 1150.4 B. t. u. Total heat is different for all pressures at which evaporation takes place. Consult Art. 14 and Table 4, Ap- pendix, for latent heat, heat of the liquid and total heat at different pressures. Convenient approximate equations for latent heat and total heat are those quoted by Regnault. Latent Heat = 1092 .695 (t 32) (3) where t temperature at which the steam is formed. Illustration.- The latent heat of steam at a temperature of 338 (pressure 100 Ibs. gage) is 1092 .695 (338 32) = 879.3 B. t. u. Total heat 1092 + .305 (t 32) (4) Illustration. The total heat above 32 of the same steam as in previous illustration is 1092 + .305 (338 '32) = 1185.3. 8. Specific Heat: The specific heat of a substance is that quantity of heat added to or subtracted from a unit weight of the substance when its temperature is changed one degree. The mean specific heat is that quantity of heat added to or subtracted from a unit weight of the substance in changing through any given number of degrees, divided by the number of degrees change. For illustration, the specific heat of water that has been considered standard for many years is obtained at the temperature of its maximum density, 39.1 F. (4 C.). This is used in much of the physi- cal and scientific calculations, but in most engineering work the tendency is to take the mean specific heat between the temperatures of 32 F. and 212 F. (0 C. and 100 C.), i. e., the heat required to raise one pound of pure water from 32 F. to 212 F. divided by 180. This is the same as the specific heat of water at 62 F. and agrees with the accepted value of the B. t. u. Table 26, Appendix, gives specific heats of substances. RADIATION 17 9. Radiation: Heat may be transmitted as a wave mo- tion in the ether of space. In this way the heat of the sun reaches the earth. Heat of this form, usually referred to as radiant heat, requires no matter for its conveyance; passes through some materials, notably rock salt, without change or appreciable loss; and follows the laws for the radiation of light. It is assumed that the heat received by the atmos- phere is obtained through contact with the bodies giving and receiving heat and that little is obtained directly from the radiant ray. TABLE 1. Radiation Constants, Values of C Material C Glass, smooth 0.154 Brass, dull 0.0362 Copper, slightly polished 0.0278 Lampblack 0.154 Wrought-iron, dull, oxidized 0.154 Wrought-iron, clean, bright 0.0562 Cast iron, rough, highly oxidized 0.157 Lime plaster, rough, white 0.151 Slate 0.115 Gold plate, shining but not polished 0.082 Clay 0.065 The capacity that any body has of absorbing the radiant ray is called its absorption capacity. Absolute black bodies theoretically absorb all the radiation received upon their surfaces and have an absorption capacity of 1. Bright or polished surfaces have a reduced absorption capacity. It is also understood that the radiation capacity is proportional to the absorption capacity. The amount of heat radiated by a substance is practically independent of the form of the sur- face and depends upon the difference of temperature be- tween the radiating and receiving- surfaces, and upon the color and character of the surfaces. The Stefan-Boltzman radiation law states that for black bodies the radiating powe'r is proportional to the fourth power of the absolute temperature of the body. For other than black bodies this law is also approximately true. Let R area of radiating surface in square feet, H = B. t. u. radiated per hour, T = 18 HEATING AND VENTILATION absolute temperature of the substance, and C = a constant; then, H = CR (T -=- 100)*. For a dead black body C = .1618. Other values of C from Hutte are shown in Table 1. Assuming- in general that radiating- surfaces for heating systems may be classified, as black bodies, the amount of heat radiated from a surface R having an absolute tempera- ture T to surrounding surfaces having an absolute tempera- ture T! is H = C R [(?' -T- 100) 4 (T l -f- 100) 4 ] Applications of the theoretical formula of radiant heat to practical problems in general give very unsatisfactory re- sults. 10. Conduction: This method of heat transmission Is very evident to the senses. If a rod of metal is heated at one end, the heat is transferred or conducted along the rod by molecular action. Conduction being essentially the way by which solids transfer heat, it is of special significance in the calculation of heat losses through the walls of a build- ing 1 . The coefficient of conduction may be defined as that quan- tity of heat which passes through a unit thickness of substance in a unit of time across a unit of surface, the dif- ference of temperature between the two sides of the sub- stance being one unit of the thermometric scale employed. The amount of heat conducted through a material in a given time is directly proportional to the difference in tem- perature between the two parallel sides of the substance and inversely proportional to the thickness. As a formula H cfb (ti /) where c = coefficient of conductivity, b =. thickness of material in inches, and t\ and / = respective temperatures. Since the complexity of building construc- tions renders it impossible to reduce all conduction losses to losses per unit thickness of the structure, the term rate of transmission may be used instead of conductivity and may be understood to include combinations of conductivities and thicknesses. This may be illustrated by the ordinary framed and studded wall where K is the rate for the com- bination (See Chapter III). 11. Convection: Gases and liquids convey heat most readily by this method, which is fundamental with warm air and hot water heating installations. If it is attempted to heat a body of water by applying heat to its upper surface, it will be found to warm up with extreme slowness. If, however, WORK AND POWER 19 the source of heat be applied below the body of water, it will be found to heat rapidly. What actually happens is this: water particles near the source of heat become lighter, volume for volume, than the colder particles near the top, and because of the change in density gravity causes an exchange of these particles, drawing the heavier to the bot- tom and allowing the heated and lighter particles to rise to the top thus forming circulation currents. This process is known as convection. It will not occur unless the medium expands upon being heated and unless the force of gravity is free to establish circulating currents. In the hot water heating system (Fig. 2), water rises by convection to the radiators, is there cooled and descends by the return circuit to the point of heat application completing the circuit. The warm air furnace installation works similarly, air, however, being the heat-carrying medium. 12. Work: Work is the overcoming of a resist- ance along a line of motion. It is the product of force and distance and is independent of time. Assuming the pound to be the unit of force and the foot to be the unit of distance, the unit of work is the foot-pound. To lift one hundred pounds one foot or one pound one hundred feet would cause the expenditure of one hundred foot pounds of work. 13. Power: Power and work are closely re- lated but are not identical. Power is the rate of -*wtf doing work and always comprehends the element Fig. 2. of time. The unit of power, called horse-power, has no reference to the power of the horse nor to the boiler horse-power, but is an arbitrary value equivalent to 1 horse-power 746 Watts = .746 K. W. 33000 ft. Ibs. of work per min. 4562.4 kilogrammeters of work per min. 33000 -*- 778 = 42.416 B. t. u. per min. . 4562.4 -f- 428 = 10.66 cal. per min. If 100 cubic feet of water, weighing 62.5 pounds per cubic foot, are lifted 100 feet per minute without friction loss, the horse-power is (100 X 62.5 X 100) -=- 33000 = 18.94. The term boiler horse-power is equivalent to 34.5 pounds 20 TITRATING AND VKNTILATH >X of water per hour evaporated from water at 212 F. to steam at 212 F. This equals 970.4 X 34.5 = 33479 B. t. u. 14. Application of Heat to Solids and Liquids: All matter in its most finely divided state is made up of minute particles called atoms which are drawn together by a force called attraction. This attraction is lessened by the applica- tion of heat, the particles tending- to separate (substance increasing- in size) until such a temperature is reached (a certain amount of heat is absorbed) when the attraction is zero. From this point further application of heat will cause repulsion and the particles will fly apart. This explains the existence of the three states of matter; solid, liquid and gaseous. No two substances act exactly alike upon the addition or subtraction of heat, but practically all sub- stances under certain conditions may exist in any one of the three states. The exact points of separation between the solid, liquid and gas, differ very much in different sub- stances; but regardless of this fact, each substance no mat- ter what its state may be solidified by cooling or vaporized by heating. The amount of heat that may be carried by any substance in any given state is called its capacity for heat. When solids change in temperature they change in vol- ume in practically all cases, increasing with rise of tempera- ture and decreasing with fall of temperature. This fact many times causes considerable annoyance to any one manu- facturing or using materials of construction. Since all metals that enter into engineering construction are subject to sudden and sometimes very extreme changes of tempera- ture, it is frequently necessary to put in compensating de- vice~s to account for such temperature changes. The steel framework of a building for example is subjected to ex- tremes of summer and winter temperatures, causing change in the building size. This change is small, but during the cold weather when the building materials have a slight re- duction in size, the steam pipes are under high temperatures and have their maximum size. During the summer when no heat is necessary, reverse conditions exist. In high buildings this change is sufficient to demand compensators or expansion joints in the steam lines, otherwise there would be contact between the pipes and the building which might be sufficient to rupture some part. Like conditions exist in street mains (conduit lines), basement mains in buildings, horizontal connections between vertical risers, APPLICATION OF HEAT TO LIQUIDS 21 riser connections between floors, boiler pipe connections, boiler settings in brick work and in many other places around the heating system of the average building. Sudden changes of temperature in any material are to be avoided when possible. This is especially true if the materials are fastened together with screws, bolts or rivets, such as boilers, heaters or piping systems. When heat is thus applied it is always more intense at one place than at another and the expansion or contraction is not uniform, causing unnecessary stresses and many times leaks and rup- tures. The force exerted by heat in expanding any substance is the same as would be required to stretch the same sub- stance an equal amount by mechanical means or to compress the enlarged piece to its former size. When heat is applied to liquids, the phenomenon of ex- pansion is apparent as in solids. One notable exception is found in water between 32 and 39.1 F. as will be seen later. Since water is the liquid universally used in heating systems, PerLJb. Psrib. Pound I Pound of Wafer ^STATE CH/JNQE or WATER UHDER ATMOSPHERIC Fig. 3. it is of interest to study its characteristics under different conditions of heat. Start with a mass of one pound of ice at some tem- perature, say 25 F. (it must be remembered that after ice is formed at 32 F. it may be cooled to any temperature below 32 by the continued extraction of heat), and while heat is being added to the mass, note the changes taking place. In Fig. 3 EFGABK is the temperature curve, LMNOC is the volume curve, the ordinates MM', NN', OD and BC represent 22 HEATING AND VENTILATION the periods of change of state, and the horizontal line at the base of the chart L'C represents heat units added. With LU representing- the volume of a pound of ice at any tempera- ture (in this case 25 F.) heat is added and the temperature curve E rises to F. The quantity of heat added is found by multiplying- the pounds of ice (in this case 1) by the specific heat, which for ice is .504, and by the rise in temperature. The addition of .504 B. t. u. for each degree rise between 25 and 32 gives the ice (32 25) X .504 = 3.528 B. t. u. and brings it to the temperature of the melting point. While the temperature has been gradually increasing the volume has also increased slightly. See MM'. More heat is added and the ice begins to melt but the temperature does not rise as would be expected. It remains constant from F to O until all the ice has changed to water, as shown by the line l/.V. In this change there has been a reduction in the vol- ume of the mass as shown by the dropping of the line MN. Notice that the volume of the water is taken as 1 and the volume of the ice at 32 as 1.09. This explains why water allowed to freeze in a pipe often causes the bursting of the pipe. The quantity of heat absorbed during the change of state from ice to water without change of temperature is found by experiment to be 144 B. t. u. per pound and is called the latent heat of fusion. Conversely, in the reverse change the same amount of heat would be given off. So far we have added to the pound of ice 3.528 + 144 = 147.528 B. t. u. and have increased the temperature only 7 degrees. From this point GNN', where the entire mass is water with a volume approximately equal to 1, the addition of heat causes a uniform rise in temperature along OA; also a slight de- crease in volume along MN to the point of maximum density 39.1, where the volume NN' is 1, and from here a uniform increase in volume along NO until the temperature has risen from 39.1 to 212 and the volume has increased from 1 to 1.034, with an addition of 212 32 180 B. t. u. To arrive at the state line AOD required the addition of 3.528 + 144 + 180 = 327.528 B. t. u., and a total of 187 degrees change. At AOD a second change of state is encountered. 970.4 B. t. u. (latent heat of vaporization) are now added to the pound of water without changing its temperature and the mass has a uniform change of state from water at 212 to steam at 212. When the temperature line reaches B the volume line of the water is at C, indicating that all the APPLICATION OF HEAT TO LIQUIDS 23 water has become steam at atmospheric pressure and now occupies a volume DABC, 1650 times the volume of the water that produced it (compare volume ABCD with small black volume D). The pound of ice has now received 327.528 + 970.4 1297.928 B. t. u. and is in a state of steam at atmos- pheric pressure and 212 temperature. Any further addi- tion of heat to this steam without being in contact with water results in an increase of temperature along" the line BK and the steam is said to be superheated. The quantity of heat added as superheat is found by multiplying the pounds of steam (in this case 1) by the specific heat and by the change in temperature. For steam the specific heat varies with the pressure. A fair average value is .48. The heat absorbed for any degree of superheat may be added to the 1297.928 B. t. u. thus giving the total heat between the two extremes of temperature and pressure selected. Ordinarily heating calculations refer only to saturated steam, i. e., steam in contact with water and superheating need not be con- sidered. By the use of Equations 3 and 4 and the steam tables compare results by filling in the blank table the values for steam at 10, 14.7, 50 and 100 pounds absolute pressure. Equation Table 10 14.7 50 100 10 14.7 50 100 Heat of the Liquid Latent Heat Total Heat Three standard tables of properties, of saturated steam are in general use, Marks and Davis, Peabody, and Goodenough. These tables check each other closely and any one may be recommended (Table 4, Appendix, is an extract from the first table). The following summary of directions for the use of any of the steam tables gives specific equations for the solution of al- most any type of problem using any vapor table. With the nomenclature of Marks and Davis, we have: HEATING AND VENTILATION FOR SUMMATION ABOVE 32 F. If Quality is 100% If Quality isX% If Superheat is D degrees Total Heat of Formation.... Intrinsic Heat of Formation External Work of Formation H h + L h + I (Apu)v h + xL h + xl (xApu)v H + CpD h + 7 + CpD (Apu), (Apu)r + (Apu) FOR SUMMATION ABOVE SOME FEED TEMPERA- TURE = t If Quality is 100% If Quality isZ% If Superheat is D degrees Total Heat of Formation H ht or h + L ht h + xL ht h + L + CpD ht Intrinsic Heat of Formation h + I ht li + xl h t h + I + CpD (Apu)* .ht External Work of Formation (Apu)v (xApu) v (Apu)r + (Apu), In these tables the subscript v refers to the condition of non-superheats, while the subscript s refers to the condition of superheat. In the term Apu, the value of A is 1/778, p pressure in pounds per sq. foot and u is the increase in vol- ume in cubic feet undergone during the process in question. Some vapor tables, (notably Peabody's) contain columns of Apu worked out and tabulated while with the use of other tables it is necessary to calculate the values of the Apu terms. These tables emphasize those facts the neglect of which causes perhaps 90 per cent, of all steam table calculation errors, viz: x cannot affect, as a factor any steam table value except L, I, and (Ajtu),-. The vapor tables are summations above 32 F., and for heat summations above any other tempera- ture, correction must be made. The external work available during formation is in- dependent of the feed temperature. 