The Useful Arts Employed in the Construction of Dwelling Houses. Second Edition

by Anonymous

Warming Buildings by Hot Water.

Lastly we have to notice the method of warming by hot water. In this method there is usually a boiler communicating by an upper and lower pipe, with an upright pipe the same height as the boiler. On the application of heat to the boiler, the column of water becomes lighter than that in the upright pipe; therefore the pressure on the water in the lower pipe being less at the end nearest to the boiler than it is at the other end, a portion of the water in this lower pipe moves forward towards the boiler, which causes a corresponding quantity to pass along the upper pipe in a contrary direction. This motion will necessarily continue as long as the column of water in the boiler is hotter, and therefore lighter than that in the upright pipe; and this must be the case so long as the boiler continues to receive heat from the fire, and the pipes to part with their heat to the air, and thereby cool the water contained in them. In whatever form the hot water apparatus is constructed, this difference of pressure of the two columns of water is the cause of the circulation.

In this form of apparatus some part or other of the water is open to the atmosphere, either at the top of the boiler or at the top of one of the pipes, so that there is no danger from the bursting action of water heated above the boiling temperature. But, on the other hand, the water cannot well be conveyed to rooms at different elevations in the building. To increase the efficacy of the arrangement in this respect, the following adaptation has been suggested. A pipe is made to dip into an open boiler, reaching only an inch or two below the surface of the water, and passing round the room to be warmed, returns again to the boiler and dips again into the water, descending quite to the bottom of the boiler. An air-pump is connected with this pipe by a small tube; and the air in the pipe being exhausted by this means, the water rises into the pipes above the level of the boiler by atmospheric pressure, and the circulation then takes place by the hot water ascending through the pipe at the top of the boiler, and passing through the whole circuit of the pipe, it returns through the upper end of the pipe which reaches to the bottom of the boiler.

In the last-described form of apparatus the water will rise in the syphon pipe to a height of about thirty feet above the boiler, being that elevation which is due to the action of the atmosphere on liquid flowing through a vacuum. But when a whole house or building is warmed by hot water in all the different floors or heights, a modification of the system, called the high-pressure system, is adopted.

The apparatus on this system consists of a spiral coil of small iron pipe built into a furnace, the pipe being carried from the upper part of the coil, and entwined round the room intended to be warmed, forming a continuous pipe when again joined to the bottom of the coil. The size of the pipe is usually only half an inch in diameter internally, and an inch externally. A large pipe of about two and a half inches diameter is connected, either horizontally or vertically, with the small pipe, and is placed at the highest point of the apparatus. This, which is called the “expansion pipe,” has an opening near its lower extremity, by which the apparatus is filled with water, the aperture being afterwards secured by a strong screw; but the expansion pipe itself cannot be filled higher than this opening. After the water has been introduced, the screw is securely fastened, and the apparatus becomes completely closed in all parts. The expansion pipe, which is thus left empty, is calculated to hold about one-tenth or one-twelfth as much water as the whole of the small pipes; this being necessary in order to allow for the expansion that takes place in the volume of the water when heated, and which otherwise would inevitably burst the pipes, however strong they might be.

In this apparatus the principle of action is different from that in the low-pressure method. Here the water is raised to so high a temperature that it wholly overcomes the effect of gravity, and rises to the highest rooms of a building if required, the circulation through the system of pipes being more rapid as the heat of the water is greater. But there are inconveniences attending the method. If the pipes be not very strong, they will be burst by the intense pressure from within; as they will likewise if the expansion pipe be too small. If, on the contrary, this latter pipe be too large, it occasions the water to be driven up into it so violently as to leave the lower part of the coil of small pipe almost empty, and therefore liable to be burned by the heat of the fire. And if all these points be properly attended to, there is still the inconvenience resulting from the decomposition of the floating particles in the air, by the highly-heated metal of the pipes. In some cases water, instead of being heated in a coil of small pipes, passes into and through large flat boxes or chambers, whose extended surface enables the surrounding air to be heated more rapidly.

The details of this chapter will enable the reader to perceive, that that part of the builder’s art which relates to the construction of the fire-place rests on more scientific principles, and is more liable to change by successive discoveries and inventions, than most others. It is not simply to make a square opening by the side of a room, to have a vertical chimney or flue above that opening, and a few bars within it; it is not by such means that the object to be answered by a fire-place can be attained; some knowledge of chemistry, pneumatics, and hydraulics, is required before we can properly regulate the combustion of our fuel, the ventilation of our apartments, or effectually warm them by the ascension of hot air, the circulation of hot water, or the condensation of steam.

Chapter VIII.
THE WINDOWS AND LEAD-WORK.

We must now give to our dwelling-house those conveniences which call for the services of the glazier and the plumber. These two occupations are so often combined by the same tradesman, and the two classes of operations thereby resulting are both so necessary to the finishing of the exterior of a house, that we may conveniently treat of them in one chapter.