In large buildings where steam is available, the water for domestic purposes is usually warmed by placing a steam coil of brass or copper pipe in the storage tank. This may be a trombone coil made up with brass fittings, or a spiral consisting of a single pipe. Heaters of these types are shown in Fig.. 19 and 20. The former must be used in tanks which are placed horizontally, and the latter in vertical tanks. If the steam is used at boiler pressure, the condensation may return directly to the boiler by gravity; but if steam at a reduced pressure is used, it must be trapped to the receiver of a return pump or to the sewer.

The cold water is supplied near the bottom of the tank, and the service pipes are taken off at the top. A drip pipe should be connected with the bottom, for draining the tank to the sewer. Gate valves should be provided in all pipe connections for shutting off in case of repairs. Sometimes a storage tank is connected with a steam-heating system for winter use, and cross connected with a coal-burning heater for summer use where steam is not available. Such an arrangement is shown in Fig. 21.

The efficiency of a steam coil surrounded by water is much greater than when placed in the air. A brass or copper pipe will give off about 200 thermal units per square foot of surface per hour for each degree difference in temperature between the steam and the surrounding water. This is assuming that the water is circulating through the heater so that it moves over the coil at a moderate velocity. In assuming the temperature of the water we must take the average between that at the inlet and outlet.

Boilers With Steam Coils 1000316

Fig. 20.

Example. - How many square feet of heating surface will be required in a brass coil to heat 100 gallons of water per hour from 38 degrees to 190 degrees, with steam at 5 pounds pressure?

Boilers With Steam Coils 1000317

Fig. 21.

Water to be heated = 100 X 8.3 = 830 pounds. Rise in temperature = 190 - 38 = 152 degrees. Average temperature of water in contact with the coils

190 + 38 = 2 = 114 degrees

Temperature of steam at 5 pounds pressure = 228 degrees.

The required B. T. U. per hour = 830 X 152 = 126,160.

Difference between the average temperature of the water and the temperature 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, and

126,160 = 5.5 square feet. Ans. 22,800

Examples For Practice

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?

Ans. 7.4 square feet.

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? Ans. 5.9 sq. ft.

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 system has a storage tank of 400 gallons. 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 temperature is raised from 50 to 130 degrees? If steam at 10 pounds pressure is used instead of a heater, how many square feet of heating coil will be required? Ans. { 11.6 sq. ft. grate.

Boilers With Steam Coils 1000318

Fig. 22.

{ 15.3 sq. ft. coil.

Temperature Regulators

Hot-water storage tanks having special heaters or steam coils should be provided with some means for regulating the temperature of the water. Fig. 22 shows a simple form attached to a coal-burning heater. It consists of a casting about nine inches long, tapped at the ends to receive a 2-inch pipe, and containing within it a second shell called the steam generator. (See Fig. 23.) The outer shell is connected with the circulation pipe as shown in Fig. 22. 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 the space below a flexible rubber diaphragm. 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 temperature of the water in the outer chamber reaches this point, the mixture boils, and its vapor creates a pressure which forces down the diaphragm and closes the draft door of the heater with which it is connected.

Temperature Regulators 1000319

Fig. 23.

A form of regulator for use with a steam coil is shown in Fig. 24. This consists of a rod made up of two metals having different coefficients of expansion, and so arranged that this difference in expansion will produce sufficient movement, when the water reaches a given temperature, to open a small valve. 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.

Temperature Regulators 1000320

Fig. 24.

Gas Fitting

Next to heating and ventilation and plumbing there is no part of interior house construction requiring so much attention as the gas piping and gas fitting.

Gas piping in buildings should be installed according to carefully drawn specifications, and only experienced workmen should be employed. The gas fitter should work from an accurate sketch plan showing the location of all gas service and distributing pipes in the building and the locations of the meter and shut-off cock. The plan should also indicate the exact location and size of the risers and the position of the lights in the different rooms.