15. Application of Heat to Gases: Pressure-volume- temperature changes in gases may be found from ideal laws which apply with close approximation, or from actual laws (modifications of the ideal laws) designed to fit actual con- ditions. The ideal laws are much more easily applied and APPLICATION OF HEAT TO GASES 25 give results that are close to average practice; consequently, they are used in most engineering- calculations. Ideal laws are known as (1) The Law of Boyle or of Mariotte, (2) The Law of Charles or of Gay Lussac. BOYLE'S LAW. When the temperature of a given weight of gas is maintained constant, the volume and the pressure vary inversely. In many pressure-volume applications to gases the tempera- ture change is either zero or so small as to be of no serious moment. This law applies in such cases. Let P, PI, P 2 , etc., absolute pressures in pounds per square foot, and V, Vi, V 2 , etc., volumes in cubic feet at the respective pressures, then PV = Pi T T i = P 2 V 2 , etc. (5) In other words, at a constant temperature the product of any pressure with its respective volume is a constant quan- tity. Thus if 100 cubic feet of air at 14.7 Ibs. absolute pres- sure be changed to 50 cubic feet without change of tempera- ture, the pressure will be (14.7 X 100) -f- 50 = 29.4 Ibs. absolute, or 14.7 Ibs. gage. CHARLES' LAW. When gases are heated, they react ac- cording to the Law of Charles; i. e., the volume of a perfect gas at constant pressure, or the pressure of a perfect gas at constant volume, is proportional to its absolute temperature. As before let P = absolute pressure in pounds per square foot, V = volume in cubic feet, and T = absolute temperature, then PV PxFi P 2 V 2 = == , etc. . (6) T TI T 2 Referring to the first part of the definition of this law, let the temperature of a cubic foot of gas (take air for illus- tration at atmospheric pressure) be 32 F., if f 32 + PV 460 = 492, P = 14.7 X 144 = 2116.8 and V = I, then - T 2116.8 X 1 . Now if the temperature of the air is changed to 492 some other temperature T lt say 100 F. at the same pressure, PV P! F! and, since PI P, the new volume is T T! 2116.8 X 1 560 560 T t = : X- = 1.14 V 492 2116.8 492 Referring to the second part of the definition of the same law, take a cubic foot of air at atmospheric pressure and 32 F. and change its temperature to 100 F. while the vol- 26 HEATING AND VENTILATION ume remains constant at one cubic foot. Now, the pressures at constant volume are proportional to the absolute tem- peratures and P X 1 PI X 1 492 560 PI 1.14 P, specific pressure Pi 1.14 j>, pounds per square inch. GENERAL EQUATION. The volume occupied by a pound of air at any given pressure and temperature (specific volume) is the reciprocal of its density at that temperature. At 32 F. and atmospheric pressure this is 1 -f- .0807 = 12.391. Sub- stituting T, = (32 + 460), P, n (14.7 X 144) and V t = 12.391, in Equation 6 and reducing PV = 53.3 T (7) This is usually written PV = 727', where R is a constant which varies for different gases. In further study of this question, it is found that 7? represents the foot pounds of external work done when the temperature of one pound of gas is raised one degree at constant pressure. For air, as found above, it is 53.3. Having the value 7? for any gas and any two of the values P, V, or T, the third may be found. Note: in Equation 7 P and V must be specific pressure and volume, respectively. To illustrate, the pressure of one pound of air having a volume of 5 cubic feet and tempera- ture of 100 F. is P = (53.3 X 560) -r- 5 = 5969.6 pounds specific pressure, or 41.5 per square inch absolute. Also, the volume of a pound of air having a pressure of 50 pounds per square inch absolute and a temperature of 60 is T -. (53.3 X 530) -r- (64.7 X 144) = 2.97 cubic feet. 10. Combustion of Fuels: Fuels used for heat produc- tion are solid, liquid and gaseous, and contain carbon (C), hydrogen (77), oxygen (O), nitrogen (A 7 ), sulphur (S), and small amounts of water and ash. In combustion the most valuable of all of these constituents are carbon and hydro- gen. Fuels with high percentages of carbon and hydrogen (heat producing agents) and low percentages of ash and water are the most desirable. Coal is the universal fuel, although oil and gas are frequently used. Carbon burns to carbon dioxide (CO 2 ) if supplied with sufficient air during combustion or to carbon monoxide (CO) if the air supply is restricted. The greatest economy is found when CO 2 is COMBUSTION OF FUELS 27 produced. Hydrogen burns, forming water, and sulphur burns to sulphur dioxide (SO 2 ). Oxygen in the fuel has the same effect as the oxygen of the air in supporting combus- tion. Nitrogen has no appreciable chemical action during combustion, but it absorbs heat and is thrown away, hence it tends to reduce the efficiency of the furnace. Water in the fuel has little chemical effect. It absorbs heat in being evaporated and superheated and passes off with the gases, causing small loss. One pound each of the above elements of the coal when completely consumed gives off heat units as follows: C to CO 2 = 14600, C to CO = 4450, CO to CO 2 = 10150, // to H 2 O 62000 (frequently used 52000 to account for loss by evaporation and superheating), and $ to 8O 2 4000. As an illustration of the chemical changes taking place in a furnace when a fuel is raised in temperature suffi- ciently high that the combustible unites with the oxygen of the air and produces combustion, burn completely one pound of coal containing C = .78, // = .04, O = .03, N = .02, 8 = .02, H 2 O = .01, and ash .10, and note the following points of interest: (A) Theoretical total heat of the fuel by equation. (B) Amount of air needed for complete combustion. (a) By analysis, (b) By equation. . (C) Probable amount of air used for combustion. (D) Temperature of the furnace when only the theoret- ical amount of air is used for complete combus- tion. (E) Temperature of the furnace when the probable amount of air is passed through the furnace. (F) Efficiency of the furnace. THEORETICAL TOTAL, HEAT OF THE FUEL (A). From the heat values given the following theoretical equation (Du Long's formula) has been compiled: O Total Heat = 14COO C + 52000 (// - ) + 4000 8 (8) X and when applied to the coal sample as stated gives .03 Total Heat = 14600 X .78 + 52000 X (.04 - ) + 8 4000 X .02 = 13353 B. t. u. Equation 8 is used when the chemical composition of the fuel is known. When this is not known, the total heat is found in the laboratory by the use of calorimeters. 28 HEATING AND VENTILATION In most furnfices combustion is not perfect. Part of the car- bon is burned to CO 2 giving- off 14600 B. t. u. per pound and part to CO giving off 4450 B. t. u. per pound. To find the heat value of the coal in such cases use a modification of Equation 8. Heat liberated = 14600 d + 4450 C a -f 52000 O (II ) + 4000 8 (9) 8 where C\ and C = weights of carbon per pound of coal burned to CO 2 and CO respectively. Suppose, for illustra- tion, that the carbon goes half and half to CO 2 and CO, then the heat liberated is 14600 X .39 + 4450 X .39 + 52000 .03 (.04 ) + 4000 X .02 9395. Compare this with the O value obtained by Equation 8. THEORETICAL AMOUNT OF AIR NEEDED FOR COMPLETE COMBUS- TION (B). (a) Since the atomic weights (relative weights of unit volumes referred to H = 1) of C = 12, H = 1, O = 16, N 14, and 8 = 32, we have 12 parts C unite with 32 parts O. (1 Ib. C + 2.66 Ibs. O 3.66 Ibs. C0 2 ) 12 parts C unite with 16 parts O. (1 Ib. C -f 1.33 Ibs. O = 2.33 Ibs. (7) 2 parts H unite with 16 parts O. (1 Ib. H + 8.00 Ibs. O = 9.00 Ibs. H 2 O) 32 parts 8 unite with 32 parts O. (1 Ib. 8 + 1.00 Ibs. O = 2.00 Ibs. S0 2 ) from which may be found the oxygen required to unite with each element for complete combustion. From the coal analysis, .78 X 2.66 = 2.075 Ibs. O for the ca.rbon .04 X 8.00 = .320 Ibs. for the hydrogen .02 X 1.00 = .020 Ibs. O for the sulphur Total 2.415 Ibs. O per Ib. of coal Less .030 Ibs. O already in the coal Net total = 2.385 Ibs. O per Ib. of coal to be taken from the air. Atmospheric air contains 23 per cent, oxygen by weight, hence it will require 2.385 -f- .23 = 10.37 pounds of air to completely burn the pound of coal if all the oxygen of the air is used. If 87 per cent, of the pound of coal is COMBUSTION OF FUELS 29 combustible, then there are needed 10.37 -H .87 = 11.91 pounds of air per pound of combustible. Where combustion is not perfect the theoretical amount of air is not used. Assume as before that the carbon divides half and half, then we have For Ci, .39 X 2.66 = 1.036 For C 2 , .39 X 1.33 = .518 For H, .04 X 8.00 = .320 For 8, .02 X 1.00 = .020 Total 1.894 Ibs. O Less .030 Ibs. O in coal Net Total 1.864 Ibs. O to be taken from the air. This makes 1.864 -f- .23 8.1 pounds of air per pound of coal burned. Compare this value with that for perfect combustion. (b) The equation usually quoted for the weight of air needed for perfect combustion is O W - 11.52 C + 34.56 (H ) + 4.32 8 (10) 8 which for the assumed coal is W = 11.52 X .78 + 34.56 .03 (.04 ) + 4.32 X .02 = 10.32 pounds. Compare with the 8 value by chemical analysis. PROBABLE AMOUNT OF AIR USED FOR COMBUSTION (C). There can be no exact value placed tfpon actual amount of air pass- ing through a furnace. The construction of the furnace, the type of grate used, the depth of the fuel bed, the quality of the fuel and the eccentricities of the fireman all influence the result. From tests that have been conducted upon vari- ous types of heating furnaces under varying conditions of service, it seems reasonable to assume that from two to three times as much air goes through the average furnace as would be needed for perfect combustion. In the most up-to- date power plants excess air is reduced to small amounts. It is not possible in furnace operation to keep the air supply down to the theoretical amount without reducing the economy of the furnace. When the fuel bed is thick and the air supply reduced, the fuel will receive too small an amount of air and carbon will be burned to CO with a loss of 10150 B. t. u. per pound. When the fuel bed is thin and the supply of air excessive, too much air will pass through the fire causing some of the carbon to pass off unburned and carry- 30 HEATING AND VENTILATION ing away heat unnecessarily by heating the excess air. (Read Technical Paper No. 137, Bureau of Mines, Washing- ton, D. C.) Of the two alternatives it is better to have too much air than not enough, and some of this air should be admitted above the fuel bed. To illustrate the economy of excess air in practice, suppose the pound of coal just con- sidered is burned in a furnace where the entering air is GO and the stack gases are 600. With the specific heat of the gases = .24 we find first, for perfect combustion with 10.37 + .9 = 11.27 pounds of stack gases, the pound of coal has available for boiler use (not counting radiation losses) 13353 [11.27 X .24 X (600 60)] = 11892.4 B. t. u. Second, if there is just enough air to burn the carbon to CO, there will be 6.8 pounds of stack gases and 5436 [6.8 X .24 X (600 r 60)] = 4555 B. t. u. available. Third, with 2.5 times as much air as is theoretically needed and all the car- bon burned to CO 2 , there will be 26.83 pounds of stack gases per pound of coal and the heat available will be 13353 - [26.83 X .24 X (600 60)] = 9875.8 B. t. u. This shows a decided advantage in favor of excess air over a much re- stricted supply. Flue gas may be analyzed by the Orsat ap- paratus and such analysis used in determining the quality of the combustion (See Art. 17). THEORETICAL TEMPERATURE OF THE FURNACE (D). When per- fect combustion occurs, the theoretical total heat is given off. If it were possible to liberate this heat in a vessel per- fectly insulated, all the liberated heat would be used in rais- ing the temperature of the gases. The theoretical rise in temperature in such an ideal furnace would be theoretical total heat (B. t. u.) tr = (11) pounds of stack gases X specific heat Applying to the coal sample above, tr 13353 -f- (11.27 X .24) = 4946 F., and if the air enters at 60, the temperature of the furnace is 4946 + 60 = 5006 F. PROBABLE TEMPERATURE OF THE FURNACE (E). Suppose 2.5 times the theoretical air is used in the furnace, then the probable temperature is 13353 t [. 60 = 2138 F. 26.83 X .24 Radiation and other losses will reduce this value somewhat. EFFICIENCY IN FURNACE COMBUSTION (F). There are five losses in fuel combustion: (a) unburned combustible material that drops through the grate with the ash, (b) unburned COMBUSTION OF FUELS 31 hydrocarbon particles that leave the chimney as smoke, (c) carbon burned to CO instead of CO 2 by incomplete combus- tion, (d) excessive air supply, (e) radiation. These losses are apportioned about as follows: (a) (Estimated) 1 to 3 per cent, of total heat in coal. (b) (Estimated) 1 to 5 per cent, of total heat in coal. (c) May vary anywhere between 10 and 50 per cent. (d) May vary anywhere between 5 and 15 per cent. (e) (Estimated) 2 to 5 per cent. It will be seen by this that a large part of the original heat in the coal is not transferred through the heating surface of the boiler to the water, but is dissipated through the five channels just mentioned. Intimately associated with the combustion losses is the idea of furnace and Idler efficiencies. The most important of these are grate efficiency, furnace efficiency and overall efficiency. Grate efficiency = weight (or heat value) of ascending combustible weight (or heat value) of combustible fired (12) If 2 per cent, of the coal drops through the grate, this is (100 2) -=- 100 = 98 per cent. Furnace efficiency = heat available for absorption by boiler (13) heat value of combustible fired With perfect combustion of the entire pound of coal and 2.5 times the required amount of air, this is 9875.8 -7- 13353 74 per cent. If there is a percentage loss through the grate, the value 9875.8 will be reduced by this amount. With im- perfect combustion, illustrated by the case where the carbon divides half and half to CO 2 and CO, this is [9395 9 X .24 (600 60)] -r- 13353 = 61 per cent. If there is a percentage loss through the grate, the value 9395 will be reduced by this amount. heat absorbed by water and steam Over-all efficiency = (14) heat value of combustible fired The heat absorbed by the water and steam is the heat value 32 HEATING AND VENTILATION of the combustible less all the losses. Suppose the losses in the sample are: through the grate, .02 X 13353 = 267.06 B. t. u.; unburned carbon (smoke), .03 X 13353 = 400.59 B. t. u. imperfect combustion, .20 X 13353 = 2670.60 B. t. u. excessive air supply, .10 X 13353 = 1335.30 B. t. u. radiation, .02 X 13353 = 267.06 B. t. u. total losses, 4940.61 B. t. u. then the over-all efficiency is (13353 4940.61) -4- 13353 = 63 per cent. When the word efficiency is mentioned in con- nection with small power and heating plants, the over-all efficiency is understood unless otherwise specified. The effi- ciency of the average boiler is 60 to 65 per cent., but efficien- cies as high as 75 per cent, may be found in continuous service in some of the better plants (For boiler operation, see Arts. 87 and 187). 17. Flue Gas Analysis. The quality of the fuel combus- tion in many plants. is determined by the Orsat, or similar apparatus, which is used in obtaining an analysis of the flue gases by volume as they leave the boiler. Values are found for CO 2 , CO and O. The CO 2 varies from 6 to 17 per cent, of the total volume of the flue gases. Between 10 and 13 per cent, is considered good practice. CO is always found in small quantities, say from to .5 per cent. When excess air is less than 25 per cent., CO is probably forming in prohibi- tive amounts. With good combustion and 100 per cent, excess air (good boiler practice), there should be but a trace of CO. Free oxygen is always found where there is an excess of air. This percentage of O (0 to 15 per cent.) may be used to determine the amount of excess air. Of the three determinations made by the use of the Orsat apparatus, the CO and O determinations are consid- ered of greatest value. When carbon and oxygen unite to form carbon dioxide gas, it is found that with the same tem- perature and pressure the carbon dioxide occupies the same volume as the oxygen entering into the combination. Assuming perfect combustion (no carbon monoxide) and just enough air to supply the oxygen, the resulting gas volumes will be 21 per cent. CO 2 and 79 per cent. N. A test with the Orsat in this case should show 21 per cent. C0 2 , per cent. CO, and per cent. O. Again, assuming perfect combustion and an excess of air (say 100 per cent.), one-half of the oxygen of the air is used for the CO 2 and the Orsat should show 10.5 per cent. FLUE GAS ANALYSIS 33 CO 2 , 10.5 per cent. O, and per cent. CO. That is to say, the sum of the CO 2 and O percentages will be 21 per cent., the same as the original oxygen volume. Again, assuming imperfect combustion and a certain amount of CO, it is found that ivith the same temperature and pressure the carbon monoxide occu- pies twice the volume of the oxygen entering into the combination and the resulting stack gases have a larger volume than the entering air by one-half of the percentage of CO present. With high percentages of CO this change in volume would need to be taken into account. In all ordinary cases, how- ever, it is satisfactory to consider the stack gases as 79 per cent. N and the remaining 21 per cent, composed of CO 2 , CO and O. 21 per cent. CO 2 shows the highest possible efficiency, i. e., no excess air and perfect combustion. This is never obtained in practice. Any value of CO., less than this indi- cates (1) excess of air, if no CO is present; (2) deficiency of air, if CO is present and no O; (3) improper mixture in the combustion chamber, if both CO and O are present. Computations to find the relation between weights of flue gas and entering air are sometimes complicated by the necessity of changing from weights to volumes and vice versa. Vol- ume readings of the Orsat are generally used directly in terins of the densities of the gases since, as above stated, equal volumes of the gases at the same temperature and pressure contain the same number of molecules. Use the equations 44 COn + 32 Oo + 28 (CO + N) W = - - X C l (15) 12 (CO., + CO) Where W weight of flue gas in pounds per pound of coal, Ci percentage of carbon in the coal, and the other symbols represent percentages of each as shown by the Orsat. 