ELEMENTS OF HEATING AND VENTILATION, described as a text-book for students, engineers and architects, by Arthur M. Greene, Jr., is a work that will appeal to those who have passed beyond the elementary stages in the design of heating and ventilating plants. All phases of the work illustrated are accompanied by actual problems for which the slide rule has been used. The author states that the data presented are founded on careful experiment and may be used with confidence. Several of the methods given for the solution of problems are new. In every case the endeavor has evidently been to include all the data that are necessary to solve any problem that may arise in connection with the warming of buildings or the supply and delivery of Published by John air. Price, $2.50 net. Wiley & Sons, New York, or may be had through the book department of THE HEATING AND VENTILATING MAGAZINE, BOYD'S WORK MEN'S COMPENSATION AND INDUSTRIAL INSURANCE, by H. T. Manning, has been received from the publishers, the BobbsIt is an exMerrill Co., Indianapolis, Ind. haustive treatment of the subject, in two volumes, and discusses in an eminently sane manner a subject that will probably have to be faced, if it has not already been faced, by It is well every employer in the country. worthy of perusal and study by those interested. DIXON'S GRAPITE BRUSHES, used with electric dynamos and motors, are described in a new catalogue published by the Joseph Dixon These Crucible Co., Jersey City, N. J. brushes, being composed almost entirely of high-grade graphite, prevent sparking and Care is also taken wear of the commutator. to prevent their gumming the commutator. Other features emphasized are their low losses from friction and the automatic lubrication they impart. Complete rules are given for using the brushes under various conditions of service. Size 3x6 in. Pp. 16. . Front Cover Buffalo Forge Co......Inside Back Cover Central Station Steam Co. Chicago Pump Co. Johns-Manville Co., H. W. National Steam Specialty Co. Patterson & Co., Frank L. 63 Front Cover 67 3 65 60 12 74 69 64 Front Cover Front Cover 8 7 4 59 59 58 6 8 Front Cover 57 63 63 3 Front Cover 56 5 67 71 65 74 9 64 Pierce, Butler & Pierce Mfg. Co. Ric-Wil Underground Pipe Covering Co. 66 Front Cover Sprague Electric Works 66 Standard Steam Specialty Co. 62 61 72 United Vacuum Appliance Co. Webster & Co., Warren Wyckoff & Sons Co., A. Zellweger & Sons, J. 10 72 71 73 D. H. BURNHAM & CO., Architects, Chicago, through their Board of Consulting Engineers and the Investigating Committee appointed by the Bank, adopted the MONASH NOISELESS SYSTEM of VACUUM HEATING for the CONTINENTAL & COMMERCIAL NATIONAL BANK BUILDING, which covers an entire city block, the largest building of its type under one roof in the world. New York 21 W. 42nd St. MONASH-YOUNKER CO. Chicago 1420 W. Jackson Blvd Please mention THE HEATING AND VENTILATING MAGAZINE when you write. 1123 BROADWAY NEW YORK Theory and Practice in Engineering III-Steam Heating BY KONRAD MEIER. AUGUST, 1913 (This series of articles commenced in the June, 1913, issue.) While the general use of hot water heating for many purposes to which it is best adapted, has been retarded through lack of understanding, the development of steam heating has also suffered from the same cause, in various ways. It is true that defective steam circulation can be overcome more easily, but there are, nevertheless, some substantial reasons for the systematic design and calculation on a scientific basis. The situation varies according to the nature of the case. With the ordinary, self-venting apparatus in which the pressure can be raised according to need and with sealed returns giving positive direction to the flow, the steam will reach all points eventually. But with unequal resistances to the points of delivery there will be a difference in the time required to fill and warm up the less favored radiators at the end of the line, which are generally in the most exposed rooms, always coldest in the morning. When, in addition, the steam generation is scant, it is likely that most or all of the supply is condensed in the nearby rooms, instead of being induced to go where most needed, which is the idea of proper distribution. At best, some of the rooms are liable to overheating and the benefits of whatever general regulation that might be possible with steam heat, are not ob tained. Also, a higher working pressure becomes necessary, which is certainly not conducive to economy. With the pipe system calculated as it should be, no branch is favored and each radiator will receive its share of the steam production from the lowest possible pressure and upwards. This will allow better utilization and at least some variation of the heat to suit the weather. The difficulties due to lack of equalization will increase with the apparatus having dry returns. As shown in the introduction to this article, the steam, under such conditions, is most liable to back up against the condensation, obstructing drainage, causing noise and retarding the removal of the air when entering radiators from both ends. POINTS TO CONSIDER IN CALCULATING A DRY RETURN SYSTEM. A dry return system, as illustrated in Fig. 4, should be calculated so that, for instance, the branch at b can pass only steam enough to fill its own radiator, plus the return branch and the run of the return main from b to m. If made of equal size as the branch at f the steam would rush first through b-1, because of least resistance, and reach k, i and possibly g before it can fill the other radia tion. The relief d-k, should be sized so that it can pass only steam enough to fill the run k-1. For some cases, however, it is difficult even to approximate this capacity. Hence a sealed relief would be appropriate. The same might be done at e-h, unless the pipe can be made sufficiently small and long to prevent an excessive rush of steam toward g. If both d-k and e-h are sealed, the condensation in the return mains from 1 to g will have to be made up by the steam passing through branch and radiator at f and running down and toward the boiler from point g. LARGE MAINS ARE NECESSARY. This method of calculation will, at than those figured from empirical tables. least for long runs, result in larger mains But this is necessary for successful operation. It will keep down the total pressure loss and prevent the water from backing up from the boiler, which is due generally to an excessive difference between the steam space in the boiler and the return end, as expressed by the water column H in Fig. 4. No check valves are necessary on return mains, when this height, which represents the total presThis is the proper way but it is plain sure loss through the movement of steam, FIG. 4.