Page:The American Cyclopædia (1879) Volume XVI.djvu/476

 456 WARMING AND VENTILATION high temperature, the principle of this ar- rangement is to warm moderately a very large amount of it, and depend upon its rapid ex- change to keep the apartments at a proper temperature. It is said to secure the cheap- ness and simplicity of the stove with the ven- tilating efficiency of more expensive apparatus. "Water has been used as a vehicle for heat, and its employment depends upon two princi- ples. First, when unequally warmed, its equi- librium is disturbed, and it is thrown into move- ment. If a tube passes into the upper part of a boiler, and, making a circuit, reenters the lower part, heating the water in the boiler gives rise to a circulation through the tube. The hot water flows away above, and, cooling, de- scends and returns to the boiler below. Sec- ond, the capacity of water for heat is so great, that is, it holds so large an amount of it, that it gives out a largo quantity as it cools, and is thus an admirable medium for its distribution. When the heat of a cubic foot of water is im- parted to air, whatever be the number of de- grees through which the water falls, it will raise through the same number of degrees 2,850 cub. ft. of air. There are two modes of warming by hot water. In one the circulation takes place through a system of small tubes distributed through the house, and constructed to fit any form and succession of rooms and passages. The pipes are coiled into heaps in various situations, and impart their heat by di- rect radiation. This is Perkins's arrangement. It has no boiler, its place being supplied by a portion of the pipe coiled up in the furnace, and is a high-pressure method, the temperature of the water rising to 300 or 350. The warmth diffused from a coil of pipes in a room is mild and pleasant, but no ventilation is provided for. In the other form of hot-water apparatus, the pipes do not ascend to any considerable height above the boiler ; there is but slight pressure, and the heat does not rise above the boiling point. The boiler and masses of pipes are placed in the cellar or basement, and air from without, warmed by passing among the coils of tubing, is distributed to the apartments through flues and registers. As the boiler and tubes contain considerable water, its tempera- ture rises slowly when fire is first applied, and, the quantity of contained heat being large, it cools with equal slowness. Hence the arrange- ment is well suited to those cases where per- manent and unvarying heat is required, as in greenhouses, graperies, &c. Hot-water pipes thus arranged are a source of steady and equa- ble heat. Steam has long been employed and is increasingly used for heating purposes. It contains a large amount of latent heat, and can be conveyed with facility through pipes to distant points, where, condensing into wa- ter, it gives out its heat, and either flows back to the boiler or falls into reservoirs at various points. Irregularities in the fire affect much more sensibly the circulation of steam than that of hot water, and want of attention may lead to condensation, so that when the fire is renewed the steam rushes into the partial va- cuum, and meeting the condensed water drives it violently forward with disagreeable noises, and often with a production of leaks. Steam is applied for heating in two ways, either by coils of pipes or combined metallic sheets (ra- diators) set up in the various apartments, which warm by direct radiation or by systems of pipes over which air is made to pass, and being heated is sent through the building as in the case of furnaces. Steam radiators give a plea- sant heat, but are wholly objectionable from lack of the slightest provision for ventilation. It has been estimated that a boiler adapted to an engine of one-horse power is sufficient for heating 60,000 cub. ft. of space; and that if steam from the boiler of a working engine is to be used for warming, the boiler requires to be enlarged at the rate of 1 cub. ft. for every 2,000 cub. ft. of space heated to the temper- ature of 70 or 80. The amount of heat lost through windows and walls, and by escaping air, has been variously estimated. Dr. Arnott says that in a winter's day, with the external temperature at 10 below freezing, it requires, to maintain an apartment at 60, a steam pipe heated to 200, or about one foot square for every 6 ft. of single glass windows ; as much for every 120 ft. of wall, roof, or ceiling, and as much for every cub. ft. of hot air escaping each minute in the way of ventilation. Hence, a room 16 ft. square by 12 ft. high, with two windows, each 7 by 3 ft., with ventilation at the rate of 16 cub. ft. per minute, would re- quire 20 sq. ft. of radiating surface. Steam for heating is used at a very low pressure, and with suitable precautions is quite safe. For heating large establishments this method has come into extensive use, but, like hot water, it is too expensive for ordinary private dwell- ings. Ventilation on a large scale is produced by fans driven by steam power. The fan con- sists of several vanes, or blades, inserted into a shaft and made to revolve with it. By the ro- tation of the blades, the air is driven by centri- fugal influence to the circumference, tending to create a vacuum at the centre. If two sides be added to the vanes, having an opening round the axis, when the fan is thrown into revolution, air will rush in through the openings and out at the circumference continuously. If tubes connect these central openings with an apart- ment, its air will be exhausted ; and if the cir- cumference be suitably connected with a room, the air will bo driven into it. The same ma- chine therefore becomes an exhaust fan or a blowing fan according to the mode of its use. Air impelled by a fan maybe heated by various expedients for use in cold weather, but this mode of ventilation is independent of warming, and is chiefly valuable in summer in large es- tablishments, as asylums and hospitals, where many persons are gathered. Ventilating chim- neys are flues, sometimes made very high and large, in which fires create powerful draughts