2V is found by differences i. e., 100 (CO 2 + CO + O). For infor- mation on the use of the Orsat apparatus see very excellent explanation in ''Coal," by Somermcicr. APPLICATION (1). Coal, having" a composition as stated in Art. 16, is being burned in a furnace without loss through the grate. Samples of the flue gas show 12 per cent. CO 2 and 9 per cent. O. What is the weight of flue gases per pound of coal burned? Compare this value with the the- oretical amount of air as in Art. 16 (B) and note the excess supplied. From Equation 15 44 X 12 + 32 X 9 + 28 X 79 W = - X .78 = 16.4 12 (12 + 0) 34 HEATING AND VENTILATION Excess air = 16.4 10.37 = 6.03 pounds. Where a grate loss js known to exist, C^ should be corrected by this amount. Thus for a 2 per cent, loss, d = .98 X .78 .764. APPLICATION (2). Coal as in application (1); 2 per cent, loss through the grate; 8 per cent. CO 2 ; 12.5 per cent. O; .5 per cent. CO. Find the weight of stack gases and excess air per pound of coal. 44 X 8 + 32 X 12.5 + 28 (.5 + 79) W = - X .764 = 22.3 12 (8 + .5) Excess air 22.3 10.37 11.93. -f9C{ HI v aiffl ^iirc air is essential to health. The most convincing argument that can be presented on this point is an analysis of the vital statistics of the country covering a large number of years. Persons afflicted with respiratory diseases are recommended by the medical fra- ternity to seek a high, dry, sunny climate, and lire in the open air. The rarefied atmosphere causes continuous deep breathing, which exercise in itself has a tendency toward strengthening the afflicted parts and throwing off disease, and the dry air probably serves the lung tissue as a cleanser as the blotter does the page of wet ink. These condi- tions, in connection with the sunshine which is one of our AIR REQUIRED PER PERSON 41 best germicides, form the only known remedy for combating such diseases. It is a safe conclusion that the element of pure air which enters so largely into the overcoming of the disease, once it is contracted, is one of the best preventives as well. Statements are made (occasionally in the technical press) that respired air is not harmful and that satisfactory ventilation may be had in inhabited rooms with much less fresh air than that usually allowed. The first of these two statements has never been proved. On the contrary the cir- cumstantial evidence of the impurity of respired air is fairly conclusive. The second may be true for ventilating systems where the air supply is subdivided into small amounts and carried directly to the person (See experiments by Professor Bass at University of Minnesota, Trans. A. S. H. & V. E., Vol. XIX, p. 328). Applications such as this, however, can not be regarded as touching general practice. The average adult, when engaged in ordinary indoor occupations, will exhale about 20 cubic inches of air per respiration. He will also have 16 to 24 respirations per minute, totaling 400 -f- cubic inches or, say .25 cubic foot of air per minute. Allowing" 4 per cent. C'O 2 in respired air the average person will exhale 60 X .25 X .04 = .6 cubic foot CO 2 per hour. This is constantly being diffused throughout the air of the room. If the carbon dioxide and other impur- ities could be disassociated from the rest of the air and ex- pelled from the room without taking large quantities of otherwise pure air with them, the problems of the heating and ventilating engineer would be simplified, but this cannot be done. Rapid diffusion of respired air throughout the room renders it necessary to dilute the room air with fresh air in order that the purity may be maintained at a safe value. Ideal conditions are found when interior air is as pure and refreshing as that of the open country, but the mechanical difficulties around such a ventilating system would be so great as to render it prohibitive. The standard of purity which should be aimed at, and which may be obtained with a first-class system, is .06 of one per cent. CO. 2 , i. e., 6 parts of CO 2 in 10000 parts of air. Systems maintaining constant ventilation at 8 parts in 10000 are considered satisfactory. Stated in a simple form for calculation, let Q' = cubic feet of atmospheric air needed per hour per person, A = cubic feet of C0 2 given off per hour per person, n standard of purity to be maintained (allowable parts of CO 2 in 10000 42 HEATING AND VENTILATION parts of air), and p = standard of purity in atmospheric air, say 4; then A Q' = (16) n p To maintain constant ventilation at 7 parts C0 2 in 10000 parts of air, with pure air at 4 parts in 10000, we have Q' = .6 -f- (.0007 .0004) = 2000 cubic feet of air per hour. Based upon .6 cubic foot of CO 2 exhaled per person per hour, Table III gives the amount of air needed to maintain constant ven- tilation at the various standards of purity. TABLE III. Cubic Feet of Air per Person per Hour. n A Q 6 .6 3000 7 .6 2000 8 .6 1500 9 .6 1200 10 .6 1000 It should be understood that no hard and fast rule can be given for the air requirement per person. This varies with the physical development and occupation of the indi- vidual, but it varies in a greater degree with the state of the person's health and the sanitary value of his surround- ings. In general, the average adult subjected to average in- door conditions requires 1800 cubic feet of fresh outdoor air per hour. Stated as an equation, the amount of air needed for ventilation is Q' = 1800 N, where N = the number of people to be provided for. The amounts of air in cubic feet per person per hour given in Table IV, may be considered good practice for the various classes of service. TABLE IV. Hospitals, Ordinary Surgery Epidemic Workshops, Ordinary " Unhealthy trades Schools, Offices, Prisons Theaters and Assembly Halls 2000-2500 2500-3000 5000-6000 1800-2000 3000-3500 1800 1400-1800 VENTILATION 43 One ordinary gas flame of 16 to 20 candle power, using 4 to 5 cubic feet of gas per hour, will vitiate as much air as four or five people. Where many open flame gas lamps are used, this fact should be taken into account. 22. Ventilation: Ventilation is the art of maintaining in- terior atmospheres at a comfortable temperature and humidity, and a purity approaching that of open country air. Such a standard may be regarded absolutely safe by any one. To accomplish this, large amounts of fresh air should be introduced to the building and distributed so the occupants will not be sub- jected to unpleasant drafts. Fans placed in the rooms to circulate the air make the room atmosphere more habitable on a warm day, but this process should not be mistaken for ventilation. The mere process of fanning the air does not purify it. Air may be tested for bacteria and micro-organisms by exposing specially prepared gelatine plates or tubes to the air of a room a certain length of time, say five or ten min- utes, permitting the organisms to germinate and counting the colonies. (See Report of Ventilation Division, Chicago Health Dept., Page 57, Vol. XX. Trans. A. S. H. & V. E.) Such tests are most satisfactory but require considerable care in application and are not generally used. The CO 2 test mentioned in Art. 20, while not a direct equivalent, is simpler and is generally employed. In testing the quality of room air by any method it is well to call attention to the fact that the ordinary running conditions of any room can- not absolutely be determined by a single test. Trials should frequently be made and records kept. Upon one day atmos- pheric conditions may be favorable and tests may show a small amount of impurity. On other days when the condi- tions are not as favorable impurities may be found in large quantities even though running conditions seem to be dupli- cated. Further, if the only requirement governing the ven- tilation of buildings is that a satisfactory <7O 2 test be passed, there is great danger of overrating or underrating the ventilating system of the building. A safe method in rat- ing ventilating systems is to require a minimum air supply in addi- tion to a maximum permissible percentage of CO% at the breathing line. For further study of this subject, see recommendations by the American Society of Heating and Ventilating Engi- neers, Jour. Apr. 1916, p. 91. Also Trans. A. S. H. & V. E.. Vol. XXII, p. 43. 23. Air Purification: Air contains dust, fine particles of mineral and animal matter, bacteria, and micro-organisms 44 HEATING AND VENTILATION held in mechanical suspension. The more heavily charged with these impurities ventilating air becomes, the more dan- gerous it is to the human system. Most materials held in mechanical suspension may be removed by filtering (passing- through fine cloth screens) or by irunliiin/ (passing through films or sprays of water). Filtering and washing systems are beneficial in all cases and are necessities in many. Fil- ters cost less to install and operate, but they occupy larger transverse areas and are not as effective as the washing systems. Washing air removes most of the mechanically suspended particles but it does not necessarily eliminate chemical impurities, bacteria and the like. The location of the air supply intake to a building carries with it a great re- sponsibility. Air supplied to a building should always be taken from the purest source possible, and when this supply is known to be bad it should be thoroughly washed before sending through the ventilating system. REFERENCES. Trans. A. S. H. & V. E. Studies in Air Clean- liness, Vol. XXI, p. 211. The Problem of City Dust, Vol. XXI, p. 225. Ozone is considered by some to be effective as an air purifier. It is an unstable form of oxygen probably contain- ing a greater number of atoms per molecule and is formed by passing air through a highly charged electrical field. Be- cause of its instability as a substance, it readily breaks up and becomes more active as an oxidizing agent than oxygen itself. In its decomposition a part becomes oxygen and the balance is said to enter into combination with substances in the air, thus cleansing the air from the'se substances. Two claims are made for ozone. The first is that it is a puri- fier, the second that it is a deodorizer. The first has not been proved satisfactorily, but the second is substantiated by many proofs. Ozone without doubt conceals odors, but it is not known if the substances producing the odors are ren- dered harmless to the human body. REFERENCES. Trans. A. S. H. & V, E. An Experiment with Ozone as an Adjunct to Artificial Ventilation at the Mt. Sinai Hospital, N. Y. C., Vol. XXI, p. 256. Air Ozonation, Vol. XX, p. 337. Ozone and Its Applications, Vol. XIX, p. 128. H. & V. Mag., Ozone, July, 1914, p. 16. 24. Moisture with Air: Moisture in the atmosphere affects the comfort of the occupants as well as the efficiency of the heating and ventilating system in any room. With HUMIDITY 45 moisture in the room a person may feel comfortable when the temperature is several degrees lower than the comfort- able temperature of dry air. A dry atmosphere takes up moisture from the room furnishings and from the skin sur- face of the occupants. The vaporization of moisture from the skin causes a loss of heat from the body and gives to the person a sense of cold which is relieved only when the temperature of the room is increased. An atmosphere that is fairly saturated with moisture demands little evaporation from the skin, in which case the body retains its heat and the person has a sensation of warmth which is relieved only by lowering the temperature of the air of the room. At low temperatures moisture in the atmosphere chills the surface of the skin by actual contact. This is not as noticeable when the air is dry. It follows from the above statements that the range of comfortable temperatures is less for moist 30 32 34 36 3S> 4O 42 44 46 48 5O 52 54 56 58 6O 62 64 RELATIVE HUMIDITY Fig-. 5. 68 70 7Z 74 76 78 air than for dry air. The Chicago Commission on Ventila- tion, under the direction of Dr. E. Vernon Hill, developed a series of curves from a large number of tests, showing 1 the best relation between the relative humidity and the comfort- able temperature in a room (See Trans. A. S. H. & V. E., page 607, Vol. XXIII). The curves in Fig. 5, are plotted from a summary of these tests. It will be noted that the condition represented by 65 and 55 per cent, humidity is as satisfac- tory as that of 70 and 35 per cent, humidity. HEATING AND VENTILATION In addition to its effects upon the human body, moisture in the atmosphere has the quality of storing convected heat. It is thus a better heat carrier than dry air and is a benefit to the heating and ventilating system in any building. REFERENCES. H. & V, Mag. The Primary Physiological Purpose of Ventilation, Sept. 1913, p. 35. Metal Worker. Humidity and House Sanitation Explained, Jan. 24, 1913, p. 159. Trans. A. S. H. & V. E. The Recirculating of Air in a School Room in Minneapolis, Vol. XXI, p. 109. Relative Humidity, Vol. XVIII, p. 106. 25. Humidity: Absolute humidity is the amount of moisture mixed with the air at any temperature, expressed in grains or in pounds per cubic foot. Relative humidity is the ratio of the amount of moisture actu- ally with the air divided by the amount of moisture which the same volume could hold at the same temperature when satu- rated. The temperature of any air at 100 per cent, saturation (100 per cent, relative humidity) is called the dew point. Relative humidity is obtained by using wet-and-dry bulb thermometers or by any one of a num- ber of hygrometers supplied by the trade. The wet-and-dry bulb hygrometer has a very simple application and is generally used. Having given two thermometers Fig. 6. (Fig. 6) let one register the temperature of the room air and the other, kept wet by a cloth which covers the bulb and projects into a vessel filled with water, a tem- perature below that of the room air. If the air is saturated the two thermometers will record the same temperature. If the air is not saturated the thermometer readings will differ according to the humidity. It will be readily seen that the lowering of the mercury in the wet thermometer is due to the extraction of the heat from the mercury column in vaporiz- ing the moisture from the bulb to the air. In taking readings, let the mercury find a constant level in each thermometer and note the difference in temperature between the two. In Table 12, Appendix, at this difference HUMIDITY 47 and at the room temperature read off the relative humidity. Having found the relative humidity take from Table 13, Appendix, the amount of moisture with saturated air at the temperature recorded by the dry thermometer (absolute humidity at saturation). Multiply this by the relative humidity found and the result is the absolute humidity at the given relative humidity, i. e., the actual amount of moisture with the air per cubic foot of volume. Fig. 7. APPLICATION. Room air, 70; difference in readings, 6. From Table 12, the humidity is 72 per cent. From Table 13, col. 7, .72 X .001153 = .00083 pounds (5.81 grains) per cubic foot. Instruments have been designed giving the relative humidity by graphical charts. Fig. 7, commonly known as the hygrodeik, shows such an instrument. To find the rela- tive humidity swing the index hand to the left of the chart and adjust the sliding pointer to that degree of the wet 48 HEATING AND VENTILATION bulb thermometer scale at which the mercury stands. Swing the index hand to the right until the sliding- pointer inter- sects the curved line extending down- ward to the left from the degree of the dry bulb thermometer scale indicated by the top of the mercury column in the dry bulb tube. At that intersection the index hand will point to the rela- tive humidity on the scale at the bot- tom of the chart. Should the tempera- ture indicated by the wet bulb ther- mometer be 60 and that of the dry bulb 70, the index hand will indicate a humidity of 55 per cent, when the pointer rests on the intersection of the GO wet bulb and 70 dry bulb lines. The instrument in most general use for humidity determinations is the Sling Psychrometer (See Fig. 8). This is a wet-and-dry bulb outfit pivoted to a handle in such a way that the ther- mometers may be revolved through the air thus causing a circulation of air Fig. 8. over them The wet bulb projects beyond the dry bulb and is covered with a fine mesh cloth. This cloth is dipped into distilled water and the ap- paratus revolved. Read the mercury level frequently and note the reading of each thermometer at the time the mer- cury in the wet bulb is at its lowest level. For accurate work the thermometers should meet a current of air of approximately 15 feet per second, according to government recommendation. Table 12, Appendix, represents U. S. Weather Bureau Standards and is used as a reference in this book. Experi- ments by Mr. Willis H. Carrier, presented in a paper to the American Society of Mechanical Engineers in 1911, show humidities differing somewhat from Table 12 (See "Psychro- metric Charts" following Table 14, Appendix). 