Clean reading copy
The Electric Plant of the Modern Tall Building
THE ELECTRIC PLANT OF THE MODERN TALL BUILDING By Frank A. Pattison Engineering Magazine, August 1897 Local OCR assembled from IA DjVu XML pages 0105-0109.
THE ELECTRIC PLANT OF THE MODERN TALL BUILDING. By Frank A. Pattison. HERE are several factors which determine the success or failure cs of a tall building, but none play a more important part than the elevators, light, heat, and ventilation. Not many years ago each and every plant installed for these purposes was an experiment, but to-day plants are installed which produce predetermined results with surety. The four requisites specified can now be successfully supplied by the electric plant. The electric equipment of a building is a plant, the finished product of which is light, heat, or power, made from the raw materials, coal and water. The plan by which an owner can get the best products cheapest and at the same time secure safety for life and property is the one to be adopted. The isolated plant is a factory where electric current is produced on a small scale, and the question whether it is cheaper for an owner to do his own manufacturing, or purchase from the central station, is one to be solved in each case, as like conditions never exist in any two cases. The first portion of the plant to be considered is the boiler. The water-tube boiler has very wisely been almost universally chosen for installation in large office-buildings. This boiler gives greatest efficiency with greatest security. The shell boiler is not fit for such service. The choice between the return tubular and the water tube is usually prompted by the fact that the latter will give greater power in a given space, and is less disastrous in case of an explosion. A poor fireman makes boiler efficiency an impossibility. It is very difficult to obtain results coinciding with theory; it is sometimes done in single or test runs, but it is a very rare exception to find a boiler plant running regularly with the best possible efficiency. If this is so in large installations, how much more is it true of the boiler plants of the size usually found in office-buildings! The situation of the boilers is determined by municipal and other regulations, so that it is necessary to group the steam-consuming machinery with reference to the boilers. The boiler pressure used to be limited to sixty or eighty pounds, but during the last year several plants have been installed for one hundred and twenty-five to one hundred and fifty pounds, and have made an excellent showing. Time will increase rather than diminish this, as greater economy is being asked for with each new 782 a
THE ELECTRIC PLANT. 783 installation. It is always best to use the steam as soon as possible after it leaves the boiler, and the engines should be placed accordingly. This has been too often neglected in the past. The number and size of boilers are too often determined by the available space; they should be determined by calculating the most efficient combination for the work in hand. The cost of property has compelled vertical rather than lateral extension, so that in future installations more boiler capacity must be designed and arranged to go in the same floor space. The foundations for boilers and all machinery require very careful study. Piles should never be used, unless it is positively known that they will always be submerged. In some soils it has proved necessary to float the foundations on grillage beams. It is necessary to take especial care to insulate from the grillage, pier, and column work of the building. This is often effected by sand, held in place by brick walls. Heavy felt is sometimes employed. The most satisfactory foundations for a number of units of rapidly-moving machinery has been found to be a single large mass of concrete or masonry. This practice has been followed in a number of plants in Chicago, Buffalo, Philadelphia, and New York. One of the most massive constructions of this kind is found in the American Surety Building on Broadway. It is sometimes best to set the boilers in a caisson sunk to the first substantial stratum. There should be no vibration; if there is the least, it must be absolutely contained within the foundation, and not allowed to enter the structure. For this reason proper supports for steam piping should rest on the floor, or on small foundations, rather than on the steel structure. The steam piping for engines has not received the careful consideration it should. This portion of the installation is now beginning to develop. The greatest care should be taken to deliver the steam to the cylinders perfectly dry. Expansion and contraction of pipes are to be amply allowed for, and vibration and noise must be prevented. This should be done by removing the cause, not by chasing it from one place to another. Noise may be heard in the upper stories and not below, and will increase rather than diminish. Given dry steam and a solid foundation, the engine and dynamo in combination become the vital factors in the daily operation of the building. Wesay combination, because the use of direct-connected machinery has become universal for such work as we are speaking of. This combination is the source of the electric current which moves the elevators, lights the building, propels the ventilating apparatus, and furnishes the exhaust steam whereby the heating is done. Experience has shown that the generating plant should be divided into three or, at most, four units. Occasionally special circumstances vary this. =
784 THE ELECTRIC PLANT OF The size and number of units should be decided upon only after careful study of an accurately-plotted load line. A reduction of the load to as few cylinders as possible is certainly to be sought for. Every cylinder in use should be working with its most efficient load. Upon the result of these calculations also depends the selection of high- or low-speed machinery. It has been general practice up to date to have simple high-speed engines. Problems and conditions are now Offering themselves that may in the near future change this. Regardless of the type of engine used, the multipolar dynamo forms the electrical portion of this transformer. ‘These elements should be placed on solid cast-iron sub-bases filled with concrete or sand. These sub-bases are made either in one or two pieces. Some engineers prefer to have all units above fifty kilowatts have a sub-base in two pieces, with the adjoining faces planed and securely bolted. This method of construction has been thoroughly tested, and found trustworthy as to alignment. It is often difficult to get a large casting without a warp or some internal stresses that may be detrimental. The dynamo and engine must run without noise or vibration, and it should be possible to run them without any holding-down bolts, although they