The required B. T. U. per hour = 830 X 152 = 126,160.
Difference between the average temperature of the water and the tem perature of the steam = 228 — 114 = 114 degrees.
B. T. U. given up to the water per square foot of surface per hour = 114 X 200 = 22,800. Therefore, No. of feet of heating surface required 126,160 = _ 5.5 square feet.
22,800 1. How many linear feet of 1-inch brass pipe will be required to heat 150 gallons of water per hour from 40 to 200 degrees, with steam at 20 pounds' pressure? ANS. 21.3 feet.
2. How many square feet of grate surface will be required in a heater to heat 300 gallons of water per hour from 50 to 170 degrees? 3. A hot-water storage tank has a steam coil consisting of 30 linear feet of 1-inch brass pipe. It is desired to connect a coal-burning heater for summer use, which shall have the same capacity. Steam at 5 pounds' pressure is used, and the water is raised from 40 to 180 degrees. How many square feet of grate surface are required? 4. A hotel has 30 bathtubs, which are used three times apiece between the hours of seven and nine in the morning. The hot-water sys tem has a storage tank of 400 gal lons. Allowing 20 gallons per bath, and starting with the tank full of hot water, how many square feet of grate surface will be required to heat the additional quantity of water within the stated time, if the tem perature is raised from 50 to 130 degrees? If steam at 10 pounds' pres sure is used instead of the heater, how many square feet of heating coil will be re quired? ANS. 15.3 sq. ft.
Sometimes a storage tank is connected with a steam heating system for winter use, and cross-connected with a coal-burning heater for sum mer use when steam is not available. Such an arrange ment is shown in Fig. 84. A cross-connection for the same purpose is often made to the fire-pot of the house-warming heater, as indicated in Fig. 85. A drain at the lowest point is essential, but so deep a dip as shown is not necessary.
Temperature Regulation. Hot-water storage tanks hav ing special heaters or steam coils, should be provided with some means for regulating the temperature of the water. Fig. 86 shows a simple form attached to a
coal-burning heater. It consists of a hollow casting about nine inches long, tapped at the ends to receive 2-inch pipe, and containing a second shell called the steam generator, shown in detail in Fig. 87. The outer shell is connected with the tion pipe as shown in Fig. 86. The generator is filled with kerosene, or a mixture of kerosene and water, depending upon the temperature at which it is wished to have the regulator operate. The inner chamber connects with a space below a flexible rubber diaphragm in a sepa rate case adapted to operate the draft lever. The boiling point of the mixture in the generator is lower than that of water alone, and depends upon the proportion of kerosene used, so that when the tem perature of the water in the outer chamber reaches this point, the mixture boils, and its vapor creates a pressure which moves the dia phragm and closes the draft door of the heater, with which it is con nected.
A form of regulator for use with a steam coil is shown in Fig. 88. This consists of a rod made up of two metals having different coeffi cients of expansion, and so arranged that the difference in expansion will produce sufficient movement to open a small valve when the water reaches a temperature. This allows water pressure from the street main with which it is connected, to flow into a chamber above a rubber diaphragm, thus closing the steam supply to the coil. When the water cools, the rod contracts, and the pressure is released above the diaphragm, allowing the valve to open and thus again admit steam to the coil.
Return circulation is provided in these installations in the way already described, being even more essential than in small jobs with shorter runs and fewer fixtures; yet one would think that the great number of fixtures served would insure at least one or another being in constant use, and thus keep warm water in the main lines without special provision for the purpose.