26. Humidity Chart: For close approximations the humidity chart (Fig. 9) may be used in determining relative humidity, absolute humidity, dew point, temperature of wet bulb and temperature of dry bulb. On the left of the chart HUMIDITY DETERMINATION 41) HYGROMETRIC CHART GIVING 140 1O 20 30 40 50 60 70 80 90 100 RELATIVE HUMIDITY IN PER CENT Fig". 9. Note. Pig. 9 represents two charts in one. First : the dry bulb temperature curve, which drops to the left, unites with the wet bulb and relative humidity coordinates. Second : the absolute humidity curve, which rises to the left, unites with the dry bulb and relative humidity coordinates. This makes it possible to use the two charts as one, through the relative humidity scale which is common to both. 50 HEATING AND VENTILATION is a scale referring- to horizontal lines giving temperatures of the wet bulb. The scale on the right, referring to the lines curving downward from right to left, is the tempera- ture scale of the room, or dry bulb temperature. The scale along the bottom of the chart gives the relative humidity. The scale of numbers up the center of the chart refers to the lines curving downward from left to right and indicates absolute humidity. For illustration, assume a dry bulb tem- perature of 70 and a wet bulb temperature 60, and find relative humidity, absolute humidity and temperature of the dew point. Starting on the right hand scale at 70, follow down the room temperature curve until it crosses the hori- zontal line of 60 wet bulb temperature. From this intersec- tion drop to the relative humidity scale and read there 55 per cent. To obtain the absolute humidity trace up the rela- tive humidity line to its intersection with the 70 abscissae (horizontal line through 70) and obtain 4.4 grains per cubic foot. If the room air should drop in temperature, the abso- lute humidity would remain the same until the dew point is reached (neglecting air contractions). Tracing down the 4.4 grain line to 100 per cent, relative humidity gives the room temperature 52. This shows that if so cooled the air begins depositing moisture at this temperature. If the tem- perature of the room air should increase to 90, the relative humidity may be obtained by following the 4.4 grain line to its intersection with the 90 abscissae line of room tempera- ture and from this intersection dropping to the relative humidity scale at 31 per cent. Thus, having air under any set of temperature and humidity conditions, the effect that a change in any one condition would have upon the others may be obtained without calculations. APPLICATION 1. The air of a room gives a dry bulb read- ing of 80 and a wet bulb reading of 69. What is the rela- tive humidity? Solution. Find intersection of dry bulb curve and wet bulb abscissae. From such intersection drop perpendicular to relative humidity scale and read 57.5 per cent. Check by Table 12, Appendix: 80 room temperature and 11 degrees difference gives 57 per cent, relative humidity. APPLICATION 2. In the above problem determine the num- ber of pounds of water vapor in the room if its capacity is 3500 cubic feet? HUMIDITY DETERMINATION 51 Solution. At the intersection of the 80 and 58 per cent. coordinates, read absolute humidity in grains of moisture per cubic foot as 6.2. Total moisture in room = 3500 X 6.2 = 21700 grains, or 21700 -H 7000 = 3.1 pounds of water in form of vapor. Check by Table 13, Appendix. From this table, column 7, the weight of the vapor in pounds present at saturation at 80 is by interpolation, .001578 per cu. ft. At 57 per cent relative humidity each cubic foot would contain .001578 X .57 .000899 pound and 3500 cubic feet would con- tain 3.15 pounds. , APPLICATION 3. To what temperature could this room be cooled before moisture would be deposited from the air, i. e., at what temperature of the air would the dew point be reached? Solution. The dew point for this room air is the tem- perature at which 6.2 grains of moisture per cubic foot rep- resents saturation, or 100 per cent, relative humidity. There- fore follow the 6.2 grain line to intersection with the 100 per cent, vertical and read 63. Check by Table 11, Appendix. Temperature at which 6.2 grains moisture becomes the sat- uration quantity is by interpolation, 62.3. APPLICATION 4. To what temperature could this room be heated without moisture addition or loss and maintain a relative humidity of not less than 50 per cent? Solution. Following the 6.2 grain line to intersection with 50 per cent, ordinate, read from the right the room tem- perature, 85. Check by Table 11, Appendix. Since 6.2 grains at the temperature sought will be 50 per cent, of the moisture of saturation at that temperature, 12.4 grains would be saturation quantity, which from Table 11 by inter- polation corresponds to 84.2. 27. Theoretical Amount of Moisture to be Added to Air to Maintain a Certain Humidity: Warm air has a much greater capacity for holding moisture than cold air. When air of a given outside temperature is heated for interior service, the volume increases with the absolute temperature (See Art. 15). On the other hand, the relative humidity de- creases rapidly as shown by the humidity curves (Fig. 9). Air that is dry is unpleasant to the occupants, as well as being detrimental to the furnishings of the room. Therefore, some means should be provided to supply moisture to the incoming air current. In calculating the amount to be HEATING AND VENTILATION added, let Q = cubic feet of air per hour entering the room at the register temperature t, Q' = corresponding volume at room temperature t' and humidity u' , Q = corresponding volume at outside temperature to and humidity o. Also let T, 7" and To be the absolute temperatures of the entering air, room air and outside air respectively. From the equations TQ' = T'Q and TQo - T Q (17) find Q' and Qo. From Tables 11 or 13, Appendix, find the amounts of moisture M f and Mo in one cubic foot of saturated air at the temperatures t' and to, multiply these by the re- spective humidities and volumes, and the difference between the two final quantities will be the amount of moisture re- quired per hour as expressed by the equation W = Q'M'u' QoMoUo (18) APPLICATION. Let Q = 5000, t = 130, t' = 70, to = 30, u' = .50, uo - .50, M' = 7.98 and .1/ = 1.935, then (/ = 5000 X 530 -i- 590 = 4490 Qo = 5000 X 490 -i- 590 = 4154 W = 13896 grains, or 1.983 Ibs. per hr. This means that approximately 2 pounds of water would be evaporated for every 5000 cubic feet of fresh air entering the room under the above conditions (See __, also application in Art. 72). 2S. Velocity in the Convection of Air by ! the Application of Heat: Let 1\<> (Fig. 10) be the height of the chimney or stack. If the temperature of the gases within the chimney CD be the same as that of the entering air there will be no natural circulation, because the column CD will just balance a corre- sponding column All upon the outside. If the temperatures of the chimney gases CD and entering air be tr and to respectively, the chimney gases being (tc to) degrees above that of the outside air, then upon entering the chimney the air becomes less dense and ex- pands according to the ratio of the absolute C temperatures before and after heating. With Fig. 10. an outside column of Jio feet, it will require a column of the chimney gases 7? + ' ic feet 'to produce equilibrium. In other words, the equivalent column of gases MEASUREMENT OP AIR VELOCITY 53 producing circulation in the chimney has a height of he feet. Assume, in the system ABCDE, that the interior cross sec- tions at all points are uniform. The volumes of AB (imag- inary column) and CE (actual column) are to each other as their respective heights, and Vo : Vo + V c :: ho : ho + lie, or ho : 460 + to :: ho + ho : 460 + tc. From this we obtain h c (460 + to) = ho (tc to) and ho (tc to) 460 + (19) Substituting for li in the equation v = V2 yh, its correspond- ing value he, we have v = V2 yhc 460 + to It is found in practice that the theoretical velocity as given by this equation is never obtained because of the loss of draft due to the friction between the column of gases and the sides of the chimney, and from wind pressures and other causes. Some engineers estimate the actual discharge from the chimney at 50 per cent, of the theoretical. This estimate may be fairly safe for medium sized chimneys but will not be realized on the smaller ones used in residences, which will probably be 25 to 50 per cent, of the theoretical. As the transverse net area becomes smaller, the percentage of friction to the total air moved increases very rapidly and soon becomes the principal factor. Prof. Kent assumed a layer of gases two to three inches thick next to the interior surface as having no velocity and consequently ineffective. Thus a minimum of 4 inches would be added to each theoret- ical cross dimension to obtain the nominal size of a rec- tangular chimney. Some uncertainty will be experienced in the selection of the best values for the average temperatures of the chimney gases, tc, and the outside temperature, to, for calculations. tc is low for residence chimneys because of the low rate of combustion (3 to 7 Ibs. per sq. ft. of grate per hr.) and high for large apartment houses, office buildings and power plants (10 to 24 Ibs. per sq. ft. of grate *)er hr.). It is low for unprotected chimneys having large heat loss from radia- tion and high for those that are housed-in with the build- 54 HEATING AND VENTILATION ing. Assume to = 70 for all calculations. Approximate values for chimney height above the grate, ho, average tem- perature of gases in chimney, tc, and temperature of gases entering chimney, tb, may be taken as in Table V. TABLE V. Residences Apartment houses ho 30 40 50 60 f 200 225 260 300 to 300 350 400 450 To estimate the approximate volume of gases circulating through the chimney per second, multiply the pounds of coal burned per hour by 25 (pounds of gases per pound of coal, maximum) times the specific volume of the gas at the tem- perature of the entering chimney gases and divide the result by 3600. Note that the average temperature of the gases is used in obtaining draft but that the entering temperature is used in obtaining area, since all transverse areas are equal and calculated to carry the gases at the entering volume. When Equation 20 is applied to hot air stacks in heating sys- tems, allowances for friction are much less because of the smooth interior of the duct. In such cases the actual veloc- ity of the air should approach more nearly the theoretical. (For applications to chimneys see Arts. 31 and 32). 29. Measurement of Air Velocities: (See also Arts. 144- 146). In ventilating work it is often of the greatest im- portance to determine air velocities accurately. The correct selection of the sizes of air propelling fans or blowers to do a given work depends largely upon the measurement of the velocity of air de- livery. In acceptance and other tests this measurement is equally important. Velocities are most commonly meas- ured by means of a vane wheel instru- ment called the anemometer. It is essen- tially a delicately pivoted wheel having from six to fifteen vanes and similar to the common wind mill wheel (See Fig. 11). To the shaft is connected a re- cording mechanism consisting of a set Fig. 11. of dials which show the velocity of the MEASUREMENT OF AIR VELOCITY 55 air traveling past the instrument. By reading this recording mechanism against a stop watch the velocity of the air per unit of time may be obtained. Since the instrument works against the friction of moving parts its readings are sub- ject to variation and even with frequent calibrations it is not wholly to be relied upon. Various tests of anemometers in comparison with the absolute readings of a gas tank have shown errprs as high as 35 per cent, slow to 14 per cent, fast, in the discharge from pipes 8 inches to 24 inches in diameter. It is not fair to condemn a type of instrument because some instruments of the class have failed through long service or lack of care, but in general it is safe to say that the anemometer as an instrument for delicate velocity measurement should be used with great care and should be frequently calibrated. Velocities are also measured by the Pitot tube, Fig. 12. This method of measurement is not as simple as the ane- mometer but when properly applied it is more accurate. The Pitot tube is essentially a pressure measurer. In every mov- ing fluid (liquid or gas) three pressures are acting. These are commonly designated dynamic, static and velocity. Let the Fig. 12. bent tube A be partially filled with mercury, oil or water as shown and let it be inserted in the pipe with the open end square against the stream. Also, let tube B be similarly constructed but let the plane of the opening be 90 degrees to A. Tube A is acted upon inside the pipe by the atmos- phere plus the total forward pressure of the stream (dy- namic pressure) and on the outside by the atmosphere. Tube B is acted upon inside the pipe by the atmosphere plus the cross pressure (static pressure) and on the outside by the atmosphere. In each case the liquid in the bent tube Shows, unequal levels, A having greater depression than B. 56 HEATING AND VENTILATION Now if the two tubes are united as in C so that the pipe pressures act on opposite sides of the same liquid column, the atmospheric pressure is eliminated and the two internal pressures subtract, giving velocity pressure, i. e., dynamic pressure static pressure = velocity pressure. C shows the instrument as commonly applied. In this the subtraction is automatic and the difference in levels, hw, is caused by the velocity pressure only. To find the actual velocity of the air in the pipe apply the equation v = V2 gh where v = velocity in feet per second, g = acceleration of gravity in feet per second, per second and h the velocity head of the air in feet. If the tube contains water at 60, the ratio between the specific gravities of air and water be- 62.37 ing - = 816.4 (See Tables 9 and 13. Appendix), the equa- .0764 tion reduces to v = V2 X 32.16 X 816.4 X hw - 12 or o = 66.2 \/h~ (21) where hw = the difference in height in inches of the water columns with both legs connected as described and at a tem- perature of 60. By a similar method this equation may be deduced for a mercury or other liquid column, or for- other temperatures than 60. Several Pitot tubes, differing from each other slightly in features of design, are in commercial use. Because of these mechanical differences their readings do not absolutely check each other or those from the theoretical formula, hence all readings must be multiplied by a constant charac- teristic of the tube in use (See Trans. A. S. II. & V. E., Vol. XXI, p. 459). In using the Pitot tube or the anemometer, the fact should not be lost sight of that the velocity varies from a minimum at the inner surface of the pipe to a maximum at the center. The friction on the inner surface causes the moving fluid to be retarded next the pipe wall and any test for velocity must account for this variation. With a circular- pipe the change of velocity may be approximately repre- MEASUREMENT OP AIR VELOCITY 57 sented by the abscissae of a parabola with its axis on the axis of the circular pipe (See Fig-. 13). The point of average velocity is variously quoted from one-fourth to one-third the radius from the wall toward the center, the value depending probably upon the character of the inner surface of the tube. For general use three-tenths will give good average values. For conduits of other shapes the position of mean velocity is difficult to determine. The only safe way is to divide the cross section into small areas and take readings in each area to obtain the average. This Fig-. 13. variation of velocity from the center of the stream lessening toward the walls may possibly account for many of the variations shown by anemometer tests. It is evident that it is difficult to locate an anemometer so that it will give the correct average reading-. In large ducts the error will be less. Pitot tube measurements are more easily applied and are more reliable. Automatic recording meters may be obtained for keep- ing permanent records of the flow of air and steam through ducts and pipes. The record from the meter indicates di- rectly the cubic feet of free air or other fluid circulating during each hour of the day. REFERENCES. Kent, Mechanical Engineers Pockct-Book. Trans. A. S. H. & V. E. Report of the Committee on the Best Way to Take Anemometer Readings, Vol. XIX, p. 202. On Stand- ardization of Use of Pitot Tube, Vol. XX, p. 210. Measure- ment of Air Flow, Vol. XXI, p. 450. Trans. A. S. M. E. Meas- urement of Air in Fan Work, Vol. XXXIV, p. 1019. The Pitot Tube, Vol. XXV, p. 184. Jour. A. S. M. E. Pitot Tubes for Gas Measurement, Sept. 1913, p. 1321. 