should not be so run, except for a test. The engine is usually made with an extended shaft, the extension being occupied by the dynamo armature. Many advocate a divided shaft with a solid or flexible coupling, but, as neither engine or dynamo is of use alone, and the precautions against sudden overload are sorefined, it seems unnecessary to take this step. There can be no question of alignment with a properly-constructed foundation and sub-base. The selfoiling of all bearings is desirable, but is not yet universally demanded. It will not be long before all engineers will demand this. Indicator cards taken for friction load with and without self-oiling arrangement make a very interesting study, and will, in the end, create a universal demand on the part of engineers for self-oiling machinery. The possibilities of given pressure of steam in the known dimensions of the cylinder should be delicately weighed against the output of the dynamo to which it is to be attached, in order to have the two pieces of apparatus form a proper unit of power. The dynamo should be compound wound, unless special connection with other apparatus prohibits. It is now considered good practice to use a broad commutator and a number of carbon brushes. Up to the present year 110-volt dynamos for light, and 110 or 220 volts for power, have been used, but the advent and commercial success of the 220-volt lamp will give engineers wider scope for economy, and lead to the use of higher pressure without sacrificing the advantage of interchangeability always to be sought.,
THE MODERN TALL BUILDING. 785 The most trying work the generating plant has to perform is the supply of current for running the elevators. The load will vary much, and between wide limits. This prohibits the running of lights and elevators from the same dynamo. A storage battery must be supplied to take the current not wanted by the elevators, or else the elevator generating units must be subdivided and placed upon the same shaft run by one engine, thus allowing the several elevators to equalize the load. The former plan is used in several large buildings in Chicago and New York. The latter is about to be tried in the New York Athletic Club, and, as the load is not sufficient, a lighting generator has been placed on the same shaft. Of course, the object to be attained is to keep the load line as straight as possible, and of such height as to insure economy in the cylinder of the engine. The switchboard is a very important element in the electric plant of the modern tall building. Every wire from each dynamo should pass to its work through the switchboard. This must be equipped with proper instruments for showing the condition and work of each dynamo, and the necessary switches for the necessary sub-division and control of the various parts. This should be absolutely fire-proof in every part, and placed where there is proper circulation of air and careful protection from meddling and accident. It is too often tucked in some corner and given too little attention. The storage battery has developed into an important part of the electric equipment of a building. It may perform one or several of the following functions: supply current to take care of the peak of the load; supply current for light during hours of light-burning; act asa balance spring between the power motors and bus-bars. Storage batteries are not needed in all large buildings, but the time is fast approaching when the designer of large isolated plants will have to give very careful consideration to this portion of the equipment. A great deal of the trouble of the past has been due to too small batteries, and that evil has not entirely disappeared. The line showing the duty required of the storage battery should be carefully plotted for each case, and the specification so drawn as to clearly show what work it will have to do. Too many batteries are installed without a very definite idea as to why or how much they are to do, or how long a time they are to be allowed to perform their work. A storage battery should be installed in a room entirely shut off from everything else, and where good ventilation can be obtained. The cells must be so arranged that each can be carefully inspected and tested. If the cells are large, they should not be placed one above the other, unless absolutely necessary. The floor should be pitched slightly, so as to be drained at one or several points. The size of cells,
786 THE ELECTRIC PLANT. the question of end-cell or counter-cell regulation, the number of cells, and the method of charging, must be decided upon for each installation, as no general rule can be made. The switchboard containing the instruments and switches for regulation should be placed near to, or built as part of, the generating plant switchboard. Too great care cannot be taken to keep the fumes from the battery away from everything. They should have no outlet, except to the outer air. In such a climate as that of New York, sufficient exhaust steam can be derived from the electric-plant engines to heat the building, except in extreme weather. The steam, after it has passed through the feedwater heater, is reduced in pressure and passed into the pipes of the heating system. The back pressure on the engines caused by using the exhaust for heating the feed water and the building should never exceed five pounds. Asa matter of fact, it is the exception when it reaches five pounds. The pumps for feeding the boilers, for raising water for the building to the tanks on the roof, and for lifting the drip water to the sewer are steam pumps. There is no reason why this work could not be done with electric pumps. They are economical and very easily controlled. The tall-building craze has spread rapidly, and it will take years to work out the requirements in the various departments. The electric elevator for skyscrapers is still in the development period, although in many buildings it is an important element of the plant. At the present time it is not possible to define the practice of the day, because each new plant brings out new methods and new apparatus. One subject should be touched upon which is of vital importance to all connected with the erection of a modern tall building, and especially to the owner,—namely, the spaces in which the machinery is placed, commonly called the engine room. This should be light, thoroughly ventilated, and constructed of such materials as may be easily kept clean. Thousands of dollars worth of machinery is often placed in little more than a hole, where it cannot possibly get proper attention, and where the heat partially disables the best of men. This space, of course, is limited by circumstances, but there is no reason why the walls and floors should not be of easily-cleaned material, why light should not be abundant, or why ventilation should not be perfect.