-SCHEDULE OF STEAM DISTRIBUTION WITH DRY RETURNS. that the volume of steam for that branch would be materially increased. Furthermore, the run b-c-d-e-f-g-h-i-k-1 is much longer than b-1 direct through the radiator. The pressure drop either way should be the same. It is necessary, therefore, to make the near branch smaller, increasing its resistance per lineal foot and, at the same time, to ease the flow of steam towards the far end by keeping down the velocities. If a pipe system is perfectly proportioned on this principle, that is, for an equal pressure drop from the boiler to all points of delivery, which latter must include the steam condensed within the returns, it will circulate smoothly and noiselessly, even while heating up. Radiators will vent under equal pressure and rooms will warm up at the same time. is kept low enough, so that the water Keeping down the water line in the return by ample mains and low resistances will make it perfectly safe, where necessary, to keep radiation closer to the level in the boiler than is generally considered good practice. The safety lies in knowing the factors in a given case, Sometimes water will be entrained by priming. Whatever the cause may be, the calculation will help to establish it and will at least prevent those numerous difficulties which are due to improper distribution of pressure. VACUUM MOST DESIRABLE WITHIN THE When exhaust from steam motors is used for heating, the working pressure must be kept close to the atmospheric. A vacuum would be most desirable in many cases, but for various reasons it is rarely maintained, within the steam lines, where it would benefit the power plant. It is generally applied only to the air lines or returns, with the main purpose of accelerating the removal of air and sometimes for curing defects in the circulation of steam and water. Considering that any low pressure steam heating apparatus, even of large dimensions, with wet or dry returns, can be made to circulate perfectly at less than 1-10 lb. per square inch, excess or back pressure, and will get rid of the air at little if any more, if the pipe system is well-designed and proportioned, it seems proper to consider whether, in a given case, a vacuum system will pay for itseif or not. It may be claimed, that the vacuum allows the use of smaller piping. Whether this would be good practice seems debatable in view of the fact that smaller steam piping inevitably increases the pressure losses and, therefore, also the back pressure, since the suction applied to automatically closing return and air valves cannot help the circulation after they are shut. When these valves are perforated to allow continuous leakage, the volume of steam to be handled will increase materially and with it the pressure drop, as the square of the velocity. Any of the suction that will penetrate the perforations is most liable to be neutralized by the greater pressure difference required to move the steam. It does not seem rational to crate several inches (mercury) of vacuum, especially when extra power must be expended, in order to pull steam and air through a series of pinholes and small return piping, when the desired result can be obtained by simple and natural means with a very small fraction of the pressure drop, which can put no material handicap on the power plant. Some initial cost might be saved by small return lines, but this would probably be more than offset by more expensive automatic valves or traps and other apparatus. The maintenance should also speak in favor of the simpler equipment. Taken altogether, it would seem that the cost of equipping an apparatus with vacuum devices can, at least in many new plants, be saved by appropriate design, developed from a study of pressure conditions and based on scientific calculation of the pipe system, which does assure a smooth working and easily venting apparatus at a working pressure that would be acceptable almost anywhere. Even when vacuum is to be applied for one reason or another, the methodical way of sizing the pipes, with a view to equalization, will amply repay the extra pains by a more responsive plant. The nature of the problem must be understood, of course, and some practice obtained in applying the data, which is also obtainable in charted form, before the best results can be expected. ADVANTAGES OF LARGE PRESSURE DROPS IN LONG RUNS. High pressure steam is used sometimes to carry heat for long distances. In such cases, a large drop of pressure between points where steam is generated and used is permissible and advantageous, as a rule. Larger pressure drop results in smaller piping, smaller heat losses and less or no condensation. Systematic calculation will show the possibilities in this respect and determine the best proportions in a given case. It will also give the heat developed by friction and its effect on the condition of the steam delivered. The study of pressure distribution again will lead to the proper disposition of reliefs, traps, etc., and assures a smoothly-working system. Taking on the whole, it is often found practicable to get along with smaller piping and less apparatus, if the result can be foretold. The margin of safety in thumb rules is eliminated. Hence the scientific way is conducive to economy. (To be continued.) |