30. To Determine the Transverse Area of a Chimney for Any Given Heig-ht: The value of any flue as a carrier 58 HEATING AND VENTILATION of heated gases depends upon both velocity and transverse area. It is not only necessary that a chimney have suffi- cient height to produce draft but it must have an area capable of carrying- the total volume of the gases. The height may be sufficient to create a good velocity but the area may not be sufficient to carry the volume of gases required and the draft becomes ineffective because of clog- ging. On the other hand, the draft may become ineffective from reduced velocity due to too large an area. In any chimney, height and area are dependent variables. The height is first determined to give a certain draft and to agree with surrounding building conditions, after which the area is determined to carry the gases at the given chimney height and resulting gas velocity. To obtain the theoretical size of a chimney, substitute Jio and the assumed values of tc and to in Equation 20 and determine the velocity of the gases per second. Divide the estimated maximum volume of gases moved per second by the velocity to de- termine the transverse area in square feet and reduce this value to a corresponding round, square or rectangle. For the actual size add a minimum of 4 inches to each theoretical dimension. 31. Small Chimneys: Application for a ten room residence. Given: total heat loss from the building per hour 100000 B. t. u., coal 13500 B. t. u. per pound, furnace efficiency 60 per cent, temperature of chimney gases at base of chimney 300, average temperature of chimney gases 200, outside tem- perature 70 and height of chimney 30 feet above the grate. A heat loss of 100000 B. t. u. per hour will require 100000 -=- (13500 X -60) zr 12.35 pounds of coal per hour at the grate. With gases 300 temperature there will be moved 12.35 X 25 X 19.14 = 5933.4 cubic feet of gases per hour. The velocity of the chimney gases according to equation is 21.8 feet per second, which gives 144 X 5933.4 -4- (3600 X 21.8) = 10 square inches, or 3.2-in. X 3.2-in. Adding 4 inches to each dimension = 7.2-in. X 7.2-in., say 8.5-in. X 8.5-in. to fit the brick work. If this were an outside wall chimney it should be 8.5-in. X 13-in. Application for an apartment house or small school. Given: total heat loss from the building per hour 1000000 B. t. u., Jio = 60, tc 300, 1i> 450, to = 70, and the coal and air con- ditions as above, find the sizes of the chimney, 8.5-in. X 8.5- CHIMNEYS 59 in. (theoretical) and 13-in. X 13-in. (actual). For an out- side chimney, at least 13-in. X 17.5-in. In small chimney construction there is a tendency to leave the interior of the brick work very rough. This should not be, but where such methods are allowed, one dimension of the actual sizes determined as above should be increased by the width of one brick. 32. Large Chimneys: Chimneys for office buildings, power plants, etc., are generally rated in terms of boiler horse-power. To calculate the sizes of such chimneys, first find the intensity of draft (pressure of the current of gases in inches of water, determined by a draft gage). This will vary from .75 in. to 1.25 in., according to the type of boiler, method of firing, and length and size of breeching. See books on power plant operation. Having the draft, find the height of the chimney, ho, by the equation po f \ T 2 T! d .52 h p f (22) where d = draft in inches of water, p = observed atmos- pheric pressure (commonly taken 14.7), T 2 = absolute tem- perature of outside air and 7\ = absolute temperature of gases in chimney. Having ho, find the diameter of a round chimney by the equation B. H. P. = 2.4 D 2 ^ho~ (23) where B. H. P. = nominal boiler horse-power and D = diameter of chimney in feet. For square chimneys find the equivalent area of the round chimney. APPLICATION. Find the height and diameter of a chim- ney for 1000 boiler horse-power. Temperature of gases 500, outside air 70 and required draft, 1-inch of water. In Equation 22 (1 1 530 960 ho = 150 ft. Also substituting in Equation 23 1000 = 2.4 D 2 V150 D = 5.8 ft., say 6 ft. 33. Chimney Notes: The ideal chimney flue is round in section. Most building construction, however, requires rec- tangular shapes. These should be kept as nearly square as possible.. No chimney flue should be built less than 8-in. x 60 HEATINC AND VENTILATION 8-in. All chimneys should be built up of Imnl hnnil brirk* well bedded in cement mortar. All joints should be struck smooth. Interiors arc improved if lined with hard burned flue tiles. Chimneys should be built free from other house con- struction so as to permit the unequal expansion and con- traction without cracking the walls of the house or the chimney. The top of the chimney should extend above the highest point of the building. If the top is below any near- by portion of the building, eddy currents will be formed which will enter the top of the flue and seriously reduce the draft. Under such conditions a shifting cowl may be ad- visable. Chimneys under 30 feet in height are unreliable in .their action. Some engineers recommend nothing under 40 feet. The chimney should have no other openings into it than the furnace or boiler smoke pipe. Chimneys in outside walls are not as satisfactory as when built-in, due to the chilling effect of the outside air. When an outside wall chim- ney is put in it should be made double walled with air space between the walls. A warm air flue by the side of a chim- ney is an ideal location for the flue. All chimneys should rest upon solid foundations. All joints between the boiler and the chimney should be tight to preserve the draft. Good draft is very essential to the success of any type of heating system, and the purchaser should be required to guarantee a sufficient draft and capacity of his chimney before the manufacturer should be expected to guarantee a stated rat- ing of his furnace, heater or boiler. REFERENCES. Christie, Chimney Design, Gebhardt, Steam Power Plant Engineering, Marks, Mechanical Engineers Handbook, Kent, Mechanical Engineers Pocket-Book, H. & V. Mag. Baldwin on Chimneys, Oct. 1913, p. 23, Jan. 1914, p. 31. 34. Cowls and Ventilator Heads: The capacity of any vent or chimney flue may be increased by properly designed cowls surmounting the top of the opening. Much of the down draft experienced under changing wind pressures may thus be eliminated. Shifting heads or cowls take advantage of any wind velocity to increase the upward movement of the air by induction and, when fitted with bearings that per- mit adjustment from the slightest wind velocity, may be considered highly desirable. CHAPTER III. HEAT LOSSKS FROM BUILDINGS 35. Heat Dissipated from Iliiildi niis : In planning" the heating system for any building-, the first and most impor- tant part of the work is to estimate the total heat lost in B. t. u. per hour from building. Unfortunately this is the part which is open to the least satisfactory calculation be- cause of varying wind conditions and imperfections in build- ing- construction, and because of the lack of accurate con- ductivity values, especially those relating to the more recent building materials. Heat is lost from a building in three ways: first, that transferred through the walls, windows and other exposed building materials by conduction and lost by radiation and convection; second, that carried away by convection air cur-* rents that pass out through wall cracks and door and win- dow openings to the outside air; third, that lost through specially prepared ventilating ducts. The third item is not included in the usual building heat loss (See Arts. 41 and 42). In the average building the conduction loss is the principal one, although it is now found that the convection loss is of much more importance than has been generally considered. In any case neither of these losses can be determined ex- actly, but close estimations may be made. 36. Conduction and Radiation Losses: These losses are considered under various heads, such as glass, wall, floor, ceiling and door losses. Available data have been obtained by experimentation but these do not agree very closely. The reason for so rmich uncertainty in this part of the heating- work is found in the fact that there are great differences in methods of building construction. Conductivity tests on simple materials give fairly uniform results, but when these same materials are assembled in building walls the quality of the workmanship often permits more heat loss by con- vection than, would be transmitted through the materials by conduction. The values quoted for glass and the more compactly built up structures such as brick walls, agree fairly well. The greatest difficulty is found in the balloon frame building with its studded walls, where the dead air space in a well constructed wall may be a good noncon- HEATING AND VENTILATION a D c ductor, or where on the other hand the same space in a poorly constructed wall may become a circulating air space to cool the walls by the movement of the air. As an illustration of what may be expected in building losses let Fig-. 14 represent a 4-inch studded wall with a tight air space between the studding. It is built up of ma- terials each having a different conductivity and is sub- jected upon one side to the room temperature t' and upon the other to the outside temperature to. Let aa' , &&', cc', etc., be planes of equal temperature, but each plane having less inten- sity of temperature, in the order named, between t' and to. Also let the curve xyz represent the temperature drop (measured on the ordinates above an arbi- trary zero, not marked) in the heat travel between the enter- ing and leaving radiant heat rays, x and z. It will be noticed that the temperature drop is not uniform along the path of heat travel. This is because of the varying conductivities of the different materials passed through. Along every heat path there are three resistances to d t> c - 14 - the flow of heat between t' and to', the air envelope in contact with the wall, the materials composing the wall and the surfaces of each material composing the wall. The summation of these resistances represents the insulating effect against heat flow. It is desir- able that these resisting surfaces and materials be of such a character as to cut off heat flow across the wall as completely as possible. The common defect found with such wall combinations is loose construction and air circulation be- tween the studding. Since the insulating effect of any ma- terial or combination of materials is proportional to the total resistance along the heat path, free air circulating be- tween the studding, say from basement to attic, would cause an increased heat loss because the resistances through the latter half of the wall would be eliminated. If, in Fig. 14, HEAT LOSSES FROM BUILDINGS 63 the air space marked stud were not tightly closed at bottom and top, the heat crossing from cc f to dd' would be carried away by convection and the insulating- qualities of the wall would be R' as compared with R in a tight wall. Still air is a good nonconductor. Convected air is a good heat car- rier. Walls of other construction give less uncertainty in heat calculation. Theoretical equations for heat losses through building walls are based upon conductivity values (reciprocals of re- sistances per unit thickness) of the various materials and do not take into account such incidental points as interven- ing air spaces and poor construction. Since the amount of heat transmitted is equal to the temperature drop divided by the sum of the resistances, we have for any combination of materials (assuming all surfaces in contact and no air spaces), Hu = (t f to) -f (R + Rb + Re + + #1 + R 2 + R a + ), where Ra, Rb, Ra, etc., are the resistances of the materials and 7?i, R 2 , R 3 , etc., are the surface resistances per unit area. With the material thicknesses m, n, o, etc., and the conduc- tivities Ku, Kb, Kc, Ki, K 2 , K 3 respectively. V to Hu (24) m n o 111 + + + + + + , etc. Ka Kb Kc K-L K 2 K 3 Collecting the conductivities in the denominator and placing the reciprocal of this summation as the combined conductivity (rate of transmission per unit area), K, we have for any area, A, H = K A (V to) (25) Equation 24 is developed to illustrate a general prin- ciple. Its application, however, is usually unsatisfactory and the laborious process is unnecessary when calculating the heat loss for buildings, and Equation 25 is used instead. Values of K commonly used are obtained by experimentation. Table VI has been compiled from a number of the best refer- ences, jjjort u, .... TABLE VI Value of K *77O T~^ '~~' ' , i : : ' v Materials . .,, .., . , ... ,. JT_ Brick wall, %W plain ; ; .v,,., 37 Brick wall, 13" plain j.. .29 Brick wall, 17 y 2 " plain 24 Brick wall, 22" plain 21 64 HEATING AND VENTILATION Brick wall, 27" plain ................................................................. 19 Brick wall, furred and plastered, use .7 times non-furred. Stone wall, use 1.5 times brick wall. Concrete, 2" solid ........................................................................... 78 Concrete, 3" solid ........................................................................... 71 Concrete, 4" solid ........................................................................... 66 Concrete, 6" solid ........................................................................... 56 Frame wall (plaster, lath, stud, clapboard) .......... , ................ 50 Frame wall (plaster, lath, stud, sheating, clapboard) ....... 28 Frame wall (plaster, lath, stud, sheating-, paper, clap- board) ......................................................................................... 23 Windows, single glass, full sash area .................................... 1.00 Plate glass, same as single window glass. Windows, double glass, full sash area ................................... 50 Skylig-ht, single glass, full sash area .................................... 1.10 Skylight, double glass, full sash area ..................................... 60 Wooden door, 1" ............................................................................ 40 Wooden door, 2" ............................................................................. 36 Hollow tile, 2", y" plaster, both sides ..................................... 41 Hollow tile, 4", %" plaster, both sides ..................................... 33 Hollow tile, 6", y 2 " plaster, both sides ..................................... 28 Solid plaster partition, 2" ...................... ....................................... 60 Solid plaster partition, 3" ............................................................. 50 Concrete floor on brick arch ..................................................... 20 Fireproof construction as flooring ........................................... 10 Fireproof construction as ceiling ............. ................................ 14 Single wood floor on brick arch ............................................... 15 Double wood floor, plaster beneath ......................................... 15 Wooden beams planked over, as flooring ............................... 17 Wooden beams planked over, as ceiling ................................. 35 Lath and plaster ceiling, no floor above ................................. 62 Lath and plaster ceiling, floor above ....................................... 25 Steel ceiling, with floor above ................................................... 35 Single %" floor, no plaster beneath ........ . ................................ 45 Single %," floor, plaster beneath ............................................... 26 APPLICATION. With zero outside temperature the heat losses through the exposed glass and wall surfaces Of the Dining Room (Fig. 18), assuming good fran glassl .^...,aa..X...U.4. With 10 outside 2097 = 4657 B. t. u. ;.. nififq "2 M&vr HEAT LOSSES FROM BUILDINGS 65 Most of the values in Tab}e VI have been reduced to chart form (Fig-. 