261. Ventilation of houses. In order to secure satisfactory ventilation it is estimated that a room should be supplied with 2000 cubic feet of fresh air per hour for each occupant (a gas burner is equivalent in oxygen consumption to four persons). A current of air moving with a speed great enough to be just perceptible has a velocity of about 3 feet per second. Hence the area of opening required for each person when fresh air is entering at this speed is about 25 or 30 square inches. The manner of supplying this requisite amount of fresh air in dwelling houses depends upon the particular method of heating employed. (See opposite page 227.) If a house is heated by stoves or fireplaces, no special provision for ventilation is needed. The foul air is forced up the chimney with the smoke by the entrance of the fresh air coming in through cracks about the doors and windows and through the walls, if highly porous. It is estimated that an annual saving of at least $100,000,000 in fuel in the United States alone would be made if the walls of 20 per cent; through (3), 25 per cent; through (4), 14 per cent A STEAM-HEATING AND VENTILATING SYSTEM FOR A DWELLING The diagram shows a simple steam-heating plant having a one-pipe circuit. Steam passes from the top of the boiler into a pipe which at all points slopes slightly downward throughout the entire circuit. Through branch pipes steam rises to the individual radiators, where it condenses and returns to the overhead pipe in the cellar and thence to the lower part of the boiler. Since the returning water occupies a volume approximately 1600 of that of steam, it is obvious that a single pipe leading to each radiator is sufficient to carry both the outgoing steam and the returning water. Adequate ventilation of a steam-heated building may be secured, as shown in the figure, by providing openings in the walls immediately above the radiators through which fresh air may enter. The rising warm air from the radiators prevents the cold air from settling to the floor. The foul air of the room passes through openings located near the floor on another side of the room and thence upward through ventilating flues leading to the top of the house. This arrangement is shown in the lower story of the diagram 262. Hot-air heating. In houses heated by hotair furnaces an air duct is usually supplied for the entrance of fresh cold air, in the manner shown in Fig. 196 (see "cold air inlet"). This cold air from outdoors is heated by passing in a circuitous way, as shown by the arrows, over the outer jacket of iron which covers the fire box. It is then delivered to the rooms. Here a part of it escapes through windows and doors, and the rest returns through the cold-air register to be reheated, after being mixed with a fresh supply from outdoors. FIG. 197. Principle of hot-water heating When the fire is first started, in order to gain a strong draft the damper C is opened so that the smoke may pass directly up the chimney. After the fire is under way, the damper C is closed.so that the smoke and hot gases from the furnace must pass, as indicated by the dotted arrows, over a roundabout path, in the course of which they give up the major part of their heat to the steel walls of the jacket, which in turn pass it on to the air which is on its way Cold water to the living rooms. 263. Hot-water and steam heating. To illustrate the principle of hot-water heating let the arrangement shown in Fig. 197 be set up, the upper vessel being filled with colored water, and then let a flame be applied to the lower vessel. The colored water will show that the current moves in the direction of the arrows. This same principle is involved in the gas-heating coil used in connection with the kitchen boiler (Fig. 198). Heat from the flame passes through the copper coil to the water, and convection begins as indicated by the arrows. When hot water is drawn from the top of the boiler, cold water enters near the bottom so as not to mingle with the hot water that is being Hot water Chimney Copper heating coils Cas flame Gas pipe FIG. 198. A gas-heating coil used. The principle is still further illustrated by the cooling systems used for keeping automobile engines from becoming overheated. Heat passes from the engine into the water, which loses heat in circulating through the coils of the radiator (see opposite page 210). The actual arrangement of boiler and radiators in one system of hot-water heating is shown in Fig. 199. The water heated in the furnace rises directly through the pipe A to a radiator R, and returns again to the bottom of the furnace through the pipes B and D. The circulation is maintained because the column of water in A is hotter and therefore possesses less density than the water in the return pipe B. Freshair inlet A To chimney B FIG. 199. Hot-water heater FIG. 200. A radiator air valve By eliminating the expansion tank and partly filling the boiler with water the system could be converted into a steam-heating plant (see opposite page 227). Air valves (Fig. 200) are placed on steam radiators to allow air within the radiator to pass out ahead of the on-coming steam. Air escapes from the small hole B, and any water which enters the valve runs back into the radiator through the tube T. When the hot steam reaches the form of valve shown in Fig. 200, the vaporization of a volatile liquid (ethyl chloride) in the closed capsule C |