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1080 CHAPTER 49 1954 Guide washing tank capacity in gallons, giving the gallons of 180 F water per day necessary to fill the tanks. 5. Add values from paragraphs 3 and 4 to obtain the total number of gallons of iou water required per day. For purposes other than dishwashing, a considerable amount of 140 F water is also used. To find the daily 140 F water requirement in a res taurant, multiply the total number of meals served per day by the gallons of 140 F water per meal. Low priced restaurants on the average utilize 0.9 gal of 140 F water per meal, while medium- and high-price restaurants use 1.2 and 1.5 gal per meal, respectively.8 METHODS OF HEATING WATER Hot water may be heated either by the direct combustion of fuel, by an intermediate carrier such as steam or hot water, or by electrically heated Table 10. Hot Wateh Demand per Fixtures for Various Types of Buildings Gallons of water per hour per fixture, calculated at a final temperature of H0 F Apart ment House Club Gym nasium Hos pital Hotel Indus trial Plant Office Build ing Pri vate Resi dence School Y.M. C.A. 1. Basins, private lavatory 2 2 2 2 2 2 2. Basins, public lavatory 4 6. . 8 .6 8 12 3. Bathtubs........................... 20 20 30 20 20 30 4. Dishwashers.............. 15 50-150 50-150 50-200 20-100 5. Foot basins...................... 3 3 12 3 3 12 6. Kitchen sink................... 10 20 20 20 20 7. Laundry, stationary tubs................................. 20 28 28 28 8. Pantry sink..................... 5 10 10 10 9. Showers............................. 75 150 225 75 75 225 10. Slop sink........................... 20 20 20 30 20 11. Demand factor............... 0.30 0.30 0.40 0.25 0.25 0.40 12. Storage capacity factor4 1.25 0.90 1.00 0.60 0.80 1.00 2 6 15 0.30 2.00 2 22 15 8 20 30 15 20-100 20-100 3 3 12 10 10 20 20 5 75 15 0.30 0.70 10 225 20 0.40 1.00 28 10 225 20 0,40 1.00 * Ratio of storage tank capacity to probable mayimtim demand per hour. surfaces. The simplest method is to have the fire on one side of a metal barrier and water on the other. In such a method, if the surfaces for transferring heat are small, and if the water carries a heavy proportion of precipitable salts, the water passages may soon become clogged with re sultant cracking or burning of the surface. A familiar example of such trouble is the water back in the kitchen stove, or the pipe coil inserted into the firebox of a warm air furnace or small boiler. The critical water tem perature at which the lime, magnesia, etc., collect on hot surfaces, varies with the character and proportions of the solids, but generally such deposits are not a serious trouble below 140 F. Coal-burning, direct-fired water heaters may be constructed of cored cast-iron sections, or of steel. In some cases the external appearance of the cast-iron sections is the same as in heating boilers, but internally the cores are changed to enable the sections to withstand the city water pres sure. In small capacity water heaters, efficiency is not considered so important as low first cost and ability to maintain a fire at a low rate of combustion, and consequently, such heaters are generally built with a dry Water Services 1081 section or fire-brick lining at the base of the fire-pot to prevent too much chilling of the fuel. While mud and scale will eventually clog the water ways of any direct-fired heater, increased life may be obtained by pro viding a three-way cock in the return line between the heater and the bottom of the storage tank, so that water can be blown through the heater or the tank separately, at full line pressure, to clean out loose sediment. Clean-out openings in the bottom of the heater are advantageous, if used by operators of water heaters for periodic cleaning out of sediment. Oil-burning, direct-fired water heaters usually are of steel, and operate with higher flame temperature and better efficiency than commensurate sized coal-burning heaters. As they have the same tendency as coal boilers to accumulate lime deposits, the water passages should be large in cross-section and accessible for periodic cleaning. Gas-burning, direct-fired water heaters may be of the instantaneous or storage type. Instantaneous heaters are generally constructed of spiral water tubes of copper, around which the products of combustion circulate upward from high capacity burners. Storage-type heaters may include Fig. 8. Indirect Water Heater in one unit an insulated storage tank, a combustion chamber, flues, burner equipment, and controls, or may consist of a separate storage tank and external direct-fired water heater, which may be a so-called side-arm heater for small capacity, or a gas-fired boiler for larger capacity. Gas boilers used for direct hot water supply must be able to withstand the city water operating pressure. While direct-fired gas heaters are used generally for residences and small installations of 100 gal storage capacity or less, indirect heaters are recommended for larger installations. Chimney connections for all direct-fired, fuel burning water heaters are an important consideration. Refer to Chapter 17. Electric water heaters for domestic hot water supply are described in the section Heating Domestic Water by Electricity in Chapter 42. In the indirect method, either steam or hot water is used for heating the water. With steam, the water to be heated is preferably circulated around fhe outside of the steam tubes which are submerged within a tank. A typical indirect heater using steam is shown in Fig. 8. The coils usually Jfre of copper, and are U-shaped to permit expansion and contraction. The shell may be of steel, with a protective coating or with a special inside Protective lining, or may be of copper or copper alloy. Where straight heating tubes are used, one end of the tube is usually expanded into a floating head to take care of expansion. The coils should be capable of