15) where the resulting- values are the total B. t. u. transmitted through 1 square foot of the surface per hour. Fig. 15. APPLICATION 1. Assume the outside temperature 10, still air, inside temperature 70 and south exposure. What is the heat loss from a square foot of 13-inch brick wall; 66 HEATING AND VENTILATION also, from a square foot of single glass window? Beginning at the right of the chart at 10 outside temperature, trace to the left to the wind velocity, then up the ordinate to the 13-inch wall, then to the left to the line indicating 70 in- side temperature, then down to the south exposure, then to the left showing 24 B. t. u. transmitted per square foot per hour. For the glass, trace from 10 to the wind velocity, then up to the single window, then to the left to the inside temperature, 70, then down to south exposure, then to the left showing 80 B. t. u. per square foot per hour. Checking this with the table for a 13-inch brick wall we have, .29 X 80 = 23.2 B. t. u. For glass, 1 X 80 = 80. The effect of the wind upon the heat loss is very marked. Locations subjected to high winds should have extra allowances. For example, take the 13-inch brick wall just mentioned. Assume the wind to be 30 miles an hour. By the same process as before we find for a south exposure, 33 B. t. u. loss as compared with 24 at zero wind velocity. APPLICATION 2. Assume the outside temperature 10, wind velocity 12 miles per hour, inside temperature 7-0 and north exposure. What is the heat loss from a square foot of 13-inch brick wall; also, from a square foot of single glass window? Trace as before and find 31 B. t. u. for the wall and 105 B. t. u. for the glass. This is an increase of approximately 30 per cent, over Application 1, due to ex- posure and wind velocity. APPLICATION 3. Assume the attic temperature 20, zero wind velocity, south exposure, room temperature 70, lath and plaster ceiling with no floor above. What is the heat loss through a square foot of ceiling per hour? Trace from 20 outside temperature and find 32 B. t. u. Checking this with the table, .62 X 50 = 31 B. t. u. APPLICATION 4. Work out Application 3 for a steel ceiling with floor above and check with the table value. APPLICATION 5. Assume a 4-inch concrete floor laid on the ground, with a ground temperature of 40 and an air temperature at the floor line of 65. What is the heat loss through a square foot of the floor per hour? Trace from 40 outside temperature to zero wind velocity, down to 4-inch solid concrete, to the left to 65 temperature, down HEAT LOSSES FROM BUILDINGS 67 to south exposure and to the left to 17 B. t. u. Check by Table VI. APPLICATION 6. Assume a 6-inch concrete floor on ground with a ground temperature of 50 and an air temperature at the floor line of 65. What is the loss through a square foot of the floor per hour? Trace from 50 outside temperature to zero wind velocity (extended), down to 6-inch solid concrete (extended), to the left to 65 temperature, down to south exposure and to the left to 9 B. t. u. Check by Table VI. 37. Loss of Heat by Air Leakage: Buildings are sub- ject to air leakage through walls, floors, ceilings and win- dow and door clearances. No effort is made to estimate the leakage through walls. In the best type of windows, metal weather strips or other insulations are used. Most of the estimates of building heat losses, however, have to do with ordinary window construction, the quality of the workman- ship of which is frequently very poor. Experiments made by H. W. Whitten, R. C. March, S. F. Voohees and H. C. Meyer (Trans. A. S. H. & V. E., Vols. 15 and 22; also, Jour. A. S. H. & V. E., Jan. 1916) to determine the amount of leak- age around windows and doors, were very successful in the specific cases. The application of the conclusions to general rules, however, is open to much guess work, since a well fitted window has approximately & -inch clearance, while a loosely fitted window may have as much as 3 3 2 -inch. In the tests it was shown also that in any given window clearance the leakage varied greatly as the outside air velocity varied. For illustration, with a clearance of ^-inch the leakage in- creased 25 per cent, per mile increase of wind velocity; or for a four mile increase in wind velocity the leakage loss In- creased 100 per cent. With such variations as this the heat loss allowance for the average window leakage is a question. Regardless of the uncertainty in "this part of the work, it is interesting to make the best approximation possible and use this in estimating the heat loss from the building. Some of the approximate values determined by the tests were: (1) Average wind velocity in localities where heating is important, miles per hr 13 (2) Averag'e sash clearance, in tV 68 H MATING AND VKNTI LATlnX (3) Air pressure equal to a 15-mile wind against a window having- i^-in. clearance will force 146 to 185 cu. ft. of air through each lineal ft. of window clearance per hr. R. P. Bol- ton recommends 90 cu. ft. Harding and Willard use 60 cu. ft. (4) Metal weather strips, etc., reduce the leakage as low as 1-5 to 1-9 of that found in the average wood frame window. (5) The lineal perimeter of the average window is numerically approximately equal to the window area in sq. ft., G. From these an estimate may be made for cubic leakage losses through the average window per hour. APPLICATION 1. What is the window leakage loss from the Living Room, Fig. 18? With a window perimeter = G, a 15 mile wind and a iV, -in. clearance we have (assuming 1 100 cu. ft. per hr. per lineal ft. of perimeter), 42 X 100 = 4200 cu. ft. of air per hr. Since the room is 13' x 15' x 10' = 1950 cu. ft. this leakage would amount to 4200 -=- 1950 = 2.15 room volumes per hr. APPLICATION 2. What is the leakage loss from (a) Dining- room? 3200 cu. ft. hr. = 1.52 room volumes (b) Study? = 4800 cu. ft. hr. = 2.53 room volumes (c) Kitchen? G only 3200 cu. ft. hr. rz 2.32 room volumes (d) Kitchen? G + door =: 5000 cu. ft. hr. = 3.62 room volumes Professor Carpenter in his heat loss equation makes al- lowance for leakage losses by using the factors n C for leakage air, in the term .02 n C, where n =. number of room volumes and C = volume of the room in cubic feet. The use of the term .02 n C is very common practice among heat- ing engineers. The constant .02 is determined as follows: The specific heat of air at 32 is .238; then the number of pounds of air heated from 32 to 33 by 1 B. t. u. is 1 ~ .238 = 4.2. If the weight of a cubic foot of air at 32 is .0807 pounds, we have 4.2 -r- .0807 = 52 cubic feet of air heated by 1 B. t. u. Since most of the heating is done at an average temperature of 70 the volume of air heated from 69 to 70 by 1 B. t. u. is 52 X 530 4- 492 = 56 cubic feet (See absolute temperature, Art. 4). It is evident that some approximation must here be made. No exact value can be taken because HEAT LOSSES FROM BUILDINGS 69 of the great range of temperature change of the air, but 55 is probably the best average. The difficulty of handling the 1 equation with the constant has led to the simple form .02. 55 (See last column Table 13, Appendix). 38. Exposure and Other Allowances: Air at high veloc- ity passing over the surface of any radiating material is more effective in removing heat than air at low velocity. The north, northwest and northeast in most sections of the country are subject to the highest winds and have the least benefit from the sun, and are therefore counted the cold por- tions of the building. In estimating heat loss a good way is to figure each room as if it were a south room (as- sumed to need no additions for exposure) and add a certain percentage of this loss for exposure to fit the real location of the room. The exact amount to add in each case is largely a matter of the judgment of the designer, who of course is supposed to know the direction of the heavy winds and the protection that is afforded by surrounding buildings. Values covering American practice vary between the limits given in Table VII. TABLE VII. Exposure. North, northeast and northwest rooms heav- ily exposed 10-25 per cent. East or west rooms moderately exposed 5-15 per cent. Rooms heated only periodically- 20-40 per cent. Heat interrupted daily but rooms kept closed.. 10 per cent. Heat interrupted daily but rooms kept open.... 25 per cent. Heat off for long periods 50 per cent. Rooms 12 to I4y 2 feet from floor to ceiling 3 per cent. Rooms 14^ to 18 feet from floor to ceiling 6 per cent. Rooms 18 feet and above from floor to ceiling 10 per cent. 39. Calculation of the Heat Losses Rule: Estimate for all rooms to be heated, the number of square feet respec- tively of exposed glass surface (full sash area), exposed wall surface (gross wall minus glass), exposed doors, floors above unheated or partially heated spaces, ceilings immediately be- low attic spaces, and partition walls between heated and un- heated spaces. With these values and by the use of Table VI, multiply each surface area by its respective value of K and by the temperature difference between the two air envelopes on the 70 HEATING AND VENTILATION sides. To the sum of these products add the amount .02 times the cubic feet of air change per hour times the temperature difference between the inside and outside air, and this will represent the heat loss for a southern exposure. For other exposures add amount allowed for losses due to location from Table VII. APPLICATION 1. Referring to Fig-. 18, the Living Room will have a heat loss on a zero day -as follows: glass, 1x42x70 = 2940 B. t. u.; wall, .23x263x70 = 4234.30 B. t. u.; floor (assuming 40 in this part of basement), 45 x 195 x 30 = 2632.50 B. t. u.; and air change (See Table VIII), .02x2x1950x70 = 5460 B. t. u. Total 15267 B. t. u. Since this is a south room there is no allowance for exposure. The above rule may be stated in equation form. Let H = B. t. u. heat loss from room per hour. With areas in square feet, let O = exposed glass, W = exposed wall minus glass, D exposed doors, F = floor or ceiling separating warm room from unheated space, etc. Also let t x {f to) difference between room temperature and outside temperature; t y = (t' t") = difference between room tem- perature and temperature of the unheated space; K, K' and K" = coefficients of heat transmission; Q nC in Arts. 37 and 40 = cubic feet of air change per hour, and a per- centage allowed for exposure. Then H = (KGtx + K'Wt* + K" Ft + Etc. + .02 Qt*) (1 + a) (26) APPLICATION 2. With same data as in previous application H = (1x42x70 + .23x263x70 + .45x195x30 + .02x2x1950x70) (1 + 0) = 15267 B. t. u. Good judgment is necessary in selecting the proper out- side temperature, to, for any locality (See Art. 63). Room temperatures for heated rooms, t', may be taken from Table IX, and temperatures for unheated rooms and spaces from Table X. Certain credits tending to reduce H are frequently made to the heat loss calculation by allowing for the heat dissi- pated from lights, persons, etc., within the room (See Art. 44). 40. Short Rules for Estimating Heat Loss: The method of estimating heat losses outlined in Art. 39 can be recom- mended for any heat loss calculations. Engineers of experi- ence, however, occasionally develop modified forms for their own use, based upon the method shown in Art. 39 and suited to average building conditions. These short cut methods HEAT LOSSES PROM BUILDINGS 71 should be used with caution by persons not thoroughly acquainted with their development. CARPENTERS' RULE. According- to Prof. R. C. Carpenter the quality of building construction and the corresponding heat losses from these buildings are so varied and uncertain that elaborate methods of figuring heat losses are unneces- sary. He recommends K = .25 for any ordinary wall sur- face and G 1 for any glass surface. Ceiling and floor sur- faces, where it is thought necessary to consider them, may be reduced to equivalent wall surfaces. The rule therefore becomes a simple modification of Equation 26, where tx = t' to. H = (O + .25 W + .02 nC) (f to) + exposure (27) TABLE VIII Values of n Residence heating: halls and bath rooms, 3; living rooms and rooms on the first floor, 2; sleeping rooms and rooms on second floor, 1. Offices and stores: first floor, 2 to 3; second floor, iy 2 to 2. Churches and public assembly rooms, % to 2. Large rooms with small ex- posure, ~y 2 to i. The author would suggest that frame construction, large window areas and relatively small volumes tend toward the larger val- ues of n; conversely, brick construction, small window areas and relatively large volumes tend toward the smaller values of n. With Equation 27, Table VIII should be used and the following wall equivalents may be employed with good effect: Doors not protected by storm doors or vestibule, with or without small amount of glass 200 per cent, of equal wall area. Floors over unheated closed spaces = same as wall. Floors over partially heated closed spaces = 50 per cent, of equal wall area. Ceilings below unheated closed spaces, no floors above 200 per cent, of equal wall area. Ceilings below unheated closed spaces, floors above 50 per cent, of equal wall area. 72 HEATING AND VENTILATION APPLICATION 3. With the same room and data as in Ap- plication 1. H [42 + .25 X (263 + .5x195) + .02x2x1950] 70 = 14707 B. t. u. HARDING AND WILLARD'S RULE. This is a modification of Carpenter's Rule with the term .02 nC replaced by a leakage factor in terms of the window and door perimeter, P. Use window and door perimeter on that outside wall having the greatest amount of window and door surface. H = ((! + .25 W + CP) (f to) + exposure (28) Where the value of C is taken for Good construction a 5 -in. sash clearance.... 1.2 Poor construction i'g-i n - sash clearance 2.4 Weather strippe'd sash 0.15 APPLICATION 4. With the same room and data as in Ap- plication 3, assuming both windows to 'be affected simul- taneously by the air pressure H, Good Const. = [42 + -25 (263 + .5 x 195) + 1.2 x 42] 70 = 12747 B. t. u. //, Poor Const. = [42 + .25 (263 + .5x195) + 2.4x42] 70 = 16303 B. t. u. One of the difficulties in the application of Equation 28 is to determine the character of the sash clearance. In all probability the average value C will approach 2.4 rather than 1.2. 41. Loss of Heat by Ventilation: Heating and Ven- tilating systems should have special provisions made for supplying fresh outdoor air for the inhabitants of the rooms and exhausting a corresponding amount of foul air. The exhausted air is usually warm air and as it leaves the rooms carries a certain amount of heat with it. This is a direct loss and should be taken into account. Since the loss by leakage is the same for any building regardless of the heating system employed, it is accounted for in the ordinary heat loss equation, but losses through ventilating systems must be considered in excess of this amount. Let Qr = cubic feet of fresh air supplied through the ventilating system per hour, /' to = drop in tempera- ture from the inside to the outside air; then the heat lost by exhausting the air is 0,. (f to) (29) 55 HEAT LOSSES FROM BUILDINGS 73 42. Combined Heat Loss, //' = (H + H v ) : In buildings where ventilation is provided, the total heat loss is that lost by conduction and radiation, H, + that lost by ventilation, Hv (See also Art. 50). Qv (f to) H' = H + - (30) 55 Rule. To find the total heat Jost from any building, add to the heat loss calculated by equation, the amount found by multiplying the number of cubic feet of ventilating air exhausted from, the building per hour by one-fifty-fifth of the difference between the inside and outside temperatures. 43. Temperatures to be Considered: In designing heat- ing systems the following temperatures may be used: TABLE IX Values of '. Living rooms, school rooms, offices, auditoriums, lecture halls and general laboratories 70 Play rooms, gymnasiums, manual training rooms, locker rooms and toilet rooms 65 Bath rooms 80 Hospitals, sick rooms and treatment rooms 75 Greenhouses 70-80 Shops and manufacturing plants, hard labor 60 Shops and manufacturing plants, light labor 65 Paint and finishing rooms 80 Outside temperatures, to, should be estimated from the lowest temperature recorded by the weather bureau for that locality, during the preceding ten years. This will range from 10 in the southern to 30 for the northern sections of the country. The most extreme low temperatures are of such short duration that one is not justified in designing for these. Usually ten degrees above the lowest recorded tem- perature is used (See Art. 63). The temperatures of rooms not specifically heated may be taken: TABLE X Values of to when applied to a room Cellars and rooms kept closed 32 Rooms often in communication with the outside air, such as passages, entrance halls, vestibules, etc 23 74 HEATING AND VENTILATION Attic rooms immediately beneath metal or slate roof 14 Attic rooms immediately beneath tile, cement, or tar and gravel roof 23 44. Heat Given Off from Lights and from Persons With- in the Room: As a credit to the heating system, some heat- ing engineers take account of the heat radiated from lights and persons within the rooms. The following values are collected from various authorities and may be considered fair averages: TABLE XI. Gas, ordinary split burner, B. t. u. per candle power hr. 300 Gas, Argand " " 200 Gas, Auer " 31 Petroleum " 160 Alcohol, incandescent " 40 Electric, incandes'nt carbon filament " " 14 Electric, metal filament ' 4 Electric, arc 5 According to Pettenkofer, the mean amount of heat given off per person per hour is 400 heat units for adults and 200 for children. 45. Performance to Guarantee Heating; Capacity: Some contracts guarantee that the heating system (steam or hot water radiation) will maintain the interior temperature of the building at 70 when the outside temperature is zero or some value below. It is frequently necessary to make tests to prove the fulfillment of such guarantees when the out- side temperature is above that stated in the guarantee. It is evident that the inside temperature of the room while under test will then be in excess of 70. To maintain the temperature that will give an equivalent heating value to the guarantee, is the object of the test. Tests of this char- acter are never as satisfactory as when conducted under guaranteed conditions, but may be estimated with a fair de- gree of accuracy. A method proposed ~by William Kent in the Engineering Record, Aug. 11, 1894 (See also M. E. Pocket Book), assumes that K is constant for any given material under temperature differences ordinarily found in practice; also, that the heat lost from the house equals the heat given PERFORMANCE OF HEATING GUARANTEE 75 up by the radiator. It is found from experimental data that K is not constant for varying- temperature differences but that it may be so considered without serious error. Let R = sq. ft. of radiator surface; Wb = sq. ft. of sur- face of exposed walls, windows, etc.; ts = temperature inside the radiator; t' = room temperature while under test; t = guaranteed room temperature; t'o = outside temperature at time of test; to = outside temperature specified on guaran- tee; Kr rate of transmission through radiator; Kb aver- age rate of transmission through building walls. From the conditions of guarantee Kr R (ts t) = Kb Wb (t to); c = (Kb Wb -H Kr R); t = (ts + cto) -T- (1 + c) and c = (ts *) -r- (t to). Then from the conditions of the test t' = (t s + ct'o) -T- (1 + c) (31) which gives the temperature of the room under test corre- sponding to the given values of ts and to. APPLICATION 1. Suppose the heating system in any de- sign is guaranteed to heat the interior of the house to 70 at 10 outside temperature, when the steam pressure is atmospheric, and that the test of acceptance is to be run when the outside temperature is 60. What will be the maintained inside temperature, t', to satisfy this guarantee? From the conditions of the guarantee find c (212 70) -r- [70 ( 10)] 1.775. Then from the conditions of the test t' = (212 + 1.775 X 60) 4- (1 + 1.775) = 115. In this same application if the heating system is guaranteed to heat to 70 when the outside temperature is we would have t' = (212 + 2.029 X 60) -^ (1 + 2.029) = 110. A second method, very similar to the preceding and found in Mechanical Equipment of Buildings, Vol. 1, Harding and Willard also makes the assumption that K is constant for varying temperatures. From the two equations, (G + .25TF + .02 nO) (t to) = Kr R (ts t) and (G + .25 W + .02 nC) (t f t' ) KrR (ts t'), we have by division (f t'o) -f- (t to) = (t s t') -=- (ts t) and ts (t'o + t to) t'o X t t' = (32) ts to APPLICATION 2. With the same conditions of guarantee and test as given in Application 1. t' = 115 for to = 10 and 110 for to = 0. A third method, by W. W. Macon, is shown in Table 48, Appendix. CHAPTER IV. FURNACE HEATING AND VENTILATING. PRINCIPLES OF DESIGN. 