Low-firessitre Heating.—In low-pressure water heating, after the water is heated in an iron or a copper boiler, it proceeds through a flow pipe—covered, to prevent chilling—first into an expansion vessel near the roof of the house and open at the top, and is thence distribnted through pipes to the different stories and rooms, where the heat is given off either by the walls of the pipes or by radiators; the water then returns to the boiler. Figure 18 gives two sectional views of one of these radiators as used in a parish school in Berlin. It consists of a wrought-iron cylinder of 2.1 feet diameter, and is provided with a nnmber of inner pipes, into which the air of the room enters from below and emerges at a higher tem perature above. The warm water, on the contrary, enters the radiator above and leaves it below; so that the heat is given off by the walls of the large cylinder as well as by those of the small air-pipes. The supply of water can be regulated or cut off entirely by cocks. If ventilation is also to be provided for, the air-pipes of the radiator must be brought into direct connection with a duct for fresh air below.
Ilig-h-pressurelf 'trio-Heating—Perkins' system—is shown in Figure 19. The flow-pipes are seen at a ; return-pipes, at b and c; and the closed expan sion-pipe (m) is shown at the upper end. A cock (n) is also placed at the highest point; this must be open while the water is being- forced in, to allow the air in the pipes to escape, while it also allows the passage of the water. A little evaporation always occurs during the heating, on account of the heavy pressure and the porosity of the iron. These pipes must be of wronght iron, and of narrower calibre than for low-pressnre beating, on account of the pressure of the superheated water. For the same reason, boilers and radiators are not used in this system, their places being sup plied by coils of pipe, of which one (A) is shown at the furnace and two others (B, C) in the rooms. As the length of the pipes is limited and ought not to exceed Szo feet, several systems with an equal number of coils are used. The latter receive heat, as shown in Figures 19 and zo 1o), from furnaces built of brick, a single fire generally serving for two coils.
The furnace designed by Engineer John Haag of Augsburg for the in sane asylum at Neustadt-Eberswald is represented in Figure zo: a is the front; b, vertical section; c, cross-section; a', ground-plan, taken horizon tally over the grate. In the elevation (a), the doors for making the fire and for the ash-pan are seen in the middle, above and below; the pipe con nections for the corresponding coils, at the right and left; the flow-pipes, at the outer ends above; and the return-pipes, nearer the inside and going farther down. A supply-pipe over the point a, proceeding from a force pump, is connected with the latter. In the longitudinal section (b) the fire-grate, lying well elevated, is seen in the middle. The gases produced
by combustion proceed from the grate through openings in the two parti tions, then through the coils downward to the common smoke-flue, which is provided with a damper. The lighter-tinted portions of the sections and ground-plans represent fire-brick. No further explanation will be neces sary for Figures c and a'.
Gurney System of Hot-water Heating.—There has been carefully devel oped an American system of hot-water beating—called the "Gurney sys tem " (fi/. 9, _figs. 2, 3, II)—which is intended to serve as a substitute for steam heating in hotels and large buildings in which it is extensively used, and also for service in dwellings. A description of its advantages includes claims that hot-water radiators will heat with a low fire, and will continue to give out beat not only as long as there is any fire under the heater, but also after the fire is completely extinguished and until the water in the apparatus becomes of the same temperature as that of the surrounding atmosphere. It is alleged that the hot-water radiators can be perfectly controlled and reg-ulated by partly closing the supply valve; that there is no danger from explosion, and no waste of water; that the consumption of fuel is less than by any other mode of heating; that equality of temperature is maintained throughout all parts of the building; that the apparatus is so safe and simple that an ordinary domestic is competent to take charge of it; that it costs little or nothing- for repairs and is considered very wholesome for dwellings.
Steam Heating closely resembles low-pressure water heating. The steam, which is generated in a boiler, proceeds through a well-covered supplv-pipe to the transmission-pipes in the rooms. In these pipes, which are generally of copper and rather large, the steam is again condensed into water by the loss of heat and returned to the boiler by a special pipe. As a substitute for such arrangenients radiators can be used, as in the hot water heating system. Figure (fii. io) shows one which was erected for the baths at Elster, in Saxony, by Engineer E. Kelling. It has an exterior and an interior cylinder; between them is the steam box (a' ), to which the steam is conducted by the pipe a, from o.6 to o.S of an inch calibre, while the condensed water drains off through the pipe c. The steam enters the shut-off space (e) at the top through the pipe a. Tltis space (c) is provided with an air-valve and contains a receptacle (g) which is thus warmed, as well as any bath linen which.may be placed in it. The condensed-water pipe (b) as it leaves e unites below with the pipe c. By means of the valve (K) the apparatus can be utilized both as a ventilating and as a circulating stove. In the former use, the fresh air enters the room when the valve is lifted; in the latter, the valve being lowered, the air of the room circulates through the inner cylinder.