Page:The New International Encyclopædia 1st ed. v. 09.djvu/753

* HEATING AND VENTILATION. 693 HEATING AND VENTILATION. Fig. 3. hot-water heating— fsfal method of piping. now than before electric power be- came so common. The great disad- vantage of either steam or hot water, when employed in direct radiation sys- tems, is that they merely warm the air already in the room, instead of bringing in a constant snpply of fresh warm air. Tliis matters little where an independ- ent system of ventilation has been pro- vided and is intelligently used; bnt in small buildings, particularly houses, there rarely is a system of ventilation. It is to meet this objection that either the indirect system or the direct-indirect is often employed in place of direct radiation. Both steam and hot-water systems require a boiler or heater, a pipe system, and radiators. As the hot water is circulated at 140° F., against 212° F. for low-pressure steam, the radiating surface for hot water must be larger than for steam. Hot-water fitting requires greater care in design and construction than steam, which, coupled with the fact that steam- er fitting has been practiced extensively for many years, has rendered the a(h)p- tion of hot water less common than steam. Of late, however, hot water has been coming to the front. It has this great advantage over steam, name- ly, that it begins to yield heat very soon after the fire is starU'd and con- tinues to do so until the water cools, while there can be no heat from st<'ani plants until a water temperature of 212° F. has been attained, and none after it falls below that point. On the other hand, steam heat may be shut olV more quickly than water, .since the lat- ter continues to give ofl' its heat for a much longer period. Steam boilers and hot-water heaters alike require a furnace, with a grate surface for burning the fuel and a heat- ing surface for imparting the heat thus derived to the water in the boiler or heater. Where steam for both power and heat is to be generated, the boiler. Fig. 4. STEAM-EU^TING — TWO-PIPE SYSTEM, Fig. 5. STEAM-HEATING — P^VKTIAL-CIItCUIT SYSTEM. will be chosen principally for its suita- bility for power; or wholly so if the exhaust steam from the engine is to be used for heating. Where the boiler is employed for heating only, low-pressure steam is likely to be "used, and the boiler need not differ very much from a water heater, except that the former has a resei'voir for steam mounted above the heating surface, while the latter has not. Low-pressure steam systems, it may be explained, show some 5 to 10 pounds pressure at the boiler, and lower through the pipes and radiators. The choice of a boiler, from the many ty]jes and styles availalde, will depend upon a variety of local and even individual conditions. Thus a ver- tical boiler may be eho.sen where hori- zontal space is scarce and vertical space is ample ; or a water-tube boiler may be selected where a high pressure is to be carried for power purposes. Where fuel is cheaj) or the service is likely to