46. Furnace System Compared with Other Systems: The plan of heating residences and other small buildings by furnaces in which the air serves as a heat carrier, is com- mon in this country. Some of the points in favor of the fui - nace system are: low cost of installation, heating combined with ventilation, and adaptability to light service and sud- den changes of outdoor temperature. Compared with that of other heating systems, a first-class furnace system can be installed for one-third to one-half the cost. In addition to this, the fact that ventilation is so easily obtained and that the consumption of fuel may be so nearly proportioned to the demands of the weather, give this method of heating many advocates. The objections to the system are: the diffi- culty of heating the windward side of the house, circulated dust, and the contamination of the air supply by the fuel gases leaking through the joints in the furnace. In a good system well installed, the only objection to be seriously con- sidered is the difficulty of heating that part of the house subjected to the pressure of the heavy wind. The natural draft from a warm air furnace is not very strong at best and any differential pressure in the various rooms will tend to force the air toward those rooms offering the least resist- ance. In a properly designed furnace plant, however, the layout may be so made as to reduce this possible differential to a minimum. The cost of operation can be largely controlled by the owner, consistent with his ideas of the quality of the ventilation needed. Arrangements may be made to carry the room air back to the furnace to be reheated, in which case (fresh air cut off entirely) the cost of heating is about the same as that of any system of direct radiation having no special provision for ventilation. Beyond this, any amount of fresh air desired may be taken from the outside and mixed with the room air for the purpose of ventilation. This FURNACE HEATING 77 requires the same amount of room air to be exhausted from the house at the room temperature and causes an increased cost of operation, as discussed in Art. 50. 47. Essentials of the Furnace System: Fundamentally this installation must contain a furnace upon a proper set- ting-, a carefully desig-necl and constructed system of fresh air supply and return ducts, and the warm air distributing- leaders, stacks and registers. Fig. 16 shows a common Fig. 16. arrangement of these essentials. Dampers in the various air lines in the basement provide means whereby fresh air may be taken from the outside or recirculated air from the rooms as desired. Return registers and ducts are placed in the coldest sections of the building (in some cases each room) and should lead by the shortest lines to the furnace. 48. Points to be Calculated in a Furnace Design: In addition to the calculated heat loss, H, which may be as- sumed the same for all methods of heating, other points in 78 HKATJX'; ,\XD VKXTILATIOX furnace plant design should be taken up in the following- order: find for each room the cubic feet of air needed as a heat carrier and determine if this amount of air is sufficient for ventilation; then obtain from this the areas of the net heat registers, gross heat registers, heat stacks, net vent registers, gross vent registers, vent stacks, leader pipes, fresh air duct and total grate area. From the total grate area select the furnace. 49. Air Circulation in Furnace Heating: The use of air in furnace heating may be considered from two stand- points, each very distinct in itself. First, air as a heat carrier; second, air as a health preserver. The first may or may not be fresh air. All that is necessary is to provide enough air to carry the required amount of heat from the furnace to the rooms, i. e., that amount of heat that will replace the heat lost by radiation plus the small amount that is carried away by leakage. With given temperatures of air at the register and in the room, the volume of air (volume at the register) may be easily calculated. The second requires that enough air be sent to the rooms to provide ventilation for the occupants. Each of these two amounts should be de- termined and the greater used in estimating the sizes of the registers and ducts. As previously stated, the cubic feet of air per hour for ventilation may be taken 1800 N, where N is the number of persons to be provided for (See Art. 21). 50. Air Circulated per Hour and Total Heat Loss: A safe temperature t, of the circulating air as it leaves the heat register, is 130. This may at times reach 150 or above, but it is not well to use the higher values in the de- sign calculations. If the room air temperature is t' = 70, the incoming air to the room will drop in temperature through 60 degrees, and since one cubic foot of air can be heated through 55 degrees by one B. t. u. it will give off 60 ^ 55 = 1.09 (say 1.1) B. t. u. Let Q = cubic feet of air per hour as a heat carrier; H = total heat loss in B. t. u. per hour by equation; t = temperature of the air at the register; and t' = temperature of the room air; then 55 H Q = (33) t t' Rule. To find, the cubic feet of air necessary to carry the heat to the rooms, multiply the heat loss calculated In/ equation by fifty- FURNACE HEATING 79 five and divide by the difference betivccn the register and the room temperatures. For ordinary furnace work this becomes H =TT Now if this air is not specially exhausted from the build- ing but is taken back to the furnace and recirculated, the only loss of heat will be H. Since air thus used would soon become unfit for the occupants to breathe, it is well to ex- haust through ventilating- flues a part or all of the air sent from the furnace. This makes an additional loss of heat corresponding to the drop in temperature from 70 to that of the outside air (See Arts. 41 and 42). If the temperature of the outside air is assumed 0, 10 and 15 respec- tively, the resulting heat loss will be H'o = H+1.27 Q f ;H'- 10 = H+ 1.45 Q?; H'- LS = H + 1.54 60 X (4, 5.5, or 7) X 3600 .0052 H 3rd floor Rule. See rule under net heat registers with changed value for velocity. The theoretical air velocity in the stack is based upon the equation v = V2#/*, where 7t = (effective height of stack) X (t ') -f- (460 + t'); v is in feet per second; t is the temperature of the stack air; and t' is the temperature of the room air. The calculated velocities from this equa- tion are much higher than those that obtain in practice be- cause of the retarding influence of the shape of the cross section, the friction of the sides, and the abrupt turns in the stack. Assuming the net register to be figured at 3.5 feet per second, the quotations by Carpenter and Bird give heat stack areas for the first floor, 88 and 75 per cent.; second floor, 70 and 53 per cent.; and third floor, 58 and 42 per cent, of the net register. Good sized stacks are always advisable (See Art. 71, but because of the limited space between the stud- ding it becomes necessary at times to put in a stack that is too small or to increase the thickness of the wall, a thing which the architect is occasionally unwilling to do. From FURNACE HEATING 83 the above figures, checked by existing plants that are work- ing satisfactorily, the following approximate figures will give good results. .008 H = .SN. H. R., first floor //. 8. .006 H = .6 N. H. R., second floor (42) .005 H = .5 N. H. R., third floor 57. Vent and Return Stacks: Estimated in the same manner as the N. V. R., these may be made V. S. ) > = .1 H. S. R. S. j (43) As a matter of practice it will be satisfactory to make these stacks in average residence rooms, one or more tin stacks, full opening between studs; the total cross sectional area approximating the equation. 58. Leader Pipes: Since all the air that passes through the stacks must pass through the leader pipes, it might be assumed that the cross sectional areas of the two would be equal. There are two reasons why this should not be. Be- cause of their vertical position, stacks offer less frictional resistance, area for area, than leader pipes with their small pitch and abrupt turns. Also there is some drop in tem- perature as the air passes through the leader pipes, conse- quently the volume entering from the furnace is greater than that going up the stack. Considering these points it would be well to make the area of the leaders (.008 to .009) H = (.8 to .9) N. H. R., first floor L.P. = (.006 to .007) H = (.6 to .7) N. H. R., second floor (44) (.005 to .006) H = (.5 to .6) N. H. R., third floor the exact figures to depend upon the length and inclination of the leader (See Art. 69). 59. Fresh Air Duct: The area of the fresh air duct is determined largely by experience as in the case of the vent and return lines. It is generally taken F. A. D. = .8 times the total area of the leaders (45) Assume the average velocity of the air in the leaders to be 6 feet per second and the area of the fresh air duct to be as stated, then if the air in each were of the same temperature, the velocity in the fresh air duct would be 6 -^ .8 = 7.5 feet per second; but since the temperatures are different, the velocities will be in proportion to the absolute temperatures. In this case 0, .78 X 7.5 = 5.8; at 25, .82 X 7.5 = 6.2; and at 50, .88 X 7.5 = 6.6 feet per second. It is seen by this that although the area of the fresh air duct is contracted to 84 HEATING AND VENTILATION 80 per cent, of that of the leaders, the velocity is below that of the leaders. It is always well to have a fresh air duct that is simple in cross sectional area and free from obstruc- tions and sharp turns. ttO. Grate Area* The grate area of a furnace is esti- mated from the total heat loss, assuming the quality of the coal, the efficiency of the furnace, and the pounds of coal burned per hour per square foot of grate. The heat value of the coal will be between 11000 and 14000 B. t. u. per pound as shown in Table 15, Appendix. The efficiency of the average furnace is approximately 60 per cent., and the coal burned per square foot of grate per hour ranges from 3 to 7 pounds (See Art. 61). Furnaces are charged from two to four times each twenty-four hours. This requires a good sized fire pot and a possibility of banking the fires. To allow 5 pounds per square foot of grate per hour is as good an average as can be made for most coals in furnace work. Let H' = total heat loss from building including ventilation loss, E = efficiency of furnace, f = value of coal in B. t. u. per pound, and p = pounds of coal burned per square foot of grate per hour. The equation for the square inches of grate area is H' X 144 G. A. = - (46) E X f X P Rule. To find the square inches of grate area for any furnace, multiply the total heat loss from the building per hour l)y one hun- dred and forty-four and divide l)y the quantity found by multiplying the total pounds of coal burned per hour by the heat value of the coal and the efficiency of the furnace. APPLICATION. In the typical residence (Art. 62), IT on a zero day is 110574 B. t. u. per hour. This will require 101000 cubic feet of air per hour as a heat carrier. Assuming as a maximum that ten people will be in the house and that" they will need 18000 cubic feet of fresh air per hour for ventila- tion, this air will carry away approximately 22900 B. t. u. per hour, making a total heat loss from the building of 133474 B. t. u. per hour. If the furnace is 60 per cent, effi- cient and burns 5 pounds of 14000 B. t. u. coal per hour per square foot of grate, we have 133474 X 144 O. A. : 458 square inches = 24 inches .60 X 14000 X 5 diameter. With coal at 13000 B. t. u. per pound, the grate FURNACE HEATING 85 would be 493 square inches or 25 inches diameter; at 12000, 534 square inches or 26 inches diameter; at 11000, 582 square inches or 27 inches diameter. In any specific case it would be wise to estimate the grate size from the heat value of the poorest grade of coal likely to be used. In this case the estimated diameter of the grate varied three inches between coal samples nominally rated at 14000 and 11000. This variation is too great to be overlooked in the selection of furnaces. With the assump- tion made above, the equation becomes G. A. rz .0035 H' for the better grades of coal, and G. A. .0044 //' for the poorer grades. For the average coals a fairly safe value is G. A. square inches = .004 //' (47) 61. Heating Surface: The right amount of heating- sur- face to require in any furnace is rather an indefinite quan- tity. Manufacturers differ upon this point. Some standards may soon be expected but at present only rough approx- imations can be stated. One of the chief difficulties is in determining what is, or what is not, heating surface. Some quotations no doubt include surfaces that are very ineffi- cient. In estimating-, only prime heating- surface should be considered, i. e., plates having direct contact with the heated flue gases on one side and the warm air current on the other. If these plates transmit K, B. t. u. per square foot per degree difference of temperature, tz, per hour; and if one square foot of grate gives to the building E x f X P B. t. u. per hour, there will be the following ratio between the heating surface and grate surface: H. 8. Efp (48) G. K. K t, APPLICATION. With K t, 2500 (Trans. A. S. H. & V. E., Vol. XII, p. 133; also, Jour. A. S. H. & V. E., Jan. 1916) and the same notations as in Art. 60. H. S. .6 X 14000 X 5 = 17 O.8. 2500 In practice this ratio varies anywhere betwen 12 and 30. From investigations by the Federal Furnace League (now The National Warm Air Heating- and Ventilating- Association), furnaces showed an average o.f \Vz square feet of direct heating surface and 1 square foot of indirect heating- sur- face, making a total of 2y 2 square feet of average heating- surface per pound of coal burned in the furnaces per hour. 86 HEATING AND VENTILATION In the tests of these furnaces combustion rates as high as eight pounds of coal per square foot of grate were obtained. At this rate of burning the ratio of the heating surface to the grate surface is 20 to 1. It is the opinion of the author that although good service is obtained in tests by combus- tion rates as high as eight pounds, furnaces should be selected at a lower value, say five pounds. 62. Application of the Above Equations to a Ten Room Residence: In every design, complete calculations should be made and the results tabulated for easy reference and comparison. Such a tabulation is shown in Table XII, which gives all the calculated quantities (in some cases modified to suit standard sizes) necessary in the installation of the furnace system illustrated in Figs. 17, 18 and 19. The value of condensing the work in this way facilitates checking and the detection of errors. For satisfactory use plans should be drawn to scale and accompanied by sectional elevations. The scale should be large enough to be convenient in pro- ducing and so the drawings may be easily read. Locate the building with reference to the compass points and state ceil- ing heights and the principal dimensions of each room. The beginner will experience some difficulty in the calculations in making proper allowances where absolute values are not obtainable, such as exposures, ceilings, floors, closets and smaller rooms where heat is not provided for. The personal element enters into this part of the work very much and a thorough practical experience is of great value. In estimating O the simplest and most convenient method is to take it the full area of the sash. That is to say, take the full window opening as glass. Values of A' for glass have been quoted from .9 to 1.25 by various author- ities. It is the opinion of the author that where the full win- dow opening is used as glass it will be best to make K 1. In Tables VI and XII this .value is used. Referring to the Living Room, adding four inches to the width and five inches to the height of each window gives 73 X 52 and 73 X 32 inches respectively 42 square feet total. Floor registers are shown on the first floor plans but these may be shifted to wall registers if preferred. Tabula- tions in Table XII show vent registers and ducts in each room. These values may be used for return registers and ducts also. Return lines should be run from each second floor room excepting Bath; also from Study, Dining Room FURNACE HEATING 87 and Reception Hall on the first floor. Increase the size of the return register in the Hall from 12-in. x 18-in. as calcu- lated to 16-in. x 20-in. and omit the return in the Living Room. Vent registers should be run to the attic from the Bath Room and Kitchen and from such other rooms as de- sired by the owner. Where the calculated area of stacks is too great to be included between the studs of a 4-inch wall, a 6-inch wall should be put in. Stacks on the first floor are omitted and where wall registers are used, a floor-wall type is recom- mended. The heat line to the Bath Room is a very bad arrange- ment but is about the best that can be done with the present room plans. To overcome the effects of the cold wall and the resistance of the offset in the floor, set the stack in an offset within the Kitchen and enter and leave the floor hori- zontal by a good sized turn. Avoid sharp corners. In selecting the various stacks and leaders it may be \vell to standardize as much as possible and avoid the extra expense of installing so many sizes. This can be done if the net area is not sacrificed. Diameter of grate allowing ventilation for ten people = 26 inches. Cold air duct = 600 square inches = 20 X 30 inches. REFERENCES. Trans. A. S. H. & V. E.. Rational Methods Applied to the Design of Warm Air Heating Systems, Vol. XXI, p. 389. Engineering Data for Designing Furnace Heat- ing Systems, Vol. XXI, p. 519. HEATING AND VENTILATION TABLE XII. H From Equation 26. bfiS G .2 i 1 I I CO - o T3 1 "ft =5 S "- 1 S 03 CM Ice S 03 * g "S > 5" 02 5 l 6 6 6 JS Q eg PQ 1 G .... 