78,000 X 20 = 28,363 B. T. U.; 55 and this divided by 400 = 71 square feet of heating surface required.
1. A schoolroom on the third floor has 50 pupils, who are to be furnished with 30 cubic feet of air per minute each. What will be the required areas in square feet of the supply and vent flues? ANs. Supply, 3.7 -I-. Vent, 6.8 -F• 2. What size of heater will be required in a vent flue 40 feet high and with an area of 5 square feet, to enable it to discharge 1,530 cubic feet per minute, when the outside temperature is 60°? (Assume an efficiency of 400 B. T. U. for the heater.) ANs. 41.7 square feet.
Registers are made of cast iron and bronze, in a great variety of sizes and patterns. The almost universal finish for cast-iron registers is black "Japan;" but they are also finished in colors and electroplated with copper and nickel. Fig. 70 shows a section through a floc; register, in which A rep resents th:. valves, which may be turned in a or hori zontal position, t b s opening or closing the register; B is the iron border; C, the register box of tin or galvanized iron; and D, the warm-air pipe. Floor registers
are usually set in cast-iron borders, one of which is shown in Fig. 71;
while wall registers may be screwed directly to wooden borders or
frames to correspond with the finish of the room. Wall registers
should be provided with pull-cords for opening and closing from the
floor; these are shown in Fig. 72. The plain lattice pattern shown in
Fig. 73 is the best for schoolhouse work, as it has a comparatively
free opening for
air-flow and is
pleasing and
ple in design.
More elaborate
patterns are used
for fine
house work.
Registers with
shut-off valves
are used for
inlets, while the
plain register
faces without the
valves are placed
in the vent
ings. The vent flues are usually gathered together in the attic, and
a single damper may be used to shut off the whole number at once.
Flat or round wire gratings of open pattern are often used in place of register faces. The grill or solid part of a register face usually takes up about of the area; hence in computing the size, we must allow for this by multiplying the required "net area" by 1.5, to obtain the
"total" or `over-all" area.
Suppose we have a flue 10 inches in width and wish to use a register having a free area of 200 square inches. What will be the required height of the register? 200 X 1.5 = 300 square inches, which is the total area required; then 300 _ 10 = 30, which is the required height, and we should use a 10 by 30-inch register. When a register is spoken of as a 10 by 30-inch or a 10 by 20-inch, etc., the dimensions of the latticed opening are meant, and not the outside dimensions of the whole register. The free opening should have the same area as the flue with which it con nects. In designing new work, one should provide himself with a trade catal'gue, and use only standard sizes, as special patterns and sizes are costly. Fig. 74 shows the method of placing gossamer check-valves back of the vent register faces to prevent down drafts, the same as described for fresh-air inlets.
Inlet registers in dwelling-house and similar work are placed either in the floor or in the baseboard; sometimes they are located under the windows, just above the baseboard. The object in view is to place them where the currents of air entering the room will not be objectionable to persons sitting near windows. A long, narrow floor-register placed close to the wall in front of a window, sends up a shallow current of warm air, which is not especially noticeable to one sitting near it. Inlet registers are preferably placed near outside walls, especially in large rooms. Vent registers should be placed in inside walls, near the floor.
Pipe Connections. The two-pipe system with dry or sealed returns is used in indirect heating. The conditions to be met are practically the same as in direct heating, the only difference being that the radiators are at the basement ceiling instead of on the floors above. The exact method of making the pipe connections will depend somewhat upon existing conditions; but the general method shown in Fig. 75 may be used as a guide, with modifications to suit any special case. The ends of all supply mains should be dripped, and the horizontal returns should be sealed if possible.