Document DMYL0eMbvNo6XVGX55N7zV4w5

988 CHAPTER 48 1950 Guide 8000 X 1/7 = 1140 gal. Duration of peak load 4 hr. Water required for 4-hr peak = 4 X 1140 = 4560. If a 1000 gal storage tank is used, hot water available from the tank = 1000 X 0.75 = 750. Water to be heated in 4 hr = 4560 - 750 = 3710 gal. Heating capacity per hour = 3710/4 = 930 gal. If instead of a 1000 gal tank, a 2500 gal tank had been installed, the required heating 4560 - (2500 X 0.75) capacity per hour would be 4 671 gal. Table 9 may be used to determine the size of water heating equipment from the number of fixtures. To obtain the probable maximum demand, multiply the total quantity for the fixtures by the demand factor in line 11. The heater or coil should have a water heating capacity equal to this probable maximum demand. The storage tank should have a capacity Table 9. Hot Water Demand per Fixture for Various Ttpes of Buildings Gallons of water per hour per fixture, calculated at a final temperature of 140F ,,- -- - - Afabtkxnt Hooaa Club Gtm- Hos KASmi pital Hotel Indus-. Office TBIAL Build Plant ing Private Resi School dence YM. C.A. 1. Basins, private lavatory___ 2 2 2 2 2 2 2 2 2 2 2. Basina, pubCc lavatory____ 4 6 8 . 6 8 12. - 15 8 3. Bathtubs. 20 20 30 20 20 30 20 ... . 30 4. Dishuasfaerfl . 15 50-150 ... 50-150 50-200 20-100 -- 15 20-100 20-100 S. Foot KmItm----- ^------- 3 3 12 3 3 12 -- 8 3 12 6. Kitchen sink____________ 10 20 -- 20 20 20 ... 10 . 10 20 7. Laundry, stationary tubs__ 20 28 ... 28 28 ... .. 20 28 8. Pantry sink. 5 10 __ 10 10 ... _ - & 10 10 9. Showers. 75 150 225 75 75 225 - 75 225 225 10. Sop sink.__ 20 20 ... 20 30 20 16 15 20 20 11. Demand factor...... ........ 0.30 030 0.40 0.25 0.25 0.40 030 030 0.40 6.40 12. Storage capacity factor*__ 1.25 0.90 L00 0.50 0.S0 13)0 2.00 070 1.00 1.00 * Ratio of storage tank capacity to probable maximum demand per boor. equal to the probable maximum demand multiplied by the storage capacity factor in line 12. Example 5 will illustrate the procedure. Example 6. Determination of heater and'Btorage tank size for an apartment building from number of fixtures. 60 lavatories........................................ X 2 = 120 gal per hour 30 bath tubs.............................. X 20 = 600 gal per hour 30 showers ..................... X 75 = 2250 gal per hour 60 kitchen sinks.................... X 10 = 600 gal per hour 15 laundry tubs......................................................... X 20 *= 300 gal per hour ' Possible maximum demand..................................... " 3870 gal per hour Probable maximum demand.............. = 3870 X 0.30 = 1161 gal per hour Heater or coil capacity................ ........................... = 1161 gal per hour Storage tank capacity.............................. = 1161 X 1.25 = 1450 gal 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 Water Services 989 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 clog with resultant crack ing 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 temperature 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 with water temperatures lower than 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 ofcombustion, and consequently such heaters are generally built with a dry section'or fire-brick lining at the base of the fire-pot to prevent too muchchilling 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 Same 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 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 16. Electric water heaters for domestic hot water supply are described in the section Heating Domestic Water by Electricity in Chapter 41. 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 the outside of the steam tubes which are submerged within a tank. A typical indirect heater using steam is 6hown in Fig. 8. The coils usually are of copper and are {/-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