42 32 48 32 16 48 42 32 32 9 333 W 263 114 192 198 390 168 246 103 148 72 1894 F, floor or ceiling 195 138 120 180 194 174 172 72 1245 H 2 2 2 2 3 1 1 1 1 2 C, cu ft. 1950 2100 1900 1380 1200 1620 1746 1566 936 648 15046 H, B t u 15267 9956 12948 12828 14059 10583 11770 9092 8892 5179 110574 N. H. R., sq. in... 152 99 129 128 140 105 117 90 88 51 H R., size '4x16 10x14 12x15 12x15 12x18 10x16 12x15 10x14 10x14 8x10 II. S., sq. in. 63 70 54 53 31 lender, diam 13 11 12 12 13 9 10 9 9 7 A T . R. R. N. V.R.FQ. in.... 106 69 90 90 140 73 82 63 62 36 R. R. V R size 10x16 8x12 L0xl4 10x14 12x18 9x12 1 ( ) \ 1 *? ft '19 ft -10 R 'in R. S. " " V. 8. sq. in 84 55 72 72 78 44 49 38 38 22 REMARKS % 3 2 2 ni E"~ cu Basement not a 3 II 4-> g g ceiled. (First floor, > a -1 3 CO o floor loss ; "cu CP * * c a X t a X temperature 40, CO o > O H f J3 f^ cu 1 K = .45. CO 3 "3 o cu cS 5* ft id c S3 a> e -o Attic floored OX3 3 ^ > 2s t_ cS 5*" 03 solid. (Second 3 1 o-g ' O I 1 -s" CO floor, ceiling loss ; 1 i 07 S ft a CU 3 "y i" o 13 temperature 20, 0.3 Q t " S 3 G ^ O 8* So K = .25 cu ^=2 - S x* O ^ o G CO +i ^ 8 >, cu C ^ c 1 i H RfDUC f R n I TO r/RN/\ p. the electric prices in the locality. 118 HEATING AND VENTILATION 77. Suggestions for Operating: Furnaces: Furnaces are designated hard coal and soft coal, depending- upon the type of design and the construction of the grate, hence the grade of coal best adapted to the furnace should be used. The size of the openings in the grate should determine the size of coal used. Keep coal in coal pile moist but not wet. Clean all furnace gas passages frequently. Keep the fire pot well filled with coal and have it evenly distributed over the grate, firing light arid often for best service. In a properly designed plant, when necessary, fir- ings may be as few as three or four per 24 hours and give good service. Keep the fire free from clinkers. They should be re- moved from the fire once or twice daily. It is not necessary to stir the fire so completely as to waste the coal through the grate. With a good chimney draft, some ashes just above the grate line will be a benefit in that it will retard the fire and tend toward less clinkering. Clinkers are formed with high volatile coals and strong draft through the grate. They are avoided by slow and steady combustion, by having a thick fuel bed of live coals and by having sloiv draft through the grate (generally draft damper fully closed and small draft above the fire). The arrangement of these dampers will be determined by experience. A good sized chunk of wood embedded into the top of the fuel bed is a coal saver. When replenishing a poor fire do not shake the fire, but put on some coal (or chunk of wood) and open the drafts. After the fuel is well ignited clean the fire. The ash pit should be cleaned each day. An accumula- tion of ashes below the grate soon warps the grate and burns it out. Sifting shovels may be used and the unburned coal put back in the furnace. Keep all dampers in working order. Have a hand damper in the smoke pipe and keep it open only as far as is necessary to create a draft. Check damper (opening to basement air) must not be open unless draft damper under grate is closed. Keep the water pans full of water and all humidity apparatus working 1 . Clean the base of the chimney, the furnace and the smoke pipe thoroughly in all parts at least once each year. FURNACE HEATING 119 Keep the fresh air duct free from rubbish and impurities. Allow plenty of pure fresh air to circulate through the furnace. In cold weather part of this supply may be cut off. When fuel saving 1 is a necessity, it may be cut off entirely. Have the basement well ventilated by means of outside wall ventilators, or by special ducts leading to the attic. Never permit the basement air to be circulated to the living rooms. To bank the fires for the night, shake down and clean the fire, bank the live coals to one side of the fire box, fill up with fresh fuel, sift the ashes and distribute the unburned coal on the fire; with a poker make a hole through the fill into the live coal bed to permit of some flame above the fuel bed, close the under drafts and open the fire door draft slightly. Caution. Never cover the entire incandescent fuel bed with fresh coal and close the drafts. If this is done, coal gas will collect above the fire and will ignite from the first flame that breaks through the fuel bed, causing an explosion. CHAPTER VI. HOT WATER AND STEAM HEATING. DESCRIPTION AND CLASSIFICATION. 78. Hot Water and Steam Systems Compared with Furnace Systems: Hot water and steam installations are more complicated in the number of parts than furnace in- stallations; they use a more cumbersome heat carrying medium, for which a return path to the boiler must be pro- vided; and have parts, in the form of radiators, which occupy valuable room space. But the hot water and steam plants have the advantage in that the circulation, and the transference of heat, are not affected by wind pressures. Hot water and steam will carry heat as readily to the wind- ward side of a house as to the leeward side, a point which is known to be quite impossible with air. Furnace heating has the advantage of inherent ventilation, while the hot water and steam systems, as usually installed, provide no ventilation except that due to air leakage. 79. Elements of Hot Water and Steam Systems: Hot water and steam systems consist of three principal parts: the boiler or heat generator, the radiators or heat distrib- utors, and the connecting pipe lines which provide the cir- cuit paths for the hot water or the steam. In the hot water system it is essential that the heat generator be located at the lowest point in the circuit for, as explained in Art. 11, the only motive force is that due to convection currents in the water. In the steam system this is not essential. The water of condensation may or may not be returned by gravity to the boiler. Hence, with a steam system a radia- tor may be. placed below the boiler, if its condensation be trapped or otherwise taken care of. Concerning piping systems and connections, several terms commonly used by heating engineers should be de- fined. The large pipes in the basement connected directly to the source of heat, and serving as feeders to the pipes running vertically in the building, are known as wains. Supply mains are those that carry water or steam from the source of heat to the radiators and return mains are those HOT WATER AND STEAM HEATING 121 that carry water or condensation from the radiators to the source of heat. The vertical pipes connecting between floors are called risers, while the short horizontal pipes between risers and radiators are riser arms or branches. As there are supply mains and return mains, so also there are supply risers and return risers. A return main traversing the basement above the water line of the boiler is designated a dry return and carries both steam and water of condensation; one in such position below the water line as to be filled with water is designated a wet return. The returns of all two- pipe radiators connecting with wet returns are said to be sealed. 80. Classifications: One classification of hot water and steam systems is based upon the position and manner in which the radiators are used. The arrangement which is most familiar is the one wherein the radiators are located within the space to be heated and are surrounded only by room air. Radiators so placed (Fig. 40) provide no ven- tilation and are designated direct radiation. In direct-indirect Fig. 40. Fig. 41. radiation the radiators are placed as in direct radiation but the lower portion of each radiator is encased and connected with the outside air as shown by Fig. 41. The direct-indirect system provides certain ventilating possibilities and should always be used in connection with inside wall ventilating stacks. Indirect radiation is installed remote from the rooms HEATING AND VENTILATION ROOM HEATED to be heated and ducts carry the heated air from the radia- tors to the rooms either by convection, or by fan or blower pressure. In residence work this radiation is usually sus- pended from the basement ceiling as shown by Fig. 42. This Fig. 43. HOT WATER AND STEAM HEATING 123 provides a combination system of steam and indirect warm air. When the radiation for an entire building- is installed in one basement room, and each room of the building has carried to it its share of heat by forced air through ducts from one large centralized fan or blower, the system is called a plenum system or fan-coil system and is given special consideration in Chapters X to XII. A second classification for hot water and steam systems is made according to the method of pipe connection between the heat generator and the radiation. The one-pipe basement main steam system (Fig. 43) is the simplest in construction and is preferred by many for steam installations. As the name indicates, its distinguishing feature is the single pipe path leading- from the source of heat to the radiator, the steam and the returning condensation both using this path. In the risers and connections the steam and condensation flow in opposite directions, thus requiring larger pipes than where a flow and a return are both provided. In the mains the condensation usually flows with the steam and not against it. In the so-called one-pipe basement main hot water system (Fig. 49), radiators have two tappings and two risers, but the flow riser is tapped out of the top of the single basement main, while the return riser is tapped into the bot- tom of that same main by either of the special fittings shown in section in Fig. 44. The theory is that the hot water from the boiler travels along the top of the main, while the cooler water from the radiators travels along the bottom of this same main and two streams re- main separate. Where mains are short and straight as in small residence in- stallations, this system seems to give satisfaction, but where mains are long and more complicated a mixing 1 of the ,,,. 4 two streams is unavoidable and the supply to the farther radiators is cooled to such a degree that the system becomes unreliable. The two-pipe basement main system (Figs. 47 and 50) is standard with both steam and hot water installations. For steam work (especially for small installations) it is prob- ably no better than the one-pipe system but for hot water work it is much preferred. In this system two separate and 124 HEATING AND VENTILATION distinct paths may be traced from any radiator to the source of heat. In the basement are two mains, the supply and the return, and the risers from these are always run in pairs, the supply riser on one side of a tier of radiators, the return riser on the other side. A two-pipe steam system should have sealed returns (See Art. 82). The attic supply system, or Mills system, has found much favor with heating engineers in the installation of the larger steam and hot water plants. In this system the supply and returns both flow downward. This is accomplished by first leading the steam or water to the attic through one large main which there branches to supply the various risers. One riser only is generally used for each tier of steam radiators. Fig. 45 shows one- and two-pipe radiator con- nections. Frequently two-pipe connec- tions are made to a single riser pipe. W T hen this is done a water type radi- ator must be used with the supply en- tering the top and the return leaving the bottom of the same side (See vapor heating systems). .1 third cldnxifirution may be made, hav- ing reference to the manner of circu- Fig. 45. lating the heating medium and to its pressure. This classifi- cation covers a multitude of inventions upon the attachment of which increased capacity and efficiency are claimed over the ordinary gravity systems. In outline, this classification may be stated as follows: Gravity Systems Steam systems, circulating steam at pressures greater than atmosphere. Water, open tank systems, circulating water by in- creased weight of water in return risers over warm water in supply risers. Modified Gravity Systems Steam systems, circulating steam at atmospheric pressure or below. HOT WATER AND STEAM HEATING 1125 Water systems, circulating' water under pressure, at temperatures above those possible with the open tank systems and with accelerated veloc- ities. Combination steam and gas systems with radiators as heaters independent of a centralized heat supply. Systems mentioned in this classification are explained in Arts. 81 to 85. GRAVITY SYSTEMS. 81. Steam and Hot Water Systems: Ordinary low pres- sure steam installations operate at pressures from 1 to 10 pounds gage. Relief valves are provided which release the steam when pressures tend to increase above the set maxi- mum and thus protect the boiler from excessive pressures. Pressures in the boiler are maximum. These decrease grad- ually along the circuit of the supply and return mains be- cause of the frictional retardation of the circulating steam, giving a pressure drop between main and return near the boiler of V 2 to 1 pound. The water in the return, therefore, stands above the water level in the boiler an amount suf- ficient to balance this differential pressure. All pipes in the system are graded for easy flow of the condensation back to the boiler. Each boiler must be fitted with a pres- sure gage, a safety valve or pop valve and a draft regulat- ing device. Each radiator must have a first-class automatic air valve. An ordinary hot water installation has an open expansion tank at the highest point of the system to permit change in volume in the water as it changes temperature, such systems operate at pressures equivalent only to the static head of the water in the system. Pressures at the boiler range from 15 to 25 pounds gage for residence work. Water tempera- tures above 212, therefore, will cause a loss of steam out the overflow of the expansion tank and are not considered advisable. Each boiler is fitted with a pressure gage or alti- tude gage to show the height of water in the expansion tank, a thermometer to show the temperature of the circulating water and a draft regulating device. Each radiator must have a compression air cock. 82. Diagrams for Gravity Steam and Hot Water Piping: Systems: Figs. 46 to 51 inclusive show some of the methods of connecting up piping systems between the source of heat and the radiators. A, B, C and D show different methods 126 HEATING AND VENTILATION ONE PIPE STEAM SYSTEM -BASEMENT MAIN Fig. 46. TWO PIPE STEAM SYSTEM-BASEMENT MAIN Fig". 4' HOT WATER AND STEAM HEATING 127 Fig". 48. ONE PIPE. 'SYSTEM-HOT WATER Fig. 49. 128 HEATING AND VENTILATION TWO PIPE. SYSTEM HOT WATER -BASE ME NT MAIN a i At aa 4 C3Q Fig. 50. of connecting- between the radiators and mains. The branches below the floor and behind the radiators are for the purpose of taking up expansion. Short connections should be avoided. It will be noticed that the two-pipe steam systems have sealed returns where they enter the main return above the water line of the boiler. Dry returns frequently interfere with the circulation of the steam to the radiators by short-circuiting. Steam from the boiler follows the path of least resistance to each radiator and many times this path leads up the return line into the radiator instead of through the supply. In Fig. 47 suppose the radiators C and D increased in number to the right C', D', C", D", etc., and all connected to the main as shown and to the return without the loop. It is easy to see that steam from the supply main would flow through the radiators C and D into the dry return where it would continue to the end of the line and affect the easy flow of steam through the end radia- tors. If the main inlet to any radiator were restricted, the steam to that radiator would be supplied through its return branch thus blocking circulation and causing icni>i